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.

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For formal advice, see our Radiation Protection Adviser pages. 


In general terms, LD-50 is used as an index to describe effectiveness of some entity producing a response in a subject, where that response occurs in 50% of the subjects. In Radiation Protection it is commonly used to describe the value of Absorbed Dose in humans which would lead to Deterministic Effects and therefore radiation sickness (leading to death without medical intervention). The quantity varies depending on the literature but is likely to be between 3 and 5 Gray (Gy) (with some variance related to medical treatments).

In the beginning, there was nothing, which exploded

– Terry Pratchett -