S. Ichikawa

Extraction behavior of rutherfordium into tributylphosphate from hydrochloric acid

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.

Selective mass separation of light lanthanoids by means of ionization of their monoxides

To strengthen elemental selectivity in isotope separation on-line, ionization of the monoxides of light lanthanoids in a thermal ion source has been studied. Currents of the monoxide ion MO+ and the metallic ion M+ were measured in off-line experiments using oxide reagents of the elements from Ba to Sm at ion-source temperatures from 1900 to 2730 K. The observed MO+M+ ratio was the highest for La and Ce, and decreased with increasing atomic number and temperature. In on-line experiments using heavy-ion fusion-evaporation reactions, La isotopes were mass-separated as La16O+, being well separated from the Cs and Ba isobars, while Pr isotopes were obtained at a higher temperature as Pr+ since the La and Ce isobars were still ionized favorably as MO+. Using this method, the isotope 121La was newly identified with a half-life of 5.3 ± 0.2 s.

Isomeric yield ratios of 134I and 136I in the proton-, 12C- and 19F-induced fission of 235U, 237Np and 238U

Short-lived nuclides of iodine produced in the proton-, 12C- and 19F-induced fission of 235U, 237Np and 238U were separated with a rapid chemical separation system SISAK. Relative yields of the nuclides were determined by γ -ray spectrometry to obtain the isomeric yield ratios of 134mI/134gI and 136mI/136gI. Angular momenta of the fission fragments, 134I and 136I, were derived from the measured isomeric yield ratios by the spin-dependent statistical model. In the light- and heavy-ion fission, variation of the observed angular momenta can be explained by the excitation energies of the fissioning nuclei and the spherical shell structure with N = 82.

Two deformation paths in proton-induced fission of 232Th☆

Abstract Velocities of complementary fission fragments have been accurately measured by a double velocity time-of-flight method in the proton-induced fission of 232 Th with incident energies from 12.0 to 14.7 MeV. The results experimentally demonstrate for the first time the correlation among the threshold energy, the total fragment kinetic energy, and the mass division mode in fission: one type of the fission process has a lower threshold energy and leads to a compact scission configuration with reflection asymmetry, and the other type has a higher threshold energy and leads to a symmetric elongated scission configuration.

Ion source development for the JAERI on-line isotope separator

Abstract In accordance with the JAERI-KEK joint radioactive nuclear beam (RNB) project, we have installed a forced electron beam induced arc discharge (FEBIAD) type integrated-target–ion source in the JAERI-ISOL to produce heavy neutron-rich RNBs with particle-induced fission of 238 U. In the present ion source, a 2.6-g 238 UC 2 target is directly attached to a plasma chamber. RNBs of 8 Li, 18 F and 20 F are also planned to be used for the study of thermal diffusion in materials in the joint project. Release profiles of 7 Li have been studied using a cavity type thermal ion source. For mass-separation of F atoms, the molecular ion formations have been examined using the FEBIAD ion source.

{alpha} decay of {sup 238}Cm and the new isotope {sup 237}Cm

Alpha decays of {sup 237}Cm and {sup 238}Cm have been studied using a gas-jet coupled on-line isotope separator. The new isotope {sup 237}Cm has been identified through the detection of 6656{+-}10 keV {alpha} particles. The {alpha} energy of {sup 238}Cm has been revised more precisely than the previous one. The {alpha} transition to the first excited 2{sup +} state in {sup 234}Pu has also been observed. It was found that the 2{sup +} energy in {sup 234}Pu is much higher than those in heavier Pu isotopes.

Performance of the multiple target He/PbI2 aerosol jet system for mass separation of neutron-deficient actinide isotopes

Abstract A multiple target He/PbI2 aerosol jet system coupled with a thermal ion source was installed in the isotope separator on line (JAERI-ISOL) at the JAERI tandem accelerator facility. The neutron-deficient americium and curium isotopes produced in the 233,235 U( 6 Li, xn) and 237 Np( 6 Li, xn) reactions were successfully mass-separated and the overall efficiency including the ionization of Am atoms was evaluated to be 0.3–0.4%. The identification of a new isotope 237 Cm with the present system is reported.

Mass separation of neutron-rich isotopes using a gas-jet coupled thermal ion source

A gas-jet coupled thermal ion source was installed in the isotope separator on line at the JAERI tandem accelerator. It was used for separation of neutron-rich isotopes produced in the reaction 238U(15 MeV-p, fission). The separation efficiencies of the whole system were measured to be 3.3% for 140Cs (T12 = 63.7 s), 2.0% for 144La (T12 = 40.8 s), 2.2% for 148Pr (T12 = 2.0 m), 1.2% for 156Pm (T12 = 26.7 s) and 1.0% for 160Eu (T12 = 44 s). A long sticking time of La atoms on the ionizer surface gave a low efficiency of about 0.1% for 148La (T12 = 1.05 s). The first observation of a new isotope 166Tb was carried out using its monoxide ions from this ion source: T12(166Tb) = 21±6 s.

Startup of transactinide chemistry in JAERI

The transactinide nuclides 261Rf and 262Db have been successfully produced in the 248Cm(18O,5n) reaction at 99 MeV and in the 248Cm(19F,5n) reaction at 100, 103, and 106 MeV, respectively, at the JAERI tandem accelerator. The on-line ion exchange experiments with an automated fast and repetitive liquid chromatography separation system were performed in the HNO3/HF system using Rf homologues 89mZr and 167,165Hf produced in the 89Y(p,n) and 152Gd(18O,xn) reactions, respectively. The radiotracers 88Zr, 175Hf, and 234Th were also prepared and the distribution coefficients on ion exchange resins were measured systematically in 1-11 M HCl and 1-14 M HNO3 with the batch method. It was found that anion exchange experiments of Rf in 8 M HNO3 and 9 M HCl provided information useful to extract the ionic radius of Rf and to verify the influence of relativistic effects.

β+ decay of unstable praseodymium isotopes: 127Pr, 126Pr and the new isotope 125Pr

Abstract The β + decay of 127,126,125 Pr was studied for on-line mass-separated sources. The decay scheme of 127 Pr reported previously was revised from the results of a more-detailed analysis of the experimental data. The 125 Pr isotope was newly identified with a half-life of 3.3(7) s and its decay scheme is presented. The γ band in 126 Ce was identified in the decay of 126 Pr and its properties are compared with the prediction of the interacting boson model 2.