Systematic study of anomalous fragment anisotropies in subbarrier complete fusion-fission reactions

Zhang Huan-Qiao，

Liu Zu-Hua，

Xu Jin-Cheng，

Qian Xing，

Qiao Yu，

Lin Cheng-Jian

Nuclear Science and Techniques

Vol.8, No.1

pp.1-5

Published in print 01 Feb 1997

37200

The complete fusion-fission is separated from the transfer-induced-fission with the fragment folding angle technique. The cross sections and fragment angular distributions for the complete fusion-fission reactions of ¹¹B+²³⁸U(²³⁷Np), ¹²C + ²³⁷Np, ¹⁶O + ²³²Th(²³⁸U) and ¹⁹F+ ²³²Th at near- and sub-barrier energies have been measured. The present fusion and fission standard models can reproduce both the excitation functions and the fragment anisotropies for the systems of ¹¹B+²³⁸U(²³⁷Np) and ¹²C+²³⁷Np; but fail to explain both the experimental data for the other 3 systems simultaneously. The evidence of the entrance-channel dependence of fission-fragment anisotropies is revealed by comparison of the ¹¹B+²³⁷Np and ¹⁶O+²³²Th data. Based on the observations, a new version model of preequilibrium fission is put forward to explain the anomaly.

Complete fusion-fission reactionsFragment anisotropiesEntrance-channel dependenceTransfer-induced fissionPreequilibrium fission

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