Gross alpha and beta in water - DOC

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					Procedure: HPD-98-LAB-002                                           March 9, 2010
Revision: 0
Page 1 of 7




UNLV Department of Health Physics
                 Laboratory Operating Procedure




      Determination of Gross Alpha and Beta
             Radioactivity in Water


Author:
               William H. Johnson                            Date

Reviewed by:
               Courtney A. Kerr                              Date
               Hazardous Materials Safety Officer

Reviewed by:
               Thomas Graham                                 Date
               Radiological Safety Officer

Reviewed by:
               Lawrence J. Tirri                             Date
               Director, Environmental Health & Safety

Approved by:
               Mark J. Rudin                                 Date
               Interim Chair, Department of Health Physics
Procedure: HPD-98-LAB-002                                                        March 9, 2010
Revision: 0
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 I.    PURPOSE

       This procedure provides a screening technique to determine the quantities of alpha- or
       beta-emitting radionuclides in a water sample. A 250-ml aliquot is evaporated and
       counted on a gas flow proportional counter. Procedures are also presented to
       determine the alpha and beta activity in the dissolved and solid phases of water.

 II.   REQUIRED EQUIPMENT AND SUPPLIES
       A. Equipment
           1. Oxford Series 5XL proportional counter system
           2. Heat lamp
           3. Hot plate
           4. Balance accurate to  0.1 mg
           5. 9” utility tongs
           6. Metal kitchen spatula
           7. Bunsen burner
           8. Tweezers
           9. 50, 400, 600, and 1000-ml glass beakers
          10. 50 L pipet
          11. 10-mL and 250-mL graduated cylinders
          12. Desiccator
          13. 500-mL filtering flask
          14. 500-mL volumetric flask
          15. 500-mL washing bottle with blue top
          16. 25-mm filter support
          17. Balance accurate to 0.1 mg
          18. Furance
          19. Stainless steel or glass drying pans
          20. Safety glasses
       B. Supplies
          1. 2-inch (5-cm) stainless steel planchets with a 2-mm lip
          2. P-10 gas
          3. PTFE coated stir bars (VWR #58948-138)
          4. 100-mm petri dishes
          5. 0.45 m membrane filters, 25-mm in diameter (VWR #28154-260)
          6. Gloves (VWR #32916-520)
          7. Plastic transfet pipet, 2.5 mL (VWR #52947-948)
       C. Chemicals
          1. Nitric acid [HNO3], conc. (70%), reagent grade (VWR #VW4815-6)
          2. Deionized (DI) water
          3. Tap water
Procedure: HPD-98-LAB-002                                                       March 9, 2010
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       D. Radioactive Standards
          1. NIST-traceable standard 241Am in liquid form (7.15 Bq mL-1)
          2. NIST-traceable standard 90Sr in liquid form (Solution A - 7.15 Bq mL-1)

III.   PROCEDURES
       A. Reagent Preparation
          1. 1 N Nitric acid
             a. Fill a 500-ml volumetric flask approximately one-half full with DI water.
             b. Add 32 ml of concentrated HNO3 to the flask.
             c. Dilute to the mark with DI water to make a 1 N HNO3 solution.
             d. Transfer solution to a labelled 500-mL washing bottle with a blue top.
       B. Estimate the solid concentration in the sample.
          1. Weigh and record the weight of metal planchet to the nearest 0.1 mg.
          2. Using a graduated cylinder, add 10 mL of sample to the planchet.
          3. Transfer the planchet to the furance or a drying oven and heat at 1155 C
                 until the sample is completely dry.
          4. Using a tweezers or a kitchen spatula, remove the planchet from the
                 furance and allow it to cool to room temperature in a dessicator.
          5. Weigh and record the weight of the planchet and the solids to the nearest
                 0.1 mg.
          6. Calculate the weight of the solids by subtracting the weight recorded in step
              5 from that in step 1.
          7. Estimate the solid concentration in mg per 100 mL by multipling the weight
              of the solids by 10.
       C. Total Sample Activity
       Note: With each batch of samples, or with at least every ten samples, at least one
             blank sample should be prepared using deionized water instead of sample.
           1. Using a graduated cylinder, add to a clean, labeled 400-ml glass beaker that
              amount of sample which will produce less than 60 mg of solid.
              a. If the sample is being analyzed only for gross beta, an amount of sample
                 equivalent to up to 150 mg of sample should be used.
              b. If the sample has a low amount of suspended solids, a larger sample
                 volume may be used. Start the procedure with an appropriate size beaker
                 and then carefully transfer the sample to a 400-mL glass beaker using a
                 stream of deionized water as evaporation nears completion.
           2. Record the sample volume used in a laboratory notebook.
           3. Using a plastic transfet pipet, carefully add one pipet of
              concentrated HNO3 per every 250 mL of sample.
           4. Place the beaker containing the water sample on a hot plate in a fume hood
              and heat on medium to high heat. Add a stir bar to the solution to prevent
              splattering by uncontrolled boiling.
           5. Without splattering, evaporate the sample to near dryness (1-2 mL).
           6. Rinse the sides and bottom of the beaker with approximately 10 mL of
Procedure: HPD-98-LAB-002                                                       March 9, 2010
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             1 N HNO3 and again evaporate to near dryness.
          7. Using utility tongs, remove the sample from the heat and dissolve the
             residue with a minimum amount of 1 N HNO3.
          8. Label, weight and record the weight of a new 2-inch stainless steel planchet
             to the nearest 0.1mg. To ensure an accurate weight during subsequent
             weighings, the planchet should handled only with a tweezers or a kitchen
             spatula. Transfer the planchet to a drying pan. Set the drying pan under a
             heat lamp.
          9. Using a small stream of DI water, transfer the liquid portion of the sample
             to the weighted planchet.
             a. Note that the planchet will contain only about 5-mL. During transfer, it
                 may be necessary to add the sample to the planchet in steps, allowing for
                 some evaporation between each step.
             b. Rinse the sides of the beaker with DI water and add to the planchet.
             c. It is often easier to transfer the sample using a plastic tranfer pipet.
         10. Energize the heat lamp and allow the sample to completely dry.
         11. If just betas are being counted, this step may be skipped as the limited
             amount of water is not expected to greatly influence beta particle range.
             a. Using a pair of tongs, carefully and slowly heat each planchet over a
                 Bunsen burner flame until it is red hot (approximately 2 minutes). This
                 will ensure that all nitrate solids which may contain water are converted
                 to oxides. This reaction will cause the sample to bubble as the water is
                 released.
         12. Using a tweezers, transfer the planchet to a desiccator and allow it to cool
             to room temperature.
         13. Weigh and record the weight of the planchet and dried sample to the
             nearest 0.1 mg. Calculate the sample weight in mg. This weight will be
             used to account for the sample self-shielding effects.
         14. Store the planchet in a desiccator until ready to count.
         15. Count sample in a gas flow proportional counter using the counter’s Gross
             Alpha/Beta in Water procedure.
             a. Record the planchet holder containing each sample in the lab book.
             b. The blank sample should be counted first and disiginated as “blank”.
             c. Designate the samples as “unknown”.
             d. For sample type select “liquid” and then enter the sample weight in mg.
     D. Activity of Dissolved Matter
         1. Using a 500-mL filtering flask with a fritted glass filter, vacuum filter
             approximately 300-mL of sample through a 0.45 m membrane filter.
         2. Analyze the liquid portion of the sample per section C (above).
Procedure: HPD-98-LAB-002                                                      March 9, 2010
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     E. Activity of Suspended Matter
         1. Weigh to the nearest 0.1 mg and record the weight of a clean, labeled,
             stainless steel planchet. Using a tweezers, transfer the planchet to a drying
             pan.
         2. Mount a 25-mm, 0.45 m membrane filter on a filter mount with a 500-mL
             filtering flask.
         3. Vacuum filter a measured volume of sample through the filter. The sample
             volume should be such that it does not contain more than 50 mg of
             suspended solids. Record the actual amount of sample used in the
             laboratory notebook.
         4. Rinse the sides of the filter with a few mL of DI water.
         5. Transfer the filter to the weighted planchet in the drying pan. Place the
             drying pan in the furnace at 600C for 1 hour to allow complete ashing of
             the filter. Allow the pan to cool in the oven to below 150C. Remove the
             pan from the oven and allow it to cool to room temperature.
         6. Handling the planchet with gloves, add several drops of concentrated 1 M
             HNO3 and carefully swirl the planchet to ensure the ash is evenly spread
             across the entire surface area of the planchet.
         7. Return the planchet to the drying pan and dry it under a heat lamp.
         8. Transfer the planchet to a desiccator and allow it to cool to room
             temperature.
         9. Weigh and record the weight of the residue and planchet.
        10. Store the sample in a desiccator until ready to count.
        11. Count the sample as per step C.15.
     F. Instrument Efficiency Calibration - Beta
              An instrument efficiency calibration should be completed at least annually on
          each instrument. It should also be completed whenever maintenance has been
          performed on the detector system. The radioactive standard planchets prepared in
          this procedure should be saved in petri dishes so they may be used in future
          calibrations. Each petri dish should be labeled with the sample density thickness,
          activity and preparation date and have a radioactive warning label affixed. The
          dishes should be stored in the radioactive source storage cabinet in room BHS-
          115. To ensure that the standard density thickness is unchanged prior to any
          subsequent calibrations, the planchets should be only handled with tweezers and
          placed under a heat lamp for at least 30 minutes prior to any use. The water
          volumes listed in Table 1 should be adjusted as necessary to obtain a range of
          standards with a density thickness of 0 to 200 mg cm-2.

          1. Label 7 new 2-inch stainless steel planchets in a manner corresponding to
              the scheme in Table 1.
Procedure: HPD-98-LAB-002                                                       March 9, 2010
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              Table 1. Standard Preparation
                                                                   90
                       Beaker      Tap    Concentrated               Sr Stock
            Label       Size     Water       HNO3                   Solution
              0        50 mL      0 mL       1 mL                   0.05 mL
             50        400 mL     50 mL      2 mL                   0.05 mL
             100       400 mL    100 mL      2 mL                   0.05 mL
             200       400 mL    200 mL      2 mL                   0.05 mL
             400       600 mL    400 mL      4 mL                   0.05 mL
             800      1000 mL 800 mL         8 mL                   0.05 mL
            Blank

          2. Weight and record the weight of each planchet to the nearest 0.1 mg. After
             weighing each planchet should be placed in a drying pan with a tweezers.
          CAUTION: Steps 3 through 7 should be performed inside of a fume hood.
            Safety glasses, gloves and other appropriate safety equipment must be
            worn.
        3. In a fume hood prepare the sample matrices in the listed size beakers. The
            90
               Sr stock solution should be carefully pipetted into each standard to ensure
            that each has a total activity of approximately 185 Bq of 90Sr (370 Bq of
            90
               Sr + 90Y). Note that the planchets labeled Blank is a blank and does
            not receive any solution.
            a. Record the actual total activity (90Sr + 90Y), in Bq, added to each
                solution.
        4. Add a magnetic stir bar to the solution to prevent splattering. Place each
            sample on a hot plate and evaporate using medium heat until near dryness
            (1-2 mL). Rinse the sides of the beakers with distilled water as necessary
            during the evaporation.
        5. Using a tongs, remove the breakers from heat.
        6. Using a rubber policeman and a small stream of DI water, carefully transfer
            the contains of each beaker to the appropriate planchet. Note that the
            planchets hold a maximum of 5 mL of solution.
        7. Set the drying pan containing the planchets underneath a heat lamp and
            allow the samples to evaporate to dryness.
        8. Allow the samples to cool to room temperature. Weight and record the
            weight of each planchet to the nearest mg.
        9. Transfer the planchets to a desiccator until ready to count.
       10. Count each planchet on the gas-flow proportional counter using the
            appropriate calibration procedure.
       11. Subtract the weight recorded in step F.2 from that recorded in step F.8 to
            obtain the sample weight in mg. Enter this value in the computer as sample
            thickness.
       12. Check the plot of detector efficiency versus sample thickness find the
            formula which results in the “best fit” of the curve.
     G. Instrument Efficiency Calibration - Alpha
Procedure: HPD-98-LAB-002                                                       March 9, 2010
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          1. Perform steps F.1 through F.9 using an 239Pu standard in place of the 90Sr
             standard. Because the thickness is greater than the anticipated alpha particle
             range, the maximum density thickness of the standards should be 100 mg
             cm-2.
          2. Count each planchet on the gas-flow proportional counter using the
             appropriate calibration procedure.
          3. Subtract the weight recorded in step F.2 from that recorded in step F.8 to
             obtain the sample weight in mg. Enter this value in the computer as sample
             thickness.
          4. Check the plot of detector efficiency versus sample thickness find the
             formula which results in the “best fit” of the curve.

IV.   UNCERTAINTIES

      A. Sample Self-Shielding
         1. Attenuation of alphas and betas in the sample matrix
         2. Efficiency and alpha multiplication factor
         3. Particle energy compared with that of the standard

      B. Counting error

      C. Sample volatilization during heating.
         1. Volatile elements will be lost during heating. This includes some iodines
            and cesiums. If these elements are expected, the samples should not be
            flamed.

 V.   REFERENCES

      ASTM. Standard test method for alpha particle radioactivity of water. ASTM
         D 1943-90; 1995.

      ASTM. Standard test method for beta particle radioactivity of water. ASTM
         D 1890-90; 1995.

      Eaton, A. D.; Clesceri, L. S.; Greenberg, A. E. Standard methods for the
          examination of water and waste water. Standard 7110.B. Evaportion method
          for gross alpha-beta. 19th ed. Washington, DC: American Public Health
          Association. 1995.

      HPD-97-LAB-013. Operation and Maintenance of a PC-5 Gas Flow Proportional
         Counter.

      Oxford series 5XL proportional counter system technical manual

				
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