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Es targetAsai, Masato; Tsukada, Kazuaki; Hirose, Kentaro; Toyoshima, Atsushi; Tomitsuka, Tomohiro; Chiera, N. M.; Ito, Yuta; Makii, Hiroyuki; Nagame, Yuichiro; Nishio, Katsuhisa; et al.
no journal, ,
Spontaneous fissions of neutron-rich heavy actinide isotopes 
Fm, 
Fm, and 
Lr have been measured at the JAEA Tandem accelerator facility. Fm and Fm were produced in a multinucleon transfer reaction with an 
O beam and an extremely rare Es target with a half-life of 276 days. Reaction products were mass-separated with an on-line isotope separator (ISOL). A transition between the typical asymmetric mass distribution and a very sharp symmetric one was clearly observed between Fm and Fm, while the spontaneous fission of Lr was found to exhibit mixture of three different fission modes.
Asai, Masato
no journal, ,
New experimental results on the symmetric fission in neutron-rich transfermium nuclei are reported. Those nuclei were produced in the multi-nucleon transfer reactions with an Es target, and reaction products were mass-separated by a gas-jet coupled on-line isotope separator at the JAEA tandem accelerator facility. Spontaneous-fission fragments of those nuclei were measured with Si detectors, and fission-fragment mass and total-kinetic-energy distributions were deduced precisely. Details of the symmetric fission in neutron-rich transfermium nuclei were discussed based on the present experimental results.
Asai, Masato; Tsukada, Kazuaki; Hirose, Kentaro; Toyoshima, Atsushi*; Tomitsuka, Tomohiro*; Chiera, N. M.*; Ito, Yuta; Makii, Hiroyuki; Nagame, Yuichiro*; Nishio, Katsuhisa; et al.
no journal, ,
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.
Asai, Masato
no journal, ,
Fission-fragment mass distributions and total kinetic energy (TKE) distributions for the spontaneous fission of Fm, Fm, Md, and Lr have been measured precisely. These nuclei were produced in the multinucleon transfer reactions with the O beam and the Es target, and in the fusion-evaporation reaction of Cm(N,4n)Lr at the JAEA tandem accelerator facility. The reaction products were mass-separated with the on-line isotope separator (ISOL), and the kinetic energies of spontaneous-fission fragments were measured with 4 pairs of Si semiconductor detectors. The results revealed that the three types of fission, the high-TKE and low-TKE symmetric fissions and asymmetric fission, compete or coexist in this neutron-rich Fm region.
Asai, Masato
no journal, ,
Fission-fragment mass and total kinetic energy (TKE) distributions for the spontaneous fission (SF) of neutron-rich Fm and transfermium nuclei have been measured precisely. The deduced mass-TKE distributions for the SF of Fm, Md, and Lr revealed that the SF of these nuclei show mixture of three types of fission with different mechanisms: the high-TKE symmetric fission, low-TKE symmetric fission, and asymmetric fission.
MdAsai, Masato; Ishibashi, Yuichi*; Tsukada, Kazuaki; Sato, Tetsuya; Aoki, Ryota*; Ito, Yuta; Uchibaba, Yuta*; Orlandi, R.; Gong, G.-M.*; Suzaki, Fumi; et al.
no journal, ,
Measurement of mass and total kinetic energy (TKE) distribution for the spontaneous fission (SF) of Md has been performed to clarify the fission mechanism in the neutron-rich fermium region. Md nuclei were produced with the Es target and O beam, and mass-separated with an on-line isotope separator (ISOL). We discuss the mechanism of fission observed in the SF of Md on the basis of the observed mass-TKE distribution.
Asai, Masato
no journal, ,
Symmetric fission properties of neutron-rich transfermium nuclei have been studied through the measurements of spontaneous fission fragments of Fm, Md, and Lr. These nuclei were produced in the multinucleon transfer reactions with the O beam and the Es target, and in the fusion-evaporation reaction of Cm(N,4n)Lr at the JAEA tandem accelerator facility. The reaction products were mass-separated with the on-line isotope separator (ISOL), and the kinetic energies of spontaneous-fission fragments were measured with 4 pairs of Si semiconductor detectors. The deduced fission-fragment mass distributions and total kinetic energy distributions have revealed the detailed properties of symmetric fissions in this neutron-rich Fm and transfermium nuclei.