Dose

For the purpose of radiation protection, individuals may be classified in one of two groups: radiation worker*or member of the public. The former group refers to individuals exposed to ionizing radiation during the course of their work, excluding medical and natural background ionizing radiation exposures. The latter group refers to those individuals who are not radiation workers. The following table summarizes the 1991 ICRP recommended dose equivalent limits for ionizing radiation.

Maximum permissible dose equivalent

Limits in a year

Applicable body organ or tissue

Radiation worker

Member of the public

Whole body

20 mSvc

1 mSv

Lens of the eye

150 mSv

15 mSv

Skin (1 cm2)

500 mSv

50 mSv

All organs

500 mSv

  • These limits are intended to prevent deterministic effects by keeping doses below the relevant threshold, and to reduce the incidence of stochastic effects to acceptable levels by demanding that all reasonable steps be taken to lower doses. For further details, consult the source ICRP 1991
  • For women who are or may be pregnant, the fetus must be protected from radiation exposure once pregnancy has been diagnosed. For the remainder of the pregnancy, the dose equivalent limit from radiation sources external to the body is 2 mSv applied to the surface of the abdomen, and the limit for radionuclides taken internally by the body is 1/20th of the allowable annual intake. If a woman is exposed to both internal and external sources, both limits apply separately and the total limit shall not exceed 1 mSv (since the fetus is considered a member of the public).
  • While dose equivalents up to 50 mSv may be permitted in a single year for special circumstances, a total limit of 100 mSv over a five-year period is recommended by the ICRP. This translates into an average annual limit of 20 mSv y-1.
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