Anomalous magnetic moment of 9C and shell quenching in exotic nuclei

Abstract

We discuss a mechanism of the anomalous spin expectation value of the 9C-9Li mirror pair in relation to the shell structure of exotic nuclei. In a similar way to the N = 20 shell gap for neutron-rich nuclei, the N = 8 shell gap should be rather narrow toward smaller Z from an empirical determination of the shell gap. The resulting ground state of 9Li is still dominated by the normal configurations, whereas that of the mirror nucleus 9C can be mixed with the intruder configurations triggered by the Thomas-Ehrman effect. This asymmetry of the ground state accounts for the experimental anomaly.