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In-beam $$gamma$$-ray study of the neutron-rich nuclei of $$^{240}$$U, $$^{246}$$Pu, and $$^{250}$$Cm produced by the ($$^{18}$$O, $$^{16}$$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 $$gamma$$ rays in the neutron-rich nuclei of $$^{240}$$U, $$^{246}$$Pu and $$^{250}$$Cm. These nuclei were produced by the ($$^{18}$$O, $$^{16}$$O) two-neutron transfer reactions with a 200, 162 and 162 MeV $$^{18}$$O beams and a $$^{238}$$U, $$^{244}$$Pu and $$^{248}$$Cm targets, respectively, using the tandem accelerator at Tokai, Japan. The $$gamma$$ rays in residual nuclei were measured by taking coincidence with scattering particles using Si $$Delta E$$-$$E$$ detectors. We have identified $$gamma$$ rays in $$^{240}$$U, $$^{246}$$Pu and $$^{250}$$Cm by selecting the kinetic energies of $$^{16}$$O particles which correspond to the excitation energies in these nuclei below their neutron separation energies. The ground-state bands of $$^{240}$$U, $$^{246}$$Pu and $$^{250}$$Cm were established up to 12$$^{+}$$ states and the $$K^{pi}=0^{-}$$ octupole band of $$^{240}$$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 $$^{248}$$Cm$$_{152}$$ is considerably larger than that of $$^{250}$$Cm$$_{154}$$. This fact supports the existence of the deformed subshell closure at $$N=152$$ in Cm isotopes. On the other hand, the moment of inertia of $$^{246}$$Pu$$_{152}$$ was found to be smaller than that of $$^{244}$$Pu$$_{150}$$, which suggests that the deformed subshell closure at $$N=152$$ weakens or disappears in Pu isotopes. These results are consistent with the prediction by a cranking model calculation.

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