ABSTRACT
Perhaps the main reason that most people fear ionizing radiation is that humans have no way to directly sense it. We need instruments to convert ionizing radiation into signals that we can observe and understand. Remember that ionizing radiation can interact with matter by ionization (creation of an ion pair) or excitation. We can take advantage of both in our quest to detect ionizing radiation. This chapter is all about how these instruments work. Special emphasis will be placed on GeigerMüller tubes (also known as Geiger counters), as they are so commonly used, and on gamma spectroscopy because of its importance to nuclear medicine.
