Inelastic Scattering of Fast Neutrons

The radiation observed in the presence of a source of fast neutrons is found to be due chiefly to the excitation of gamma-rays in the lead block used in these experiments. The true absorption of fast neutrons in several elements is less than previous measurements had indicated, and hence an absorption process cannot account for the soft gamma-rays produced by the action of fast neutrons on matter. The capacity of fast neutrons to produce gamma-rays in lead and copper is considerably diminished as a result of their passage through various substances. Therefore the energy of the gamma-rays must be derived from the kinetic energy of the fast neutrons by a process of inelastic scattering.