Glossary

Radiation-related terms

---

Absorbed dose: The amount of energy deposited in a unit of biological tissue. The units of absorbed dose are the rad and gray. Alpha radiation: Radiation consisting of helium nuclei that are discharged by radioactive disintegration of some heavy elements, including uranium-238, radium-226, and plutonium-239. Alpha, the first letter of the Greek alphabet, is written as . Beta radiation: Radiation consisting of beta particles, which are electrons or positrons (positively charged electrons), emitted by certain elements in the course of radioactive decay, at high speeds. Beta, the second letter of the Greek alphabet, is written as . Effective dose equivalent (EDE): An equivalent dose to the whole body, calculated by multiplying the dose to a particular organ (or collection of organs) by a factor that allows a rough representation of equivalent whole body dose and hence the risk of radiogenic cancer. Electron: An elementary particle carrying one unit of negative electric charge. Its mass is 1/1836th that of a proton. External radiation dose: The dose from sources of radiation outside the body. This is most often from gamma rays, though beta rays can contribute to dose in the skin and other relatively superficial tissues. Gamma radiation: High energy electromagnetic waves, such as those released during radioactive decay of some nuclei. Gamma, the third letter of the Greek alphabet, is written as . Internal radiation dose: The dose to the organs of the body from radioactive material that has entered the body through inhalation, ingestion, or through cuts and wounds. It may consist of any combination of alpha, beta, and gamma radiation caused by incorporated radioactive material. Internal dose also includes indirect ionization cause by neutrons traversing the body. Ionize: To strip one or more electrons from an atom or to break up a neutral molecule, thus leaving the parts as electrically charged particles. Neutral atoms: Atoms that bear no net electrical charge because their negative and positive charges (electrons and protons, respectively) are exactly balanced. At temperatures such as those occurring on Earth, atoms of elements are neutral. Neutron: An elementary particle slightly heavier than a proton, with no electric charge. Free neutrons are unstable, decaying into protons and electrons with a half-life of about 12 minutes. Positron: An elementary particle with a positive electric charge, but in other respects identical with an electron. Proton: An elementary particle with a positive electric charge and a mass that is given the value 1 on the scale of atomic weights. Relative biological effectiveness (RBE): A factor that is used to express the relative amount of biological change caused by a unit of energy deposited by a particular type of ionizing radiation into a specific part of the body. The RBE is complex and organ-specific. Due to its complexity, a simple parameter, called the quality factor, is applied to different types of radiation as a matter of regulatory practice for the purpose of estimating biological damage and the resulting cancer risk.