On the scattering of fast neutrons by protons.

1. Introduction. Recent experiments by Amaldi arid his collaborators on the scattering of high-energy neutrons (of 10—15MeV.) by protons (2) have disclosed a considerable anisotropy in the angular distribution of the scattered particles. Theoretical discussions of this problem show an interesting feature in that the results depend sensitively on the basic assumptions involved with regard to the charge dependence of the neutron-proton interaction. This can be seen in particular from calculations by Rarita and Schwinger(3) and by Ferretti(4). The former authors started from the assumption of a distance dependence of this interaction represented by a square well, while the angular and spin dependence included terms of the axial dipole type. If the charge dependence was further assumed to be of the ' symmetrical' type, they found a value for the anisotropy in strong disagreement with experiment, whereas the total cross-section agreed with the measured value; a 'neutral' theory, on the other hand, yielded agreement as regards anisotropy, but a total cross-section too large by a factor of the order of 1-5. Ferretti investigated the scattering on Bethe's neutral meson theory (5) and found satisfactory agreement with regard to both angular distribution and total cross-section. It should be stressed that all calculations mentioned were performed in the approximation in which only the contributions of the Sand P-waves are considered. From the point of view of the 'mixed' theory of Moller and Rosenfeld(6) the scattering has been treated by Ferretti (7) and Hulthen(8); these authors have put it beyond doubt that Amaldi's results are irreconcilable with the symmetrical form of this theory!.