裂变碎块角分布与鞍点结构

从Jacob和Wick所推导的具有自旋粒子的散射矩阵元一般表示式出发,采用适当近似后,分析了中子引起Th²³⁰,Th²³²,U²³⁴,U²³⁶,U²³⁸裂变的阈能附近碎块角分布的实验数据。分析结果说明:1)阈能附近碎块角分布可以用裂变是通过鞍点上少数转动带(每一带具有确定的宇称)来解释;2)这些转动带与Nilsson的渐近能谱图所预言的基本上一致。同时利用对称裂变鞍点比非对称裂变鞍点高的观点,讨论了裂变碎块角分布各向异性与质量比之间的关系。

ANGULAR DISTRIBUTION OF THE FISSION FRAGMENTS AND THE STRUCTURE AT THE SADDLE POINT

On the basis of the general expression of the scattering matrix between two particles with spin, derived by Jocob and Wick, with certain approximations we have analysed the experimental data of the angular distribution of the fission fragments from Th²³⁰,Th²³²,U²³⁴,U²³⁶, and U²³⁸, bombarded by neutron whose energy is in the region near the fission threshold. The results of this analysis show: (1) The angular distribution of the fission fragments, in the region near the threshold, can be explained by a few rotational bands (every band has a definite parity) above the saddle point. (2) These rotational bands are consistent with the asymptotic energy levels of Nilsson.Furthermore, based on the idea that the barrier of the saddle point of the symmetric fission is higher than that of the asymmetric, we discussed the correlation between the anisotropy of the angular distribution of fission fragments and its mass ratio.