Spin distribution of fission fragments involving bending and wriggling modes

TL;DR

This paper provides a theoretical model explaining the high spin distributions of fission fragments through bending and wriggling modes, validated by experimental data from thorium, uranium, and californium fission.

Contribution

It introduces an analytical description of spin distributions based on vibrational modes of pre-fragments, offering a new mechanism for high spin generation in nuclear fission.

Findings

Reasonable agreement with experimental spin distributions

The model reproduces the sawtooth pattern of spin with fragment mass

Comparison with other models highlights differences in spin predictions

Abstract

This paper presents a theoretical description of the spin distributions of fragments from low-energy induced and spontaneous nuclear fission, expressed in an analytical form. The mechanism of pumping high spin values for deformed fission fragments is explained. The idea is that the source of the generation of high relative orbital moments and spins of the fragments are the transverse wriggling and bending vibrations of the pre-fragments, while the nucleus remains "cold" until the moment of fission. To verify this hypothesis, experimental distributions for the induced fission of $\rm ^{232}Th$ and $\rm ^{238}U$ nuclei, as well as the spontaneous fission of $\rm ^{252}Cf$, were compared. The results show reasonable agreement both in the magnitude of the mean spin values and in the sawtooth shape of the sip distribution with respect to the fragment mass number. The results are also compared with other approaches to the description of these quantities, and possible reasons for their discrepancies are discussed.