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The effect of water on radon exhalation from South Texas Uranium mine soil Benjamin Draper; Felischa Cullins; Brendan Hughes; Philippe Tissot Outline I. Introduction II. Background and Goals III. Equipment and Materials IV. Theoretical Concentration V. Dry and Immersed Soil Tests VI. Radon in Water VII. Results VIII. Discussion IX. Acknowledgements Introduction • Radon-222 is a naturally occurring gas as part of the uranium-238 decay chain • The EPA estimates 15-20 thousand lung cancer deaths each Figure 1. Adapted from thinkquest.org year from radon Introduction cont… • Radon can seep through the ground and into water supplies • Surface waters like lakes and reservoirs exhale radon with wind and other natural processes • Ground water wells do Figure 2. Adapted from Radon not allow this exhalation Schematics by Mark Beaman General Study Context • Address radon exposure as a public health issue • Evaluate the risk of private wells in South Texas • Establish an effective method for measuring radon exhalation Figure 3. Map of South Texas adapted from tfsfrp.tamu.edu/FDreporting/vfd/images/region/11.gif Study Goals • Evaluate the accuracy of the E-Perm® detection system for measuring radon levels in water • Measure the radon exhalation from uranium mine soil • Test hypothesis that water opens clay channels allowing a higher radon exhalation Equipment • A High Purity Germanium (HPGe) gamma ray spectrometer was used to evaluate the activity of the radium soil sample • The Rad-elec E-perm® system was used to evaluate the radon exhaled by the samples • A Whatman® Polydisc® AS 0.45 micron inline filter was used to separate the soil from the water for the water only tests RadElec E-PERM • The E-Perm® system uses a charged Teflon® disc called an electret • Readings are taken using a voltage drop that results from the ionization of air inside the chamber caused Figure 4. S-Chamber Adapted from Rad by radon decay Elec inc. Catalog Materials • Five 200g samples were prepared by mixing the uranium mine soil with Tidy Cat® cat litter • The cat litter was used to simulate a low activity gravel Radium Dirt Gravel Activity (mBq/g) • Samples were mixed Sample 1 200g 0g 4900 Sample 2 150g 50g 4000 and ground to Sample 3 100g 100g 1200 promote homogeneity Sample 4 50g 150g 800 Sample 5 0g 200g 36 Theoretical Radon Computation • Using the activity of the samples, the following set of differential equations can be used to find the theoretical concentration of radon Rn(t) = ((λRaxRao)/λRn)x(1-e-λRn*t) 1/T 0 (Cra/λRn)x(1-e^-λRn*t)dt T CRa/(T x λRa)x(T+((e^- λRn*T)/ λRn)-(1/ λRn) Theoretical Accumulation Average Concentration (mBq/g) 100000 75000 Sample 1 Sample 2 Sample 3 50000 Sample 4 25000 0 0 10 20 30 40 50 60 Time (hours) Experimental Procedure • Three experiments were designed to evaluate radon exhalation in: – Dry soil Samples – Water Immersed soil Samples – Water exposed to soil samples Dry Sample Tests • 20g of each sample was placed in the E- perm system chamber • Timed tests were run for 8, 12, 16, 20, and 48hrs • The S-chamber was used to measure the radon exhalation Dry Sample Average Radon Concentration 700 600 Average Radon Concentration (mBq/g) 500 48 hr 400 20 hr 16 hr 300 12 hr 8 hr 200 100 0 0 20 40 60 80 100 120 Radium Soil (%) 160 Dry Sample Corrected 140 Average Radon Concentration (mBq/g) 120 100 48 hr 20 hr 80 16 hr 12 hr 8 hr 60 40 20 0 0 20 40 60 80 100 120 Radium Soil (%) Immersed Sample Analysis • 20g of each sample was immersed in 120mL DIW • Water was conjectured to increase exhalation of radon by increasing pore spacing • Timed tests were run for 8, 12, 16, 20, and 48hrs • The S-chamber was used to measure radon exhalation Immersed Sample Analysis 250 Average Radon Concentration (mBq/g) 200 48 hr 150 20 hr 16 hr 12 hr 100 8 hr 50 0 0 20 40 60 80 100 120 Radium Dirt (%) Dry and Immersed Comparison • Both sets of data were compared to the theoretical build up • An exhalation percentage was found for both the wet and the dry soil • The dry tests showed 0.13% exhalation • The immersed tests showed a 0.16% exhalation • The combined data showed a 0.15% exhalation Measured vs. Theoretical 250 Wet y = 0.0016x + 44.497 200 Measured (mBq/g) 150 Dry Wet Dry Linear (Wet) y = 0.0013x + 26.628 Linear (Dry) 100 50 0 0 20000 40000 60000 80000 100000 120000 Theoretical (mBq/g) Combined Comparison Graph 250 y = 0.0015x + 35.563 200 Measured (mBq/g) 150 100 50 0 0 20000 40000 60000 80000 100000 120000 Theoretical (mBq/g) Radon in Water • Samples were placed in separate bottles and filled with DIW • All five samples were then partially emptied into the E-perm chamber leaving the soil behind • Theoretical build up was computed using the combined exhalation percentage of 0.15% Results • Comparison of experimental results shows the E-perm® system to be effective in measuring the exhalation of radon from all samples • Large error did result from samples with activities lower than 20Bq • A percent error of 31% was measured when using 0.15% exhalation to determine the theoretical build up Discussion • The E-perm® system did allow successful radon measurements in water • A more diverse sampling of South Texas water wells will help evaluate the possible public health concerns from radon in water • Water showed no significant changes in the exhalation of radon • Further testing with a liquid that increases pore spacing is recommended Acknowledgements • Supported by the National Science Foundation and Department of Defense #0453329 • Texas A&M-Corpus Christi University • Texas Division of Nearshore Research • Dr. Philippe Tissot Questions?
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