Interpretation of the excitation and decay of180Tamthrough aK

The production and survival of Ta in stars presents a nuclear structure and astrophysics puzzle. From earlier work in the laboratory, photon scattering from the 9 , 75 keV isomeric state has been shown to result in eventual de-excitation to the relatively short-lived 1 1 ground state, through intermediate states whose character is uncertain. It is suggested here that the lowest observed photon resonances match the energies of known states in the rotational band based on the recently assigned K55 state at 592 keV, states which are accessible byE1 excitation from the 9 isomer. Analysis of the previously observed resonance strengths and the known in-band properties implies g-ray E1 transition probabilities which are stronger than expected given the nominalK forbiddenness. Predicted widths for ‘‘back’’-decay to the 9 2 isomer and its rotational band are calculated and shown to be significant. Their observation would have implications for the proposed associations and mixing effects above the yrast line.