*2.1.2 222Rn determination using beta counter*

Assuming that there is secular equilibrium between 222Rn and its progeny, the beta particles of 214Pb and 124Bi on a filter can be used for determining the radon concentration by measuring their beta activity. Beta counter such as Geiger Muller counter is used to count the radon progeny on filter paper. Also, plastic scintillators installed on photomultipliers tubes can be used to determine activity.

## *2.1.3 Direct progeny monitoring technique*

One of the ways to measure a time integrated radon progeny for determination of radon is with direct radon progeny sensor, which is made up of solid-state nuclear track detector fitted with absorber of sufficient thickness. The direct radon progeny absorber comprises aluminized Mylar and cellulose nitrate appropriate thickness of 37 cm, whereby 7.67 MeV alpha particles emitted from 214Po are detected [18].
