ASTM D6239-2003e2 516 Standard Test Method for Uranium in Drinking Water by High-Resolution Alpha-Liquid-Scintillation Spectrometry.pdf

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1、Designation: D 6239 032Standard Test Method forUranium in Drinking Water by High-Resolution Alpha-Liquid-Scintillation Spectrometry1This standard is issued under the fixed designation D 6239; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r

2、evision, 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.1NOTEAdded research report reference to Section 14 editorially in March 2008.2NOTEAdded research report refer

3、ence to Section 14 editorially in September 2008.1. Scope1.1 This test method covers determining the total solubleuranium activity in drinking water in the range of 0.037 Bq/L(1 pCi/L) or greater by selective solvent extraction andhigh-resolution alpha-liquid-scintillation spectrometry. The en-ergy

4、resolution obtainable with this technique also allowsestimation of the238Uto234U activity ratio.1.2 This test method was tested successfully with reagentwater and drinking water. It is the users responsibility toensure the validity of this test method for waters of untestedmatrices.1.3 The values st

5、ated in SI units are to be regarded asstandard. The values given in parentheses are for informationonly.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

6、health practices and determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements, see Section 9.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 1193 Specifications for Reagent WaterD 2777 Practice for Determination of Precision

7、and Bias ofApplicable Methods of Committee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3648 Practices for the Measurement of Radioactivity3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, referto Terminology D 1129. For terms not include

8、d in this refer-ence, refer to other published glossaries (1)34. Summary of Test Method4.1 This test method is based on solvent extraction technol-ogy to isolate and concentrate uranium in drinking water forcounting via a high-resolution alpha-liquid-scintillation spec-trometer.4.2 To determine tota

9、l uranium, as well as limited isotopicuranium (238U and234U) by activity in drinking water, a200mL acidified water sample is first spiked with232Uasanisotopic tracer, boiled briefly to remove radon, and evaporateduntil less than 50 mL remain. The solution is then madeapproximately 0.01 M in diethyle

10、netriaminepentaacetic acid(DTPA) and the pH is adjusted to between 2.5 and 3.0. Thesample is transferred to a separatory funnel and equilibratedwith 1.50 mL of an extractive scintillator containing a dialkylphosphoric acid extracting agent. Under these conditions onlyuranium is quantitatively transf

11、erred to the organic phase whilethe extraction of undesired ions is masked by the presence ofDTPA. Following phase separation, 1.00 mL of the organicphase is sparged with dry argon gas to remove oxygen, achemical quench agent, and counted on a high-resolutionalpha-liquid-scintillation spectrometer a

12、nd multichannel ana-lyzer (MCA).4.3 The alpha spectrum of a sample that contains naturaluranium and that is analyzed with an internal232U tracer willappear similar to the spectrum in Fig. 1. An approximateresolution of 250 keV FWHM for238U (4.2 MeV) allowsresolution and analysis of the238U,234U, and

13、232U energyspectrum peaks when their activities are of the same order ofmagnitude. Resolution of the235U (4.4 MeV) alpha peak is notpossible, but its activity, which accounts for approximately2.2 % of the total natural uranium activity, is included in thetotal uranium activity calculated when the238

14、U and234U peaksare in the region of interest (ROI). When the238U and234U1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.04 on Methods of Radiochemi-cal Analysis.Current edition approved June 10, 2003. Published August 200

15、3. Originallyapproved in 1998. Last previous edition approved in 2002 as D 623902.2For 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 pag

16、e onthe ASTM website.3The boldface numbers in parenthesis refer to the list of references at the end ofthe text.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.peaks are integrated separately, a portion of the235U activitywill be inc

17、luded in the238U activity and the rest in the234Uactivity, depending on the exact ROIs selected. Likewise, ifpresent,236U and233U will not be resolved by the spectrometer;however, their activity will be included in the total uraniumROI.5. Significance and Use5.1 This test method is a fast, cost-effe

18、ctive method that canyield limited isotopic activity levels for238U and234U, as wellas total uranium activity. Although232U is incorporated as atracer, uranium recoveries for this test measured during thedevelopmental work on this test method were usually between95 and 105%.5.2 The high-resolution a

19、lpha-liquid-scintillation spectrom-eter offers a constant 99.6 6 0.1 % counting efficiency andinstrument backgrounds as low as 0.001 counts per minute(cpm) over a 4 to 7 MeV energy range according to McDowelland McDowell (2). Count rates for extractive scintillatorblanks and reagent blanks usually r

20、ange from 0.01 cpm to 0.1cpm.6. Interferences6.1 During the development work on this method, less than1% of241Am,238Pu,210Po,226Ra,222Rn, and230Th present inthe original sample were found to extract under the conditionsdescribed for the extraction of uranium by this procedure.Uranium extraction is q

21、uantitative at pH values from 1.0 to 5.0but extraction of230Th and238Pu increased slightly at pHvalues below 2.5 and phase separation was slower and lesscomplete at pH values above 3.5. DTPA concentration is notcritical in the range of 0.001 M to 0.1 M as long as astoichiometric excess relative to t

22、he concentration of interfer-ing ions, especially ferric ion (Fe3+), is maintained.As much as30 mg of Fe3+did not interfere with the extraction of uraniumwhen the DTPA concentration was 0.010 M, and as much as250 mg of Fe3+did not interfere when the DTPAconcentrationwas increased to 0.10 M. As much

23、as 2000 mg of calcium ion(Ca2+) did not present an interference in a 0.010 M DTPAsolution. Sulfate ion (SO42-) did not interfere with the extrac-tion of uranium at concentrations as high as 1 M, but hydrogenoxalate (HC2O4) concentrations greater than 0.001 M anddihydrogen phosphate (H2PO4) concentra

24、tions greater than0.2 M resulted in decreased uranium recovery. These concen-trations, however, are several orders of magnitude higher thanthe normal concentration of these ions in drinking water.6.2 Beta- and gamma-emitting radionuclide interference isminimized (typically 99.95 % rejection of beta/

25、gamma pulses)according to McDowell and McDowell (2) by the pulse-shapediscrimination of the high-resolution alpha-liquid-scintillationspectrometer.6.3 Quenching, often a problem with liquid scintillationcounting, is significantly reduced by the use of extractivescintillator technology and will only

26、result in a normallyinsignificant spectral energy shift with this procedure. No alphacounts will be lost due to quenching.6.4234U and238U may exist in the232U tracer.The extent ofthe positive bias should be determined periodically.7. Apparatus7.1 Caps, vinyl or cork for culture tubes.7.2 Funnels, se

27、paratory, 125-mL, pear-shaped, polytet-rafluoroethylene or polypropylene.7.3 Meter, pH, with gel electrode or low leak-rate referenceelectrode.7.4 Multichannel Analyzer (MCA), 512 channels or more,ADC/memory or better.7.5 NIM Bin and Power Supply.7.6 Power Supply, high voltage (+1000 volt 1 ma), ori

28、ntegral to the spectrometer, see item 7.10.7.7 Sample, counting reference, normal uranium.4Thiscounting reference sample is an approximately 50/50 mix of238U and234U by activity in 1.00 mL of the extractivescintillator solution and enclosed in a 10 by 75 mm glassculture tube and is for standardizati

29、on purposes only.7.8 Source,137Cs, approximately 1.85 3 105Bq (5 micro-curies). This item is for standardization purposes only.7.9 Sparging Gas Conditioner5This apparatus providesconditioned argon gas to remove oxygen, a chemical quenchagent, from the sample, thus improving pulse shape discrimi-nati

30、on and energy resolution. It consists of a specially-madeglass tube, partially filled with silicone oil, that serves as apressure-limiter, a gas drying tower filled with CaSO4(6 to 8mesh) for additional drying of the argon gas, a gas washingbottle containing toluene and molecular sieve to saturate t

31、heargon with toluene and prevent sample evaporation while4The sole source of supply of the238U and234U normal uranium countingreference sample known to the committee at this time is from ORDELA, Inc., 1009Alvin Weinberg Drive, Oak Ridge, TN, 37830. If you are aware of alternativesuppliers, please pr

32、ovide this information to ASTM Headquarters. Your commentswill receive careful consideration at a meeting of the responsible technicalcommittee that you may attend.5The sole source of supply of the sparging gas conditioner known to thecommittee at this time is ORDELA, Inc., 1009 Alvin Weinberg Drive

33、, Oak Ridge,TN, 37830. If you are aware of alternative suppliers, please provide this informationto ASTM Headquarters. Your comments will receive careful consideration at ameeting of the responsible technical committee that you may attend.FIG. 1 Alpha Energy Spectrum of Natural Uranium and232UTracer

34、 Measured on a High-Resolution Alpha-Liquid-ScintillationSpectrometerD62390322deoxygenating, and plastic tubing of various lengths to serve asconnections between the pieces. The inlet from the compressedargon cylinder is connected to one side arm of the pressurelimiter; the opposite side arm of the

35、pressure limiter isconnected to the inlet (bottom) of the gas drying tower. Theoutlet (top) of the drying tower is connected to the inlet(dispersion tube) of the gas washing bottle. The outlet of thegas washing bottle is connected to a disposable Pasteur pipetthat serves as the sparging lance for th

36、e sample. For furtherinformation, consult the spectrometer (see 7.10) instructionmanual.7.10 Spectrometer, high-resolution pulse-shape discriminat-ing alpha-liquid-scintillation spectrometer. Typical perfor-mance specifications include greater than 99 % alpha countingefficiency, 99.95 % beta/gamma r

37、ejection, energy resolution of200 to 250 keV FWHM for the 4.78 MeV226Ra spectrum peakand instrument backgrounds of 0.001 counts per minute over a4 to 7 MeV energy range.67.11 Tubes, 10 by 75 mm borosilicate glass. These tubesserve as sample-counting cells for the spectrometer (see 7.10).8. Reagents

38、and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society(3). Other grades may be used, provided it is

39、 first ascertainedthat the reagent is of sufficiently high purity to permit its usewithout lessening the accuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D 1193, Type III, or better.8.

40、3 Argon Gas, Compressed99.999 % pure, with two-stage pressure regulator.8.4 Ascorbic AcidReagent grade, solid ascorbic acid(C6H8O6).8.5 Dialkyl Phosphoric Acid Extractive ScintillatorSeeRef (4).78.6 Diethylenetriaminepentaacetic Acid (DTPA)(0.1 M)Add 3.93 g of solid DTPA (C14H23N3O10) to 50 mL of wa

41、ter.Adjust the pH approximately 7 by the dropwise addition of 6M sodium hydroxide (NaOH) while stirring to completedissolution. Dilute to 100 mL with water.8.7 Hydrochloric Acid (sp gr 1.19)Concentrated hydro-chloric acid (HCl).8.8 Molecular SieveType 4A, activated, indicating, 4-8mesh (Na12AlO2)12(

42、SiO2)12xH2O).8.9 Nitric Acid (sp gr 1.42)Concentrated nitric acid(HNO3).8.10 Sodium Hydroxide (6 M)Slowly and with coolingadd 240 g sodium hydroxide (NaOH) pellets to 500 mL ofwater and stir to dissolve. Dilute to 1 L with water.8.11 TolueneReagent grade (C6H5CH3).8.12232U Solution, StandardNominall

43、y 0.04 Bq/mL ac-tivity and standardized as per Practice D 3648.9. Hazards9.1 Use extreme caution when handling all acids and bases.They are extremely corrosive and skin contact could result insevere burns.9.2 When diluting concentrated acids, always use safetyglasses and protective clothing, and add

44、 the acid to the water.9.3 Toluene is flammable.Avoid breathing vapors. Use withadequate ventilation and avoid open flames.10. Sampling10.1 Collect the sample in accordance with the applicablemethods as described in Practice D 3370.11. Calibration and Standardization11.1 Use a normal uranium countin

45、g reference sample (thatconsists of an approximate 50/50 mixture of238U and234U, byactivity) to establish an initial region of interest (ROI) on themultichannel analyzer (MCA).NOTE 1The actual ROI for any given sample may differ slightly fromthis initial ROI setting depending on the nature of the sa

46、mple and theextractive scintillator used. This reference sample may be made using thetechniques cited in Burnett and Tai (5). Set the pulse shape discriminator(PSD) of the high-resolution alpha-liquid-scintillation spectrometer priorto counting each individual sample.A1.85 3 105Bq (5 microcurie)137C

47、sgamma source may be used to aid in setting the PSD by quickly inducinga beta/gamma peak (4). For additional information, refer to the instrumentinstruction manual.NOTE 2Setting the pulse shape discriminator (PSD) is a quick, butcritical procedure. Inaccurate activity determinations will result if t

48、he PSDis set improperly.11.2 A reagent blank, without tracer, must be made inexactly the same way as the sample determination.11.3 For general guidance on calibration and standardiza-tion, refer to Practice D 3648.12. ProcedureNOTE 3This procedure applies to analysis of water samples, whetherpreserv

49、ed with HNO3or HCl or unpreserved.12.1 Measure 200 mL of a water sample into a 400-mLborosilicate glass beaker.12.2 Acidify the sample with 0.5 mL of concentrated nitricacid (HNO3) and 0.5 mL of concentrated hydrochloric acid(HCl).12.3 Add an accurately measured activity (depending on theexpected uranium activity of the sample) of232U tracersolution.NOTE 4It is recommended that the tracer activity corresponds roughly(0.75 to 1.25 times the expected234U activity) to the234U activity so as tominimize uncertainties in determining the integral peak areas. I