Role of multifragmentation in spallation reactions

TL;DR

This paper discusses the role of nuclear multifragmentation in high-energy spallation reactions, emphasizing its universality, connection to phase transitions, and the use of the Statistical Multifragmentation Model to describe these processes.

Contribution

It introduces the application of the Statistical Multifragmentation Model to spallation reactions, integrating low-energy compound processes with high-energy multifragmentation.

Findings

Multifragmentation occurs at excitation energies above 3 MeV per nucleon.

It dominates over traditional decay processes at high excitation energies.

The model links nuclear fragmentation to liquid-gas phase transition phenomena.

Abstract

In nuclear reactions induced by hadrons and ions of high energies, nuclei can disintegrate into many fragments during a short time (~100 fm/c). This phenomenon known as nuclear multifragmentation was under intensive investigation last 20 years. It was established that multifragmentation is an universal process taking place in all reactions when the excitation energy transferred to nuclei is high enough, more than 3 MeV per nucleon, independently on the initial dynamical stage of the reactions. Very known compound nucleus decay processes (sequential evaporation and fission), which are usual for low energies, disappear and multifragmentation dominates at high excitation energy. For this reason, calculation of multifragmentation must be carried on in all cases when production of highly excited nuclei is expected, including spallation reactions. From the other hand, one can consider multifragmentation as manifestation of the liquid-gas phase transition in finite nuclei. This gives way for studying nuclear matter at subnuclear densities and for applications of properties of nuclear matter extracted from multifragmentation reactions in astrophysics. In this contribution, the Statistical Multifragmentation Model (SMM), which combines the compound nucleus processes at low energies and multifragmentation at high energies, is described. The most important ingredients of the model are discussed.