Answer to Question #9895 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I read on the Nuclear Regulatory Commission website: "The dose in any unrestricted area from external sources, exclusive of the dose contributions from patients administered radioactive material and released in accordance with 10 CFR 35.75, does not exceed 0.002 rem (0.02 mSv) in any one hour." If I use a survey meter to measure an area and find that readings exceed 0.02 mSv per hour when the linear accelerator is on, does that mean that the area is not safe for the public? Or do I need to include all the factors like occupancy factor, number of cases per day, and radiation on time for the calculations?
Yes, you do need to take into consideration all the occupancy factors, number of cases per day, and projected or estimated radiation "on" time for the calculations to ensure that no member of the public exceeds 0.02 mSv h-1.
Licensees also must evaluate potential radiation doses received by any individual working in or frequenting restricted areas. All individuals working with or around licensed materials should receive safety instruction commensurate with their assigned duties and, if it is likely that they could receive doses over 1 mSv in a year, they must receive instruction as specified by 10 CFR 19.12. For example, a licensee might determine that housekeeping staff, while not likely to receive doses over 1 mSv, should be informed of the nature of the licensed material and the meaning of the radiation symbol and should be instructed not to touch the licensed material and to remain out of the room if the door to the licensed material storage location is open. Providing minimal instruction to ancillary staff (e.g., housekeeping, security, etc.) may assist in controlling abnormal events, such as loss of radioactive material.
The Nuclear Regulatory Commission has issued guidance in this area that will be of help to you (NUREG-1556, Vol. 6, Consolidated Guidance about Materials Licenses: Program-Specific Guidance about 10 CFR Part 36 Irradiator Licenses and NUREG-1556, Vol. 9, Consolidated Guidance about Materials Licenses: Program-Specific Guidance about Medical Use Licenses).
Cynthia G. Jones, PhD