Onset of collectivity in96,98Sr studied via Coulomb excitation

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

doi:10.1051/epjconf/20146602021

Abstract

A rapid onset of quadrupole deformation is known to occur around the neu- tron 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 stud- ies 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

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 f m4 and extracted for the first time a
Does the 2+ energy in 96Kr reflect a large mixing of the different configurations as established in the light isotopes close to the N=Z line [9] or the gain in binding energy due to the deformation and/or correlation is not strong enough only 2 proton away from the Sr isotopes ? Does any shape isomer exist in this isotope ? Extending the level scheme in 96Kr is the purpose of experiment being part of the EXOGAM campaign at ILL (EXILL)
We have investigated the collectivity and the deformation in 96,98Sr at N=60 using the Coulomb excitation technique at REX-ISOLDE

Summary

Introduction

The strong dependence of related spectroscopic properties on the number of protons and/or neutrons makes of these nuclei a very challenging case for various theoretical models In this framework, we have investigated the shape transition in the Sr isotopic chain using Coulomb excitation reaction. A standard χ2 function is constructed from the measured γ-ray yields of both the projectile and the target, and those calculated from a complete set of electromagnetic matrix elements, both transitional and diagonal, between all known states involved in the excitation process. One can notice the similarity in terms of B(E2) and Qs between the 2+1 →0+1 and 2+2 →0+2 in 96Sr and 98Sr, respectively, 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