Development of high sensitivity radon detectors

High sensitivity detectors for radon in air and in water have been developed. We use electrostatic collection and a PIN photodiode for these detectors. Calibration systems have been also constructed to obtain collection factors. As a result of the calibration study, the absolute humidity dependence of the radon detector for air is clearly observed in the region less than about 1.6 g/m(3). The calibration factors of the radon detector for air are 2.2. +/- 0.2 (counts/dayM)/(mBq/m(3)) at 0.08 g/m(3) and 0.86 +/- 0.06 (counts/day)/(mBq/m(3)) at 11 g/m(3). The calibration factor of the radon detector for water is 3.6 +/- 0.5 (counts/day)/(mBq/m(3)). The background level of the radon detector for air is 2.4 +/- 1.3 counts/day. As a result, one standard deviation excess of the signal above the background of the radon detector for air should be possible for 1.4 mBq/m(3) in a one-day measurement at 0.08 g/m(3). (C) 1999 Elsevier Science B.V. All rights reserved.