EPA-NERL: 901.1: Gamma Emitting Radionuclides in Water by Gamma Spectroscopy
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Official Method Name
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Gamma Emitting Radionuclides in Drinking Water |
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Current Revision
| August 1980 |
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Media
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WATER |
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Instrumentation
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Gamma Radiation Detector |
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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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This method describes the use of gamma spectroscopy for the measurement of gamma photons emitted from radionuclides without separating, them from the sample matrix. This technique makes It possible to ascertain whether a hazardous concentration of a specific gamma emitter is present in a drinking water sample.A homogeneous aliquot of drinking water is put into a standard geometry for gamma counting. The counting efficiency for this geometry must have been determined with standard (known) radionuclide activity. Sample aliquots are counted long enough to meet the required sensitivity of measurement. The gamma spectrum is printed or stored for data processing and calculation of radionuclide concentrations in the sample. |
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Scope and Application
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The method is applicable for analyzing water samples that contain radionuclides emitting gamma photons with energies ranging from about 60 to 2000 keV. The required sensitivity of measurement for the more hazardous gamma emitters is listed in the National Interim Drinking Water Regulations, Section 141.25. for a method to be in compliance, the detection limits for photon emitters must be 1/10 of the applicable limit. The detection limits for cesium-l34 and cesium-137, which are 10 and 20 pCi/l respectively, are met by this procedure. |
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Applicable Concentration Range
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60-2,000 keV |
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Interferences
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Significant interference occurs when counting a sample with a NaI (Tl) detector and the sample radionuclides emit gamma photons of nearly identical energies. Such interference is greatly reduced by counting the sample with a Ge(Li) detector. Sample is important to gamma count reproducability and counting efficiency validity. When sample radionuclides are adsorbed on the walls of the counting container, the sample is no longer homogeneous. This problem can be lessened by adding 15 mL 1N nitric acid per liter of sample at collection time. |
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Quality Control Requirements
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Calibration of instrument. |
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Sample Handling
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Preserve samples with nitric acid to pH <2.
If samples are to be collected without preservation, they should be brought to the laboratory within 5 days, then preserved and held in the original container for a minimum of 16 hours before analysis or transfer of the sample. |
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Maximum Holding Time
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Relative Cost
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$51 to $200 |
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Sample Preparation Methods
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