The average equilibrium charges qave of heavy recoil ions moving in helium gas were measured by a gas-filled recoil ion separator (GARIS). A new empirical formula to calculate qave for superheavy recoil ions with a low velocity was derived. This formula was applicable to the search for a superheavy nuclide of 266Bh.
The recoil properties of 14, 24, 26, 31, 21 and 20 radionuclides formed in photospallation reactions on natV, natCu, 93Nb, natAg, natTa, and 197Au, respectively, induced by bremsstrahlung of end-point energies (E0) from 600 to 1100 MeV, have been investigated using the thick-target thick-catcher method based on the two-step vector model. The measured forward-to-backward ratios (F/B) were found to be independent of the mass difference (ΔA) between a product (Ap) and a target (At) and also of At. The recoil velocities ν from the first step and the mean kinetic energies T of the residual nuclei in the second step were deduced and discussed by comparing with the reported results on proton-induced reactions. A comparison with T values calculated by the PICA (Photon-Induced Intranuclear Cascade Analysis) code at E0 = 400 MeV was also performed. It was found that although the code well reproduces the experimental results of natV and natCu, the same calculation for heavier targets gives T values lower than the experimental results, indicating some nuclear-structure effect, such as a medium effect notably at At ≥ 100. The parameter values of εs = T/(ΔA/At), the average kinetic energy of the emitted particles in a random-walk process of both the photon- and proton-reactions, were found to increase along with an increase of At, but change slopes to become constant above At = 100.
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.
The reaction yields of 63 radionuclides with the mass number A = 56 − 135 produced in the photofission of 209Bi by bremsstrahlung of end-point energies (E0) from 450 to 1100 MeV have been measured using a catcher foil technique with the aid of intensive chemical separation. The charge distribution was well reproduced by a Gaussian function with the most probable charge (Zp) expressed by a linear function of A, i.e., Zp = RA + S, and with the A-independent full width at half maximum (FWHMCD). The charge distribution parameters R, S and FWHMCD were independent of E0 above 600 MeV, reflecting the resonance nature in photonuclear reactions at intermediate energies. The weighted mean values at E0 ≥ 600 MeV were R = 0.421 ± 0.001, S = 0.6 ± 0.1 and FWHMCD = 2.1 ± 0.1 charge unit (c.u.). The numbers of pre- and post-fission neutrons were deduced to be νpre = 12 ± 1 and νpost = 1.4 ± 0.3, respectively, assuming the Unchanged Charge Distribution (UCD). Based on the charge distribution parameters, the symmetric mass yield distributions with the most probable mass Ap of 96 ± 1 mass unit (m.u.) and the width FWHMMD of 33 ± 1 m.u. were also obtained. The characteristics of the charge and mass yield distributions are discussed by referring to those for 197Au based on the results of calculations using the Photon-induced Intranuclear Cascade Analysis code combined with the Generalized Evaporation Model (PICA3/GEM).
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.
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%.