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 term 'Background' can be applied to either natural 'Background Radiation', or anywhere where a measurement of Ionising Radiation is required. In analytical Contamination and Radiation measurements it is usual to subtract the background count from the source counts of interest.

    Background Radiation

    Ionising Radiation in our environment which we are all exposed to, the exact magnitude depending on our location in the world. Examples include Radon Gas, Cosmic Rays and K-40.


    The SI unit for Activity. The Becquerel (Bq) is equivalent to 1 disintegration per second (dps) . Also see the older unit of activity, the Curie.

    Beta Particle

    The beta particle has the form of a high speed negatively charged electron (or a positively charged electron in the case of the positron). In beta decay (electron emission) a neutron in the nucleus is converted to a proton with the release of a high speed electron and an anti neutrino. For example, C-14 decays to N-14 and the atomic number has increased by one whilst the mass number at 14 is unchanged. The beta particle is more penetrating than alpha particles but still much less so than gamma rays or x-rays. For every beta emitter there is a unique energy spectrum characterised by average and maximum beta energy. For Tritium (H-3) this is around 18.5 KeV, for C-14 its 156 KeV and for P-32 it is about 1.7 MeV.

    Biological Dosimetry

    Biological dosimetry is a branch of the field of Dosimetry which uses biological samples, usually taken from individuals who have been exposed to radioactive materials, as a means to assess intakes by Inhalation and Ingestion. For example analysis of urine can be used to assess Tritium uptake whilst analysis of faecal matter can be used to determine Actinide uptake. Biological sampling can also be used to assess direct body Irradiation from External Radiation hazards.

    Biological Half-Life

    The biological half-life is the time taken for half of a Radioactive material, (present in a body as a result of Inhalation, Ingestion, Injection or Absorption), to be eliminated by the biological processes in that body.


    Brachytherapy is a type of cancer treatment where Radioactive seeds (Sealed Sources) are placed in or near a tumour, therefore giving a high Radiation Dose to the tumour while minimising the radiation exposure in the surrounding healthy tissues. Years ago the sources would be manual placed into the tumour site by using tweezers or a needle, where as modern techniques place the source remotely using an afterloader unit.

    Braking Radiation

    See Bremsstrahlung radiation.


    Bremsstrahlung, also known as Braking Radiation occurs when ever a charged particle undergoes a change of velocity as it interacts with an absorber. Electromagnetic Radiation (X-Rays) are the result. For Radiation Protection purposes, Bremsstrahlung radiation resulting from the interaction of fast moving Electrons (Beta Particles) with shielding materials, are of particular concern. Here, the degree of conversion to Bremsstrahlung radiation and the magnitude of its energy is proportional to the incident electron energy and the atomic number of the absorber. Hence shielding for high energy Beta emitters like P-32, needs low atomic number material such as Perspex.

There are children playing in the street who could solve some of my top problems in physics, because they have modes of sensory perception that I lost long ago.

– J. Robert Oppenheimer -