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Morita, Kosuke*; Morimoto, Koji*; Kaji, Daiya*; Akiyama, Takahiro*; Goto, Shinichi*; Haba, Hiromitsu*; Ideguchi, Eiji*; Kanungo, R.*; Katori, Kenji*; Kikunaga, Hidetoshi*; et al.
AIP Conference Proceedings 891, p.3 - 9, 2007/03
A series of experiments studying the productions and their decays of the heaviest elements have been performed by using a gas-filled recoil separator GARIS at RIKEN. Results on the isotope of the 112th element, 
112, and on that of the 113th element, 
113, are reviewed. Two decay chains which are assigned to be ones originating from the isotope 112 were observed in the 
Pb(
Zn, n) reaction. The results provide a confirmation of the production and decay of the isotope 112 reported by a research group at GSI, Germany, produced via the same reaction by using a velocity filter. Two decay chains, both consisted of four consecutive alpha decays followed by a spontaneous fission, were observed also in the reaction 
Bi(Zn, n). Those are assigned to be the convincing candidate events of the isotope of the 113th element, 113, and its daughter nuclei. 
Rg, 
Mt, 
Bh, and 
Db.
Si + 
U at subbarrier energiesNishio, Katsuhisa; Hofmann, S.*; He
berger, F. P.*; Ackermann, D.*; Antalic, S.*; Comas, V. F.*; Gan, Z.*; Heinz, S.*; Heredia, J. A.*; Ikezoe, Hiroshi; et al.
AIP Conference Proceedings 891, p.71 - 79, 2007/03
Seaborgium isotopes were produced in the fusion reaction Si + U as evaporation residues (ERs), and the cross sections were determined. The experiment was carried out at GSI in Darmstadt, Germany. At the center-of-mass energy of E
= 144 MeV, three 
decay chains starting from 
Sg were observed, and the corresponding ER cross section was determined to be 67 pb. At the sub-barrier energy of E= 133 MeV, three spontaneous fission events of a new isotope 
Sg were detected. The cross section was 10 pb. The half-life of Sg was determined to be 120 ms. The ER cross sections were compared with a statistical model calculation. In the fusion process, the coupled channel calculation taking into account the prolate deformation of U was adopted to determine the capture cross section. The calculated capture cross section agrees well with the fission cross section of Si + U obtained at the JAEA tandem accelerator. The measured cross section of Sg at the sub-barrier energy is factor 10
larger than the calculation based on the one-dimensional model in the fusion process, showing the fusion enhancement caused by the deformation of U. However, disagreement with the calculation suggests the presence of quasi-fission channel. At the above barrier energy of E = 144 MeV, the measured cross section is well reproduced by the calculation. This means that the interaction of Si at the equotorial side of U has advantage on the fusion process.
Tatsuda, Sayuki*; Hashizume, Kazuaki*; Wada, Takahiro*; Ota, Masahisa*; Sumiyoshi, Kosuke*; Otsuki, Kaori*; Kajino, Toshitaka*; Koura, Hiroyuki; Chiba, Satoshi; Aritomo, Yoshihiro*
AIP Conference Proceedings 891, p.423 - 426, 2007/03
We investigate the fission-fragment mass distribution on about 2000 nuclides, which should have a critical impact on the r-process nucleosynthesis through fission (
). The mass distribution of fission fragment is thought to be one of the most important elements on some astrophysical conditions for the theoretical estimation of the r-process abundance pattern. We calculated the potential energy surface (PES) by means of the liquid-drop model with the shell energy correction by the Two-Center shell model in 3-dimensional parameter space. We derive fission-fragment mass distribution by considering the location and the depth of the valley of PES near the saddle point and the scission point of nuclei with the use of the Langevin calculation. We determine the fission asymmetry by examining the valley depth and its location in the deformation parameter space. The consistency of our mass asymmetry with available experimental data is discussed.
