A non-equilibrium microscopic description of spallation

TL;DR

This paper presents a microscopic, non-equilibrium model for spallation reactions, highlighting a frustrated fragmentation process that produces intermediate-mass fragments, differing from traditional statistical decay mechanisms.

Contribution

It introduces a novel non-equilibrium microscopic description using the Boltzmann-Langevin equation to explain IMF production in spallation reactions.

Findings

Identification of frustrated fragmentation as a key IMF production mechanism

IMF production can mimic asymmetric fission with few fragments

The process is relevant for heavy-ion collisions near fragmentation threshold

Abstract

We investigate the prompt emission of few intermediate-mass fragments in spallation reactions induced by protons and deuterons in the 1 GeV range. Such emission has a minor contribution to the total reaction cross section, but it may overcome evaporation and fission channels in the formation of light nuclides. The role of mean-field dynamics and phase-space fluctuations in these reactions is investigated through the Boltzmann-Langevin transport equation. We found that a process of frustrated fragmentation and re-aggregation is a prominent mechanism of production of IMFs which can not be assimilated to the statistical decay of a compound nucleus. Very interestingly, this process may yield a small number of IMF in the exit channel, which may even reduce to two, and be wrongly confused with ordinary asymmetric fission. This interpretation, inspired by nuclear-spallation experiments, can be generalised to heavy-ion collisions approaching the fragmentation threshold.