A method for sampling of Rn in air was experimentally studied. Radon gases flowing at 5l/min are adsorbed on activated charcoal (5g) in a column which is set in a coolant with dry ice and ethanol. The adsorbed Rn is transferred to an ionization chamber by heating the charcoal trap. The activity of Rn is then determined by the currents. The gross collection efficiency of this system was evaluated to be 0.88±0.05 in the region of 50-1, 200pCi/m3. An example of measurements obtained by this method is presented. The air concentration of Rn in a closed room is found to be 4, 000-5, 000pCi/m3.
