1、Designation: E 181 98 (Reapproved 2003)Standard Test Methods forDetector Calibration and Analysis of Radionuclides1This standard is issued under the fixed designation E 181; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、of last revision. A 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 These methods cover general procedures for the cali-bration of radiation detectors and the analysis of radionuclid
3、es.For each individual radionuclide, one or more of these methodsmay apply.1.2 These methods are concerned only with specific radio-nuclide measurements. The chemical and physical propertiesof the radionuclides are not within the scope of this standard.1.3 The measurement standards appear in the fol
4、lowingorder:SectionsSpectroscopy Methods:Calibration and Usage of Germa-nium Detectors 3-12Calibration and Usage of ScintillationDetector Systems: 13-20SectionsCalibration and Usage of ScintillationDetectors for Simple Spectra 16Calibration and Usage of ScintillationDetectors for Complex Spectra 17C
5、ounting Methods:Beta Particle Counting 25-26Aluminum Absorption Curve 27-31Alpha Particle Counting 32-39Liquid Scintillation Counting 40-481.4 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user of this standard to
6、 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Document2.1 ASTM Standards:E 170 Terminology Relating to Radiation Measurementsand Dosimetry2SPECTROSCOPY METHODS3. Terminology3.1 Definitions:3.1.1 certified rad
7、ioactivity standard sourcea calibratedradioactive source, with stated accuracy, whose calibration iscertified by the source supplier as traceable to the NationalRadioactivity Measurements System (1).33.1.2 check sourcea radioactivity source, not necessarilycalibrated, that is used to confirm the con
8、tinuing satisfactoryoperation of an instrument.3.1.3 FWHM(full width at half maximum) the full widthof a gamma-ray peak distribution measured at half the maxi-mum ordinate above the continuum.3.1.4 national radioactivity standard sourcea calibratedradioactive source prepared and distributed as a sta
9、ndardreference material by the U.S. National Institute of Standardsand Technology.3.1.5 resolution, gamma raythe measured FWHM, afterbackground subtraction, of a gamma-ray peak distribution,expressed in units of energy.3.2 Abbreviations:Abbreviations:3.2.1 MCAMultichannel Analyzer.3.2.2 SCASingle Ch
10、annel Analyzer.3.2.3 ROIRegion-Of-Interest.3.3 For other relevant terms, see Terminology E 170.3.4 correlated photon summingthe simultaneous detec-tion of two or more photons originating from a single nucleardisintegration.3.5 dead timethe time after a triggering pulse duringwhich the system is unab
11、le to retrigger.NOTE 1The terms “standard source” and “radioactivity standard” aregeneral terms used to refer to the sources and standards of NationalRadioactivity Standard Source and Certified Radioactivity StandardSource.1These methods are under the jurisdiction of ASTM Committee E10 on NuclearTec
12、hnology and Applications .Current edition approved June 10, 1998. Published January 1999. Originallyapproved in 1961 T. Last previous edition approved in 1998 as E 181 98.2Annual Book of ASTM Standards, Vol 12.02.3The boldface numbers in parentheses refer to the list of references at the end ofthese
13、 methods.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.CALIBRATION AND USAGE OF GERMANIUMDETECTORS4. Scope4.1 This standard establishes methods for calibration, usage,and performance testing of germanium detectors for themeasuremen
14、t of gamma-ray emission rates of radionuclides. Itcovers the energy and full-energy peak efficiency calibration aswell as the determination of gamma-ray energies in the 0.06 to2-MeV energy region and is designed to yield gamma-rayemission rates with an uncertainty of 63 % (see Note 2). Thismethod ap
15、plies primarily to measurements that do not involveoverlapping peaks, and in which peak-to-continuum consider-ations are not important.NOTE 2Uncertainty U is given at the 68 % confidence level; that is,U 5 =(si21 1/3(di2where diare the estimated maximum system-atic uncertainties, and siare the rando
16、m uncertainties at the 68 %confidence level (2). Other methods of error analysis are in use (3, 4).5. Apparatus5.1 A typical gamma-ray spectrometry system consists of agermanium detector (with its liquid nitrogen cryostat, pream-plifier, and possibly a high-voltage filter) in conjunction with adetec
17、tor bias supply, linear amplifier, multichannel analyzer,and data readout device, for example, a printer, plotter,oscilloscope, or computer. Gamma rays interact with thedetector to produce pulses which are analyzed and counted bythe supportive electronics system.6. Summary of Methods6.1 The purpose
18、of these methods is to provide a standard-ized basis for the calibration and usage of germanium detectorsfor measurement of gamma-ray emission rates of radionu-clides. The method is intended for use by knowledgeablepersons who are responsible for the development of correctprocedures for the calibrat
19、ion and usage of germanium detec-tors.6.2 A source emission rate for a gamma ray of a selectedenergy is determined from the counting rate in a full-energypeak of a spectrum, together with the measured efficiency ofthe spectrometry system for that energy and source location. Itis usually not possible
20、 to measure the efficiency directly withemission-rate standards at all desired energies. Therefore acurve or function is constructed to permit interpolation be-tween available calibration points.7. Preparation of Apparatus7.1 Follow the manufacturers instructions for setting upand preliminary testin
21、g of the equipment. Observe all of themanufacturers limitations and cautions. All tests described inSection 12 should be performed before starting the calibra-tions, and all corrections shall be made when required. A checksource should be used to check the stability of the system atleast before and
22、after the calibration.8. Calibration Procedure8.1 Energy CalibrationDetermine the energy calibration(channel number versus gamma-ray energy) of the detectorsystem at a fixed gain by determining the channel numberscorresponding to full energy peak centroids from gamma raysemitted over the full energy
23、 range of interest from multipeakedor multinuclide radioactivity sources, or both. Determinenonlinearity correction factors as necessary (5).8.1.1 Using suitable gamma-ray compilations (6-14), plot orfit to an appropriate mathematical function the values for peakcentroid (in channels) versus gamma e
24、nergy.8.2 Effciency Calibration:8.2.1 Accumulate an energy spectrum using calibrated ra-dioactivity standards at a desired and reproducible source-to-detector distance. At least 20 000 net counts should beaccumulated in each full-energy gamma-ray peak of interestusing National or Certified Radioacti
25、vity Standard Sources, orboth (see 12.1, 12.5, and 12.6).8.2.2 For each standard source, obtain the net count rate(total count rate of region of interest minus the Comptoncontinuum count rate and, if applicable, the ambient back-ground count rate within the same region) in the full-energygamma-ray p
26、eak, or peaks, using a tested method that providesconsistent results (see 12.2, 12.3, and 12.4).8.2.3 Correct the standard source emission rate for decay tothe count time of 8.2.2.8.2.4 Calculate the full-energy peak efficiency, Ef, as fol-lows:Ef5NpNg(1)where:Ef= full-energy peak efficiency (counts
27、 per gamma rayemitted),Np= net gamma-ray count in the full-energy peak (countsper second live time) (Note 3) (see 8.2.2), andNg= gamma-ray emission rate (gamma rays per second).NOTE 3Any other unit of time is acceptable provided it is usedconsistently throughout.8.2.5 There are many ways of calculat
28、ing the net gamma-ray count. The method presented here is a valid, commonmethod when there are no interferences from photopeaksadjacent to the peak of interest, and when the continuum varieslinearly from one side of the peak to the other.8.2.5.1 Other net peak area calculation methods can also beuse
29、d for single peaks, and must be used when there isinterference from adjacent peaks, or when the continuum doesnot behave linearly. Other methods are acceptable, if they areused in a consistent manner and have been verified to provideaccurate results.8.2.5.2 Using a simple model, the net peak area fo
30、r a singlepeak can be calculated as follows:NA5 Gs2 B 2 I (2)where:Gs= gross count in the peak region-of-interest (ROI) in thesample spectrum,B = continuum, andI = number of counts in the background peak (if there isno background peak, or if a background subtraction isnot performed, I = 0).E 181 98
31、(2003)28.2.5.3 The net gamma-ray count, Npis related to the netpeak area as follows:Np5NATs(3)where Ts= spectrum live time.8.2.5.4 The continuum, B, is calculated from the samplespectrum using the following equation (see Fig. 1):B 5N2nB1s1 B2s! (4)where:N = number of channels in the peak ROI,n = num
32、ber of continuum channels on each side,4B1s= sum of counts in the low-energy continuum region inthe sample spectrum, andB2s= sum of counts in the high-energy continuum regionin the sample spectrum.NOTE 4These equations assume that the channels that are used tocalculate the continuum do not overlap w
33、ith the peak ROI, and areadjacent to it, or have the same size gap between the two regions on bothsides. A different equation must be used, if the gaps are of a different size.The peaked background, I, is calculated from a separatebackground measurement using the following equation:I 5TsTbIb(5)where
34、:Ts= live time of the sample spectrum,Tb= live time of the background spectrum, andIb= net background peak area in the background spec-trum.If a separate background measurement exists, the net back-ground peak area is calculated from the following equation:Ib5 Gb2 Bb(6)where:Gb= sum of gross counts
35、in the background peak region(of the background spectrum), andBb= continuum counts in the background peak region (ofthe background spectrum).The continuum counts in the background spectrum arecalculated from the following equation:Bb5N2nB1b1 B2b! (7)where:N = number of channels in the background pea
36、k ROI,n = number of continuum channels on each side (as-sumed to be the same on both sides),B1b= sum of counts in the low-energy continuum region inthe background spectrum, andB2b= sum of counts in the high-energy continuum regionin the background spectrum.8.2.5.5 If the standard source is calibrate
37、d in units ofBecquerels, the gamma-ray emission rate is given byNg5 APg(8)where:A = number of nuclear decays per second, andPg= probability per nuclear decay for the gamma ray(7-14).8.2.6 Plot, or fit to an appropriate mathematical function,the values for full-energy peak efficiency (determined in 8
38、.2.4)versus gamma-ray energy (see 12.5) (15-23).9. Measurement of Gamma-Ray Emission Rate of theSample9.1 Place the sample to be measured at the source-to-detector distance used for efficiency calibration (see 12.6).9.1.1 Accumulate the gamma-ray spectrum, recording thecount duration.9.1.2 Determine
39、 the energy of the gamma rays present byuse of the energy calibration obtained under, and at the samegain as 8.1.9.1.3 Obtain the net count rate in each full-energy gamma-ray peak of interest as described in 8.2.2.9.1.4 Determine the full-energy peak efficiency for eachenergy of interest from the cu
40、rve or function obtained in 8.2.5.9.1.5 Calculate the number of gamma rays emitted per unitlive time for each full-energy peak as follows:Ng5NpEf(9)When calculating a nuclear transmutation rate from agamma-ray emission rate determined for a specific radionu-clide, a knowledge of the gamma-ray probab
41、ility per decay isrequired (7-14), that is,A 5NgPg(10)9.1.6 Calculate the net peak area uncertainty as follows:SNA5Gs1SN2nD2B1s1 B2s! 1STsTbD2SIb!2(11)4For simplicity of these calculations, n is assumed to be the same on both sidesof the peak. If the continuum is calculated using a different number
42、of channels onthe left of the peak than on the right of the peak, different equations must be used.FIG. 1 Typical Spectral Peak With Parameters Used in the PeakArea Determination IndicatedE 181 98 (2003)3where:SIb5Gb1SN2nD2B1b1 B2b! (12)andSNA= net peak area uncertainty (at 1s confidence level),Gs=
43、gross counts in the peak ROI of the sample spec-trum,Gb= gross counts in the peak ROI of the backgroundspectrum,N = number of channels in the peak ROI,n = number of continuum channels on each side (as-sumed to be the same on both sides for theseequations to be valid),B1s= continuum counts left of th
44、e peak ROI in the samplespectrum,B2s= continuum counts right of the peak ROI in thesample spectrum,B1b= continuum counts left of the peak ROI in thebackground spectrum,B2b= continuum counts right of the peak ROI in thebackground spectrum,Ts= live time of the sample spectrum, andTb= live time of the
45、background spectrum.If there is no separate background measurement, or if nobackground subtract is performed, SIb=0.9.1.7 For other sources of error, see Section 11.10. Performance Testing10.1 The following system tests should be performed on aregularly scheduled basis (or, if infrequently used, pre
46、cedingthe use of the system). The frequency for performing each testwill depend on the stability of the particular system as well ason the accuracy and reliability of the required results. Wherehealth or safety is involved, much more frequent checking maybe appropriate. A range of typical frequencie
47、s for noncriticalapplications is given below for each test.10.1.1 Check the system energy calibration (typically dailyto semiweekly), using two or more gamma rays whose energiesspan at least 50 % of the calibration range of interest. Correctthe energy calibration, if necessary.10.1.2 Check the syste
48、m count rate reproducibility (typi-cally daily to weekly) using at least one long-lived radionu-clide. Correct for radioactive decay if significant decay (1 %)has occurred between checks.10.1.3 Check the system resolution (typically weekly tomonthly) using at least one gamma-ray emitting radionuclid
49、e(24).10.1.4 Check the efficiency calibration (typically monthly toyearly) using a National or Certified Radioactivity Standard (orStandards) emitting gamma rays of widely differing energies.10.2 The results of all performance checks shall be recordedin such a way that deviations from the norm will be readilyobservable. Appropriate action, which could include confirma-tion, repair, and recalibration as required, shall be taken whenthe measured values fall outside the predetermined limits.10.2.1 In addition, the above performance checks (see 10.1)should be mad
