Mirror energy differences above the 0f7/2 shell: First γ-ray spectroscopy of the Tz = −2 nucleus 56Zn

A Lvarez Fernández ,B Mauss,V Vaquero,T Koiwai,S Pigliapoco,F Recchia,R Taniuchi,A Poves,R Yajzey,B Longfellow,R Wadsworth,P Doornenbal,K Wimmer,P Ruotsalainen,N Imai,N Kitamura,F Browne,A Jungclaus,S Uthayakumaar,R Lozeva,Dirk Rudolph ,D R Napoli ,M A Bentley ,S M Lenzi ,M L Cortés ,T Arıcı ,M Nııkura ,X Pereira-López ,H Sakuraï

doi:10.1016/j.physletb.2021.136784

Abstract

Excited states in 56Zn were populated following one-neutron removal from a 57Zn beam impinging on a Be target at intermediate energies in an experiment conducted at the Radioactive Isotope Beam Factory at RIKEN. Three γ rays were observed and tentatively assigned to the 6+→4+→2+→0+ yrast sequence. This turns 56Zn into the heaviest Tz=−2 nucleus in which excited states are known. The excitation-energy differences between these levels and the isobaric analogue states in the Tz=+2 mirror partner, 56Fe, are compared with large-scale shell-model calculations considering the full pf valence space and various isospin-breaking contributions. This comparison, together with an analysis of the mirror energy differences in the A=58, Tz=±1 pair 58Zn and 58Ni, provides valuable information with respect to the size of the monopole radial and the isovector multipole isospin-breaking terms in the region above doubly-magic 56Ni.

Highlights

The exchange symmetry between protons and neutrons is one of the fundamental symmetries of modern physics and led to the concept of isospin in nuclear physics
To analyze the experimental findings, large-scale shell-model calculations were performed for the A = 56, T z = ±2 mirror pair and the T z = ±1 nuclei 58Zn and 58Ni
The calculations for the A = 57, 58 nuclei had to be constrained to t = 8 particle-hole excitations across the N = Z = 28 shell gaps

Summary

Introduction

The exchange symmetry between protons and neutrons is one of the fundamental symmetries of modern physics and led to the concept of isospin in nuclear physics. Systematic studies of pairs of mirror nuclei, i.e. nuclei with interchanged proton and neutron numbers, over the last two decades have revealed that additional isospin-breaking (ISB) multipole effects exist Isospin-symmetry studies of heavier systems often depend on ad hoc assumptions and clearly suffer from the lack of decisive data points [15,16,17,18,19]. To tackle this question, we present in this Letter the first γ -ray spectroscopy of 56Zn ( Z = 30, N = 26), which has an isospin projection of T z = −2.

Experiment and results

Discussion

Findings

Summary