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 radiation protection, in particular by providing recommendations and guidance on all aspects of protection against ionising radiation. Follow this link to the ICRP website.

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

This is defined in the UK Ionising Radiations Regulations 2017 (IRR17) as the use of ionising radiation to sterilise, process or alter the structure of products or materials. Often the term 'Industrial Sterilisation' is used to mean the same thing where ionising radiation is used (although non radiation techniques such as ethylene oxide processing could also be defined by the same term). 

When considering the term for use with the UK IRR17,  it represents the primary intention (e.g. sterilisation, cross-linking, polymerisation and similar) - often termed a specified practice (i.e. 'industrial irradiation'). Although use of x-rays for producing an image of an object could in theory have sterilising  / structural changing potential, it would not be treated as industrial irradiation as this is not the primary intention. 

Some typical applications of industrial irradiation

Medical device sterilisation: Large industrial irradiators using radioactive Co-60 (or electron beam / x-ray systems) can deliver high doses in the 10-50 kGy region to sterilise medical consumables, equipment and implant devices (e.g. replacement joints).

Food sterilisation: Large doses of ionising radiation can kill bugs / insects and larvae, slow ripening process, and inhibit sprouting in fruits, vegetables, and grains. It can also be used to kill salmonella bacteria in meat products (particularly in poultry). Food sterilisation does not take place in the UK although ingredients used in UK sold produce may have been irradiated elsewhere in the world. Typically several kGy are used depending on product type. 

Changing the properties of materials (e.g. strengthening): Industrial irradiation can be used to modify the chemical, physical or biological properties of materials. This often uses electron beam systems  - for example flexible rubber pipework can be formed into shape and then 'fixed' (hardened). 

Gemstone colour change: Irradiation using intense electron beams (or gamma rays from Co-60, or neutrons from a nuclear reactor) can be used to alter the colour of gemstones, potentially increasing their value. For example, topaz can be turned from white to pale yellow or blue depending on the irradiation technique. 

Ion Implantation:  Accelerators are often used in ion implantation.  Semiconductor doping and surface finishing are example applications. 

Industrial radiography is the use of ionising radiation in non destructive testing (NDT). NDT is a process where an article is "tested", and in the case of industrial radiography uses ionising radiation (via a radioactive source, x-ray tube or accelerator) to form an image on radiation sensitive film or real time imaging systems, to detect potential or actual defects. Examples of this would include testing for a crack in a gas pipe, a defective pipe weld, integrity of a pressure vessel or similar. The UK IRR17 defines this exactly as follows 'means the use of ionising radiation for non-destructive testing purposes where an image of the item under test is formed (but excluding any such testing which is carried out in a cabinet which a person cannot enter)' (Reg 2-1). Note here the word "test" (of an item). It follows that Industrial Radiography does not include any of the following:

• X-ray screening for security purposes (e.g. in cargo and freight etc)
• X-ray diagnostic imaging or patients (this is a medical exposure - diagnostic radiology).
• X-ray imaging of a painting, museum specimen or similar.
• X-ray of animals (e.g. veterinary x-ray) - note this is not diagnostic radiology as that only applies to medical x-rays of humans.

Note that 'excluding any such testing which is carried out in a cabinet which a person cannot enter' has created some discussion between RPAs, users and the regulators during 2024. 'Where a person cannot enter' is not defined in IRR17 with respect to 'reasonably practicable' (to enter), so could mean 'wherever is possible' (regardless of practicability). More recent discussion with the regulator (HSE) has clarified that this means where 'a cabinet cannot be entered without climbing in to, contorting to access' (and similar). Therefore, whilst IRR17 has not been amended, it is reasonable to assume that 'which a person cannot enter' can be tested by application of reasonably practicable. Therefore, 'testing' in a small cabinet (which cannot be reasonably practicably entered) would not be defined as NDT (IRR17) and would not need a consent. 

For a detailed discussion of industrial radiography, check out the following link (December 2023): Potential occupational, non-occupational and accidental radiation exposures in industrial radiography using radioactive sources.

When ionising radiation is used for industrial sterilisation, the process is a subset of industrial irradiation.  See Industrial irradiation for a more detailed description.  

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 process 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 cornerstones of radiation protection and is used with the Distance Rule. It is not always reliable where the distance between source and measurement position is small compared to the size of the source. Generally, the rule will work mathematically where the distance between the source and the calculation point, is at least 10 times the largest dimension of the source.

If r is the distance from the source, the dose dose (or dose rate) D is proportional to 1/r² as shown below.

\[\text{ D (Dose or Dose rate)}\propto \frac{1}{r^{2}}\]

This can be expanded to consider two dose rates at two different distances in the following form:

\[\frac{D_{1}}{D_{2}}=\frac{r_{2}^{2}}{r_{1}^{2}}\]

Here D₁ is dose rate at distance r₁ and D₂ is dose rate at r₂ (some greater distance from the source). This can be rearranged in several ways, the example below allows us to find D₂ if we known D₁ and both distances r₁ and r₂ .

\[ D_{2}=D_{1}\frac{(r_{1})^{2}}{(r_{2})^{2}}\]

The graphic below is from our radiation protection widget resource where you can see this process interactively.

Try out the inverse square law widget now!

[Updated March 2024]

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 whereby an Atom or molecule gains or loses 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 lead 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 tend to have a slow response time and are susceptible to changes in 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 2017 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 Ionising Radiations Regulations 2017 (IRR17) are a UK statutory law regarding work with ionising radiation. They apply to all UK employers (and the self-employed) and detail the requirements for protecting employees who work with ionising radiation, other person who may be affected and members of the public. Ionactive has produced an online guide to the regulations and can be found here: IRR17 Radiation Protection Guide by Ionactive.

External link to Ionising Radiations Regulations 2017 (IRR17) (2017 No. 1075 on the gov.uk website)

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. This type of irradiation is very different to the x-raying of items for security control where the exposures are much lower (see also Industrial Irradiation which is specifically defined in the UK Ionising Radiations Regulations (IRR17). 

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.