Chapter 10.1. Introduction

Ionizing radiation is defined as radiation that by its nature and energy has the capacity to interact with and remove electrons from (i.e. ionize) the atoms of substances through which the radiation passes. Sufficiently energetic radiations may cause permanent changes in the nuclei of the atoms of the substance. Radiation may be propagated in the form of electromagnetic radiation (X-rays and γ-rays) or particles (β and α particles, neutrons, protons, and other nuclear particles).

In the list of definitions that follows SI units will be used. The relation between these SI units and the earlier system of units is given in Table 10.1.1.

The energy per unit mass imparted to matter by ionizing radiation at the place of interest [SI unit = gray (Gy)].

The number of nuclear transformations per unit time occurring in a radionuclide.

Protection against ionizing radiations such that the radiation doses received by an individual from internal or external sources, or both, are as low as reasonably achievable and do not exceed the maximum levels given in Table 10.1.2.

Ionizing radiation other than that to be measured, but which contributes to the quantity being measured.

The SI unit of activity 1 Bq corresponds to one nuclear transformation per second. It replaces the curie (Ci).

An area where the occupational exposure of personnel to radiation or radioactive material is under the supervision of a designated radiation safety officer.

Product of absorbed dose and quality factor (Subsection 10.1.1.24). This enables the dose received by individuals to be expressed on a scale common to all ionizing radiations. Where the term `dose' is used without qualification it is implied that `dose equivalent' is meant.

A measure of the radiation at a certain place based on its ability to produce ionization in air. [SI unit = coulomb kg⁻¹. It replaces the röntgen (R).]

Ionizing radiation received by the body from sources outside the body.

A closed box having polymer gloves and viewing ports that is used to enclose completely radioactive materials whilst being manipulated.

The SI unit of absorbed dose. [SI unit = 1 J kg⁻¹. It replaces the rad.]

The period of time in which half the nuclei in a given sample of a particular radionuclide undergo decay.

Radiation received from the body from sources within the body.

Apparatus capable of producing ionizing radiation.

All radiation except the useful beam coming from within a protective housing.

The amount of any radionuclide or mixture thereof that is permitted under statutory regulations.

The concentration of a radionuclide in the air when breathed or water when ingested that would result in an individual receiving the maximum permissible dose (to the whole body or to a specific organ depending on the radionuclide in question).

Ionizing radiation received by the body from natural sources (cosmic radiation or naturally occurring radionuclides).

Effects on a biological system in which the severity of the effect varies with the dose and for which a threshold is likely to occur.

A species of atom characterized by the number of protons and neutrons in its nucleus.

An area that may be occupied by personnel and where a radiation hazard may exist.

A housing of an X-ray tube or of a sealed source intended to reduce the leakage radiation to a specified level.

A non-dimensional factor used to reduce the biological effects of radiation to a common scale (see Table 10.1.3).

A laboratory in which irradiating apparatus or sealed radioactive sources are used or stored. It does not contain any unsealed radioactive material.

The contamination of any material, surface or environment, or of a person by radioactive material.

Any substance that consists of, or contains any, radionuclide provided that the activity of such material is greater than 0.1 Bq kg⁻¹.

A laboratory in which unsealed radioactive material is used or stored. It does not contain any irradiating apparatus.

The potential danger to health arising from exposure to ionizing radiation.

A laboratory in which unsealed radioactive material and/or sealed radioactive material or irradiating apparatus is used or stored.

Species of atom that undergoes spontaneous nuclear transformation with consequent emission of corpuscular and/or electromagnetic radiations.

The toxicity attributable to ionizing radiation emitted by a radionuclide (and its decay products). It is related to both radioactivity and chemical effects.

Any radioactive material firmly bonded within metals and sealed in a capsule or similar container of adequate mechanical strength so as to prevent dispersion of the active material into its surroundings under foreseeable conditions of use and wear.

The SI unit for dose equivalent.

Effects on a biological system in which the probability of an effect occurring rather than its severity is regarded as a function of dose without threshold.

A source that is not a sealed source and that can produce contamination under normal conditions.

That part of the primary and secondary radiation that passes through the aperture, cone, or other device for collimating a beam of ionizing radiation.

In laboratories using ionizing radiations, a clearly defined chain of responsibility has to be established with the employer accepting the responsibility for the provision of services and equipment for the implementation of radiation-protection procedures under whatever legal or administrative procedures are valid for the country in question.

The radiation safety officer (RSO) is responsible for the controlled areas within a given establishment. He (or she) is responsible to his employer for the implementation of a radiation-protection programme. His duties will vary according to the legislation and administrative arrangements applicable to his institution but will include, inter alia:

In English common law, the employer is responsible for the actions of his employees but this does not absolve personnel from a duty of care to their fellows. Ultimately, the responsibility for radiation protection lies with the worker concerned. He (or she) should:

Two classes of people are envisaged:

In Table 10.1.2, the maximum primary dose (MPD) for those in class (i) and class (ii) is tabulated. SI units are shown in bold type, and the earlier units are shown in parentheses in light type.

Planned special exposures are permissible in emergency circumstances provided that in any single exposure twice the annual dose limit is not exceeded, and in a lifetime five times the limit.

Also, to allow for the different biological effectiveness of different types of radiation, the quality factor listed in Table 10.1.3 is applied to determine the dose.