Measurements of ${}^{160}$Dy($p,\gamma$) at energies relevant for astrophysical $\gamma$ process

Abstract

Rare information on photodisintegration reactions of nuclei with mass numbers $A\approx 160$ at astrophysical conditions impedes our understanding of the origin of $p$-nuclei. Experimental determination of the key ($p,\gamma$) cross sections has been playing an important role to verify nuclear reaction models and to provide rates of relevant ($\gamma ,p$) reactions in $\gamma$-process. In this paper we report the first cross section measurements of ${}^{160}$Dy($p,\gamma$)${}^{161}$Ho and ${}^{161}$Dy($p,n$)${}^{161}$Ho in the beam energy range of 3.4 - 7.0 MeV, partially covering the Gamow window. Such determinations are possible by using two targets with various isotopic fractions. The cross section data can put a strong constraint on the nuclear level densities and gamma strength functions for $A\approx$ 160 in the Hauser-Feshbach statistical model. Furthermore, we find the best parameters for TALYS that reproduce the A $\sim$ 160 data available, ${}^{160}$Dy($p,\gamma$)${}^{161}$Ho and ${}^{162}$Er($p,\gamma$)${}^{163}$Tm, and recommend the constrained ${}^{161}$Ho($\gamma ,p$)${}^{160}$Dy reaction rates over a wide temperature range for $\gamma$-process network calculations. Although the determined ${}^{161}$Ho($\gamma$, p) stellar reaction rates at the temperature of 1 to 2 GK can differ by up to one order of magnitude from the NON-SMOKER predictions, it has a minor effect on the yields of ${}^{160}$Dy and accordingly the $p$-nuclei, ${}^{156,158}$Dy. A sensitivity study confirms that the cross section of ${}^{160}$Dy($p$, $\gamma$)${}^{161}$Ho is measured precisely enough to predict yields of $p$-nuclei in the $\gamma$-process.

Comments: 12 pages,9 figures