At the 1987 Workshop of the Speciality Committee for Radon and Thoron Measurements, an intercomparison among twelve organization in Japan that practice measurements of radon and radon daughter products was carried out as one of the Visiting Researchers Programs of the Kyoto University Research Reactor Institute. Measured items were radon concentration (222Rn), daughter concentartion assuming radioactive equilibrium among radon daughter products in air (Rn-dts), total 218Po, 214Pb, and 214Bi concentrations, the potential alpha energy (PAE) concentration, and unattached 218Po, 214Pb, and 214Bi concentrations; not all of these items were measured by every participant. Each participant selected an instrument or a method in compliance with his thought. The instruments and methods used were as follows: 222Rn: liquid scintillation method, a scintillation cell, an ionization chamber, a flow-type ionization chamber, a plane multiwire-electrode ionization chamber, electrostatic collecting method and charcoal trap method; radon daughter products: filter sampling method (two-count and/or three-count method); unattached radon daughter products: wire-screen method. Measurements were performed at two radon concentration levels of about 100Bq·m-3 and 400Bq·m-3, which were prepared by radon gas that emanated naturally from building walls to a laboratory room. The results were as follows: the coefficients of variance of averaged value were 7.7-16.2 for 222Rn, 13.9-20.7 for Rn-dts, 10.7-33.5, 11.6-15.3, and 11.9-13.1 for total 218Po, 214Pb, and 214Bi, respectively, 41.8-43.1 for PAE, and 33.1, 16.7, and 30.8 for unattached 218Po, 214Pb, and 214Bi, respectively. Considering the differences between the various applied techniques for measuring radon, fair agreement between the obtained concentration data was observed, whereas discrepancies of a factor of two or three were observed among the obtained PAE concentration data.
