Nucleon-nucleon bremsstrahlung at intermediate energies

Energetic photon production in proton-neutron as well as in proton-proton collisions at intermediate bombarding energies are investigated in a meson-exchange potential model calculation in an effort to provide a more reliable basis for calculations of hard photon production in heavy-ion collisions. Special attention is paid to the role of the one-body rescattering contribution, which has been neglected in previous work. It is shown that this contribution enhances the cross section for photon energies only near the maximum value allowed kinematically. As a function of photon energy, both pn and pp bremsstrahlung inclusive cross sections are shown to be rather flat except in the low photon energy region. The shape of the angular distribution is, to a large extent, determined by the convection current contribution, which in the soft-photon limit has a well-known dipole shape in the case of pn bremsstrahlung and a quadrupole shape in the case of pp bremsstrahlung. For photon energies above ∼150 MeV where the magnetic current contribution dominates over the convection contribution, the shape of the angular distribution is roughly of a ${\cos }^2$θ form. The internal current gives rise to a nearly isotropic angular distribution. The ppγ cross section is shown to be very small compared to the pnγ cross section, even for considerably high-energy photons, because of the two-body current contribution, which is mostly absent in pp bremsstrahlung. The present calculation yields np bremsstrahlung cross sections which still tend to underpredict the data, although the measurements have large uncertainties.