A simple passive monitor for integrating measurements of indoor thoron concentrations

A simple passive monitor was developed for integrating measurements of indoor thoron concentrations. The monitor was remodeled from a commercially available radon monitor with allyl diglycol carbonate (CR-39) detector. By adding four holes (phi=12 mm) and covering them with high permeability of filter paper, the air exchange rate of the monitor was largely enhanced. The technical characteristics of both the radon and thoron monitors were examined through calibration experiments. A high conversion factor of 1.32+/-0.14 tracks cm(-2).(kBq m(-3) h(-1))(-1) and the low lower detection limit for thoron measurements provide the essential conditions for measuring thoron more precisely and sensitively. Furthermore, the main physical advantages of the monitor are its simple construction, light weight, and compactness as well as its low cost, which are preferable for large-scale and long-term indoor surveys. Simultaneous measurements of both indoor thoron and radon are indispensable for accurate assessments of public exposure to radon. (C) 2002 American Institute of Physics.