Answer to Question #9121 Submitted to "Ask the Experts"
Category: Medical and Dental Equipment/Shielding — Equipment
The following question was answered by an expert in the appropriate field:
I am a student studying medical physics. Regarding shielding of a linear accelerator, I want to know if there is any maximum permissible dose rate limit for the general public in an uncontrolled area.
In the United States we typically follow the Nuclear Regulatory Commission
regulations 10 CFR 20 (CFR = Code of Federal Regulations) for shielding. For the general public in unrestricted areas the following requirements hold:
The dose in any unrestricted area from external sources, exclusive of the dose contributions from patients administered radioactive material and released in accordance with § 35.75, does not exceed 0.002 rem (0.02 millisievert) in any one hour.
Thus, instead of the concept of instantaneous dose rate, the concept of integrated dose in one hour is used. Having said that, I will point out that there are a few exceptions where some states use an instantaneous dose rate of 0.02 millisievert h-1.
Nisy Elizabeth Ipe, PhD, CHP
Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table
. You can also view a diagram
to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here
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