Coulomb excitation of 180Ta

The existence of a low energetic intermediate state (IS) in Ta-180 which provides a coupling of the stable isomer and the radioactive ground state was investigated by means of Coulomb excitation. Natural tantalum foils were irradiated by protons with incident energies between 3.0 and 3.7 MeV, and with ct particles in the energy range 12-20 MeV. Subsequently, the foils were counted for the induced ground state activity of Ta-180. From the thick target yields an IS between 0.6 and 2.2 MeV excitation energy was inferred. The population of the IS in the stellar environment of the s process depends critically on the prevailing temperatures. Current stellar models suggest s-process temperatures below 3.1X10(8) K which lead to a negligible population of intermediate states above 1.2 MeV. Thus, the present data do not allow stringent conclusions about the destruction of Ta-180 under these conditions, but an s process origin seems still. possible. Furthermore, the experiments support the existence of a new isomer in Re-184.