This section contains the following information:

Topic

External Radiation Dose Limits

Internal Radiation Dose Limits

Personnel Dosimetry

External Radiation Dose Limits

The USDA has adopted the external radiation dose limits in 10 CFR Part 20 as the limits for its radiation safety program. These are as follows:

- Annual Occupational Dose for a Radiation Worker

Whole Body (Head, Trunk, Upper Arms, and Thighs)                                                 5.0 Rems

[Total Effective Dose Equivalent]

Lens of the eye                                                                                                     15.0 Rems

[Eye Dose Equivalent]

Skin or an Extremity                                                                                             50.0 Rems

[Shallow Dose Equivalent]

- Annual Occupational Dose for a Minor

The annual dose limits for a minor working in a restricted area are 10% of the doses for an adult radiation worker. This is 0.5 Rems or 500 millirems for a whole body dose.

- Annual Dose for an Embryo-Fetus

The dose to an Embryo-Fetus, as a result of an occupational exposure of its mother, shall not exceed 0.5 Rems during the entire period of gestation.
 

- Annual Occupational Dose for a Declared Pregnant Worker

A woman who works in an area that is restricted for purposes of controlling radiation exposure, may, upon learning that she is pregnant, declare her pregnancy in writing to her supervisor, and request that the dose limits for the Embryo-Fetus apply to her for the duration of her pregnancy.

When this occurs, the supervisor must contact the LRPO and the RSS to obtain proper guidance and assistance in implementing this request, and maintain records of actions taken to meet the dose limit of 0.5 Rems.

Specific guidance can be found in the Technical Bulletin "Radiation Safety Considerations for the Declared Pregnant Worker".

Internal Radiation Dose Limits

The radiation dose from the inhalation or ingestion of radioactive materials must also be considered in the USDA Radiation Safety Program.

The Nuclear Regulatory Commission places limits on the amount of radioactive materials that a radiation worker can take into their body over the course of a working year. This is called the Annual Limit on Intake (ALI). These values have been calculated for several radioisotopes and are listed in 10 CFR Part 20, Appendix B.

If a radiation worker receives 1 ALI, the calculated radiation dose from that intake will be 5 rems. This dose is called the Effective Dose Equivalent.

Currently, only the thyroid dose is actively monitored by the Radiation Safety Staff. Worksheets have been developed to measure the uptake of radioiodine in the thyroid, and using standard tables, the whole body effective dose equivalent is estimated.

Regulations require that the total external and internal radiation dose to a worker not exceed 5 rems in one year. The sum of these doses is called the Total Effective Dose Equivalent.

Personnel Dosimetry

Personnel monitoring for radiation exposure is not required as part of the USDA broad scope radioactive materials license, but is a requirement for all irradiator operators.

Through years of monitoring, the USDA has determined that no individual working with radioactive materials or with radiation emitting equipment is likely to receive in excess of 10% of the annual dose limits.

Radiation monitoring is required when an individual's radiation exposure is likely to exceed 10% of the dose limit, when a new activity is being initiated, or when there is no other method that can adequately determine a dose in an accident situation.

NOTE: For more detailed information on dosimetry, refer to the USDA Permit Condition for Personnel Monitoring in Section 6.1.