Cross section measurements of the181Ta(γ,n)180Tareaction near neutron threshold and thep-process nucleosynthesis

Abstract

New measurements of the photoneutron reaction on ${}^{181}\mathrm{Ta}$ have been conducted with the AIST-LCS (laser Compton scattering) beam in the $7.8\ensuremath{\lesssim}E[\mathrm{MeV}]\ensuremath{\lesssim}12$ energy range. The major advantage of the present $\ensuremath{\gamma}$-ray experiment is its intense peaking in the energy window of astrophysical interest, i.e., close to the neutron threshold. Details on photon beams from the laser Compton scattering, neutron counting, and experimental determination of the ${}^{181}\mathrm{Ta}$ photoneutron cross section are given. The present experimental data are in good agreement with the IAEA evaluation. Reaction rate calculations in the Hauser-Feshbach statistical model are performed and confronted with the experimental data. The data provide constraints on the low-energy tail of the dipole strength function. It is found that among the three different models for the $E1$-strength considered, only the microscopic quasiparticle random phase approximation model can reproduce the extra strength observed in the ${}^{181}\mathrm{Ta}(\ensuremath{\gamma}{,n)}^{180}\mathrm{Ta}$ reaction at energies of about 8.5 MeV. Such an experiment helps to improve the determination of the corresponding stellar photodisintegration rate of ${}^{181}\mathrm{Ta}$ which directly influences the p-process production of ${}^{180}\mathrm{Ta}.$