Photo-induced depopulation of the ${}^{180}{\mathrm{Ta}}^m$ isomer via low-lying intermediate states: Structure and astrophysical implications

The photo-induced depopulation of the quasistable isomer ${(t}_{1/2}>~1.2\times {10}^{15}\hspace{0.5em}\mathrm{yr})$ in ${}^{180}\mathrm{Ta}$ with angular momentum and parity $J^{\pi }{=9\mathrm{}}^{-}$ at an excitation energy $E_x=75\mathrm{}\hspace{0.5em}\mathrm{keV}$ was studied at the new bremsstrahlung irradiation facility installed at the Stuttgart 4.3 MV DYNAMITRON accelerator in the energy range of bremsstrahlung end point energies between $E_0=0.8\mathrm{}–3.1\hspace{0.5em}\mathrm{MeV}.$ The onset of the isomer depopulation could be observed starting at an end point energy of $E_0\approx 1\hspace{0.5em}\mathrm{MeV},$ i.e., at an intermediate state of ${}^{180}\mathrm{Ta}$ at or below that energy. Higher-lying intermediate states were found at 1.22, 1.43, 1.55, 1.85, 2.16, 2.40, 2.64, and 2.80 MeV. The extracted integrated cross sections show a remarkably strong depopulation of the ${}^{180}{\mathrm{Ta}}^m$ isomer by photoexcitation. The results are compared with previous experiments and recent quasiparticle-phonon model calculations. Implications of the results for a possible nucleosynthesis of ${}^{180}\mathrm{Ta}$ in the s process and the neutrino process are discussed.