The $\ensuremath{\gamma}$ process is an explosive astrophysical scenario, which is thought to be the primary source of the rare proton-rich stable $p$ nuclei. However, current $\ensuremath{\gamma}$-process models remain insufficient in describing the observed $p$-nuclei abundances, with disagreements up to two orders of magnitude. A sensitivity study has identified ${}^{111}\mathrm{In}$ as a model-sensitive $(\ensuremath{\gamma},p)/(\ensuremath{\gamma},n)$ branching point within the $\ensuremath{\gamma}$ process. Constraining the involved reaction rates may have a significant impact on the predicted $p$-nuclei abundances. Here we report on measurements of the cross sections for $^{102}\mathrm{Pd}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{103}\mathrm{Ag},\phantom{\rule{0.28em}{0ex}}^{108}\mathrm{Cd}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{109}\mathrm{In}$, and $^{110}\mathrm{Cd}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{111}\mathrm{In}$ reactions for proton laboratory energies 3--8 MeV using the high efficiency total absorption spectrometer and the $\ensuremath{\gamma}$-summing technique. These measurements were used to constrain Hauser-Feshbach parameters used in talys 1.9, which constrains the $^{111}\mathrm{In}(\ensuremath{\gamma},p)\phantom{\rule{0.16em}{0ex}}^{110}\mathrm{Cd}$ and $^{111}\mathrm{In}(\ensuremath{\gamma},n)\phantom{\rule{0.16em}{0ex}}^{110}\mathrm{Ag}$ reaction rates. The newly constrained reaction rates indicate that the $^{111}\mathrm{In}\phantom{\rule{4pt}{0ex}}(\ensuremath{\gamma},p)/(\ensuremath{\gamma},n)$ branching point occurs at a temperature of $2.71\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.28em}{0ex}}\mathrm{GK}$, well within the temperature range relevant to the $\ensuremath{\gamma}$ process. These findings differ significantly from previous studies and may impact the calculated abundances.

Four (alpha, gamma) cross-section measurements on stable nuclei in the A = 100 mass range were performed at the University of Notre Dame Nuclear Science Laboratory. The Pd-102(alpha, gamma)Cd-106 and Cd-110(alpha, gamma)Sn-114 reactions were measured for the first time. The Zr-90(alpha, gamma)Mo-94 and Cd-108(alpha, gamma)Sn-112 results extended the measured range down to energies lower than those of the previous experiments. These reactions were studied as possible branching points in gamma-process reaction networks. The measured cross-section values were compared to the NONSMOKER database as well as to calculations performed with TALYS 1.9. The combination of parameters available in TALYS that gave the best fit to the data was found and the corresponding reaction rates were obtained. The inverse (gamma, alpha) rates were then obtained and compared to the corresponding (gamma, n) rates to investigate the relative strength between the two reaction pathways. It was found that in all four cases the (gamma, alpha) reaction pathway begins to dominate within the 1.5-3.5 GK temperature range.

The gamma process is an explosive astrophysical scenario, which is thought to be the primary source of the rare proton-rich stable p nuclei. However, current gamma-process models remain insufficient in describing the observed p-nuclei abundances, with disagreements up to two orders of magnitude. A sensitivity study has identified In-111 as a model-sensitive (gamma, p)/(gamma, n) branching point within the gamma process. Constraining the involved reaction rates may have a significant impact on the predicted p-nuclei abundances. Here we report on measurements of the cross sections for Pd-102(p, gamma) Ag-103, Cd-108(p, gamma) In-109, and Cd-110(p, gamma) In-111 reactions for proton laboratory energies 3-8 MeV using the high efficiency total absorption spectrometer and the gamma-summing technique. These measurements were used to constrain Hauser-Feshbach parameters used in talys 1.9, which constrains the In-111(gamma, p) Cd-110 and In-111(gamma, n) Ag-110 reaction rates. The newly constrained reaction rates indicate that the In-111(gamma, p)/(gamma, n) branching point occurs at a temperature of 2.71 +/- 0.05 GK, well within the temperature range relevant to the gamma process. These findings differ significantly from previous studies and may impact the calculated abundances.