Giant Monopole Resonance in even-A Cd isotopes, the asymmetry term in nuclear incompressibility, and the "softness" of Sn and Cd nuclei

TL;DR

This study investigates the giant monopole resonance in Cd isotopes to understand nuclear incompressibility and the persistent 'softness' issue in open-shell nuclei like Sn and Cd, combining experimental and theoretical approaches.

Contribution

It provides new experimental data on Cd isotopes' ISGMR and evaluates theoretical models, highlighting discrepancies and the ongoing 'softness' debate in nuclear physics.

Findings

The asymmetry term in nuclear incompressibility is confirmed as approximately -555 MeV.

Relativistic RPA models overestimate ISGMR centroid energies in Cd isotopes.

The 'softness' of open-shell nuclei like Sn and Cd remains an unresolved issue.

Abstract

The isoscalar giant monopole resonance (ISGMR) in even-A Cd isotopes has been studied by inelastic ${\alpha}$-scattering at 100 MeV/u and at extremely forward angles, including 0deg. The asymmetry term in the nuclear incompressibility extracted from the ISGMR in Cd isotopes is found to be $K_{\tau} = -555 \pm 75$ MeV, confirming the value previously obtained from the Sn isotopes. ISGMR strength has been computed in relativistic RPA using NL3 and FSUGold effective interactions. Both models significantly overestimate the centroids of the ISGMR strength in the Cd isotopes. Combined with other recent theoretical effort, the question of the "softness" of the open-shell nuclei in the tin region remains open still.