First measurement in the Gamow window of a reaction for the γ-process in inverse kinematics: 76Se(α,γ)80Kr

The p-nuclei are the few stable nuclei heavier than iron on the neutron-deficient side of the valley of stability that cannot be produced through astrophysical neutron-capture reactions. The limited experimental data on reactions through which the p-nuclei might be produced leaves the origin of their production largely unknown. This work presents the first cross section measurements of the 76Se( α , γ )80Kr reaction. The rate of the time reversed reaction, 80Kr( γ , α )76Se, is one of the most uncertain of possible reactions which can occur at the 80Kr branching point on the γ-process photo-disintegration pathway. The reaction flow through 80Kr will directly affect the final abundance of the p-nuclide 78Kr. Experimental cross sections at two astrophysically relevant energies are reported and compared to cross sections calculated using Hauser-Feshbach codes talys, non-smoker, and smaragd. The success of these first ( α , γ ) cross section measurements performed in inverse kinematics in the energy region of the γ-process opens the door for future studies of reactions on radioactive γ-process nuclides.