Up-to-date radon-thoron discriminative detector for a large scale survey

An up-to-date radon-thoron discriminative detector has been developed for conducting a large scale survey. Comparing with our previous detector, some functional problems have been solved. The lowest and highest detection limits of the detector were estimated to be around 5 and 1000 Bq m(-3) for radon, and 15 and 1000 Bq m(-3) for thoron, respectively, with a 6 month exposure and several theoretical assumptions. Small indoor survey were carried out in Japan and in Hungary using the present detector. The presence of thoron was demonstrated in any indoor surveys by the two results. Since any measurements without discrimination of radon isotopes will result in different risk estimates from actual situations, a special attention should be paid to thoron and its concentration should be accordingly measured as well as the radon concentration. (c) 2005 American Institute of Physics.