Evolution of quadrupole collectivity inN=80isotones toward theZ=64subshell gap: TheB(E2;21+→01+)value ofSm142

Abstract

It was shown that the evolution of the $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ 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 $^{136}\mathrm{Ba}$ and $^{140}\mathrm{Nd}$. To investigate this shell sensitivity toward the $Z=64$ subshell gap, the $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ value of the unstable nucleus $^{142}\mathrm{Sm}$ 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 $32\phantom{\rule{0.16em}{0ex}}(4)\phantom{\rule{0.16em}{0ex}}\mathrm{W}.\mathrm{u}.$ reflects the impact of the $\ensuremath{\pi}(1{g}_{7/2}\phantom{\rule{0.16em}{0ex}}2{d}_{5/2})$ subshell closure at $Z=64$ with respect to a linear scaling of collectivity with valence proton number.