ASTM_D_4962_-_18.pdf

Designation:D496218Standard 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 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 practice covers the measurement of radionuclidesin water by means of gamma-ray spectrometry.It is applicableto nuclides emitting gamma-rays 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 electronic 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 nuclide 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 in a mixture of radionuclides but thatability is limited when using low energy resolution Na(Tl)detectors as compared to High Purity Germanium(HPGe)detectors.General information on radioactivity and the mea-surement of radiation has been published(11 and 12).Infor-mation on specific application of gamma-ray spectrometry isalso available in the literature(13-16).1.3 The values stated in SI units are to be regarded asstandard.The values given in parentheses after SI units areincluded for information only and are not considered standard.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,health,and environmental practices and deter-mine the applicability of regulatory limitations 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 TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:3D1129 Terminology Relating to WaterD3648 Practices for the Measurement of RadioactivityD7902 Terminology for Radiochemical AnalysesE181 Test Methods for Detector Calibration and Analysis ofRadionuclides3.Terminology3.1 Definitions:3.1.1 For definitions of terms used in this standard,refer toTerminologies D1129 and D7902.4.Summary of Practice4.1 Gamma-ray spectra are commonly measured withmodular equipment consisting of a detector,amplifier,analog-to-digital converter,multi-channel analyzer device,and acomputer(17 and 18).4.2 Thallium-activated sodium-iodide crystals,NaI(Tl),which can be operated at ambient temperatures,are often usedas gamma-ray detectors in spectrometer systems.However,their energy resolution limits their use to the analysis of singlenuclides or simple mixtures of a few nuclides.A resolution ofabout 7%(45 keV full width at one half the137Cs peak height)at 662 keV can be expected for a NaI(Tl)detector in a 76 mmby 76 mm-configuration.There are solid scintillators such ascerium doped LaBr3that may provide a performance advan-tage over NaI(Tl)in terms of energy resolution but whosesuitability should be evaluated and documented before beingconsidered as a substitute for NaI(Tl).4.3 Interaction of a gamma-ray with the atoms in a NaI(Tl)detector results in light photons that can be detected by a1This 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 Oct.1,2018.Published November 2018.Originallyapproved in 1989.Last previous edition approved in 2017 as D4962 17.DOI:10.1520/D4962-18.2The 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 to the standards Document Summary page onthe ASTM website.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 Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued