Evaluation of gas-filled ionization chamber method for radon measurement

For quality assurance of the ionization chamber method, a calibration exercise was conducted at the Environmental Measurements Laboratory (EML) environmental chamber, which was one of the reference facilities for radon calibration. The radon concentrations estimated with the ionization chambers were compared with the EML values. As a result of comparison through the secondary standard (AlphaGUARD), the ionization chamber values were in good agreement with the EML values (ratio to EML: 1.01 ± 0.03). The AlphaGUARD used in the present study was the same instrument that was calibrated at the Physikalish-Technischen Bundesanstalt (PTB), the German national institute for the science and technology. The EML values were in good agreement with the PTB values. These results indicated the accuracy of the ionization chamber method currently used in Japan. Experimental conditions, ionization chamber, continuous monitor of electrostatic collection type, pulse-ionization chamber, data analysis, and the results are reported. (S.Y.)