CONTINUOUS RADON MONITOR USING A 2-FILTER METHOD

To facilitate the accurate continuous measurement of radon in the atmo sphere, a two-filter radon monitor was developed. Short term variation s in radon concentration were monitored with a silicon semiconductor d etector sensitive to Po-218 alpha particles. The deposition of radon p rogeny on the internal surface of the cylindrical vessel was investiga ted using Gormley and Kennedy's formula as well as Ingham's formula. C omparing the experimental results with the predicted values, Ingham's formula was found to provide better agreement. The influence of absolu te humidity on the sensitivity of the monitor was also investigated. I t was found to have little influence in the range of 11-27 g.m(-3) (22 -29 degrees C, 10-90%). The minimum detectable concentration of the mo nitor is 2.7 Bq.m(-3) for a 30 min counting interval. As this instrume nt is stable over long periods, it is suitable for determining very lo w radon concentrations in the natural environment.