U.S. Nuclear Regulatory Commission

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Question 149: 10 CFR 20.1003 defines the shallow-dose

equivalent as the dose equivalent at a tissue depth of

0.007 cm. (a) Does this mean that the dose to the skin of

the whole body is the sum of the non-penetrating dose

equivalent beta and low energy photons) and the deep dose

equivalent? (b) Is it proper to calculate the extremity

dose by summing the dose equivalent measured on an

extremity dosimeter (which may only be worn for part of the

monitoring period) with the deep dose equivalent?



Answer: General response: 10 CFR 20.1502 requires

monitoring of external dose for individuals who are likely

to receive, in a year, a dose in excess of 10% of the

applicable limits. Requirements to measure / assess the dose

equivalent at depths of 0.007, 0.3, and 1 cm exist under

old Part 20 as well as revised Part 20. In old Part 20,

these requirements are included in the instructions for

Item 5 of NRC Form 5. In the revised Part 20, these

requirements are in Part 20 itself, together with new dose

limits and special names in the definitions for the dose

equivalents at these three depths. The only explicit

requirements concerning the precision and accuracy of

personnel dosimetry are the NVLAP accreditation

requirements, which are the same in old Part 20 [10 CFR

20.202 (c)] and revised Part 20 [10 CFR 20.1501 (c)].

Methods that have been acceptable for measuring / assessing

dose equivalent at these three depths in the past should

continue to be acceptable in the future.



Answers to the specific questions are as follows:



(a) No. The "dose to the skin of the whole body" is the

shallow dose equivalent. The shallow-dose equivalent is

the dose equivalent at a depth of 0.007 cm (7 mg/square cm)

from all types of radiation, whether "penetrating" such as

gamma rays and neutrons) or "non-penetrating" (such as weak

beta radiation and lower energy x-rays).



(b) No, not in general. The question does not make it

clear whether or not the dose summing is for dose during

the same time period. It is never proper to calculate an

extremity dose (shallow-dose equivalent) for a particular

time period by adding a deep dose equivalent to the

shallow-dose equivalent. If the question refers to a

monitoring period during which an extremity dosimeter

(measuring shallow-dose equivalent) was used only part of

the time, but during which a whole-body dosimeter was used

all of the time, the answer depends on the circumstances of

the individual's exposure. It would be acceptable to

assume, for the times during which the extremity dosimeter

is not used, that the extremity dose (shallow-dose

equivalent) is equal to the shallow-dose equivalent

measured by the whole-body dosimeter. If only the

deep-dose equivalent is measured by the whole-body

dosimeter, it would be acceptable to assume, for times

during which the extremity dosimeter is not used, that the

extremity dose is equal to the deep-dose equivalent

(measured by the whole-body dosimeter) if it can be shown

that types and levels of radiation to which the extremity

was exposed would not have resulted in a significantly

higher shallow-dose equivalent to the extremity than the

deep dose equivalent to the whole body. (Reference: 10 CFR

20.1003)