Cross sections of the Rb83(p,γ)Sr84 and Kr84(p,γ)Rb85 reactions at energies characteristic of the astrophysical γ process

We have measured the cross section of the Rb83(p,γ)Sr84 radiative capture reaction in inverse kinematics using a radioactive beam of Rb83 at incident energies of 2.4 and 2.7A MeV. Prior to the radioactive beam measurement, the Kr84(p,γ)Rb85 radiative capture reaction was measured in inverse kinematics using a stable beam of Kr84 at an incident energy of 2.7A MeV. The effective relative kinetic energies of these measurements lie within the relevant energy window for the γ process in supernovae. The central values of the measured partial cross sections of both reactions were found to be 0.17–0.42 times the predictions of statistical model calculations. Assuming the predicted cross section at other energies is reduced by the same factor leads to a slightly higher calculated abundance of the p nucleus Sr84, caused by the reduced rate of the Sr84(γ,p)Rb83 reaction derived from the present measurement.