The B(E2 :4+2→2+2) value in 152Sm and β-softness in phase coexisting structures

The lifetime of the 4+2 level in 152Sm has been measured by the recoil distance method using Coulomb excitation. The result, 12±2 ps, gives a B(E2 :4+2→2+2) value of 204 W.u., which is much smaller than the literature value. This removes an anomaly among collective transitions and a serious discrepancy with existing calculations. This result is interpreted by exploiting the concept of Q-invariants. The extensive data on 152Sm is used to establish for the first time the validity of certain approximate expressions for the Q-invariants. Both exact and approximate expressions are then shown to reflect and support recent discussions of phase coexistence and β-softness in 152Sm by applying them to the yrast states, and for the first time, to an excited family of levels based on the 0+2 level as well.