1、Designation: C 1402 04 (Reapproved 2009)Standard Guide forHigh-Resolution Gamma-Ray Spectrometry of Soil Samples1This standard is issued under the fixed designation C 1402; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year o
2、f last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the identification and quantitativedetermination of gamma-ray emitting radionuclides in soilsample
3、s by means of gamma-ray spectrometry. It is applicableto nuclides emitting gamma rays with an approximate energyrange of 20 to 2000 keV. For typical gamma-ray spectrometrysystems and sample types, activity levels of about 5 Bq (135pCi) are measured easily for most nuclides, and activity levelsas low
4、 as 0.1 Bq (2.7 pCi) can be measured for many nuclides.It is not applicable to radionuclides that emit no gamma rayssuch as the pure beta-emitting radionuclides hydrogen-3,carbon-14, strontium-90, and becquerel quantities of mosttransuranics. This guide does not address the in situ measure-ment tech
5、niques, where soil is analyzed in place withoutsampling. Guidance for in situ techniques can be found in Ref(1) and (2).2This guide also does not discuss methods fordetermining lower limits of detection. Such discussions can befound in Refs (3), (4), (5), and (6).1.2 This guide can be used for eithe
6、r quantitative or relativedeterminations. For quantitative assay, the results are expressedin terms of absolute activities or activity concentrations of theradionuclides found to be present. This guide may also be usedfor qualitative identification of the gamma-ray emitting radio-nuclides in soil wi
7、thout attempting to quantify their activities.It can also be used to only determine their level of activitiesrelative to each other but not in an absolute sense. Generalinformation on radioactivity and its measurement may befound in Refs (7), (8), (9), (10), and (11) and Standard TestMethods E 181.
8、Information on specific applications ofgamma-ray spectrometry is also available in Refs (12) or (13).Practice D 3649 may be a valuable source of information.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard m
9、ay involve hazardous material, opera-tions, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with itsuse. It is the responsibility of the user of this standard toestablish appropriate safety and health practices and deter-mine the applicability o
10、f regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C 998 Practice for Sampling Surface Soil for RadionuclidesC 999 Practice for Soil Sample Preparation for the Deter-mination of RadionuclidesC 1009 Guide for Establishing a Quality Assurance Pro-gram for Analytical Chemi
11、stry Laboratories Within theNuclear IndustryD 3649 Practice for High-Resolution Gamma-Ray Spec-trometry of WaterE 181 Test Methods for Detector Calibration and Analysisof RadionuclidesIEEE/ASTM-SI-10 Standard for Use of the InternationalSystem of Units (SI) the Modern Metric System2.2 ANSI Standards
12、:4N13.30 Performance Criteria for RadiobioassayN42.14 Calibration and Use of Germanium Spectrometersfor the Measurement of Gamma-Ray Emission Rates ofRadionuclidesN42.23 Measurement Quality Assurance for RadioassayLaboratoriesANSI/IEEE-645 Test Procedures for High Purity Germa-nium Detectors for Ion
13、izing Radiation3. Summary of Guide3.1 High-resolution germanium detectors and multichannelanalyzers are used to ensure the identification of the gamma-ray emitting radionuclides that are present and to provide thebest possible accuracy for quantitative activity determinations.3.2 For qualitative rad
14、ionuclide identifications, the systemmust be energy calibrated. For quantitative determinations, thesystem must also be shape and efficiency calibrated. Thestandard sample/detector geometries must be established aspart of the efficiency calibration procedure.1This guide is under the jurisdiction of
15、ASTM Committee C26 on Nuclear FuelCycle and is the direct responsibility of Subcommittee C26.05 on Methods of Test.Current edition approved June 1, 2009. Published July 2009. Originally approvedin 1998. Last previous edition approved in 2004 as C 1402 04.2The boldface numbers in parentheses refer to
16、 the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available
17、 from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.3 The soil samples typically need to be pretreated (forexample, dr
18、ied), weighed, and placed in a standard container.For quantitative measurements, the dimensions of the containerholding the sample and its placement in front of the detectormust match one of the efficiency-calibrated geometries. Ifmultiple geometries can be selected, the geometry chosenshould reflec
19、t the detection limit and count rate limitations ofthe system. Qualitative measurements may be performed innon-calibrated geometries.3.4 The identification of the radionuclides present is basedon matching the energies of the observed gamma rays in thespectrum to computer-based libraries of literatur
20、e referencessee Refs (14), (15), (16), (17),or(18). The quantitativedeterminations are based on comparisons of observed countrates to previously obtained counting efficiency versus energycalibration data, and published branching ratios for the radio-nuclides identified.4. Significance and Use4.1 Gam
21、ma-ray spectrometry of soil samples is used toidentify and quantify certain gamma-ray emitting radionu-clides. Use of a germanium semiconductor detector is neces-sary for high-resolution gamma-ray measurements.4.2 Much of the data acquisition and analysis can beautomated with the use of commercially
22、 available systems thatinclude both hardware and software. For a general descriptionof the typical hardware in more detail than discussed in Section6, see Ref (19).4.3 Both qualitative and quantitative analyses may be per-formed using the same measurement data.4.4 The procedures described in this gu
23、ide may be used fora wide variety of activity levels, from natural backgroundlevels and fallout-type problems, to determining the effective-ness of cleanup efforts after a spill or an industrial accident, totracing contamination at older production sites, where wasteswere purposely disposed of in so
24、il. In some cases, thecombination of radionuclide identities and concentration ratioscan be used to determine the source of the radioactivematerials.4.5 Collecting samples and bringing them to a data acqui-sition system for analysis may be used as the primary methodto detect deposition of radionucli
25、des in soil. For obtaining arepresentative set of samples that cover a particular area, seePractice C 998. Soil can also be measured by taking the dataacquisition system to the field and measuring the soil in place(in situ). In situ measurement techniques are not discussed inthis guide.5. Interferen
26、ces5.1 In complex mixtures of gamma-ray emitters, the degreeof interference of one nuclide in the determination of anotheris governed by several factors. Interference will occur when thephotopeaks from two separate nuclides overlap within theresolution of the gamma-ray spectrometer. Most modern anal
27、y-sis software can deconvolute multiplets where the separation ofany two adjacent peaks is more than 0.5 FWHM (see Refs (20)and (21). For peak separations that are smaller than 0.5FWHM, most interference situations can be resolved with theuse of automatic interference correction algorithms (22).5.2
28、If the nuclides are present in the mixture in very unequalradioactive portions and if nuclides of higher gamma-rayenergy are predominant, the interpretation of minor, lessenergetic gamma-ray photopeaks becomes difficult due to thehigh Compton continuum and backscatter.5.3 True coincidence summing (a
29、lso called cascade sum-ming) occurs regardless of the overall count rate for anyradionuclide that emits two or more gamma rays in coinci-dence. Cobalt-60 is an example where both a 1173-keV and a1332-keV gamma ray are emitted from a single decay. If thesample is placed close to the detector, there i
30、s a finiteprobability that both gamma rays from each decay interactwithin the resolving time of the detector resulting in a loss ofcounts from both full energy peaks. Coincidence summing andthe resulting losses to the photopeak areas can be considerable(10 %) before a sum peak at an energy equal to
31、the sum of thecoincident gamma-ray energies becomes visible. Coincidencesumming and the resulting losses to the two individual photo-peak areas can be reduced to the point of being negligible byincreasing the source to detector distance or by using a smalldetector. Coincidence summing can be a sever
32、e problem if awell-type detector is used. See Test Methods E 181 and (7) formore information.5.4 Random summing is a function of count rate (not deadtime) and occurs in all measurements. The random summingrate is proportional to the total count squared and to theresolving time of the detector and el
33、ectronics. For mostsystems, uncorrected random summing losses can be held toless than1%bylimiting the total counting rate to less than1000 count/s. However, high-precision analyses can be per-formed at high count rates by the use of pileup rejectioncircuitry and dead-time correction techniques. Refe
34、r to TestMethods E 181 for more information.6. Apparatus6.1 Germanium Detector AssemblyThe detector shouldhave an active volume of greater than 50 cm3, with a full widthat one half the peak maximum (FWHM) less than 2.0 keV forthe cobalt-60 gamma ray at 1332 keV, certified by themanufacturer. A charg
35、e-sensitive preamplifier should be anintegral part of the detector assembly.6.2 Sample Holder AssemblyAs reproducibility of resultsdepends directly on reproducibility of geometry, the systemshould be equipped with a sample holder that will permit usingreproducible sample/detector geometries for all
36、sample con-tainer types that are expected to be used at several differentsample-to-detector distances.6.3 ShieldThe detector assembly should be surrounded bya radiation shield made of material of high atomic numberproviding the equivalent attenuation of 100 mm (or more in thecase of high background
37、radiation) of low-activity lead. It isdesirable that the inner walls of the shield be at least 125 mmdistant from the detector surfaces to reduce backscatter andannihilation radiation. If the shield is made of lead or has a leadliner, the shield should have a graded inner shield of appropri-ate mate
38、rials, for example, 1.6 mm of cadmium or tin-linedwith 0.4 mm of copper, to attenuate the induced 88-keV leadfluorescent X-rays. The shield should have a door or port forC 1402 04 (2009)2inserting and removing samples. The materials used to con-struct the shield should be prescreened to ensure that
39、they arenot contaminated with unacceptable levels of natural or man-made radionuclides. The lower the desired detection capability,the more important it is to reduce the background. For very lowactivity samples, the detector assembly itself, including thepreamplifer, should be made of carefully sele
40、cted low back-ground materials.6.4 High-Voltage Power/Bias SupplyThe bias supply re-quired for germanium detectors usually provides a voltage upto 65000 V and 1 to 100 A. The power supply should beregulated to 0.1 % with a ripple of not more than 0.01 %. Noisecaused by other equipment should be remo
41、ved with r-f filtersand power line regulators.6.5 AmplifierA spectroscopy amplifier which is compat-ible with the preamplifier. If used at high count rates, a modelwith pile-up rejection should be used. The amplifier should bepole-zeroed properly prior to use.6.6 Data Acquisition EquipmentA multicha
42、nnel pulse-height analyzer (MCA) with a built-in or stand-alone analog-to-digital converter (ADC) compatible with the amplifieroutput and pileup rejection scheme. The MCA (hardwired or acomputer-software-based) collects the data, provides a visualdisplay, and stores and processes the gamma-ray spect
43、ral data.The four major components of an MCA are: ADC, memory,control, and input/output. The ADC digitizes the analog pulsesfrom the amplifier. The height of these pulses represents energydeposited in the detector. The digital result is used by the MCAto select a memory location (channel number) whi
44、ch is used tostore the number of events which have occurred at the energy.The MCA must also be able to extend the data collection timefor the amount of time that the system is dead while processingpulses (live time correction).6.7 Count Rate MeterIt is useful but not mandatory tohave a means to meas
45、ure the total count rate for pulses abovethe amplifier noise during the measurement. If not provided bythe MCA, a separate count rate meter may be used for thispurpose. In the absence of a rate meter, count rates that are toohigh to provide reliable results may also be detected bymonitoring the syst
46、em dead time or peak resolution, or both.6.8 PulserRequired only if random summing effects arecorrected with the use of a stable pulser (23) and (24).6.9 ComputerMost modern gamma-ray spectrometers areequipped with a computer for control of the data acquisition aswell as automated analysis of the re
47、sulting spectra. Suchcomputer-based systems are readily available from severalcommercial vendors. Their analysis philosophies and capabili-ties do differ from each other somewhat. See ANSI N42.14 fora series of tests on how to tell if a particular gamma-spectrometry software package has adequate ana
48、lysis capabili-ties. In addition to the analysis capabilities, it is important toconsider the overall user interface and architecture of thesoftware. For small-scale operations, a few samples per week,a user interface that requires a lot of user intervention issufficient. For larger-scale operations
49、, with hundreds ofsamples per week on multiple detectors, a software packagethat permits some kind of batch processing and automatedoperation is recommended.7. Container for a Test Sample7.1 Sample holders and containers must have a reproduciblegeometry. Considerations include commercial availability, easeof use and disposal, and the containment of radioactivity forprotection of the working environment, personnel, and thegamma-ray spectrometer from contamination. For small soilsamples (up to a few grams), plastic bottles are convenientcontainers, while large samples (u
