When higher energy particles such as alphas, betas, protons, or deuterons interact with atoms in an absorbing material the predominant site of interaction is with the orbital electrons of the absorber atoms. This leads to ionisation of the atom, and liberation of excited electrons by the transfer of energy in the interaction. The liberated electrons themselves may have sufficient energy to cause further ionisation of neighboring atoms and the electrons liberated from these subsequent interactions are referred to as delta rays.
Positron annihilation is an example of a particulate radiation interacting with matter. We have already examined this process in detail.
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