1、Designation: D2460 07 (Reapproved 2013)Standard Test Method forAlpha-Particle-Emitting Isotopes of Radium in Water1This standard is issued under the fixed designation D2460; 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the separation of dissolvedradium from water for the purpose of measuring its radioac-tivit
3、y. Although all radium isotopes are separated, the testmethod is limited to alpha-particle-emitting isotopes by choiceof radiation detector.The most important of these radioisotopesare223Ra,224Ra, and226Ra. The lower limit of concentration towhich this test method is applicable is 3.7 10-2Bq/L(1 pCi
4、/L).1.2 This test method may be used for absolute measure-ments by calibrating with a suitable alpha-emitting radioiso-tope such as226Ra, or for relative methods by comparingmeasurements with each other. Mixtures of radium isotopesmay be reported as equivalent226Ra. Information is alsoprovided from
5、which the relative contributions of radiumisotopes may be calculated.1.3 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
6、applica-bility of regulatory limitations prior to use. For a specificprecautionary statement, see Section 9.2. Referenced Documents2.1 ASTM Standards:2C859 Terminology Relating to Nuclear MaterialsD1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD1943 Test Method for Alpha Par
7、ticle Radioactivity ofWaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3454 Test Method for Radium-226 in WaterD3648 Practices for the Measurement of RadioactivityD4448 Guide for Sam
8、pling Ground-Water Monitoring WellsD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD6001 Guide for Direct-Push Groundwater Sampling forEnvironmental Site Characterization3. Terminology3.1 Definition:3.1.1 For definitions of terms used in this stan
9、dard, seeTerminologies C859 and D1129. For terms not included inthese, reference may be made to other published glossaries (1,2).34. Summary of Test Method4.1 Radium is collected from the water by coprecipitationwith mixed barium and lead sulfates. The barium and leadcarriers are added to a solution
10、 containing alkaline citrate ionwhich prevents precipitation until interchange has taken place.Sulfuric acid is then used to precipitate the sulfates, which arepurified by nitric acid washes. The precipitate is dissolved inammoniacal EDTA. The barium and radium sulfates arereprecipitated by the addi
11、tion of acetic acid, thereby separatingthem from lead and other radionuclides. The precipitate isdried on a planchet, weighed to determine the chemical yield,and alpha-counted to determine the total disintegration rate ofalpha-particle-emitting radium isotopes. This procedure isbased upon published
12、ones (3, 4).5. Significance and Use5.1 Radium is one of the most radiotoxic elements. Itsisotope of mass 226 is the most hazardous because of its longhalf-life. The isotopes 223 and 224, although not as hazardous,are of some concern in appraising the quality of water.5.2 The alpha-particle-emitting
13、isotopes of radium otherthan that of mass 226 may be determined by difference ifradium-226 is measured separately, such as by Test MethodD3454. Note that one finds226Ra and223Ra together in variableproportions (5, 6), but224Ra does not normally occur with1This test method is under the jurisdiction o
14、f ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.04 on Methods of Radiochemi-cal Analysis.Current edition approved Jan. 1, 2013. Published January 2013. Originallyapproved in 1966. Replaces D246066 T. Last previous edition approved in 2007 asD2460 07. DOI: 10.1520/D2
15、460-07R13.2For 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 page onthe ASTM website.3The boldface numbers in parentheses refer to the l
16、ist of references at the end ofthis standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1them. Thus,223Ra often may be determined by simply sub-tracting the226Ra content from the total: and if226Ra and223Raare low,224Ra may be det
17、ermined directly. The determinationof a single isotope in a mixture is less precise than if it occurredalone.6. Interferences6.1 A barium content in the sample exceeding 0.2 mg willbias chemical yield high and lead to falsely low sample results.6.2 The presence of suspended solids or insoluble preci
18、pi-tates which fail to dissolve during step 12.5 will bias chemicalyield high and lead to falsely low sample results.6.3 The total alpha particle emission rate from the preparedsample changes over time. This will influence the radiumdetection efficiency of the counting system used. Initially, thetot
19、al emission rate will increase as the short-lived radonprogeny ingrow in the processed sample. After reaching amaximum, the alpha emission rate will decline at the half lifeof the radium isotope of interest. In samples of pure isotope,maximum emission rate after radium separation is reachedafter a p
20、eriod of 4 hours for223Ra, 24 hours for224Ra, and 28days for226Ra. (See Fig. 1.)6.4 The alpha particle detection efficiency decreases withincreasing precipitate mass. Controlling the precipitate massrelative to that used for calibration of the test will minimize theintroduction of significant bias i
21、nto sample results.6.5 The changing alpha emission rate and self-absorptioneffects noted in 6.3 and 6.4 can be addressed by reproducingthese conditions during the calibration of the instrument. Aseries of standards analyzed per 11.2 may be used to generatea curve describing efficiencies over a range
22、 of precipitatemasses and a series of time encompassing the ingrowth curve(30 days) of222Rn daughters. (See Fig. 2).7. Apparatus7.1 For suitable gas-flow proportional or alpha-scintillationcounting equipment, refer to Test Method D1943.8. Reagents8.1 Purity of ReagentsReagent grade chemicals shall b
23、eused 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,where such specifications are available.4Other grades may beused, provided it is first ascertained that the re
24、agent is ofsufficiently high purity to permit its use without lessening theprecision, or increasing the bias, of the determination.8.2 Purity of Water Unless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D1193, Type III.8.3 Radioactivity
25、 Purity of Reagents , shall be such that themeasured results of blank samples do not exceed the calculatedprobable error of the measurement or are within the desiredprecision.8.4 Acetic Acid, Glacial (sp gr 1.05).8.5 Ammonium Hydroxide (sp gr 0.90)Concentrated am-monium hydroxide (NH4OH).8.6 Ammoniu
26、m Hydroxide (7 M)Mix 1 volume of con-centrated ammonium hydroxide (NH4OH, sp gr 0.90) with 1volume of water.4Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of Reagents notlisted by the American Chemical Society,
27、see Analar Standards for LaboratoryChemicals, BDN Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacuetical Convention, Inc. (USPC), Rockville,MD.NOTE 1Vertical scale is ratio of the total alpha radioactivity at later time, t, to radioactivity, A0, at i
28、nitial time of separation.FIG. 1 Growth and Decay of Alpha Activity into Initially Pure Radium IsotopesD2460 07 (2013)28.7 Barium Nitrate Carrier SolutionStandardized (10.0mg Ba+/mL)Dissolve 1.90 g of barium nitrate (Ba(NO3)2)in water and dilute to 100 mL.8.7.1 To perform standardization (in triplic
29、ate):8.7.1.1 Pipette 2.0 mL carrier solution into a centrifuge tubecontaining 15 mL water.8.7.1.2 Add 1 mL 18 N H2SO4while stirring and digestprecipitate in a water bath for 10 min.8.7.1.3 Allow to cool. Centrifuge, and decant supernatant.8.7.1.4 Wash precipitate with 15 mL water. Centrifuge anddeca
30、nt supernatant.8.7.1.5 Transfer the precipitate to a tared stainless steelplanchet with a minimum of water.8.7.1.6 Dry under infrared lamp, store in desiccator, andweigh as BaSO4.NOTE 10.5884 gram Ba+is equivalent to 1.000 gram BaSO4.8.8 Citric Acid Solution (350 g/L)Dissolve 350 g of citricacid (an
31、hydrous) in water and dilute to 1 L.8.9 Disodium Ethylendiamine Tetraacetate Solution (EDTA)(93 g/L)Dissolve 93 g of disodium ethylenediamine tetraac-etate dihydrate in water and dilute to 1 L.8.10 Lead Nitrate Carrier Solution (104 mg Pb/mL)Dissolve 33.2 g of lead nitrate (Pb(NO3)2) in water and di
32、luteto 200 mL.8.11 Methyl Orange Indicator Solution Dissolve 1.0 g ofmethyl orange in water and dilute to 1 L.8.12 Nitric Acid (sp gr 1.42)Concentrated nitric acid(HNO3).8.13 Sulfuric Acid (9 M)Cautiously add with stirring 1volume of concentrated sulfuric acid (H2SO4, sp gr 1.84) to 1volume of water
33、.9. Safety Precautions9.1 When diluting concentrated acids, always use safetyglasses and protective clothing, and add the acid to the water.10. Sampling10.1 Collect the sample in accordance with PracticesD3370, Guide D4448, or Guide D6001, as applicable.10.2 Sample 1 L, or a smaller volume, provided
34、 that it isestimated to contain from 3.7 to 370 Bq (100 to 10 000 pCi) ofradium. Add 10 mL of HNO3/L of sample.11. Calibration and Standardization11.1 For absolute counting, the alpha-particle detector mustbe calibrated to obtain the ratio of count rate to disintegrationrate.Burns, D. C., “Growth an
35、d Decay of Alpha Activity into Initially Pure Radium Isotopes,” Calibration Plot, Paragon Analytics, Inc., Fort Collins, CO, 2003.FIG. 2 Typical Alpha Particle Efficiency as Function of Time and Precipitate MassTABLE 1 Growth of Alpha Activity into Initially Pure Radium-226Time, h Correction, F0 1.0
36、0001 1.01602 1.03623 1.05784 1.07985 1.10176 1.123524 1.488648 1.904372 2.251396 2.5408120 2.7823144 2.9839192 3.2925240 3.5073360 3.8006480 3.9193720 3.9867D2460 07 (2013)311.2 Use226Ra standards traceable to a national standardslaboratory (such as NIST or NPL). Analyze two or moreportions of such
37、solution, containing known disintegrationrates, in accordance with Section 12. After counting, correctthe measured activity for chemical yield, and calculate theefficiency, E (see Section 13), as the ratio of the observedcounting rate to the known disintegration rate.11.3 The ratio of the net count
38、rate to known226Radisintegration rate is a function of precipitate mass and timeelapsed between the formation of the final barium sulfateprecipitate and counting.12. Procedure12.1 Add to a measured volume of sample 5 mL of citricacid solution and make alkaline (pH 7.0) with 7 M NH4OH.Confirm the alk
39、alinity with pH-indicating paper or strip.Add 2mL of lead carrier and 1.00 mL of barium carrier, and mix.12.2 Heat to boiling and add 10 drops of methyl orangepH-indicator solution. With stirring, add 9 M H2SO4until thesolution becomes pink, then add 5 drops more.12.3 Digest the precipitate with con
40、tinued heating for 10min. Let cool and collect the precipitate in a centrifuge tube.When large volumes are handled, collection will be facilitatedby first letting the precipitate settle, and then decanting most ofthe clear liquid. Centrifuge, then discard the supernatant liquid.12.4 Wash the precipi
41、tate with 10 mL of HNO3, centrifugeand discard the washings. Repeat this wash of the precipitate.12.5 Dissolve the precipitate in 10 mL of water, 10 mL ofEDTA solution, and 4 mL of 7 M NH4OH. Warm if necessaryto effect dissolution.12.6 Reprecipitate barium sulfate (BaSO4) by the dropwiseaddition of
42、acetic acid, then add 3 drops more. Record the time.Centrifuge, then discard the supernatant liquid. Add 10 mL ofwater, mix well, centrifuge, and discard the supernatant liquid.12.7 Clean, flame, cool, and weigh a stainless steel planchetthat fits the alpha-particle counter being used. Transfer thep
43、recipitate to the planchet with a minimum of water. Dry,flame, and weigh the precipitate to determine the chemicalyield.12.8 Promptly count the planchet in an appropriate alpha-particle counter, recording the time. Reserve the planchet foradditional measurements, if desired (see 13.6).12.9 Measure t
44、he background count rate of the detector bycounting an empty, cleaned and flamed planchet for at least aslong as the precipitate was counted.13. Calculation13.1 Calculate the fractional radium recovery (chemicalyield of the carrier) as follows:5Y 5 MB2 MP!/0.01699 (1)where:MB= mass of planchet with
45、the dried barium sulfateprecipitate, g,MP= mass of planchet only, g, and0.01699 = mass of barium sulfate precipitate if all of theadded barium carrier (10.0 mg) were recovered,g.13.2 Calculate the concentration AC of alpha-emitting ra-dium radionuclides as226Ra in Bq of radium per litre asfollows:AC
46、 5RnEVYIF(2)where:Rn= alpha counting rate, net counts/s (sample counts/sminus background counts/s),E = detection efficiency of the counter for alpha particles,counts/disintegration,V = sample volume, L,Y = fractional chemical yield for the separation, and5Eq 1 assumes that exactly 10.0 mg Ba+carrier
47、 is added. The theoretical massof BaSO4precipitate assuming 100 % recovery (0.01699 g) is derived by dividingthe mass, in grams, of barium (Ba+) added by 0.5884 g Ba+/ g BaSO4(forexample, 0.01699 = 0.010 g Ba+/ 0.5884). If the standardized concentration of thebarium carrier is found to differ from 1
48、0.0 mg/mL, the denominator of Eq 1 ismodified to reflect the actual quantity of barium carrier added.TABLE 2 Important Alpha-Particle-Emitting Isotopes of Radiumand their DescendantsANuclide RadiationHalf-LifeParentDescendents TypeBEnergy, MeVC226Ra 4.784 (94.5 %) 1.60 103years4.601 (5.6 %)222Rn 5.4
49、90 (99.9 %) 3.83 days218Po 6.003 (100.0 %) 3.10 min214Pb () 26.8 min214Bi () 19.9 min214Po 7687 (100.0 %) 1.64 104s224Ra 5.685 (94.9 %) 3.66 days5.449 (5.1 %)220Rn 6.288 (99.9 %) 55.6 s216Po 6.778 (100.0 %) 0.15 s212Pb () 10.6 h212Bi (64.1 %) ()1.1 (35.9 %) 6.090 (9.75 %)6.051 (25.1 %)Others212Po 8.785 0.299 s208Tl () 3.05 min223Ra () 5.716 (51.6 %) 11.4 days5.607 (25.2 %)5.747 (9.0 %)5.540 (9.0 %)5.434 (2.2 %)5.502 (1.0 %)5.871 (1.0 %)Others219Rn () 6.819 (79.4 %) 3.96 s6.552 (12.9 %)6.425 (7.5 %)215Po 7.386 (
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