1、Designation: C1402 17Standard Guide forHigh-Resolution Gamma-Ray Spectrometry of Soil Samples1This standard is issued under the fixed designation C1402; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber 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 soilsamples by means of gamma-
3、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 as 0.1 Bq (2.7 pCi)
4、 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 techniques, where soil i
5、s 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 either quantitative or re
6、lativedeterminations. 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 without attempting to
7、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 E181. Information on specif
8、ic applications of gamma-ray spectrometry is also available in Refs (12) or (13). PracticeD3649 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 may involve hazardous
9、material,operations, 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 of regulatory limitation
10、s prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization Techn
11、icalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3C859 Terminology Relating to Nuclear MaterialsC998 Practice for Sampling Surface Soil for RadionuclidesC999 Practice for Soil Sample Preparation for the Determi-nation of RadionuclidesC1009 Guide for Establishing and Ma
12、intaining a QualityAssurance Program forAnalytical Laboratories Within theNuclear IndustryD3649 Practice for High-Resolution Gamma-Ray Spectrom-etry of WaterD7282 Practice for Set-up, Calibration, and Quality Controlof Instruments Used for Radioactivity MeasurementsE181 Test Methods for Detector Cal
13、ibration and Analysis ofRadionuclidesIEEE/ASTM-SI-10 Standard for Use of the InternationalSystem of Units (SI) the Modern Metric System2.2 ANSI Standards:4N13.30 Performance Criteria for RadiobioassayN42.14 Calibration and Use of Germanium Spectrometersfor the Measurement of Gamma-Ray Emission Rates
14、 ofRadionuclidesN42.23 American National Standard Measurement and As-sociated InstrumentationIEEE-325 Standard Test Procedures for GermaniumGamma-Ray Detectors1This guide is under the jurisdiction of ASTM Committee C26 on Nuclear FuelCycle and is the direct responsibility of Subcommittee C26.05 on M
15、ethods of Test.Current edition approved June 1, 2017. Published July 2017. Originally approvedin 1998. Last previous edition approved in 2009 as C1402 04 (2009). DOI:10.1520/C1402-17.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM
16、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 from American National Standards Institute (ANSI), 25 W. 43rd St.,4th F
17、loor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decis
18、ion on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1Mon Apr 30 23 3. Terminology3.1 Except as otherwise defined herein, definitions of termsare as given in Terminology C859.4.
19、Summary of Guide4.1 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.4.2 For qualitative radionuclide identifi
20、cations, 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.4.3 The soil samples typically need to be pretreated (forex
21、ample, dried), 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 chosenshou
22、ld reflect the detection limit and count rate limitations ofthe system. Qualitative measurements may be performed innon-calibrated geometries.4.4 The identification of the radionuclides present is basedon matching the energies of the observed gamma rays in thespectrum to computer-based libraries of
23、literature 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.5. Significance and U
24、se5.1 Gamma-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.5.2 Much of the data acquisition and analysis can beautomated with the use of com
25、mercially available systems thatinclude both hardware and software. For a general descriptionof the typical hardware in more detail than discussed in Section7, see Ref (19). For best practices on set-up, calibration, andquality control of utilized spectrometry systems, see PracticeD7282.5.3 Both qua
26、litative and quantitative analyses may be per-formed using the same measurement data.5.4 The procedures described in this guide 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 spil
27、l or an industrial accident, totracing contamination at older production sites, where wasteswere purposely disposed of in soil. In some cases, thecombination of radionuclide identities and concentration ratioscan be used to determine the source of the radioactivematerials.5.5 Collecting samples and
28、bringing them to a data acqui-sition system for analysis may be used as the primary methodto detect deposition of radionuclides in soil. For obtaining arepresentative set of samples that cover a particular area, seePractice C998. Soil can also be measured by taking the dataacquisition system to the
29、field and measuring the soil in place(in situ). In situ measurement techniques are not discussed inthis guide.6. Interferences6.1 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
30、 when thephotopeaks from two separate nuclides overlap within theresolution of the gamma-ray spectrometer. Most modern analy-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
31、0.5FWHM, most interference situations can be resolved with theuse of automatic interference correction algorithms (22).6.2 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, lessenerge
32、tic gamma-ray photopeaks becomes difficult due to thehigh Compton continuum and backscatter.6.3 True coincidence summing (also 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 bot
33、h a 1173-keV and a1332-keV gamma ray are emitted from a single decay. If thesample is placed close to the detector, there is 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. Coincidenc
34、e summing andthe resulting losses to the photopeak areas can be considerable(10 %) before a sum peak at an energy equal to 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 be
35、ing negligible byincreasing the source to detector distance or by using a smalldetector. Coincidence summing can be a severe problem if awell-type detector is used. See Test Methods E181 and (7) formore information.6.4 Random summing is a function of count rate (not deadtime) and occurs in all measu
36、rements. The random summingrate is proportional to the total count squared and to theresolving time of the detector and electronics. For mostsystems, uncorrected random summing losses can be held toless than1%bylimiting the total counting rate to less than1000 counts/s. However, high-precision analy
37、ses can be per-formed at high count rates by the use of pileup rejectioncircuitry and dead-time correction techniques. Refer to TestMethods E181 for more information.7. Apparatus7.1 Germanium Detector AssemblyThe detector shouldhave an active volume of greater than 50 cm3, with a full widthat one ha
38、lf the peak maximum (FWHM) less than 2.0 keV forC1402 172Mon Apr 30 23 the cobalt-60 gamma ray at 1332 keV, certified by themanufacturer. A charge-sensitive preamplifier should be anintegral part of the detector assembly.7.2 Sample Holder AssemblyAs reproducibility of resultsdepends directly on repr
39、oducibility of geometry, the systemshould be equipped with a sample holder that will permit usingreproducible sample/detector geometries for all sample con-tainer types that are expected to be used at several differentsample-to-detector distances.7.3 ShieldThe detector assembly should be surrounded
40、bya radiation shield made of material of high atomic numberproviding the equivalent attenuation of 100 mm (or more in thecase of high background 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 backscatt
41、er andannihilation radiation. If the shield is made of lead or has a leadliner, the shield should have a graded inner shield of appropri-ate materials, 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 d
42、oor or port forinserting and removing samples. The materials used to con-struct the shield should be prescreened to ensure that 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 ba
43、ckground. For very lowactivity samples, the detector assembly itself, including thepreamplifer, should be made of carefully selected low back-ground materials.7.4 High-Voltage Power/Bias SupplyThe bias supply re-quired for germanium detectors usually provides a voltage upto 65000 V and 1 to 100 A. T
44、he power supply should beregulated to 0.1 % with a ripple of not more than 0.01 %. Noisecaused by other equipment should be removed with r-f filtersand power line regulators.7.5 AmplifierA spectroscopy amplifier which is compat-ible with the preamplifier. If used at high count rates, a modelwith pil
45、e-up rejection should be used. The amplifier should bepole-zeroed properly prior to use.7.6 Data Acquisition EquipmentA multichannel 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 (
46、hardwired or acomputer-software-based) collects the data, provides a visualdisplay, and stores and processes the gamma-ray spectral 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 r
47、epresents energydeposited in the detector. The digital result is used by the MCAto select a memory location (channel number) which 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
48、 is dead while processingpulses (live time correction).7.7 Count Rate MeterIt is useful but not mandatory tohave a means to measure 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
49、the absence of a rate meter, count rates that are toohigh to provide reliable results may also be detected bymonitoring the system dead time or peak resolution, or both.7.8 PulserRequired only if random summing effects arecorrected with the use of a stable pulser (23) and (24).7.9 ComputerMost modern gamma-ray spectrometers areequipped with a computer for control of the data acquisition aswell as automated analysis of the resulting spectra. Suchcomputer-based systems are readily available from severalcommercial vendors. Their analysis philosophies and capabi
