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November 26, 2010
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The two Auger electron emitting radionuclides of bromine, namely 77 Br ( T 1/2 =57.04 h) and 80m Br ( T 1/2 =4.4 h), are promising candidates for internal radiotherapy. In this work, nuclear reaction cross sections were determined for their production using enriched Se targets. Thin Se samples were irradiated with incident protons of energies up to 85 MeV and the induced radioactivity was measured via non-destructive γ-ray spectroscopy, allowing the determination and extension of the excitation functions of the four reactions 77,78,80 Se( p ,ߙ xn ) 77 Br and 80 Se( p ,ߙ n ) 80m Br. The possible thick target yields were calculated and the different production routes discussed, especially with regard to the yield and the radionuclidic purity of the produced radionuclides.
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November 26, 2010
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A liquid–liquid extraction system suitable for studies of chemical properties of Hs (element 108), in the form of HsO 4 , was developed using γ-emitting isotopes of its homologue Os. The system is targeted for the fast on-line extraction system SISAK, which operates in a continuous manner and is suitable for liquid-phase studies of transactinide elements. The distribution of OsO 4 between various dilute NaOH solutions and toluene was studied. Both batch and SISAK on-line experiments were performed to develop an appropriate system. From analysis of the extraction curves equilibrium constants for the formation of the presumed complexes, Na[OsO 4 (OH)] and Na 2 [OsO 4 (OH) 2 ], were obtained: K 1 =(1±0.5)×10 4 and K 2 =12±8, respectively. The SISAK system includes a liquid-scintillation detection system for α measurements. Due to quenching effects it is not possible to perform direct measurement of the aqueous phase α´s. Therefore, a two-stage extraction method that provides an indirect measurement of the activity in the aqueous phase was developed as part of the proposed system for Hs: Acidification of the raffinate from the first stage result in recovery of OsO 4 , which is highly extractable into toluene. The yield of extraction in the second step, from 0.01 M NaOH solution after acidification with H 2 SO 4 solution, was (90±3) %.
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November 26, 2010
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The formation constants of mononuclear hydrolysis species of Pu(VI) were determined by absorption spectroscopy under carefully designed experimental conditions. In order to exclude the formation of polynuclear hydrolysis species, the concentration of plutonium was diluted below 50 μM. To maintain the oxidation state of Pu(VI), NaOCl was applied as an oxidant. The trace amount of Pu(V) was monitored by the measurement of redox potential and absorption spectroscopy by using a liquid waveguide capillary cell with the optical path length of 100 cm. The determined molar absorption coefficients (ε, M −1 cm −1 ) were 272±26 and 436±33 for PuO 2 (OH) + and PuO 2 (OH) 2 (aq) species, respectively. The formation constants of mononuclear hydrolysis species of Pu(VI) at ionic strength of 0.01 M NaClO 4 were determined as follows: logߙ * β ′ 1 ߙ(for PuO 2 (OH) + ) = −5.8±0.3, logߙ * β ′ 2 ߙ(for PuO 2 (OH) 2 (aq)) = −13.4±0.2 and logߙ * β ′ 3 ߙ(for PuO 2 (OH) 3 − ) = −24.3±0.8.
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November 26, 2010
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The rare-earth element pattern was used as an additional tool for the identification and origin assessment of uranium ore concentrates (yellow cakes) for nuclear forensic purposes. By this means, the source of an unknown material can be straightforwardly verified by comparing the pattern with that of a known or declared sample. In contrast to other indicators used for nuclear forensic studies, the provenance of the material can also be assessed in several cases even if no comparison sample is available due to the characteristic pattern. The milling process was found not to change the pattern and no significant elemental fractionation occurs between the rare-earth elements, thus the pattern in the yellow cakes corresponds to that found in the uranium ore.
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November 26, 2010
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A mesh-type liquid cadmium cathode (LCC) structure has been devised to improve the performance of the electro-winning process for the recovery of actinides in a molten chloride system. For the verification of its performance, electrodeposition experiments of uranium from the molten LiCl-KCl-UCl 3 salt were conducted at 773 K for different current densities using the mesh-type LCC structure. Uranium was successfully collected over 5ߙwt.ߙ% in the LCC without growing uranium dendrites. The mesh-type LCC structure prevented the uncontrolled growth of uranium dendrites into the electrolyte phase above the cadmium surface and caused the LCC deposit to accumulate at the higher in the cadmium phase over uranium solubility in cadmium. After cooling the LCC crucible, its solid deposits were identified as an intermetallic compound UCd 11 by EPMA and XRD analysis. The cathode potential profiles from the electrochemical experiments and the chemical structure of the LCC deposits showed that it could be applied practically to recover the actinides above their solubility in cadmium.
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November 26, 2010
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U(VI) sorption on a purified Na-bentonite was investigated from 298±2 to 353±2 K by using a batch experimental method as a function of pH, U(VI) concentration, carbonate concentration and solid-to-liquid ratio ( m / V ). The data at 298±2 K could be well described by a surface complexation model (SCM) with a complex located on layer sites (X 2 UO 2 ) and three complexes located on edge sites (≡SOUO 2 + , ≡SO(UO 2 ) 3 (OH) 5 , and ≡SO(UO 2 ) 3 (OH) 7 2− ). The intrinsic equilibrium constants ( K int ) of the surface reactions at 333 ± 2 and 353±2 K were obtained by fitting U(VI) sorption curves vs. pH on the Na-bentonite. The model enables U(VI) sorption in the presence of carbonate ( p CO 2 =10 −3.58 atm) to be described without considering any ternary surface complexes involving carbonate, except for underestimation around pH 7 (6<pH<7.5). The standard enthalpy changes (Δ r H m θ ) of the surface reactions were evaluated from the K int values obtained at three temperatures (298±2, 333±2 and 353±2 K) via the van´t Hoff equation. The proposed SCM and Δ r H m θ of the surface reactions enable U(VI) sorption on the Na-bentonite at other temperatures to be predicted.
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November 26, 2010
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A new rapid method for the determination of actinides in soil and sediment samples has been developed at the Savannah River Site Environmental Lab (Aiken, SC, USA) that can be used for samples up to 2 g in emergency response situations. The actinides in soil method utilizes a rapid sodium hydroxide fusion method, a lanthanum fluoride soil matrix removal step, and a streamlined column separation process with stacked TEVA, TRU and DGA resin cartridges. Lanthanum was separated rapidly and effectively from Am and Cm on DGA resin. Vacuum box technology and rapid flow rates are used to reduce analytical time. Alpha sources are prepared using cerium fluoride microprecipitation for counting by alpha spectrometry. The method showed high chemical recoveries and effective removal of interferences. This new procedure was applied to emergency soil samples received in the NRIP Emergency Response exercise administered by the National Institute for Standards and Technology (NIST) in April, 2009. The actinides in soil results were reported within 4–5 h with excellent quality.
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November 26, 2010
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Extraction of Eu(III), Tb(III) and Lu(III), as representatives of lanthanides, has been studied with picrolonic acid [1- p -nitrophenyl-3-methyl-4-nitro-5-pyrazolone (HPA)] as extractant in various solvents such as acetylacetone (ACAC), 1-octanol (ONL), n -hexanol (HNL), 1-butanol (nBNL), 2-butanol (iBNL), cyclohexanone (CHN), n -butyl ether (BE), di(1,2-dichloroethyl)ether (DCEE), diisobutylketone (DIBK), benzene and toluene from aqueous solution of pH 1–2, having ionic strength of 0.01 mol dm −3 (K + /H + , Cl − ). The composition of the extracted adduct has been determined as M(PA) 3 except in DCEE where it is M(PA) 3 ·(HPA). Extraction constants (logߙ K ex ) were calculated and on the basis of logߙ K ex , the role of diluents in the extraction process has been discussed. The solvents with respect to their extractability of the rare earth metal ions can be arranged in the order ACAC>DIBK>BE>DCEE>ONL>HNL>CHN.
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November 26, 2010
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Radioarsenic labelled radiopharmaceuticals could add special features to molecular imaging with positron emission tomography (PET). For example the long physical half-lives of 72 As ( T 1/2 =26 h) and 74 As ( T 1/2 =17.8 d) in conjunction with their high positron branching rates of 88% and 29%, respectively, allow the investigation of slow physiological or metabolical processes, like the enrichment and biodistribution of monoclonal antibodies in tumour tissue or the characterization of stem cell trafficking. A method for separation and purification of no-carrier-added (nca) arsenic from irradiated metallic germanium targets based on distillation and anion exchange is developed. It finally converts the arsenic into an * As(III) synthon in PBS buffer and pH 7 suitable for labelling of proteins via As-S bond formations. The method delivers radioarsenic in high purity with separation factors of 10 6 from germanium and an overall yield from target to labelling synthon of >40%. In a proof-of-principle experiment, the monoclonal antibody Bevacizumab, directed against the human VEGF receptor, was labelled with a radiochemical yield >90% within 1 h at room temperature with nca 72/74/77 As.
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November 26, 2010
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PHOTOFRIN ® was labelled with 99m Tc using SnCl 2 ·2H 2 O as reducing agent. Instant thin layer chromatography (ITLC-SG) in 0.05 M NaOH was used for evaluation of radiochemical purity. Labelling efficiency was dependent on various factors that include the ligand/reductant ratio, pH and time of incubation. Therefore, optimum conditions of labelling were also determined. The stability of 99m Tc-PHOTOFRIN ® in serum was checked by using fresh human serum. Tissue distribution of 99m Tc-PHOTOFRIN ® was evaluated in Sprague Dawley rats. PHOTOFRIN ® was labelled with an efficiency of >95% under optimum conditions, which were PHOTOFRIN ® : 200 μg, pH: 3–4, SnCl 2 ·2H 2 O: 15 μg and 30 min incubation at room temperature. The 99m Tc-labelled PHOTOFRIN ® remained stable in human serum for 24 h. Biodistribution study in rats revealed maximum concentration of the labelled compound in liver, lungs and spleen at 0.5 h, and significant activity was also seen in the bladder and urine, indicating the mode of urinary excretion of PHOTOFRIN ® .
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November 26, 2010
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The standard of a primary specialized journal depends to a large extent on the quality of the peer-review process. During the last four years the following persons reviewed one or more manuscripts submitted to Radiochimica Acta, and gave advice to improve the presentations.
