Nucleon-Nucleon Scattering

Nucleon-nucleon scattering data from 0 to 274 Mev are discussed by means of a boundary-condition approximation. For internucleon distances greater than the core radius, which may depend on the state under discussion, the nucleon-nucleon interaction is assumed to vanish, while at the core radius the logarithmic derivative of the wave function or the reaction matrix satisfies a boundary condition. Assuming charge independence, it has been found possible to fit most of the experimental data with all but one boundary condition energy-independent. The core radius for the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ state is assumed to decrease with increasing energy. We find that $p-p$ scattering is composed mostly of scattering in the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ states, both of which give isotropic distributions. The scattering from the ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state is close to the scattering by a repulsive sphere of radius 1.32×${10}^{-13\mathrm{}}$ cm. The scattering in the isotopic singlet state below 100 Mev, assuming that the $n-p$ angular distribution is symmetric about 90°, is entirely determined by the low-energy fit to triplet (${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}+{}_{}{}^3{}_{}{}^{}D_1^{}{}_{}{}^{}$) $n-p$ scattering. Above 100 Mev the (${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}+{}_{}{}^3{}_{}{}^{}D_1^{}{}_{}{}^{}$) states make the major contribution to the isotopic singlet scattering. The predicted cross sections fail significantly in only one detail: they are not sufficiently large for $n-p$ scattering near 180°. Regardless of the validity of this particular fit, the boundary-condition approximation is found to provide a comparatively simple method for the broad correlation and understanding of the experimental results.