Radiation Protection Glossary

A radiation protection glossary for Radiation Protection Supervisors (RPS), Radiation Protection Advisers (RPA) and anyone else interesting in radiation safety terms and definitions. The glossary is a mixture of health physics , phrases related to radiation protection legislation, transport, practical safety, technical terms and similar.

Search the Glossary by either clicking on a letter or typing a keyword into the search box. This glossary is relational so when looking at one term you can click through to other related terms as required.

For formal advice, see our Radiation Protection Adviser pages. 


The positron has properties which are identical to those of a negatively charged Electron, except that it has a positive charge. Positrons are unstable in matter and disappear by Annihilation with negatively charged electrons. This produces two photons, each of 0.511 MeV which move in opposite directions. In simple terms positron emitters (e.g. O-15 and F-18) decay by a Proton changing into a Neutron and releasing a positron. One can say that the Nucleus of the parent has too much energy, but not enough to release an Alpha Particle and so releases a positron instead.

What's the matter? What's the antimatter? Does it antimatter?

– Wes Nisker -