1、Designation: C 1402 04Standard 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 of last revision. A
2、 number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 gam
3、ma-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 p
4、Ci) 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 soi
5、l 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 either quantitative or
6、 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 without attempting
7、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. Information on sp
8、ecific applications ofgamma-ray spectrometry is also available in Refs (12) or (13).Practice D 3649 may be a valuable source of information.1.3 This standard may involve hazardous material, opera-tions, and equipment. This standard does not purport toaddress all of the safety concerns, if any, assoc
9、iated 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 limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C 998 Practice for Sampling Surface Soil for RadionuclidesC
10、999 Practice for Soil Sample Preparation for the Deter-mination of RadionuclidesC 1009 Guide for Establishing a Quality Assurance Pro-gram for Analytical Chemistry Laboratories Within theNuclear IndustryD 3649 Practice for High-Resolution Gamma-Ray Spec-trometry of WaterE 181 Test Methods for Detect
11、or Calibration and Analysisof RadionuclidesIEEE/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
12、 Rates ofRadionuclidesN42.23 Measurement Quality Assurance for RadioassayLaboratoriesANSI/IEEE-645 Test Procedures for High Purity Germa-nium Detectors for Ionizing Radiation3. Summary of Guide3.1 High-resolution germanium detectors and multichannelanalyzers are used to ensure the identification of
13、the gamma-ray emitting radionuclides that are present and to provide thebest possible accuracy for quantitative activity determinations.3.2 For qualitative radionuclide identifications, the systemmust be energy calibrated. For quantitative determinations, thesystem must also be shape and efficiency
14、calibrated. Thestandard sample/detector geometries must be established aspart of the efficiency calibration procedure.3.3 The soil samples typically need to be pretreated (forexample, dried), weighed, and placed in a standard container.For quantitative measurements, the dimensions of the container1T
15、his guide is under the jurisdiction of ASTM Committee C26 on Nuclear FuelCycle and is the direct responsibility of Subcommittee C26.05 on Methods of Test.Current edition approved June 1, 2004. Published July 2004. Originally approvedin 1998. Last previous edition approved in 1998 as C 1402 98.2The b
16、oldface numbers in parentheses refer to the list of references at the endof this 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 Sum
17、mary page onthe ASTM website.4Available from American National Standards Institute, West 42nd St. 13thFloor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.holding the sample and its placement in front of the dete
18、ctormust match one of the efficiency-calibrated geometries. Ifmultiple geometries can be selected, the geometry chosenshould reflect the detection limit and count rate limitations ofthe system. Qualitative measurements may be performed innon-calibrated geometries.3.4 The identification of the radion
19、uclides present is basedon matching the energies of the observed gamma rays in thespectrum to computer-based libraries of literature referencessee Refs (14), (15), (16), (17),or(18). The quantitativedeterminations are based on comparisons of observed countrates to previously obtained counting effici
20、ency versus energycalibration data, and published branching ratios for the radio-nuclides identified.4. Significance and Use4.1 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 fo
21、r high-resolution gamma-ray measurements.4.2 Much of the data acquisition and analysis can beautomated with the use of commercially 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 B
22、oth qualitative and quantitative analyses may be per-formed using the same measurement data.4.4 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
23、 a spill 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.4.5 Collecting sampl
24、es and 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 C 998. Soil can also be measured by taking the dataacquisition system
25、 to the field and measuring the soil in place(in situ). In situ measurement techniques are not discussed inthis guide.5. Interferences5.1 In complex mixtures of gamma-ray emitters, the degreeof interference of one nuclide in the determination of anotheris governed by several factors. Interference wi
26、ll occur 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 small
27、er than 0.5FWHM, most interference situations can be resolved with theuse of automatic interference correction algorithms (22).5.2 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, le
28、ssenergetic gamma-ray photopeaks becomes difficult due to thehigh Compton continuum and backscatter.5.3 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 w
29、here both 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. Co
30、incidence 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 poi
31、nt of being 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 E 181 and (7) formore information.5.4 Random summing is a function of count rate (not deadtime) and occurs in
32、all measurements. 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 count/s. However, high-precisi
33、on analyses can be per-formed at high count rates by the use of pileup rejectioncircuitry and dead-time correction techniques. Refer 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 width
34、at one half the peak maximum (FWHM) less than 2.0 keV forthe cobalt-60 gamma ray at 1332 keV, certified by themanufacturer. A charge-sensitive preamplifier should be anintegral part of the detector assembly.6.2 Sample Holder AssemblyAs reproducibility of resultsdepends directly on reproducibility of
35、 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.6.3 ShieldThe detector assembly should be surrounded bya radiation
36、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 backscatter andannihila
37、tion 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 door or port fo
38、rinserting 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,C1402042the more important it is to reduce the backgrou
39、nd. For very lowactivity samples, the detector assembly itself, including thepreamplifer, should be made of carefully selected 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 pow
40、er 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.6.5 AmplifierA spectroscopy amplifier which is compat-ible with the preamplifier. If used at high count rates, a modelwith pile-up r
41、ejection should be used. The amplifier should bepole-zeroed properly prior to use.6.6 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 (hardwi
42、red 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 represe
43、nts 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 is de
44、ad while processingpulses (live time correction).6.7 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 the ab
45、sence 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.6.8 PulserRequired only if random summing effects arecorrected with the use of a stable pulser (23) and (24).6.9 ComputerMost modern gamm
46、a-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 capabili-ties do differ from each other somewhat
47、. See ANSI N42.14 fora series of tests on how to tell if a particular gamma-spectrometry software package has adequate analysis capabili-ties. In addition to the analysis capabilities, it is important toconsider the overall user interface and architecture of thesoftware. For small-scale operations,
48、a few samples per week,a user interface that requires a lot of user intervention issufficient. For larger-scale operations, 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 Te
49、st 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 (up to several kilograms),which require greater sensitivity, are frequently packaged inMarinelli beakers. For analyzing low-energy gamma rays atclose geometries, the consistency of th
