Dose rate is the dose of radiation per unit time. Excitation is a change in energy level of an orbital electron and occurs when the energy lost by the incident radiation is insufficient to cause ionization. It can result from interactions involving incident photons of gamma or x-radiation or from inelastic collisions of particles. When the excited electron returns to its ground-state energy level, it must give off energy in the form of a photon of a electromagnetic radiation, which is usually of low enough energy to be detected with a photomultiplier tube. Ionization is the separation of an electrically neutral atom or molecule into electrically charged components termed an ion pair.
Specific ionization is the number of ion pair per unit distance formed along the path of a particle.
The distance specified is usually centimeters. The density of ionization produced by a given particle is a function of its charge and its velocity. A more slowly moving particle spends more time in the vicinity of the atom or molecule, increasing the chance of ionization occurring. The gas amplification factor is defined as the ratio of the number of electrons collected by the anode to the number of electrons formed by the primary radiation interaction. If sufficient potential difference is applied across a detector's electrodes, the free electrons resulting from ionization are accelerated toward the anode with enough energy to ionize the neutral gas atoms that are in their path, resulting in secondary ionization.