doses and high dose rates—for example, 100,000 mrad (100 rad) in less than 1 week—may include nausea, diarrhea, fatigue, hair loss, sterility, and easy bruising. In appropriately managed workplaces, such exposures are impossible unless various barriers, alarms, and other safety systems are deliberately destroyed or bypassed. Single-dose exposures higher than 500 rem are probably fatal. A single dose of ~100 rem may cause a person to experience nausea or skin reddening, although recovery is likely. However, if these doses are cumulative over a period of time rather than a single dose, the effects are less severe. Long-term effects, which develop years after a high-dose exposure, are primarily cancer. Exposure of the fetus in utero to radiation is of concern, and the risk of damage to the fetus increases significantly when doses exceed 15,000 mrem. The USNRC has set limits for whole-body occupational exposure at 5,000 mrem/year, with minors and declared pregnant workers allowed only 500 mrem/year (or 9-month gestation period), and members of the public allowed only 100 mrem/year (see Table 4.12). Exposure limits are lower in facilities operated by the U.S. Department of Energy and other agencies. Note that properly managed work with radioactive materials in the vast majority of laboratory research settings can be performed without any increase in a worker’s exposure to radiation.

As with all laboratory work, protection of laboratory personnel against the hazard consists of good facility design, operation, and monitoring, as well as good work practices. The ALARA (as low as reasonably achievable) exposure philosophy is central to both levels of protection. The amount of radiation or radioactive material used should be minimized. Exposures should be minimized by shielding radiation sources, laboratory personnel, and visitors and by use of emergency alarm and evacuation procedures. The amount of time spent working with radioactive materials should be minimized. Physical distance between personnel and radiation sources should be maximized, and whenever possible, robotic or other remote operations should be used to reduce exposure of personnel. (Also see Chapter 6, section 6.E.)

TABLE 4.12 U.S. Nuclear Dose Limits Regulatory Commission


Area of Dose

Occupational Dose Limits (mrem/year)

Public Dose Limits (mrem/year)


Total effective dose equivalent (or whole body: external + internal)

5,000

100*

Committed dose equivalent (or any organ dose)

50,000

NA

Eye dose equivalent (or lens of the eye)

15,000

NA

Shallow dose equivalent (or skin dose)

50,000

NA

Extremity dose (or shallow dose to any extremity)

50,000

NA

Minor (less than 18 years of age)

10% of occupational limits for adults

NA

Embryo/fetus of declared pregnant woman (limit taken over time of pregnancy)

500

NA

Personnel dosimetry is required if occupational dose is likely to exceed 10% of the limit (for embryo/fetus, it is required if worker’s dose is likely to exceed 100 mrem during gestation period)


*NOTE: For 10 CFR § 35.75 patient release, limit is 500 mrem.



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