Unified description of fission in fusion and spallation reactions

TLDR

The study introduces a statistical‑model description of fission within compound‑nucleus decay that simultaneously reproduces data from heavy‑ion fusion and 1 GeV proton‑induced spallation reactions. The model uses the Liège intranuclear cascade to generate the initial compound‑nucleus population, incorporates fission transients by adjusting the saddle‑to‑ground level‑density ratio, and compensates finite‑range barrier changes by scaling the Bohr‑Wheeler decay width per Kramers. The model reproduces experimental fission probabilities and fragment mass distributions for both reaction types with a single parameter set, though no unique set was found for fission probability alone, and it predicts fission probabilities accurately up to 300 MeV excitation energy and spin 60 ħ.

Abstract

We present a statistical-model description of fission, in the framework of compound-nucleus decay, which is found to simultaneously reproduce data from both heavy-ion-induced fusion reactions and proton-induced spallation reactions at around $1$ GeV. For the spallation reactions, the initial compound-nucleus population is predicted by the Li\`ege intranuclear cascade model. We are able to reproduce experimental fission probabilities and fission-fragment mass distributions in both reactions types with the same parameter sets. However, no unique parameter set was obtained for the fission probability. The introduction of fission transients can be offset by an increase of the ratio of level-density parameters for the saddle-point and ground-state configurations. Changes to the finite-range fission barriers could be offset by a scaling of the Bohr-Wheeler decay width as predicted by Kramers. The parameter sets presented allow accurate prediction of fission probabilities for excitation energies up to $300$ MeV and spins up to $60$ $\ensuremath{\hbar}$.