Development of an SSNTD based system for the measurement of unattached fraction of radon progeny

Occurrence of radon progeny in the atmosphere can be broadly divided into two modes 'attached' and the 'unattached' fractions which are the important physical parameters in all lung dosimetry models used to estimate radiation doses from the inhaled daughter products. Conventional methods used to measure the unattached fraction involve direct counting of the daughter products deposited on the filter paper and wire mesh. So, the methods give result based on the activity collected for the last one hour only when the system is of a continuous sampling type. With these constraints, a simple system have been developed based on the different collection efficiencies of attached and unattached fractions on the wire mesh due to the difference in their diffusion coefficients. SSNTD (LR-115 type II) films are used as passive detector. Tracks are continuously registered on the detector and the average activity distribution over a long interval of time can be assessed in areas where the concentrations are low and varying. (author)