Radiation Protection Glossary

The rad is the old (non SI) unit for Absorbed Dose , where 100 rad = 1 Gray (Gy). It follows that the rad represents an energy absorption of 0.01 Joules / kg of absorbing medium.

Radiation is a general term for energy which radiates out from a source and which can be particulate or part of the Electromagnetic spectrum . It is more useful to specify the quality of the radiation, for example Ionising Radiation or Non-Ionising Radiation .

Radiation Protection is a general term applied to the profession / science related to protecting man and the environment from Radiation hazards. Strictly speaking it should represent all forms of radiation (e.g. Ionising and Non-Ionising ) but is mostly applied to ionising radiations. See Health Physics for related definition.

A Radiation Protection Adviser (RPA) is a title used in the UK and is given to those who are competent to advise radiation employers on the safe and compliant use of Ionising Radiations . The post is a legally recognised position and is a requirement of the Ionising Radiations Regulations 1999. The RPA needs to be appointed by the radiation employer in writing, where the scope of the advice required is clearly defined. The radiation employer also needs to determine if the RPA is suitable to advise on the types of sources of ionising radiation being used. The RPA is required to show the radiation employer that they are 'competent' to be a RPA, this competence being formally and legally recognised (e.g. by RPA2000).

The Radiation Weighting Factor is used to modify the Absorbed Dose (Gray ) by multiplying to obtain a quantity called the Equivalent Dose (Sv ). It is defined by the ICRP and used because some types of radiation, such as Alpha Particles , are more biologically damaging internally than other types such as the Beta Particle . The factor is similar to the Quality Factor determined by the US Nuclear Regulatory Commission (NRC).

Radioactive can generally describe the property of a substance (or more accurately atomic nuclei) which are unstable and spontaneously Decay (disintegrate) with the release of energy, the energy being either Electromagnetic Radiation , particulate or both. This process may occur in both naturally occurring radioactive material and man made substances. For any given element there will be a number of Isotopes , some of which may be radioactive. The point at which a substances can be said to be radioactive requires careful interpretation of law and may depend on particular circumstances. For example, in the UK, material with an Activity < 0.4 Bq / g is not considered radioactive (Radioactive Substances Act 1993).

Radioactive decay describes the process where by Radioactive substances decay spontaneously with the release of energy in the form of Electromagnetic Radiation or particulate radiation. The rate of radioactive decay will depend on the Half-Life .

For the purposes of Radiation Protection , radioactive waste can be defined as any Radioactive substances which is no longer required and has no further useful purposes. There are some exact definitions, some which relate to legal meaning. For example, in the Radioactive Substances Act 1993, radioactive waste is define as '...a substance or article which, if it were not waste, would be radioactive material...' or '...a substance or article which has been contaminated in the course of the production, keeping or use of radioactive material, or by contact with or proximity to other waste..'. See Low Level Waste (LLW).

A radionuclide is a type of Nuclide which is Radioactive and will undergo spontaneous Radioactive Decay.

Radium consists of 16 isotopes, the most abundant being the Radioactive Radium-226. This is a metallic substance, has a Half-Life of 1602 years and Decays via a complicated chain, eventually leading to stable Lead-206. Along the way it decays to Radon Gas (Rn-222). Radium was isolated from pitchblende in 1898 by Marie and Pierre Curie. The activity of 1g of radium was used to define the activity unit, the Curie (Ci). Radium is difficult to shield needing significant quantities of lead. In addition, radium contaminated dust is a particular inhalation hazard due to its abundant Alpha Particle decay.

Radon is a naturally occurring Radioactive gas which is derived from the Uranium and Thorium decay series. Radon (Rn-222) is a colourless, odourless, dense and chemically un-reactive substances and is the daughter of radium within the above described series. It can be found in houses and workplace, more so where the ground contains Uranium decay series bearing rocks (e.g. granite). Radon is considered a health hazard because it decays to solid daughter products with the emission of Alpha Particles . For example, Rn-222 decays with a Half-Life of 3.8 days to Polonium-218, which itself then decays again (with a smaller half life of 3 minuets) by an alpha particle to Lead-218. The decay series continues until stable Lead-206 is formed.

The term Reasonably Foreseeable is used in a number of areas of Radiation Protection , including Risk Assessment , Safety Cases and Probabilistic Safety Assessments (PSA) . Reasonably foreseeable can be taken to mean an incident or accident which is thought to be Credible . It can be expressed numerically and this value will differ depending on the situation being assessed (but perhaps in the range of 10-5 to 10-6). The term does not appear to be defined exactly in legislation and there is certainly an interchange in interpretation with 'Credible'.

The rem is the old unit of Equivalent Dose (or more accurately Dose Equivalent ) and is derived by multiplying Absorbed Dose (in Rads ) by a Quality Factor . The modern SI unit is the Gray (Gy). 1 Gy = 100rem. See equivalent dose for a explanation of why the absorbed dose is modified to reflect the relative effectiveness of Ionising Radiations in causing biological damage.

In general terms risk can be defined as the potential for unwanted, adverse consequences to human life, property, health, environment or society. The calculation (or estimation) of risk is usually based on the Probability of the event occurring multiplied by the consequence of the event given that it has occurred. In order to do this a Risk Assessment has to be made which looks at all the hazards, severities and conditional probabilities.

With respect to Radiation Protection , risk assessment is essentially about assessing risk of radiation exposure in order to mitigate that exposure, ensuring doses are as low as reasonably practicable (ALARP ) and certainly below Dose Limits . In the UK risk assessment is a requirement of Regulation 7 of the Ionising Radiations Regulations 1999. A basic risk assessment requires that the radiation hazards are identified, an assessment of what can go wrong to realise those hazards is made, prediction of how likely something will go wrong and produce the hazard, and finally what are the consequences of the radiation exposure. Radiation risk assessments can be simple or complicated depending on the circumstances.

RPA2000 is a non profit making company set up by The Society for Radiological Protection; The Institute of Physics and Engineering in Medicine; the Institute of Radiation Protection and the Association of University Radiation Protection Officers (the Societies), solely for the purpose of certifying competence in Radiation Protection practice. Certification is intended for members of the Societies however it is also open to non-members practicing in the United Kingdom.