Rotational Excitation with Neutron Inelastic Scattering

Abstract

The recent experiments have shown that the excitation function of the inelastic sc:;tttering of neutrons depends on the nature of . the excited states of the nucleus. For instance, as W eisskopf pointed out about the results of the experiments by KiehnGoodmann1> •2>, the nucleus which shows t4e Bohr-Mottelson spectrum would not have the excitation functi~n of ·¥£-type expected from the statistical theory of the nuclear reaction but the one which is like linear type (Lead, etc.). The nuclei having the excitation function of -Y'E-type (Iron, etc.) have been .analysed mostly by means of the statistical theory of the nuclear reaction. ~ecently S. Hayakawa-S. Y oshida3> and D. M. Brink4> dealt with this pro~;ess by taking into account the direct interaction, but they concluded that the main contribution comes from the reaction process through the compound nu~leus. On the other hand the collective model of the nucleus proposed by A. Bohr succeeded to describe well the properties of the low excited states in the heavy nucleus. And we think such low excited states play an important role in the inelastic scattering. Therefore we adopt, h~re, the collective model to describe the compound nucleus and the target nucleus, and calculate the excitation function according to the compound theory of TeichmannWigner. We are mainly interested in the rotational excitation of the strongly deformed nuclear surface, so w~ use the strong coupling approximation in this calculation. When an incident neutron with the spin u and the orbital angular momentum l collides with a target nucleus having , the spin I, forming the compound nucleus with the spin J and the other quantum number A, the reduced width r,.,1 for the channel s is given by5>