EML THORON GAS MEASUREMENTS

The Environmental Measurements Laboratory's experience with two method s of measuring thoron gas, and its findings on the feasibility of usin g these measurements to diagnose indoor air flow paths, are presented. One method is an updated version of the two-filter tube, and the othe r is a modified Falk-More-Nyblom delayed coincidence method. Measureme nts made with these instruments in six houses indicated that thoron co ncentrations are very low (median about II Bq.m(-3)); this is consiste nt with values previously reported for US housing. Both methods had di fficulty measuring these low levels, particularly in houses with high radon gas levels. At one house, thoron levels measured outdoors over b are earth were higher than indoor levels. At the low levels encountere d and with the current measuring technology, it seems unlikely that th oron gas measurements can be used to trace indoor air motion.