High radon emanation coefficients of porous matters produced through filtration and precipitation

Previous theoretical predictions of high radon emanation coefficients were verified in experiments using porous matters artificially produced through filtration and precipitation. Such porous matters were prepared by replicating uranium-bearing waste generating processes used in fuel fabrication facilities in Japan except that radium was employed instead of uranium. In the replication, a liquid containing a trace amount of naturally occurring radium was processed by filtration or precipitation, resulting in radium adsorption on the surfaces of the matrices used as agents for the processing. The matrices were diatomaceous earth for filtration and iron (III) hydroxide for precipitation. Radon emanation coefficients of these matrices were measured and proved to be very high as expected from the authors' previous theoretical calculations which predicted that chemical procedures like filtration or precipitation could lead to very high radon emanation coefficients. Filtration and precipitation are the most common processes employed in chemical industries. Therefore, the present study also provides important information on radon emanation coefficients for workers in those chemical industries which handle substances containing naturally occurring radium. The findings further imply that man-made artificial industrial products containing naturally occurring radium should be distinguished from ubiquitous minerals, rocks and soils containing naturally occurring radium from a radiological exposure viewpoint, because the radon emanation coefficients of the former are generally higher than those of the latter.