A device that measures the total energy deposited by a particle or group of particles is known as a calorimeter, in analogy with the laboratory instrument that measures the amount of deposited heat. We have already encountered several devices, such as sodium iodide scintillation counters and total absorption Cerenkov counters, that can be used as calorimeters for photon detection. We will consider properties of these “continuous” calorimeters again in Chapter 14. In this chapter we consider a class of calorimeters that periodically sample the development of a shower initiated by an incident particle. There are two major types of sampling calorimeters, depending on whether the incident particle initiates an electromagnetic or hadronic shower. Each type of calorimeter is optimized to maximize the rejection of the other type of shower.

Calorimeters have found wide use in particle physics experiments. Neutral particles can only be detected by using this method. Sampling calorimeters of very large size have been used as neutrino detectors. We have seen that at high energy, particle multiplicities grow with increasing energy, and the angular distribution of groups of the produced secondaries are highly collimated (jet effect). Under these conditions calorimeters can provide a useful trigger for interesting events based on the total energy deposited in a localized area. Calorimeters can easily be modularized and made to cover large solid angles. In addition, we shall see that the size of a calorimeter needed to measure the energy of a particle scales like ln(E), whereas the size of a magnetic deflection device would scale like E½.