Particle Detector Common Nuclear Detectors Method of Detection Remarks

We have just concluded the study of radiation interaction with matter in which the basic mechanisms of charged particle, neutron and gamma interactions were discussed separately. A topic which makes use of all this information is the general problem of detection of nuclear radiation detection. Although this subject properly belongs to a course dealing with experimental aspects of applied nuclear physics, it is nevertheless appropriate to make contact with it at this point in the course. There are two reasons for this. First, radiation detection is a central part of the foundational knowledge for all students in the department of Nuclear Science and Engineering. Even though we cannot do justice to it due to the limited time remaining in the syllabus, it is worthwhile to make some contact with it, however brief. Secondly, an analysis of the features observed experimentally in pulse-height spectra of gamma radiation is timely given what we have just learned about the γ -interaction processes of Compton scattering, photoelectric effect and pair production. We start by noting that regardless of the type of nuclear radiation, the interactions taking place in a material medium invariably result in ionization and excitation which then can be detected. Heavy charged particles and electrons produce ion pairs in ionization chambers, or light emission (excitation of atoms) in scintillation counters, or electron-hole pairs in semiconductor detectors. Neutrons collide with protons which recoil and produce ionization or excitation. In the case of gammas, all 3 processes we have just discussed give rise to energetic electrons which in turn cause ionization or excitation. Thus the basic mechanisms of nuclear radiation detection involve measuring the ionization or excitation occurring in the detector in a way to allow one to deduce the energy of the incoming radiation. A useful summary of the different types of detectors and methods of detection is given in the following table [from Meyerhof, p. 107].