1、Designation:D496202(Reapproved 2009)Standard Practice forNaI(Tl)Gamma-Ray Spectrometry of Water1This standard is issued under the fixed designation D4962;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A num
2、ber in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers the measurement of radionuclidesin water by means of gamma-ray spectrometry.It is applicableto nuclides emitting gamma-ra
3、ys with energies greater than 50keV.For typical counting systems and sample types,activitylevels of about 40 Bq(1080 pCi)are easily measured andsensitivities of about 0.4 Bq(11 pCi)are found for manynuclides(1-10).2Count rates in excess of 2000 counts persecond should be avoided because of electroni
4、c limitations.High count rate samples can be accommodated by dilution orby increasing the sample to detector distance.1.2 This practice can be used for either quantitative orrelative determinations.In tracer work,the results may beexpressed by comparison with an initial concentration of agiven nucli
5、de which is taken as 100%.For radioassay,theresults may be expressed in terms of known nuclidic standardsfor the radionuclides known to be present.In addition to thequantitative measurement of gamma-ray activity,gamma-rayspectrometry can be used for the identification of specificgamma-ray emitters i
6、n a mixture of radionuclides.Generalinformation on radioactivity and the measurement of radiationhas been published(11 and 12).Information on specificapplication of gamma-ray spectrometry is also available in theliterature(13-16).1.3 The values stated in SI units are to be regarded asstandard.No oth
7、er units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of r
8、egulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:3D3648 Practices for the Measurement of RadioactivityD4962 Practice for NaI(Tl)Gamma-Ray Spectrometry ofWaterE181 Test Methods for Detector Calibration and Analysis ofRadionuclides3.Summary of Practice3.1 Gamma-ray spectra a
9、re commonly measured withmodular equipment consisting of a detector,amplifier,multi-channel analyzer device,and a computer(17 and 18).3.2 Thallium-activated sodium-iodide crystals,NaI(Tl),which can be operated at ambient temperatures,are often usedas gamma-ray detectors in spectrometer systems.Howev
10、er,their energy resolution limits their use to the analysis of singlenuclides or simple mixtures of a few nuclides.Resolution ofabout 7%(45 keV full width at one half the137Cs peakheight)at 662 keV can be expected for a NaI(Tl)detector in a76 mm by 76 mm-configuration.3.3 Interaction of a gamma-ray
11、with the atoms in a NaI(Tl)detector results in light photons that can be detected by amultiplier phototube.The output from the multiplier phototubeand its preamplifier is directly proportional to the energydeposited by the incident gamma-ray.These current pulses arefed into an amplifier of sufficien
12、t gain to produce voltageoutput pulses in the amplitude range from 0 to 10 V.3.4 A multichannel pulse-height analyzer is used to deter-mine the amplitude of each pulse originating in the detector,and accumulates in a memory the number of pulses in eachamplitude band(or channel)in a given counting ti
13、me(17 and18).For a 0 to 2 MeV spectrum two hundred data points areadequate.3.5 The distribution of the amplitudes(pulse heights)of thepulse energies,represented by the pulse height,can be sepa-rated into two principal components.One of these componentshas a nearly Gaussian distribution and is the re
14、sult of total1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.04 on Methods of RadiochemicalAnalysis.Current edition approved Feb.1,2009.Published March 2009.Originallyapproved in 1989.Last previous edition approved in 2002 a
15、s D4962 02.DOI:10.1520/D4962-02R09.2The boldface numbers in parentheses refer to the references at the end of thispractice.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 t
16、o the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 absorption of the gamma-ray energy in the detector;this peakis normally referred to as the full-energy peak or photopeak.The other component is a continuous one,lower in energy thanthe photopeak.This continuous curve is referred to as theCompton continuum and results from interactions wherein thegamma photons lose only part of thei
