Photo-Induced depopulation of the $^{180m}$Ta isomer

The $^{180m}$Ta nucleus is the rarest isotope in the universe, existing only in an isomeric state at 77.2 keV (J$^\pi$ = 9$^{-}$) with half-life of greater than 7.1$\times $10$^{15}$ years. The stellar production of this high-spin isomer has been a challenging astrophysical problem. Cross-section measurements for the depopulation of the $^{180m}$Ta isomer with monoenergetic photon beams of energies 2.5 and 3.1 MeV have been carried out at the HI$\gamma $S facility. The activated Ta foils of natural abundance and containing 14.4 mg of $^{180m}$Ta were $\gamma $-ray counted at TUNL's low background facility using a 13\% planar HPGe detector. A 8$''$$\times $12$''$ NaI detector in combination with the standard HI$\gamma $S scintillator paddle system was employed for absolute photon-flux determination. Preliminary results will be discussed, and measurements at lower energies are planned.