The existence of a low energetic intermediate state (IS) in ${}^{180}\mathrm{Ta}$ 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 $\alpha$ particles in the energy range $12-20\hspace{0.5em}\mathrm{MeV}.$ Subsequently, the foils were counted for the induced ground state activity of ${}^{180}\mathrm{Ta}.$ 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 $3.1\times {10}^8\hspace{0.5em}\mathrm{K}$ 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 ${}^{180}\mathrm{Ta}$ under these conditions, but an $s$ process origin seems still possible. Furthermore, the experiments support the existence of a new isomer in ${}^{184}\mathrm{Re}.$

• Received 7 April 1998

DOI:https://doi.org/10.1103/PhysRevC.58.1790