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:

Q

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.

A
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.
Answer posted on 4 August 2010. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.