Isospin dependence of electromagnetic transition strengths among an isobaric triplet

Abstract

Electric quadrupole matrix elements, Mp, for the Jπ=2+→0+, T=0, T=1transitions across the A =46isobaric multiplet 46Cr-46V-46Ti have been measured at GSI with the FRS-LYCCA-AGATA setup. This allows direct insight into the isospin purity of the states of interest by testing the linearity of Mpwith respect to Tz. Pairs of nuclei in the T=1triplet were studied using identical reaction mechanisms in order to control systematic errors. The Mpvalues were obtained with two different methodologies: (i) a relativistic Coulomb excitation experiment was performed for 46Cr and 46Ti; (ii) a “stretched target” technique was adopted here, for the first time, for lifetime measurements in 46V and 46Ti. A constant value of Mpacross the triplet has been observed. Shell-model calculations performed within the fpshell fail to reproduce this unexpected trend, pointing towards the need of a wider valence space. This result is confirmed by the good agreement with experimental data achieved with an interaction which allows excitations from the underlying sdshell. A test of the linearity rule for all published data on complete T=1isospin triplets is presented.