Ion-pulse ionization chamber for direct measurement of radon concentration in the air

A large-volume (24.8 l in total volume, 16.8 l in fiducial volume) multiwire pulse ion collection ionization chamber was examined as a detector of α particles from radon decays in the air inside the chamber. The possibility of obtaining spectrometric information from slow ion pulses was tested. An energy resolution of 3.9% for 5.49-MeV α particles was obtained in preliminary measurements. It was shown that a detector of this kind could be used for direct measurements of radon activities in flowing air at a level less than 1 Bq/m3. A radon concentration at a level of 10 Bq/m3 can be measured with an accuracy better than 10% for a counting time of 103 s. The detector will be used for continuous accurate monitoring of the 222Rn concentration in the air of low-background laboratories