# A new spectroscopic probe to search for magic numbers at high-excitation energies

## TL;DR

This paper introduces a spectroscopic method to detect magic numbers at high excitation energies by analyzing nuclear polarizability drops, supporting shell-model calculations and challenging the universality of the Brink-Axel hypothesis.

## Contribution

It proposes a novel spectroscopic probe based on polarizability drops to identify shell effects at high energies, extending the understanding of magic numbers beyond ground states.

## Key findings

- Polarizability drops indicate shell effects at high excitation energies.
- Supports shell-model calculations in the quasi-continuum region.
- Challenges the universality of the Brink-Axel hypothesis.

## Abstract

Empirical drops in ground-state nuclear polarizabilities indicate deviations from the effect of giant dipole resonances and may reveal the presence of shell effects in semi-magic nuclei with neutron magic numbers $N=50$, 82 and 126. Similar drops of polarizability in the quasi-continuum of nuclei with, or close to, magic numbers $N=28$, 50 and 82, could reflect the continuing influence of shell closures up to the nucleon separation energy. These findings open a new avenue to investigating magic numbers at high-excitation energies and strongly support recent large-scale shell-model calculations in the quasi-continuum region, which describe the origin of the low-energy enhancement of the photon strength function as induced paramagnetism. The nuclear-structure dependence of the photon-strength function asserts the generalized Brink-Axel hypothesis as more universal than originally expected.