Uncertainties

DOE-STD-1121-98

Table VII. Default Background PAEC Values

222

220

Location

Progeny

Indoors

0.006 WL

0.002 WL

Outdoors

0.002 WL

0.001 WL

7.5.9 Correcting for Relatively High Background PAECs

If the background radon progeny concentration is determined to be greater than 0.03 WL indoors or

0.01 WL outdoors, there is a significant probability that an unidentified source of radon exists. Therefore,

if background is found to be greater than these concentrations, the cause of this elevated concentration

should be determined before using it as the background value in occupational radon progeny exposure

calculations. If a previously unidentified radon source is discovered, then a background value should be

redetermined that is independent of any contribution from this source.

7.6 SIMPLIFIED METHOD FOR DOSE ASSESSMENT FOR SMALL INTAKES

When intakes can be established on the basis of bioassay data and are small (i.e., leading to doses

below administrative control levels, or leading to HE,50 < 100 mrem), it is permissible to assign HE,50

values using Eq. (20), which amounts to using default assumptions. When doses approach limiting values

for workers, it is often appropriate to refine dose assessments by using individual-specific parameters

rather than default assumptions. The level of effort expended in dose assessment is generally in

proportion to the projected dose.

7.7 UNCERTAINTIES

While internal dose assessments may be among the most accurate dosimetry available (e.g.,

following an intake of tritiated water or 137Cs that occurs at a known time), in many cases uncertainties are

very large (e.g., following a small intake of plutonium in an unknown chemical form at an uncertain

time). Unlike external dose assessments, internal dose assessments change in many cases as information

accrues over time. The availability of additional data may result in a reduction of uncertainty or a change

in a point estimate of dose, or both.

Assessing doses starting from air activity concentrations and times requires more assumptions than

does assessing doses from excreta measurements or in vivo count data. Thus, uncertainties are

significantly larger for this method than they are from bioassay or in vivo counts. A summary of

uncertainties and their relative impact on assessment of internal doses from in vivo and in vitro bioassay,

and from air monitoring is given in Table VII.