Shell-model calculation of E2 effective charges: Application to carbon isotopes

A theoretical approach based on the shell model is presented to calculate effective charges of electric quadrupole transitions. The shell-model calculation with single-particle 2ℏω excitations in the first order perturbation qualitatively reproduces existing experimental B(E2) values for carbon isotopes with neutron number 5⩽N⩽16 and shows a sudden change of the isovector effective charge beyond N=8.