Naturally occurring radiation comprises radiation from outer space (known as cosmic radiation), from the ground and from the air (referred to as radon). Small amounts of naturally occurring radiation are also present in the food we eat. Natural radiation accounts for 85.5% of the total radiation received by the UK population. This belongs to a class of radiation known as electromagnetic radiation which transports energy through space in the form of electric and magnetic waves. Electromagnetic radiation is encountered in our day‐to‐day lives; in fact, life as we know it would not be possible without electromagnetic radiation.

Electromagnetic radiation provides radio and television signals, microwaves, visible light, X‐rays and gamma rays. It is well known that, as well as providing many benefits, there are potentially serious health effects associated with electromagnetic radiation. The nature of these effects varies depending on which part of the spectrum the radiation belongs to. Radiation may also be encountered in the form of particles, rather than waves. Particulate radiation is capable of producing ionization and can therefore produce biological effects. The radiation particles most commonly used in hospitals are streams of electrons, known as beta radiation.

Artificial sources of radiation, including medical exposures, discharges from industrial premises and fall‐out from atomic weapons testing, make up the remaining 14.5% of the radiation received by the population. Of these, medical exposures are the largest contributor.

Radiation is capable of disrupting the chemical balance in the cell by damaging the DNA. This is caused by the introduction of free radicals – atoms/molecules with unpaired electrons (HPA [27]) – that may lead to cell death or cancer at some time in the future. Therefore, substantial emphasis is placed on reducing the amount of radiation given during medical exposures.

Radiation is used in treating malignant disease and includes: X‐rays produced artificially by electron bombardment of a metal target; gamma rays (a natural emission in the nuclear decay of radioisotopes), sometimes referred to as ‘photon’ radiation; and beta particles (capable of ionization). These are distinguishable from electromagnetic radiation by their characteristic of carrying a negative electrical charge. Beta particles result when a neutron within the nucleus disintegrates to form a proton and an electron. The electron is ejected from the nucleus, producing beta radiation (IPEM/RCN [31]).

Radiation used in nuclear medicine, in laboratory tests and for certain types of radiotherapy treatments is emitted by specific radioactive materials. In a process known as radioactive decay, the amount of radiation emitted by a radioactive material diminishes continuously over time until the material no longer produces radiation.

The time taken for the radioactivity in a radioactive material to be halved is known as the half‐life. Different materials have different half‐lives, ranging from a few seconds or minutes to many years. Most radioactive materials used within hospitals have relatively short half‐lives and so diminish to insignificant levels within a few hours or a few days (HPA [27]).

Radioactive material may be encountered in solid (sealed), liquid or gaseous form (unsealed). Liquid or gaseous radioactive materials have the important advantage that they can be used in vivo to study metabolic processes. As radioactive materials emit radiation in all directions, they are usually kept in lead containers for safety.

Ionizing radiation is the term used to describe energetic particles (e.g. alpha, beta) or electromagnetic waves with a wavelength of no more than 100 nanometres because they are capable of producing ions by ejecting electrons from their atoms (DH [15]).

Radioisotopes are measured in becquerels (Bq). A becquerel is the Système International (SI) unit of activity and is 1 disintegration per second:

The half‐life of a radioactive substance is the time taken for it to decay to half its original number of radioactive atoms (Bomford [7]). The sensitive target appears to be DNA in the nucleus of the cell. The ionizing radiation passes through the cells and tissues, and the dose of radiation received is measured in terms of energy absorbed. The unit of absorbed dose is known as a gray:

For the purposes of radiation protection for staff and patients, the dose calculated to the whole body must be known. Whereas the absorbed dose is measured in grays, the dose to the whole body is measured in sieverts. For example, staff over 18 years of age who are not pregnant must wear a monitoring badge to monitor their individual exposure to radiation. There is an annual dose limit of 20 millisieverts (mSv), but the dose to staff should be kept below 6 mSv (DH [15]). In practice, any person being exposed to over 5 mSv in the UK will be a classified worker (IRMER [35]).