Comparison Experiments For Radon And Thoron Measuring Instruments At Low-Level Concentrations In One Room Of A Japanese Concrete Building

A comparison on commercially available radon (Rn-222) measuring instruments (three types of continuous monitors and a passive Rn-222-thoron (Rn-220) discriminative alpha track detector) was carried out at low-level concentrations in one room of a concrete building. The agreements between the continuous monitors were within 15%, while the agreements between each instrument were within 20%. It was also observed that the indoor Rn-220 concentration measured by the continuous monitor was quite different from those by the passive detectors due to the mean concentration less than the limit of detection of both measuring instruments.