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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
20?
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)