Radiation Protection Glossary

The International Commission on Radiological Protection (ICRP) is an independent registered charity, established to advance, for the public benefit, the science of radiological protection, in particular by providing recommendations and guidance on all aspects of protection against ionising radiation . A link to the ICRP can be found in our links section.

An immersion source represents a 'cloud source' or similar where the body being exposed (e.g. a person) is effected because they are immersed in the activity. Exposure can occurred from direct radiation (e.g. External Radiation hazard) of by breathing in the activity (Internal Radiation hazard).

With respect to Radiation Protection , ingestion describes one possible mode by which Radioactive materials may enter the body and therefore present an Internal Radiation protection hazard. Ingestion may occur where ever loose Contamination exists, either in the work place, where it can be picked up on the hands and transferred to the mouth, or in the environment where foodstuffs are contaminated.

With respect to Radiation Protection , inhalation describes one possible mode by which Radioactive materials may enter the body and therefore present an Internal Radiation hazard. Inhalation can occur where the radioactive material is airborne, volatile or being processed in such a way as to make the inhalation route possible.

With respect to Radiation Protection , injection describes a route by which Radioactive materials may enter the body - thus presenting an Internal Radiation hazard. Injection routes can obviously occur where needles are used to handle or administer radioactive materials, but may also be present where any sharp object is contaminated with radioactive materials which then causes a wound.

The internal radiation (hazard) exists where radioactive materials enter the body. The materials can enter via inhalation, ingestion, absorption or injection. Once in the body they will enter the systemic system where they will then migrate to the organs of accumulation (for example I-125 will go to the thyroid and Ca-45 will migrate to the bone). The actual radiation dose delivered will depend on the radioactive nature of the material (its half-life and principal emitters) and its physical and chemical properties (its particle size and the biological half-life).

The inverse square law applies to any entity which radiates out from a point in space (see Point Source and Fluence Rate to expand on this concept). With respect to Radiation Protection , the law says if you double your distance from a source of Ionising Radiation you will reduce your exposure by 4. It follows that if you triple your distance from the source the exposure will reduce to 1/9 of the original value. This concept is one of the corner stones of radiation protection and is used with the Distance Rule. It is not reliable where the distance between source and measurement position is small compared to the size of the source.

An ion is a charged Atom or molecule. The ion is charged because the number of Electrons do not equal the number of Protons in the atom or molecule. If the atom or molecule contains an excess of electrons it will be negatively charged (e.g. OH-) where as if it is depleted in electrons it will have a net positive charge (e.g. H+).

Ion pairs are created when an Atom or molecule undergoes the process of Ionisation . They either loose or gain Electrons leading a net positive or negative charge. In simple terms, if water (H2O) undergoes ionisation it will form OH- and H+ ions (an ion pair).

Ionisation is the process where by an Atom or molecule gains or looses an Electron and thus becomes an Ion . Ionising Radiation has sufficient energy to be able to ionise atoms and molecules and thus produce ions.

The ionisation chamber is a device designed to measure Ionising Radiation exposure. In simple terms it consists of a chamber which may either be sealed (containing a gas) or vented to free air. Within the chamber are two electrodes to which a high potential difference (voltage) is applied. If an ionisation event occurs within the chamber it will create an Ion Pair within the fill gas. These ion pairs will migrate to the respective positive and negative electrodes which leads to a reduction in current which, can be detected and measured within external circuitry. Air-filled chambers made of tissue equivalent materials are particularly useful for measuring body radiation exposure (Absorbed Dose ). They they tend to have a slow response time and are susceptible to changes of climate.

Ionising radiation can be described in a number of ways - the simplest being that it consists of Gamma Rays , X-Rays , Alpha & Beta particles and other heavy Ions which have sufficient energy to cause ionisation in materials through which they interact . A less useful (but correct) definition can be found in the Ionising Radiations Regulations 1999 which states 'means transfer of energy in the form of particles or electromagnetic waves of a wavelength of 100 nanometers or less or a frequency of 3 E15 hertz or more capable of producing ions directly or indirectly'.

The process by which an article or body is exposed to a source of Ionising Radiation (either deliberate or by accident). A deliberate type of irradiation uses Gamma Rays or Electron beams to sterilize medical or food products.

An isotope represents Atoms of the same Element that have the same number of Protons but a different number of Neutrons . They therefore have different Atomic Masses but the same chemical properties. A radio-isotope is an isotope which is Radioactive .