Nuclear-charge polarization at scission in proton-induced fission of light actinides

軽アクチノイド陽子誘起核分裂における切断点での核電荷分極

西中 一朗; 谷川 勝至*; 永目 諭一郎 ; 中原 弘道*

Nishinaka, Ichiro; Tanikawa, Masashi*; Nagame, Yuichiro; Nakahara, Hiromichi*

ThとUの12MeV陽子誘起核分裂における核分裂片の質量分布と即発中性子数を飛行時間測定法によって精度よく求めた。さらに、これらの実験値と文献にある核分裂生成物の収率から、切断した直後の分裂片の核電荷分極を導き出した。核電荷分極は原子核の液滴的性質と陽子数50の核構造に特徴付けられ、ウランの熱中性子核分裂とよく類似していることを見いだした。このことから、軽アクチノイドの非対称に質量分割する核分裂において、分裂片の核電荷分極は、分裂核の質量数と励起エネルギーに依存しないことを明らかにした。

In the 12 MeV proton-induced fission of Th and U, primary and secondary fragment mass yields as well as the average neutron multiplicity have been studied with a double time-of-flight technique. From these experimental data of fission fragments and the literature data of fission products, the nuclear-charge polarization at scission was derived. It was found that the nuclear charge polarization is characterized by the liquid-drop properties of nuclei and the proton shell effects = 50 of heavy fragments. The fragment mass dependence of the nuclear-charge polarization in the present systems agrees with that in the thermal-neutron-induced fission of U, indicating that the nuclear-charge polarization is practically insensitive to mass and excitation energy of the fissioning nucleus for the asymmetric fission in the region of light actinides.