Evolution of quadrupole collectivity in N=80 isotones toward the Z=64 subshell gap: The B(E2; 21+ → 01+) value of Sm 142

Abstract

It was shown that the evolution of the B(E2;21+→01+) values in N = 80 isotones from Te to Nd is affected by the underlying subshell structure. This manifests itself in the observation of the local suppression of the B(E2) value at Z=58 with respect to the neighboring nuclei Ba136 and Nd140. To investigate this shell sensitivity toward the Z=64 subshell gap, the B(E2;21+→01+) value of the unstable nucleus Sm142 was measured utilizing the projectile Coulomb excitation technique. The radioactive ion beam (RIB) experiment was performed at the REX-ISOLDE facility at CERN. The B(E2) value of 32(4)W.u. reflects the impact of the π(1g7/22d5/2) subshell closure at Z=64 with respect to a linear scaling of collectivity with valence proton number.