Why is Tin so soft?

TL;DR

This paper investigates why tin isotopes exhibit unexpectedly low giant monopole resonance energies, highlighting a challenge for nuclear models to accurately describe nuclear softness without losing predictive success.

Contribution

It applies a relativistic random-phase-approximation model to analyze monopole strength in Sn isotopes and discusses the discrepancy in GMR energies, posing a key challenge for nuclear theory.

Findings

The model successfully reproduces ground-state and collective excitations in several nuclei.

It overestimates GMR energies in Sn isotopes.

The softness of tin isotopes remains an unresolved challenge for nuclear models.

Abstract

The distribution of isoscalar monopole strength in the neutron-even 112-124Sn-isotopes has been computed using a relativistic random-phase-approximation approach. The accurately-calibrated model used here (``FSUGold'') has been successful in reproducing both ground-state observables as well as collective excitations - including the giant monopole resonance (GMR) in 90Zr, 144Sm, and 208Pb. Yet this same model significantly overestimates the GMR energies in the Sn isotopes. It is argued that the question of ``Why is Tin so soft?'' becomes an important challenge to the field and one that should be answered without sacrificing the success already achieved by several theoretical models.