Standard Methods: 7120B: Gamma-emitting isotopes by Gamma Spectroscopic Method
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Official Method Name
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Gamma Spectroscopic Method |
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Current Revision
| Standard Methods Online |
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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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Because gamma spectroscopy is nondestructive, it is possible to analyze for gamma-emitting radionuclides without separating them from the sample matrix. This technique makes it possible to identify and quantitate gamma-emitting radionuclides when the gross beta screen has been exceeded or it is otherwise necessary to define the contribution of gamma-emitters to the total radioactivity present. |
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Scope and Application
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This method describes the use of gamma spectroscopy, using either germanium (Ge) diodes or thallium-activated sodium iodide [NaI(Tl)] crystals, for the measurement of gamma photons emitted from radionuclides present in water. |
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Applicable Concentration Range
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The method is applicable to samples that contain radionuclides emitting gamma photons with energies ranging from about 60 to 2000 KeV. |
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Interferences
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Significant interference occurs when a sample is counted with a NaI(Tl) detector and the sample radionuclides emit gamma photons of nearly identical energies. Interferences can occur with Ge detectors from cascade peak summing, which results when two or more gamma rays are emitted in one disintegration, e.g. with cobalt-60, where 1172 and 1333 KeV gamma rays are emitted in cascade. |
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Quality Control Requirements
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Make duplicate analyses for one out of every ten samples. Analyze a known-addition sample for one out of every ten samples. Find and identify any background lines that may be present. Check the energy calibration daily or before each use with a multi-line source. Check detector efficiency daily or before each use with a stable multi-line source in a reproducible geometry. Other QA/QC information to be found in Section 7020. |
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Sample Handling
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Collect samples in polyethylene or glass bottles. Preserve with conc HCl or HNO3 to pH <2. |
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Maximum Holding Time
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1 year |
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Relative Cost
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$51 to $200 |
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Sample Preparation Methods
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None given |
