Neutron-proton scattering at small angles

Neutron-proton scattering has been measured from 6 to 61$\cdot $5 degrees c.m. for neutrons of effective energy 105 $\pm $ 3 and 137 $\pm $ 5 MeV using a liquid hydrogen scatterer and a large neutron counter. The results confirm previous measurements and show a near symmetry around 90 degrees at 105 MeV, and a fairly definite asymmetry at 137 MeV. The 'Serber force' does not, therefore, give a good approximation to the experimental data at 137 MeV.