ASTM C1871-22

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1871 − 22
Standard Test Method for
Determination of Uranium Isotopic Composition by the
Double Spike Method Using a Thermal Ionization Mass
Spectrometer
This standard is issued under the fixed designation C1871; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ments of low enriched or natural uranium isotopic reference
materials on a regular basis.
1.1 This test method describes the determination of the
isotope amount ratios of uranium material as nitrate solutions 1.6 TheDSmethodcanonlybeappliedtouraniumsamples
233 –5
by the double spike (DS) method using a thermal ionization with relative isotope abundances U/U below 10 and
236 –4
mass spectrometer (TIMS) instrument. U/Ubelow5×10 ,theDSmethodisthereforemainlyused
for low enriched or close to natural uranium samples.
1.2 The analytical performance in the determination of the
235 238
U/ UmajorisotopeamountratiobytheDSmethodisfive 1.7 Units—The values stated in SI units are to be regarded
to ten times better in terms of the internal and external as the standard. When no SI units are provided, the values are
reproducibility compared to the (“classical”) total evaporation for information only.
(TE) method as described in Test Method C1672 and the
1.8 This standard does not purport to address all of the
“modified total evaporation” (MTE) as described in Test
safety concerns, if any, associated with its use. It is the
MethodC1832.Thisisduetotheuseofan internalratherthan
responsibility of the user of this standard to establish appro-
external mass fractionation correction by using a double spike
priate safety, health, and environmental practices and deter-
233 236
material with a known or certified U/ U isotope ratio,
mine the applicability of regulatory limitations prior to use.
which is mixed with the sample prior to the measurement,
1.9 This international standard was developed in accor-
either during the sample preparation or directly on the TIMS
dance with internationally recognized principles on standard-
filament.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.3 The DS method cannot be applied for the determination
236 238
mendations issued by the World Trade Organization Technical
of the U/ U minor isotope amount ratio, and is also not
234 238
Barriers to Trade (TBT) Committee.
recommended for the determination of the U/ U minor
isotope amount ratio.
2. Referenced Documents
1.4 In case the uranium amount concentration of the double
2.1 ASTM Standards:
spike is known or certified, the uranium amount concentration
C753Specification for Nuclear-Grade, Sinterable Uranium
of the sample can be determined using the isotope dilution
Dioxide Powder
mass spectrometry (IDMS) method as described in Test
C776SpecificationforSinteredUraniumDioxidePelletsfor
Method C1672, by blending the sample gravimetrically with
Light Water Reactors
the double spike and performing a DS measurement.
C787Specification for Uranium Hexafluoride for Enrich-
1.5 An external mass fractionation correction by measure-
ment
ments of a certified reference material loaded on different
C833Specification for Sintered (Uranium-Plutonium) Diox-
filaments and measured in the same measurement sequence, as
ide Pellets for Light Water Reactors
recommended for TE and required for MTE measurements, is
C859Terminology Relating to Nuclear Materials
not necessary for the DS method. However, for quality control
C967Specification for Uranium Ore Concentrate
(QC) purposes it is recommended to perform DS measure-
C996Specification for Uranium Hexafluoride Enriched to
Less Than 5% U
ThistestmethodisunderthejurisdictionofASTMCommitteeC26onNuclear
Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of
Test. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Feb. 1, 2022. Published March 2022. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2018. Last previous edition approved in 2018 as C1871–18a. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/C1871-22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1871 − 22
C1008 Specification for Sintered (Uranium-Plutonium) 3.3 Acronyms:
DioxidePellets—Fast Reactor Fuel (Withdrawn 2014) 3.3.1 CRM—certified reference material
C1068Guide for Qualification of Measurement Methods by
3.3.2 DS—double spike
a Laboratory Within the Nuclear Industry
3.3.3 DU—depleted uranium
C1128Guide for Preparation of Working Reference Materi-
3.3.4 EU—European Union
als for Use in Analysis of Nuclear Fuel Cycle Materials
C1156Guide for Establishing Calibration for a Measure-
3.3.5 FAR—Faraday Cup
ment Method Used toAnalyze Nuclear Fuel Cycle Mate-
3.3.6 HEU—high enriched uranium
rials
3.3.7 IAEA—International Atomic Energy Agency
C1347Practice for Preparation and Dissolution of Uranium
Materials for Analysis
3.3.8 ICPMS—inductively coupled mass spectrometry
C1411Practice for The Ion Exchange Separation of Ura-
3.3.9 IRMM—Institute for Reference Materials and Mea-
nium and Plutonium Prior to Isotopic Analysis
surements (since 1 July 2016 called JRC-Geel, the only unit
C1672Test Method for Determination of Uranium or Pluto-
working with nuclear materials at JRC-Geel is JRC-G.2)
nium Isotopic Composition or Concentration by the Total
3.3.10 ITU—Institute for Transuranium Elements (since 1
Evaporation Method Using a Thermal Ionization Mass
July 2016 called JRC-Karlsruhe, the only unit involved with
Spectrometer
thermalionizationmassspectrometrymeasurementsofnuclear
C1832Test Method for Determination of Uranium Isotopic
materials at JRC-Karlsruhe is JRC-G.II.6)
Composition by Modified Total Evaporation (MTE)
Method Using Thermal Ionization Mass Spectrometer
3.3.11 JRC—Joint Research Centre
D1193Specification for Reagent Water
3.3.12 LEU—low enriched uranium
E2586Practice for Calculating and Using Basic Statistics
3.3.13 MTE—modified total evaporation
E2655Guide for Reporting Uncertainty of Test Results and
Use of the Term Measurement Uncertainty inASTM Test 3.3.14 NBL—New Brunswick Laboratory (since 15 May
2016 called NBL-Program Office)
Methods
3.3.15 NML—Nuclear Material Laboratory (part of the
3. Terminology
IAEA)
3.1 Terminology C859 contains terms, definitions, descrip-
3.3.16 QC—quality control
tions of terms, nomenclature, and explanations of acronyms
3.3.17 RSD—relative standard deviation—SD (see below)
and symbols specifically associated with standards under the
divided by the mean value of the observations in repeated
jurisdiction of Committee C26 on Nuclear Fuel Cycle.
sampling.
3.2 Definitions:
3.3.18 RSE—relative standard error—SE (see below) di-
3.2.1 abundance sensitivity, n—in isotope amount ratio
vided by the mean value of the observations in repeated
measurements, the ratio of the measured intensity of an ion
sampling.
beam at a mass, m, to the measured intensity from the same
3.3.19 SD—standard deviation—according to Practice
isotope measured at one mass unit difference (for example, m
6 1). E2586, 3.1.30: The square root of the sum of the squared
deviations of the observed values in the sample divided by the
3.2.1.1 Discussion—Abundance sensitivity is a measure of
the magnitude of the peak tailing correction. For measuring sample size minus 1.
uranium on thermal ionization mass spectrometer (TIMS) and
3.3.20 SE—standard error—according to Practice E2586,
inductively coupled plasma mass spectrometry (ICP-MS)
3.1.29: Standard deviation of the population of values of a
instruments,theabundancesensitivityistypicallycalculatedas
sample statistic (that is, the mean value) in repeated
the ratio of the measured signal intensities at masses 237 and
measurements, or an estimate of it.
238 using a suitable uranium sample.
3.3.20.1 Discussion—According to Practice E2586, 3.1.30:
3.2.2 modified total evaporation, MTE, n—analytical If the standard error (SE, see above) of a statistic is estimated,
method for determination of isotope amount ratios of uranium, it will itself be a statistic with some variance that depends on
as described in Test Method C1832. the sample size, that is, the number of observed values in the
sample (Practice E2586, 3.1.26).
3.2.3 total evaporation, TE, n—analytical method for deter-
3.3.20.2 Discussion—According to Practice E2655, 5.8.4.1:
mination of isotope amount ratios of uranium or plutonium, as
Fromstatisticaltheory,a95%confidenceintervalforthemean
described in Test Method C1672, also called “classical” total
of a normal distribution, given n independent observations x ,
evaporation in this test method. 1
x ,.,x drawnfromthedistribution,isx¯ 6t×SD/√n,where
2 n
3.2.4 turret, n—holder for sample filaments.
x¯ is the sample mean, SD is the standard deviation of the
3.2.4.1 Discussion—Alternate names for turret are carousel,
observations (see above), and t is the 0.975 percentile of the
magazine, and wheel.
Student’s t distribution with n-1 degrees of freedom. Because
Student’s t distribution approaches the normal as n increases,
the value of t approaches 1.96 as n increases. This is the basis
The last approved version of this historical standard is referenced on
www.astm.org. forusingthe(coverage)factor2forexpandeduncertainty.The
C1871 − 22
standard error (SE) of the mean value of a series of n This measurement can be performed using the TE or MTE
independent repeated measurements can be derived from that methods (Test Methods C1672 and C1832, respectively).
by usingt=1,sothe standard error (SE) is given by SD /√n.
5. Significance and Use
3.3.21 TIMS—thermal ionization mass spectrometry
5.1 Uranium material is used as a fuel in certain types of
3.3.22 WRM—working reference material
nuclear reactors. To be suitable for use as nuclear fuel, the
starting material shall meet certain specifications such as those
4. Summary of Test Method
described in Specifications C753, C776, C787, C833, C967,
4.1 The double spike method has been developed with the
C996, and C1008, or as specified by the purchaser. The
235 238
intention to improve the precision and decrease the uncertain-
U/ U isotope amount ratios and the amount content of
235 238
ties for U/ U major isotope ratio measurements compared
uranium material can be measured by mass spectrometry
to the known methods such as the “classical” total evaporation
following this test method to ensure that they meet the
technique (1-4), alsodescribedinTestMethodC1672,andthe
specification.
modified total evaporation technique (5 and 6), also described
5.2 The double spike method has been used for studies of
in Test Method C1832. For the double spike method the mass
uranium fractionation effects in isotope geochemistry and
235 238
fractionation correction for the U/ U ratio is performed
cosmochemistry, for uranium source attribution in nuclear
internally throughout the measurement rather than externally,
forensics and for investigation of conversion or sampling
by using the mass fractionation observed for a double spike
processes in nuclear industry and nuclear safeguards (7-11).
233 236
materialwithaknownorcertified U/ Uisotoperatio(also
Most recently, the double spike method has been used for the
spanning three mass units), which is mixed with the sample
validation of the Cristallini sampling method of UF (12 and
prior to the measurement, either during the sample preparation
13). The double spike method can be used for a wide range of
or directly on the TIMS filament. If necessary, uranium is
sample sizes even in samples containing as low as 50 µg of
separated from plutonium and other elements (to eliminate
uranium. The concentration of the loading solution for the DS
isobaric interferences) by selective extraction, anion exchange
method has to be in the range of 1 to 6 mg/g to allow a sample
(see Practice C1411), or extraction chromatography. The puri-
loading of 4 to 6 µg of uranium. A minimum loading of 4 µg
fied uranium fraction as nitrate solution is loaded onto an
uranium per filament is recommended.
evaporation filament (made of metals such as rhenium, zone-
236 238
5.3 The measurement of U/ U ratios using this method
refined rhenium, or tungsten with high evaporation
is not possible due to the large isobaric interference from the
temperature), and blended with an appropriate amount of
236 236
Uionbeamofthedoublespikeontothe Uionbeamfrom
double spike solution, and converted to an oxide by controlled
the sample (>50.000 times for close to natural material, for
heating of the filament under atmospheric conditions. In case
235 238
example, like IRMM-184).
only the U/ U ratio of the sample has to be determined, it
is recommended to mix the sample with the double spike
5.4 The application of the double spike method for mea-
235 238
duringtheloadingprocessonthefilament.Incasetheuranium
surements of U/ U ratio is limited by the isobaric inter-
amount concentration of the sample has to be determined, the
ference between the U from the double spike material and
sample solution has to be blended gravimetrically with the
the U contained in the sample. As a consequence, the
double spike solution prior to filament loading, for which
method is not suitable for samples which contain significant
236 235
weighable amounts have to be used.
amounts of U due to prior neutron capture from Uinthe
236 238
predecessor materials. For samples with U/ U ratios
4.2 The sample amount to be loaded for DS analyses is
–6
higher than about 10 , the double spike method should be
within a range of about 4 to 6 µg to achieve ion beam signals
appliedwithcarefortheisobariccorrection.Foranappropriate
ofabout20to30Vforthemajorisotope UforDU,NU,and
236 238
isobaric correction, the U/ U ratios of the samples should
LEU samples.
be determined separately using a suitable measurement
235 238
4.3 The U/ U isotope amount ratios are corrected for
method, for example, the modified total evaporation MTE
mass fractionation for each integration step individually. This
method (Test Method C1832, Ref (5) and (6)).
is accomplished in an internal manner, the magnitude of the
234 238
5.5 The measurement of U/ U ratios using this method
mass fractionation is calculated from the measured mass
233 236
isverylimitedintheanalyticalperformanceduetotheisobaric
fractionation of the U/ U ratio. The peak tailing contribu-
234 234
interference of the U from the double spike with the U
tions are determined at two mass positions, 0.5 mass units
from the sample (range from 5 to 15%). The correction
below and 0.5 mass units above the isotope masses of interest.
algorithms are presented in 14.3, but statements for precision
4.4 For the correction of isobaric interferences, a separate
and bias are not given. Other methods like MTE (Test Method
measurement of the isotopic composition of the (unspiked)
C1832, Ref (5) and (6)) are better suited and more reliable for
sampleisrequired,unlessthisinformationisalreadyavailable.
234 238
measurements of U/ U ratios.
5.6 The DS method described here can also be extended to
4 measurement of elements other than uranium, if a suitable
The boldface numbers in parentheses refer to a list of references at the end of
this standard. double spike material is available.
C1871 − 22
6. Interferences 7.1.3 Amultiple Faraday collector system to allow simulta-
+
neousdetectionofisotopebeamsfrom m/z=233to238forU
6.1 Isobaric nuclides such as Pu interfere in the uranium
ions;
measurements. The removal of interferences is generally ac-
7.1.4 For the Faraday cups used to measure the major ion
complished by chemical separation leading to ionization of
235 238
beams of U and U, there shall be current amplifiers
uranium only and improved precision of measured isotope
11 233
equipped with 10 Ω resistors and, for the ion beams of U
amount ratios.
and U, there shall be current amplifiers equipped with at
234 235 236 238
11 12
6.2 For the isotopes U, U, U, and U isobaric
least 10 Ω, and preferably 10 Ω resistors to improve the
interferences between the sample and the double spike occur.
signal-to-noise ratio. In case the ion beam of U is below the
233 236
The accurate correction of isobaric interferences is a prerequi-
ion beams of U and U, the use of an amplifier equipped
site for obtaining results for the DS method with satisfactory
with a 10 Ω resistor is recommended, if available.
precisionandaccuracy.Thecorrectionsdependstronglyonthe
7.1.5 A sample turret to allow automatic measurement
mixing proportions between the sample and the double spike.
sequencesofseveralreplicatefilamentloadingspersampleand
Usually the sample/spike amount ratio is adjusted in such a
per quality control standard (preferentially a CRM);
manner that the ion beam intensity at mass m/z=236 is lower
7.1.6 A pumping system that is able to attain a vacuum of
–5 –7
compared to that at mass m/z=235, in order to reduce the
<4.0 × 10 Pa (3 × 10 torr) in the ion source, the analyzer,
influences from low-mass tailings, that is, abundance
and the detector is required. Tailing corrections are dependent
sensitivities, at one mass unit below and beyond the U peaks.
on the vacuum levels inside the mass spectrometer. Analyzer
–7 –9
Therefore a sample-to-spike amount ratio of >20 is recom-
pressures below 7.0 × 10 Pa (5 × 10 torr) are preferred;
mended. The correction of isobaric interferences is explained
7.1.7 Amechanism to scan masses by varying the magnetic
in detail in Section 14 (“calculations”) of this test method.
field or the accelerating voltage or both;
7.1.8 Acomputer for control of the data acquisition accord-
6.3 It has to be ensured that samples are not contaminated
ing to a predefined sequence.
by environmental uranium. The level of effort required to
minimize contamination shall be based upon the sample size
7.2 Special MTE Capabilities—Itisrecommendedtohavea
and the levels of contamination present in the analytical
massspectrometersoftwaretobeflexibleenoughtoimplement
facility. For extremely small samples or extremely low U
a user-defined filament-heating program as for MTE.
abundances, residual uranium from chemicals used for sample
7.3 Aseparate filament degassing device for cleaning of the
dissolution and sample preparation is possible source for bias
filaments before sample loading can be used.
in the isotopic data.
7.4 Apipette or microsyringe to transfer microliter volumes
6.4 Samples shall be chemically purified to assure reliable
of solution.
analyses by TIMS. Impurities, especially alkali elements,
7.5 A separate filament heating device for drying and
produce unstable ion emission leading to poor precision in the
isotopeamountratios.Organiccontaminantsoroxidelayerson oxidizing the sample on the filament ribbon after loading.
the filaments also adversely influence TIMS analyses. Isobaric
interferences, if not removed, will bias the isotope amount 8. Reagents and Materials
ratios.Contaminantsinreagents,labware,orfilamentmaterial
8.1 Purity of Reagents—Ultra-high purity reagents shall be
are also sources for bias in the isotope amount ratios.
used for processing small sample amounts or samples with
6.5 The performance of the instrument can be adversely extremely small isotope amount ratios. The level of uranium
affected by changes in the environmental conditions of the contamination from chemicals, water, and the sample handling
laboratory, that is, temperature and humidity. For this reason, environments shall be determined to ensure that the materials
controlled laboratory environmental conditions should be andtheenvironmentaresufficientlypureforthesamplesbeing
maintained (within the manufacturer’s specifications) during analyzed.
instrument operation.
8.2 Nitric Acid (HNO , 15.8 M)—Concentrated nitric acid.
8.3 Nitric Acid (HNO , 1 M)—One volume of concentrated
7. Apparatus
nitric acid (HNO , 15.8 M) brought to 15.8 volumes with
7.1 Thesuitabilityofthemassspectrometerforcarryingout
water.
measurements by the DS method shall be evaluated by means
8.4 Purity of Water—Unless otherwise indicated, references
of performance tests. The relevant instrument characteristics
to water shall be understood to mean laboratory accepted
are as follows:
demineralized or deionized water as described by Type I of
7.1.1 A thermal ionization source for using single, double,
Specification D1193.
or triple filament assemblies with rhenium or tungsten
filaments, or both;
7.1.2 A mass analyzer sufficient to resolve adjacent masses
The sole source of supply of the apparatus known to the committee at this time
inthemass-to-chargerangebeingstudied, m/z=233to238for
+ is Thermo Fisher Scientific Inc., 81 Wyman St., Waltham, MA 02451. If you are
U . Resolution shall be greater than 350 (full width at 1% of
aware of alternative suppliers, please provide this information to ASTM Interna-
peakheight)andtheabundancesensitivityatmass237forions
tional Headquarters.Your comments will receive careful consideration at a meeting
238 –6
of U less than8×10 ; of the responsible technical committee, which you may attend.
C1871 − 22
8.5 Filaments—Filaments with sufficient purity, for 11. Preparation of Apparatus
example, zone refined or high purity Re or W, should be used.
11.1 Filament Degassing—Filaments can be degassed be-
The size and configuration of the filament is instrument
foreusingthemforDSmeasurements.Thisisrecommendedin
dependent.
casetheheatingofthefilamentsduringthemassspectrometric
8.6 Liquid Nitrogen—Liquid nitrogen can be filled into the
measurement is causing the vacuum pressure in the ion source
–4 –6
cold trap of a mass spectrometer to improve the vacuum
to increase beyond 1.3 × 10 Pa (1 × 10 torr) is reached.
pressure.
Recommended filament currents for degassing are in the range
4.0 to 5.0 A, corresponding to temperatures in the range of
9. Hazards
1700 to 2000°C. Perform the degassing for a duration of at
least 30 min.
9.1 TIMS instruments operate at 8 to 10 kV electrical
potential. Ensure that the high-voltage is switched off before
11.2 “Initialization” of the Sample Turret—Adjust, if
insertion or removal of the sample turret into/from the
needed, the position of the sample turret in the ion source and
instrument,andworkingwiththeionsource,oraccessingother
verify proper electrical connections for both the evaporation
electronic components.
and ionization filament for each sample loading position. It
9.2 The filaments reach temperatures in excess of 2000°C. shall be ensured that the electrical contact is not interrupted in
The filament holders, sample wheel, and ion sources parts are
case the turret is slightly moved for the purpose of ion beam
expected to be hot. Ensure that a sufficient time has lapsed focusing.
since the last filament heating before accessing the filaments,
11.3 Electronics Test—Modern mass spectrometric instru-
sample turrets, and ion source.
ments offer an automated routine for testing the stability and
9.3 Wear eye protection and suitable gloves when filling
performance of the electronic systems (for example, Faraday
coldtrapswithliquidnitrogen.Protecthands,torso,andfeetin
cup amplifier baselines and gains, high-voltage unit, and
the event of splashing or spilling of the liquid nitrogen.
magnet current supply units). A report is produced flagging
systems or components that are out of specification. Users of
9.4 Handle radioactive materials with appropriate attention
the instruments should perform routine checks of the perfor-
to radiological safety.
mance of the electronic systems and ensure that the perfor-
9.5 Handle chemical hazards and toxins like uranium with
mance is within manufacturer’s specifications. The frequency
appropriate care.
for this test shall be established by the user based on manu-
facturer recommendations or as specified in the user’s quality
10. Sampling, Test Specimens, and Test Units
assurance program.
10.1 Isotope Reference Materials—Uranium reference ma-
11.4 Amplifier Signal Decay Adjustment—Adjust the signal
terials used in the analysis should be prepared from certified
decay characteristics of the current amplifiers of the Faraday
reference materials (CRMs) traceable to SI units. Examples
cups. This is important for measuring isotope amount ratios
include the Double Spikes IRMM-3636 (1 mg U/g), IRMM-
with a large dynamic range, high precision and accuracy, or
3636a (0.1 mg U/g), and IRMM-3636b (0.01 mg U/g), which
both. Depending on the combination of the capacitance and
all have the same isotopic composition (uncertainties with
resistance of the current amplifier, the response time for a
coverage factor k = 2, 95% confidence level):
sudden change in the ion beam signal to the Faraday cup can
233 236
U/ U = 1.01906(16),
234 236
reach up to 5 s. For amplifier resistances higher than the 10
U/ U = 0.00036606(48),
235 236
U/ U = 0.000045480(74), and
Ω, longer response times of about 15 s can be expected. The
238 236
U/ U = 0.00023481(38).
DS method has to be designed by taking into consideration the
In addition, various in-house double spike materials are
required response times. The amplifier response can be
being used at numerous facilities, which have been calibrated
checked either using a custom-made software module within
using isotope reference materials, like NBL CRM U500
the operating software (when available), or “manually” by
235 238
( U/ U > 1) or IRMM-184 (close to natural U). For the
means of a large ion beam that is abruptly directed into a
preparation of in-house double spike reference materials, see
Faraday cup to check the signal ingrowth time, or away from
Guide C1128 for additional guidance on preparation of trace-
a Faraday cup (for example, by closing a valve between ion
able working reference materials.
source and analyzer) to check the signal decay time.
10.2 Uraniumsamplestobemeasuredandisotopereference
11.5 Ion Source and Analyzer Pressure—It is important to
materialsusedforqualitycontrolpurposesshallbeinthesame
achieve a certain level of vacuum before the isotope amount
medium, same concentration and in the same oxidation state.
ratio measurements can be started; see 7.1.6 for the recom-
The solutions for loading onto the filaments are usually 1 to 5
mended pressure. The peak tailing depends strongly on the
Mnitricacidsolutions.Theloadinganddryingsequenceofthe
vacuumpressureinthedetectorsystemsincethenumberofion
filaments shall also be similar.
collisionswithgasmoleculesinsidethemassspectrometerisa
10.3 In the case of characterization studies of test materials, direct function of the ambient pressure. An increase of the
possible inhomogeneity between test units shall be evaluated pressure within the ion source caused by the heating of the
statistically and included in the uncertainty calculations of the ionization and evaporation filaments can be subdued, to a
isotope amount ratios assigned. certain extent, by using a cold trap filled with liquid nitrogen.
C1871 − 22
12. Calibration and Standardization performedpriortotheFaradaycupefficiencytest.TheFaraday
NOTE 1—The measurement method may be qualified following Guide cup efficiency test can be performed in several ways, as
C1068 and calibrated following Guide C1156.
described in 12.5.1 – 12.5.4.
12.1 Mass Calibration—The relationship between the 12.5.1 The calibration may be performed by switching a
stable ion beam of Re (from a blank filament) between each
known atomic masses and the magnetic field necessary to
direct the isotope beams into the detectors shall be updated on Faraday cup and a reference Faraday cup. In case a relative
efficiency between the detectors is significantly different from
aregularbasis.Masscalibrationshallbeperformedatintervals
unity, this result can be used to correct for differences in the
specified by the manufacturer or the user’s quality assurance
detector response. This procedure can be performed with a
program.
relative uncertainty at the level of <0.1%.
12.2 Peak Centering—Thepeakcenteringroutineisusedas
12.5.2 Aseries of peak-jumping measurements between all
afineadjustmenttoensurethattheionbeamiscenteredwithin
Faraday cups and a reference cup to be checked can also be
thedetector.Peakcenteringusuallyoccursviafineadjustments
performed using a sufficiently large uranium sample and one
of the accelerating voltage, and any difference between the
large stable ion beam, for example, a 10 to 20 V ion beam of
value optimized during peak centering from the default accel-
U from a LEU or natural uranium sample. The drift of the
erating voltage requires a readjustment of the mass calibration
signal intensity shall be corrected for using the operating
curve. Peak centering shall be performed for at least at three
software. This procedure can be performed with a relative
uranium masses as part of the mass calibration before the start
uncertainty at the level of <0.01%.
of each DS measurement sequence. During the DS
12.5.3 A series of comparative neodymium (Nd) isotope
measurement, peak centering is performed on a regular basis.
amount of ratio measurements can be performed in two
12.3 Amplifier Baseline Calibration—The baselines of the
different modes such as the multi-dynamic mode and the static
TM
Faraday cup amplifiers, that is, the amplifier responses without
mode with “amplifier rotation” (only for TRITON TIMS,
incoming ion beam to the cup, shall be measured on a regular
also called “virtual amplifier”: each Faraday cup is connected
basis and checked for stability. During the DS measurements,
toeachamplifierforregulartimeintervalsduringthemeasure-
baseline measurements are performed on a regular basis. Note
ment). This procedure can be performed with a relative
that the integration time for the baseline measurement has a
uncertainty at the level of few ppm (5). It shall be repeated
significant influence on the uncertainty of Faraday cup
until all Faraday cups of interest for DS measurements have
measurements, particularly at lower ion beam intensities.
been included.
Therefore, the integration time of the baseline (within a
12.5.4 A series of static measurements can be performed
measurement) shall be comparable to the integration time of
using special “multi-isotope” reference materials, such as
theactualionbeamsignalintegration.Thelong-termhistorical 233 235 236 238
IRMM-3100a ( U/ U/ U/ U=1/1/1/1), IRMM-072/1,
233 235 238
baseline data shall be regularly reviewed by the user to assure
IRMM-074/1, or IRMM-199 ( U/ U/ U=1/1/1), to in-
that the system performance is within manufacturer specifica-
clude all Faraday cups. This procedure can be performed with
tions and quality system requirements.
relative uncertainties of about 0.03%.
12.4 Amplifier Gain Calibration—The stability and re-
12.6 Linearity Test—There are various procedures to check
sponse of individual Faraday detector amplifiers shall be
the linearity of an isotope mass spectrometer detection system.
measured and differences between amplifiers corrected for via
The procedures described in 12.6.1 and 12.6.2 are mainly
the amplifier gain calibration. Gain calibration is normally
applicable for Faraday multi-collector systems.
performed by sequentially applying a stable calibration current
12.6.1 The linearity of the mass spectrometer is determined
to the input of each Faraday cup amplifier and the output is
over the working range of the Faraday cups by measuring the
then normalized to a reference value to generate a gain 235 238
U/ U ratios of various reference materials under identical
calibration factor for each amplifier.Again calibration shall be
conditions. The mass spectrometer system is linear if the K
performed prior to each automatic DS sequence. Historical 235 238
factor, that is, the ratio of the certified U/ U ratio to the
235 238
gaincalibrationdatacanbeusedtoevaluatethestabilityofthe
measured U/ U ratio, is independent of the isotopic
amplifiers.
composition of the material. For this procedure, the NBL
U-seriesofreferencematerials(U005atoU970,0.5to97%of
12.5 Faraday Cup Effıciency Test—The response of indi-
U) is ideal and can be combined with the IRMM-183-187
vidual Faraday cups depends on several factors, for example,
series(0.3to5%of U)andtheIRMM019-029series(0.17
extent of usage, manufacturing variability, and can also be
to5%of U,tobeconvertedfromUF ).Thisprocedureshall
affected by an insufficient electron suppression voltage. The
be performed sequentially for all Faraday cups of the multi-
relative response of the Faraday cups, therefore, shall be
collector system needed for the DS analyses.
determined periodically. Usually, the Faraday cups of a multi-
collector system are only intercalibrated for the current ampli- 12.6.2 The IRMM-072 and IRMM-074 series of reference
238 235
fiers connected to them (see 12.4) but not for the differences in materials are characterized by U/ U ratios of ≈1 and
233 235 –6
the efficiencies of the Faraday cups themselves. The efficien- U/ U ratios ranging from ≈1 down to ≈10 for the 15 or
cies of the Faraday cups are expected to be similar to each 10units,respectively,oftheusedseries.Foreachunit,thebias
238 235
other,whichmeansthattherelativeefficiencies(relativetoone ofthemeasured U/ Uratiosfromthecertifiedonescanbe
reference cup) are normally close to unity. Note that an used for internal mass fractionation correction of the measured
233 235 233 235
(electronic) amplifier gain calibration (see 12.4) shall be U/ U ratios. The comparison of the corrected U/ U
C1871 − 22
ratios with the certified ones allows the linearity of the 13.1.3 Sample Purification—Use Practice C1411 or similar
detection system to be checked over a dynamic range of six procedure to separate uranium from plutonium and other
orders of magnitude for the ion beam intensity. A detailed impurities, if necessary.
description of the procedure is given in (14). This procedure
13.2 Sample Loading and Conditioning—Samples for the
shallbeperformedsequentiallyforallFaradaycupsneededfor
DS method are usually directly loaded on the filament by drop
the DS analyses.
deposition. Samples and QC materials shall be prepared for
12.7 Peak Overlap—When a Faraday multi-collector sys-
analysis by the same method at similar mass loadings. Drop
temforthesimultaneousdetectionofseveralmassesisused,it deposition onto the filament can be accomplished with the use
needstobeensuredthatthepeakoverlapisacceptable.Amass
ofamicrosyringeorpipettefittedwithaplastictip.Changethe
scan, usually by scanning the magnetic field, shall be per- tipbetweensampleloadingstopreventcrosscontamination.In
formed by which all ion beams are simultaneously moved
particular for loading and mixing a sample solution and the
through the respective cups. The measured intensities for all double spike solution on the same filament, cross contamina-
detectors shall be plotted versus the mass of a reference
tion between these solutions has to be prevented by changing
detector to make the peak overlap visible.All peaks shall have pipette tips. It is recommended to load the double spike
a symmetric shape with a common flat region in the center, solution first and the sample afterwards in order to minimize
withthepeakcentersreasonablyclosetogether,asspecifiedby
the risk of contaminating the double spike solution with any
themanufacturerortheuserqualitysystem.Afterasatisfactory sample material. For filaments loaded by drop deposition, the
peak overlap is realized (by moving cups relative to one
solution shall be evaporated by passing sufficient electrical
another if necessary), the positions of all detectors shall be current through the filament to cause gentle drying without
saved, for example, as a Faraday cup configuration file. The
boiling. Samples for DS are usually prepared ina1to5 M
positionsshallbecheckedandpossiblyreadjusted,manuallyor nitric acid with a uranium concentration between 1 to 6 mg/g,
using stepping motors, as needed before a new automatic
whichisequivalentto1to6µg/µL.Dependingontheuranium
measurement sequence. amount to be loaded, more than 1 µL of the sample solution
may be needed. The recommended uranium amount for load-
12.8 Mass Fractionation Correction:
ing is 4 to 6 µg. Deposit drops very carefully and slowly. It is
12.8.1 For the double spike method the mass fractionation
235 238
recommended to keep the filament heated by passing 0.5 to
correction for the U/ U ratio is performed for each
0.7A current and depositing 1-µL-drops at a time. After all
integration step (called “mass cycle,” see below) internally
drops are loaded, the solution on the filament is heated until
throughout the measurement rather than externally, by using
dryness, for at least one more minute, and then heated for
the mass fractionation observed for a double spike material
233 236
several seconds at a higher current of 1.5 to 2.0A for
with a known or certified U/ U isotope ratio (also span-
conditioning. Alternatively, a stepped-heating program can be
ning three mass units).
used to condition samples, that is, to convert samples to
12.8.2 The mass fractionation correction factor, K, is calcu-
suitable chemical forms. Avoid quick evaporation of the
lated as follows:
sample or melting the filament.At different facilities, different
K 5 ~R ⁄ R ! (1)
c m
loadingandconditioningprocedureshavebeenestablishedand
validated. Each procedure shall be applied in a consistent
where:
manner for all samples, and quality control samples.
K = mass fractionation correction factor,
233 236
R = measured U/ U isotope amount ratio for the
m 13.3 Mountallsamplefilamentsandionizationfilamentson
double spike, and
a sample turret and insert the sample turret into the ion source
233 236
R = known or certified U/ U isotope amount ratio
c
of the mass spectrometer.
value for the double spike.
13.4 Close the source and start evacuating.
Details about the mass fractionation and further correction
13.5 Perform adjustment (also called initialization) of the
algorithms are presented in 14.2.
sample turret if needed. In case of problems with electrical
13. Procedure
connections, the source might have to be vented again to
resolve the problem.
13.1 Sample Preparation:
13.1.1 Sample Dissolution—Dissolveanappropriatesample
13.6 Evacuate ion source to the manufacturer’s recom-
amount to obtain the desired filament loading solution for the
mended minimum pressure or according to the user’s proce-
mass spectrometric analysis. See Practice C1347 for the
dure.
dissolution of uranium.
13.7 Add liquid nitrogen to the cold trap if desired.
13.1.2 Prepare the sample and any reference material solu-
13.8 Isotope Amount Ratio Measurement—The following
tions as purified nitrates, using identical chemical preparation
steps 13.8.1 – 13.10 are typically performed automatically
and handling steps. For uranium samples hydrolyzed from
under computer control depending upon the instrument.
uranium hexafluoride, it is recommended that the samples are
13.8.1 Perform an amplifier gain calibration for each new
converted to U O before dissolution in nitric acid and analy-
3 8
sis. The solution concentrations shall be chosen to allow for a automatic sequence.
convenient filament loading (for example, a 2-mg U/mL 13.8.2 Measure the baseline during the course of each
solution yields 2 µg of uranium per µL, see also 13.2). measurement of a sample and QC standard.
C1871 − 22
13.8.3 Usually under computer control, the ionization fila- 13.9 Interblock Actions and Filament Heating for DS:
ment is heated up to a temperature of about 1800 to 1950°C. 13.9.1 Peak Centering and Baseline—Each measurement
For automatic sequences, usually the magnitude of the Re block usually consists of a maximum of five mass cycles, with
ion beam is used as the regulated quantity instead of the each cycle having a duration of about 60 to 90 s. Before each
filament temperature by a pyrometer because only the narrow block, a peak centering is performed using the U isotope.
sides of the filaments are oriented towards the pyrometer. Additionally, an ion source focusing is performed before each
187 11
Typical Re ion beams of about 300 to 600 mV(on a 10 Ω block. Typically, every five blocks, the electronic baselines of
resistor) are used for non-zone refined filaments and lower all the Faraday cup amplifiers are re-measured. In case 10 Ω
values of 150 to 400 mV are used for zone-refined filaments, resistors are used in some of the amplifiers, the idle times for
depending on the thickness and brand. the baseline measurements have to be sufficiently long, for
13.8.4 The Re ion beam is peak centered and focused. If example, at least 15 s.
necessary, the Re ion beam size is readjusted towards the 13.9.2 DS Interblock Heating—The DS interblock heating
target value, which shall be similar (within about 20%) for isrecommendedtobeperformedsimilartotheMTEinterblock
each measurement within an automatic sequence, by changing heating as described in Test Method C1832. The filament
the filament current. heatingiscontrolledbyaspecialprogramscriptexecutedafter
13.8.5 The sample filament is heated to a temperature each measurement block. This program script first measures
235 235 238
sufficient to yield and ion beam sum intensity from U and the actual sum intensity (mainly from U and U) and
238 11
U of about 1 to 4V(on an amplifier with a 10 Ω resistor). compares it with the predefined (initial) target sum intensity.
The beam is focused and peak centered using the largest U ion This predefined target sum intensity is typically in the range of
beam, which is usually the U beam. 20 to 30 V, selected by the operator depending on the sample
13.8.6 Data acquisition is started. The data acquisition is amount loaded, the experience with the ion source and the
performedonaperblockbasisinwhicheachblockconsistsof instrument transmission. Based on the comparison of the
a minimum of two and a maximum of five mass cycles and actually measured sum intensity with the target sum intensity,
each mass cycle of (usually) four integration steps. The data the following filament heating step is calculated. A detailed
acquisition is usually continued until the whole sample is description of the interblock heating script is given in Test
evaporated; see 13.10. Method C1832.
13.8.7 DS Mass Cycle—The DS mass cycle consists of four
13.10 Termination of DS Measurement—The DS measure-
steps as shown in Table 1. Depending on the ion beam
ment is terminated when the sum intensity is below a user-
intensities observed the use of amplifiers with 10 Ω resistors
defined limit of 1 to 2 V.
is recommended. For the recommended sample-to-spike
233 236
14. Calculations
amount ratios >20, the U and U intensities coming from
thedoublespikeshallbedetectedusingamplifierswith10 Ω
14.1 Within this section, the DS data evaluation and calcu-
resistors, if available, in case of depleted samples with low
lation of the various correction factors is discussed. The mass
235 238
U ion beams this applies as well.
fractionation correction for the major ratios U/ Uis
13.8.7.1 The first step is the main integration for all iso-
performed internally for each mass cycle throughout the
233 236
topes; the integration time is usually about 16 s.
measurement based on the results of the U/ U ratio using
13.8.7.2 In Steps 2 and 3 of the DS mass cycle, the
the exponential fractionation law. The differences between
background intensities at the low and high mass side of all
different fractionation laws, for example, power law, exponen-
uranium isotopes of interest are measured. The mutual back-
tiallaw,linearlaw,orRayleighlawareattheleveloffewparts
235 236
grounds for U and U are the most critical ones and
per million for heavy elements like uranium, which is insig-
dependalotonthesampletospikeratio.Duetothedifferences
nificant for the DS measurements.
in the tailing effect between the low and high mass sides, an 235 238
14.2 Evaluation for Major Ratio U/ U:
interpolation for the isotope ratios shall be performed, using a
233 236
14.2.1 The K factor is derived from the U/ U ratio for
linear appr
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