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  • Author: H. Kikunaga x
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Abstract

The half-lives of 196Au and 202Tl have been precisely obtained by repeated measurements for 40 samples of 196Au and 16 samples of 202Tl using germanium detectors. The dead-time was corrected by the simultaneous detection of 662-keV γ rays from a reference source of 137Cs. The half-life value of 6.1451 ± 0.0013 (tot.) d, 0.35% shorter than the recommended value of ENSDF [1], has been obtained for 196Au. The error contains the statistical uncertainty and other random uncertainty. The half-life of 202Tl is determined to be 12.4706 ± 0.0055 (tot.) d with improved accuracy as compared to the latest measurement by a factor of 15.

Abstract

Trivalent actinides Am(III), Cm(III), and Cf(III) were successfully separated for the first time using capillary electrophoresis in 2-hydroxyisobutyric acid/acetic acid. It was found that the ionic radius was primarily important for separation of trivalent actinides as well as lanthanides in this condition. The stability constants of the Am(III) complexes with 2-hydroxyisobutyrate were estimated using the correlations between the molar fraction ratio of lanthanides and their ionic radii.

Abstract

We have produced 90mNb and 99mTc in the reactions of natZr(p,xn)90mNb and 100Mo(γ,n)99Mo, followed by disintegration to 99mTc, respectively, and measured the half-lives of these nuclides by using a reference source method. In order to determine the short half-lives of 90mNb precisely, an on-line gas-jet system has been employed. As a result, the half-lives of these nuclides were determined with good precision on the order of magnitude of 0.1%.

Abstract

Solvent extraction behavior of carrier-free Mo and W from 0.1–11 M HCl into 0.05 M Aliquat 336-chloroform solution was investigated and compared with that of macro amounts of Mo and W. The distribution ratios of carrier-free Mo and W were in good agreement with those of macro amounts of Mo and W in 6–11 M HCl, while the extraction efficiencies of carrier-free Mo and W were different from those of macro amounts of Mo and W in <6 M HCl. Therefore, it appears that the carrier-free as well as macro amounts of Mo and W form mononuclear species in 6–11 M HCl. The disagreement in <6 M HCl is probably due to the formation of polynuclear species of the macro amounts of Mo and W.

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.

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.