Depopulation of 180Tam by Coulomb excitation and possible astrophysical consequences.

Abstract

The depopulation of [sup 180]Ta[sup [ital m]] by Coulomb excitation was investigated in a thick-target experiment using beams of [sup 32]S and [sup 36]S with energies of 70--130 MeV on disks of natural tantalum. The resulting [sup 180]Ta ground-state population was measured by detecting its eight-hour decay. At the higher incident energies the observed [sup 180]Ta yield is dominated by sub-Coulomb neutron pickup transfer reactions on the 10[sup 4] times more abundant [sup 181]Ta. At the lower incident energies in [sup 180]Ta ground-state yield is found to be compatible with Coulomb excitation of the isomer to an intermediate level with energies [ital E][sub [ital x]][lt]1 MeV and a reduced transition probability [ital B]([ital E]2)[congruent]0.02--0.25 Weisskopf units. Consequences for the astrophysical production mechanism of [sup 180]Ta are discussed.