Spontaneous fission studies for neutron-rich Fm and Lr isotopes

Asai, Masato  ; Tsukada, Kazuaki  ; Hirose, Kentaro  ; Toyoshima, Atsushi*; Tomitsuka, Tomohiro*; Chiera, N. M.*; Ito, Yuta   ; Makii, Hiroyuki   ; Nagame, Yuichiro* ; Nishio, Katsuhisa   ; Orlandi, R.  ; Ratha, K. K.*; Sato, Tetsuya   ; Suzuki, Hayato*; Tokoi, Katsuyuki*; Vermeulen, M.*; Yanagihara, Rikuto*; Nishinaka, Ichiro*; Kamada, Hiroki*; Shibata, Michihiro*; Goto, Shinichi*; Hirose, Hikaru*; Hayashi, Hiroaki*; Sakama, Minoru*; Andreyev, A. N.

We have studied spontaneous fission of neutron-rich Fm and Lr isotopes. The neutron-rich Fm isotopes were produced with the Es target and the O beam delivered by the JAEA tandem accelerator. The neutron-rich Lr isotope were produced with the Cm target and the N beam. Reaction products were mass-separated with an on-line isotope separator (ISOL), which enabled us to obtain non-contaminated samples and to measure fission fragments precisely. From the deduced fission-fragment mass and total kinetic energy distributions, we have obtained a new insight into the competition between the symmetric and asymmetric fission which is characteristic in this neutron-rich region.