An on-line actinide-in-air monitor to operate at concentrations below 0.1 ICRP MPCsub(a)

A prototype on-line actinide-in-air monitoring system has been built which has sufficient sensitivity to determine average concentrations as low as 0.04 dpm m-3 (8 x 10-3 ICRP MPCsub(a)) over an 8 h shift. Routine measurements at 0.3 dmp m-3 (0.075 ICRP MPCsub(a)) can be made with a probability of < 1% per shift of a false alarm, even in the presence of unusually large concentrations of radon daughter products. The system uses a combination of inertial particle size separation, alpha energy discrimination and isotope decay analysis to achieve this performance, which is between 10 and 100 times better than commercially available equipment. (U.K.)