A new active method for continuous radon measurements based on a multiple cell proportional counter

A new active method for continuous airborne radon activity concentration measurements is developed. It is based upon the use of a specially designed radon Multiple Cell Proportional Counter (MCPC). The constructed MCPC prototype is described and its operation principle presented. This gas-flow counter is a pile-up of 20 adjacent multiwire proportional counters. It uses argon-propane (1%) as the main counting gas mixture to which an appropriate fraction of ambient air is admixed. The airborne radon activity concentration is to be continuously measured through a periodic integral counting of the α particles emitted by 222Rn and its short-lived decay products within the sensitive volume. A Monte Carlo simulation program, taking into account the major physical processes that determine directly the detector performances, has been written and used for design optimization purposes. The simulation results show that the admixture of 10% of ambient air seems to be sufficient to continuously assess radon activity concentration levels ranging from about 15 Bq m−3 up to 2.6×105 k Bq m−3 for an integral counting time period of 10 min. The expected radon sensitivity is about 1.16 cpm/10 Bq m−3 with a radon counting efficiency of about 180%. The detector α-pulse height spectra obtained by simulation show a very good agreement with those delivered by the constructed MCPC prototype in its minimal configuration.