Cross sections of the Rb 83 (p,γ) Sr 84 and Kr 84 (p,γ) Rb 85 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.