Nuclear Radiations and Their Interaction with Matter

Abstract

Detection of radiation is possible because in the interaction of radiation with matter, photons, electron-ion pairs, or electron-hole pairs can be produced. Gas counters (ionization chambers, proportional counters, and Geiger counters), cloud chambers, bubble chambers, and spark counters work because the radiations produce ions. In scintillation counters, radiation-induced excitation produces light quanta (photons) and in semiconducting counters, radiation produces electron-hole pairs. The number of ions, photons, or electron-hole pairs depends on the fraction of the energy of the radiation expended in the sensitive volume, on the properties of the material, and sometimes on the nature of the radiation. In the design of counters and in the analysis of information obtained from them, it is important to know how fast tile radiations expend their energy in a medium, how much of it goes into producing ions, photons, or electron-hole pairs, what is the relationship between the number of ions and the energy, and how much material is needed to stop a radiation of a given energy. Some of these problems are discussed in this chapter. Neutral radiations like gamma rays and neutrons do not directly produce these effects and therefore their detection depends on an intermediate interaction in which charged particles are produced. Interactions of neutral radiations are discussed in the latter part of this chapter. However, it is appropriate at this point to become familiar with nuclear radioactivity, nuclear reactions, and terms such as decay constant, half-life, and reaction cross section. These topics are now discussed.