[ Index of Health Physics Questions and Answers | NRC Home Page ]
Question 427: The word "external" in 10 CFR 20.1302 (b)
(2) (ii) refers to any radiation source which could
irradiate an individual from outside the body. Since
sources include both airborne radioactive materials and
contained sources, the dose from airborne radioactive
materials could be double-counted -- as a concentration
pursuant to 10 CFR 20.1302 (b) (2) (i) and as direct
radiation pursuant to 10 CFR 20.1302 (b) (2) (ii). In a
situation where the licensee was approaching the 50 mrem/yr
limit from direct radiation from contained sources, the
additional direct radiation component from airborne
releases may cause this limit to be exceeded. Clearly,
this situation could be addressed through use of 10 CFR
20.1302 (b) (1); however, the intent of the revised Part 20
appears to provide viable alternatives to complying with
the regulations whenever feasible. Must a licensee who
elects to use the method of 10 CFR 20.1302 (b) (2) for
demonstrating compliance with the public dose limits
"double-count" the dose from airborne radioactive materials?
Answer: No. External sources ordinarily include all
radiation sources outside of the body, such as direct
radiation from contained sources and direct radiation from
airborne radioactive materials. To the extent that doses
from airborne radioactive materials (e.g., noble gases) are
accounted for as concentration values pursuant to 10 CFR
20.1302 (b) (2) (i), they need not be accounted for as
external sources under 10 CFR 20.1302 (b) (2) (ii) in
determining compliance with the 50 mrem/yr limit.
(However, airborne radioactive material does need to be
accounted for in determining compliance with the limit of 2
mrem in any one hour). (References: 10 CFR 20.1302, 10
CFR 20.1301).