Spontaneous fission measurements for nuclei around neutron-rich Fm region produced by using an Es target

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. J.; Yanagihara, Rikuto; Nishinaka, Ichiro*; Kamada, Hiroki*; Shibata, Michihiro*; Goto, Shinichi*; Hirose, Hikaru*; Hayashi, Hiroaki*; Sakama, Minoru*

Spontaneous fissions of Fm, Fm, and Lr have been measured using an Es target at the JAEA Tandem Accelerator Facility. These three nuclei show different fission properties: the asymmetric fission, the high total-kinetic-energy (TKE) symmetric fission, and the low TKE symmetric fission, and the mechanisms of these three fissions should be very different. It is of great interest to elucidate how these differences occur. We have produced Fm in multinucleon-transfer reactions with a Es target and O projectiles, and produced Lr in the Cm(N,4n) fusion-evaporation reaction. The reaction products were mass-separated with a gas-jet-coupled on-line isotope separator, and were delivered into a rotating wheel alpha- and fission-fragment detection system. By comparing the mass and TKE distributions deduced from the present experimental data, we will discuss the differences in fission mechanism among Fm, Fm, and Lr.