Onset of collectivity in neutron-rich Sr and Kr isotopes: Prompt spectroscopy after Coulomb excitation at REX-ISOLDE, CERN

E Clément ,C Fransen,A Dijon,J Iwanicki,B Bastin,M Seidlitz,A Petts,P Reiter,C Bauer,P Delahaye,I Stefanescu,R Lutter,J Srebrny,C Sotty,A Blazhev,K Moschner,C Fitzpatrick,P Marley,B Siebeck,B Bruyneel,J Van De Walle,H De Witte,K Wrzosek-Lipska,N Warr,N Bree,J Ljungvall,P A Butler ,Nusair Hasan ,A C Larsen ,A Wiens ,R Gernhäuser ,P Napiórkowski ,S Siem ,G M Tveten ,J.m Butterworth ,A Görgen ,H Hess ,M Zielińska ,M J Vermeulen ,Andreas Ekström ,T Renstrøm ,J Pakarinen ,W Körten ,Г Георгиев ,D G Jenkins

doi:10.1051/epjconf/20136201003

Abstract

A rapid onset of quadrupole deformation is known to occur around the neutron number 60 in the neutron-rich Zr and Sr isotopes. This shape change has made the neutron-rich A = 100 region an active area of experimental and theoretical studies for many decades now. We report in this contribution new experimental results in the neutron rich 96,98 Sr investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross section supporting the scenario of shape coexistence/change at N = 60. Future perspectives are presented including the recent experimental campaign performed at ILL-Grenoble.

Highlights

Fission fragment spectroscopy has been used for decades to probe shells and shape evolution far from stability
A rapid onset of quadrupole deformation is known to occur around the neutron number 60 in the neutron-rich Zr and Sr isotopes. This shape change has made the neutronrich A = 100 region an active area of experimental and theoretical studies for many decades. We report in this contribution new experimental results in the neutron rich 96,98Sr investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN
Combining the data set from both target and using the differential Coulomb excitation cross section, we have significantly improved the measurement of the B(E2,2+1 → 0+1 ) = 462(11) e2 value for the spectroscopic quadrupole moment of the fm4 first and extracted for 2+1 state equal to the Qs first time a preliminary = −6(9) efm2

Summary

Introduction

Fission fragment spectroscopy has been used for decades to probe shells and shape evolution far from stability. Beyond N = 60, the observed rotational ground-state band of 98Sr points to a large ground-state deformation and the 0+2 state at 215 keV, which decays to the ground state via an enhanced E0 transition of 2(E0) = 0.053 [18], supports the scenario of shape coexistence with a high mixing. Most calculations predict slightly oblate ground-state deformations for the lighter isotopes and strongly deformed prolate shapes for the heavier ones. The goal of the present experimental program is to measure spectroscopic quadrupole moments in both ground state and excited bands around N = 60. Taioqsnoinfumddati7dihclB0reaau0(triEpig(nt1ory2go8l,e2iu6an+2n)mldetae→ o2-rrsfmgmmteae2st4npe+1,otr)sofbv=lhaeBanart(yve7dEe5d2sh(bei)4amefav6oenie)rnldmaeber2Qaxeftmtetsiornoa4bn.cteehtTtaseewnthdadeebBfeolfB(niorEs(rhttE2hhet,2hee2d,e+1242w+2+1+12→+2i,t→ →6hs+10t0va,+10+2at8)+1el)+1ueiawenqsnstauda9seat62eqlaSs+2utlrosaw.o→l|iFQetthioxn0sta|a+2rBnla≤l(ciyaEnt,v4e29ed8p,6r2reSawe+2fgrlmiieta→ mh2nv.idaanO0lau9p+1n8reryS)eeorl=ci,fsmaprn3eeins7–cnpa(t1or6er5otyc)i0stcecivee2voaffelptmmluhiyece, supporting the shape coexistence scenario This complete set of electromagnetic matrix elements will be compared with advanced theoretical models and in particular with calculations beyond the mean-field which provide B(E2)’s and spectroscopic quadrupole moments for a large number of excited states

Spectroscopy at EXILL and perspective

Findings

Conclusion