Mean-field instabilities and cluster formation in nuclear reactions

TL;DR

This paper reviews recent theoretical and experimental studies on cluster formation in nuclear reactions, emphasizing the role of mean-field instabilities and fluctuations in heavy ion collisions and spallation reactions.

Contribution

It compares modern transport models (SMF and BLOB) to analyze cluster production mechanisms and their relation to mean-field instabilities in nuclear reactions.

Findings

Cluster production linked to low-density mean-field instabilities.

Differences between one and two-body effects in models.

Thermal expansion can trigger instabilities in spallation reactions.

Abstract

We review recent results on intermediate mass cluster production in heavy ion collisions at Fermi energy and in spallation reactions. Our studies are based on modern transport theories, employing effective interactions for the nuclear mean-field and incorporating two-body correlations and fluctuations. Namely we will consider the Stochastic Mean Field (SMF) approach and the recently developed Boltzmann-Langevin One Body (BLOB) model. We focus on cluster production emerging from the possible occurrence of low-density mean-field instabilities in heavy ion reactions. Within such a framework, the respective role of one and two-body effects, in the two models considered, will be carefully analysed. We will discuss, in particular, fragment production in central and semi-peripheral heavy ion collisions, which is the object of many recent experimental investigations. Moreover, in the context of spallation reactions, we will show how thermal expansion may trigger the development of mean-field instabilities, leading to a cluster formation process which competes with important re-aggregation effects.