Lifetime measurements of excited states in 169,171,173Os: Persistence of anomalous B(E2) ratios in transitional rare earth nuclei in the presence of a decoupled i13/2 valence neutron

W Zhang,T Grahn,C Scholey,P Rahkila,A Ertoprak,T Calverley,H Badran,R Julin,E Ideguchi,V Modamio,M J Taylor ,Y Fang ,J Partanen,C M Petrache ,Chong Qi ,S Matta,S Juutinen,J Uusitalo,M Sandzelius,B Cederwall,D M Cox ,M Giles,P Papadakis,J Sorri,J Pakarinen,S Stolze,H Li,P Ruotsalainen,P Subramaniam,P T Greenlees ,D M Cullen ,Ö Aktaş ,H Liu,R J Liotta ,M Doncel,J Hilton,M Kumar Raju,J Sarén,D Hodge,T Braunroth,B S Nara Singh ,J J Valiente-Dobón

doi:10.1016/j.physletb.2021.136527

Abstract

Lifetimes of low-lying excited states in the νi13/2+ bands of the neutron-deficient osmium isotopes 169,171,173Os have been measured for the first time using the recoil-distance Doppler shift and recoil-isomer tagging techniques. An unusually low value is observed for the ratio B(E2;21/2+→17/2+)/B(E2;17/2+→13/2+) in 169Os, similar to the “anomalously” low values of the ratio B(E2;41+→21+)/B(E2;21+→0gs+) previously observed in several transitional rare-earth nuclides with even numbers of neutrons and protons, including the neighbouring 168,170Os. Furthermore, the evolution of B(E2;21/2+→17/2+)/B(E2;17/2+→13/2+) with increasing neutron number in the odd-mass isotopic chain 169,171,173Os is observed to follow the same trend as observed previously in the even-even Os isotopes. These findings indicate that the possible quantum phase transition from a seniority conserving structure to a collective regime as a function of neutron number suggested for the even-even systems is maintained in these odd-mass osmium nuclei, with the odd valence neutron merely acting as a “spectator”. As for the even-even nuclei, the phenomenon is highly unexpected for nuclei that are not situated near closed shells.

Highlights

The emergence of collective behaviour and deformation in atomic nuclei due to the residual interactions between valence particles outside closed-shell configurations represents one of the most important challenges for the description of finite many-body quantum systems [1,2]
The evolution of B(E2; 21/2+ → 17/2+)/B(E2; 17/2+ → 13/2+) with increasing neutron number in the odd-mass isotopic chain 169,171,173Os is observed to follow the same trend as observed previously in the eveneven Os isotopes. These findings indicate that the possible quantum phase transition from a seniority conserving structure to a collective regime as a function of neutron number suggested for the even-even systems is maintained in these odd-mass osmium nuclei, with the odd valence neutron merely acting as a “spectator”
Such effects imply that the wave function has spread out over multiple, coherent particle-hole components and are commonly associated with experimental observables such as a lowering of the first excited 2+1 state energy accompanied by an increase in the 2+1 → 0+gs reduced electric quadrupole transition probability, B(E2), in atomic nuclei with even numbers of neutrons and protons

Summary

Introduction

The emergence of collective behaviour and deformation in atomic nuclei due to the residual interactions between valence particles outside closed-shell configurations represents one of the most important challenges for the description of finite many-body quantum systems [1,2]. Such effects imply that the wave function has spread out over multiple, coherent particle-hole components and are commonly associated with experimental observables such as a lowering of the first excited 2+1 state energy accompanied by an increase in the 2+1 → 0+gs reduced electric quadrupole transition probability, B(E2), in atomic nuclei with even numbers of neutrons and protons. These are generally followed by the gradual evolution of increasingly deformed shapes towards the well-developed axiallysymmetric shapes and their associated rotational excitations and maximal B(E2) values when the Fermi level is situated at midshell

Results

Discussion

Conclusion