ASTM C1477-00
(Test Method)Standard Test Method for Isotopic Abundance Analysis of Uranium Hexafloride by Multi-Collector, Inductively Coupled Plasma-Mass Spectrometry
Standard Test Method for Isotopic Abundance Analysis of Uranium Hexafloride by Multi-Collector, Inductively Coupled Plasma-Mass Spectrometry
SCOPE
1.1 This test method covers the isotopic abundance analysis or 234U, 235U and 238U in samples of hydrolysed uranium hexafluoride (UF6) by inductively coupled plasma source, multi-collector, mass spectrometry (ICP-MC-MS). This test method is also describe in ASTM STP 1344.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: C 1477 – 00
Standard Test Method for
Isotopic Abundance Analysis of Uranium Hexafluoride by
Multi-Collector, Inductively Coupled Plasma-Mass
Spectrometry
This standard is issued under the fixed designation C 1477; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope acid. Subsequently, an internal reference of either thorium or
lead isotopes is added to each diluted sample.
1.1 This test method covers the isotopic abundance analysis
234 235 236 238
3.2 The samples are contained in polythene tubes that are
of U, U, U,and Uinsamplesofhydrolyseduranium
inserted into the auto-sampler rack of the mass spectrometer.
hexafluoride (UF ) by inductively coupled plasma source,
Sample details are input to the computer and the instrument is
multi-collector, mass spectrometry (ICP-MC-MS). This test
prepared for measurement. The automatic measuring sequence
method is also described in ASTM STP 1344.
is initiated.
1.2 This standard does not purport to address all of the
3.3 Uranium isotopic reference materials (UIRMs) are used
safety concerns, if any, associated with its use. It is the
to calibrate the instrument. Each UIRM is prepared in aqueous
responsibility of the user of this standard to establish appro-
solution (acidified with nitric acid) and spiked with the same
priate safety and health practices and determine the applica-
internal reference as the samples. This calibration solution is
bility of regulatory limitations prior to use.
measured and a mass bias parameter is calculated that is stored
2. Referenced Documents
and subsequently imported into each of the sample measure-
ments to correct the measured uranium isotopic ratios.
2.1 ASTM Standards:
3.4 Measurement of isotopic ratios in the calibration solu-
C 761 Test Methods for Chemical, Mass Spectrometric,
tion and the subsequent samples is initiated by customized
Spectrochemical, Nuclear, and Radiochemical Analysis of
software. The measurement sequence is determined by the
Uranium Hexafluoride
internal reference used. Using the lead internal reference, the
C 787 Specification for Uranium Hexafluoride for Enrich-
sequence is as follows:
ment
207 208
Pb/ Pb
C 996 Specification for Uranium Hexafluoride Enriched to
234 238 235 238
235 2
U/ U and U/ U
less than 5 % U
235 238 236 238
U/ U and U/ U
D 1193 Specification for Reagent Water
207 208
Pb/ Pb
2.2 Other Document:
Using the mean of the two lead ratios and the mass bias
STP 1344 Applications of Inductively Coupled Plasma-
parameter imported from the calibration, the current mass bias
Mass Spectrometry (ICP-MS) to Radionuclide Determi-
factor is computed.The mass bias factor is then used to correct
nations
the measured uranium isotopic ratios. These corrected ratios
234 235 236
3. Summary of Test Method
are used to calculate the abundances of U, U, and U.
3.5 Using the thorium internal reference, the sequence is as
3.1 Samples are received either in the form of uranium
follows:
hexafluoride (UF ) or aqueous uranic solution. The UF
6 6
236 238
U/ U
samples are hydrolysed, diluted, and acidified with nitric acid.
230 232 234 238 235 238
Th/ Th, U/ U, and U/ U
Uranic solution samples are diluted and acidified with nitric
230 232
Using the Th/ Th ratios (that are acquired simultaneously
234 238 235 238
to the U/ U and U/ U ratios) and the mass bias
parameterimportedfromthecalibration,themassbiasfactoris
This test method is under the jurisdiction ofASTM Committee C26 on Nuclear
Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of
Test.
Current edition approved June 10, 2000. Published August 2000. Thorium is preferred as the internal reference because thorium data can be
Annual Book of ASTM Standards, Vol 12.01. acquired simultaneously to uranium data.
3 6
Annual Book of ASTM Standards, Vol 11.01. The uranium isotopic reporting limits and reporting errors are listed in section
Available from ASTM Headquarters. 16 and Appendix X1 respectively.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 1477
computed. The mass bias factor is then used to correct the the 6.2 Polypropylene Sample Tubes, Screw-Cap,50mL.
234 238 235 238
measured U/ U and U/ U ratios in “real time.” 6.3 Polypropylene Sample Tubes, Screw-Cap,10mL.
236 238
The U/ U is retrospectively corrected for mass bias. The 6.4 Fixed-Volume Pipette and Tips to Suit, 0.01 mL.
abundances are expressed as % atomic. A printout of results 6.5 Fixed-Volume Pipette and Tips to Suit, 1 mL.
and mass spectrometer parameters is obtained for each sample. 6.6 Variable-Volume Dispenser, 1 to 5 mL, fitted to a 1-L
Details of the mass bias correction are presented in Appendix glass storage bottle.
X1.
7. Reagents
4. Significance and Use
7.1 Purity of Water—Demineralised water as defined by
4.1 The test method is capable of measuring uranium
Type I of Specification D 1193.
234 235 236 238
isotopic abundances of U, U, U, and U as required
7.2 ICP Standard Pb Solution (1000 ppm).
by Specifications C 787 and C 996.
7.3 Nitric Acid Solution, analytical grade, various concen-
trations. Necessary dilutions can be inferred from the stated
5. Interferences
acid strength (for example, 2 % nitric acid solution requires a
5.1 Mass Bias—Electrostatic repulsion between uranium
350 dilution of the concentrated acid).
ions causes a so-called “mass bias” effect. Mass bias is
7.4 Reference Solution containing 140 ppb of Th and 7
observed as an enhancement in the number of ions detected at
ppm of Th.
the collectors from the heavier uranium isotopes relative to the
7.5 Uranium Isotopic Reference Materials.
lighter uranium isotopes. A calibration procedure is used to
correct the mass spectrometer for mass bias.
8. Internal References
5.2 Adjacent Isotopic Peaks—The abundance sensitivity of
8.1 Requirements—As described in Section 3, either lead or
the ICP-MC-MS at mass 237 is specified to be less than 2 parts
thorium can be used as an internal reference to be added to the
per million of the U ion beam. For all enrichment plant
UIRMs and uranium samples. The internal reference must
samples, the U isotopic abundance is currently no more than
contain at least one pair of isotopes in a fixed ratio. It is not
6 % mass, consequently, interference effects with the U
236 necessary for this isotopic ratio to be accurately known, as the
and U ion beams are negligible.
samereferenceisaddedtoboththecalibrationmaterialandthe
5.3 Isobaric Molecular Interferences—Any UH+ ions
236 subsequent samples. Minor fluctuations in instrument calibra-
formed in the plasma produce an interference with the U ion
tion (mass bias) are reflected in the measured ratio of the
beam. The magnitude of the UH+ ion has been assessed by
internal reference in the samples. Subsequent correction of the
measuring the mass 236 peak of a natural uranium reference
236 235 235
mass bias parameter using the measured ratio of the internal
material containing no U. The ratio of UH to U was
236 reference provides the necessary adjustment to the mass bias
recorded and subsequently used to correct U measurements.
factor prior to result calculation.
5.4 Memory Effects:
8.2 Lead—Ifleadisusedastheinternalreference,the Pb/
5.4.1 Contamination of the sample introduction system
Pb ratio is monitored. The lead is prepared by using a 2 %
from previous samples produces memory interference effects.
nitric acid solution to dilute a 1000-µg/mL lead stock standard
Such effects are accentuated when samples that are depleted
to 7 µg/mL. The dilute lead solution is stored in a 1-L bottle
in U are measured after enriched samples. Memory effects
fitted with an adjustable dispenser set to 1 mL.A1-mLaliquot
can be readily assessed by aspirating a 2 % nitric acid solution
238 238
of the lead solution is dispensed into 6 mL of sample solution
and measuring the background U ion beam. If the U
containing 1.2 µg/mL of uranium. The resultant concentration
background ion beam exceeds 1E-14 amps, then the sample
of the both the uranium and lead internal reference is 1 µg/mL.
introduction system is stripped and cleaned.
8.3 Thorium—If thorium is used as the internal reference,
5.4.2 If thorium is used as the internal reference, then it is
230 232
235 238
the Th/ Th ratio is monitored. The thorium solution is
possible to correct for uranium background ( U and U
230 232
preparedbyadding Thtoacalculatedquantityof Thfrom
only) by measuring a (blank) solution of 2 % nitric acid spiked
a 1000-µg/mL stock standard which is then diluted with 2 %
with the thorium isotopes. In practice, it has been found
nitric acid. The quantity of Th added is such that the final
unnecessary to apply a background correction to UIRMs or
235 diluted reference should contain 140 ng/mL of Th and 7
samples enriched in U.
µg/mL of Th. This solution is stored in a 1-L bottle fitted
6. Apparatus
with an adjustable dispenser set to 1 mL. A 1-mL aliquot of
thorium solution is dispensed into 6 mL of sample solution
6.1 Mass Spectrometer:
containing 1.2 µg/mL of uranium. The resultant concentration
6.1.1 The mass spectrometer has an inductively coupled
230 232
of This20ng/mLandtheresultantconcentrationof This
plasma (ICP) source and a double-focussing electrostatic/
1 µg/mL.
magnetic sector analyser equipped with seven Faraday detec-
tors and one Daly detector. 230
NOTE 1—The Th is radioactive (a-emitter) and consequently, the
6.1.2 The mass spectrometer is fully computer controlled
quantity of Th is minimised to comply with local disposal safety
using customized software and is equipped with an auto-
regulations.
sampler.
7 8 230
The VG Elemental, Plasma54 (P54) is such a mass spectrometer. Th is supplied by AEA Technology, Harwell, Didcot, Oxfordshire, UK.
C 1477
9. Uranium Isotopic Reference Materials (UIRMs) UF is 5 mg/mL, for example, if the weight of UF transferred
6 6
is 0.2 g, dilute to 40 mL with demineralized water.
9.1 UIRMs are used to calibrate the instrument for multi-
11.1.4 Using a fixed-volume pipette, take a 0.01-mLaliquot
collection measurements.The Institute for Reference Materials
of solution and transfer to a clean 50-mL screw-cap polypro-
and Measurements (IRMM) reference material IRMM-024 is
pylene tube. Dilute to a volume of 28 mL using a 2 % nitric
used for enriched samples and the New Brunswick Labora-
acidsolution.Theresultingsolutioncontains1.8µg/mLofUF
tory Certified Reference Material CRM U005-A is used for
which is equivalent to 1.2 µg/mL of uranium.
samples of natural or depleted U abundances. The UIRMs
11.1.5 Pour 6 mL of solution into a 10-mL polypropylene
arepreparedasuranylnitratesolutionscontaining1.2µg/mLof
tube.
uranium and the same quantity of internal reference as de-
11.1.6 Add 1 mL of the 7-µg/mL internal reference and
scribed in Section 8.
thoroughly mix the solution.
11.1.7 Place the tube in the designated rack position in
10. Instrument Setup
accordance with Section 13.
10.1 Choice of internal reference determines the position of
11.2 SamplesReceivedasAqueousUranylNitrateSolutions
the adjustable Faraday collector buckets. Buckets are posi-
of Known Uranic Concentration:
tioned under software control. If lead is chosen as the internal
11.2.1 Dilute the sample with a 2 % nitric acid solution so
reference, then the distances between the collectors are tabu-
that the uranium concentration is 1.2 µg/mL
lated as follows:
11.2.2 Proceed in accordance with 11.1.5-11.1.7.
A
Collector L2 L1 Ax H1 H2 H3 H4
A 11.3 Blank Solution (used only if thorium is the internal
Separation 1Pb 1U 1U 1U 1U 1U
reference):
A
Key to Symbols:
11.3.1 Pour 6 mL of 2 % nitric acid solution into a 10-mL
Ax = axial collector.
H = collector on high-mass side of the axial collector.
polythene tube.
L = collector on low-mass side of the axial collector.
11.3.2 Add 1 mL of the 7-µg/mL thorium internal reference
1U = unit mass dispersion for uranium isotopes.
and thoroughly mix the solution.
2U = twice unit mass dispersion for uranium isotopes.
1Pb = unit mass dispersion for lead isotopes.
11.3.3 Place the tube in the designated rack position in
If thorium is chosen as the internal reference, then the
accordance with Section 13.
distances between the collectors are again tabulated as follows:
A
12. Calibration
Collector L2 L1 Ax H1 H2 H3 H4
A
Separation 2U 2U 1U 1U 1U 1U
12.1 Calibration of the mass spectrometer using a UIRM
A
Key to Symbols: producesamassbiasfactor.ThemassbiasfactorfortheUIRM
Ax = axial collector.
in question is defined in Eq 1.
H = collector on high-mass side of the axial collector.
L = collector on low-mass side of the axial collector. 1
U Dm
1U = unit mass dispersion for uranium isotopes.
quoted
2U = twice unit mass dispersion for uranium isotopes. 238
U
1Pb = unit mass dispersion for lead isotopes.
Mass bias factor 5 (1)
U
EitheraDalyorFaradaydetectorcanbeselectedastheaxial
1 2
measured
U
collector. To optimize measurement uncertainty, all minor
234 236
isotope ( U and U) measurements are on theAxial (Daly)
where
collector. The analyser magnet must be calibrated across the
Dm = ratio mass difference (that is, 3).
mass range from 207 to 238. The magnet must be re-calibrated
12.2 The mass bias factor is applied to the measured isotope
if the calibration drifts by more than the 0.2 atomic mass units
ratiooftheinternalreferencetoproduceamassbiasparameter.
(at uranium).
This parameter is exported to all subsequent sample measure-
ments to correct for mass bias effects. Details of how the mass
11. Sample and Blank Preparation
bias correction is applied can be found in Appendix X1. As
11.1 Samples Received as UF :
stated in Section 9, IRMM-024 is used to calibrate for mass
11.1.1 Transfer between 0.2 and 0.25 g of UF gas into a
bias for samples enriched in U, and NBL CRM 005-A is
glass sample tube cooled by liquid nitrogen.
used to calibrate for mass bias for natural samples or samples
11.1.2 Working in a fume cupboard, hydrolyse the UF 235
depleted in U. Stock solutions of both these uranium
using demineralised water from a wash bottle. The operator
reference materials (containing 1.2 µg/mLof uranium in a 2 %
should keep the sample tube pointed away at all times since
nitric acid solution) are held in the laboratory. Mass bias
toxic HF gas is produced.
calibration is an integral part of each sample run (that is, no
11.1.3 Pour the hydrolyzed UF into a 50-mL screw-cap
...
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