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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

($$^{18}$$O, $$^{16}$$O)反応を利用したインビーム$$gamma$$線分光による中性子過剰核$$^{240}$$U, $$^{246}$$Pu, $$^{250}$$Cmの研究

石井 哲朗; 重松 宗一郎*; 牧井 宏之; 浅井 雅人; 塚田 和明; 豊嶋 厚史; 松田 誠; 牧嶋 章泰*; 静間 俊行; 金子 順一*; Hossain, I.*; 當銘 勇人; 小原 雅子*; 市川 進一; 河野 俊之*; 小川 雅生*

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*

中性子過剰核$$^{240}$$U, $$^{246}$$Pu, $$^{250}$$Cmの励起準位構造をインビーム$$gamma$$線分光法により研究した。これらの原子核は、原子力機構・東海タンデム加速器施設において、$$^{238}$$U, $$^{244}$$Pu, $$^{248}$$Cm($$^{18}$$O, $$^{16}$$O) 2中性子移行反応により生成した。Si $$Delta E$$-$$E$$検出器を用いて散乱粒子$$^{16}$$Oを識別し、さらに$$^{16}$$Oの運動エネルギーを選択することにより、残留核$$^{240}$$U, $$^{246}$$Pu, $$^{250}$$Cmの脱励起$$gamma$$線を同定した。$$gamma$$線測定の結果より、これらの原子核の基底回転バンドを12$$^{+}$$ 状態まで確立した。回転バンドの慣性能率より、中性子数152の変形閉殻が陽子数96のCmまでは存在し、陽子数94のPuでは消失することを明らかにした。

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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パーセンタイル:40.66

分野:Physics, Nuclear

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