United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

Question 146: The term "not present," which is defined in

paragraph 5 of the Note (concerning mixtures of

radionuclides) following Appendix B of the old Part 20, is

not defined in the corresponding "Note" in the revised Part

20. Does this definition from the old Part 20, which

indicates when a radionuclide may be considered as not

present in a mixture, continue to apply in the revised Part


Answer: No. Nothing in the old Part 20 (§§20.1-20.601)

applies in the revised Part 20 (§§20.1001-20.2401). This

definition of "not present" is not included in the revised

Part 20; however, 10 CFR 20.1204 (g) stipulates the

conditions under which licensees may disregard certain

radionuclides in a mixture when determining internal dose.

See the answer to the related Question 121 for

clarification of 10 CFR 20.1204 (g). (References:

Appendix B, 10 CFR 20.1204)

Page Last Reviewed/Updated Thursday, March 29, 2012