The IUPAC (International Union of Pure and Applied Chemistry) Periodic Table of the Elements and Isotopes (IPTEI) was created to familiarize students, teachers, and non-professionals with the existence and importance of isotopes of the chemical elements. The IPTEI is modeled on the familiar Periodic Table of the Chemical Elements. The IPTEI is intended to hang on the walls of chemistry laboratories and classrooms. Each cell of the IPTEI provides the chemical name, symbol, atomic number, and standard atomic weight of an element. Color-coded pie charts in each element cell display the stable isotopes and the relatively long-lived radioactive isotopes having characteristic terrestrial isotopic compositions that determine the standard atomic weight of each element. The background color scheme of cells categorizes the 118 elements into four groups: (1) white indicates the element has no standard atomic weight, (2) blue indicates the element has only one isotope that is used to determine its standard atomic weight, which is given as a single value with an uncertainty, (3) yellow indicates the element has two or more isotopes that are used to determine its standard atomic weight, which is given as a single value with an uncertainty, and (4) pink indicates the element has a well-documented variation in its atomic weight, and the standard atomic weight is expressed as an interval. An element-by-element review accompanies the IPTEI and includes a chart of all known stable and radioactive isotopes for each element. Practical applications of isotopic measurements and technologies are included for the following fields: forensic science, geochronology, Earth-system sciences, environmental science, and human health sciences, including medical diagnosis and treatment.
The IUPAC Periodic Table of the Elements and Isotopes (IPTEI), shown in Fig. 1.1, is modeled on the familiar Periodic Table of the Chemical Elements. The IPTEI effort was launched during the 2011 International Year of Chemistry (IYC-2011) , . While the familiar Periodic Table indicated similarities of chemical element properties (terms that appear in the text in bold font appear in a glossary in Section 5), the IPTEI emphasizes some of the unique properties of each element. It is intended to familiarize students, teachers, and non-professionals with the nature and properties of isotopes of the chemical elements. A large-format IPTEI is intended to hang on the walls of chemistry laboratories and classrooms, just as the Periodic Table of the Chemical Elements is commonly displayed.
Atoms of all chemical elements are composed of positively charged particles called protons, an equal number of negatively charged particles called electrons, and electrically neutral particles called neutrons. The number of protons in each atom is its atomic number, symbol Z, and determines the chemical element; for example, for hydrogen atoms Z=1 and for gold atoms Z=79. The number of neutrons, symbol N, in an atom of a given element may vary. The total number of protons and neutrons (Z+N) in a specific atom is the mass number, symbol A, where A=Z+N. A nuclide is an atom with a specific number of protons and a specific number of neutrons; that is, a specific atomic number and mass number. The terms Nickel-64 and 64Ni both refer to a nuclide of the element nickel with a mass number of 64. Nuclides of a given element that have different numbers of neutrons, but the same number of protons, are called isotopic nuclides or isotopes. The term “isotope” is commonly used in discussions of atomic properties of an atom and “nuclide” is used for discussions of nuclear properties. For any particular element, only certain isotopes are stable. 64Ni, with 28 protons and 36 neutrons, is stable, whereas 65Ni, with 37 neutrons, is unstable. A stable isotope is defined as an isotope for which no radioactive decay has been experimentally detected . An unstable isotope (also called a radioactive isotope or radioisotope) is energetically unstable and will decay (disintegrate) over time to another isotope of the same element or to a nuclide of a different element. The time it takes for one half of the atoms of a given isotope in a sample to decay is called the half-life, symbol t1/2, of that isotope. The term isotope applies to both stable and radioactive isotopes.
The world surrounding us, including the water we drink and the air we breathe, is made up of substances comprised of isotopes of the elements, e.g. hydrogen, oxygen, and nitrogen. The fraction of the amount of a specified isotope in a substance (amount fraction) is also called the mole fraction, the atom fraction, and the isotopic abundance. Many isotopes that occur naturally are radioactive and have half-lives ranging from a fraction of a second to much greater than 1010 years, which is greater than the age of the Earth. In natural terrestrial substances, a radioactive isotope with a sufficiently long half-life is said to have a characteristic terrestrial isotopic composition, e.g. xenon-136 and potassium-40. Considering all chemical elements that have been discovered in nature (in contrast to elements that have been synthesized or produced by humans), natural terrestrial samples contain a total of 289 different isotopes that have characteristic terrestrial isotopic compositions that are listed in IUPAC’s Table of Isotopic Compositions of the Elements . Of these isotopes, 253 are stable and 36 are radioactive with long half-lives (greater than 3.25×104 years, e.g. for protactinium). In addition to these 289 isotopes, more than 3000 other natural and artificial isotopes are known, corresponding to the radioactive isotopes of all elements, most with short half-lives (less than 1 month).
The relative atomic mass which, for historical reasons, is called atomic weight (and is used in this document throughout), of an element E in any particular sample, Ar(E), is calculated from the sum of the products of the relative atomic mass and isotopic abundances of each stable isotope and each radioactive isotope having a sufficiently long half-life and sufficiently large isotopic abundance that a characteristic terrestrial isotopic composition can be listed in IUPAC’s Table of Isotopic Compositions of the Elements  of that element in a given sample. In contrast to the atomic weight of an element in any given material, the standard atomic weight (standard relative atomic mass) is a quantity that represents the atomic weight of an element in normal terrestrial materials.
Each element cell of the IUPAC Periodic Table of the Elements and Isotopes (Fig. 1.1) provides the chemical name, chemical symbol, atomic number, and standard atomic weight of that element, as is shown in the cadmium legend in Fig. 1.2. Each cell displays the current standard atomic weight  for each element with its estimated uncertainty in the last digit. For the 13 elements with standard atomic-weight intervals (hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, argon, bromine, and thallium), the standard atomic weight is given as an interval to stress that standard atomic weights are not constants of nature . Each is shown as lower and upper bounds (limits) (Figs. 1.1 and 1.2). Some users of atomic-weight data need a value that is not an interval, such as for purposes of trade and commerce. For these users, a conventional atomic-weight value  is provided for each of these 13 elements and is shown in white (Figs. 1.1 and 1.2). A color-coded pie chart displays all of the stable isotopes and radioactive isotopes having characteristic terrestrial isotopic compositions that determine the standard atomic weight of that element, e.g. eight isotopes for cadmium. The mole fraction (isotopic abundance) of each of these isotopes is indicated by the relative size of the pie slice associated with that isotope. The mass numbers of each of these isotopes appear around the outside of the pie chart. Mass numbers are shown in black for stable isotopes (e.g.112Cd) and in red for radioactive isotopes (e.g.113Cd). More than 3000 radioactive isotopes with half-life values too short or isotopic abundances too low to impact the standard atomic weights are excluded from the IUPAC Periodic Table of the Elements and Isotopes, but they are included in the accompanying element-by-element review (Section 4).
In the following element-by-element review, there are often expressions in the textual material of nuclear reactions, which are listed in the form A(a,b)B, where A is a target that reacts with an incoming projectile, a, and forms the residual, B, and emits the outgoing projectile, b. In many cases, there may be a subsequent radioactive decay reaction associated in a two-step reaction process, with the notation B→C+c. This secondary decay reaction indicates that the residual, B, is unstable and decays with a characteristic half-life to another residual, C, via the c decay. The c could be a negatively charged beta particle (electron), a positively charged beta particle (positron), or a positively charged alpha particle, α. It could indicate a negatively charged electron capture reaction, ec, or a neutral particle, a neutron (see Section 2.10.1 (ii), page 50 of ref ).
The background color scheme for an element cell in the IPTEI (Fig. 1.1) depends in part on the number of isotopes that are used to determine the standard atomic weight of the element:
Yellow is the background color if an element has two or more isotopes that are used to determine its atomic weight. The standard atomic weight is given as a single value with an uncertainty that includes both measurement uncertainty and uncertainty due to isotopic abundance variations. The variations in isotopic abundances may be too small to exceed the measurement uncertainty and affect the atomic weight value. An example is cadmium, shown in Fig. 1.2, with a standard atomic weight of 112.414(4).
Blue is the background color if only one isotope is used to determine the standard atomic weight. The standard atomic weight is invariant and is given as a single value with an IUPAC-evaluated measurement uncertainty. An example is arsenic, with a standard atomic weight of 74.921 595(6), where the uncertainty in the last digit, 5, is indicated by the value, 6, in parentheses (Fig. 1.1).
White is the background color if an element has no standard atomic weight because all of its isotopes are radioactive and no isotope occurs in normal materials with a characteristic terrestrial isotopic composition from which a standard atomic weight can be determined. An example is americium, for which no standard atomic weight is listed (Fig. 1.1).
Pink is the background color if an element has two or more isotopes that are used to determine its atomic weight and the variation in isotopic abundances and atomic weights in normal materials is large and well known. The standard atomic weight is given as lower and upper bounds within square brackets, [ ]. An example is boron, with a standard atomic weight of [10.806, 10.821] (Fig. 1.1). In this case, the standard atomic-weight value indicates that known boron atomic-weight values, found in normal materials, are as low as 10.806 and as high as 10.821. The standard atomic weight should not be expressed as the average of the lower and upper bounds. These elements do not have an IUPAC-assigned uncertainty.
The printed version of the IPTEI is accompanied by an electronic interactive version, which runs on a variety of platforms and devices. The global launch of the electronic, interactive version of the IPTEI took place in August 2016 at the 24th IUPAC Conference on Chemistry Education, held in Kuching, Malaysia. This electronic, interactive version, developed by the King’s Centre for Visualization in Science (KCVS), can be found at www.isotopesmatter.com. A click on a chemical element cell in Fig. 1.1 on that site will display additional information from the element-by-element review (Section 4) about the isotopes of that element, including a table of the naturally occurring isotopes for each element, their atomic masses, and their isotopic abundances (mole fractions). There is a list of all radioactive isotopes and an indication of their half-life value within one of three half-life ranges. This electronic, interactive IPTEI has been designed to be used both as a stand-alone digital learning object and as an object to be embedded in a set of electronic learning resources that will (a) stress the importance of isotopes in everyday life, (b) connect the knowledge of isotopes to core concepts in chemistry and physics curricula, and (c) help students and teachers understand the evidential basis for our knowledge of isotopes through the use of tools such as mass spectrometry.
For each of the 118 elements, the following is presented:
The element cell from the IUPAC Periodic Table of Elements and Isotopes.
A table of stable isotopes or long-lived isotopes that have a characteristic terrestrial isotopic composition and contribute to the value of a standard atomic weight. For each isotope the relative atomic mass, abridged from Wang et al. , is listed. The mole fraction of each isotope is listed and is taken from column 9 of the Table of Isotopic Compositions of the Elements 2013 , except for ytterbium, whose standard atomic weight and isotopic abundances were updated in 2015 , , and for iridium, whose standard atomic weight and isotopic abundances were updated in 2018 , . For the 13 elements having an interval for the standard atomic weight (hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, argon, bromine and thallium) the isotopic abundance of each stable isotope is given as an interval to denote the set of isotopic-abundance values in normal materials.
A chart of all known isotopes of each element. Mass numbers of radioactive isotopes are red and the cell background categorizes the half-life range. Mass numbers of stable isotopes are black and the background colors are from the pie diagram sections of the isotopic abundances of the element.
Selected applications of stable and/or radioactive isotopes in one or more of the following categories:
Isotopes in biology
Isotopes in Earth/planetary science
Isotopes in forensic science and anthropology
Isotopes in geochronology, which encompasses isotopic dating
Isotopes in industry
Isotopes in medicine
Isotopes used as a source for radioactive isotopes
The applications provided are only examples and are not intended to encompass all isotope applications of an element.
Molecules, atoms, and ions of the stable isotopes of hydrogen possess slightly different physical and chemical properties and they are commonly fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights (Fig. 4.1.1). Hydrogen has the largest relative mass difference among its isotopes and consequently exhibits the largest variation in isotopic composition of any element that does not have radioactive or radiogenic isotopes. Ranges in the stable isotopic composition of naturally occurring hydrogen-bearing materials are shown in Fig. 4.1.1. These variations enable hydrogen isotopes to be used as tracers in environmental studies .
A primary use of stable hydrogen isotopes is in isotope hydrology. Although the evolution of the stable hydrogen and oxygen isotopic composition of precipitation begins with the evaporation of water from the oceans, their local and global relationship arises primarily from equilibrium isotopic fractionation of heavier (2H and 18O) and lighter (1H and 16O) isotopes of hydrogen and oxygen during condensation as a tropospheric vapor mass follows a trajectory to higher latitudes and over continents , . As a consequence, the hydrogen isotopic composition of precipitation, rivers, and tap waters varies with elevation, season, and distance from the ocean-continent boundary. Figure 4.1.2 shows the variation in the atomic weight of hydrogen in water from rivers across the United States. These variations in the hydrogen isotopic composition of environmental water are often combined with stable oxygen isotopic compositions and have been used to identify the origin of water samples and to investigate the interaction between groundwater and surface water (e.g. lakes, streams, and rivers) .
Measurements of relative 2H abundances are used to determine the breeding grounds of many species of migrant songbirds. These species of songbirds only grow their feathers before migration, and they grow them on or close to their breeding grounds. Therefore, the isotopic composition of a bird’s feathers correlates to the isotopic composition of the growing season’s precipitation , , .
Measurements of relative 2H abundances of human hair samples collected at archeological sites are used to determine the geographic region in which a subject lived based on the hydrogen isotopic composition of the water they drank. This is possible because hair stores a daily record of the hydrogen isotopic composition of intake water, which correlates to local meteoric water , .
3H (tritium), with a half-life of 12.31 years, decays to 3He. The relative variations in n(3He)/n(3H) ratios can be interpreted in terms of elapsed time for dating purposes. The dates of groundwater recharge (water moving downward from the surface), where large amounts of 3H were received from precipitation following thermonuclear bomb test periods, come from the elapsed time since a water mass became isolated from the atmosphere in the time range from the mid-1950s to the present .
3H is used for self-luminous exit signs in aircraft and commercial buildings. It is found in luminous dials, gauges, wristwatches, and luminous paints . 2H, in the form of heavy water, is used in CANDU (CANada Deuterium Uranium) nuclear reactors as a moderator and coolant .
2H is used for the isotopic labeling of drugs and nutrients to trace their uptake and metabolism in the human body , . 2H, in the form of heavy water, is used to study human metabolism. For example, 2H is used in combination with 18O (double labeled water) to measure energy expenditure .
3He is a product of the radioactive decay of 3H (half-life of 12.31 years). The relative variations in the amount ration(3He)/n(3H) can be interpreted in terms of elapsed time. This has been especially useful in aquatic systems, including oceans, lakes, and aquifers, that received large inputs of 3H from precipitation following thermonuclear bomb test periods. 3H-3He dating provides the elapsed time since a water mass became isolated from the atmosphere in the time range from the mid-1950s to the present. Such studies are important for establishing the sustainability of groundwater resources in shallow aquifers , .
4He is a product of radioactive decay in the uranium and thorium decay series. As a result, 4He concentration is used to estimate the relative ages of minerals and groundwater. In closed systems (systems that do not exchange matter with their surroundings), relative variations in the amount ratio n(4He)/n(U) can be interpreted in terms of elapsed time, although other processes can alter the distribution of helium, which is highly mobile in terrestrial environments , .
4He concentrations commonly increase along groundwater flow paths through a cumulative release from aquifer materials. This rate of accumulation is used to estimate the time since the groundwater was recharged at the surface. The 4He accumulation method of groundwater dating is typically used in deeper aquifers, where groundwater is relatively old and the 3H-3He method cannot be used because of the relatively short half-life of 12.31 years for 3H .
3He has a large absorption cross section for neutrons, which makes it especially useful for radioactivity detection , . In this application, neutrons produced by the radioactive decay of elements, such as uranium and plutonium, enter the detector, where the reaction 3He (n, p) 3H produces 1H and 3H atoms. This induces further collisions and the release of electrons, which interact with charged surfaces to generate an electric current. Large amounts of 3He are used to produce neutron detectors in portal monitors for detecting illicit radioactive materials at ports, border crossings, and airports (Fig. 4.2.1). Unfortunately, the isotope3He is rare and there is a need to incorporate alternative gases for use in neutron detectors. 3He neutron detectors are also used in devices that determine the proportions of water, oil, and gas in wells drilled for energy production. Other important uses of 3He include lasers, gyroscopes used for missile stability and guidance, and cryogenic research (ultra-low temperature, less than 1 K).
The global supply of 3He available for research and practical applications has become severely limited in recent years, such that prices have increased substantially and some uses have been curtailed , . A major source of 3He is from nuclear weapons containing 3H, recovered when the warheads are reconditioned or dismantled. 3He accumulates in such devices as a radiogenic product of 3H decay. The annual supply of new 3He has decreased with reductions in nuclear arsenals.
3He is used as an inhalant to improve magnetic resonance imaging (MRI) of the lungs .
Because molecules, atoms, and ions of the stable isotopes of lithium possess slightly different physical and chemical properties, they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. Natural terrestrial materials show a substantial variation in lithium isotopic abundance (Fig. 4.3.1), and these natural isotopic abundances have been used to determine sources of dissolved lithium and to investigate environmental processes , .
Variations in isotope-amount ratiosn(7Li)/n(6Li) can help determine the source of some water. Because the relative abundances of lithium isotopes can change during hydrothermal processes, isotopic analysis of lithium in water can help distinguish water derived from marine sedimentary rocks from water derived from hydrothermally altered igneous rocks (Fig. 4.3.2) , .
7Li, as hydroxide monohydrate (7LiOH•H2O), is used to maintain the pH level of the coolant used in pressurized water reactors in the nuclear power industry , . Lithium plays a role in the construction of a thermonuclear bomb, which differs from a fission weapon in that it uses the energy released when two light atomic nuclei (i.e. deuterium (2H) and tritium (3H)) fuse to form helium and a high energy neutronvia this DT reaction. 6Li is used, in the form of 6Li deuteride (6Li2H), as fusion fuel capable of producing tritium when bombarded with neutrons within the weapon via the reaction 6Li (n, 3H) 4He .
Li-based laboratory reagents have found their way into surface water and can be easily identified. Although a military secret in the 1950s, it is now known that substantial amounts of 6Li (normally having an isotopic abundance of 0.076) were removed from chemical reagents to be used in nuclear weapon development. Reagents containing the remaining lithium depleted in 6Li (having an isotopic abundance as low as 0.025) were sold to both chemical manufacturers and to laboratory chemists for their use . The distinctive isotopic signature of depleted 6Li, having a n(7Li)/n(6Li) ratio of 39, compared to a ratio of 12 in naturally occurring terrestrial materials, enables easier detection of this lithium source in polluted waterways and the environment , .
7Li is a decay product of the 10B (neutron, alpha) 7Li reaction, which has a peak value for room temperature neutrons. Brain tumor cells are typically found some 5 to 7 cm below the surface of the skull. After 10B has been introduced to or entered the tumor cells, a beam of neutrons of energy slightly above room temperature is introduced to the affected areas. The energy of these neutrons is reduced to room temperature by the time they react with the 10B, which then disintegrates into high energy charged particles (7Li and 4He), which deposit their kinetic energy in nearby (predominately cancerous) cells and destroys them. Any adjacent normal cells are unaffected .
Cosmogenic10Be and 7Be isotopes are produced in the atmosphere, largely by cosmic-ray spallation of nitrogen and oxygen. Because of its relatively short half-life (7Be, half-life t1/2=53 d, compared to that of 10Be, half-life t1/2=1.39×106 a, where the unit symbol “d” stands for day and “a” stands for year), measurements of cosmogenic 7Be, and especially the isotope-amount ration(7Be)/n(10Be), have been used to study rates of atmospheric circulation, mixing, formation of aerosols (fine solids or liquids suspended in a gas; e.g. smoke and mist are aerosols), and particle deposition . Cosmogenic atmospheric beryllium isotopes (7Be and 10Be) are deposited on the Earth’s surface, where they accumulate in soils, sediments, and snow while decaying away. Measurements of cosmogenic beryllium isotopes in such deposits are used to explore rates of soil formation, erosion, sedimentation, and snow accumulation on time scales ranging from months (7Be) to millions of years (10Be) , . The minerals in rocks at the Earth’s surface interact with cosmic rays and form substantial quantities of 10Be and 7Be, thus providing a tool to determine the ages of geologic processes. In some situations, it is possible to estimate “exposure ages” for rocks in eroding terrains , , . By comparing measured 10Be concentrations with estimated rates of in situ cosmogenic 10Be production, the rate of rock erosion and formation of canyons and other geologic features can be determined (Fig. 4.4.1).
Anthropogenic10Be was produced by nuclear bomb explosions largely through the reaction of fast neutrons (neutrons produced by nuclear fission having high kinetic energy) with 13C via the 13C (n, alpha) 10Be reaction in atmospheric CO2. Although the quantity of 10Be produced in this way is small, its presence above natural background concentrations in some environmental samples can potentially provide information about bomb-related processes and contamination .
Molecules, atoms, and ions of the stable isotopes of boron possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. Natural terrestrial materials show a substantial variation in boron isotopic abundance (Fig. 4.5.1). The relative abundances of 10B and 11B have been used in a variety of environmental tracer applications , . The isotope-amount ration(11B)/n(10B) of boron in a water sample depends on the source of the water and region through which the water flows, and it may also be affected by some types of contamination, such as dissolved borate in domestic wastewater. Different water sources may have their own distinct boron isotopic composition, e.g. seawater versus water from continental sources (Fig. 4.5.1).
The large value of the absorption cross section of 10B for thermal neutrons makes this isotope useful for counting neutrons. 10B is being studied as a potential replacement for 3He in radiation detectors , , . The large thermal absorption cross section of 10B makes the isotope useful in control rods (Fig. 4.5.2) .
10B has a high thermal neutron absorption cross section and can readily absorb neutrons via the reaction 10B+n→7Li+α. The alpha particles resulting from this reaction carry away a relatively large kinetic energy and are useful for the treatment of malignant tumors in cancer patients , , .
Because of above-ground nuclear bomb testing, the neutrons released reacted with CO2 to increase atmospheric 14C via the 14N (n, p) 14C reaction, and 14C started rising in about 1955 (Fig. 4.6.1) and reached a peak in the mid-1960s . With the curtailment of above-ground nuclear testing in the 1960s, the atmospheric 14C concentration has since been decreasing exponentially (Fig. 4.6.1). This variation in 14C concentration is used to establish when cells in biology were born and how quickly they are renewed . This technique is commonly called carbon-14 bomb pulse biology and it has provided information on the age of cells and their regeneration. Figure 4.6.2 shows the average age of selected cells in a 30-year-old human.
Because molecules, atoms, and ions of the stable isotopes of carbon possess slightly different physical and chemical properties, they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. Carbon in natural terrestrial materials shows a substantial variation in isotopic abundance (Fig. 4.6.3), providing many different ways of distinguishing sources of materials and processes affecting them . Variations in the isotope-amount ration(13C)/n(12C) in tree rings and in CO2 trapped in ice cores have been used to study causes of variations in atmospheric CO2 levels . Variations in the isotope-amount ratio n(13C)/n(12C) and in the 14C concentration of surface ocean waters have been used to trace the incorporation and movement of atmospheric CO2 in the ocean .
Variations in the isotope-amount ratio n(13C)/n(12C) of biological products can be observed using isotope-ratio mass spectrometry (IRMS) to detect adulteration (the addition of inferior ingredients) in honey and other food products.
The isotope-amount ratio n(13C)/n(12C) can fluctuate between carbon sources, for example C3 plants (found in temperate climates and which use atmospheric carbon dioxide to make a 3-carbon molecule during photosynthesis — examples include rice, potatoes, tomatoes, and sugar beets), C4 plants (found in hot climates and which use atmospheric carbon dioxide to make a 4-carbon molecule during photosynthesis — examples include corn and sugar cane), animal carbon, atmospheric CO2, etc. This commonly makes it possible to detect whether these different carbon sources have been mixed by using isotope or mass balance to distinguish, for example, between beet sugar and cane sugar. Complications in source identification can arise with plants that open stomata at night to collect carbon dioxide to use a third mechanism to fix atmospheric carbon dioxide (CAM or crassulacean acid metabolism). The isotope-amount ratio n(13C)/n(12C) of CAM plants overlaps that of C3 or C4 plants — examples include pineapples and jade plants. The following adulterations are commonly detected using stable carbon isotope IRMS:
Variations in the isotope-amount ratio n(13C)/n(12C) of honey are used to detect the addition (and potential adulteration) of high fructose corn syrup, corn, or sugar cane .
Variations in the isotope-amount ratio n(13C)/n(12C) of fruit juice have been used to detect the addition of a sugar .
Variations in the isotope-amount ratio n(13C)/n(12C) of natural vanilla extract have been used to detect the addition of artificial vanillin or p-hydroxybenzaldehyde .
Variations in the isotope-amount ratio n(13C)/n(12C) of beer are used to detect C4 carbon, which would indicate that a beer company may have added ingredients that are not traditionally used in brewing beer. Therefore, this ratio is used to detect the misrepresentation of a product as being pure , .
Stable carbon IRMS has been used to determine if the botanical origin of an alcoholic spirit has been mislabeled and if chaptalization (the process of adding sugar to increase the alcoholic content) of wine has occurred , . 14C scintillation counting has been used to determine the age of wine and alcoholic spirits , . Variations in the isotope-amount ratio n(13C)/n(12C) of urine has been used to determine if steroids in urine are natural or of synthetic origin. These measurements enable anti-doping laboratories to perfect their methods for detecting steroid doping in athletes , , . Variations in the isotope-amount ratio n(13C)/n(12C) of marijuana can provide information to determine if the plants were grown “inside” a building or greenhouse or were “open grown” (Fig. 4.6.4). Plant carbon isotopic compositions are controlled by atmospheric CO2 and the supply and demand of CO2 in photosynthesis (the process used by plants to convert light energy from the sun into chemical energy). “Open grown” plants are grown in an area that is well ventilated and receives natural CO2. In contrast, plants grown “inside” receive supplemented CO2 and the photosynthesis process is more confined. Additionally, CO2 from a tank of compressed gas used to augment atmospheric CO2 to increase the growth of marijuana plants is commonly highly depleted in 13C as a refinery by-product. These differences change the carbon isotope ratios of the plants and the ratios vary enough to enable the determination of the growing and cultivation process of marijuana , .
Radioactive 14C is the basis for the radiocarbon dating method to determine the ages of carbon-bearing materials. 14C is formed naturally in the atmosphere by cosmic-ray interactions and was also released by above-ground, nuclear weapons testing (Fig. 4.6.1). Atmospheric 14C is incorporated into plants, animals, soils, groundwater, and ocean water, and it decays with a half-life of ~5700 years. This makes it useful for dating objects, such as archaeological remains and water masses in oceans and aquifers, on time scales ranging from hundreds of years to tens of thousands of years . Plants and animals living since the 1950s can be identified by bomb-peak 14C in their cells (see Section 4.6.1).
14C is used to create isotopically labeled drugs to study their uptake and metabolism in humans , , . 13C is used in breath tests to detect Helicobacter pylori bacteria (bacteria in the stomach linked to ulcers), which can cause cancers .
Isotopic fractionation can cause the isotope-amount ration(15N)/n(14N) to increase systematically through food chains through assimilation of nitrogen compounds in biomolecules such as proteins. When lower-order organisms are ingested by higher-order organisms, 15N may be selectively retained and 14N may be selectively excreted such that higher-order organisms tend to have higher n(15N)/n(14N) ratios than their food sources. Isotopic fractionation occurs as a result of assimilation, storage, and excretion of proteins and other nitrogen compounds. Biologists can use isotope-amount ratio n(15N)/n(14N) measurements to test hypotheses about predator-prey relations and detect disruptions to trophic structure of ecosystems that might be caused by toxic contaminants, invasive species, or harvesting of organisms. Similar principles are used to detect differences in diets among animals, including humans, both today and in the distant past , , .
Artificially enriched 15N tracers are used to study movement and transformation of nitrogen in biological and environmental systems, such as the uptake and loss of nitrogen fertilizers by crops (Fig. 4.7.1). A common experiment involves introducing an isotopically labeled compound into the environment and then analyzing various samples taken from the environment for the presence of the enriched isotope to determine where the labeled compound moved and whether it transformed into other compounds (Fig. 4.7.2). Artificially enriched 15N is used to study uptake and dispersal of nitrogen in feed supplies used in food production industries such as aquaculture .
The stable isotopes of nitrogen are subject to isotopic fractionation by physical, chemical, and biological processes. Variations in the isotope-amount ratio n(15N)/n(14N) are substantial (Fig. 4.7.3) and commonly are used to study Earth-system processes, especially those related to biology because nitrogen is a major nutrient for growth . For example, isotope fractionation occurs when dissolved solutes, such as nitrate (NO3-), are transformed to more reduced compounds (i.e. nitrogen gas) because nitrate with higher 14N abundances tends to be more readily broken down. This leaves the residual unreacted nitrate with a higher n(15N)/n(14N) ratio than the initial ratio prior to reaction. Changes in the isotopic composition of biologically reactive compounds can be used to detect such reactions in aquatic environments, which are important mechanisms for removing reactive contaminants like nitrate , .
Variations in the isotope-amount ratio n(15N)/n(14N) are used to determine sources of nitrogen contamination in the atmosphere, oceans, groundwater, and rivers, where the isotopic composition of a contaminant molecule preserves evidence of the nitrogen sources and processes involved in its creation. An example is nitrate derived from artificial fertilizer, manure, power-plant emissions, or natural sources , , .
Stable hydrogen, carbon, and nitrogen isotopic compositions are used to determine the origin of pseudoephedrine from seized methyl-amphetamine made from the pseudoephedrine (drug used as a nasal decongestant or as a stimulant) .
Molecules, atoms, and ions of the stable isotopes of oxygen possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are substantial variations in the isotopic abundances of oxygen in natural terrestrial materials (Fig. 4.8.1). These variations are useful in investigating the origin of substances and studying environmental, hydrological, and geological processes .
A primary use of stable oxygen isotopes is in isotope hydrology. Although the evolution of the stable hydrogen and oxygen isotopic composition of precipitation begins with the evaporation of water from the oceans, their local and global relationship arises primarily from equilibrium isotopic fractionation of heavier (2H and 18O) and lighter isotopes (1H and 16O) of hydrogen and oxygen during condensation as a tropospheric vapor mass follows a trajectory to higher latitudes and over continents , . As a consequence, the isotopic composition and atomic weight of oxygen in precipitation, rivers, and tap waters varies with elevation, season, and distance from the ocean-continent boundary. Figure 4.8.2 shows the variation in stable oxygen isotopic composition of water from rivers across the United States. These variations in oxygen isotopic composition of environmental water are often combined with hydrogen isotopic compositions and have been used to identify the origin of water and to investigate the interaction between groundwater and surface water (e.g. lakes, streams, and rivers) .
Measurements of relative 18O abundances have been used to determine the breeding grounds of many species of migrant songbirds. These species of songbirds only grow their feathers before migration, and they grow them on or close to their breeding grounds. Therefore, the isotopic composition of a bird’s feathers correlates to the isotopic signature of the growing season’s precipitation , .
Measurements of relative 18O abundances of human hair or nail samples collected at archeological sites have been used to determine the geographic region in which a subject lived based on the oxygen isotopic composition of the water they drank (Fig. 4.8.3). This is possible because hair stores a daily record of oxygen isotopic composition of intake water, which correlates to local meteoric water .
17O has been used as a tracer to study cerebral oxygen utilization . Variations in stable oxygen and hydrogen isotopes are used in energy expenditure studies in animals and humans. The subject is administered a dose of doubly labeled water (water enriched in both 2H and 18O). Measurements of the elimination rates of 2H and 18O in the subject over time through regular sampling of body water (by sampling saliva, urine, or blood) provide information on energy expenditure because the hydrogen isotopic composition of body water is affected primarily by water loss (mainly urination), but the oxygen isotopic composition is affected by both respiration and water loss .
18F is a radioactive fluorine isotope that is used in an 18F-FDG compound (18F-labeled, fluoro-deoxy glucose) for imaging the organs, bones, tissues, and brain of the body with a technique called positron emission topography (PET). The 18F-FDG compound is injected and the isotopically labeled glucose is consumed by any cell requiring glucose as a source of energy , .
18F emits positrons that collect in tissue and interact with regular negative electrons when injected into the body. The positrons and electrons annihilate each other, producing two gamma rays that are emitted in opposite directions. The radiation is detected on a PET camera, which generates a picture of the body part being examined (Fig. 4.9.1).
Because 18F has a short half-life of about 110 min, there is little chance of radiation damage to the patient.
Neon is subject to stable isotopic fractionation by physical processes, such as exchange between gas, liquid, and solid phases. Small variations in the isotope-amount ration(22Ne)/n(20Ne) have been used to examine gas-liquid exchange processes during groundwater recharge (water moving downward from the surface) and discharge , , .
Some 21Ne and 22Ne form naturally in the Earth’s crust largely by reactions of 18O and 19F in minerals with neutrons and alpha particles emitted from uranium and thorium decay, called nucleogenic neon isotopes , . In addition, neon isotopes can form at the surface of the Earth and in extraterrestrial bodies by cosmic-ray-induced spallation reactions on magnesium, silicon, aluminum, and sodium , . Analyses of all three stable neon isotopes may be used to distinguish these sources from primordial neon. The relative amounts of atmospheric neon and crustal nucleogenic neon isotopes in deep groundwaters and natural gases have been used in studies of solid-water-gas interactions and migration (Fig. 4.10.1). The cosmogenic component is mainly detected in 21Ne and can be used to determine cosmic-ray exposure ages of rock samples, including meteorites exposed during travel through space and boulders exposed by melting of glacial ice (Fig. 4.10.1).
Masers (Microwave Amplification by Stimulated Emission of Radiation) containing 20Ne have been used to study quantum physics. 21Ne may also play a role in maser studies of quantum physics .
22Na is a cosmogenic isotope with a half-life of 2.6 years that has been used to study the residence time of water in freshwater basins. It has been used for dating of young (up to a few decades old) surface water and groundwater (Fig. 4.11.1) .
22Na is used as a source to calibrate positron emission tomography (PET) imaging scanners to check that the instruments are functioning properly .
Natural magnesium enriched in the stable isotopes25Mg and 26Mg has been used as tracers in human studies to assess absorption, excretion, distribution, and utilization of magnesium in basic and applied research , , .
Molecules, atoms, and ions of the stable isotopes of magnesium possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are substantial variations in the isotopic abundances of magnesium in natural terrestrial materials (Fig. 4.12.1). These variations are useful in investigating the origin of substances and studying environmental, hydrological, and geological processes , , .
26Mg is a stable isotope and is the radiogenic product of 26Al decay. 26Al is produced by cosmic rays in space and in the atmosphere, and it was present in the primordial solar nebula. The anomalous abundance of 26Mg in meteorite inclusions indicate that this material must have been formed early in the development of the Solar System before all primordial 26Al (with half-life of 7.1×105 years) had decayed .
26Al is a radioactive isotope (half-life of 7.1×105 years) that can be detected at the ultra-trace level (attogram range; 10−18 g levels) using accelerator mass spectrometry. 26Al is used as a tracer to study the uptake, distribution, and retention of aluminium in plants, animals, and humans under different physiological conditions , .
26Al is produced from spallation reactions of protons, produced by cosmic rays, on argon. 26Al has been used for dating geological samples, such as marine sediments, manganese nodules, rocks, and meteorites , . The abundances of 26Al to 10Be have been used to study erosion and transport of soil and sediments on a thousand- to million-year time scale, because production rates of 26Al to 10Be are greatest at the surface and decrease exponentially with depth (Fig. 4.13.1) , .
Intense cosmic-ray bombardment in space produces 26Al in meteorites and other bodies, such as the Moon. After a meteorite falls to Earth, 26Al production ceases due to atmospheric shielding; the decay of 26Al to 26Mg has been used to determine the terrestrial age of a meteorite (i.e. the time elapsed since the meteorite fell to Earth) .
Because molecules, atoms, and ions of the stable isotopes of silicon possess slightly different physical and chemical properties, they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are substantial variations in the isotopic abundances of silicon in natural terrestrial materials (Fig. 4.14.1). These variations are useful in investigating the origin of substances and studying environmental, hydrological, and geological processes , . Diatoms, a major group of algae, need silicon to build up their opaline shells and prefer 28Si while taking up Si(OH)4, which is the biologically available form of silicon in the marine environment. This progressively enriches surface waters with 29Si and 30Si . 32Si-labeled silicic acid of high specific radioactivity is used to measure uptake rates of Si and estimate marine sedimentation of biogenic (created by living organisms) silica (by diatoms and sea shells). By performing uptake kinetic experiments, the 32Si activity can be measured as 32P using counting of Cherenkov radiation (radiation produced by charged particles passing through a medium at a speed greater than that of light through the same medium — after Soviet physicist Pavel A. Cherenkov) with a liquid scintillation analyzer (measuring ionizing radiation using the interaction of radiation on a material and counting the resulting photon emissions).
Cosmogenic32Si has a half-life of about 150 years and is produced by cosmic-ray spallation of argon in the stratosphere and troposphere . 32Si in dust is precipitated in snow, making it possible to date dust in snow and glacial ice (Fig. 4.14.2). Glaciers are archives for global climate history because they contain a variety of proxies (imprints of past environmental conditions used to interpret paleoclimate) for climate forcing and climate response. Cosmogenic 32Si that is stored in glaciers and ice-core samples can be analyzed using accelerator mass spectrometry to date when sections of glaciers formed , .
At Keio University in Japan, the Itoh Research Group has developed a method that utilizes 29Si to store and process information. The Itoh Research Group focused on manipulating the nanostructure of materials at an atomic level, especially with semiconductors such as silicon. Their manipulations and observations demonstrate that differences in the nuclear spin and mass of an isotope affects the ease of further manipulation of the isotope , .
Silicon crystals enriched to higher than 99.99 percent purity of 28Si are being used in the Avogadro Project. This project is intended to remeasure the Avogadro constant (NA), which is the proportionality factor between the amount of substance and number of elementary entities .
32P (half-life of 14.3 days) is a radioactive isotope of phosphorus that is used to help understand the biological and chemical processes in plants. It is chemically identical to other isotopes of phosphorous and can be substituted in biological and chemical reactions. For example, a phosphate solution containing 32P (which has the identical behavior of non-radioactive 31P) can be inserted into the roots of a plant and its movement can then be tracked throughout the plant with the use of a Geiger counter. This movement detection study helps scientists to better understand how plants use phosphorous to reproduce and grow , .
At the molecular level, 32P can substitute for 31P in nucleotides of DNA or RNA (ribonucleic acid, a single stranded molecule that regulates genes). Radioactive probes can be created to help identify the presence, absence, and quantity of genes in a system , .
32P has been used as a tracer to help determine phosphorus nutrient cycling in eutrophied lakes (lakes rich in organic and mineral nutrients commonly leading to the excessive growth of phytoplankton, a self-feeding water organism) (Fig. 4.15.1). In one experiment, phosphoric acid labeled with 32P was added to a lake that had been experimentally eutrophied. 32P was measured in microphytoplankton (plankton visible only with a microscope), phytoplankton, and zooplankton (tiny animals that live suspended in fresh or salt water), and the amount of incorporated 32P was determined .
33P has been used to better understand phosphorus dynamics in the environment at the sediment-surface level. Phosphorus is a necessary nutrient for many biota (the plant and animal life of a particular habitat, region, or geological period). Understanding bioavailability and sorption (bonding) of this nutrient to particles in soil is important for understanding ecosystem health. Organic and inorganic phosphorus substrates isotopically labeled with 33P can be tracked within a sediment system to determine their transport properties and availability to biota .
32P was added to tires in the 1950s by Goodrich Laboratories to help determine the location and depth of tire wear in performance tests .
Beta emissions from the radioactive isotope 32P can be used in drug therapy of cancerous bone masses. By injecting a patient with a 32P pharmaceutical, tumors and other cells can be targeted for cell death, which also helps to alleviate pain , . For example, Polycythemia vera is the condition of having excess red blood cells in the bone marrow: 32P can be used to treat this condition by reducing the number of red blood cells. However, there is no cure for this condition . Using a 32P labeled bio-silicone product, 32P has been used as the radioactive target in brachytherapy of solid tumors in the lung . Depending on the type of 32P-labeled compound (antibody or pharmaceutical drug), when it is ingested or injected into the body, specific body parts (blood, tumors, joints, or bones) can be targeted for visualization and imaged using a gamma camera. This is useful for imaging cancer sites and for treatment monitoring of oncologic patients , , .
The stable sulfur isotope-amount ration(34S)/n(32S) has been used to distinguish whether animal tissues grew in freshwater or in marine ecosystems. The isotopes do not fractionate (separate) substantially with trophic influences (the movement of sulfur through and into plant and animal systems), and the isotope-amount ratio n(34S)/n(32S) is usually substantially different between freshwater and marine environments. As an example, by analyzing sulfur isotope-amount ratios in bird feathers, the environment in which the bird was living when these feathers developed can be determined. This enables one to track bird habitats and migration patterns throughout the year (Fig. 4.16.1) .
Molecules, atoms, and ions of the stable isotopes of sulfur possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are substantial variations in the isotopic abundances of sulfur in natural terrestrial materials (Fig. 4.16.2). These variations are useful in investigating the origin of substances and studying environmental, hydrological, and geological processes , . The isotope-amount ratio n(34S)/n(32S) can be used to trace natural and anthropogenic sources of sulfur. Examples include studies of acid mine drainage, the cycling of sulfur in agricultural watersheds, groundwater contamination from landfills, and sources of salinity in coastal aquifers , , .
The isotope-amount ratio n(34S)/n(32S) can be used to authenticate the dietary source of cattle. First, stable isotopes are measured to infer the dietary source of the cattle. Once the source of the diet is found, the isotopic compositions can be traced in certain muscle groups of the cattle and can be used to determine if the diet of the animal has been changed or if the feed is consistent with what the animal has been claimed to have been fed .
35S has a half-life of 87 days, which is an ideal duration for use as a conservative tracer in atmospheric processes. 35SO2 gas is produced as a natural product of argon exposure to cosmic rays in the atmosphere. Because 35SO2 gas is present in the atmosphere and then precipitates and falls as moisture in the form of 35SO42-, 35S can act as a tracer to study air mass transport dynamics and atmospheric oxidation capacity . Analyses of 35S in lake water and precipitation can also be used as a tracer to monitor contributions of sulfur that originated in precipitation to surface waters. If a water tests positive for the isotope 35S, it provides evidence that the water had been affected by recent (<~1 year) precipitation , , . 35S is used in direct labeling of elemental sulfur or sulfate sources to trace the fate of sulfur in fertilizers .
Because molecules, atoms, and ions of the stable isotopes of chlorine possess slightly different physical and chemical properties, they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are substantial variations in the isotopic abundances of chlorine in natural terrestrial materials (Fig. 4.17.1). These variations are useful for investigating the origin of substances and studying environmental, hydrological, and geological processes. Chlorine is subject to isotopic fractionation by physical and chemical processes. Variations in isotopic compositions of stable chlorine isotopes provide evidence for ultrafiltration and crystallization of brines and indicate sources of chlorine-bearing contaminants, such as solvents and rocket fuels, in the environment , .
Analyses of chlorine isotopes and other environmental tracers can help to identify whether an environmental contaminant is of anthropogenic origin or naturally occurring. For example, perchlorate (ClO4-) can be of anthropogenic origin and is also found naturally. Perchlorate is a widespread groundwater contaminant that can interfere with hormone production in the thyroid gland by displacing iodide. Both the stable chlorine isotope-amount ration(37Cl)/n(35Cl) and the mole fraction of 36Cl, n(36Cl)/n(Cl), can provide useful information about origins of perchlorate in the environment (Fig. 4.17.2). Such information may be important for legal reasons and for remediation of contaminated areas , .
Radioactive 36Cl provides a useful tool to determine ages in geology and hydrology. Some radioactive 36Cl is cosmogenic and enters the terrestrial environment in precipitation. Because of its long half-life of 3.01×105 years, the level of 36Cl in aquifers can be measured and used to estimate ages (on the order of 105 to 106 years) of old meteoric groundwater (water that was originally precipitation) .
Thermonuclear bomb tests in the ocean produced large amounts of 36Cl by neutron reactions with 35Cl in seawater. This was especially prevalent in the late 1950s. Large amounts of this anthropogenic 36Cl were distributed throughout the atmosphere, deposited with precipitation, and incorporated into terrestrial soils and groundwater. This enriched 36Cl has been used as a tracer of meteoric water from that era .
Argon’s chemically inert properties and three stable isotopes make it an ideal tracer of Earth processes , , , , , , , , , , , . Measurements and models of the isotope-amount ration(40Ar)/n(36Ar) can provide insights about the evolution of the atmosphere and orogenic (mountain-building) history of the Earth. The comparison of results from potassium-argon and n(40Ar)/n(39Ar) isotope-amount-ratio dating methods with results from other dating methods has been used to study temperature histories of rocks through differences in apparent ages caused by excess argon or partial argon gas loss. The isotope-amount ratio n(40Ar)/n(36Ar) of dissolved argon in groundwater can provide hydrologic information, such as rates of crustal degassing and relative groundwater age. 38Ar produced by cosmic-ray bombardment of rocks and soils at Earth’s surface can provide information about surface exposure history and erosion rate.
The first technique is potassium-argon dating (K-Ar), which is based on the decay of radioactive 40K to stable 40Ar. By comparing the concentrations of potassium and 40Ar in a sample, it is possible to determine how long the sample has been accumulating radiogenic40Ar to determine the “age” of the sample. The half-life of 40K is approximately 1.25×109 years, making this a useful tool for dating rocks range in age from about 106 to 109 years.
A modification of the potassium-argon dating technique is the n(40Ar)/n(39Ar) isotope-amount-ratio technique, in which a sample is irradiated in a nuclear reactor to produce 39Ar from 39K. The isotope-amount ratio n(40Ar)/n(39Ar) is then determined, and from this, the approximate age of the rock can be calculated (Fig. 4.18.2).
The study of 37Ar (half-life of 35 days), 39Ar (half-life of 268 years), and 40Ar concentrations in groundwater can provide information about the production and release of these isotopes from rocks and other sources into groundwater and the relative ages of different groundwaters , , , , , .
38K (half-life of 7.6 min), which is produced by the reactions 38Ar (p, n) 38K and 40Ar (n, 3n) 38K, is a widely used blood-flow tracer. Because 38Ar is more expensive, 40Ar, which also offers many additional advantages as a target, is more commonly used to produce 38K for medical purposes , . 41Ar (half-life of 1.82 h) is used as an industrial gas-flow tracer to help track the movement of gases because its inert properties, half-life, and gamma radiation make it well suited for this purpose .
The mole fraction of 40K, n(40K)/n(K), is used to study the effects of potassium in soil on the growth of plants. Plants need potassium to promote growth and reproduction, and potassium also helps plants resist drought and diseases. The mole fraction of 40K is being studied at different depths in several soil types to determine how soil properties affect the fractionation of 40K .
The amount ration(40K)/n(40Ar) is used in potassium-argon dating by geologists, archaeologists, and paleoanthropologists to determine the age of rocks. This dating method is based on the radioactive decay of 40K, having a half-life of 1.248×109 years, to 40Ar. When lava crystalizes, 40Ar can no longer escape and begins increasing in concentration in a rock (Fig. 4.19.1) , .
38K, which has a half-life of 7.6 min and is produced by a nuclear reaction involving 38Ar and 40Ar as targets, is a widely used blood-flow tracer. Because 38Ar is more expensive, 40Ar, which also offers many additional advantages as a target, is more commonly used to produce 38K for medical purposes , , .
Molecules, atoms, and ions of the stable isotopes of calcium possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights (Fig. 4.20.1). The isotope-amount ration(44Ca)/n(40Ca) is used to quantify the calcium cycle (sources and sinks of calcium) in the ocean. Calcium isotopes fractionate (separate) in terrestrial and marine environments owing to biological and inorganic processes, which discriminate against heavy calcium isotopes. The calcification process controls the removal of calcium from the ocean, which is mostly balanced by hydrothermal and riverine calcium input. Calcium has a long residence time, symbol τ, in seawater (τCa about 1 to 2 million years) relative to the short mixing time of the global ocean (about 1000 years), which has allowed the calcium isotopic composition of modern seawater to homogenize globally. This was likely the case in the geological past as well, which makes the n(44Ca)/n(40Ca) ratio useful when quantifying the oceanic calcium cycle , . The isotope-amount ratio n(44Ca)/n(40Ca) has been used to trace sources of calcium in soil and river water . The isotope-amount ratio n(44Ca)/n(40Ca) ratio of calcium carbonate may serve as a paleothermometer to determine seawater temperatures in the past, making use of the temperature-dependent isotopic fractionation between 40Ca and 44Ca , .
The radioactive isotope45Ca (half-life of 163 days) is used to study calcium behavior in soils, detergents, water-purification systems, and glassy materials. 45Ca is introduced into a system and monitored to measure various types of calcium responses within the system and to investigate how calcium of one matrix may interact with another (i.e. calcium of soil mixing with that of fertilizers). 45Ca has been used to investigate the transport of contaminants in groundwater through the unsaturated zone .
Stable isotopes of calcium (42Ca, 44Ca, 46Ca, and 48Ca) and radioisotopes of calcium (45Ca and 47Ca, with a half-life of 109 h) can be used for tracing calcium uptake, utilization, and excretion in the body. For example, most of our knowledge on the efficiency by which calcium is absorbed in the intestine (bioavailability) comes from studies in which calcium in the diet was labeled with stable or radioactive isotopes. In such studies, the isotope-labeled food is ingested and fecal matter tested for the presence and quantity of unabsorbed isotope. When coupling oral ingestion of food labeled with one calcium isotope with an intravenous injection of a second calcium isotope, this technique can be used as a means to measure calcium absorption within the body by measuring excretion of both tracers in the urine. In a similar fashion, dietary absorption of magnesium and zinc can be studied , .
Stable and radioactive isotopes are used in biomedical research and clinical practice to study disorders associated with calcium metabolism, in particular in relation to bone health and calcium accumulation in body tissues (vascular calcification, kidney stone formation). Stable isotope tracers have been used successfully to study bone calcium balance during space-flight and in-bed-rest studies. A long-living calcium radioisotope (41Ca), with a half-life of 9.9×104 years, has been used successfully for labeling of bone calcium to measure bone calcium turnover via urinary excretion of the tracer .
Radioactive 46Sc is used as a non-absorbed isotopic reference material for determining digestibility, absorption in the gut, and secretion sites for nutrients associated with feed residues in ruminating animals (animals that chew their food repeatedly for an extended period of time) .
The radioactive isotope46Sc has been used for sediment labeling to determine the transportation of sediments by water flow in rivers, estuaries, harbors, and seas. The half-life of 46Sc is about 84 days and when released into an estuary with similar grain density and grain size, a gamma spectrometer (instrument for measuring the intensity of gamma radiation versus the energy of each photon) can be used to measure the intensities of 46Sc in the sediments and the movement of the sediments can be determined , , .
46Sc is a beta emitter and has been used as a tracer in oil refinery crackers for crude oil (converting crude oil into gasoline and other lower-molecular weight hydrocarbon fractions). Its beta radiation enables the substance to be tracked as the oil travels . Due to its easily traceable properties, coastal engineers use 46Sc to develop dredging strategies and to design navigation channels based on silt movement .
46Sc is used in isotope-carrying antibodies for bonding with tumor-associated cell surface antigens (substances that causes the production of an antibody when introduced into the body, e.g. toxins, bacteria, and viruses). 46Sc is added to DTPA-derivatized (process by which a compound is chemically changed, producing a new compound that has properties more amenable to a particular analytical method) monoclonal antibodies and has been shown to target tumor cells, specifically in vivo, where it accumulates to high levels in the tumor (Fig. 4.21.1) , .
The isotope-amount ration(50Ti)/n(46Ti) is used to study the early history of the Solar System. The value of the ratio can help determine whether the Solar System was created from a well-homogenized source , . For example, variations in titanium isotopic compositions of various groups of meteorites can be observed (Fig. 4.22.1) .
The isotope-amount ratio n(48Ti)/n(49Ti) has been used in Isotope Ratio Method (IRM) analysis (initial titanium ratio/final titanium ratio) to estimate the energy production of nuclear reactors. This ratio can also be used to confirm that a reactor is being used for non-proliferation purposes (purposes other than to assist in the formation of nuclear weapon grade materials) .
The isotopic abundances of 50V and 51V have been used as an indicator of planetary core formation processes (Fig. 4.23.1). Vanadium is greatly depleted in the Earth’s mantle compared with that in chondritic meteorites (chondrites). It is assumed that the deficit of vanadium in the Earth’s crust is accounted for by its partitioning into the core . The ratios of 50V and 51V have been used as a test of the X-wind model, which accounts for a portion of the extinct radioactive nuclides present in the early Solar System by radiation from the young Sun . 51V is depleted in meteorites compared to Earth .
51V is used in solid state Nuclear Magnetic Resonance (NMR) to provide information to material scientists about surface species of vanadium oxide catalysts (substances that increase the rate of chemical reactions without themselves undergoing any permanent chemical change), their interaction with the supporting material, and their reactions during catalytic processes .
Molecules, atoms, and ions of the stable isotopes of chromium possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable variations in the isotopic abundances of chromium in natural terrestrial materials (Fig. 4.24.1).
SiC grains are formed in very high-temperature events that occurred before the formation of the Solar System. The chemical and isotopic composition of certain elements in these grains, such as chromium, provides insights into the origin of the Solar System. The 54Cr nucleus is only produced by supernovae. Excess amounts of this isotope in the SiC grains (relative to terrestrial isotopic composition) in primitive meteorites suggest a heterogeneous distribution of 54Cr in the early Solar System and different sources of material to our Solar System . The early solar nebula was divided into two components. One contained chromium depleted in the lighter isotopes and the other contained heavier chromium isotopes. Isotopic studies indicate these components formed a homogeneous mixture in the early Earth, but they separated during partitioning of the Earth’s core (Fig. 4.24.1) , .
Mobility and toxicity of chromium metal depend largely on the oxidation state of the element. Isotopes of chromium are fractionated by reduction-oxidation (redox) chemical reactions. The isotopic composition has been used to trace the origin of the element in the environment and provide information on reduction-oxidation chemical processes .
Stable isotopes of chromium are used to investigate the metabolism of chromium (III), which is an essential nutrient. Chromium stable isotopes (53Cr and 54Cr) have been administered to patients and the relative metabolic activity of each isotope is measured to study insulin function in patients suffering from diabetes (a disease in which the body is unable to produce any or enough insulin, and/or is not able to properly use the insulin that it does produce, resulting in elevated levels of glucose in the blood) . 51Cr and 53Cr have been used to label red blood cells to determine blood volume and life-time of red blood cells in the body .
The radioactive isotope53Mn is formed by the interaction of protons, produced by cosmic rays, on iron in rocks. The accumulation of 53Mn, having a half-life of 3.7×106 years, at the Earth’s surface enables determination of exposure ages of landforms to cosmic rays and quantification of erosion rates. For example, Schaefer et al.  measured 13 samples from nine dolerite (igneous rock containing plagioclase, pyroxene, and olivine) surfaces in the Dry Valleys, Antarctica. They found that the terrestrial 53Mn concentrations correlate well with cosmic-ray-produced 3He and 21Ne concentrations in the same samples (Fig. 4.25.1), which suggests that 53Mn is produced continuously in place and retained over millions of years without loss. Their results suggest that 53Mn concentrations in rocks can be used to monitor Earth-surface processes on time scales exceeding 10×106 years.
51Mn, 52Mn and 52mMn (with half-lives of 46 min, 5.6 days, and 21 min, respectively) are radioactive isotopes that emit positrons that are used in positron emission tomography (PET) imaging , . The m in the superscript of 52mMn indicates a metastable state of the isotope.
Natural iron enriched in its least abundant stable isotopes, 57Fe and 58Fe, are used as a tracer in human studies to assess absorption, excretion, distribution, and utilization of iron in basic and applied research , , , , , . The two radioisotopes, 55Fe and 59Fe, have sufficiently long half-lives of 2.75 years and 44.5 days, respectively, to be used as tracers, but potential health and environmental hazards limit their use to diagnostic applications in patient care (i.e. disorders of blood and of iron metabolism) , , .
60Fe is an extinct radionuclide with a half-life of 2.6×106 years that has fully decayed to 60Ni since formation of the Solar System. The distribution of the product (radiogenic) 60Ni in extraterrestrial material, such as meteorites, has been used to gain insight into the early history of the Solar System . Because molecules, atoms, and ions of the stable isotopes of iron possess slightly different physical and chemical properties, they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable variations in the isotopic abundances of iron in natural terrestrial materials (Fig. 4.26.1). Small variations in stable iron isotopic compositions caused by physical and chemical isotopic fractionation processes have been used to study mass transfer processes in nature and chemical equilibria , , .
55Fe is a beta emitting nuclide that serves as an electron source together with 63Ni (with a half-life of 99 years) in electron-capture detectors. Electron-capture detectors are used as thickness gauges or as detectors for organic analytes in gas chromatography .
52Fe, with a half-life of 8.3 h, emits positrons and is used in positron emission tomography (PET) studies. It can be produced in a cyclotron from stable 50Cr by alpha particle capture , , .
60Co (with a half-life of 5.27 years) is used to irradiate food sources as a method of preserving food (Fig. 4.27.1). The gamma radiation from 60Co kills bacteria and other organisms that cause disease and spoilage of food (see Fig. 4.27.1). The use of radioactive compounds for preserving food is not always viewed positively. Some individuals are concerned that harmful compounds will be produced during the irradiation process. However, there is no evidence to support the claim that irradiation is dangerous for food preservation . Many medical products today are sterilized using gamma rays from a 60Co source. This technique of sterilization is generally much cheaper and more effective than steam-heat sterilization because it is a cold process. For example, it can be performed on packaged items, such as disposable syringes. This sterilization technique is applicable to a wide range of heat-sensitive items, such as powders, ointments, and solutions, as well as biological preparations, such as bone, nerve, skin, etc., used in tissue grafts .
60Co is also used in industrial radiography to detect structural flaws in metal parts. The radiation can penetrate metals and the X-ray pattern produced by the radiating material can provide information on its strength, composition, and other properties . Because of the above property, 60Co is also used in leveling devices and thickness gauges used to test welds and castings .
60Co is a radioactive metal isotope that is used in cancer treatments by radiotherapy. When 60Co undergoes radioactive decay, high-energy gamma rays (energies of 1.17 MeV and 1.33 MeV) are emitted and have been used in brachytherapy to treat various types of cancer. Brachytherapy (brachy is Greek meaning “short distance”) is a method of radiation treatment in which sealed sources are used to deliver a radiation dose at a distance of up to a few centimeters by surface, intracavitary (insertion of the radioactive isotope in a body cavity), or interstitial (between cells) application . 60Co is used as a source of high-energy ionizing gamma radiation that can be directed to cancer cells from a device outside the body (external radiotherapy).
60Co (and sometimes 57Co and 58Co, with half-lives of 0.75 year and 71 days, respectively) is the key component of the Schilling test, which is a method for determining whether a patient’s body is making and using vitamin B12 properly. The cobalt isotope is used to label cobalt in vitamin B12 to monitor how the body processes this essential vitamin .
57Co delivers the smallest radiation dose of all the cobalt isotopes. As a result, it has been used in the past for imaging and estimating organ size and location and in evaluating tumors of the head and neck , , , , .
Because molecules, atoms, and ions of the stable isotopes of nickel possess slightly different physical and chemical properties, they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable variations in the isotopic abundances of nickel in terrestrial silicate rocks (Fig. 4.28.1) .
Anomalies in 60Ni abundance caused by decay of now extinct 60Fe have been used to study the early history of our Solar System (see section 4.26.2). 59Ni is a cosmogenic radionuclide with a half-life of 7.6×104 years. Decay of 59Ni has been used to assess the terrestrial age of meteorites and to determine abundances of extraterrestrial dust in ice and sediment .
63Ni (with a half-life of 99 years) is produced from stable 62Ni and is a beta-emitting radionuclide that serves as an electron source together with 55Fe in electron-capture detectors. Electron-capture detectors are used as thickness gauges or as detectors for organic analytes in gas chromatography (Fig. 4.28.2) . 63Ni is also used to ionize substances in ion mobility spectrometry–the basis of the instrument used in airports to screen passengers for drugs and bombs . 63Ni is also used as a fluorescence-inducing source in elemental analysis by X-ray fluorescence spectroscopy and in miniaturized long-lived nuclear batteries . Until the mid-1980s, nuclear batteries were used in pacemakers, but then they were replaced by long-lasting lithium batteries .
61Ni is used as a radiation target for production of the radioactive isotope61Cu (with a half-life of 3.3 h), which emits positrons for positron emission tomography (PET) applications using the 61Ni (p, n) 61Cu reaction. 64Ni is used as a radiation target for production of 64Cu (with a half-life of 12.7 h), which is used in radioimmunotherapy by attaching it to an antibody for delivery of cytotoxic radiation (toxic to living cells) to a target cell via the 64Ni (p, n) 64Cu reaction . 60Ni is used for the production of 57Co (with a half-life of 0.75 year), which is used as a reference source for gamma cameras that are used in nuclear medicinevia the 60Ni (p, 4He) 57Co reaction .
Molecules, atoms, and ions of the stable isotopes of copper possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable variations in the isotopic abundances of copper in natural terrestrial materials (Fig. 4.29.1). 63Cu and 65Cu have been used to study copper isotope science of supergene (formed by descending solutions) copper minerals for potential use as an indicator of the paleohydraulic (ancient hydraulic) gradient, and for potential to provide a vector toward unrecognized copper source regions . Copper isotope ratios of iron oxides and supergene copper sulfides in surface samples or fossil leached caps of ore deposits are being used in prospecting to rank prospects and focus on drilling areas that have the greatest potential for mature enrichment profiles .
The copper isotope-amount ration(65Cu)/n(63Cu) along with the silver isotope-amount ratio n(109Ag)/n(107Ag) and lead isotope-amount ratios n(206Pb)/n(204Pb), n(207Pb)/n(204Pb), and n(208Pb)/n(204Pb) have been used to determine the origin of European coins and the flow of goods in the historical world market. Metals from Peru and Mexico and those from European mining sites have distinct isotopic signatures that enable the origin of the metal to be determined based on the isotopic compositions of silver, copper, and lead in the coins. Silver from mines in Mexico and Peru in the 16th century was used to mint coins but did not influence the European coin market until the 18th century .
The radiopharmaceutical62Cu-PTSM, which contains radioactive 62Cu (with a half-life of 9.7 min), is used as a tracer in positron emission tomography (PET) to quantify myocardial perfusion (heart blood-flow measurements) , . The radioisotope64Cu (with a half-life of 12.7 h) is used for PET imaging and radiotherapy to diagnose, understand, and monitor disease (Fig. 4.29.2) , . The stable isotope 65Cu has been used as a tracer to study copper absorption, utilization, and excretion in humans , .
Molecules, atoms, and ions of the stable isotopes of zinc possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable variations in the isotopic abundances of zinc in natural terrestrial materials (Fig. 4.30.1). Stable zinc isotopes have been used as tracers to investigate biogeochemical and chemical processes in environmental contamination sites . The isotope-amount ration(66Zn)/n(64Zn) can be used as an environmental tracer for detecting the pathways of anthropogenic zinc , , .
Oral tracers of enriched 67Zn and intravenously injected stable isotopic tracers with enriched 70Zn are used simultaneously to determine the fraction of dietary zinc absorbed in humans, maintaining the amount or concentration of a nutrient or biomolecule in organs and body fluids. For example, zinc-isotope tracers can be administered to humans to determine if zinc absorption in their bodies may be impaired by ingestion of certain foods, food components, or dietary supplements. One such study conducted with Peruvian women showed that prenatal iron supplements affected the absorption of zinc during pregnancy. Another isotope tracer study investigated zinc deficiency in children with Crohn’s disease (an inflammatory disease of the intestines, especially the colon and ileum) , . Zinc radioisotopes (e.g.65Zn, with a half-life of 244 days) can also be used for determining zinc absorption in humans, but they are now used rarely because of radiation hazards , . ZnO nanoparticles enriched with 67Zn have been used as biological/environmental nanotoxicity tracers .
The 68Zn (p, 2p) 67Cu (with a half-life of 62 h) reaction in which targets with zinc enriched in 68Zn are irradiated and the neutron induced reaction 67Zn (n, p) 67Cu are both processes for producing 67Cu for radiotherapy . Irradiation of 64Zn with a deuteron (the nucleus of 2H, consisting of a proton and a neutron) in a cyclotron will produce the radioisotope 64Cu (with a half-life of 12.7 h), which can be used for therapeutic applications and diagnosis with positron emission tomography (PET) via the 64Zn (d, 2p) 64Cu reaction .
68Ga (with a half-life of 68 min) is a radioactive isotope that emits positrons, which are used to produce high-resolution imaging with positron emission tomography (PET). Unlike 18F, which is most commonly used, 68Ga is more easily produced using a cost-effective generator with the parent radionuclide68Ge (with a half-life of 271 days) (Fig. 4.31.1). Once produced, 68Ga easily couples to biomolecules (most commonly peptides) that target G-protein coupled receptors, which are over-expressed on human tumor cells. The labeled protein acts as a radioactive tracer for cancer diagnostics. PET images are often coupled with CT images to get a more complete picture of the body , , , , , , . Radiopharmaceutical67Ga (with a half-life of 78 h) is a gamma-emitting isotope used in scintigraphy for medical imaging , , .
Because molecules, atoms, and ions of the stable isotopes of germanium possess slightly different physical and chemical properties, they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable variations in the isotopic abundances of germanium in terrestrial materials (Fig. 4.32.1).
68Ge is used to calibrate positron emission tomography (PET) scanners, which have been used for medical diagnostic procedures .
72Ge and 74Ge are used to produce the radioactive isotopes72As and 74As, with half-lives of 26 h and 17.8 days, respectively. The arsenic nuclei can attach to tumors and the decay of these isotopes is used to image the location of cancerous tumors in vivovia the 72Ge (n, p) 72As reaction and the 74Ge (n, p) 74As reaction . 70Ge, 72Ge, and 74Ge have all been used to produce the medical radioisotope73Se via the 70Ge (4He, n) 73Se reaction, via the 72Ge (4He, 3n) 73Se reaction and via the reaction 74Ge (4He, 5n) 73Se, respectively .
73As and 76As (with half-lives of 80.3 days and 1.1 days, respectively) are important radioactive tracers used in environmental and biomedical studies to quantify arsenic uptake . 74As (with a half-life of 17.8 days) has been used to investigate the biotransformation (modification of a chemical compound by an organism) of arsenate by mammals. In one study rabbits were injected with 74As-labeled arsenate. After a given amount of time, blood and blood products were sampled and tested for the presence and quantity of labeled arsenate metabolites . Inhalation of dust or smoke containing 74As is thought to be a causal agent of lung cancer. In one study , the “absorption rate from the bronchial tree (a respiratory tract, which conducts air into the lungs) was rapid for the first several days and then tapered off slowly. In three patients an average of 45 percent of the inhaled arsenic was eliminated in the urine in 10 days and about 0.5 percent in the stools. The remainder must be assumed to have been deposited in the body, exhaled, and/or eliminated in body secretions and excreta over a long period of time.” See Fig. 4.33.1.
72As (with a half-life of 26 h) and 74As are useful in molecular imaging because they are radioactive isotopes that emit positrons that can be designed to bind to monoclonal antibodies (moAb), which accumulate in tumors and then 72As- or 74As-labeled ligands will bind to the moAbs. Once the 72As- or 74As-labeled ligand binds to the moAb, positron emission tomography (PET) is used to visualize the exact location of the tumor . A specific example of using radiolabeled antibodies for better imaging of tumors is the combination of 74As with bavituximab, which is an antibody that binds strongly to unique lipids on the surface of tumors. When a thiol group is introduced to bavituximab, arsenic is able to bind covalently, creating a simple and elegant radio-label for targeting cancerous tumors .
Molecules, atoms, and ions of the stable isotopes of selenium possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable variations in the isotopic abundances of selenium in natural terrestrial materials (Fig. 4.34.1).
75Se (with a half-life of 120 days) is used for X-ray radiography of welds to visualize welds and ensure that each weld is appropriate for its purpose .
75Se-selenomethionine (organic compound that combines to form proteins, found in Brazil nuts and soybeans) has been used to study the production of digestive enzymes (biological catalysts that accelerates chemical reactions) . Selenium stable isotopes are used in metabolic studies to monitor selenium intake and output , .
77Se and 78Se are used to produce the therapeutic radioisotope77Br via the 77Se (n, p) 77Br and the 78Se (n, 2p) 77Br reactions, respectively. 80Se is used to produce 80mBr via the reaction 80Se (n, p) 80mBr. The m the superscript of 80mBr indicates a metastable state of the isotope.
Molecules, atoms, and ions of the stable isotopes of bromine possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are substantial variations in the isotopic abundances of bromine in natural terrestrial materials (Fig. 4.35.1). These variations are useful in investigating the origin of substances and studying environmental, hydrological, and geological processes , . 79Br has been used as a groundwater tracer (Fig. 4.35.2). Introduction of a solution spiked with 79Br to groundwater and measurement of the change in the isotope-amount ration(79Br)/n(81Br) over time has been used to monitor tracer breakthrough and to calculate bromide travel time .
77Br (with a half-life of 57 h) is used to label radiopharmaceuticals that bind to estrogen receptors for tumor imaging. 75Br (with a half-life of 97 min) is being used with positron emission tomography (PET) imaging .
79Br is used in the proton cyclotron to produce 77Kr, which decays to 77Br via the reaction 79Br (p, 3n) 77Kr, which decays into 77Br .
85Kr (with a half-life of 10.7 years) has been used in atmospheric monitoring programs to track the effect of atomic facilities on the surrounding environment. 85Kr is co-generated with plutonium in the fuel elements of nuclear fission reactors and can be monitored at short distances (i.e. 1 to 5 km) from an area of clandestine plutonium separation from spent fuel from the nuclear reactor. The differences in 85Kr levels in the atmosphere have been used to estimate the amount of plutonium separated at weekly intervals. The production of plutonium for nuclear weapons and the output from commercial reprocessing plants have released large amounts of 85Kr into the atmosphere .
85Kr has minimal natural production in the Earth, but its concentration in the atmosphere has increased steadily because of human activities related to the nuclear industry. 85Kr enters oceans, lakes, and groundwater through equilibration of the water with air. 85Kr is produced terrestrially as a fission product of nuclear reactors and released into the atmosphere with the noble gases. It is also produced in the atmosphere via the cosmic ray neutron-activation reaction, 84Kr (n, γ) 85Kr. Thus, the 85Kr specific activity can be used to determine the time since water was isolated from the atmosphere (Fig. 4.36.1). This approach provides a valuable addition to the use of tritium (3H) as an indicator of ocean circulation and groundwater age on decadal (a period of 10 consecutive years) time scales , .
Krypton stable isotopes react in the upper atmosphere by cosmic-ray-induced spallation and neutron activation to produce radioactive 81Kr, with a half-life of approximately 2.1×105 years. In the atmosphere, 81Kr is chemically inert and has a long residence time; because of these characteristics, it is expected that 81Kr has a relatively constant and well-constrained atmospheric source. Natural cosmogenic81Kr is incorporated from air into infiltrating groundwater and has been used to determine the age of groundwater over time scales ranging to over 106 years , , , .
85Kr has been used as the illumination element of indicator lights of appliances and can be combined with phosphors to create materials that glow in the dark. Light is created when radiation from 85Kr strikes the phosphor . 85Kr can be used to detect container leaks by placing the radioactive gas inside a container and measuring (with a radiation detecting device) the amount of radioactive 85Kr that escapes. Because the gas is inert, Kr will not react with anything else in the container .
A patient can inhale gaseous radioactive 85Kr, which is then absorbed in the bloodstream, enabling the blood flow of the patient to be studied. Movement of the 85Kr can be tracked with a radiation detector to reveal pathways followed by the blood and to quantify blood velocity , , .
Due to biological similarities between rubidium and potassium, the radionuclide86Rb (with a half-life of 18.7 days) is used as a tracer in biological or medical investigations for applications where the half-life of the radioactive-tracer42K (half-life of 0.5 day) is too short . 86Rb (with a half-life of 18.7 days) has been used measure the metabolism in small vertebrates (Fig. 4.37.1), such as dunnarts (furry, narrow-footed marsupials about the size of a mouse) . The advantage of this technique over the standard doubly labelled water method, using water enriched in 2H and 18O, include lower equipment requirements, lower technical expertise, and longer time spans over which measurements can be made. This technique could be very useful for measuring the metabolism of amphibians and insects.
87Rb (with a half-life of 4.97×1010 years) is a long-lived radioisotope that is transformed into 87Sr by emission of a beta-minus particle (an electron) and an antineutrino. From the abundance of 87Sr and the Rb/Sr amount ratio in a rock, its age of crystallization can be calculated. Rb/Sr dating is one of the most widely employed techniques for dating geological samples .
82Rb (with a half-life of 75 s) acts similarly to potassium and is used for imaging of the heart to better assess heart muscle function as a radioactive analog to potassium , . 82Rb is being considered as an alternative to highly-enriched uranium for producing medically important radioisotopes .
Stable isotopic fractionation of strontium is small because the relative differences between the masses of strontium stable isotopes are small (mass numbers are 86, 87, and 88 for the most abundant stable isotopes). Also, strontium is not subject to reduction-oxidation reactions in normal terrestrial environments, which would cause isotopic fractionation to be more evident. Nevertheless, current studies are exploring potential applications of stable strontium isotopic fractionation; for example, it has been used as a proxy for temperature during coral growth and for insights into the diets of ancient populations , .
The relative abundance of natural radiogenic87Sr in seawater is related to the relative rates of processes that add or remove strontium in the ocean (seafloor spreading, mid-ocean-ridge hydrothermal activity, and continental weathering). Over geologic time, these processes have fluctuated and the isotope-amount ration(87Sr)/n(86Sr) has changed systematically. By measuring the n(87Sr)/n(86Sr) ratio in marine fossils of known age, it is possible to identify when such environmental changes occurred. Conversely, it is possible to estimate the ages of marine deposits by comparing measured n(87Sr)/n(86Sr) ratios with the global time chart; this process is known as strontium isotope stratigraphy .
The isotope-amount ratio n(87Sr)/n(86Sr) is highly variable in rocks, minerals, soils, and waters, and it can be transmitted to plants (Fig. 4.38.1), animals, and manufactured materials. Measurements of n(87Sr)/n(86Sr) ratios are used for forensic applications in food authentication (determining where food came from), archaeology, crime-scene investigation, and human migration , .
The 87Rb-87Sr dating technique utilizes the fact that 87Sr is a product of radioactive 87Rb decay (half-life of 4.97×1010 years) and is a useful tool for determining ages of rocks and minerals spanning the age of the Earth (Fig. 4.38.2) .
Carbon nanotubes (CNT), which are nano-scaled carbon tubes, are being examined in nanobiotechnology research studies because it has been discovered that CNTs labeled with 86Y (with a half-life of 0.6 day) are soluble when they are injected into mice. This discovery was made after mice were given an intravenous or intraperitoneal (directly into a body cavity) injection with the 86Y CNT and then were examined using positron emission tomography (PET) scans to observe whether the 86Y had been flushed from their systems. The PET scan determined that accumulation of 86Y occurred in the liver, kidney, and spleen with very rapid blood clearance. This has broad implications for developing drug treatments . Radiomicrosphere therapy (RT) that uses 90Y (with a half-life of 64 h) microspheres is a proven therapy that helps treat hepatic (liver) cancer (Fig. 4.39.1) . 90Y is also used in radiosynovectomy to reduce joint pain .
Zirconium enriched in 90Zr has been proposed for the cladding (covering) of reactor fuel elements (Fig. 4.40.1) because it has a lower neutron absorption cross section than natural abundances of zirconium and is well suited for coverage of metal parts without absorbing neutrons .
Nuclear physicists are trying to study the generation of new isotopes and their elements in stars (astrophysical nucleosynthesis) via the rapid neutron capture process (r-process). Physicists at the Radioactive Isotope Beam Facility (RIBF) of the RIKEN Nishina Center for Accelerator-Based Science in Wako, Japan, have begun creating and studying highly neutron-rich isotopes that are thought to only be produced by the r-process. The data for many neutron-rich isotopes is incomplete, and the RIKEN team is filling in key missing information that is needed to simulate the r-process (including information on the half-lives of the neutron-rich isotopes). So far, the half-lives of 38 neutron-rich isotopes have been measured from krypton to technetium, including 111Nb and 112Nb. When the missing information has been obtained, physicists will have a better understanding of the r-process and how elements are created , .
95Nb and 95mNb (with a half-life of 3.6 days) have been used in tumor research and tumor imaging studies (Fig. 4.41.1) , , . The m in the superscript of 95mNb indicates a metastable state of the isotope.
Molybdenites display a variation in isotopic composition (Fig. 4.42.1) . The isotopic composition of molybdenum in ocean sediments depends on oxygen levels in the ocean. When oxygen levels are high, the lighter isotopes of molybdenum are scavenged by iron and manganese oxides into sediments. However, when oxygen levels are low, the mechanism for molybdenum removal becomes more efficient and more of the heavier isotopes of molybdenum are found in iron and manganese oxides. Thus, the molybdenum isotopic composition of these sediments can be used as a proxy for oxygen levels in the paleo oceans (history of the oceans in the geological past) to gain insights into mechanisms that may have been responsible for mass-extinction events in the Earth’s history .
Depleted 95Mo has been used in the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (Tennessee, USA). The use of U-10Mo fuel elements (90 percent uranium, 10 percent molybdenum) would allow the conversion from high-enrichment uranium (HEU) fuel, 92 percent, to low-enrichment uranium (LEU) fuel, below 20 percent, for nuclear non-proliferation purposes .
95Mo is used to produce medical radioisotope97Ru via the 95Mo (4He, 2n) 97Ru reaction. The isotope 99Mo is commercially produced by the fission of 235U and is the parent radionuclide of 99mTc, which is the most widely used radiopharmaceutical in the world. The much longer half-life of 99Mo (about 66 h) enables the radionuclide to be transported more easily than the short-lived (6 h half-life) 99mTc. The n(99Mo)/n(99mTc) amount-ratio generator was originally developed at Brookhaven National Laboratory (Fig. 4.42.2) in the early 1960s and is now a patented system .
99mTc is an isomer of 99Tc with a half-life of approximately 6 h that is used to label peptides for morphologic (the form and structure of an organism) and dynamic modeling of renal (kidney), hepatic (liver), bone, and cardiac imaging , . 99mTc radiopharmaceuticals absorb to a variety of tumors. These tumors can be imaged using single-photon emission computed tomography (SPECT) coupled with non-invasive computed tomography (CT scan), which provides a high level of functional and anatomical information in a three-dimensional image (Fig. 4.43.1) , . Medronate is a radioactive pharmaceutical, which has been used to find, treat, or study certain diseases or body functions. 99mTc-labeled medronate (99mTc-MDP) is used in a diagnostic test to detect metastases from prostate, lung or thyroid cancer, making use of a gamma camera to record the distribution of 99mTc-MDP within the body. A two-dimensional image of the affected areas is produced.
100Ru is the product of a rare (and hence very long-lived) nuclear decay process from the double beta decay of 100Mo. A careful measurement of the half-life for this decay, which is 7.1×1018 years, can be used to place an upper limit on the mass of the electron neutrino, which is a neutral and weakly interacting subatomic particle first postulated by Wolfgang Pauli in 1930 .
Ruthenium and molybdenum share many similarities. They both have seven isotopes (96, 98, 99, 100, 101, 102, and 104 for ruthenium and 92, 94, 95, 96, 97, 98, and 100 for molybdenum), and their isotopes are formed by the same nucleosynthesisp-processes, r-processes, and s-processes, namely, p, r, s and r, s only, s and r, s and r, and r, respectively. The molybdenum and ruthenium isotopic composition of most meteorites lie along a mixing line (Fig. 4.44.1). The ruthenium and molybdenum of silicates in the Earth also lie on this line, which supports the hypothesis that the Earth accreted homogeneously. That is, the feeding zone of the Earth did not change substantially over time as both the bulk of the Earth and the late veneer accreted from material having the same ruthenium-molybdenum isotopic reservoir .
106Ru plaque brachytherapy has been used for eye preservation and tumor control of uveal (the middle layer of the wall of the eye) melanoma . The half-life of 106Ru is 373 days.
96Ru is used to produce radioisotopes94Ru (with a half-life of 52 min) and 95Ru (with half-life of about 1.64 h) via the reactions 96Ru (n, 3n) 94Ru and 96Ru (n, 2n) 95Ru, respectively (Fig. 4.44.2) , . 104Ru is used to produce the radioisotope 105Rh (with a half-life of about 35 h) via the reaction 104Ru (p, γ) 105Rh. 105Rh has been used in the treatment of bone pain .
The beta particles of 105Rh (with a half-life of about 35 h) are used in target radiotherapy to kill cancer cells or cause cancer cell sterilization . The gamma rays from 105Rh enable in vivo tracking during radiotherapy . 105Rh has been used in the treatment of bone pain (Fig. 4.45.1) , .
Ocular brachytherapy currently is performed using 125I (with a half-life of about 59 days) or 106Rh (with a half-life of about 30 s) seeds . Brachytherapy can allow a good spatial dose distribution over the ocular tumor with lower radiation on adjacent tissues. In the case of irradiation of the eyeball with 106Rh, 80 percent of the dose has been absorbed within a depth of 5.2 mm and 90 percent has been absorbed within 7.2 mm (Fig. 4.45.2). This limits the application of 106Rh; however, when 106Rh can be used, the radiation dose can be lower, which is preferred.
Small palladium nucleosynthetic anomalies in isotopic composition (related to s-process variability) were identified in type IVB iron meteorites . These nucleosynthetic isotope anomalies may represent spatial and/or temporal heterogeneity in the early solar nebula or may be due to chemical processing within the solar nebula , . Palladium and molybdenum isotopic compositions on selected iron meteorites are correlated (Fig. 4.46.1). One possible conclusion is that “a common presolar carrier must have been thermally processed on which the more volatile (a measure of the tendency of a substance to vaporize) Pd was lost and homogenized in the solar nebula, resulting in the deviation from the s-process” variability . Because these palladium (and other element) anomalies are persistent throughout the measured iron meteorites, the thermal processing must have occurred prior to the formation of the parent body that produced iron meteorites .
The isotope-amount ration(107Pd)/n(107Ag) is used in geochronology to help date major thermal events in the Solar System. Although 107Ag is naturally occurring, 107Ag is also the daughter product of the beta decay of 107Pd. If both excess 107Ag and 107Pd (with a half-life of 6.5×106 years) are present in a sample of extraterrestrial origin, then the material would have formed sometime after 107Pd decayed. The n(107Pd)/n(107Ag) amount ratio can be measured to help determine when the 107Pd decay process began and how much time has elapsed since the material was formed , , , , .
Seeds of the radioactive isotope103Pd are internally placed in the body to fight prostate and other cancers locally. 103Pd has a half-life of 16.99 days and releases energy at about 80 X-rays and 186 Auger electrons per 100 decays of 103Pd. Therefore, this makes this isotope an ideal candidate for internal radiotherapy for the treatment of cancers .
The radioisotope109Pd (with a half-life of 13.5 h) can be used as a form of cancer therapy. For example, 109Pd-labeled porphyrins or porphyrin-like substances are used as diagnostic and therapeutic techniques to help locate and address areas of tumorous growth. Porphyrins accumulate in tumors of the body and when radiolabeled porphyrins are introduced to the body, the X-rays and energy released can help determine the location and even treat the cancerous tumors .
104Pd is the major target used for cyclotron production of the medically important radioactive isotope 103Pd via the reaction 104Pd (p, p n) 103Pd .
The measurement of relative amounts of 107Ag and 109Ag is used to study the processes responsible for the isotopic fractionation of silver isotopes in ore deposits, which depends on the specific minerals and environmental conditions. This is currently an area of active research and it is thought that the relative amounts of the isotopes of silver are altered during the formation of the ore , .
Silver isotope-amount ratiosn(107Ag)/n(109Ag) along with isotope-amount ratios of copper n(65Cu)/n(63Cu), and isotope-amount ratios of lead (n(206Pb)/n(204Pb), n(207Pb)/n(204Pb) and n(208Pb)/n(204Pb)) have been used to determine origins of European coins and information on the flow of goods in the world market over time (Fig. 4.47.1). Metals from Peru and Mexico and those from European mining have distinct isotopic signatures that enable the origin of the metal to be determined by examining the isotopic compositions of silver, copper, and lead in the coins. Abundant silver sources, mined in Mexico and Peru in the 16th century, were used to mint coins, but they were not a major influence in the European coin market until the 18th century (Fig. 4.47.1) .
The amount ration(107Pd)/n(107Ag) is used in geochronology to date major events in the Solar System , , , , , . Although 107Ag is naturally occurring, it is also the daughter product by beta decay of 107Pd. If both excess 107Ag and 107Pd are present in a sample of extraterrestrial origin, then the material would have formed sometime after 107Pd decayed (i.e. sometime after the 6.5-million-year half-life of 107Pd). The n(107Pd)/n(107Ag) amount ratio can be measured to help determine when the 107Pd decay process began and determine how much time has elapsed since the material was formed.
107Ag is being studied as a possible target for cyclotron production of 103Pd (with a half-life of 17 days) via the 107Ag (p, α n) 103Pd reaction. 103Pd releases X-rays and Auger electrons at the rate of about 80 X-rays and 186 Auger electrons per 100 decays of 103Pd, which makes this isotope an ideal candidate for internal radiotherapy for the treatment of cancers. The production of this isotope in a no-carrier form (not formed in another solution) is important for its medical uses. By using neutrons, photons, and charged particles to force reactions with isotopes of a higher mass number than 103, 103Pd will occur in a fraction of those reactions. The most common methods of 103Pd production use targets of rhodium or other isotopes of palladium. However, 107Ag has also been studied as a feasible option , . 109Ag is used to produce the gamma reference source 110mAg to help calibrate gamma detectors , .
Metal accumulation is a threat to our world’s water systems and wildlife. As a way to measure the influence of heavy metals on wildlife utilizing mass spectrometric techniques, some researchers use animal food enriched in specific cadmium isotopes. These experiments work by exposing the animals to a diet enriched in 106Cd and/or other stable isotopes of metals (for example, 65Cu and/or 62Ni) for a period of time. Depending on the purpose of the experiment, the residence time of the food in the gut is determined and isotopic compositions of the gut and/or feces are measured viainductively coupled plasma mass spectrometry (ICP-MS). This information is used to measure bio-uptake (absorption and incorporation of a substance by living tissue) and accumulation rates of metals in an exposed animal , .
Molecules, atoms, and ions of the stable isotopes of cadmium possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are small but measureable variations in the isotopic abundances of dissolved cadmium in ocean water, which are a consequence of isotopic fractionation associated with biological uptake (Fig. 4.48.1) , , .
112Cd is used to produce the diagnostic radioisotope111In (with a half-life of 2.8 days) via the reaction 112Cd (p, 2n) 111In .
111In (with a half-life of 2.8 days) is used in indium leukocyte imaging (Fig. 4.49.1), in which white blood cells that are abundant at sites of infection are labeled with 111In to help locate the source of the infection , , .
Molecules, atoms, and ions of the stable isotopes of tin possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable variations in the isotopic abundances of tin in natural terrestrial materials (Fig. 4.50.1) .
117mSn (with a half-life of 14 days) DTPA is routinely used for diagnostic bone imaging and for the treatment of bone pain caused by the spread of cancer to bones. The m in the superscript of 117mSn indicates a metastable state of the isotope. By using 117mSn DTPA, marrow toxicity can be reduced, and the therapeutic efficacy of using radionuclides is maintained . 117mSn is a promising radionuclide for therapeutic applications because the radionuclide decays in a way that causes less damage to healthy tissues and bone marrow than other available treatments. These properties of 117mSn make it useful for the treatment of inflammatory synovial disease (i.e. rheumatoid arthritis) .
112Sn is used to produce the radioisotope113Sn (with a half-life of 115 days) via the reaction 112Sn (n, γ) 113Sn. This is used for n(113Sn)/n(113mIn) generators for the elution (extracting one material from another) of 113mIn (with a half-life of 1.66 h) as chloride for blood pool imaging. The m the superscript of 113mIn indicates a metastable state of the isotope. 117mSn is a medical radioisotope that can be produced using 116Sn and 117Sn .
Molecules, atoms, and ions of the stable isotopes of antimony possess slightly different physical and chemical properties, and they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are measureable substantial variations in the isotopic abundances of antimony in natural terrestrial materials (Fig. 4.51.1) . The stable isotopes 121Sb and 123Sb have been used to measure movement of sediments and rocks originating from locations high in antimony. 121Sb and 123Sb move with the sediments and have been used as tracers in areas low in antimony to determine the originating location of certain metal/metalloid contaminants in streams , , .
In the 1950s, 124Sb and 125Sb (with half-lives of 60 days and about 1000 days, respectively) were used commercially as tracers. They were injected into oil pipelines as a way to detect the residence time and flow rate of the substance through the pipeline. The presence of these isotopes could be detected by means of a Geiger counter held above the pipeline. If the pipeline had a leak, the tracer would escape and its contamination and movement could be detected in the soil. 124Sb and 125Sb are now both treated as environmental contaminants .
123Sb is used to produce 124I (with a half-life of 100 h), which is used in radioimmunotherapy and also in positron emission tomography. It can be produced from the 123Sb (3He, 2n) 124I reaction . 121Sb and 123Sb can both be used for the production of 123I (with a half-life of 13.2 h) via3He and alpha particle-induced reactions with 121Sb and 123Sb, although the most common production route is via124Xe or 123Te .
Tellurium isotopes are a mixture of r-process, s-process, and p-process nucleosynthesis products, making them useful for studying the contribution of stellar products to the molecular cloud from which the Sun and planets were formed (Fig. 4.52.1) , , .
The double beta decay of 130Te (with a half-life of 7×1020 years) has been used for the determination of gas-retention ages of tellurium minerals .
120Te is used for the production of 120gI, where “g” indicates ground state, via the 120Te (p, n) 120gI reaction, which is used as a positron emission tomography (PET) and beta-emitting isotope , . 120gI has a half-life of 1.36 h. 122Te is used in the production of the radioisotope122I (with a half-life of 3.6 min) via the reaction 122Te (p, n) 122I, which is used in gamma imaging . 123Te is used for the production of radioactive 123I (with a half-life of 13.2 h) via the 123Te (p, n) 123I reaction, which is used in thyroid imaging  and for in vivo medical studies using single-photon emission computed tomography (SPECT) . 124Te is used for the production of both 123I and the PET isotope 124I via the 124Te (p, 2n) 123I and 124Te (p, n) 124I reactions, respectively , , , . The half-life of 124I is 100 h.
131I (with a half-life of about 8 days) and 129I are both fission products; 129I is a long-lived fission product with a half-life of 1.7×107 years that can be helpful in the detection of the movement of radiation after a radioactive event, such as occurred at the Japanese reactors at Fukushima. In nuclear reactors and weapons tests, uranium and plutonium undergo fission processes in which one of the fission products is the long-lived isotope129I. This isotope has been used as a groundwater tracer to determine evidence of nuclear fission, and it can also be tracked in rainwater as evidence of a fission event in the air (weapons explosion; Fig. 4.53.1) , , .
Natural cosmogenic129I enters groundwater and other terrestrial environments from the atmosphere and then decays to 129Xe. The isotope-amount ration(129I)/n(127I) can be used as a clock to estimate time since cosmogenic 129I entered the system. The amount of product 129Xe in such cases is too small to measure; however, excess quantities of 129Xe can be found in meteorites and other very old samples that contained extinct primordial129I. Younger water bodies also can be differentiated from older water bodies by determining the amount of anthropogenic129I released since the 1960s from sources such as nuclear bomb tests , .
125I, which has a half-life of about 59 days, is used encapsulated in radiotherapy to target and treat sites of cancerous tumors . 120gI (with a half-life of 1.36 h), where the “g” indicates ground state, and 124I (with a half-life of 100 h) are radioactive isotopes that emit positrons and they are used in quantitative, diagnostic imaging of the body using positron emission tomography (PET) , , , , , . 123I and 131I (with half-lives of 0.55 day and 8 days, respectively) are used with single-photon emission computed spectroscopy (SPECT) for basic three-dimensional imaging , . Radioactive iodine isotopes are produced from radioactive tellurium isotope (see Section 4.52.3).
Radiogenic xenon isotopes are produced by nuclear reactions in atomic bombs and nuclear reactors. For example, 131Xe, 133Xe, and 135Xe are some of the fission products of 235U and 239Pu, and finding these isotopes would be evidence of a nuclear bomb reaction. Measurements of xenon isotopes (e.g. in the atmosphere or the subsurface) have been used to identify contamination from these sources, for example, to detect faults in nuclear reactors or to monitor compliance with nuclear test bans (Fig. 4.54.1) .
The stable isotopes of xenon hold many clues about the formation of the elements, solar-system history, and Earth processes , . For example, 129Xe has been used as a detector of “extinct” radionuclides. Some 129Xe is radiogenic as a result of being produced by the radioactive decay of 129I (half-life of 1.7×107 years). Because the half-life of 129I is much smaller than the age of the Earth, primordial129I (i.e. that which was present at the beginning of Earth’s history) is essentially gone after it decayed to 129Xe over geologic time. This means that radiogenic 129Xe could be a marker of the former existence of the “extinct” isotope 129I. Because primordial 129I was produced largely in supernovae, detection of radiogenic 129Xe in meteorites and terrestrial samples also implies that the time elapsed between 129I supernova nucleosynthesis and planetary condensation was short compared to the subsequent history of the Solar System. The many isotopes and reaction mechanisms of xenon have contributed numerous insights into Earth processes through the study of “xenology” (xenon isotopic variations used as geodynamic tracers to study the dynamics of the Earth) .
Xenon isotopes are used in numerous ways to investigate the movement of inhaled gases in lungs and other parts of the body. If radioactive isotopes of xenon [127Xe (with a half-life of 0.1 year), 133Xe, and hyperpolarized (having non-equilibrium alignment of nuclear spins, suitable for magnetic resonance) 129Xe] are inhaled, they can be tracked throughout the body by externally monitoring their decay products using magnetic resonance microscopy [high resolution magnetic resonance imaging (MRI) at microscopic (nanometer) levels] (Fig. 4.54.2). This imaging technique is used to assess how well oxygen is taken up and transported by the blood .
124Xe is used in the production of radioisotopes123I and 125I (with half-lives of 0.55 day and 59 days, respectively) via the reactions 124Xe (n, n p) 123I and 124Xe (n, γ) 125I, respectively, which are used in diagnostic procedures and cancer treatment, respectively .
137Cs (with a half-life of 30 years) can be used as a tracer in fungal mycelia (an extensive matrix of underground hyphae (stems of growth from a fungus)) to monitor the immobilization of this radioactive caesium isotope. After the nuclear reactor accident at Chernobyl, large quantities of 137Cs were released as fission products into the environment. Areas with large fungal populations and fungal mycelia seemed to immobilize the 137Cs isotope, which limited the spread of the radioactive isotope , .
River floodplains are an important site for storing suspended sediments and contaminants transferred from upstream catchments. 137Cs measurements of floodplain sediments provide a technique for estimating overbank sediment deposition, and it can provide information on spatial patterns of sediment deposition (Fig. 4.55.1) , , .
Nuclear fission of 235U (or other fissionable materials) yields 137Cs as a product. Although 137Cs is not naturally present in the environment, it can be collected from nuclear reactor processing and then used as an environmental tracer. 137Cs adheres tightly to porous sediments and will follow the movement of the sediment. By exposing sediments to 137Cs and allowing this combination to move dynamically, gamma ray spectrometry can then be used to measure the activity of 137Cs and monitor the movement of the radioactive sediments , , .
137Cs dating of sediments not older than 60 years is useful in natural and artificial lakes and other environments because of its widespread production and release during atmospheric nuclear weapons testing, which began in the late 1940s, plus subsequent releases, such as during the accident at the Chernobyl nuclear reactor in April 1986. The 137Cs concentration profile in a sediment core can be matched with the historical record of 137Cs release to determine the approximate age profile of the sediment , .
High-energy gamma rays from 137Cs serve as food irradiation devices to remove bacteria and other harmful microorganisms (living single celled organisms such as virus, algae and fungus) from food. Although 137Cs is not used commercially for large-scale food irradiation, it has been proposed that it can be used this way. Gamma rays from the radioactive 137Cs destroy the DNA of organisms to enable foods to last longer (i.e. irradiation of fruits and vegetables stops the ripening process) and be contamination free , .
Because molecules, atoms, and ions of the stable isotopes of barium possess slightly different physical and chemical properties, they can be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. von Allmen et al.  observed barium isotopic fractionation in the global barium cycle (Fig. 4.56.1).
High-precision barium isotope measurements reveal differences of up to 25 parts per million in the isotope-amount ration(137Ba)/n(136Ba) and 60 parts per million in the n(138Ba)/n(136Ba) ratio between chondrites and the Earth. These differences probably arose from incomplete mixing of nucleosynthetic material in the solar nebula. Barium isotopes may be the decay products of now-extinct 135Cs (with a half-life of about 1.6×106 years), which is thought to be a nucleosynthetic component. Chondritic meteorites have a slight excess of supernova-derived material as compared to Earth, demonstrating that the solar nebula was not perfectly homogenized upon formation (Fig. 4.56.1) , , .
Studies have shown that 138La (with a half-life of 1.06×1011 years) can be used along with 138Ce and 136Ce to measure time elapsed from a supernova explosion producing large numbers of neutrinos .
138La decays to 138Ce and 138Ba, respectively, by beta decay with a half-life of 1.06×1011 years and by electron capture with a half-life of 1.56×1011 years. The isotope-amount ration(138Ce)/n(142Ce) has been used for dating rocks on long time scales (billions of years) and as a chemical tracer in geochemistry . The increase in radiogenic138Ba in rocks enriched in rare earth elements, such as allanite, enables one to determine the age of such rocks (Fig. 4.57.1) .
139La is used for the production of the medical radioisotope139Ce via the 139La (p, n) 139Ce reaction .
When combined, 138La–138Ce and 147Sm–143Nd are two decay systems that are useful for studying processes affecting the light-rare-earth elements (lanthanum, cerium, praseodymium, neodymium, and samarium) and the igneous evolution of the Moon and Earth because different igneous materials have different cerium isotopic compositions (Fig. 4.58.1) and can be used in mass balance investigations , .
138Ce is a radiogenic isotope produced by decay of 138La, with a half-life of 1.06×1011 years, one of the longest clocks in geochronology. Thus, the isotope-amount ration(138Ce)/n(142Ce) can be used for dating rocks on long time scales (billions of years) and can also be used as a chemical tracer in geochemical studies.
144Ce (with a half-life of 0.78 year) has been used for brachytherapy applications in cells and vessels of the body. The half-life and specific activity of 144Ce give it a potential advantage over the commonly used isotope192Ir of higher dose rate at shorter distances and lower irradiation of organs outside the tumor . 144Ce enables the treatment of larger arteries as compared with 32P, another isotope commonly used for this style of radiotherapy.
Because of its relatively short half-life (19.12 h) and decay primarily by beta decay (96.3 percent beta decay and 3.7 percent alpha decay), 142Pr has been proposed for two main innovative applications in medicine, namely in microsphere brachytherapy and in eye plaque brachytherapy . 142Pr is advantageous because penetration of the beta fraction of the radiation is limited to a few millimeters in tissue, therefore limiting the dose of radiation to the treated site. 142Pr may be produced either by fast neutron activation or thermal neutron activation of stable 141Pr.
Research in metal-bearing radiopharmaceuticals is being conducted to determine the most efficient way to produce and process radioactive metals for in vivo tracing. This research has led to the development of a potential radionuclide generator that administers radioactive metal complexes to be observed during positron emission tomography (PET) imaging. A n(140Nd)/n(140Pr) amount-ratio radionuclide generator has been designed to administer 140Pr complexes, such as 140Pr-DTPA, to be used as a tracer during a PET scan . The half-life of 140Pr is 3.4 min. The n(140Nd)/n(140Pr) ratio radionuclide generators can also be used for administering 140Pr-phosphonate complexes to identify the development of skeletal metastases. Once the skeletal metastases are found, 153Sm-EDTMP can be administered as a radiotherapeutic agent to treat bone cancer (Fig. 4.59.1) . The half-life of 153Sm is 1.9 days.
143Nd is a radiogenic isotope produced by decay of 147Sm, with a half-life of 1.06×1011 years. Thus, the isotope-amount ration(143Nd)/n(144Nd) can be used for dating rocks on long time scales and as a chemical tracer in geochemistry (Fig. 4.60.1) , . The very small accumulation of 142Nd in billion-year-old metamorphosed rocks from Greenland [from the relatively short-lived (about 68×106 years) alpha decay of 146Sm] provided evidence that the crust of the Earth formed before the young planet was more than 100×106 years old. This is because only a short amount of time could have elapse to incorporate the 146Sm parent radionuclide into the ancient Greenland minerals before it decayed , .
146Nd has been used in the production of 147Pm (with a half-life of 2.6 years), via the reaction 146Nd (n, γ) 147Nd, which is followed by a subsequent electron decay reaction, 147Nd→147Pm+β- reaction. 147Pm is a radioactive power-generation source .
The beta-particle-emitting isotope147Pm (with a half-life of 2.68 years) is used in the nuclear fuel industry to measure the thickness of the inner surface layer of graphite in the cladding tube where the nuclear fuel rod is placed in a nuclear fuel reactor (Fig. 4.61.1). The graphite serves as a protective layer against mechanical contact between the nuclear fuel rod and the Zircaloy cladding (fuel-rod holding tube) and as a diffusion barrier against fission products. By placing a layer of 147Pm along the inner surface of the cladding before the graphite, the long half-life of 147Pm and constant beta-particle emission provide a reliable and simple technique to measure the thickness of the graphite along the inner surface of the tube (called the beta-ray backscatter technique) , , .
The beta decay property of 147Pm makes this radioisotope an ideal candidate for nuclear batteries (beta voltaics). Long-lived power supplies for remote and sometimes hostile environmental conditions are needed for space and sea missions, and nuclear batteries can uniquely serve this role. A nuclear battery using beta voltaics can have an energy density (quantity of energy per unit mass) near a thousand watt-h per kilogram with 21 percent efficiency, which is much greater than the best chemical batteries .
One possible origin for the Moon is from debris ejected by an indirect giant impact of Earth by an astronomical body the size of Mars when the Earth was forming . The kinetic energy liberated is thought to have melted a large part of the Moon forming a lunar magma ocean. Samarium isotope measurement results , along with measurements of isotopes of hafnium, tungsten, and neodymium, suggest that lunar magma formed about 70×106 years after the Solar System formed and had crystallized by about 215×106 years after formation. 147Sm (with a half-life of 1.06×1011 years) is used to study the formation of potassium, rare earth elements, and phosphorus-rich rocks .
147Sm bombarded with 40Ca produces the radioisotope 182Pb .
For more than 40 years, weapons-grade plutonium was manufactured by the Krasnoyarsk Mining and Chemical Combine in the now closed town of Krasnoyarsk Krai, Russia, using single-pass uranium-graphite production reactors . Water from the Yenisei River was used for heat removal from the reactor core. Radioactively contaminated water was discharged into the Yenisei River and was a primary source of contamination of bottom sediments and floodland for hundreds of kilometers down gradient from the Krasnoyarsk Mining and Chemical Combine. In 2002, radioactive contamination of the bottom sediments and floodlands was composed primarily of 137Cs, 152Eu, 154Eu, and 60Co . The decrease in the isotope-amount ration(154Eu)/n(152Eu) down the depth profiles (Fig. 4.63.1) enables one to determine the age of bottom sediments and floodlands of the Yenisei River and calculate their average formation rates .
Europium isotopes have been used in nuclear-control applications because they are good neutron absorbers . 152Eu (with a half-life of 13.5 years), which is produced by 151Eu via the neutron capture reaction 151Eu (n, γ) 152Eu, and 154Eu (with a half-life of 8.59 years) are used as reference sources for calibration in gamma ray spectroscopy (Fig. 4.63.2) .
Reactions on 153Eu can produce the therapeutic radionuclide153Sm (with a half-life of about 1.9 days) via fast neutron irradiation 153Eu (n, p) 153Sm .
The lunar surface is continuously exposed to cosmic radiation, and the interaction between planetary material and cosmic rays produces secondary neutrons. The neutron flux can be investigated using the large neutron capture cross sections of 149Sm, 155Gd, and 157Gd. For example, 157Gd will absorb neutrons and be converted to 158Gd. On a cross plot of n(158Gd)/n(160Gd) isotope-amount ratio and n(157Gd)/n(160Gd) isotope-amount ratio (Fig. 4.64.1), values will move from the lower right corner to the upper left corner of the cross plot with increasing time or increasing flux.
The addition of 157Gd to Neutron Capture Therapy (NCT) has been shown to be more effective at targeting tumors than the previous method of using only 10B for the treatment (Fig. 4.64.2) . 153Gd (with a half-life of 0.66 years) is used in the production of photon line sources (an optical source that emits one or more spectrally narrow lines as opposed to a continuous spectrum) to manufacture 153Gd line sources . 153Gd is also used as a photon source of the dual-photon absorptiometry (DPA) technique that is used to measure bone mineral content (BMC). Studies for this technique have been conducted in horses and humans , .
149Tb (with a half-life of 4.1 h) is being used in targeted radiotherapy using alpha particles for labeling radioimmunoconjugates in cancer treatments , . 161Tb (with a half-life of 6.9 days) attached to a bioconjugate (two covalently linked molecules, one or more of which is a biomolecule), is being used in cancer therapy as a targeted radiation treatment of cancer cells , . 161Tb is being used for imaging as it allows for on-line monitoring of its distribution using gamma cameras . 149Tb is produced by the reaction 142Nd(12C,5n)149Dy, which is followed by a subsequent positron decay reaction 149Dy→149Tb+β+. It can also be produced by the reaction 141Pr(12C,4n)149Tb; beam geometry is important for satisfactory yield of 149Tb (Fig. 4.65.1) .
The isotopes of dysprosium are highly magnetic and have been the subject of physics research involving interactions of isotopes and the structure of lattice supersolids (spatially ordered material with superfluid properties, i.e. zero viscosity). The Magneto-Optical Trapping (MOT) chamber is used for slowing atoms (isotopes) to study the physics of neutral atoms by using a laser light to cool atoms (“Doppler cooling”) and magnetic quadrupole fields to slow and “trap” the neutral atoms (Fig. 4.66.1) , .
164Dy has a large neutron absorption cross section, so dysprosium is used for control rods . 161Dy has been a key isotope for studying the Mössbauer Effect, which is the resonance and absorption of gamma ray emissions on nearby atoms in a solid state .
165Dy (with a half-life of 140 min) is commonly used in arthritis therapy (radiosynovectomy). Rheumatic inflammation of the membranes of joints is often treated by the injection of 165Dy-ferric oxide directly into the joint space of the knee. Leakage from the joint has been shown to be minimal .
Radiosynovectomy with 166Ho-radiopharmaceutical agents can be used for treatment of arthritis. The half-life of 166Ho is 1.1 days. 166Ho ferric hydroxide macroaggregate ([166Ho] FHMA) radiosynovectomy is being used because FHMA minimizes extra-articular (outside a joint) leakage of the radioisotope , . 166Ho has been used for radioimmunotherapy (RIT) with labeled antibodies . The 166Ho-chitosan complex (a linear polysaccharide, which is a long-chain molecule like cellulose that is used by the body for energy storage) is being used for hepatic (liver) cancer therapy . 166Ho-labeled radiopharmaceuticals have been used for alleviating pain from bone metastases , , .
166Ho microspheres have been used for intra-arterial radioembolization (treatment where radioactive particles are delivered to a tumor through the bloodstream) of liver metastases (Fig. 4.67.1) . 166Ho is paramagnetic and emits both beta and gamma radiation, which makes it ideal for radioembolization. These properties also enable the distribution of 166Ho microspheres to be visualized with magnetic resonance imaging and single-photon emission computed tomography (SPECT) .
The 166Ho-Patch is a specially designed radioactive skin patch that is used for external radiation of superficial skin cancers and Bowen’s disease in areas that are sensitive and difficult to treat by methods that are more destructive and have poor cosmetic results (i.e. areas of the face) , .
Radiolabeled171Er (with a half-life of 7.5 h) tablets have been used to study bowel movements of individuals using external scintigraphy. Such tablets have an enteric coating and contain small amounts of stable erbium oxide (170Er) initially. The tablets are then irradiated at a low neutron flux to produce radioactively labeled 171Er tablets, via the 170Er (n, γ) 171Er reaction. This method is a noninvasive approach for determining gastric emptying rates and visualizing segments of the digestive system in an individual , .
169Er (with a half-life of 9.4 days) is used in radiosynovectomy, which is a regularly practiced radiotherapy, on rheumatoid arthritis patients whose condition is resistant to standard methods of treatment (Fig. 4.68.1). Rheumatoid arthritis is a chronic, inflammatory, autoimmune disease of the joint capsule (synovial sac), which is lined with a thin membrane called the synovium, of an individual’s moveable joints (synovial joints). In radiosynovectomy, the radiopharmaceutical called 169Er- citrate colloid, which contains colloidal particles that are labeled with β-emitting 169Er, is directly injected into the synovial cavity (the cavity between the bones in a moveable joint inside of the synovium) of the affected joint. These radioactive-colloid particles are then phagocytized (engulfed) by macrophage-like synoviocytes as well as other phagocytizing inflammatory cells in the patient’s synovium. Necrosis (tissue death) and the inhabitation of cell proliferation (increase in number of cells) result from the radiation of the synovium and therefore, temporarily halts synovitis (which is the condition of when the synovium thickens with inflammation) and improves synovial joint function , , , .
170Tm (with a half-life of about 130 days) is used in the petrochemical industry for industrial radiography to test welds in pipes and tanks .
167Tm (with a half-life of 9.2 days) is useful for tumor and bone studies . Stable 169Tm can be bombarded in a nuclear reactor to create 170Tm, via the 169Tm (n, γ) 170Tm reaction, which emits X-rays and has been used in portable X-ray equipment as a radiation source . 170Tm has been used in high-dose-rate (HDR) brachytherapy  and for use in radiosynovectomy of medium sized joints (Fig. 4.69.1) .
169Yb (with a half-life of 32 days) emits gamma rays and can be used to create a radiographic image of an object without the use of electricity. A capsule containing 169Yb is placed on one side of the object being screened and photographic film is placed on the other. The result will indicate flaws in metal casting or welded joints , . Gamma cameras use 169Yb as a radiation source (Fig. 4.70.1). Gamma cameras are used to locate sealed radioactive sources and hot spots in historical waste. Images of the gamma ray intensity are made and then the 2-D distribution is superimposed on a picture or video image , .
The radioisotope169Yb is manufactured using 168Yb via the reaction 168Yb (n, γ) 169Yb.
176Lu (with a half-life of 3.73×1010 years) is used in labeling experiments to quantify absolute protein abundance (absolute quantities of proteins in a cell) and examine the extent of synthesis of proteins under specific biological conditions . 175Lu has been used as a yield tracer in inductively coupled plasma mass spectrometry (ICP-MS) determination of plutonium in urine .
Some 176Hf is radiogenic as a result of it being formed as a product of beta decay of radioactive 176Lu (half-life of 3.73×1010 years) . Thus, relations between the isotope-amount ratiosn(176Hf)/n(177Hf) and n(176Hf)/n(176Lu) have been used to determine the ages of minerals and rocks. Because of the long half-life of 176Lu, these ratios have been used in geochronology studies that document some of the oldest rocks in the Solar System and on Earth (Fig. 4.72.1).
Hafnium isotopic compositions of terrestrial materials evolved differently depending on the relative rates of 176Hf production. Geologists can use calculated lutetium-hafnium ages and the initial isotope-amount ratio n(176Hf)/n(177Hf) along with other isotopic data from the oldest rocks in the Earth to infer that the Earth’s crust differentiated within the first few hundred million years after condensation of the oldest solid matter in the Solar System .
Radioactive 182Hf decays to 182W with a half-life of 8.9×106 years, which is much less than the age of meteorites and the Earth. Therefore, measurements of the amounts of hafnium and tungsten isotopes in meteorites and terrestrial samples reveal the earlier presence of 182Hf. As a result, this provides information about chemical differentiation and evolution of the early Solar System , .
178 Ta (with a half-life of 9.3 min) is used in medical studies, such as first-pass radionuclide angiography of mice, to better understand cardiovascular disease. Radionuclide angiography uses a pinhole lens fitted to a high-speed multiwire proportional camera and a n(178W)/n(178Ta) amount-ratio generator for minimally invasive quantification of murine ventricular (heart) functions (Fig. 4.73.1) , . The multiwire gamma camera has a 178Ta generator incorporated in its housing, and it provides portable and laboratory ventricular function assessments for cardiovascular patients , . Intravenous injections of 178Ta are used in gated equilibrium blood pool imaging . 183Ta (with a half-life of 5.1 days) has potential for use in radionuclide pharmaceuticals and as a tracer for toxicity studies of ecosystems .
181Ta is used to produce 178W, which decays to 178Ta via the reaction 181Ta (p, 4 n) 178W, which is followed by a subsequent electron capture decay reaction of 178W to finally yield 178Ta. 178Ta is important for medical studies as noted in Section 4.73.1.
182W is the stable product of the decay of 182Hf, which has a half-life of 8.9×106 years. Although 182Hf was present at the dawn of the Solar System, this isotope has long since decayed. During the formation of the planets, including Earth, the elements hafnium and tungsten were partitioned into silicate minerals (rock forming minerals with silicon-oxygen bonds that constitute more than 90 percent of the Earth’s crust) and metal phases, respectively. The measurement of excessive amounts of 182W, arising from the decay of 182Hf that accumulated in silicate minerals, has been used to estimate the time that elapsed between the formation of the Solar System and accretion of the planets (Fig. 4.74.1) , .
Tungsten-rhenium generators use 188W, which is produced from 186W, via the following double neutron capture reaction 186W (n, γ) 187W (n, γ) 188W.
The rhenium-osmium dating method is of special interest for the dating of rhenium-bearing ores, gold deposits, copper-nickel deposits, and meteorites. This method is based on the beta-decay of 187Re (having a half-life of 41.6×109 years) to 187Os, an example of which appears in Fig. 4.75.1 .
186Re (with a half-life of 89 h) is a beta-emitting radioisotope that is used for cancer treatment, in particular for pain relief in bone cancer and in rheumatoid arthritis (see radiosynovectomy). It is produced from the stable isotope185Re via the 185Re (n, γ) 186Re reaction . 186Re is also used for radiolabeling of cancer therapeutic agents . 188Re (with a half-life of 17 h) is used to irradiate coronary arteries with beta particles during insertion of an angioplasty balloon (a tiny balloon that is inserted into an artery and inflated to flatten plaque build-up and improve blood flow) and in palliative therapy, particularly for bone metastases. The beta irradiation can decrease scar tissue formation after the overstretching of arteries by angioplasty.
The isotope-amount ration(187Os)/n(186Os) in rocks can be transferred to fluids, such as magmas, groundwaters, rivers, and oceans. Variations in the inherited n(187Os)/n(186Os) ratios can provide a useful tracer for fluid sources and migration paths, including different layers of the Earth , , , . Meteorites and meteorite dust impacting the Earth have different osmium isotopic compositions than terrestrial rocks and sediments. As a result, n(187Os)/n(186Os)-ratio studies provide evidence of continuing extraterrestrial additions to the Earth over geologic time, as well as providing a method for prospecting in the sedimentary record for large meteorite impact events that may have affected life on Earth .
Some 187Os is radiogenic as a result of being formed by the beta decay of radioactive 187Re, which has a half-life of 4.16×1010 years. Variations in the isotope-amount ratio n(187Os)/n(186Os) and amount ration(187Re)/n(186Os) are used for geochronology; for example, variations in these ratios have been used to determine the ages of the Earth, Moon, and meteorites . Kirk et al.  measured rhenium-osmium isotopic abundances in gold and pyrites from conglomerates of the Central Rand Group of South Africa (Fig. 4.76.1), which have produced over 48 000 metric tons of gold and have accounted for 40 percent of the world’s total historic production . The gold and rounded pyrites from the conglomerates yield an age of ~3.0×109 years. Kirk et al. find that this age is much older than that of the conglomerate, and they conclude that the gold is detrital (material wearing away by weathering or erosion) and was not deposited by later hydrothermal fluids.
192Os can be used for the production of the medical radioisotope195mPt via the 192Os (α, n) 195mPt reaction.
Metallic 192Ir (with a half-life of 74 days) is used as a radiation source in gamma cameras for non-destructive testing of products for manufacturing flaws, such as aircraft parts, boilers, and pipeline welds (Fig. 4.77.1) .
Metallic 192Ir is used in brachytherapy , , , . 191mIr (with a half-life of 5 s) is used for blood flow imaging (angiography), especially in pediatric populations , . The m in the superscript 191mIr indicates a metastable state of the isotope.
Iridium consists of two stable isotopes (191Ir and 193Ir) from which the radioactive isotopes192Ir and 195mPt (with a half-life of 4 days) can be produced. Both are used in nuclear medicine. The m in the superscript 195mPt indicates a metastable state of the isotope.
Astrophysicists have confirmed an anomaly in the isotopic composition of platinum in the chemically peculiar HgMn star χ Lupi, where the platinum isotopic composition was shown to be a mixture of 196Pt and 198Pt (Fig. 4.78.1) .
The decay of 190Pt (with a half-life of 4.9×1011 years) to 186Os over time has been used for dating rocks and iron meteorites .
195mPt (with a half-life of 4 days) is used for pharmacokinetic studies of platinum-based anti-tumor agents in cancer diagnosis and cancer therapy . The m in the superscript of 195mPt indicates a metastable state of the isotope. 195mPt can be produced from the stable isotopes192Os or 195Pt via the 192Os (α, n) 195mPt reaction and the 195Pt (n, n′) 195mPt reaction, respectively.
195Au (with a half-life of about 0.51 year) has been used to study particle movement within the lungs of rats . 198Au (with a half-life of 2.7 days) was used in a study to model gold cycling in plants. This study demonstrated that gold particles are retained by humates (organic constituents of soil), which contain fulvic acid, humic acid, ulmic acid, and lignin and would therefore be likely to accumulate in mull humus or forest litter .
As a diagnostic tool, colloidal 198Au is injected into the affected organ. Normal cells will take up the gold colloid, but tumor cells will not. Therefore, an abscess will show up as a “cold area” on a scan .
As a treatment option, gold is intended to provide localized irradiation and can be implanted or injected into the affected area. When implanted, the gold “seed” offers an advantage over other materials in that it can be left in place due to its short half-life (2.7 days). As a colloidal injection, 198Au has been found to produce improvement from a wide variety of cancers . Figure 4.79.1a and 4.79.1b, respectively, show squamous cell carcinoma (cancer) on the lower left eyelid of a cat and the eyelid 6 weeks after implantation of 198Au seeds .
Recent studies have shown the effectiveness of 198Au nanoparticles and nanodevices in reducing tumor size in mice while minimizing radiation spread to other areas , , . 198Au has been studied and successfully used as an anti-inflammatory (a substance or treatment that reduces the body tissues response to harmful stimuli, such as swelling) for improving arthritic conditions , .
198Hg, 200Hg, and 202Hg are stable isotopes of mercury that can be used to study environmental sources and environmental sinks of this element in aquatic and terrestrial ecosystems. For example, in an ecosystem, different stable isotopes of mercury can be added to an upland region for run-off evaluation, to a lake for direct deposition analysis, and to a wetland region for outflow contribution analysis (Fig. 4.80.1). As a result, it is possible to determine the entry points of mercury into an ecosystem and determine how the inputs of mercury affect the accumulation of this element in local fish populations. An international consortium of scientists is conducting an experiment called METAALICUS (Mercury Experiment To Assess Atmospheric Loading In Canada and the U.S.). This experiment includes determination of whether mercury contamination in fish is old or new mercury. Tracer studies were performed in northwestern Ontario at the Experimental Lakes Area of the Department of Fisheries and Oceans Canada .
202Hg is used to produce radioactive 203Hg (with a half-life of 46.6 days) via the 202Hg (n, γ) 203Hg reaction, which is used in gamma radiation calibration and medical tests.
Because molecules, atoms, and ions of the stable isotopes of thallium possess slightly different physical and chemical properties, they commonly will be fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. There are substantial variations in the isotopic abundances of thallium in natural terrestrial materials (Fig. 4.81.1). These variations are useful in investigating the origin of substances and studying environmental, hydrological, and geological processes . The isotope-amount ration(205Tl)/n(203Tl) has been used to study how trace metals are transported and distributed in hydrothermal fluids . The n(205Tl)/n(203Tl) ratio has also been used to study the cycling, distribution, and behavior of thallium in the marine environment .
201Tl scintigraphy is used to detect coronary artery disease . Imaging of 201Tl (with a half-life of 3 days), can be used for exercise perfusion tests of the myocardium (muscular tissue of the heart), which determine damage to the heart caused by a heart attack or by heart disease (Fig. 4.81.2) .
203Tl is used in the production of 201Tl via the 203Tl (p, 3 n) 201Pb reaction, which is followed by a subsequent electron capture decay reaction of 201Pb to finally yield 201Tl. 205Tl is used as an alternative target in the production of 201Tl.
The study of lead isotopic compositions is used to model the distribution of pollution in water and on land (Fig. 4.82.1). For example, in one study of Lake Härsvatten in Sweden, the isotope-amount ration(206Pb)/n(207Pb) measured at different sediment depths in different areas throughout the lake showed patterns of accumulation of lead pollution. In some cases, these patterns could be related to sediment distribution patterns. Another study used 210Pb (with a half-life of 22.6 years) dating methods to study the vertical accretion of sediments in canals and wetland areas in Louisiana over the last 80 to 100 years , .
Three of the stable isotopes of lead (206Pb, 207Pb, and 208Pb) are produced by the radioactive decay of isotopes of uranium and thorium (238U, 235U, and 232Th, respectively) and are largely unaffected by environmental and metallurgical processes. Therefore, by examining various isotope-amount ratios of lead isotopes, it is possible to approximate the age of a material. It is also possible to use this information to trace the origins of an object or material , , , .
Different geographic regions may have characteristic terrestrial lead isotopic compositions because of variations in the ages and chemical composition of the rocks and minerals in the local environment. Therefore, lead produced at a particular location can have a unique lead isotopic composition and it is possible to trace the history and origins of pollutants by measuring the relative amounts of the four stable isotopes of lead (208Pb, 207Pb, 206Pb, and 204Pb) (Fig. 4.82.2) , . Using isotopic abundance data, the source of this toxic metal can be identified as it moves through air and water and eventually to living systems , . Scientists have analyzed lead in air pollution in California and found that it originated from Asia. Airborne particles from China have relatively higher amounts of 208Pb, which distinguishes the lead isotopic signature between airborne particles from Asia and North America. This knowledge could have implications in understanding the mixing of particles in the atmosphere and how pollutants are transported over vast distances , , , . Mapping the distribution of lead pollution by studying 204Pb, 206Pb, 207Pb and 208Pb also allows the identification of those human activities that contribute the highest amounts of lead to the environment , , .
The measurement of the isotopic composition of lead in blood can help to determine the source of this toxic element in the body . Lead is stored in bones and teeth. If a person moves to a different geographical region, the isotopic composition of the lead in the teeth is maintained, recording their place of origin. Bone can store lead for long periods of time (about 20 years), and some skeletal lead may be older and have a different isotopic composition than other skeletal lead. These differences reflect exposure to lead of different origins. By studying the isotope-amount ratio n(206Pb)/n(204Pb) and n(207Pb)/n(206Pb) in bone and teeth, it is possible to determine someone’s place of origin. For example, isotopes of lead were analyzed in the teeth and bones of a human mummy, known as the “Iceman”, to help determine his place of origin , .
210Pb is a relatively short-lived radioactive isotope of lead that is constantly produced by the decay of 222Rn in the atmosphere. While living, humans naturally incorporate 210Pb from the environment into bones and tissues. The amount of 210Pb in the body reaches equilibrium such that the 210Pb ingested is in equilibrium with the 210Pb that decays. When a person dies, this incorporation of 210Pb ceases and the relative amount of this isotope in the body decreases. Therefore, measurement of the 210Pb activity in a corpse can help determine time of death , .
Lead isotope-amount ratios n(206Pb)/n(204Pb), n(207Pb)/n(204Pb), and n(208Pb)/n(204Pb)) along with isotope-amount ratio of silver, n(107Ag)/n(109Ag), and isotope-amount ratio of copper n(65Cu)/n(63Cu) have been used to determine the origin of European coins (see Section 4.29 on copper) and to investigate the flow of goods in the world market over time . Metals from Peru and Mexico and those from European mining have distinct isotopic signatures that enable the origin of the metal to be determined by examining the isotopic compositions of silver, copper, and lead in the coins. Abundant silver sources mined in Mexico and Peru in the 16th century were used to mint coins, but were not a major influence in the European coin market until the 18th century .
The three natural radioactive-decay chains beginning with 238U, 235U, and 232Th each have comparable half-lives that are much longer than the radioactive isotopes that follow until the production of stable isotopes of 206Pb, 207Pb, and 208Pb, respectively. Therefore, one can measure the relative amounts of the radiogenic isotopes of lead to determine the length of time that has elapsed since uranium and thorium atoms were incorporated into rocks and minerals. Typically, this method is used to date minerals that are tens of millions to billions of years old. The uranium-lead dating method was used to determine some of the first accurate ages of the Earth (about 4.55×109 years) , , .
212Bi and 213Bi (with half-lives of 1 h and 0.76 h, respectively) are both used in medicine for radioimmunotherapy as bismuth-labeled monoclonal antibodies to treat cancer cells from melanoma (skin cancer) (Fig. 4.83.1) and ovarian cancer . Figure 4.83.2 compares the biologic effect of 131I and 213Bi using a specific monoclonal antibody, B-B4, coupled to 213Bi by a chelating agent (a substance that can form multiple bonds to a single metal ion). 213Bi is a mixed alpha and beta emitter with a half-life of 0.76 h. The primary mode of decay is by beta emission to the very short-lived alpha emitter 213Po. The 8.4 MeV alpha particle emitted by 213Po has a path length of 76 μm in human tissue and is responsible for its cytotoxic effects (toxic to living cells). 213Bi is produced from a series of alpha particle decays beginning with 225Ac, which is a pure alpha emitter with a half-life of 10 days. A schematic of the Institute for Transuranium Elements (ITU) Standard 225Ac/213Bi Radionuclide Generator is shown in Fig. 4.83.3.
212Bi has been used for radioimmunotherapy of leukemia and for targeting the vascular endothelial cells (thin layer of simple squamous cells that forms the interface between circulating blood or lymph and the remainder of the vessel wall) of tumors .
209Bi is bombarded with neutrons in a nuclear reactor to form radioactive 210Bi. The 210Bi (with a half-life of 5 days) decays via the reaction 210Bi→210Po+β−. The half-life of 210Po is 138 days and it is used in static eliminators in machinery .
210Po (with a half-life of 138 days) is used as static eliminator to remove static electricity in machinery. This is useful in machinery that produces electricity easily, for example, via rolling paper, manufacturing sheet plastics, and spinning synthetic fibers, which all readily produce static , . 210Po can also make use of its static eliminating properties when used in brushes that function to clean camera lenses and photographic films (Fig. 4.84.1) . 210Po has been used to manufacture atomic weapons. When combined with beryllium, polonium can act as a neutron-producing initiator. However, because of its short half-life, 210Po is no longer used in this manner .
211At (with a half-life of 7.2 h) is known to accumulate in the thyroid and occasionally is the preferred treatment for hyperthyroidism and thyroid cancer because the particles emitted from 211At provide more energy than radiolabeled iodine, the other treatment method (Fig. 4.85.1). However, astatine has shown a tendency to induce tumors, so its use is limited . The 211At-labeled di-carborane (cluster of boron, carbon, and hydrogen atoms) ligand known as the Venus Flytrap Cluster (VFC) has been used as a robust pharmaceutical in radiotherapy treatment .
Both 220Rn and 222Rn (with half-lives of 56 s and 3.8 days, respectively) are used to study underground environmental and atmospheric gaseous-transport processes , , . The interaction of radon with streams and rivers enables it to be used as a tracer in groundwater studies (Fig. 4.86.1). 222Rn has a short residence time in streams and river channels, which leads to radon loss. As a result, if an area of a stream or river has a high concentration of radon, it suggests that there are local groundwater inputs , , . In a deep (100 m) contaminated aquifer at a refinery site in Mexico, where the contaminated source was too deep to be directly accessible for sampling, Schubert et al.  collected groundwater samples from a few wells available at the site. They used the partitioning of the natural tracer 222Rn between uncontaminated groundwater and the NAPL (non-aqueous phase-liquid, such as oil, gasoline, and petroleum) source zone, and they were able to approximately identify the location of the NAPL source zone. As noted in Section 4.88.1, 222Rn has been used to quantify submarine groundwater discharge .
Francium was discovered in 1939 by Marguerite Perey, a physicist at the Curie Institute in Paris, France (Fig. 4.87.1). 223Fr (with a half-life of 22 min) occurs naturally in uranium minerals as a result of actinium decay. However, it is estimated that no more than approximately 30 g of francium is present in the Earth’s crust at any time. Francium can be produced artificially for research by bombarding thorium with protons. Francium was named in honor of Perey’s home country, France , , . Francium has no known isotopic applications outside of scientific research.
The radioactive isotopes223Ra (with a half-life of 275 h), 224Ra (with a half-life of 88 h), 226Ra (with a half-life of 1600 years), and 228Ra (with a half-life of 5.75 years) are used as tracers to determine water flow rates. They are ideal environmental tracers because they behave conservatively once released into a water mass (meaning only mixing and decay processes affect their distribution) . The activity ratios A(224Ra)/A(223Ra), A(223Ra)/A(226Ra), A(224Ra)/A(228Ra), and A(228Ra)/A(226Ra) have been used in lake studies to monitor and detect water inflow and mixing, to determine sources of inflowing water, and to monitor introduced water masses as they move within a body of water (i.e. a lake) , . For example, submarine groundwater discharge is an important pathway that transports dissolved substances from aquifers below a seabed to the coastal ocean. Submarine groundwater discharge can be difficult to quantify because it is both spatially and temporally variable. As a result, its relative importance in coastal ocean chemical budgets is commonly poorly known. Peterson et al.  used an hourly time series of measurements of multiple radium isotopes223Ra, 224Ra, and 226Ra to quantify submarine groundwater discharge. They also used 222Rn (with a half-life of 3.8 days) measurements to independently quantify submarine groundwater discharge.
226Ra and 228Ra can be used for dating materials up to a few thousand years in age because the half-lives of 226Ra and 228Ra are 1600 years and 5.75 years, respectively, even though the long-lived 226Ra is found in nature as a result of its continuous production by the decay of 238U. For example, long-lived 226Ra has been used to date a limestone cave in central Switzerland, corals in the Indian Ocean, and Pleistocene gravel terraces . The activity ratio A(224Ra)/A(223Ra) is a potential age calculator for old lake water because the low 223Ra and 224Ra activities in old lake water are relatively unaffected by mixing .
226Ra is used in brachytherapy (Fig. 4.88.1), which is a method of localized treatment of various types of cancer. A sealed implant (such as a rod, seed, or needle) containing the radioactive isotope 226Ra is inserted into or near a patient’s tumor to apply a high dose of radiation to the tumor. The sealed implant is inserted by a physician or by an automated device (called a remote afterloader), and it is removed from the patient once the tumor is destroyed , .
227Ac (with a half-life of 21.77 years) has been used as a tracer of deep-sea mixing in the oceans. By determining concentrations of 227Ac in a water column, scientists can study the rates and patterns of mixing and other vertical exchange processes . As a product of the 235U decay chain, 227Ac and other radioisotopes have been used to determine information about the movement of fluids in mid-oceanic ridges and basaltic melts , .
225Ac (with a half-life of 10 days) can be used in cancer treatments (Fig. 4.89.1). The isotope is attached to a chelating agent (a substance that can form multiple bonds to a single metal ion) and delivered to the problem site. The emissions of alpha particles from actinium and its daughter products cause tumor death . 225Ac in a series of alpha decays produces 213Bi (with a half-life of 0.76 h), which is also used for radioimmunotherapy .
225Ac, which is a pure alpha emitter, is used to produce 213Bi with an 225Ac/213Bi radionuclide generator (Fig. 4.89.2). 213Bi is a mixed alpha and beta emitter. The primary mode of decay is by beta emission to the very short-lived, alpha emitter 213Po. The 8.4 MeV alpha particle emitted by 213Po has a path length of 76 μm in human tissue and is responsible for its cytotoxic effects.
234Th (with a half-life of 24 days) has been used as a tracer for estimating the flux of organic carbon in the ocean (Fig. 4.90.1) , . 234Th has been used for estimating the residence time of suspended particulate matter (SPM) in water columns .
The decay of 232Th (with a half-life of 1.40×1010 years) to 208Pb is used to date rocks based on the accumulation of the stable daughter product208Pb. The half-lives of the isotopes between the parent radionuclide232Th and stable endpoint 208Pb all have much shorter half-lives than thorium. Therefore, the amount of 208Pb that accumulates in a sample is determined primarily by the amount of 232Th parent radionuclide present when the mineral was formed and the time that has elapsed since the mineral solidified .
Another dating method, the 230Th/234U method, is based on the hypothesis that the sample contains uranium, but no 230Th at the time of its formation. Then, the age of the specimen is determined mainly by the amount of 230Th in the specimen. Reliable ages with this method range from several thousand to approximately 350 thousand years .
The most precise time and frequency measurements are performed with optical atomic clocks that use as a frequency standard the optical frequency generated as electrons change energy levels. It has been proposed that a nuclear clock, using a nuclear transition could outperform an electron transition. 229mTh, with a half-life of 13.9 h, has been confirmed as a possible candidate for a nuclear clock . The m in 229mTh indicates a metastable state of the isotope. The further development of a nuclear frequency standard will require more precise determinations of the energy and half-life of the isomer.
231Pa (with a half-life of 3.25×104 years) and 230Th (with a half-life of 7.56×104 years) are produced in seawater by radioactive decay of 235U and 234U. The amount ratio of radioactive production of 231Pa and 230Th, n(231Pa)/n(230Th), is 0.093. 230Th is removed from seawater in settling particulates more efficiently than 231Pa, while 231Pa tends to be transported farther in ocean currents. Therefore, the amount ratio n(231Pa)/n(230Th) in settling particulates tends to be less than the production ratio of 0.093 unless the water mass is stationary and allows both products to settle out. Thus, sedimentary records of excess n(231Pa)/n(230Th) amount ratios can provide information for changes in the relative magnitude of major ocean circulation (Fig. 4.91.1) , .
231Pa is a natural radiogenic isotope produced by alpha decay of 235U to 231Th, followed by beta emission to form 231Pa. Although its behavior in the environment as a transient member of the U-series decay chain may be complex, measurements and modeling of 231Pa in relation to the isotopes of uranium and thorium have been used in a variety of geochronologic applications on time scales of 103 to 105 years , . Studies include movement of water masses and particles in the oceans, rates of magma melting and movement beneath volcanoes, and ages of carbonate mineral deposits, including corals, in relation to climate change.
234U (with a half-life of 2.432×105 years) is a daughter product of 238U (with a half-life of 4.47×1010 years) and makes up only 0.0054 percent of the total uranium today. During the decay of the parent radionuclide238U nucleus (first to 234Th (with a half-life of 24 days) by alpha decay, then to 234Pa (with a half-life of 6.7 h) by beta-minus, and finally to 234U by beta-minus), the energy released will damage the chemical and physical bonds holding the 234U product nuclei in a mineral. As a result, 234U may be leached more easily from water or rock samples than 238U and the isotope-amount ration(234U)/n(238U) will vary depending on the extent of water-rock interaction .
The three natural radioactive decay chains beginning with 238U, 235U, and 232Th each have comparable half-lives that are much longer than the radioactive isotopes that follow until the production of stable isotopes of 206Pb, 207Pb, and 208Pb, respectively. When undisturbed, the activities of daughter isotopes in each decay chain are equal to their parents and one can measure the accumulation of the stable isotopes of lead to date the time that has elapsed since a mineral became a closed system (a system that does not exchange matter with its surroundings). Rocks formed hundreds of millions to billions of years ago can be dated using this technique . If a mineral is disturbed at some point during the decay and isotopes in the decay chain are preferentially removed from the system, the equilibria in a decay sequence will be disturbed. For example, one can measure the excess of 230Th (with a half-life of 7.56×104 years) relative to the 234U parent radionuclide to date carbonates (speleothems or corals) that are less than 5×105 years old .
Nuclei of 235U are split when bombarded by thermal neutrons. The process is known as nuclear fission and can release tremendous amounts of energy per uranium nucleus. The nucleus that splits will release additional neutrons that, if slowed down sufficiently, can cause subsequent fission events. When properly controlled, 235U fission can be used to generate heat to drive steam turbines, which in turn produces electricity (Fig. 4.92.1). If the fission process is not controlled, then a rapid and explosive release of energy will occur, similar to that of nuclear weapons . Uranium depleted in 235U by fission in nuclear reactors (and hence greatly enriched in 238U compared to “natural” uranium) is used in the manufacture of DUCRETE concrete (Fig. 4.92.2). The incorporation of the large 238U nuclei makes this material an effective absorber of neutrons and gamma rays, and DUCRETE concrete is used to reduce fluxes of neutrons and high-energy photons. The alpha particles produced by the decay of 238U are effectively absorbed by the concrete and do not pose a health risk. DUCRETE is being proposed as a suitable material for the storage of radioactive waste , .
237Np (with a half-life of 2.14×106 years) is fissionable, meaning that neptunium can be bombarded with neutrons and, as a result, create more neutrons that are free to interact with nearby material and can be used in fast neutron reactors or in nuclear weapons (Fig. 4.93.1) , , . 237Np is used in neutron detection instruments .
237Np is used in the production of 238Pu (with a half-life of 87.7 years), which is an emitter of alpha particles used in thermoelectric generators and radioisotope-heater units. When 237Np captures a neutron, it becomes 238Np, with a half-life of 2.117 days, which decays to 238Pu .
238Pu (with a half-life of 87.7 years) is used in radiothermal generators as a heat source to produce electricity. These radiothermal generators are used to power unmanned spacecraft and interplanetary probes that venture too far from the Sun to use solar power, such as the Cassini Orbiter, the Galileo spacecraft, and the Huygens and Galileo probes , , , . 238Pu has been used in the Apollo lunar missions as part of a nuclear battery. The SNAP-27 (systems nuclear auxiliary power) system produced approximately 75 W of electrical power at 30 VDC per unit (Fig. 4.94.1). The energy source was a 2.5-kg rod of 238Pu providing thermal power of approximately 1250 W . 238Pu is used in pacemakers (Fig. 4.94.2).
239Pu (with a half-life of 2.41×104 years) is used in nuclear weapons. 239Pu is easily made in nuclear reactors by bombarding 238U with neutronsvia the reaction 238U (n, γ) 239U and 239U→239Pu+β−. The 239Pu made by this reaction can itself be split by neutrons to release energy and is used for energy generation in nuclear reactors , , .
Americium does not occur naturally in the Earth’s crust. In 1944, it was first synthesized by Glenn T. Seaborg and his team at the University of California Laboratory in Berkeley via multiple neutron capture reaction on 239Pu to produce 241Am : 239Pu (n, γ) 240Pu, 240Pu (n, γ) 241Pu, and 241Pu→241Am+β−.
241Am (with a half-life of 433 days) is used in smoke detectors as an ionization source to detect smoke (Fig. 4.95.1). A small piece of 241Am oxide is housed inside ionizing smoke detectors. The americium compound emits alpha particles that strike air molecules in their path, causing them to ionize. The ions carry a current from one plate in the detector to a second plate. Current flows continuously until smoke disrupts the current between the two plates. The alarm sounds when the current is disrupted by smoke , , .
241Am is used for the control and measurement of industrial material thickness and product quality. In manufacturing, for example, a small piece of 241Am is placed above a conveyer belt and a Geiger counter (used to count alpha particles) is placed below the conveyor belt. A specific quantity of radiation is expected to be measured by the Geiger counter. If the product being manufactured (i.e. glass) is thicker than expected, less radiation will be measured, and the product will be rejected . The gamma radiation of 241Am is also used in a variety of gauges. Thickness gauges, fluid-density gauges, aircraft fuel gauges, and distance-sensing devices use the density-measuring capabilities of the emitting gamma rays and radiation detector to function.
When 241Am is mixed with beryllium (241AmBe), it emits neutrons at a high rate. This high rate of neutron generation is useful in oil-well operations to monitor the rate of oil production, and it can also be used in well logging to log the porosity (fraction of void volume to total volume of a material) of the geologic units along the sides of a borehole. Gamma rays from 241Am are also used as portable X-ray machines to determine where new wells should be drilled. When a small pellet of 241Am is placed in a sealed titanium capsule, it can serve as a portable source for gamma radiography, which is more penetrating than X-rays, to test various materials for defects, such as invisible cracks or faulty welds in pipelines , , .
Gamma-ray emissions from 241Am have been used as a radiation source for medical diagnostic tests. In particular, 241Am has helped to provide accurate diagnoses of thyroid function, but this use of americium is now obsolete .
Curium does not occur naturally in the Earth’s crust. It was first synthesized in 1944 by Glenn T. Seaborg and his team at the University of California in Berkeley using the reaction 239Pu (4He, n) 242Cm. The element was named after Pierre and Marie Curie, who discovered radium and polonium.
244Cm and 242Cm (with half-lives of 18.1 years and 163 days, respectively) are strong alpha emitters (see alpha decay). The alpha emission from these isotopes creates a considerable quantity of heat that makes them useful as alpha particle sources, as well as heat generators in RTGs (radioisotopic thermoelectric generators) . During a number of space missions based in America and Europe, 244Cm was the source used for the alpha particle X-ray spectrometer that was on board vehicles such as the Mars Exploration Rover and the Rosetta/Philae , . 244Cm has a large neutron capture to neutron fission cross-section ratio and has been used in a nuclear reactor to produce higher mass radio-isotopes of curium (Fig. 4.96.1) , .
Berkelium does not occur naturally in the Earth’s crust. It was first synthesized in December 1949 by Stanley G. Thompson, Glenn T. Seaborg, and Albert Ghiorso at the University of California in Berkeley using the nuclear reaction 241Am (4He, 2n) 243Bk in the Berkeley 60-inch cyclotron. The element was named for the town in California where it was first synthesized. The first isotope of berkelium produced from this experiment had a mass number of 243 and a half-life of 4.5 h. 247Bk has a half-life of 1.4×103 years, which makes it one of the least radioactive isotopes of berkelium. 249Bk has a half-life of 320 days, which makes it possible to isolate and study on a macroscopic scale, although studies have found that the radiation given off from berkelium creates health hazards. For example, lengthy exposure to the radiation from berkelium has been shown to cause an accumulation of berkelium in the skeletal system of rats. The radiation is also unfavorable to the formation of red blood cells , , , , . Berkelium has no known isotopic applications aside from scientific research, in which it served as a target for the production of tennessine (Fig. 4.97.1).
Californium does not occur naturally in the Earth’s crust. It was first synthesized in 1950 by Glenn T. Seaborg and his team at the University of California using the reaction 242Cm (4He, n) 245Cf. The element was named for the state where it was first synthesized.
252Cf is a very active source of neutrons (2.3×106 neutrons per second per microgram) with a half-life of 2.65 years. The energy spectrum of the neutrons is very similar to that of a fission reactor and small amounts of 252Cf provide an ideal portable source for low neutron flux applications , , . 252Cf is used for PGNAA (prompt gamma neutron activation analysis, a method for detecting many chemical elements in samples simultaneously) in the analysis of coal, cement, minerals, weapon components, and chemical munitions . This method provides a quick and non-destructive elemental analysis of a sample. For example, 252Cf, as the neutron source for PGNAA, is used to detect the presence of antitank mines .
Neutron activation analysis (NAA) uses 252Cf as a portable neutron source to bombard a small sample from the area of interest with neutrons and analyze the radioactive emissions from that bombardment to help identify silver or gold ore . 252Cf has been used in neutron moisture gauges to locate water . 252Cf is used in borehole geophysical logging for subsurface PGNAA investigation of waste (Fig. 4.98.1) .
Formation fluid identification uses 252Cf as a chemical neutron source for elastic/inelastic neutron backscattering and/or neutron activation methods in well-logging to determine water- and oil-bearing layers and other downhole properties of the well bore .
252Cf is sometimes used in boron neutron capture therapy (BNCT) as a source of neutrons that can be delivered close to the region of a tumor , , . Brachytherapy can use 252Cf to treat many types of cancer , , .
Einsteinium does not occur naturally in the Earth’s crust. It was first identified in December 1952 by American scientists from the Argonne National Laboratory near Chicago, Illinois, the Los Alamos National Laboratory in Los Alamos, New Mexico, and The University of California Laboratory in Berkeley, California in the debris of thermonuclear weapons. The element was named for Albert Einstein (Fig. 4.99.1). 253Es was the first isotope identified; it has a half-life of 20.47 days. The isotope with the longest half-life is 252Es, with a half-life of 472 days , .
There are no uses for isotopes of einsteinium outside of basic scientific research for the production of higher transuranic elements and studies of actinide science. Due to the radiation and heat given off by einsteinium isotopes, it is difficult to use them in experiments and studies .
Fermium does not occur naturally in the Earth’s crust. It was first identified in December 1952 by American scientists from the Argonne National Laboratory near Chicago, Illinois, the Los Alamos National Laboratory in Los Alamos, New Mexico, and The University of California Laboratory in Berkeley, California in the debris of thermonuclear weapons (Fig. 4.100.1). The element was named for Enrico Fermi, who built the first man-made nuclear reactor. 255Fm (with a half-life of 20 h) was the first fermium isotope identified. Fermium is the heaviest element that can be formed by neutron bombardment of lighter elements and is thus the heaviest element that can be synthesized in macroscopic quantities , .
Fermium is of interest in particle physics research, but it has no commercial applications. 253Fm was one of the decay products used to confirm synthesis of copernicium in a particle accelerator experiment .
Mendelevium does not occur naturally in the Earth’s crust. It was first synthesized in 1955 by Glenn T. Seaborg and his team at the University of California using the reactions 253Es (4He, n) 256Md and 253Es (4He, 2n) 255Md. Mendelevium is named for the Russian scientist, Dmitri Mendeleev (Fig. 4.101.1), who developed the Periodic Table of the chemical elements , . There are no applications for isotopes of mendelevium aside from scientific research.
Nobelium does not occur naturally in the Earth’s crust. It was first synthesized in 1966 by Russian scientists from the Joint Institute for Nuclear Research (JINR) in Dubna, Russia under Georgi Flerov. Earlier claims to have synthesized “nobelium” beginning in 1957 were shown to be erroneous. This element was originally named for Alfred Nobel (Fig. 4.102.1), the inventor of dynamite and founder of the Nobel prizes. The name was later retained because of its widespread use throughout the scientific literature , . There are no uses for isotopes of nobelium outside of scientific research.
Lawrencium does not occur naturally in the Earth’s crust. Credit for the first synthesis of this element in 1971 is given jointly to Albert Ghiorso and his team at the University of California in Berkeley and Georgi Flerov and his team at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia (Fig. 4.103.1). The element is named for Ernest O. Lawrence (Fig. 4.103.2), who developed the cyclotron. The chemical symbol for lawrencium was originally proposed as Lw. At the IUPAC General Assembly in 1963, lawrencium was officially accepted by IUPAC, but the symbol was changed to Lr because the Commission on Inorganic Nomenclature determined that the letter ‘w’ presented a problem in languages other than English , , , . There are no known isotopic applications for lawrencium outside of scientific research.
Rutherfordium does not occur naturally in the Earth’s crust. Credit for the first synthesis of this element is given jointly to Albert Ghiorso and his team at the University of California in Berkeley and Georgi Flerov and his team at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. The element is named for Ernest Rutherford (Fig. 4.104.1), who won the Nobel Prize for developing the theory of radioactive transformations .
Rutherfordium is of interest in particle physics research, but it has no commercial applications. 261Rf was one of the decay products used to confirm the synthesis of copernicium in a particle accelerator experiment .
Dubnium does not occur naturally in the Earth’s crust. Credit for the first synthesis of this element is given jointly to Albert Ghiorso and his team at the University of California in Berkeley and Georgi Flerov and his team at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia (Fig. 4.105.1). The element is named for the location of the Joint Institute for Nuclear Research (JINR) laboratory in Dubna, Russia , . Dubnium has no isotopic applications outside of scientific research.
Seaborgium does not occur naturally in the Earth’s crust. In 1974, seaborgium was first synthesized by Albert Ghiorso and his team at the University of California in Berkeley using the nuclear reaction 249Cf (18O, 4n) 263Sg. The element is named for Glenn T. Seaborg (Fig. 4.106.1), who synthesized a number of trans-uranium elements , .
Seaborgium has no commercial applications. However, 265Sg was one of the decay products used to confirm the synthesis of copernicium in a particle accelerator experiment.
Bohrium does not occur naturally in the Earth’s crust. Bohrium was first synthesized by German scientists at the GSI Center for Heavy Ion Research in Darmstadt, Germany in 1981 using the nuclear reaction 209Bi (54Cr, n) 262Bh. The element is named for Niels Bohr (Fig. 4.107.1), the Nobel Prize winning physicist , . Bohrium has no known isotopic applications aside from scientific research.
Hassium does not occur naturally in the Earth’s crust. Hassium was first synthesized by German scientists at the GSI Center for Heavy Ion Research in Darmstadt, Germany in 1984 using the nuclear reaction 208Pb (58Fe, n) 265Hs (Fig. 4.108.1). The element is named for Hassia (the Latin name for the German state of Hesse), whose former capital was Darmstadt , , . Hassium is used in chemical and heavy element research.
Meitnerium does not occur naturally in the Earth’s crust. Meitnerium was first synthesized by German scientists at the GSI Center for Heavy Ion Research in Darmstadt, Germany in 1984 using the nuclear reaction 209Bi (58Fe, n) 266MtHs. The element is named for the physicist, Lise Meitner (Fig. 4.109.1), who discovered the element protactinium , . Meitnerium is used only for scientific research.
Darmstadtium does not occur naturally in the Earth’s crust. Darmstadtium was first synthesized by an international team of scientists from the GSI in Darmstadt, Germany, the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, the Comenius University in Bratislava, Slovakia and the University of Jyväskylä, Finland at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt (Fig. 4.110.1), Germany in 1994 using the nuclear reaction 208Pb (62Ni, n) 269Ds. The element was named darmstadtium after the place where the first synthesis was made , , , . Darmstadtium has no known isotopic applications aside from scientific research.
Roentgenium does not occur naturally in the Earth’s crust. Roentgenium was first synthesized by an international team of scientists from the GSI in Darmstadt, Germany, the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, the Comenius University in Bratislava, Slovakia, and the University of Jyväskylä, Finland at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany in 1994, using the nuclear reaction 209Bi (64Ni, n) 272Rg. The credit for the first synthesis was confirmed in 2003. The element was named after Wilhelm Conrad Roentgen (Fig. 4.111.1), who discovered X-rays in 1895 , , . Roentgenium has no known isotopic applications aside from scientific research.
Copernicium does not occur naturally in the Earth’s crust. Copernicium was synthesized by scientists at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany in 1996 (Fig. 4.112.1). Sigurd Hofmann and an international team of scientists used the nuclear reaction 208Pb (70Zn, n) 277Cn. The observed alpha decays led to the known nuclide, 269Sg. The name, copernicium, was given to element 112 to honor astronomer Nicholas Copernicus, who is known for his heliocentric theory of how the planets orbit the Sun , . Copernicium has no known isotopic applications aside from scientific research.
Nihonium does not occur naturally in the Earth’s crust. The name nihonium and the symbol Nh are the accepted ones for element 113. Nihon is one of the two ways to say “Japan” in Japanese and means “the land of the Rising Sun.” It is the first element to have been discovered in an Asian country , , .
The synthesis of nihonium was first announced in 2004. The Joint Institute for Nuclear Research (JINR) and the Lawrence Livermore National Laboratory were able to produce two super-heavy elements by bombarding a rotating 243Am disc with an ion beam of 48Ca in a U-400 cyclotron. During the reaction, isotopes of moscovium, previously known as ununpentium, were synthesized and decayed in a tenth of a second to nihonium, which then decayed to roentgenium. Because the atoms of moscovium only existed for a tenth of a second, radiochemical proof was needed to support its syntheses. A Swiss scientist at the Paul Scherrer Institute (PSI) performed the radiochemical experiment by analyzing a copper plate that had been placed behind the 243Am disc in the cyclotron. This copper plate collected all moscovium atoms that were synthesized and was processed through liquid chromatography techniques that yielded five times more moscovium atoms than produced by fusion alone. The direct synthesis of nihonium was announced later that year by a team of Japanese scientists from the Cyclotron Center of the RIKEN Research Institute. These scientists bombarded atoms of 209Bi with a beam of 70Zn in a RIKEN heavy-ion linear accelerator (RILAC), shown in Fig. 4.113.1, and gas-filled recoil ion separator (GARIS), shown in Fig. 4.113.2. Nihonium has no known isotopic applications aside from scientific research.
Flerovium does not occur naturally in the Earth’s crust. Flerovium was named for the Flerov Laboratory for Nuclear Reactions of the Joint Institute for Nuclear Research (JIRN). In 1999, a collaboration of scientists from the Joint Institute for Nuclear Research in Dubna, Russia (Figs. 4.114.1 and 4.114.2) and the Lawrence Livermore Laboratory in the USA synthesized flerovium. They used nuclear reaction experiments to eventually produce 287Fl by cross-bombardments of 48Ca with both (even-A) 242Pu and (odd-A) 245Cm. The intermediate nuclide 283Cn was observed with known decay characteristics that established the synthesis of flerovium , . Flerovium has no known isotopic applications aside from scientific research.
Moscovium does not occur naturally in the Earth’s crust. The name moscovium and the symbol Mc, are the accepted ones for element 115. The name is in recognition of the Moscow region and honors the ancient Russian land that is home to the Joint Institute for Nuclear Research (JIRN), where the discovery experiments were conducted using the Dubna gas filled recoil separator in combination with the heavy ion accelerator capabilities of the Flerov Laboratory of Nuclear Reactions.
48Ca and 243Am were bombarded together in a cyclotron during a series of experiments from 14 July to 10 August 2003 (Fig. 4.115.1). In February 2004, the results from these experiments were released in a report that stated “ununpentium” had been synthesized. This initial name means “115” in the IUPAC systematic naming scheme, which combines Latin and Greek names to produce un-un-pentium for 115. Moscovium has no known isotopic applications aside from scientific research.
Livermorium does not occur naturally in the Earth’s crust. In 2000, scientists from the Joint Institute for Nuclear Research (JINR) in Dubna, Russia (Fig. 4.116.1) worked with scientists from the Lawrence Livermore National Laboratory at the University of California and other collaborators to synthesize element 116. This element was first given the placeholder name ununhexium; in May of 2012 it was granted the name livermorium, with the symbol Lv. Researchers first studied livermorium as a decay product of oganesson and then synthesized livermorium by bombarding atoms of 248Cm with ions of 48Ca. The initial reaction of 248Cm with 48Ca produced the isotope292Lv. Researchers were also able to produce livermorium by bombarding 245Cm with 48Ca. There are four known isotopes of livermorium , . Livermorium has no known isotopic applications aside from scientific research.
Tennessine does not occur naturally in the Earth’s crust. The name tennessine and the symbol Ts, are the accepted ones for element 117. The name is in recognition of the contribution of the Tennessee region, including Oak Ridge National Laboratory (ORNL), Vanderbilt University, and the University of Tennessee at Knoxville, to super-heavy element research, including the production and chemical separation of unique actinide target materials for super-heavy element synthesis at ORNL’s High Flux Isotope Reactor (HFIR) and Radiochemical Engineering Development Center (REDC) , , , .
In 2009, two isotopes, 293Ts and 294Ts were synthesized from the bombardment of 48Ca ions with 249Bk nuclei (Fig. 4.117.1) in the Dubna gas filled recoil separator and the heavy ion cyclotron U-400. Tennessine has no known isotopic applications aside from scientific research.
Oganesson does not occur naturally in the Earth’s crust. The name oganesson and symbol Og are the accepted ones for element 118. The name is in line with the tradition of honoring a scientist and recognizes Prof. Yuri Oganessian (Fig. 4.118.1; born 1933) for his pioneering contribution to trans-actinoid element research. His many achievements include the discovery of super-heavy elements and significant advances in the nuclear physics of super-heavy nuclei, including experimental evidence for the “island of stability.”
In 2005, experiments were performed in Dubna’s U-400 cyclotron, where 48Ca bombarded a spinning target of 249Cf at nearly 3×104 km/s to produce oganesson. With the success of creating oganesson, scientists from Livermore and Joint Institute for Nuclear Research (JINR) are starting experiments to create element 120 by bombarding a 244Pu target with a beam of 58Fe , , , . Oganesson has no known isotopic applications aside from scientific research.
Definitions of selected terms in this article are organized in the form of a glossary and are listed in alphabetical order. These definitions apply only to this publication. For formal definitions, the reader should consult the IUPAC Gold Book  and IUPAC recommendations.
absorption cross section – the probability of the absorption of an incident particle by a target nucleus.
accelerator mass spectrometry (AMS) – technique for measuring long-lived radionuclides in which ions are accelerated to extraordinarily high kinetic energies before mass analysis. The special strength of AMS among mass spectrometric methods is its power to separate a rare isotope from the isotope of another element of similar mass, e.g.41K from 41Ca.
accrete – form a body by collecting matter, such as under the force of gravitation.
activity – the activity A of a radioactive substance B is given by A=λ NB, where λ is the decay constant and NB is the number of decaying entities B. The unit of A is “becquerel”, symbol Bq, and 1 Bq=1 s−1 (see Section 2.5, p. 20 of ref ).
alpha decay (α-decay) – radioactive decay process resulting in emission of alpha particles.
alpha particle – a positively charged nuclear particle identical with the nucleus of a helium atom consisting of two protons and two neutrons.
alpha particle capture – the absorption of an alpha particle by a target nucleus.
amount fraction (mole fraction or isotopic abundance, x) – the amount (symbol n) of a given isotope (atom) in a sample divided by the total amount of all stable isotopes and long-lived radioactive isotopes of the chemical element in the sample.
amount ratio – amount of a specified constituent (usually molecules, atoms, or ions) divided by the amount of another constituent in the same system.
AMS – see accelerator mass spectrometry.
analyte – the component of a system to be analyzed .
anthropogenic – resulting from human activity.
antineutrino (anti-neutrino) – see neutrino.
atomic number (Z) – The number of protons in the nucleus of an atom.
atomic weight (relative mean atomic mass) – the sum of the products of the relative atomic mass and the mole fraction of each stable isotope and long-lived radioactive isotope of that element in the sample. The symbol of the atomic weight of element E is Ar(E), and the symbol of the atomic weight of an atom (isotope) of element E having mass numberA is Ar(AE). Because relative atomic masses are scaled (expressed relative) to one-twelfth the mass of a carbon-12 atom, atomic weights are dimensionless.
Auger electron – an electron that is ejected from an atom when an inner-shell electron is lost and an electron with a higher energy level takes its place. The excess energy is carried off by the electron and no photon is emitted in the process.
Avogadro constant (NA) – fundamental physical constant (symbols: NA or L) representing the number of entities in one mole (6.022 140 76×1023 mol−1) , where the elementary entities may be atoms, ions, molecules, electrons, or other particles or specified groups of particles. The Avogadro constant is the scaling factor between the microscopic (atomic scale) and the macroscopic properties of matter.
beta decay (β-decay) – radioactive decay process resulting in the emission of a beta particle of either positive or negative charge (an electron or positron).
brachytherapy – the treatment of cancer, especially prostate cancer, by the insertion of radioactive implants directly into the tissue near the tumor.
chondrites (or chondritic meteorites) – non-metallic meteorites which have not undergone compositional change due to melting because they were part of primitive asteroids, and thus reflect the composition of the solar nebula from which our Solar System formed.
CIAAW – Commission on Isotopic Abundances and Atomic Weights (of IUPAC).
control rods – a rod of a neutron-absorbing element used to vary the output power of a nuclear reactor by inserting the rods into the core to absorb neutrons or withdrawing the rods from the core to allow more neutrons to interact with the fuel in the core. The results will cause fewer neutron fissions and decrease the power or cause more neutron fissions and increase the power, respectively.
conventional atomic-weight value – an atomic-weight value of an element having a standard atomic-weight interval that is not an interval, such as is used for trade and commerce or for education when a single representative value is needed, e.g. for molecular weight calculations. These values have no uncertainty values associated with them. They have been selected so that most or all atomic-weight variation in normal materials is covered in an interval of plus or minus one in the last digit .
cosmogenic – produced by the interaction of Earth materials (soil, rock, and atmosphere) and meteorites with high-energy cosmic rays, resulting in protons and neutrons being expelled from an atom (termed cosmic ray spallation).
cosmic rays – extremely high-energy radiation, mainly originating outside the Solar System, consisting of one or more charged particles, such as protons, alpha particles, and larger atomic nuclei.
covalently – sharing electron pairs between atoms with a stable balance of attractive and repulsive forces between atoms.
CT scan (X-ray computed tomography or X-ray CT, computerized axial tomography scan or CAT scan) – a computerized tomography (CT) scan combines a series of X-ray images taken from different angles and uses computer processing to create cross-sectional images, or slices, of the bones, blood vessels, and soft tissues inside your body .
cyclotron – an apparatus in which charged atomic and subatomic particles are accelerated by a rapidly varying (radio frequency) electric field while following an outward spiral path in a constant magnetic field.
decay product – (daughter product), any nuclide produced by a specified radionuclide (parent) in a decay chain.
DNA – deoxyribonucleic acid, a double stranded molecule carrying genetic instructions for reproduction of organisms.
double beta decay – a type of radioactive decay in which two protons are simultaneously transformed into two neutrons inside the nucleus of an atom, decreasing the atomic number of the atom by two.
DTPA – diethylene triamine pentaacetic acid. The U.S. Food and Drug Administration approved DTPA treatment for eliminating ingested radioactive material, such as plutonium, americium, and curium from the body.
EDTMP – ethylenediamine tetra (methylene phosphonic acid).
electron – elementary particle of matter with a negative electric charge and a rest mass of about 9.109×10−31 kg.
electron-capture detector (ECD) – an apparatus for detecting trace amounts of atoms and molecules (such as halogens, organometallic compounds, nitriles, or nitro compounds). The ECD uses an electron emitter (commonly the radioactive isotope63Ni) to produce a current in the detector. Any electron-absorbing compound in the carrier gas reduces the current and is thus detected.
element (chemical element) – a species of atoms; all atoms with the same number of protons in the atomic nucleus. A pure chemical substance composed of atoms with the same number of protons in the atomic nucleus .
excretion – the process of eliminating waste matter.
first-pass effect – a phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced, e.g. by the liver, before reaching the rest of the body, substantially reducing the bioavailability of the drug.
fission – the spontaneous or particle collision-induced splitting of a heavy nucleus into a pair (or, only rarely, more) of nearly equal fission fragments (fission products), generally with some neutrons. Fission is accompanied by the release of a large quantity of energy.
fissionable – capable of undergoing fission by interaction with particles, usually neutrons.
G-protein coupled receptors (GPCRs) – the largest and most diverse group of membrane receptors in eukaryotes (living organisms other than bacteria and archaeabacteria). These cell surface receptors act like an inbox for messages in the form of light energy, peptides, lipids, sugars, and proteins. Experts estimate that between one-third and one-half of all marketed drugs act by binding to GPCRs .
gamma camera (scintillation camera or Anger camera) – instrument used to track the distribution in body tissue of radioactive isotopes (tracers) that emit gamma radiation (high energy photons), a technique known as scintigraphy.
gamma radiation – see gamma rays.
gamma rays (gamma radiation) – a stream of high-energy electromagnetic radiation given off by an atomic nucleus undergoing radioactive decay. The energies of gamma rays are higher than those of X-rays; thus, gamma rays have greater penetrating power.
gas chromatography (GC) – a physical method of separation of gases within a tube in which the components to be separated are distributed between two phases, one of which is stationary (stationary phase), while the other (mobile phase) is a gas (commonly helium) that moves in a definite direction.
gated equilibrium blood pool imaging – see radionuclide angiography.
geochronology – the science of dating and determining the time sequence of events in the history of the Earth .
Geiger counter – instrument for detecting and measuring ionizing radiation.
half-life (radioactive) – the time interval that it takes for the total number of atoms of any radioactive isotope to decay and leave only half the original number of atoms.
heavy water – water containing a substantial fraction (up to 100 percent) of deuterium (2H) in the form of 2H2O or H2HO .
hyperthyroidism – a condition in which too much hormone is produced in the body by the thyroid.
igneous – type of rock formed by the cooling and solidification of lava.
in vivo – in the living body (plant or animal).
inductively coupled plasma mass spectrometry (ICPMS) – a type of mass spectrometry in which the analyte is inductively heated and analyzed in a plasma created with an electromagnetic coil.
intravenous (IV) – administered into a vein.
ionizing – pertaining to the process by which an atom, molecule, or substance acquires a negative or positive charge. Commonly, one or more electrons are removed to give a positive charge.
IPTEI – IUPAC Periodic Table of the Elements and Isotopes.
IRMS – see isotope-ratio mass spectrometry.
isochron – a line indicating the age of formation of a suite of rock or mineral samples on a cross plot of amount ratios of isotopes of one element or two different elements, one of which has a radioactive isotope that decays to an isotope of the other element. The apparent isochron age can indicate the time since metamorphism, crystallization, shock events, differentiation of precursor melts, etc. For examples, see neodymium Fig. 4.60.1, samarium Fig. 4.62.1, rhenium Fig. 4.75.1, and osmium Fig. 4.76.1.
isomer – a gamma-ray emitting excited state of an isotope.
isotope – one of two or more species of atoms of a given element (having the same number of protons in the nucleus) with different atomic masses (different number of neutrons in the nucleus). The atom can either be a stable isotope or a radioactive isotope.
isotope ratio (R) – number (symbol N) of atoms of one isotope divided by the number of atoms of another isotope of the same chemical element in the same system .
isotope-amount ratio (r) – amount (symbol n) of an isotope divided by the amount of another isotope of the chemical element in the same system .
isotope-ratio mass spectrometry (IRMS) – the scientific field pertaining to the use of a mass spectrometer to measure the relative abundance of isotopes in a given sample, usually with an instrument having multiple ion collectors.
isotopic abundance – see amount fraction.
isotopic composition – term indicating that qualitative or quantitative isotopic information has been gathered . Although this is not an SI quantity, this term is often followed by SI-quantity values.
isotopic dating – radiometric or radioactive dating technique that applies to all methods of age determination based on the nuclear decay of naturally occurring radioactive isotopes .
isotopic fractionation (stable-isotope fractionation) – preferential enrichment of one isotope of an element over another, owing to slight variations in their physical or chemical properties .
isotopic reference material – substance that is sufficiently stable and homogeneous in isotopic composition to serve as a measurement standard in the measurement of isotope ratios .
isotopically labeled (compound) – a mixture of an isotopically unmodified compound with one or more analogous isotopically substituted compound(s) .
IUPAC – International Union of Pure and Applied Chemistry.
IYC – International Year of Chemistry.
luminous – relating to light as perceived by the human eye.
ligand – the atoms or groups joined to the central atom .
magnetic resonance imaging (MRI) – medical imaging technique that uses strong magnetic fields to form images of the body.
malignant – pertaining to a medical condition with the tendancy to become progressively worse.
mass number (A) – total number of heavy particles (protons and neutrons, jointly called nucleons) in the nucleus of an atom .
mass spectrometer (mass spectrometry) – an instrument for separating a substance into isotopes, molecules, and molecular fragments according to their differing mass to charge ratios by acceleration in an electric field and dispersion into a curved trajectory by a magnetic field.
measurement uncertainty – see uncertainty of measurement.
metabolism – the chemical processes that occur within a living organism in order to maintain life.
metastable state – an excited state of an isotope with a specific half-life for de-excitation, usually by the emission of a gamma ray.
metastases – the spread of a disease-producing agency (such as cancer cells) from the initial or primary site of disease to another part of the body .
meteoric water – pertaining to water of recent atmospheric origin .
meteorite – a meteoroid that has survived atmospheric passage and fallen to the Earth’s surface in one or more recoverable fragments. See also chondrites .
mole ratio (amount ratio, r) – amount of a specified constituent (usually molecules, atoms, or ions) divided by the amount of another constituent in the same system.
monoclonal antibodies (mAb or moAb) - identical immune cells that are all clones of a unique parent cell, in contrast to polyclonal antibodies, which are made from several different immune cells.
MRI – see magnetic resonance imaging.
neutrino – an elementary particle with no charge; its mass is tiny compared to other subatomic particles. An anti-matter equivalent is called an antineutrino (or anti-neutrino). Neutrinos and antineutrinos can be created in certain types of radioactive decay, in nuclear reactions such as those that take place in the Sun, in nuclear reactors, in cosmic ray interactions with atoms, and in supernovae.
neutron – an elementary particle with no net charge and a rest mass of about 1.675×10−27 kg, slightly more than that of the proton. All atoms contain neutrons in their nucleus except for protium (1H).
NMR – Nuclear Magnetic Resonance.
normal materials – a reasonably possible source for an element or its compounds for commerce, industry or science; the material is not itself studied for some extraordinary anomaly and its mole fractions (isotopic abundances) have not been modified significantly in a geologically brief period include all substances, except (1) those subjected to substantial deliberate, undisclosed, or inadvertent artificial isotopic modification, (2) extraterrestrial materials, and (3) isotopically anomalous specimens, such as natural nuclear reactor products from Oklo (Gabon) or other unique occurrences .
nuclear battery – a device that uses radioactive decay to generate electricity.
nuclear medicine – the branch of medicine that deals with the use of radiopharmaceuticals to diagnose and treat disease.
nucleosynthesis – the production of a chemical element from simpler nuclei (as of hydrogen), especially in a star. See r-process, s-process, and p-process .
ocular – of or relating to the eyes or vision.
over-expressed – the excessive expression of a gene, as in making too many copies of a protein or other substance, which may play a role in cancer development.
p-process – a nucleosynthesis process responsible for proton-rich nuclei .
palliative – providing relief from the symptoms of an illness without treating its underlying cause.
parent radionuclide – a radioactive isotope, commonly in a radionuclide generator, that decays to produce a radioactive daughter. For example, the parent radionuclide 99Mo decays to 99mTc, which is used in radionuclide angiography.
peptides – amides derived from two or more amino carboxylic acid molecules (these molecules may be the same or different) by the formation of a covalent bond from the carbonyl carbon of one to the nitrogen atom of another with formal loss of water. The term is usually applied to structures formed from α-amino acids, but it includes those derived from any amino carboxylic acid .
perfusion test – a test using medical imaging to observe and record the passage of fluid through the lymphatic system or blood vessels to an organ or tissue.
PET scan – see positron emission tomography.
petrochemical – relating to or denoting substances obtained by the processing of oil and natural gas.
pharmacokinetics – the study of the time course of drug absorption, distribution, metabolism, and excretion .
photon – elementary particle of electromagnetic radiation carrying energy proportional to the radiation frequency, but with zero electric charge and zero mass.
porphyrin – pigment widely distributed throughout nature consisting of four pyrroles (C4H4NH) joined in a ring (porphin) structure.
positron – the antimatter counterpart of the electron, with a mass identical to that of the electron and an equal but opposite (positive) charge.
positron emission tomography (PET) scan – an imaging technique that is used to observe metabolic activity within the body. The system detects pairs of gamma rays emitted indirectly by a radioactive isotope used as a tracer, which emits positrons and which is introduced into the body on a biologically-active molecule. Three-dimensional images of the concentration of the radioactive isotope within the body are then constructed by computer analysis. The imaging is often performed with an X-ray CT scan in the same instrument.
primordial – existing from the beginning of time.
proton – an elementary particle having a rest mass of about 1.673×10−27 kg, slightly less than that of a neutron, and a positive electric charge equal and opposite to that of the electron. The number of protons in the nucleus of an atom is the atomic number.
proxy – a measured quantity that can be used to represent the value of another quantity in a calculation.
r-process (rapid neutron capture process) – nucleosynthesis process that occurs when supernovae collapse, resulting in neutron-rich atomic nuclei heavier than iron.
radioactive decay – the process by which unstable (or radioactive) isotopes lose energy by emitting alpha particles (helium nuclei), beta particles (positive or negative electrons), gamma radiation, neutrons, or protons to reach a final stable energy state.
radioactive isotope (radioisotope) – an atom for which radioactive decay has been experimentally measured (also see half-life).
radiogenic – produced by radioactive decay; the resulting atom (isotope) may or may not be radioactive.
radiography – an imaging technique that uses electromagnetic radiation other than visible light, especially X-rays and gamma rays, to view the internal structure of non-uniform objects, such as metal parts, welded pipes, and the human body.
radioimmunotherapy (RIT) – a combination of radiation therapy and immunotherapy used to treat cancer. RIT uses engineered monoclonal antibodies isotopically labeled with a radionuclide to deliver radiation toxic to living cells to a target cell.
radioimmunoconjugate – radioactive substance that carries radiation directly to cancer cells and is made by attaching a radioactive molecule to an immune substance, such as a monoclonal antibody, that can bind to cancer cells; used to kill cancer cells without harming normal cells .
radioisotope – see radioactive isotope.
radiolabel – a mixture of an isotopically unmodified compound with one or more analogous radioactive isotopically substituted compound(s).
radionuclide – a nuclide that is radioactive .
radionuclide angiography (also called gated equilibrium blood pool imaging) – a test using the radioactive isotope99mTc to evaluate the function of the right and left ventricles of the heart by measuring radioactivity over the anterior chest as the radioactive blood flows through the large vessels and the heart chambers.
radiopharmaceutical – radiolabeled compound used for diagnostic or therapeutic purposes.
radiotherapy (radiation therapy) – the treatment of disease by means of radiation from radioactive substances or X-rays.
radiosynovectomy – a procedure using radioactive isotopes therapeutically to provide relief from a condition in which the synovial membrane, which encloses each joint and secretes a lubricating fluid to enable ease of joint motions, has become inflamed and irritated.
reduction-oxidation (redox) – reduction is the gain of one or more electrons by an atom, and oxidation is the loss of one or more electrons by an atom.
relative atomic mass (atomic weight) – the ratio of the average mass of the atom to the unified atomic mass unit.
residence time – the average amount of time (or time duration) that a collection of particles spends in a specified system.
s-process (slow-neutron-capture-process) – a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars, producing isotopes of the elements heavier than iron. The s-process is important in controlling the chemical evolution of the galaxy.
scintigraphy – see gamma camera.
scintillation counting – measuring ionizing radiation using the interaction of radiation on a material and counting the resulting photon emissions.
semiconductors – a material or object that allows some electricity or heat to move through it and that is used for this purpose, especially in electronic devices .
single-photon emission computed spectroscopy (SPECT) – a nuclear medicine imaging technique that is able to provide true three-dimensional information using gamma rays from a radiopharmaceutical.
solar nebula – the cloud of dust and gas from which the solar system is believed to have condensed, mainly by gravitational attraction, about 4.5×109 years ago.
spallation – a process in which fragments of a solid (spall) are ejected from the solid due to impact or stress. In nuclear physics, spallation is the process in which a nucleus of a heavy element emits a large number of nucleons (isotopes) as a result of being hit by a high-energy particle (e.g. a cosmic ray), resulting in a substantial loss of its atomic weight.
stable isotope – an atom for which no radioactive decay has ever been experimentally measured.
standard atomic weight – an evaluated quantity assigned by the IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW) to encompass the range of possible atomic weights of a chemical element that might be encountered in all samples of normal terrestrial materials. It is comprised of either an interval (currently used for 13 elements) or a value and an uncertainty (a standard atomic-weight uncertainty), which are currently used for 71 elements. A standard atomic weight is determined from an evaluation of peer-reviewed scientific publications.
standard atomic-weight interval – the upper and lower bounds determined for the standard atomic weight of an element when its isotopic and atomic weight variations in normal material exceed the measurement uncertainty of its standard atomic weight. This interval is determined by an IUPAC project through the evaluation of peer-reviewed scientific publications. Currently only 13 elements have been evaluated and assigned atomic-weight intervals.
standard atomic-weight uncertainty – the standard atomic weights of 71 elements (those not expressed as intervals) are reported as central values ± decisional uncertainty values. The decisional atomic-weight uncertainty is a conservative estimate of the combined effects of measurement uncertainty and known atomic-weight variability in naturally occurring terrestrial sources of an element. The atomic weight of any normal material containing an element should lie between the lower and upper bounds of the decisional uncertainty limits for that element with great certitude.
substrate – the surface or substance on which an organism lives.
supernova (plural supernovae) – a star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass.
tracer – a substance, which can be an isotope, used for tracking purposes.
thermal neutron – a neutron not bound to an atomic nucleus in thermal equilibrium with its surroundings and thus having relatively low kinetic energy.
thermoneutrality – a state of thermal balance between an organism and its environments such that bodily thermoregulatory mechanisms are inactive .
thermonuclear bomb – a nuclear weapon that uses the energy from a primary fission reaction to compress and ignite a secondary nuclear DT (deuterium-tritium; hydrogen-2, hydrogen-3) fusion reaction.
thiol – any of various compounds, having the general formula RSH, which are analogous to alcohols but in which sulfur replaces the oxygen of the hydroxyl group and which have flowery, fruity, salty, sharp, or bad smelling odors .
tropospheric – pertaining to the lowest layer of the atmosphere, extending to about 10 km.
uncertainty of measurement – parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurement (the quantity being measured) .
voltaics – of, relating to, or producing direct electric current by chemical action (as in a battery) .
X-rays – electromagnetic radiation with a wavelength ranging from 0.01 to 10 nanometers – shorter than those of ultraviolet rays and typically longer than those of gamma rays.
X-ray fluorescence (XRF) spectroscopy – the branch of science concerned with the investigation and measurement of characteristic “secondary” (or fluorescent) X-ray spectra produced when a material has been bombarded with high-energy X-rays or gamma rays – widely used for elemental analysis and chemical analysis.
Membership of the Inorganic Chemistry Division Committee for the period 2014–2015 was as follows:
President: J. Reedijk (Netherlands); Secretary: M. Leskelä (Finland); Vice President: L. R. Öhrström (Sweden); Past President: R. D. Loss; Titular Members: T. Ding (China); M. Drábik (Slovakia); E. Y. Tshuva (Israel); D. Rabinovich (USA); T. Walczyk (Republic of Singapore); M. E. Wieser (Canada); Associate Members: J. Buchweishaija (Tanzania); J. Garcia-Martinez (Spain); P. Karen (Norway); A. Kilic (Turkey); K. Sakai (Japan); R.-N. Vannier (France); National Representatives: F. Abdul Aziz (Malaysia); L. Armelao (Italy); A. Badshah (Pakistan); V. Chandrasekhar (India); J. Galamba Correia (Portugal); S. Kalmykov (Russia); L. Meesuk (Thailand); S. Mathur (Germany); B. Prugovecki (Croatia); N. Trendafilova (Bulgaria).
Membership of the Committee on Chemistry Education for the period 2014–2015 was as follows:
Chair: Chiu, Mei-Hung (China/Taipei); Secretary: Apotheker, Jan (Netherlands); Titular Members: Aremo, Nina (Finland); Boniface, Suzanne (New Zealand); Kamata, Masahiro (Japan); Mamlok-Naaman, Rachel (Israel); Sözbilir, Mustafa (Turkey); Towns, Marcy (USA); National Representatives: Adhikari, Rameshwar (Nepal); Al-Najjar, Abdulaziz (Kuwait); Brandt, Ludo (Belgium); Cardellini, Liberato (Italy); Childs, Peter (Ireland); Elmgren, Maja (Sweden); Hoffman, Morton (USA); Lazo Santibanez, Leontina (Chile); Mahmood, Farzana (Pakistan); Maitra, Uday (India); Overton, Tina (UK); Pokrovsky, Alexander (Russia); Rahman, M. Muhibur (Bangladesh); Reiners, Christiane (Germany); Riedel, Miklós (Hungary); Shuai, Zhigang (China/Beijing); Solomon, Theodros (Ethiopia); Soon, Ting-Kueh (Malaysia); Tantayanon, Supawan (Thailand); Wright, Anthony (Australia); Ex Officio Membrer: West, Bernard (Committee on Chemistry and Industry); Division Representatives: Chen, Yi (Analytical Chemistry); Dassenakis, Manos (Chemistry and the Environment); Duffus, John (Chemistry and Human Health); García-Martínez, Javier (Inorganic Chemistry); Garson, Mary (Organic and Biomolecular Chemistry) Hartshorn, Richard (Chemical Nomenclature and Structure Representation); Mormann, Werner (Polymer); Russell, Andrea (Physical and Biophysical Chemistry).
Funding: This project was supported by the IUPAC Inorganic Chemistry Division Committee and IUPAC Committee on Chemistry Education (IUPAC project 2007-038-3-200) and by the U.S. Geological Survey National Research Program.
We thank Prof. D. Brynn Hibbert (University of New South Wales, Sydney, Australia), Prof. Robert Loss (Curtin University, Perth, Australia), Prof. Eva Åkesson (Vice-Chancellor, Uppsala University, Uppsala, Sweden), Ms. Jena Ashworth (U.S. Geological Survey volunteer), Mrs. Jennifer Lorenz (U.S. Geological Survey), Ms. Sarah Dade (U.S. Geological Survey), Ms. Miranda Marvel (U.S. Geological Survey), and Ms. Becca Fielding (U.S. Geological Survey volunteer) for helpful comments that improved the manuscript. IUPAC project 2007-038-3-200 contributed to this Technical Report. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
 N. E. Holden, T. B. Coplen, J. K. Böhlke, M. E. Wieser, G. Singleton, T. Walczyk, S. Yoneda, P. G. Mahaffy, L. V. Tarbox. Chem. Int.33(4), 20 (2011). Search in Google Scholar
 N. E. Holden, T. B. Coplen. J. Chem. Educ.90, 1150 (2013). Search in Google Scholar
 N. E. Holden. Nucl. Data Sheets.120, 169 (2014). Search in Google Scholar
 J. Meija, T. B. Coplen, M. Berglund, W. A. Brand, P. D. Bièvre, M. Gröning, N. E. Holden, J. Irrgeher, R. D. Loss, T. Walczyk, T. Prohaska. Pure Appl. Chem.88, 265 (2016). Search in Google Scholar
 J. Meija, T. B. Coplen, M. Berglund, W. A. Brand, P. D. Bièvre, M. Gröning, N. E. Holden, J. Irrgeher, R. D. Loss, T. Walczyk, T. Prohaska. Pure Appl. Chem.88, 293 (2016). Search in Google Scholar
 T. B. Coplen, N. E. Holden. Chem. Int.33(2), 10 (2011). Search in Google Scholar
 E. R. Cohen, T. Cvitaš, J. Frey, B. Holmström, K. Kuchitsu, R. Marquardt, I. Mills, F. Pavese, M. Quack, J. Stohner, H. L. Strauss, M. Takami, A. J. Thor. Quantities, Units and Symbols in Physical Chemistry. 3rd ed., IUPAC & The Royal Society of Chemistry Publishing, Cambridge (2011). Search in Google Scholar
 M. Wang, G. Audi, F. G. Kondev, W. J. Huang, S. Naimi, S. Xu. Chin. Phys. C41, 030003-1 (2017). Search in Google Scholar
 International Union of Pure and Applied Chemistry. Standard Atomic Weight of Ytterbium Revised, International Union of Pure and Applied Chemistry (2018), 9 March; http://www.iupac.org/news/news-detail/article/standard-atomic-weight-of-ytterbium-revised.html. Search in Google Scholar
 IUPAC press release. Standard Atomic Weights of 14 Chemical Elements Revised, International Union of Pure and Applied Chemistry (2018), 14 Aug; https://iupac.org/standard-atomic-weights-of-14-chemical-elements-revised/. Search in Google Scholar
 M. W. Wieser, T. B. Coplen. Pure Appl Chem.83, 359 (2011). Search in Google Scholar
 W. Dansgaard. Tellus16, 436 (1964). Search in Google Scholar
 I. D. Clark, P. Fritz. Environmental Isotopes in Hydrogeology, p. 328, Lewis Publishers, New York (1997). Search in Google Scholar
 C. Kendall, T. B. Coplen. Hydrol. Processes.15, 1363 (2011). Search in Google Scholar
 T. B. Coplen, J. A. Hopple, J. K. Böhlke, H. S. Peiser, S. E. Rieder, H. R. Krouse, K. J. R. Rosman, T. Ding, R. D. Vocke, K. Revesz, A. Lamberty, P. D. P. Taylor, P. D. Bièvre. United States Geological Survey Water-Resources Investigations Report, 01-4222, (2002). Search in Google Scholar
 Z. D. Sharp, V. Atudorei, H. O. Panarello, J. Fernández, C. Douthitt. J. Archaeolog. Sci.30, 1709 (2003). Search in Google Scholar
 K. A. Hobson. Oecologia120, 314 (1999). Search in Google Scholar
 K. A. Hobson, L. I. Wassenaar. Oecologia.109, 142 (1996). Search in Google Scholar
 T. B. Coplen, H. Qi. Forensic Sci. Int.266, 222 (2016). Search in Google Scholar
 United States Nuclear Regulatory Commission. NRC: Fact Sheet on Tritium Exit Signs, (2013), November 12; http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/fs-tritium.html. Search in Google Scholar
 S. P. O’Grady, A. R. Wende, C. H. Remien, L. O. Valenzuela, L. E. Enright, L. A. Chesson, E. D. Abel, T. E. Cerling, J. R. Ehleringer. PLoS One5, e11699 (2010). https://doi.org/10.1371/journal.pone.0011699. Search in Google Scholar
 M. van Lieshout, C. E. West, R. B. van Breemen. Am. J. Clin. Nutr.77, 12 (2003). Search in Google Scholar
 D. A. Schoeller, E. Ravussin, Y. Schutz, K. J. Acheson, P. Baertschi, E. Jequier. Am. J. Physiol. Regul. Integr. Comp. Physiol.250, R823 (1986). Search in Google Scholar
 D. K. Solomon, P. G. Cook. “3H and 3He”, in Environmental Tracers in Subsurface Hydrology, P. G. Cook and A. L. Herczeg (Eds.), Kluwer Academic Publishers, Boston (2000). Search in Google Scholar
 P. Schlosser, M. Stute, H. Dörr, C. Sonntag, K. O. Münnich. Earth Planet. Sci. Lett.89, 353 (1988). Search in Google Scholar
 M. Ozima, F. A. Podosek. Noble Gas Geochemistry: 2nd Edition, p. 286, Cambridge University Press, Cambridge, UK (2002). Search in Google Scholar
 D. K. Solomon. “4He in groundwater”, in Environmental Tracers in Subsurface Hydrology, P. G. Cook and A. L. Herczeg (Eds.), Kluwer Academic Publishers, Boston (2000). Search in Google Scholar
 D. Kramer. Phys. Today63, 22 (2010). Search in Google Scholar
 G. V. Jean. Advancing Hidden Nuclear Material Detection, National Defense Industrial Association (2014), Feb. 28; http://www.nationaldefensemagazine.org/archive/2010/December/Pages/AdvancingHiddenNuclearMaterialDetection.aspx. Search in Google Scholar
 Technology Assessment: Neutron Detectors: Alternatives to Using Helium-3, GAO-11-753. U.S. Government Accountability Office Washington, DC (2011). Search in Google Scholar
 M. Ebert, T. Grossmann, W. Heil, E. W. Otten, R. Surkau, M. Thelen, M. Leduc, P. Bachert, M. V. Knopp, L. R. Schad. Lancet347, 1297 (1996). Search in Google Scholar
 H. P. Qi, T. B. Coplen, Q. Z. Wang, Y. H. Wang. Anal. Chem.69, 4076 (1997). Search in Google Scholar
 T. D. Bullen, Y. K. Kharaka. “Isotopic composition of Sr, Nd, and Li in thermal waters from the Norris-Mammoth corridor, Yellowstone National Park and surrounding region”, in Water-Rock Interaction. in 7th International Symposium on Water-Rock Interaction, Rotterdam, Balkema Publishers (1992). Search in Google Scholar
 E. Caldwell. Resources on Isotopes-Periodic Table-Lithium, U.S. Geological Surve (2011), November 3; http://wwwrcamnl.wr.usgs.gov/isoig/period/li_iig.html. Search in Google Scholar
 Pacific Marine Environmental Laboratory Earth-Ocean Interactions Program. Vent Fluid Chemistry, Diagram of Hydrothermal Vent Processes, Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration (2014), Feb. 16; http://www.pmel.noaa.gov/eoi/chemistry/fluid.html. Search in Google Scholar
 International Atomic Energy Agency. Assessment and Management of Ageing of Major Nuclear Power Plant Components Important to Safety, IAEA-TECDOC-1361. 235 (2003). Search in Google Scholar
 F. Nordmann. “Aspects on chemistry in french nuclear power plants”, in 14th International Conference on the Properties of Water and Steam in Kyoto, Kyoto, Japan. Search in Google Scholar
 N. E. Holden. Chem. Int.32(1), 12 (2010). Search in Google Scholar
 R. F. Barth. J. Neurooncol.62, 1 (2003). Search in Google Scholar
 C. E. Jordan, J. E. Dibb, R. C. Finkel. J. Geophys. Res. Atmos.108, (2003). Search in Google Scholar
 J. M. Kaste, S. A. Norton, C. T. Hess. Rev. Mineral. Geochem.50, 271 (2002). Search in Google Scholar
 J. A. Graly, P. R. Bierman, L. J. Reusser, M. J. Pavich. Geochim. Cosmochim. Acta.74, 6814 (2010). Search in Google Scholar
 P. R. Bierman, M. W. Caffee, P. T. Davis, K. Marsella, M. Pavich, P. Colgan, D. Mickelson, J. Larsen. Rev. Mineral. Geochem.50, 147 (2002). Search in Google Scholar
 P. Bierman, E. A. Zen, M. Pavich, L. Reusser. U.S. Geol. Surv. Circ.1264, 191 (2004). Search in Google Scholar
 L. Reusser, P. Bierman, M. Pavich, J. Larsen, R. Finkel. Am. J. Sci.306, 69 (2006). Search in Google Scholar
 N. E. Whitehead, S. Endo, K. Tanaka, T. Takatsuji, M. Hoshi, S. Fukutani, R. G. Ditchburn, A. Zondervan. J. Environ. Radioact.99, 260 (2008). Search in Google Scholar
 A. Vengosh, K. G. Heumann, S. Jaraske, R. Kasher. Environ. Sci. Technol.28, 1968 (1994). Search in Google Scholar
 A. Vengosh. Biol. Trace Elem. Res.66, 145 (1998). Search in Google Scholar
 L. Foulke. Director of Nuclear Education Outreach, University of Pittsburgh. Introduction to Reactivity and Reactor Control, IAEA Workshop on Desktop Simulation (2014), Feb. 22; http://www.iaea.org/NuclearPower/Downloadable/Meetings/2011/2011-10-03-10-14-WS-NPTD/Foulke.1-Introduction.Reactivity.pdf. Search in Google Scholar
 P. Frame. Boron Trifluoride (BF3) Neutron Detectors, Oak Ridge Associated Universities (2014), Feb. 22; http://www.orau.org/PTP/collection/proportional%20counters/bf3info.htm. Search in Google Scholar
 D. Gabel. Radiother Oncol.30, 199 (1994). Search in Google Scholar
 D. N. Slatkin. Neutron News1, 25 (1990). Search in Google Scholar
 R. F. Barth, J. A. Coderre, M. C. G. Vicente, T. E. Blue. Clin. Cancer Res.11, 3987 (2005). Search in Google Scholar
 Q. Hua, M. Barbetti, A. Z. Rakowski. Radiocarbon55, 2059 (2013). Search in Google Scholar
 K. L. Spalding, R. D. Bhardwaj, B. A. Buchholz, H. Druid, J. Frisén. Cell122, 133 (2005). Search in Google Scholar
 K. M. Heinemeier, P. Schjerling, J. Heinemeier, S. P. Magnusson, M. Kjaer. FASEB J.27, 2074 (2013). Search in Google Scholar
 G. D. Weinstein, E. J. V. Scott. J. Invest. Dermatol.45, 257 (1965). Search in Google Scholar
 K. L. Spalding, E. Arner, P. O. Westermark, S. Bernard, B. A. Buchholz, O. Bergmann, L. Blomqvist, J. Hoffstedt, E. Näslund, T. Britton, H. Concha, M. Hassan, M. Rydén, J. Frisén, P. Arner. Nature453, 783 (2008). Search in Google Scholar
 D. Shemin, D. Rittenberg. J. Biol. Chem.166, (1946). Search in Google Scholar
 N. Lynnerup, H. Kjeldsen, S. Heegaard, C. Jacobsen, J. Heinemeier. PloS One3, e1529 (2008). https://doi.org/10.1371/journal.pone.0001529. Search in Google Scholar
 RealClimate. How Do We Know That Recent CO2 Increases Are Due to Human Activities? RealClimate (2014), Feb. 22; http://www.realclimate.org/index.php/archives/2004/12/how-do-we-know-that-recent-cosub2sub-increases-are-due-to-human-activities-updated/. Search in Google Scholar
 C. Cordella, I. Moussa, A. C. Martel, N. Sbirrazzuoli, L. Lizzani-Cuvelier. J. Agric. Food. Chem.50, 1751 (2002). Search in Google Scholar
 J. R. Brooks, N. Buchmann, S. Phillips, B. Ehleringer, R. D. Evans, M. Lott, L. A. Martinelli, W. T. Pockman, D. Sandquist, J. P. Sparks, L. Sperry, D. Williams, J. R. Ehleringer. J. Agric. Food. Chem.50, 6413 (2002). Search in Google Scholar
 B. D. Ahrens, A. W. Butch. Drug Test Anal.5, 534 (2013). Search in Google Scholar
 E. Bulska, D. Gorczyca, I. Zalewska, A. Pokrywka, D. Kwiatkowska. J. Pharm. Biomed. Anal.106, 159 (2015). Search in Google Scholar
 A. Casilli, T. Piper, F. A. de Oliveira, M. Costa Padilha, H. Marcelo Pereira, M. Thevis, F. R. de Aquino Neto. Drug Test Anal.8, 1204 (2016). Search in Google Scholar
 E. K. Shibuya, J. E. Souza Sarkis, O. N. Neto, M. Z. Moreira, R. L. Victoria. Forensic Sci. Int.160, 35 (2006). Search in Google Scholar
 J. B. West, J. M. Hurley, J. R. Ehleringer. J Forensic Sci.54, 84 (2009). Search in Google Scholar
 United States Drug Enforcement Administration. Marijuana-Indoor Marijuana Grow, United States Department of Justice (2014), Feb. 22; http://www.justice.gov/dea/pr/multimedia-library/image-gallery/images_marijuana.shtml. Search in Google Scholar
 J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf. Search in Google Scholar
 GI & Liver Laboratory at Centre for Liver & Digestive Disorders, The Royal Infirmary of Edinburgh. GI & Liver Laboratory Patient Leaflet. Search in Google Scholar
 S. L. Kitson. Tracking Human Metabolism with Carbon-14, Drug Discovery and Development (2014), Feb. 23; http://www.dddmag.com/articles/2013/02/tracking-human-metabolism-carbon-14. Search in Google Scholar
 Medical Health Tests. Reasons, Procedure and Preparation for C Urea Breath Test-Carbon Urea Breath Test, Medical Health Tests (2014), Feb. 23; http://www.medicalhealthtests.com/urea-breath-test/c-urea-breath-test.html. Search in Google Scholar
 P. L. Koch, M. L. Fogel, N. Tuross. “Tracing the diets of fossil animals using stable isotopes”, in Stable Isotopes in Ecology and Environmental Science, K. Lajtha and R. H. Michener (Eds.), Blackwell Scientific Publications, Boston (1994). Search in Google Scholar
 J. P. Montoya. “Nitrogen isotope fractionation in the modern ocean: implications for the sedimentary record”, in Carbon Cycling in the Glacial Ocean: Constraints on the Ocean’s Role in Global Change. NATO ASI Series (Series I: Global Environmental Change), R. Zahn, T. F. Pedersen, M. A. Kaminski, L. Labeyrie (Eds.), vol. 17. Springer, Berlin, Heidelberg (1994). Search in Google Scholar
 R. E. M. Hedges, L. M. Reynard. J. Archaeolog. Sci.34, 1240 (2007). Search in Google Scholar
 M. A. Burford, N. P. Preston, P. M. Glibert, W. C. Dennison. Aquaculture206, 199 (2002). Search in Google Scholar
 J. K. Böhlke, R. C. Antweiler, J. W. Harvey, A. E. Laursen, L. K. Smith, R. L. Smith, M. A. Voytek. Biogeochemistry93, 117 (2009). Search in Google Scholar
 Stable Isotopes in Ecology and Environmental Science: 2nd Edition, ed. R. Michener and K. Lajtha, p. 566, Blackwell Publishing Ltd., Malden, MA (2007). Search in Google Scholar
 J. Granger, D. M. Sigman, M. F. Lehmann, P. D. Tortell. Limnol. Oceanogr.53, 2533 (2008). Search in Google Scholar
 A. Mariotti, A. Landreau, B. Simon. Limnol. Oceanogr.52, 1869 (1988). Search in Google Scholar
 T. H. E. Heaton. Chem. Geol.59, 87 (1986). Search in Google Scholar
 C. Kendall, R. Aravena. “Nitrate isotopes in groundwater systems”, in Environmental Tracers in Subsurface Hydrology, P. G. Cook and A. L. Herczeg (Eds.), Kluwer Academic Publishers, Boston (2000). Search in Google Scholar
 B. Mayer, E. W. Boyer, C. Goodale, N. A. Jaworski, N. Van Breemen, R. W. Howarth, S. P. Seitzinger, G. Billen, K. Lajtha, K. J. Nadelhoffer, D. Van Dam, L. J. Hetling, M. Nosal, K. Paustian. Biogeochemistry57 & 58, 171 (2002). Search in Google Scholar
 R. L. Smith, J. K. Böhlke, S. P. Garabedian, K. M. Revesz, T. Yoshinari. Water Resour. Res.40, 1 (2004). Search in Google Scholar
 H. Salouros, G. J. Sutton, J. Howes, D. B. Hibbert, M. Collins. Anal. Chem.85, 9400 (2013). Search in Google Scholar
 D. M. O’Brien, M. J. Woller. Rapid Commun. Mass Spectrom.21, 2422 (2007). Search in Google Scholar
 I. Fraser, W. Meier-Augenstein, R. M. Kalin. Rapid Commun. Mass Spectrom.20, 1109 (2006). Search in Google Scholar
 International Atomic Energy Agency. Cyclotron Produced Radionuclides: Physical Characteristics and Production Methods, Technical Reports Series No. 468. International Atomic Energy Agency Vienna (2009). Search in Google Scholar
 M. Sajjad, R. M. Lambrecht, A. P. Wolf. Radiochim. Acta39, 165 (1986). Search in Google Scholar
 T. Arai, S. Nakao, K. Mori, K. Ishimori, I. Morishima, T. Miyazawa, B. Fritz-Zieroth. Rapid Commun. Mass Spectrom.169, 153 (1990). Search in Google Scholar
 J. R. Speakman. Theory and Practice, Doubly Labelled Water. Springer Scientific, London (1997). Search in Google Scholar
 R. Krebs. The History And Use Of Our Earth’s Chemical Elements: A Reference Guide, 2nd ed. Greenwood Press, Westport, CT (2006). Search in Google Scholar
 P. K. Thanos, G. J. Wang, N. D. Volkow. Positron Emission Tomography as a Tool for Studying Alcohol Abuse, National Institute on Alcohol Abuse and Alcoholism (NIAAA) (2014), Feb. 24; http://pubs.niaaa.nih.gov/publications/arh313/233-237.htm. Search in Google Scholar
 Noble Gases in Geochemistry and Cosmochemistry: Reviews in Mineralogy and Geochemistry, D. Porcelli, C. J. Ballentine, and R. Wieler (Eds.), p. 844, Mineralogical Society of America and the Geochemical Society, Washington, DC (2002). Search in Google Scholar
 F. Peeters, U. Beyerle, W. Aeschbach-Hertig, J. Holocher, M. S. Brennwald, R. Kipfer. Geochim. Cosmochim. Acta.67, 587 (2003). Search in Google Scholar
 T. E. Cerling, H. Craig. Annu. Rev. Earth Planet. Sci.22, 273 (1994). Search in Google Scholar
 D. Lal, B. Peters. “Cosmic ray produced radioactivity on the earth”, in Cosmic Rays II, K. Sitte (Ed.), Springer-Verlag, New York (1967). Search in Google Scholar
 J. Lippmann-Pipke, B. S. Lollar, S. Niedermann, N. A. Stroncik, R. Naumann, E. V. Heerden, T. C. Onstott. Chem. Geol.283, 287 (2011). Search in Google Scholar
 W. R. Bennett. Phys. Rev.126, 580 (1962). Search in Google Scholar
 R. Policroniades, E. Moreno, A. Varela, G. Murillo, A. Huerta, M. E. Ortiz, E. Chávez. Rev. Mex. Fis. S.54, 46 (2008). Search in Google Scholar
 World Nuclear Association. Radioisotopes in Industry: Industrial Uses of Radioisotopes, World Nuclear Association (2014), Feb. 24; http://www.world-nuclear.org/info/inf56.html. Search in Google Scholar
 Australian Government, Australian Nuclear Science and Technology Organisation (Ansto). [Radioisotopes]:/their Role in Society Today/, Australian Government, Australian Nuclear Science and Technology Organisation (Ansto) (2014), Feb. 24; http://www.ansto.gov.au/__data/assets/pdf_file/0018/3564/Radioisotopes.pdf. Search in Google Scholar
 AUS-e-TUTE for Astute Science Students. Chemistry Tutorial: Summary of Radioactive Particles, Isotopes, Properties and Uses, AUS-e-TUTE for Astute Science Students (2014), Feb. 24; http://www.ausetute.com.au/nuclesum.html. Search in Google Scholar
 D. G. Fleishman. J. Environ. Radioact.99, 1203 (2008). Search in Google Scholar
 T. Hasegawa, K. Oda, Y. Wada, Y. Sato, T. Yamada, M. Matsumoto, H. Murayama, T. Takeda, T. Sasaki, K. Kikuchi, Y. Abe, H. Miyatake, K. Miwa, K. Akimoto, K. Wagatsuma. “Application of novel calibration scheme based on traceable point-like 22Na sources to various types of PET scanners”, in Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012 IEEE. Search in Google Scholar
 M. Sabatier, W. R. Keyes, F. Pont, M. J. Arnaud, J. R. Turnlund. Am. J. Clin. Nutr.77, 1206 (2003). Search in Google Scholar
 M. Sabatier, F. Pont, M. J. Arnaud, J. R. Turnlund. Am. J. Physiol.285, R656 (2003). Search in Google Scholar
 J. G. Montes, R. A. Sjodin, A. L. Yergey, N. E. Vieira. Biophys. J.56, 437 (1989). Search in Google Scholar
 S. Sahijpal, J. N. Goswami. Astrophys. J.509, L137 (1998). Search in Google Scholar
 C. Steinhausen, G. Kislinger, C. Winklhofer, E. Beck, C. Hohl, E. Nolte, T. H. Ittel, M. J. Alvarez-Brückmann. Food Chem. Toxicol.42, 363 (2004). Search in Google Scholar
 B. Kleja, W. Standring, D. H. Oughton, J. P. Gustafsson, K. Fifield, A. R. Fraser. Geochim. Cosmochim. Acta.69, 5263 (2005). Search in Google Scholar
 United States Geological Survey. Resources on Isotopes-Periodic Table-Aluminum, United States Geological Survey (2014), Feb. 24; http://wwwrcamnl.wr.usgs.gov/isoig/period/al_iig.html. Search in Google Scholar
 D. E. Granger. Geol. Soc. Spec. Pap.415, 1 (2006). Search in Google Scholar
 K. K. Nichols, P. R. Bierman, R. L. Hooke, E. M. Clapp, M. Caffee. Geomorphology45, 105 (2002). Search in Google Scholar
 D. Lal. Annu. Rev. Earth Planet. Sci.16, 355 (1988). Search in Google Scholar
 S. Kristiansen, T. Farbrot, L. J. Naustvoll. Limnol. Oceanogr.45, 472 (2000). Search in Google Scholar
 C. Schnabel, J. Beer, H. B. Clausen. Geophys. Res. Abstr.11, (2009). Search in Google Scholar
 SAHRA – Sustainability of Semi-Arid Hydrology and Riparian Areas. Silicon, SAHRA – Sustainability of Semi-Arid Hydrology and Riparian Areas (2014), Feb. 24; http://web.sahra.arizona.edu/programs/isotopes/silicon.html. Search in Google Scholar
 GNS Science. Climate Change Studies & Ice Core Research, GNS Science (2014), Feb. 24; http://www.gns.cri.nz/Home/Services/Laboratories-Facilities/Tritium-and-Water-Dating-Laboratory/Research-Programmes/Climate-change-studies-ice-core-research. Search in Google Scholar
 U. Morgenstern, C. B. Taylor, Y. Parrat, H. W. Gäggeler, B. Eichler. Earth Planet. Sci. Lett.144, 289 (1996). Search in Google Scholar
 Kohei ITOH research group at Keio University, Japan. Itoh Group at Keio University, Japan, Kohei ITOH research group at Keio University, Japan (2014), Feb. 24; http://www.appi.keio.ac.jp/Itoh_group/research/. Search in Google Scholar
 T. Itahashi, H. Hayashi, M. R. Rahman, K. M. Itoh, L. S. Vlasenko, M. P. Vlasenko, D. S. Poloskin. Phys. Rev. B87, 075201-1 (2013). Search in Google Scholar
 R. Marquardt, J. Meija, Z. Mester, M. Towns, R. Weir, R. Davis, J. Stohner. Pure Appl. Chem.90, 175 (2018). Search in Google Scholar
 B. Singh, J. Singh, A. Kaur. Int. J. Biotechnol. Bioeng. Res.4, 167 (2013). Search in Google Scholar
 S. N. Levine, M. P. Stainton, D. W. Schindler. Can. J. Fish. Aquat.Sci.43, 366 (1986). Search in Google Scholar
 E. K. J. Pauwels, F. J. Cleton. Radiother. Oncol.1, 333 (1984). Search in Google Scholar
 C. B. Wilson, A. A. Epenetos. Baillieres Clin. Gastroenterol.1, 115 (1987). Search in Google Scholar
 L. Tuominen, H. Hartikainen, T. Kairesalo, P. Tallberg. Water Res.32, 2001 (1998). Search in Google Scholar
 Popular Science Monthly: Mechanic and Handicraft, 91 (1951). Search in Google Scholar
 E. B. Silberstein, A. H. Elgazzar, A. Kapilivsky. Semin. Nucl. Med.22, 17 (1992). Search in Google Scholar
 S. C. Srivastava. Braz. Arch. Biol. Technol.45, 45 (2002). Search in Google Scholar
 Mayo Clinic staff. Polycythemia Vera: Treatments and Drugs, Mayo Clinic (2017), April 4; http://www.mayoclinic.org/diseases-conditions/polycythemia-vera/diagnosis-treatment/treatment/txc-20307498. Search in Google Scholar
 A. S. W. Goh, A. Y. F. Chung, R. H. G. Lo, T. N. Lau, S. W. K. Yu, M. Chng, S. Satchithanantham, S. L. E. Loong, D. C. E. Ng, B. C. Lim, S. Connor, P. K. H. Chow. Int. J. Radiat. Oncol. Biol. Phys.67, 786 (2007). Search in Google Scholar
 C. E. Hebert, M. Bur, D. Sherman, J. L. Shutt. Ecol. Appl.18, 561 (2008). Search in Google Scholar
 International Atomic Energy Agency. Guidelines for the use of Isotopes of Sulfur in Soil–Plant Studies, International Atomic Energy Agency Vienna, Austria (2003). Search in Google Scholar
 I. M. Cozzarelli, J. M. Suflita, G. A. Ulrich, S. H. Harris, M. A. Scholl, J. L. Schlottmann, S. Christenson. Environ. Sci. Technol.34, 4025 (2000). Search in Google Scholar
 M. Edraki, S. D. Golding, K. A. Baublys, M. G. Lawrence. Appl. Geochem.20, 789 (2005). Search in Google Scholar
 B. Bahar, A. P. Moloney, F. J. Monahan, S. M. Harrison, A. Zazzo, C. M. Scrimgeour, I. S. Begley, O. Schmidt. J. Anim. Sci.87, 905 (2009). Search in Google Scholar
 Y. Hu, H. Shang, H. Tong, O. Nehlich, W. Liu, C. Zhao, J. Yu, C. Wang, E. Trinkausd, M. P. Richards. Proc. Natl. Acad. Sci.106, 10971 (2009). Search in Google Scholar
 A. Priyadarshi, G. Dominguez, J. Savarino, M. Thiemens. Geophys. Res. Lett.38, L13808 (2011). Search in Google Scholar
 INSTAAR University of Colorado Boulder. Sulfur 35, INSTAAR University of Colorado Boulder (2014), Feb. 24; http://snobear.colorado.edu/Daniel/isotopes/sulfur35.html. Search in Google Scholar
 Y. Kim, K. S. Lee, D. C. Koh, D. H. Lee, S. G. Lee, W. B. Park, G. W. Koh, N. C. Woo. J. Hydrol.270, 282 (2003). Search in Google Scholar
 Y. L. Hong, G. Kim. Anal. Chem.77, 3390 (2005). Search in Google Scholar
 H. G. M. Eggenkamp, R. Kreulen, A. F. Koster Van Groos. Geochim. Cosmochim. Acta59, 5169 (1995). Search in Google Scholar
 M. A. Stewart, A. J. Spivack. Rev. Mine