Decay of a K-pi = 21/2(-), 17-ms isomer in Ta-185

Abstract

High-spin states in the neutron-rich nucleus Ta185, populated in the decay of a long-lived, three-quasiparticle state, have been studied using deep-inelastic reactions with Xe136 ions and a W186 target. The lifetime of the isomer has been measured as 17(2) ms and the spin and parity determined to be Kπ=21/2-, leading to a π7/2+[404]ν3/2-[512]11/2+[615] configuration assignment. The isomer decays into the rotational band built upon the π9/2-[514] intrinsic state via K-forbidden transitions with reduced hindrances of 52 and 71. The π9/2-[514] state is itself an isomer with a lifetime of 17(3) ns. It decays via K-allowed E1 transitions to states in the π7/2+[404] band with strengths that are similar to equivalent transitions in the lighter tantalum isotopes.