Preliminary determination of the Radon-222 baseline in Houston, Tex.
Moed, Barbara A.
Adams, John A. S.
Master of Arts
Radon-222 is a naturally occurring radionuclide that is present in rocks, sediments, and soils in detectable quantities. The migration of radon-222 is promoted by nonreactive chemical properties and by a. 3.82 day half life. A large fraction of the natural radioactivity in surface air is comprised of radon-222 and its short-lived progeny. The activity of radon-222 in soil gas and in surface air exhibits great variability spatially and temporally. This study investigated the temporal variation of radon-222 activities in soil gas and in the surface layer of the atmosphere. The alpha activity in soil gas was monitored at one site for a period of six months. Integrated countrates were recorded daily. Atmospheric radon-222 activities were monitored continuously at an adjacent site during four months of the same period. This difference in the span of monitoring periods was caused by equipment downtime in the air monitoring system. Meteorological data were concurrently tabulated. Univariate graphs were constructed to show the variation of daily mean atmospheric radon-222 activities and of soil gas activities versus mean temperature, mean barometric pressure, average wind speed, and resultant wind direction. The effects of rainfall on these activities were also assessed. The mean of daily soil gas activities is 4.2 counts/ minute; the range of these observations is 1. - 11. counts/ minute. The mean of the atmospheric radon activities is .39 pCi/1; the range of daily mean values is .22 - .79 pC/1. Atmospheric radon activities exhibited distinct diurnal variations. Composite soil samples from the vicinity of the monitoring site were collected and analyzed for uranium-238 and thorium-232 concentrations. The radon-222 and radon 22 emanating powers of these samples were also determined.