The elasticity of the collisions of alpha particles with hydrogen nuclei

Abstract

The normal collisions between alpha particles and atomic nuclei are known from scattering experiments to be approximately elastic. The only cases in which inelastic nuclear collisions have been established with certainty are those in which a proton is ejected from a light nucleus. In the case of nitrogen this is known to be associated with the capture of the alpha particle. It is, however, possible that inelastic nuclear collisions do occur, in which a nucleus is deformed but not disintegrated. Smekal has suggested the occurrence of inelastic collisions of this type. Again, it is possible that an appreciable amount of energy might be radiated by the two rapidly accelerated nuclei during a close collision. For although calculation shows that, if the inverse square law is obeyed at all distances, the energy radiated classically by the accelerated particles will be extremely small (of the order of 10-4 of the total kinetic energy), it might conceivably reach a detectable amount if the forces near the nucleus vary as a very high power of the distance. The existence of such forces is required by the rigid ellipsoidal model of the alpha particle proposed by Chadwick and Bieler. There is some experimental evidence of the excitation of radiation by the impact of alpha particles on matter. These various possibilities make the detailed study of the elasticity of nuclear collisions of considerable interest. The use of the Wilson method for the purpose has been described by Blackett. The method will be discussed here in greater detail and some new results will be given.