1、Designation: C 1477 06Standard Test Method forIsotopic Abundance Analysis of Uranium Hexafluoride andUranyl Nitrate Solutions by Multi-Collector, InductivelyCoupled Plasma-Mass Spectrometry1This standard is issued under the fixed designation C 1477; the number immediately following the designation i
2、ndicates 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the isotopic a
3、bundance analysisof234U,235U,236U and238U in samples of hydrolysed uraniumhexafluoride (UF6) by inductively coupled plasma source,multi-collector, mass spectrometry (ICP-MC-MS). The methodapplies to material with235U abundance in the range of 0.2 to6 % mass. This test method is also described in AST
4、MSTP 1344.1.2 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 regulatory limitations prior to use.2. Re
5、ferenced Documents2.1 ASTM Standards:2C 761 Test Methods for Chemical, Mass Spectrometric,Spectrochemical, Nuclear, and Radiochemical Analysis ofUranium HexafluorideC 787 Specification for Uranium Hexafluoride for Enrich-mentC 996 Specification for Uranium Hexafluoride Enriched toLess Than 5 %235UD
6、1193 Specification for Reagent Water2.2 Other Document:STP 1344 Applications of Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) to Radionuclide Determi-nations33. Summary of Test Method3.1 Samples are received either in the form of uraniumhexafluoride (UF6) or aqueous uranic solution. The UF6s
7、amples are hydrolysed, diluted and acidified with nitric acid.Uranic solution samples are diluted and acidified with nitricacid. Subsequently, an internal reference of thorium isotopes isadded to each diluted sample.3.2 The samples are contained in polypropylene tubes thatare inserted into the auto-
8、sampler rack of the mass spectrom-eter. Sample details are input to the computer and the instru-ment is prepared for measurement. The automatic measuringsequence is initiated.3.3 Uranium Isotopic Reference Materials (UIRMs) areused to calibrate the instrument. Each UIRM is prepared inaqueous solutio
9、n (acidified with nitric acid) and spiked with thesame internal reference as the samples. This calibration solu-tion is measured and a mass bias parameter is calculated that isstored and subsequently imported into each of the samplemeasurements4to correct the measured uranium isotopic ra-tios.3.4 Me
10、asurements of isotopic ratios in the calibration solu-tion and the subsequent samples are initiated by customisedsoftware. Using the230Th /232Th ratios (that are acquiredsimultaneously to the234U/238U,235U/238U and236U/238Uratios) and the mass bias parameter imported from the calibra-tion, the mass
11、bias factor is computed. The mass bias factor isthen used to correct the measured234U/238U,235U/238Uand236U/238U ratios in “real time.” The abundances areexpressed as % atomic. Details of the mass bias correction arepresented in Appendix X1.4. Significance and Use4.1 The test method is capable of me
12、asuring uraniumisotopic abundances of234U,235U,236U and238U as requiredby Specifications C 787 and C 996.5. Interferences5.1 Mass BiasElectrostatic repulsion between uraniumions causes a so-called “mass bias” effect. Mass bias isobserved as an enhancement in the number of ions detected atthe collect
13、ors from the heavier uranium isotopes relative to the1This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest .Current edition approved July 1, 2006. Published August 2006. Originallyapproved in 2
14、000. Last previous edition approved in 2000 as C 1477 00.2For 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.3Ava
15、ilable from ASTM Headquarters.4The uranium isotopic measurement precision, limit of detection and uncertaintyof measurement are listed in Section 15, Section 16 and Appendix X1 respectively.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United St
16、ates.lighter uranium isotopes. A calibration procedure is used tocorrect the mass spectrometer for mass bias.5.2 Adjacent Isotopic PeaksThe abundance sensitivity ofthe ICP-MC-MS at mass 237 is specified to be less than 0.5parts per million of the238U ion beam. The method is limitedto the measurement
17、 of235U isotopic abundances below 6 %,consequently interference effects with the234U and236U ionbeams are negligible.5.3 Isobaric Molecular InterferencesA molecular inter-ference exists at mass 236 between236U and a hydride of235U,which is formed in the plasma. This interference is “real-time”correc
18、ted by measuring the beam height of the238U hydride atmass 239, and applying the correction defined in Eq 1, to themeasured236U beam:5236Uc5236UmS235U 3238UH238UD(1)where:236Uc= the corrected236U signal,236Um= the measured236U signal,235U = the measured235U signal,238UH = the measured238U hydride si
19、gnal, and238U = the measured238U signal.5.4 Memory Effects:5.4.1 Contamination of the sample introduction systemfrom previous samples produces memory interference effects.Such effects are accentuated when samples that are depletedin235U are measured after enriched samples. Memory effectscan be readi
20、ly assessed by aspirating a 2 % nitric acid solutionand measuring the background238U ion beam. The sampleintroduction system should be periodically disassembled andcleaned, to minimise the background238U ion beam.5.4.2 A background correction is performed during themeasurement run by monitoring the2
21、30Th,232Th,234U,235U,236U and238U signals of the 2 % nitric acid wash solution. Thebackground correction is measured prior to the mass calibra-tion and is re-measured before each subsequent sample.6. Apparatus6.1 Mass Spectrometer:6.1.1 The mass spectrometer has an inductively coupledplasma (ICP) so
22、urce and a double focussing electrostatic/magnetic sector analyser equipped with twelve Faraday detec-tors and two ion counters.66.1.2 The mass spectrometer is fully computer controlledusing customised software and is equipped with an auto-sampler.6.2 Polypropylene Sample Tubes, Screw-Cap,50mL.6.3 P
23、olypropylene Sample Tubes, Screw-Cap,10mL.6.4 Fixed-Volume Pipette, and Tips to Suit, 0.01 mL.6.5 Fixed-Volume Pipette, and Tips to Suit, 1 mL.6.6 Variable-Volume Dispenser, 1 to 5 mL, fitted to a 1-Lglass storage bottle.7. Reagents7.1 Purity of WaterDemineralised water as defined byType I of Specif
24、ication D 1193.7.2 Nitric Acid Solution, high purity, various concentrations.Necessary dilutions can be inferred from the stated acidstrength (for example, 2 % nitric acid solution requires a 350dilution of the concentrated acid).7.3 Reference Solution containing 140 ng/mL of230Th7and7 g/mL of232Th.
25、7.4 Uranium Isotopic Reference Materials (see Section 9 fordetails).8. Internal References8.1 RequirementsAs described in Section 3, thorium isused as an internal reference to be added to the UIRMs anduranium samples. The internal reference must contain at leastone pair of isotopes in a fixed ratio.
26、 It is not necessary for thisisotopic ratio to be accurately known as the same reference isadded to both the calibration material and the subsequentsamples. Minor fluctuations in instrument calibration (massbias) are reflected in the measured ratio of the internalreference in the samples. Subsequent
27、 correction of the massbias parameter using the measured ratio of the internal refer-ence provides the necessary adjustment to the mass bias factorprior to result calculation.8.2 ThoriumThe230Th /232Th ratio is monitored. Thethorium solution is prepared by adding230Th to a calculatedquantity of232Th
28、 from a 1000 g/mL stock standard which isthen diluted with 2 % nitric acid. The quantity of230Th addedis such that the final diluted reference should contain 14 ng/mLof230Th and 0.7 g/mL of232Th. This solution is stored in a 1L bottle fitted with an adjustable dispenser set to 1.0 mL. A 1.0mL aliquo
29、t of thorium solution is dispensed into 2.0 mL ofsample solution containing 1.5 g/mL of uranium. The result-ant concentration of230Th is 4.7 ng/mL and that of232Th is0.23 mg/mL.NOTE 1The quantity of230Th is minimised to comply with localdisposal safety regulations.NOTE 2The decay of234Uto230Th may p
30、resent a problem with theanalysis of aged-uranic solutions. This should not present a problem withuranium hexafluoride samples that are taken in the gaseous phase, asgaseous UF6separates from any non-volatile thorium compounds.9. Uranium Isotopic Reference Materials (UIRMs)9.1 UIRMs are used to cali
31、brate the instrument for multi-collection measurements. The Institute for Reference Materialsand Measurements8(IRMM) reference material IRMM-024 isused for enriched samples and the New Brunswick Laboratory9Certified Reference Material CRM U005-Ais used for samplesof natural or depleted235U abundance
32、s. The UIRMs areprepared as uranyl nitrate solutions containing 1.5 g/mL of5This correction can only be applied to samples which do not contain239Pu.6The Nu Instruments “Nu Plasma” is such a mass spectrometer.7 230Th was supplied by AEA Technology, Harwell, Didcot, Oxfordshire, UK.8Institute for Ref
33、erence Materials and Measurement, Retieseweg, B-2440 Geel,Belgium.9New Brunswick Laboratory, D-350, 9800 South CassAvenue,Argonne, Illinois60439.C1477062uranium and the same quantity of internal reference as de-scribed in Section 8 (which reduces the uranium content downto 1 g/mL).10. Instrument Set
34、up10.1 Many ICP-MC-MS designs require the Faraday collec-tors to be mechanically positioned to align with the ion beams.The instrument used for this work adopts a different approach,where a “zoom lens,” which alters the dispersion of theinstrument, is used to focus the beams onto a fixed array ofdet
35、ectors. The zoom lens settings were adjusted under softwarecontrol to achieve the configuration shown in Table 1.10.2 To minimise measurement uncertainty all minor iso-tope (234U and236U) measurements are on the ion counters.The analyser magnet must be calibrated across the mass range230 to 238, how
36、ever the instrument manufacturer recommendscalibrating across the mass range 80 to 238 (achieved using thebeam from theArgon dimer). The magnet must be re-calibratedif the calibration drifts by more than the 0.2 atomic mass units(at uranium).11. Sample and Blank Preparation11.1 Samples Received as U
37、F6:11.1.1 Transfer between 0.2 g and 0.25 g of UF6gas into aglass sample tube cooled by liquid nitrogen.1011.1.2 Working in a fumecupboard, hydrolyse the UF6usingdemineralised water from a wash bottle. The operator shouldkeep the sample tube pointed away at all times since sometoxic HF gas is produc
38、ed.11.1.3 Pour the hydrolysed UF6into a 50 mL screw-cappolypropylene tube and dilute so that the final concentration ofUF6is 5 mg/mL. For example, if the weight of UF6transferredis 0.2 g, dilute to 40 mL with demineralised water.11.1.4 Using a fixed volume pipette, take a 0.01 mL aliquotof solution
39、and transfer to a clean 50 mL screw-cap polypro-pylene tube. Dilute to a volume of 23 mL using a 2 % nitricacid solution. The resulting solution contains 2.2 g/mL of UF6which is equivalent to 1.5 g/mL of uranium.11.1.5 Pour 2 mL of solution into a 10 mL polypropylenetube.11.1.6 Add 1 mL of the 0.7 g
40、/mL thorium internal refer-ence and thoroughly mix the solution.11.1.7 Place the tube in the designated rack position inaccordance with Section 13.11.2 Samples Received As Aqueous Uranyl Nitrate Solu-tions Of Known Uranic Concentration:11.2.1 Dilute the sample with a 2 % nitric acid solution sothat
41、the uranium concentration is 1.5 g/mL11.2.2 Proceed in accordance with 11.1.5-11.1.7.12. Calibration12.1 Calibration of the mass spectrometer using a UIRMproduces a mass bias factor. The mass bias factor for the UIRMin question is defined in Eq 2.Mass Bias Factor 51235U238Uquoted235U238Umeasured21Dm
42、(2)whereDm = ratio mass difference (that is, 3).12.2 The mass bias factor is applied to the measured isotoperatio of the internal reference to produce a mass bias parameter.This parameter is exported to all subsequent sample measure-ments to correct for mass bias effects. Details of how the massbias
43、 correction is applied can be found in Appendix X1.Asstated in Section 9, IRMM-024 is used to calibrate for massbias for samples enriched in235U and NBLCRM 005-Ais usedto calibrate for mass bias for natural samples or samplesdepleted in235U. Stock solutions of both these uranium refer-ence materials
44、 (containing 1.5 g/mL of uranium in a 2 %nitric acid solution) are held in the laboratory. Mass biascalibration is an integral part of each sample run (that is, noseparate calibration procedure is necessary).13. Operational Procedure13.1 The instrument software is used to assign samplenames, measure
45、ment procedures and auto-sampler rack posi-tions to UIRMs and samples. Two sample racks are used. Thefirst rack contains the UIRM IRMM-024 and those samplesthat are enriched in235U. The second rack contains the UIRMNBL CRM U005-A and those samples at natural level ordepleted in235U. The plasma is th
46、en struck and after a periodof 60 minutes (to allow the system to thermally stabilise), atuning solution of UIRM IRMM-024 is aspirated and the ionbeams are optimised. The automatic measurement sequence isthen initiated under computer control.14. Calculation14.1 The measurement software produces thre
47、e mass biascorrected ratios as follows:10Subsampling of UF6is detailed in ASTM Standard Test Method C 761.TABLE 1Collector L6 L5 L4 IC1 L3 IC0 L2 L1 Ax H1 H2 H3 H4 H5Separation 2U 1U 1U 1U 1U 1U 1U 1U 1U 1U 1U 2U 2UIon Beam230Th232Th 234U235U236U238U238UHwhere:Ax = Axial Faraday collector,L and H =
48、low and high mass Faraday collectors (with respect to the Axial collector),IC = ion counters, andU = unit mass dispersion for uranium isotopes.C1477063r45234238r55235238r65236238The235U abundance is calculated from the following expres-sion:235U 5r51 1 r41 r51 r63 100 % atomic (3)similarly234U 5r41
49、1 r41 r51 r63 100 % atomic (4)and236U 5r61 1 r41 r51 r63 100 % atomic (5)Finally the238U % atomic is calculated by difference:238U 5 100 234U 1235U 1236U! % atomic (6)Before reporting, the isotopic abundancies in % atomic areconverted to % mass.235U 5b 3 Ba 3 A! 1 b 3 B! 1 c 3 C! 1 d 3 D!3 100 % mass(7)where:a =234U% atomicb =235U atomicc =236U atomicd =238U atomicA = atomic weight of234U (234.0409)B = atomic weight of235U (235.0439)C = atomic weight of236U (236.0457)D = atomic weight of238U (238.0508)similarly234U 5a 3 Aa 3 A!1b 3 B!1c 3 C!1d 3
