Production of ${}^{180m}$Hf in photoproton reaction ${}^{181}$Ta(γ, p) at energy E${}_{\gamma max}$ = 35-95 MeV

The production of the ${}^{180m}$Hf nuclei in the photoproton reaction ${}^{181}$Ta(γ, p) was studied at end-point bremsstrahlung energies E${}_{\gamma max}$ = 35-95 MeV. The experiment was performed at the electron linear accelerator LUE-40 NSC KIPT with the use of the γ activation and off-line γ-ray spectroscopy. The experimental values of the bremsstrahlung flux-averaged cross-sections $⟨$σ(E${}_{\gamma max}$)${⟩}_m$ for the ${}^{181}$Ta(γ, p)${}^{180m}$Hf reaction were determined, and at E${}_{\gamma max}$ > 55 MeV obtained for the first time. The measured values, as well as the literature data, significantly (by more that an order of magnitude) exceed the theoretical flux-averaged cross-sections $⟨$σ(E${}_{\gamma max}$)${⟩}_{th}$. The $⟨$σ(E${}_{\gamma max}$)${⟩}_{th}$ values were calculated using the cross-section σ(E) computed with the TALYS1.95 code for six different level density models. A comparative analysis of the calculated total cross-sections from the TALYS computation for the reactions ${}^{181}$Ta(γ, p)${}^{180}$Hf and ${}^{181}$Ta(γ, n)${}^{180}$Ta was performed. It was shown that the photoproton (γ, p) to photoneutron (γ, n) strength ratio is consistent with the estimates based on the isospin selection rules and the value from the (e, e' p) experiment.