Long-standing problem: The nuclear level density angular-momentum dependence and isomeric data assessment

TL;DR

This paper discusses the challenges in modeling nuclear level density dependence on angular momentum, highlighting the importance of the moment of inertia and the need for further experimental data.

Contribution

It analyzes the impact of different moment of inertia assumptions on nuclear level density models and emphasizes the need for direct measurements to improve accuracy.

Findings

Using half of the rigid-body moment of inertia improves isomeric cross section predictions.

Current models struggle to accurately describe NLDs with fixed moment of inertia assumptions.

Further measurements of resonance spacings are crucial for model validation.

Abstract

Recent 91,92,93Tc activation for deuterons incident on natMo has become a challenge for the nuclear level density (NLD) angular-momentum dependence. Actually, replacement of the moment of inertia rigid-body value Ir by half of it, within a given NLD parameter set, demands a change of the rest of NLD parameters significantly beyond their fitted limits. The corresponding uncertainty of calculated cross sections versus the NLD parameter accuracy is also higher, while use of either the same or distinct compound-nucleus and preequilibrium emission spin distributions becomes significant at higher incident energies. Nevertheless, the current way to describe experimental isomeric cross sections by using at most half of Ir values provides agreement of the measured and calculated data at the price of less and less correct NLDs. The moment of inertia relevance for the NLD correctness also emphasizes the value of a direct method to endorse it. Further measurements of average resonance spacings of s-wave neutrons and protons, corresponding to different spins of the same nucleus, are therefore highly demanded.