How do we infer shell effects at high-excitation energies? A new spectroscopic probe to search for magic numbers

Department of Physics & Astronomy, University of the Western Cape, P/B X17 Bellville ZA-7535, South Africa

^* e-mail: 3344489@myuwc.ac.za
^** e-mail: jnorce@uwc.ac.za

Published online: 4 December 2019

Abstract

The nuclear dipole polarizability is mainly governed by the dynamics of the giant dipole resonance and, assuming validity of the brink-Axel hypothesis, has been investigated along with the effects of the low-energy enhancement of the photon strength function for nuclides in medium- and heavy-mass nuclei. Cubic-polynomial fitsto both data sets extrapolated down to a gamma-ray energy of 0.1 MeV show a significantreduction of the nuclear dipole polarizability for semi-magic nuclei, with magic numbers N =28, 50 and 82, which supports shell effects at high-excitation energies in the the quasi-continuum region. This work assigns σ_-2 values as sensitive measures of long-range correlations of the nuclear force and provides a new spectroscopic probe to search for “old” and “new” magic numbers at high-excitation energies.