Portable and high-sensitive apparatus for measurement of environmental radon using CR-39 track detector

Highly sensitive, electrostatic collection chambers have been developed for low-level radon measurements using CR-39 plastic track detectors. Chambers with outer electrodes shaped as a cone and a hemisphere with lines of electric force that were focused on the center of the collector electrode gave alpha-track distributions similar to a 2-dimensional Gaussian with a FWHM of less than 3 mm. The sensitivities, defined as the track density for a radon exposure of 1 Bq h/m 3 , were more than 4 tracks/cm 2 using a chamber with a volume of about 300 cm 3 . The dependencies of the sensitivity and the track distribution on the collector voltage and humidity were investigated.