Cross sections of the Rb-83(p, ?)Sr- 84 and Kr-84(p, ?) Rb-85 reactions at energies characteristic of the astrophysical ? process

We have measured the cross section of the( 83)Rb(p, ? ) Sr-84 radiative capture reaction in inverse kinematics using a radioactive beam of Rb-83 at incident energies of 2.4 and 2.7A MeV. Prior to the radioactive beam measurement, the Kr-84(p, ? ) Rb-85 radiative capture reaction was measured in inverse kinematics using a stable beam of Kr-84 at an incident energy of 2.7A MeV. The effective relative kinetic energies of these measurements lie within the relevant energy window for the ? 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 Sr-84, caused by the reduced rate of the Sr-84(? , p) Rb-83 reaction derived from the present measurement.