The B(E2:42+ → 22+) value in 152Sm and β-softness in phase coexisting structures

The lifetime of the 4(2)(+) level in Sm-152 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 Sm-152 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 beta -softness in Sm-152 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. (C) 2000 Published by Elsevier Science B.V.