Role of wriggling vibrations of fissile nuclei in the formation of angular and spin distributions of neutrons and gamma-quanta emitted by fission fragments

Abstract

Possible orientations of the compound fissile nuclei associated with the polarization and alignment of these nuclei for the spontaneous and low-energy induced binary and ternary fission of nuclei by cold neutrons and their effect on the emergence of anisotropies and different kinds of asymmetry in the angular distributions of fission fragments and light prescission and evaporated third particles are considered. On the basis of quantum fission theory, the determining role of wriggling vibrations of the compound fissile nucleus in the vicinity of the point of its scission into fission fragments in the formation of the angular and spin distributions of evaporated neutrons and gamma quanta emitted by these fission fragments is demonstrated. It is shown that the wriggling vibrations resulting in high values of fission fragments spins are responsible for the retention in the spin tensors of these fragments of only the even-order orientations determining the alignment of these fragments and lead to anisotropy in the angular distributions of evaporated neutrons and gamma quanta. It is demonstrated that even with appreciable polarization of a compound nucleus having the low spin values associated with the presence of odd values of orientation orders, allowing for wriggling vibrations leads only to low polarization values of fission fragments and thus to low values of the polarization of evaporated neutrons and the circular polarization of evaporated gamma-quanta.