Since the volume and electrical field of the nucleus are very small when compared to the rest of the atom, most of the interactions are between orbital electrons and the incident particle or photon. This usually occurs through the removal of one or more orbital electrons from the atom or molecule. Whenever a particle or ray drives an electron out of its normal orbit we have an ionization process, since the remaining atom is no longer electrically balanced. The energy required to produce a single ion pair is very small by ordinary standards. The electron volt, kev, and MeV are extremely small quantities of energy.
Electromagnetic radiation includes x-rays and gamma rays.
Each specific type of ionizing radiation can be identified by its varying ability to penetrate matter and produce ionization. The following pages contain a brief discussion of the most common types of ionizing radiation. Although alpha radiation is not routinely encountered at Baylor, some sealed sources are used which are alpha emitters, such as 241Americium. Alpha particles, composed of 2 protons and 2 neutrons, are extremely efficient ionizers due to their relatively large mass and high positive charge. They cannot travel very far, even in air, without interacting with matter by way of both direct collisions and electrical field interactions.