Gamma-ray spectrometry of soil samples is used to identify and quantify certain gamma-ray emitting radionuclides. Use of a germanium semiconductor detector is necessary for high-resolution gamma-ray measurements.
Much of the data acquisition and analysis can be automated with the use of commercially available systems that include both hardware and software. For a general description of the typical hardware in more detail than discussed in Section 6, see Ref (19).
Both qualitative and quantitative analyses may be performed using the same measurement data.
The procedures described in this guide may be used for a wide variety of activity levels, from natural background levels and fallout-type problems, to determining the effectiveness of cleanup efforts after a spill or an industrial accident, to tracing contamination at older production sites, where wastes were purposely disposed of in soil. In some cases, the combination of radionuclide identities and concentration ratios can be used to determine the source of the radioactive materials.
Collecting samples and bringing them to a data acquisition system for analysis may be used as the primary method to detect deposition of radionuclides in soil. For obtaining a representative set of samples that cover a particular area, see Practice C 998
1.1 This guide covers the identification and quantitative determination of gamma-ray emitting radionuclides in soil samples by means of gamma-ray spectrometry. It is applicable to nuclides emitting gamma rays with an approximate energy range of 20 to 2000 keV. For typical gamma-ray spectrometry systems and sample types, activity levels of about 5 Bq (135 pCi) are measured easily for most nuclides, and activity levels as low as 0.1 Bq (2.7 pCi) can be measured for many nuclides. It is not applicable to radionuclides that emit no gamma rays such as the pure beta-emitting radionuclides hydrogen-3, carbon-14, strontium-90, and becquerel quantities of most transuranics. This guide does not address the in situ measurement techniques, where soil is analyzed in place without sampling. Guidance for in situ techniques can be found in Ref (1) and (2). This guide also does not discuss methods for determining lower limits of detection. Such discussions can be found in Refs (3), (4), (5), and (6).
1.2 This guide can be used for either quantitative or relative determinations. For quantitative assay, the results are expressed in terms of absolute activities or activity concentrations of the radionuclides found to be present. This guide may also be used for qualitative identification of the gamma-ray emitting radionuclides in soil without attempting to quantify their activities. It can also be used to only determine their level of activities relative to each other but not in an absolute sense. General information on radioactivity and its measurement may be found in Refs (7), (8), (9), (10), and (11) and Standard Test Methods E 181
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This s......
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