Low-spin states in Ge80 populated in the β decay of the Ga80 3− isomer

S Sekal,G S Simpson,C Bernards,M J G Borge,T Sava,Z Dlouhý,P Hoff,C Benchouk,L M Fraile,B Olaizola,W Kurcewicz,J Jolie,V Paziy,M Rudigier,R Mărginean,L Stroe,W B Walters,C J Chiara,D Ghiţă ,H Mach ,U Köster ,A Aprahamian ,I Gheorghe ,J.-M Régis ,R Lică ,J A Briz ,Z Méliani ,N Mărginean ,M Stănoiu ,B Bucher

doi:10.1103/physrevc.104.024317

Abstract

The structure of Ge80 has been investigated at the ISOLDE facility at CERN. A previous study reported for the first time a low-lying 02+ intruder state at 639 keV, based on the coincidence with a previously unobserved 1764-keV γ ray, and suggested it as evidence for shape coexistence in Ge80. We used the β decay from the 3− 22.4-keV state in Ga80 to enhance the population of low-spin states in Ge80, including any excited 0+ level, and γγ coincidences to investigate it. We observed a 1764-keV γ ray in coincidence with strong transitions in Ge80, thus not feeding the proposed 639-keV 02+. No connecting transitions from previously known levels to the 639-keV and 2403-keV 23+ states could be established either. Shell-model calculations for Ge isotopes and N=48 isotones were performed. They succeed to explain most of the experimental levels, but fail to reproduce the presence of a 02+ state below ≈1200 keV in Ge80. Our experimental findings and shell-model calculations are difficult to reconcile with a very low-lying 02+ state in Ge80.1 MoreReceived 20 October 2020Revised 23 July 2021Accepted 27 July 2021DOI:https://doi.org/10.1103/PhysRevC.104.024317Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasIsomer decaysNuclear structure & decaysProperties59 ≤ A ≤ 89TechniquesRadiation detectorsRadioactive beamsSpectrometers & spectroscopic techniquesNuclear Physics

Highlights

The 80Zn 0+ ground state mostly decays to the 80Ga 3− isomer [10], which β decays to 80Ge
The data analyzed in this work were obtained in the IS441 experiment performed by the fast-timing collaboration at the ISOLDE facility at CERN, with the aim of investigating neutron-rich nuclei populated in the β decay of Zn isotopes
The strong 1773-keV peak in the spectrum corresponds to a transition in 80Ge already placed in the level scheme in previous studies [16], whereas the 1742-keV peak arises from the summing of the strongest 1083-keV and 659-keV γ rays in the high-purity germanium (HPGe) detectors

Summary

INTRODUCTION

The competition and coexistence at low energy of the configurations arising from the standard shell-model orbitals and those originating from excitations across shell gaps have been identified in several areas of the table of nuclei. The latter (intruder) configurations may exhibit different collective properties than the normal ones, which could be interpreted as a distinct intrinsic shape once an appropriate reference frame is defined.

PHYSICS CASE

EXPERIMENTAL DETAILS

RESULTS

LEVEL SYSTEMATICS

SHELL-MODEL CALCULATIONS

SUMMARY AND CONCLUSIONS