A correction is needed to calculate the activity concentration of airborne tritium oxide when dried silica gel is used as the collector. A tracer study using tritiated water with silica gel showed that the concentration of tritium in desorbed water is lower than that in adsorbed water by a fraction that increases with the amount of adsorbed water. The hypothesis was tested that adsorbed tritiated water is diluted by isotopic exchange with both non-tritiated water and hydroxyl groups within the silica gel matrix. The extent of dilution was measured from 4% to 14% adsorbed water, which is typical of moisture on field collectors for monitoring airborne tritium oxide. For this range of percent adsorbed water, the inferred percent exchangeable water in the silica gel under study was 6.3 +/- 0.1%. This value compares to the silica gel weight loss of 5.3% after heating to 1,050 degrees C. An explanation of the difference between 6.3% and 5.3% is proposed. The contribution of the HTO/H2O vapor pressure isotope effect was considered in calculating isotopic exchange. A curve is presented for correcting the measured tritium concentration in the distillate from the silica gel as a function of the amount of adsorbed water. The tritium tracer procedure is recommended for determining the percent exchangeable water in other silica gels to correct tritium measurements of water vapor collected by them.
In the early 1960's, an area of privately owned swamp adjacent to the Savannah River Site was contaminated by site operations. Studies conducted in 1974 estimated that approximately 925 GBq of Cs and 37 GBq of Co were deposited in the swamp. Subsequently, a series of surveys was initiated to characterize the contaminated environment. These surveys-composed of 52 monitoring locations-allow for continued monitoring at a consistent set of locations. Initial survey results indicated maximum Cs concentrations of 19.5 Bq g in soil and 8.7 Bq g in vegetation. By the 2004-2005 surveys, maximum concentrations had declined to 1-2 Bq g in soil and 0.4 Bq g in vegetation.
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