Before a particle can be detected, it must first undergo some sort of interaction in the material of a detector. Processes that result from the electromagnetic interaction are the most important for particle detection. In this chapter we will consider four major topics. The first is the loss of energy by charged particles heavier than the electron due to the excitation or ionization of atomic electrons. We will calculate the most probable value of the ionization energy loss and the distribution of the fluctuations in that quantity. Second, we will consider the interactions of electrons. These include ionization losses and the loss of energy due to photon emission (bremsstrahlung). The third topic is the interaction of photons with matter. The most important of these are the photoelectric effect, the Compton effect, and pair production. Lastly, we will examine Coulomb scattering of charged particles with the atomic nucleus, which is responsible for multiple scattering.

There are additional processes that, although they are electromagnetic in nature, are more appropriately discussed in other sections of the book. These include scintillation light (Chapter 7), Cerenkov light (Chapter 8), ionization in gases (Chapter 9), electromagnetic showers (Chapter 11), and transition radiation (Chapter 12). Strong and weak nuclear interactions of particles in matter are discussed in Chapter 3.

A rigorous treatment of electromagnetic effects requires calculations using QED. This theory describes the interactions in terms of the exchange and emission of photons.