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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
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posted:9/24/2011
language:English
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