Experimental g factors and B(E2) values in Ar isotopes: Crossing the N=20 semi-magic divide

Measurements of g factors and lifetimes of the 21+ states in 36,38Ar have been performed via α-transfer reactions using 32S and 34S ions in inverse kinematics combined with the techniques of transient magnetic fields and Doppler-shift-attenuation. The variations, with the neutron number, of the measured g factors and B(E2) values of 36,38,40Ar have been explained by large-scale shell model calculations. The good agreement achieved between experiment and theory demonstrates the impact of the effective nucleon-nucleon interactions and the magic N=20 shell closure. The present new results are a very good show-case for the universal difference in sensitivity of excitation energies, magnetic moments and electromagnetic transition probabilities to nuclear wave functions behaviour as closed shells are approached, crossed, and left behind. Aspects of the collectivity of these nuclei are also discussed from the perspective of a simple vibrational model.