1、Designation: D 2460 07Standard Test Method forAlpha-Particle-Emitting Isotopes of Radium in Water1This standard is issued under the fixed designation D 2460; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 This test method covers the separation of dissolvedradium from water for the purpose of measuring its radioac-tivity. Although all
3、 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 3 10-2Bq/L(1 pCi/L).1.2 This
4、 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 which the re
5、lative 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 applica-bili
6、ty of regulatory limitations prior to use. For a specificprecautionary statement, see Section 9.2. Referenced Documents2.1 ASTM Standards:2C 859 Terminology Relating to Nuclear Materials3D 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 1943 Test Method for Alpha Particle R
7、adioactivity ofWaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3454 Test Method for Radium-226 in WaterD 3648 Practices for the Measurement of RadioactivityD 4448 Guide for Sampl
8、ing Ground-Water MonitoringWellsD 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD 6001 Guide for Direct-Push Ground Water Sampling forEnvironmental Site Characterization3. Terminology3.1 Definition:3.1.1 For definitions of terms used in this stan
9、dard, seeTerminologies C 859 and D 1129. For terms not included inthese, reference may be made to other published glossaries (1,2).44. 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 soluti
10、on 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 ad
11、dition 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 publishe
12、d 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-emittin
13、g isotopes of radium otherthan that of mass 226 may be determined by difference ifradium-226 is measured separately, such as by Test MethodD 3454. Note that one finds226Ra and223Ra together invariable proportions (5, 6), but224Ra does not normally occurwith them. Thus,223Ra often may be determined b
14、y simply1This 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 15, 2007. Published July 2007. Originallyapproved in 1966. Replaces D 246066 T. Last previous
15、edition approved in 2005as D 2460 05.2For 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.3Withdrawn.4The boldface
16、 numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.subtracting the226Ra content from the total: and if226Raand223Ra are low,224Ra may be determined direc
17、tly. Thedetermination of a single isotope in a mixture is less precisethan if it occurred alone.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 precipi-tates whic
18、h 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, thetotal emission r
19、ate 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 period of 4 ho
20、urs 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 into sample re
21、sults.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 of precipita
22、temasses 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 D 1943.8. Reagents8.1 Purity of ReagentsReagent grade chemicals shall beused in all
23、 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.5Other grades may beused, provided it is first ascertained that the reagent is ofs
24、ufficiently high purity to permit its use without lessening theprecision, or increasing the bias, 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.8.3 Radioactivity Purity of R
25、eagents, 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 Ammonium Hydroxide (
26、7 M)Mix 1 volume of con-centrated ammonium hydroxide (NH4OH, sp gr 0.90) with 1volume of water.5Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of Reagents notlisted by the American Chemical Society, see Analar St
27、andards 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 initial time o
28、f separation.FIG. 1 Growth and Decay of Alpha Activity into Initially Pure Radium IsotopesD24600728.7 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 triplicate):8.7.1.1 Pipette
29、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 anddecant supernatant.8.7.1.
30、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 (anhydrous) in water and
31、 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 diluteto 200 mL.8.11 Me
32、thyl Orange Indicator SolutionDissolve 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.9. Safety Precautions
33、9.1 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 PracticesD 3370, Guide D 4448, or Guide D 6001, as applicable.10.2 Sample 1 L, or a smaller volume, provided that it isestimate
34、d 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.11.2 Use226Ra standards traceable to a nati
35、onal standardslaboratory (such as NIST or NPL). Analyze two or moreportions of such solution, containing known disintegrationrates, in accordance with Section 12. After counting, correctthe measured activity for chemical yield, and calculate theBurns, D. C., “Growth and Decay of Alpha Activity into
36、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 1.00001 1.01602 1.03623 1.05784 1.
37、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 3.9867D2460073efficiency, E (see Section 13), as the ratio of the observedcounting rate to the known disintegration rate.11.3 The ratio of the net count rate to known226Ra disinte-
38、gration rate is a function of precipitate mass and time elapsedbetween the formation of the final barium sulfate precipitateand 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 alkalinity with pH-indicatin
39、g 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 continued heating for 10min
40、. 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 precipitate with 10 mL of HNO3,
41、 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 acetic acid, then add 3
42、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 theprecipitate to the planch
43、et 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 the background count rate
44、 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:6Y 5 MB MP! / 0.01699 (1)where:MB= mass of planchet with the dried barium sulfat
45、eprecipitate, 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 5RnEVYIF(2)where:Rn= a
46、lpha 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,6Eq 1 assumes that exactly 10.0 mg Ba+carrier is added. The theoretical massof BaSO4precipitate assuming 100 % recovery (
47、0.01699 g) is derived by dividingthe mass, in grams, of barium (Ba+) added by 0.5884 g Ba+/ g BaSO4(for example,0.01699 = 0.010 g Ba+/ 0.5884). If the standardized concentration of the bariumcarrier is found to differ from 10.0 mg/mL, the denominator of Eq 1 is modified toreflect the actual quantity
48、 of barium carrier added.TABLE 2 Important Alpha-Particle-Emitting Isotopes of Radiumand their DescendantsANuclide RadiationHalf-LifeParent Descendents TypeBEnergy, MeVC226Ra a 4.784 (94.5 %) 1.60 3 103years4.601 (5.6 %)222Rn a 5.490 (99.9 %) 3.83 days218Po a 6.003 (100.0 %) 3.10 min214Pb b (g) 26.8
49、 min214Bi b (g) 19.9 min214Po a 7687 (100.0 %) 1.64 3 104s224Ra a 5.685 (94.9 %) 3.66 days5.449 (5.1 %)220Rn a 6.288 (99.9 %) 55.6 s216Po a 6.778 (100.0 %) 0.15 s212Pb b (g) 10.6 h212Bi b (64.1 %) (g)1.1a (35.9 %) 6.090 (9.75 %)6.051 (25.1 %)Others212Po a 8.785 0.299 s208Tl b (g) 3.05 min223Ra a (g) 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 a (g) 6.819 (79.4 %) 3.96 s6.552 (12.9 %)6.425 (7.5 %)215Po a 7.386 (100.0 %) 1.78 ms211Pb b (g) 36.1 min211Bi a (g) 6.623 (83.5 %) 2.14 min6.278 (1
