EPA-RCA: 9315: Alpha-emitting radium isotopes in water by Alpha Scintillation or AGPC
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Official Method Name
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Alpha-Emitting Radium Isotopes |
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Current Revision
| September, 1986. |
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Media
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WATER |
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Instrumentation
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Alpha Scintillation Gas Particle Counter |
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Method Subcategory
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Radiochemical |
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Method Source
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Citation
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Brief Method Summary
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The radium in the surface water or ground water sample is collected by coprecipitation with barium and lead sulfate and purified by reprecipitation from EDTA solution. Citric acid is added to the water sample to assure that complete interchange occurs before the first precipitation step. The final BaSO4 precipitate, which includes radium-226, radium-224, and radium-223, is alpha counted to determine the total disintegration rate of the radium isotopes. The radium activities are counted in an alpha counter where efficiency for determining radium-226 has been calibrated with a standard of known radium-226 activity. By making a correction for the ingrowth of alpha activity in radium-226 for the elapsed time after separation, one can determine radium activity in the sample. Because some daughter ingrowth can occur before the separated radium is counted, it is necessary to make activity corrections for the count rate. |
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Scope and Application
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This method covers the measurement of the total soluble alpha-emitting radioisotopes of radium, namely radium-223, radium-224, and radium-226, in surface and ground waters.
Although the method does not always give an accurate measurement of the radium-226 content of the sample (when other radium alpha emitters are present), it can be used to screen samples. When the total radium alpha activity of a drinking water sample is greater than 5 pCi/L, then the radium-226 analysis is required. If the level of radium-226 exceeds 3 pCi/L, the sample must also be measured for radium-228 (Method 9320). Because this method provides for the separation of radium from other water-dissolved solids in the sample, the sensitivity of the method is a function of sample size, reagent and instrument background, counting efficiency, and counting time. Absolute measurement can be made by calibrating the alpha detector with standard radium-226 in the geometry obtained with the final precipitate. Both Alpha Scintillation and Alpha Gas Particle Counter are appropriate counting instruments. |
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Applicable Concentration Range
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Interferences
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Since the radiochemical yield of the radium activity is based on the chemical yield of the BaSO4 precipitate, the presence of significant natural barium in the sample will result in a falsely high chemical yield. Radium isotopes are separated from other alpha-emitting radionuclides by this method. The alpha count of the separated radium must be corrected for its partially ingrown alpha-emitting daughters. |
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Quality Control Requirements
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Minimum of one blank per sample batch. Include one spike duplicate for ever 10 samples. Spiked samples or standard reference materials shall be periodically employed to ensure that correct procedures are being followed and that all equipment is operating properly. |
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Sample Handling
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Samples should be preserved when collected by adding enough 1 N HNO3 to the sample to bring it to pH 2 (15 mL of 1 N HNO3 per liter of sample is usually sufficient). |
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Maximum Holding Time
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Not included |
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Relative Cost
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$51 to $200 |
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Sample Preparation Methods
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