= the concentration of 212Pb;
= the concentration of 212Bi; and
= the concentration of 220Rn (thoron).
To assess radon progeny exposure from a time-integrated measurement using a nuclear track
detector, one must understand the measurement itself4. The fundamental result of a measurement with a
nuclear track detector is an observed number of tracks per unit area. Nuclear track detectors typically
have an area of 10 to 20 mm2. The number of tracks per mm2 is empirically related to a number of
radioactive transitions (of radon) per unit volume of air that occurred during exposure, that is, a time-
integrated radon concentration. One commonly reported unit is picocurie-days per liter (pCi-d/L), where
The average concentration and average equilibrium equivalent concentration, ' and EE', during the
where the numerical conversion factors are given to five significant figures to prevent round-off error.
exposure, uncorrected for background, can be calculated by knowing the exposure time, tE (d), the
number of transitions per unit volume, NV, and the equilibrium factor using
However, PAEE is directly proportional to NV without the need for the intermediate step of
calculating an average concentration:
Committed effective dose equivalent is assessed directly from PAEE using
The commercial nuclear track detectors for radon are insensitive to thoron.