Calculating Committed Dose Equivalent to Lung, and Intakes and Identities

DOE-STD-1121-98

7.5.5 Calculating Committed Dose Equivalent to Lung, and Intakes and Identities of

Radon, Thoron and Their Progeny

The lung is the only tissue significantly irradiated by radon and thoron progeny. Since workplace air

measurements yield HE,50, one must calculate H50,lung from that portion of the committed effective dose

equivalent due to radon or thoron progeny using

(38)

where 0.12 is wT for lung in 10 CFR 8355. While this is the opposite of the usual practice of calculating

committed effective dose equivalent from the sum of committed dose equivalent to tissues multiplied by

the weighting factor for those tissues, it is necessary because air concentration measurements lead to HE,50,

not to H50,lung.

The 1988 Federal Guidance Report 11 lists the "Annual Limit on Intake" for 222Rn as 4 WLM and

for 220Rn as 12 WLM, and identifies these values as the "Primary guide" (Eckerman et al. 1988).

However, these values are more correctly termed Annual Limits on Exposure. The concept of intake for

radon and thoron progeny, as explained in ICRP Publication 32 (ICRP 1981b), is expressed not in activity

units (e.g., :Ci or Bq), but in potential alpha energy units (MeV or joules, J). Intake, I, of radon

or thoron progeny by a worker breathing at Reference Man's rate of 1.2 m3 h-1 is given by

(39)

In Equation 40, it is acceptable to substitute the individual worker's actual breathing rate if it has been

measured and documented doing identical or similar work.

When intake of radon progeny or thoron progeny is specified in joules, the identity of the

radionuclides should be specified as "radon progeny" or "thoron progeny." When intake of radon gas or

thoron gas is reported, units of :Ci should be used, and the intake, I, in units of :Ci of ambient radon

(:Ci) should be converted to equilibrium equivalent intake, EEI, using

(40)

Numerical conversions for 222Rn and 220Rn quantities are given in Table IV.

Other values of wT have been used in other contexts, e.g., 0.08 in NCRP Report 91 and 0.06 for each

of two regions in ICRP Publication 32.