General · EdgepediaSeptember 17, 20265 min read

Radiation protection

Radiation protection, also known as radiological protection, is the science and practice of protecting people and the environment from the harmful effects of ionizing radiation, which is widely used in industry and medicine and can damage living tissue at a microscopic scale. The field is organized internationally through the International System of Radiological Protection, developed and maintained by the International Commission on Radiological Protection (ICRP), whose recommendations national regulators incorporate into law.¹ Its governing principles are justification, optimization (ALARA/ALARP), and dose limitation; justification and optimization apply across planned, emergency, and existing exposure situations, whereas dose limitation applies only to planned exposure situations, excluding patients' medical exposure.¹ Dose limits include 20 mSv per year averaged over five years for workers, with no more than 50 mSv in any single year, and 1 mSv in a year for members of the public, while the European Union's basic safety standards directive exempts medical exposures from dose limits.²^•³

Exposure may come from a source outside the body or from internal irradiation after radioactive material is inhaled or ingested.

Key fact	Detail
Governing principles	Justification, optimization (ALARA/ALARP), and dose limitation¹
Exposure situations	Planned, emergency, and existing¹
Occupational dose limit	20 mSv per year averaged over five years, with no more than 50 mSv in any single year²
Public dose limit	1 mSv in a year²
Medical exposure	Dose limits do not apply to medical exposures under the EU basic safety standards directive³
Basis	ICRP Publication 103 (2007 Recommendations), which replaced the 1990 Recommendations¹

Health effects to be controlled

Ionizing radiation is widely used in industry and medicine and can damage living tissue at a microscopic scale. Two categories of health effect drive the protection system. At high doses, tissue effects (also called deterministic effects) have a threshold dose below which they are not expected, and their probability and severity generally increase as the dose rises above it; these are conventionally indicated by the unit gray and include acute radiation syndrome.

The three principles of protection

ICRP Publication 103, the 2007 Recommendations that formally replaced the 1990 Recommendations, maintains three fundamental principles: justification and optimisation apply to all controllable exposure situations, while dose limitation applies only to planned exposure situations, excluding medical exposure of patients.¹

Justification permits no unnecessary use of radiation: the advantages of a practice must outweigh its disadvantages. Optimisation applies to practices that have been justified. It requires that the likelihood of incurring exposures, the number of people exposed, and the magnitude of individual doses be kept As Low As Reasonably Achievable (ALARA), or As Low As Reasonably Practicable (ALARP) in UK usage, taking economic and societal factors into account.

The system also allows increased doses when justified, for example in medical imaging or radiotherapy, to achieve the best possible outcome for the patient.⁴ Consistent with this, dose limits in the European Union's basic safety standards directive do not apply to medical exposures.³

Exposure situations

The ICRP recognizes three categories of exposure situation.¹

Planned exposure situations are those where protection can be planned in advance, before exposures occur, and the magnitude and extent of exposures can be reasonably predicted; occupational work in a known radiation environment is the typical case.
Emergency exposure situations are unexpected situations that may require urgent protective actions, such as a nuclear accident.
Existing exposure situations already exist when a decision on control must be taken, for example exposure to naturally occurring radioactive materials in the environment.

Dose limits are situational.

Dose limits in regulation

In European Union law, Council Directive 2013/59/Euratom sets the occupational limit at 20 mSv in any single year, with a higher effective dose of up to 50 mSv authorized in special circumstances or for certain exposure situations specified in national legislation, provided the five-year framework is respected, and requires Member States to set the public limit at 1 mSv in a year.³ The directive requires a radiation protection system based on justification, optimization, and dose limitation, and defines clearance and exemption levels, the thresholds below which materials containing radionuclides may be released from regulatory control.³

The pathway from recommendation to enforceable rule runs through national authorities. The Basic Safety Standards, first issued by the IAEA in 1962 and revised in 1996, are based primarily on the ICRP system of radiological protection,⁶ and most countries apply these standards in their own legislation and regulatory requirements.² The 2014 revision of the International Basic Safety Standards was co-sponsored by the World Health Organization among other agencies.⁵

Reducing dose in practice

Fundamental to protection is the avoidance or reduction of dose using three simple measures: time, distance, and shielding. Reducing the duration of exposure reduces effective dose proportionally; increasing distance from the source reduces dose according to the inverse square law; and placing absorbing material between source and person attenuates the radiation.

Internal exposure arises through four pathways: inhalation of airborne contaminants such as radon gas and radioactive particles, ingestion of contamination in food or liquids, absorption of vapors such as tritium oxide through the skin, and injection of medical radioisotopes such as technetium-99m.

The optimization principle is illustrated in radiology. Medical radiation aids diagnosis and treatment, but patient exposure should be kept low enough that the statistical probability of stochastic effects stays below an acceptable level and deterministic effects such as skin reddening or cataracts are eliminated.

References

Topic: Encyclopedia › Physical world and mathematics › Physics › Physics methods, practice, and community › Applied and interdisciplinary physics › Medical and health physics › Health physics and radiation protection › Regulatory dose limits and protection standards

Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026 · Edited: Sep 30, 2026; Oct 15, 2026; Oct 25, 2026 · Last review: Sep 30, 2026

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