Neutron-Proton Bremsstrahlung Calculations

The neutron-proton bremsstrahlung cross section between 14 and 208 MeV is calculated by including the external radiation terms to all orders in the momentum of the photon, $K$, and by using the low-energy theorem to compute the internal scattering contribution to order $K^0$. These calculations, which employ a simple off-shell calculations of the elastic phase shifts, are in good agreement with the data at 208 MeV. These off-shell calculations are also compared to calculations using the corresponding on-shell phase shifts in order to determine the strength of the off-shell terms. In coplanar scattering where ${\theta }_p+{\theta }_n\le \sim 60°$, these off-shell effects constitute as much as 50% or more of the cross section, while for $60°\le {\theta }_p+{\theta }_n\le 90°$, the offshell contributions are much smaller.