Test of the πg7/2 subshell closure at Z=58

A simultaneous lifetime and relative g-factor measurement of the 21+ levels in 138,142Ce was performed using the Time Dependent Recoil Into Vacuum (TDRIV) technique. The excitation mechanism was Coulomb excitation in inverse kinematics, and the experimental setup included the Yale plunger device and the Gammasphere array. The latter was used to extract angular distributions for the 21+→0+γ-ray transitions at various target-to-stopper distances. A g(21+) factor of 0.26(8) for 138Ce was obtained relative to the literature value of g(21+)=0.21(5) in 142Ce. In addition, high-precision values of the B(E2;21+→0+) strengths were obtained. The new data support a proposed subshell closure for the πg7/2 orbital at Z=58