Spin distribution of fission fragments involving bending and wriggling modes

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.