Radiation Exposure

In order to understand the concepts of radiation exposure and measurement, a few simplified terms should be explained. For purposes of measuring occupational radiation exposure, the standard unit is the rem. The rem is a measurement of radiation dose to a human that attempts to account for variations in radiation type, energy, and the type of tissue exposed. Other units are used to define this concept - the roentgen (R), and the rad. Technically, these units describe the quantities of exposure and absorbed dose, respectively. Since this booklet focuses only on radiation as it affects workers, the rem will be used to describe all concepts of radiation exposure, absorbed dose, and dose equivalent.

In the State of California, limits are placed on the amount of radiation to which an employee may be exposed. These limits are found in the California Code of Regulations (CCR), Title 17. These regulations are compatible with the national regulations from the Nuclear Regulatory Commission found in Chapter 10 of the Code of Federal Regulations, Part 20 (10 CFR 20). The limits are listed in Table 1.

Table 1. Occupational Dose Limits

It should be noted that exposure to the embryo/fetus is limited for declared pregnant women only. In order for the embryo/fetal dose limit to apply, a pregnant worker must notify her employer in writing. Please contact the Office of Radiation Safety for instruction in this matter.

Since most personnel exposure is less than one rem, it is often more convenient to use a smaller increment, most commonly, the millirem (abbreviated mrem).

1 rem = 1000 mrem

Reports of personnel exposure from the Office of Radiation Safety are listed in mrem.

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