Conversion factors for calculating working levels using continuous radon progeny time-integrating monitors

A theoretical analysis has been carried out of the growth of integrated radon progeny and thoron progeny activity deposited on the sampling filter of continuous, time-integrating, Working Level Monitors. With available microprocessor technology it is shown that the results of this analysis can be used to convert alpha particle count rate into Working Level as a function of sampling time from the beginning of the sampling period. This feature is not commonly available in commercial instrumentation which, therefore, does not provide true measurements of the Working Level until a radioactive steady-state in the sampling filter has been attained. This steady-state condition occurs after about 3 h of sampling for the radon progeny and about 15 h for the thoron progeny. (author)