Proton channelling through thin crystals

Abstract

The channelling of energetic protons in crystals is reviewed briefly, and the validity of a classical interpretation of the phenomenon is discussed. Experimental results are presented in the form of angular distribution measurements recorded on x-ray film, and energy spectrum measurements made with a collimated semiconductor detector, for protons within the energy range 1–5 MeV transmitted by a variety of thin, single crystals. These results are discussed in the light of a model based upon an effective potential due to atomic rows and planes in the lattice. The diffusion of proton trajectories due to elastic scattering processes within the crystal is shown to explain the behaviour of the angular distributions, and the influence upon them of crystal thickness. A distinction is drawn between axial and planar channelling and a barrier is shown to exist between the two types of channel.