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Oregon State University

5. Radiation Dose Limits

5.1. Policy

Work with sources of ionizing radiation will be conducted so that doses received by individuals do not exceed the applicable limit, and so that doses are maintained as low as reasonably achievable (ALARA).

5.2. Definitions

5.2.1. Annual limit on intake (ALI) - the derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year.  ALI is the smaller value of intake of a given radionuclide in a year by the "reference man" that would result in a committed effective dose equivalent of 0.05 Sv (5 rem) or a committed dose equivalent of 0.5 Sv (50 rem) to any individual organ or tissue.

5.2.2. Dose equivalent - the product of the absorbed dose in tissue and the quality factor (a value that reflects the biological impact of a particular type of ionizing radiation). Measured in rem or Sievert (Sv).

5.2.3. Occupational dose - the dose received by an individual in a restricted area or while performing assigned duties that involve exposure to sources of radiation.

5.2.4. Member of the public - an individual who is not in a restricted area and who is not performing assigned duties that involve exposure to sources of radiation.

5.2.5. Committed dose equivalent (CDE) - the dose equivalent to organs or tissues of reference that will be received from an intake of radioactive material by an individual during the 50-year period following intake.

5.2.6. Committed effective dose equivalent (CEDE) - the sum of the products of the weighting factors applicable to each of the body organs or tissues that are irradiated and the committed dose equivalent (CDE) to each of these organs or tissues. This is a measure of the overall risk associated with internal deposition of radioactive material.

5.2.7. Eye dose equivalent (LDE) - the dose equivalent to the lens of the eye at a tissue depth of 0.3 cm (300 mg/cm2).

5.2.8. Shallow dose equivalent (SDE) - the dose equivalent at a tissue depth of .007 cm (7 mg/cm2) averaged over 1 cm2; applies to external whole body or extremity exposure.

5.2.9. Deep dose equivalent (DDE) - the dose equivalent at a tissue depth of 1 cm; applies to external exposure.

5.2.10. Total Effective Dose Equivalent (TEDE) - the sum of the deep dose equivalent (DDE) for external exposures and the committed effective dose equivalent (CEDE) for internal exposures.

5.2.11. Total Organ Dose Equivalent, Maximum Organ (TODE) - the sum of the deep dose equivalent (DDE) and the committed dose equivalent (CDE) to the organ receiving the highest dose.

5.3. Occupational Dose Limits for Adults

5.3.1. An annual limit of 5 rem (0.05 Sv) total effective dose equivalent (TEDE).

5.3.2. An annual limit of 50 rem (0.50 Sv) to an individual organ or tissue other than the lens of the eye, as determined by the deep-dose equivalent and the committed dose equivalent.

5.3.3. An annual limit of 15 rem (0.15 Sv) to the lens of the eye.

5.3.4. An annual limit of 50 rem (0.50) Sv) to the skin.

5.3.5. An annual limit of 50 rem (0.50 Sv) to each of the extremities.

5.3.6. The above limits must be reduced by the amount of occupational dose received while employed by someone other than Oregon State University during the current year.

5.4. Occupational Dose Limits for Minors (under age 18)

5.4.1. The occupational dose limits for minors are 10 percent of the above occupational dose limits for adults.

5.5. Dose to an Embryo or Fetus

5.5.1. A limit of 0.5 rem (5 mSv) during the entire pregnancy due to occupational exposure of a declared pregnant woman. The dose equivalent to an embryo/fetus must be taken as the sum of:

5.5.1.1. The deep-dose equivalent to the declared pregnant woman; and

5.5.1.2. The dose equivalent to the embryo/fetus from the radionuclides in the embryo/fetus and radionuclides in the declared pregnant woman.

5.5.2. If the dose equivalent to the embryo/fetus is found to have exceeded 0.5 rem (5 mSv), or is within 0.05 rem (0.5 mSv) of this dose, by the time the woman declares the pregnancy to the licensee, the licensee shall be deemed to be in compliance with subsection (3)(a) of this rule if the additional dose equivalent to the embryo/fetus does not exceed 0.05 rem (0.5 mSv) during the remainder of the pregnancy.

5.5.3. An effort will be made to avoid substantial variation above a uniform monthly dose rate to a declared pregnant woman. The Radiation Safety Officer will investigate any report of a dose in excess of 0.050 rem (0.5 mSv) to a declared pregnant worker within 7 working days of receiving knowledge of the dose.

5.5.4. A woman is not a declared pregnant woman unless she says so in writing without being coerced.  Unless a woman declares her pregnancy, she is to be treated as any other radiation worker.

5.6. Dose Limits for Individual Members of the Public

5.6.1. An annual limit of 0.1 rem (1 mSv) total effective dose equivalent (TEDE)

5.6.2. An hourly limit from external sources of 0.002 rem (0.02 mSv) in unrestricted areas.

5.7. As Low As Reasonably Achievable (ALARA)

In addition to maintaining radiation doses below the limits set forth above, work with sources of ionizing radiation shall be planned and conducted to keep doses as low as reasonably achievable.