An on-Line Monitor for Alpha-Emitting Aerosols

An extremely sensitive on-line monitor for alpha-emitting aerosols has been developed. The monitor incorporates discrimination against background radon and thoron daughter product activity which is based on two factors. Firstly, the background activity is associated with small-sized dust particles, while the aerosol to be monitored has most of its activity associated with large-sized particles. Secondly, the alpha-particle energies from the two sources are different. The monitor utilizes virtual impactors to concentrate the largesized particles into a reduced flow. This size-selected sample is then collected on a filter which is viewed by a detector. The monitor is capable of detecting less than one maximum permissible airborne concentration, MPCa, of these hazardous aerosols in less than one-half hour.