Core excitations across the neutron shell gap in 207Tl

E Wilson,M Bowry,B Szpak,B Fornal,Zs Podolyák,R.S Kempley,H Grawe,G Lotay,T Lauritsen,M Bunce,N Cieplicka-Oryńczak,C Rodríguez Triguero,S Zhu,D Seweryniak,F G Kondev ,M W Reed ,R V F Janssens ,P H Regan ,George Dracoulis ,C Shand ,A Y Deo ,C J Chiara ,M P Carpenter ,C R Hoffman ,G J Lane ,B A Brown ,P M Walker

doi:10.1016/j.physletb.2015.04.055

Abstract

The single closed-neutron-shell, one proton–hole nucleus 207Tl was populated in deep-inelastic collisions of a 208Pb beam with a 208Pb target. The yrast and near-yrast level scheme has been established up to high excitation energy, comprising an octupole phonon state and a large number of core excited states. Based on shell-model calculations, all observed single core excitations were established to arise from the breaking of the N=126 neutron core. While the shell-model calculations correctly predict the ordering of these states, their energies are compressed at high spins. It is concluded that this compression is an intrinsic feature of shell-model calculations using two-body matrix elements developed for the description of two-body states, and that multiple core excitations need to be considered in order to accurately calculate the energy spacings of the predominantly three-quasiparticle states.

Highlights

The single closed-neutron-shell, one proton–hole nucleus 207Tl was populated in deep-inelastic collisions of a 208Pb beam with a 208Pb target
Based on shell-model calculations, all observed single core excitations were established to arise from the breaking of the N = 126 neutron core
It is concluded that this compression is an intrinsic feature of shell-model calculations using two-body matrix elements developed for the description of two-body states, and that multiple core excitations need to be considered in order to accurately calculate the energy spacings of the predominantly three-quasiparticle states

Summary

Introduction

The single closed-neutron-shell, one proton–hole nucleus 207Tl was populated in deep-inelastic collisions of a 208Pb beam with a 208Pb target. Based on shell-model calculations, all observed single core excitations were established to arise from the breaking of the N = 126 neutron core. While the shell-model calculations correctly predict the ordering of these states, their energies are compressed at high spins.

Results

Conclusion