PET Scanning Systems

Abstract

The detection and measurement of radiation is based on the interaction of radiations with matter discussed in Chap. 1. In gases, ionizing radiations, particulate or electromagnetic, interact with gas molecules to produce positive and negative ions, which are then collected as current or count by the application of a voltage. The amount of ionization is proportional to the amount of energy deposited by the radiation. At low voltages, the ionization is measured as current that is proportional to the amount of radiation. Dose calibrators, pocket dosimeters, and ionization chambers operate on this principle at low voltages (∼ 150 V). At high voltages (∼ 900 V), ions are multiplied in an avalanche of interactions producing a pulse that is independent of the energy and type of radiation. Each event of interaction is detected as a count, and this principle is applied in Geiger--Müller (GM) counters, which are used as radiation survey meters.