Microscopic calculations of effective charges and quadrupole transition rates in Si, S and Ar isotopes.

Quadrupole transition rates and effective charges are calculated for even-even Si, S and Ar isotopes based on sd and sdpf -shell model spaces. Shell model calculations are performed with sd shell-model space for neutron number (N) ≤ 20 and sdpf shell-model space for N 20. Excitation out of major shell space are taken into account through a microscopic theory which allows particle-hole excitation from the core and model space orbits to all higher orbits with 2hω excitation. Effective charges are obtained for each isotope. The results show a systematic increase in the B(E2) values for N 20. Shell model calculation predicts the erosion of the N=28 magicity in the neutron rich 42Si. No clear indications about the erosion of the shell gap closure in 44S and 46Ar isotope.