Micrometer-sized short-lived radioactive aerosol particles for convenient use in laboratory measurements.

For calibration and testing of radioactive aerosol measuring equipment such as continuous air monitors and cascade impactors, and other research applications, it is helpful to have a convenient and relatively safe means of producing radioactive aerosol particles of controlled size and activity. We describe a technique for producing such particles in the micrometer-diameter size range using electrostatic deposition of radon decay products onto otherwise nonradioactive powders of different sizes. An electric field focuses radon decay products (primarily 218Po) onto the surface of a powdered substrate that is then suspended by a technique such as pneumatic dry dispersion. Only a modest-activity commercial 222Rn source (e.g., containing as little as 10(5) Bq of 226Ra) is required, and issues of radioactive cleanup and contamination are minimized due to the short half-lives (26.8 min or less) of the decay products. We report representative results using powders of glass beads, iron oxide, and iron and gold metals in the size range of 0.3 to 30 microm. Yields for the deposited radioactivity per unit concentration of 222Rn gas were of the order of 5 x 10(-7) Bq (214Bi) per milligram substrate per Bq m(-3) of 222Rn for an electrostatic collection time of 30 min.