Quadrupole and monopole transition properties of $0^+_2$ in Gd isotopes

TL;DR

This paper investigates the properties of the second 0+ states in Gd isotopes using a mean-field and RPA approach, successfully reproducing transition strengths and suggesting a vibrational nature rather than shape coexistence.

Contribution

It provides a detailed theoretical analysis of 0+2 states in Gd isotopes, challenging the shape-coexistence interpretation and emphasizing a vibrational excitation model.

Findings

Transition strengths vary by nearly two orders of magnitude and are well reproduced.

0+2 states are described as β vibrations on deformed ground states.

The model accurately reproduces multiple observables for Gd isotopes.

Abstract

The longstanding problem of characterization of the $0^+_2$ states in Gd isotopes is revisited by adopting the Nilsson$+$BCS mean field and the random-phase approximation. The interband electric quadrupole transition strengths varying almost two orders of magnitude are nicely reproduced at the same time as other observables. These results indicate that the $0^+_2$ states, in particular, those in lighter isotopes are well described as $\beta$ vibrations excited on top of deformed ground states without recourse to the shape-coexistence picture.