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  • Author: A. Toyoshima x
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Abstract

The ion-exchange behavior of Zr and Hf in H2SO4 and H2SO4/HClO4 mixed solutions has been studied by a batch method using the carrier-free radiotracers 88Zr and 175Hf. It is found that the ion-exchange behavior of Zr and Hf is basically similar to each other, and that Zr and Hf are adsorbed on the cation-exchange resin as well as on an anion-exchange one in H2SO4. In 0.11−0.99 M H2SO4, the logarithmic values of distribution coefficients (K d) of Zr and Hf on the cation- and anion-exchange resins linearly decrease with log[H+]eq and log[HSO4 -]eq, respectively, indicating that M4+ and M(SO4)3 2- (M=Zr and Hf) are the predominant cationic and anionic species adsorbed on the resins, respectively. The K d values of Zr and Hf on the cation-exchange resin in H2SO4/HClO4 at [H+]eq=1.0 M also decrease with an increase of [HSO4 -]eq, reflecting successive formation of sulfate complexes. The slope analysis demonstrates that Zr and Hf are coordinated by one SO4 2- ion at 0.011 and 0.020 M [HSO4 -]eq, respectively, and by two SO4 2- ions at 0.079 and 0.20 M [HSO4 -]eq, respectively.

Summary

We developed a new apparatus for the study of electrochemical properties of the heaviest elements. The apparatus is based on a flow electrolytic cell combined with column chromatography. Glassy-carbon fibers modified with Nafion perfluorinated cation-exchange resin are used as a working electrode as well as a cation-exchanger. The elution behavior of 139Ce with the number of 1010 atoms in 0.1 M ammonium α-hydroxyisobutyric acid solution from the column electrode was investigated at the applied potentials of 0.2–1.0 V versus the Ag/AgCl reference electrode in 1.0 M LiCl. It was found that 139Ce3+ is successfully oxidized to 139Ce4+ even with tracer concentration at around the redox potential determined by cyclic voltammetry for the macro amounts of Ce with 1017 atoms (10−3 M). The present oxidation reaction and separation of Ce4+ was accomplished within a few minutes.

Summary

Chemical studies on element 104, rutherfordium (Rf), at JAERI (Japan Atomic Energy Research Institute) are reviewed. The transactinide nuclide 261Rf has been produced in the reaction 248Cm(18O, 5n) at the JAERI tandem accelerator with the production cross section of about 13 nb. On-line anion-exchange experiments on Rf together with the lighter homologues, group-4 elements Zr and Hf, in acidic solutions have been conducted with a rapid ion-exchange separation apparatus. From the systematic study of the anion-exchange behavior of Rf, it has been found that the properties of Rf in HCl and HNO3 solutions are quite similar to those of Zr and Hf, definitely confirming that Rf is a member of the group-4 elements. However, we have observed an unexpected chemical behavior of Rf in HF solutions; the fluoride complex formation of Rf is significantly different from those of the homologues. Prospects of extending chemical studies on transactinide elements in the near future at JAERI are briefly considered.

Abstract

Anion-exchange chromatography of element 105, dubnium (Db), produced in the 248Cm( 19F, 5n) 262Db reaction is investigated together with the homologues Nb and Ta, and the pseudo-homologue Pa in 13.9 M hydrofluoric acid (HF) solution. The distribution coefficient (K d) of Db on an anion-exchange resin is successfully determined by running cycles of 1702 chromatographic column separations. The result clearly indicates that the adsorption of Db on the resin is significantly different from that of the homologues and that the adsorption of anionic fluoro complexes of these elements decreases in the sequence of Ta≈ Nb>Db≥Pa.

Abstract

The cation-exchange behavior of 261Rf (T 1/2= 78 s) produced in the 248Cm(18O, 5n) reaction was studied on a “one-atom-at-a-time” scale in 0.15–0.69 M H2SO4/HNO3 mixed solutions ([H+]=1.0 M) using an automated ion-exchange separation apparatus coupled with the detection system for alpha-spectroscopy (AIDA). It was found that adsorption probabilities ( decrease with an increase of [HSO4 ], showing a successive formation of Rf sulfate complexes. Rf exhibits a weaker complex formation tendency compared to the lighter homologues Zr and Hf. This is in good agreement with theoretical predictions including relativistic effects.

Abstract

We carried out solvent extraction on the trivalent actinides of Am, Cm, Cf, and Fm and the lanthanides (except Pm) using di(2-ethylhexyl)phosphoric acid (HDEHP) in benzene by a batch method. The extraction constants of the HDEHP complexes for these elements were determined systematically under identical conditions. The tetrad effect was clearly observed in the variation of the extraction constants of the lanthanide series. We found that the extraction constant for Fm(III) is much smaller than that for Dy(III), which have similar ionic radii. The extraction constants for Am(III), Cm(III), and Cf(III) are similar to those for corresponding Ln(III) having similar ionic radii. Two possibilities that account for the lower extraction constant of Fm(III) is suggested.

Abstract

Production cross-sections of the isotope 256Lr in the 249,250,251Cf +11B, 243Am +18O, and 248Cm +14N reactions were measured using a He/KCl gas-jet transport system and a rotating wheel α-particle detection apparatus. The α-particle energy of 256Lr was distributed from 8.3 to 8.7 MeV and its half-life, T 1/2, was measured to be 28 ± 1 s. The maximum cross sections in the 249Cf(11B, 4n)256Lr and 243Am(18O, 5n)256Lr reactions were determined to be 122 ± 36 nb at the beam energy of 63 MeV and 26 ± 7 nb at 96 MeV, respectively. In the 248Cm(14N, 6n)256Lr reaction, the cross section was measured to be 27 ± 10 nb at 91 MeV.

Summary

Formation of anionic fluoride-complexes of element 104, rutherfordium, produced in the 248Cm(18O,5n) 261Rf reaction was studied by anion-exchange on an atom-at-a-time scale. It was found that the hexafluoro complex of Rf, [RfF6]2−, was formed in the studied fluoride ion concentrations of 0.0005–0.013 M. Formation of [RfF6]2− was significantly different from that of the homologues Zr and Hf, [ZrF6]2− and [HfF6]2−; the evaluated formation constant of [RfF6]2− is at least one-order of magnitude smaller than those of [ZrF6]2− and [HfF6]2−.

The extraction behavior of rutherfordium (Rf) into tributylphosphate (TBP) from hydrochloric acid (HCl) has been studied together with those of the lighter group-4 elements Zr and Hf. The extractability of 261Rf, 169Hf, and 85Zr into TBP was investigated under identical conditions in 7.2–8.0 M HCl by on-line reversed-phase extraction chromatography. The percent extractions of Rf, Hf, and Zr into the TBP resin increase steeply with increasing HCl concentration, and the order of extraction is Zr > Hf ≈ Rf. By considering the order of chloride complexation among these elements, it is suggested that the stability of the TBP complex of Rf tetrachloride is lower than those of Zr and Hf.

Abstract

Chemical studies of superheavy elements require fast and efficient techniques, due to short half-lives and low production rates of the investigated nuclides. Here, we advocate for using a tubular flow reactor for assessing the thermal stability of the Sg carbonyl complex – Sg(CO)6. The experimental setup was tested with Mo and W carbonyl complexes, as their properties are established and supported by theoretical predictions. The suggested approach proved to be effective in discriminating between the thermal stabilities of Mo(CO)6 and W(CO)6. Therefore, an experimental verification of the predicted Sg–CO bond dissociation energy seems to be feasible by applying this technique. By investigating the effect of 104,105Mo beta-decay on the formation of 104,105Tc carbonyl complex, we estimated the lower reaction time limit for the metal carbonyl synthesis in the gas phase to be more than 100 ms. We examined further the influence of the wall material of the recoil chamber, the carrier gas composition, the gas flow rate, and the pressure on the production yield of 104Mo(CO)6, so that the future stability tests with Sg(CO)6 can be optimized accordingly.