Identification of isomeric states in the N=73 neutron-deficient nuclei 132Pr and 130La

Abstract

Decays from isomeric states in the neutron-deficient N = 73 nuclei 132Pr and 130La have been observed for the first time. Half-lives of 486(70) ns and 2.46(4) μs were measured for two isomeric states in 132Pr. The decay from the 486 ns (8−) isomer has been interpreted as a hindered E1 transition from the bandhead state of the excited πh11/2 ⊗ νg7/2 configuration. The decay from the 2.5 μs (8+) isomer is consistent with the Weisskopf estimate for a low-energy E2 transition. An analogous 0.74(3) μs decay from an (8+) isomer in the neighboring isotone 130La has also been observed which similarly can be explained if the transition has E2 character. The Weisskopf interpretation for the isomer hindrance is strengthened by the lack of evidence for shape or K isomerism due to the γ -soft shapes predicted by configuration-constrained potential-energy-surface calculations.