Effect of compound nucleus spin correlations on fission fragment angular distribution

TL;DR

This paper introduces a new model incorporating spin correlations in compound nuclei, explaining anisotropic fission fragment distributions and mass-angle correlations observed in sub-barrier nuclear collisions.

Contribution

It extends conventional fusion-fission models by including spin state correlations, revealing their significant impact on angular distributions and anisotropy in nuclear fission.

Findings

Spin off-diagonal phase relaxation timescale is about 10^{-19} sec.

Correlations cause strong anisotropy and mass-angle correlation in fission fragments.

The model explains anomalous angular distributions in specific nuclear collisions.

Abstract

We extend a conventional description of the fusion-fission fragment angular distributions by introducing the correlation between compound nucleus states carrying different total angular momenta. This correlation results in the strong anisotropy and mass-angle correlation of fission fragments for compact saddle-point nuclear shapes for which the conventional description predicts almost isotropic angular distributions. The spin off-diagonal phase relaxation timescale, $\simeq 10^{-19}$ sec, obtained from analysis of anomalous fission fragment angular distributions in $^{12}$C+$^{236}$U, $^{16}$O+$^{232}$Th and $^{16}$O+$^{238}$U collisions at the sub-barrier energies is three orders of magnitude longer than the timescale of the compound nucleus thermalization. Expression for the angle-dependent time power spectrum for quasifission is also presented.