United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

Question 121: 10 CFR 20.1204 (g) provides that when a

mixture of radionuclides in air exists, licensees may

disregard certain radionuclides in the mixture if the

licensee uses the total activity of the mixture in

demonstrating compliance with the dose limits in section

20.1201 and if certain other conditions are met. How can a

licensee both disregard certain radionuclides and use the

total activity?

Answer: The term "total activity" in this section refers

to "gross activity" measurements that are correlated with

other measurements of individual radionuclides. For

example, "gross beta" measurements of air samples might be

used for determining intakes of a mixture of beta-emitting

radionuclides when (a) gamma-ray spectrometry of

representative air samples has identified radionuclides

that account for more than 70% of the activity in the air

samples (i.e., the percentage of radionuclides disregarded

does not exceed 30%) and (b) the concentration of any

radionuclide disregarded is less than 10% of its DAC.

(Reference: 10 CFR 20.1204)

Page Last Reviewed/Updated Thursday, March 29, 2012