Measurement of evaporation residue cross-sections of the reaction Si + U at subbarrier energies

Nishio, Katsuhisa   ; Hofmann, S.*; Heberger, F. P.*; Ackermann, D.*; Antalic, S.*; Comas, V. F.*; Gan, Z.*; Heinz, S.*; Heredia, J. A.*; Ikezoe, Hiroshi; Khuyagbaatar, J.*; Kindler, B.*; Kojouharov, I.*; Kuusiniemi, P.*; Lommel, B.*; Mazzocco, M.*; Mitsuoka, Shinichi; Nagame, Yuichiro ; Otsuki, Tsutomu*; Popeko, A. G.*; Saro, S.*; Schtt, H. J.*; Sulignano, B.*; Svirikhin, A.*; Tsukada, Kazuaki  ; Tsuruta, Kaoru*; Yeremin, A.*

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.