Nuclear level densities: from empirical models to microscopic methods

TL;DR

This paper reviews empirical and microscopic models of nuclear level densities, highlighting recent advances in microscopic approaches like AFMC and their importance for nuclear reaction theories.

Contribution

It provides a comprehensive overview of both empirical and microscopic methods for calculating nuclear level densities, emphasizing recent developments beyond mean-field approximations.

Findings

Microscopic approaches like AFMC include correlations beyond mean-field.

Empirical models are summarized alongside experimental methods.

Recent methods improve accuracy of nuclear level density calculations.

Abstract

The level density is among the most important statistical nuclear properties. It appears in Fermi's golden rule for transition rates and is an important input to the Hauser-Feshbach theory of compound nucleus reactions. We discuss empirical models of level densities and summarize the main experimental methods used to determine them. The microscopic calculation of level densities in the presence of correlations is a challenging many-body problem. We review recent microscopic approaches to calculate level densities. Mean-field and combinatorial methods have been applied across the nuclear chart, but often need to be augmented with empirical collective enhancement factors. The moment method and the auxiliary-field quantum Monte Carlo (AFMC) method are formulated in the context of the configuration-interaction shell model approach, and include correlations beyond the mean-field approximation.