Abstract
The nature of the spin distribution (SD) of fragments oflow-energy induced and spontaneous double fission of nuclei isdescribed theoretically. For two deformed fission prefragments, amechanism for pumping large values of their relative orbitalmomenta \(L\) and spins \(J\) , due to the combined influence ofbending and wriggling vibrations, is established, and analyticalformulas for describing SP within the framework of such amechanism are obtained for the first time. It is emphasized thatfor this mechanism the nucleus remains ‘‘cold’’ in the fissionprocess, while in the statistical model it heats up totemperatures of \({\approx}1\) MeV. A comparison of the calculatedSDs for forced double fission of actinide nuclei \({}^{232}\text{Th}\left(n,f\right)\) and \({}^{238}\text{U}\left(n,f\right)\) with the available experimentaldata showed reasonable agreement both in terms of the magnitude ofthe average spin values and in the sawtooth shape of thedependence of SP on the atomic number of fragments, which confirmsthe reliability of the pumping mechanism of large spin values ofdeformed fission fragments. For spontaneous double fission of thenucleus \({}^{252}\text{Cf}\left(s,f\right)\) , possiblereasons for the discrepancy between the theoretical SD and theexperiment are indicated.
