In-beam -ray study of the neutron-rich nuclei of U, Pu, and Cm produced by the (O, O) reaction

Ishii, Tetsuro  ; Shigematsu, Soichiro*; Makii, Hiroyuki   ; Asai, Masato  ; Tsukada, Kazuaki  ; Toyoshima, Atsushi; Matsuda, Makoto  ; Makishima, Akiyasu*; Shizuma, Toshiyuki; Kaneko, Junichi*; Hossain, I.*; Tome, Hayato; Ohara, Masako*; Ichikawa, Shinichi; Kono, Toshiyuki*; Ogawa, Masao*

We have measured deexcitation rays in the neutron-rich nuclei of U, Pu and Cm. These nuclei were produced by the (O, O) two-neutron transfer reactions with a 200, 162 and 162 MeV O beams and a U, Pu and Cm targets, respectively, using the tandem accelerator at Tokai, Japan. The rays in residual nuclei were measured by taking coincidence with scattering particles using Si - detectors. We have identified rays in U, Pu and Cm by selecting the kinetic energies of O particles which correspond to the excitation energies in these nuclei below their neutron separation energies. The ground-state bands of U, Pu and Cm were established up to 12 states and the octupole band of U was established up to 9 state. Because the deformations of these nuclei are well developed, the moments of inertia reflect the pairing gap, which is expected to be smaller, resulting in a larger moment of inertia, at the deformed shell closure. We have found that the moment of inertia of the ground-state band of Cm is considerably larger than that of Cm. This fact supports the existence of the deformed subshell closure at in Cm isotopes. On the other hand, the moment of inertia of Pu was found to be smaller than that of Pu, which suggests that the deformed subshell closure at weakens or disappears in Pu isotopes. These results are consistent with the prediction by a cranking model calculation.