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

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.

Electric dipole polarizability of low-lying excited states in atomic nuclei

“…In this work, we further explore how the E1 polarizability evolves from the ground state to the first excitation of selected p-and sd-shell nuclides. Where possible, we perform 1ÿω SM calculations, compare with available data and explore deviations from the hydrodynamic model [59,60,[63][64][65]. Similar SM calculations of the E1 polarizability for ground states have already been published in [52].…”