https://doi.org/10.1351/goldbook.08724
Beam of particles capable of removing one or more orbital electrons in a single quantum event from a specified atom resulting in an ion.
Notes:
- To have sufficient energy for direct ionization, most ionizing particles are electrically charged, for example, alpha particles, beta particles, electrons, positrons, protons. Photons can ionize atoms directly through the photoelectric effect or the Compton effect.
- When considering the health effects of radiation, the distinction may be made between multiple ionizations by charged particles as they move through a material (called 'direct ionization') and a single event of ionization caused by a photon.
See also: indirectly-ionizing radiation