Combinatorial level densities for practical applications

S Hilaire,S Goriely,R Capote,M Girod,M Sin,A.J Koning

doi:10.1051/epjconf/20100204005

Abstract

We review our calculated energy-, spin- and parity-dependent nuclear level densities based on the microscopic combinatorial model described in ref. [1]. We show that this model predicts the experimental sand p-wave neutron resonance spacings with a degree of accuracy comparable to that of the best global models available and also provides reasonable description of low energies cumulative number of levels as well as of the experimental data obtained by the Oslo group [2]. We also provide a renormalization recipe which enables to play with the tabulated results for practical applications. Finally, we study the impact of temperature dependent calculation on s-wave neutron resonance spacings.

Highlights

The knowledge of nuclear level densities (NLDs) has been a matter of interest and study for years going back at least to 1936 with Bethe’s pioneering work [3]
Level densities are required when modeling nuclear reactions as soon as the number of levels to which decay occurs is too large to allow for an individual description
The new NLD are compared with experimental data

Summary

Introduction

The knowledge of nuclear level densities (NLDs) has been a matter of interest and study for years going back at least to 1936 with Bethe’s pioneering work [3]. Cross section predictions have relied on more or less phenomenological approaches, depending on parameters adjusted to scarce experimental data or deduced from systematical relations While such predictions are expected to remain reliable for nuclei not too far from experimentally accessible regions, the predictive power of analytical models in general, and of analytical level densities expressions in particular, is more and more questionable when dealing with more and more exotic nuclei. To face such difficulties, it is preferable to rely on approaches as fundamental as possible. Such microscopic description by a physically sound model based on first principles ensures a reliable extrapolation away from experimentally known region

The combinatorial method

Results

Temperature effect on combinatorial level densities

Conclusion