COULOMB-EXCITATION OF TA-180

The existence of a low energetic intermediate state (IS) in Ta-180 whi ch provides a coupling of the stable isomer and the radioactive ground state was investigated by means of Coulomb excitation. Natural tantal um 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. Sub sequently, the foils were counted for the induced ground state activit y of Ta-180. From the thick target yields an IS between 0.6 and 2.2 Me V excitation energy was inferred. The population of the IS in the stel lar environment of the s process depends critically on the prevailing temperatures. Current stellar models suggest s-process temperatures be low 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 co nclusions about the destruction of Ta-180 under these conditions, but an s process origin seems still. possible. Furthermore, the experiment s support the existence of a new isomer in Re-184.