ABSTRACT
Radioactivity is the spontaneous emission of ionizing radiation or particles from the decay or de-excitation of unstable nuclei. Typically, these nuclear processes occur on energy scales of millions of electron volts. While the term radioactivity often has negative connotations, humans are constantly exposed to low-level radioactivity from natural sources such as rocks, cosmic rays, and even some kinds of food like bananas and table salt. Common media used for the direct detection of ionizing particles are gases and semiconductor devices, in which the energy deposition frees charges in the active volume of the detector that can be collected by their interaction with an electric field in the detector. Solid or liquid scintillators coupled to a photomultiplier tube or various kinds of semiconductor photodiodes or photomultipliers can also be used to detect ionizing radiation. Geiger tubes are typically not used for neutron counting unless gases with high neutron-capture cross sections are used in the tube.
