Mass dependence of the effective isovector charge in the sd-shell

Abstract

In order to map out a possible mass and isospin dependence of the effective charges in the sd-shell, we performed an intermediate energy Coulomb excitation experiment with the semi-magic, proton-rich nucleus 38Ca. The transition between the first excited state (21+, E*=2206 keV) and the ground state (0gs+) was studied, and the reduced transition strength and the proton transition matrix element were deduced. The nucleus 38Ca was chosen for this study, as it is at the upper mass end of the sd-shell, and will together with already existing high precision data for the lower mass end of the shell most clearly show a systematic trend in the effective charges. Our study also helps to fill the void of available high quality data for proton-rich nuclei in this mass region. We compare our data to theoretical shell model predictions with mass dependent, and mass independent effective charges, and to experimental values of the neutron-rich mirror nucleus 38Ar.