Estimation of radon progeny equilibrium factors and their uncertainty bounds using solid state nuclear track detectors

For the assessment of inhalation doses due to radon and its progeny to uranium mine workers, it is necessary to have information on the time integrated gas concentrations and equilibrium factors. Passive single cup dosimeters using solid state nuclear track detectors (SSNTD) are best suited for this purpose. These generally contain two SSNTDs, one placed inside the cup to measure only the radon gas concentration and other outside the cup for recording tracks due to both radon gas and the progeny species. However, since one obtains only two numbers by this method whereas information on four quantities is required for an unambiguous estimation of dose, there is a need for developing an optimal methodology for extracting information on the equilibrium factors. Several techniques proposed earlier have essentially been based on deterministic approaches, which do not fully take into account all the possible uncertainties in the environmental parameters. Keeping this in view, a simple ‘mean of bounds’ methodology is proposed to extract equilibrium factors based on their absolute bounds and the associated uncertainties as obtained from general arguments of radon progeny disequilibrium. This may be considered as reasonable estimates of the equilibrium factors in the absence of a knowledge of fluctuation in the environmental variables. The results are compared with those from direct measurements both in the laboratory and in real field situations. In view of the good agreement found between these, it is proposed that the simple mean of bounds estimate may be useful for practical applications in inhalation dosimetry of mine workers.