ASTM C1832-23

Standard Test Method for Determination of Uranium Isotopic Composition by Modified Total Evaporation (MTE) Method Using Thermal Ionization Mass Spectrometer

SIGNIFICANCE AND USE
5.1 Uranium material is used as a fuel in certain types of nuclear reactors. To be suitable for use as nuclear fuel, the starting material shall meet certain specifications such as those described in Specifications C753, C776, C787, C833, C967, C996, and C1008, or as specified by the purchaser. The isotope amount ratios of uranium material can be measured by mass spectrometry following this test method to ensure that they meet the specification.  
5.2 The MTE method can be used for a wide range of sample sizes even in samples containing as low as 20 µg of uranium. If the uranium sample is in the form of uranium hexafluoride, it has to be converted into a uranium nitrate solution for measurement by the MTE method. The concentration of the loading solution for MTE has to be in the range of 1 mg/g to 6 mg/g to allow a sample loading of 2 µg to 6 µg of uranium. A minimum loading of 3 µg uranium per filament is strongly recommended. This is needed to have a sufficient and stable ion signal especially for the two minor isotopes (234U and 236U) thus enabling the internal calibration of SEM versus the Faraday cups using the 234U ion beam signal during the measurement.  
5.3 Until now, the instrument capabilities for the MTE method have only been implemented on the TRITON™ TIMS instrument.5 Therefore, all recommendations for measurement parameters in this test method are specified for the TRITON instrument. The manufacturers of other TIMS instruments (for example, IsotopX and Nu Instruments) have indicated plans to implement the modifications needed in their instruments to use the MTE method.  
5.4 The MTE method described here can also be extended to measurement of elements other than uranium. Note that the MTE method has already been implemented for plutonium and calcium.
SCOPE
1.1 This test method describes the determination of the isotope amount ratios of uranium material as nitrate solutions by the modified total evaporation (MTE) method using a thermal ionization mass spectrometer (TIMS) instrument.  
1.2 The analytical performance in the determination of the 235U/238U major isotope amount ratio by MTE is similar to the (“classical”) total evaporation (TE) method as described in C1672. However, in the MTE method, the evaporation process is interrupted on a regular basis to allow measurements and subsequent corrections for background from peak tailing, perform internal calibration of a secondary electron multiplier (SEM) detector versus the Faraday cups, peak centering, and ion source refocusing. Performing these calibrations and corrections on a regular basis during the measurement, improves precision, and significantly reduces uncertainties for the minor isotope amount ratios 234U/238U and 236U/238U as compared to the TE method.  
1.3 In principle, the MTE method may yield major isotope amount ratios without the need for mass fractionation correction. However, depending on the measurement conditions, small variations are observed between sample turrets. Therefore, a small correction based on measurements of a certified reference material is recommended to improve consistency. The uncertainty around the mass fractionation correction factor usually includes unity.  
1.4 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 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 issu...

General Information

• Status: Published
• Publication Date: 31-Dec-2022
• ICS: 27.120.30 - Fissile materials and nuclear fuel technology
• Technical Committee: C26 - Nuclear Fuel Cycle
• Drafting Committee: C26.05 - Methods of Test

Relations

• Refers: ASTM C859-24 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM C1672-23 - Standard Test Method for Determination of the Uranium, Plutonium or Americium Isotopic Composition or Concentration by the Total Evaporation Method Using a Thermal Ionization Mass Spectrometer
• Effective Date: 01-Dec-2023
• Refers: ASTM C1411-20 - Standard Practice for The Ion Exchange Separation of Uranium and Plutonium Prior to Isotopic Analysis
• Effective Date: 01-Jul-2020
• Refers: ASTM C996-20 - Standard Specification for Uranium Hexafluoride Enriched to Less Than 5&#x2009;%&#x2009;<sup > 235</sup>U
• Effective Date: 01-Mar-2020
• Refers: ASTM C787-20 - Standard Specification for Uranium Hexafluoride for Enrichment
• Effective Date: 01-Mar-2020
• Refers: ASTM C967-20 - Standard Specification for Uranium Ore Concentrate
• Effective Date: 01-Feb-2020
• Refers: ASTM E2655-14(2020) - Standard Guide for Reporting Uncertainty of Test Results and Use of the Term Measurement Uncertainty in ASTM Test Methods
• Effective Date: 01-Jan-2020
• Refers: ASTM C1625-19 - Standard Test Method for Uranium and Plutonium Concentrations and Isotopic Abundances by Thermal Ionization Mass Spectrometry
• Effective Date: 15-Sep-2019
• Refers: ASTM E2586-19e1 - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 01-Apr-2019
• Refers: ASTM C1156-18 - Standard Guide for Establishing Calibration for a Measurement Method Used to Analyze Nuclear Fuel Cycle Materials
• Effective Date: 01-Sep-2018
• Refers: ASTM C1871-18 - Standard Test Method for Determination of Uranium Isotopic Composition by the Double Spike Method Using a Thermal Ionization Mass Spectrometer
• Effective Date: 01-Feb-2018
• Refers: ASTM C1672-17 - Standard Test Method for Determination of Uranium or Plutonium Isotopic Composition or Concentration by the Total Evaporation Method Using a Thermal Ionization Mass Spectrometer
• Effective Date: 01-Jan-2017
• Refers: ASTM C753-16 - Standard Specification for Nuclear-Grade, Sinterable Uranium Dioxide Powder
• Effective Date: 01-Feb-2016
• Refers: ASTM C996-15 - Standard Specification for Uranium Hexafluoride Enriched to Less Than 5 % ²³⁵U
• Effective Date: 01-Jul-2015
• Refers: ASTM C787-15 - Standard Specification for Uranium Hexafluoride for Enrichment
• Effective Date: 01-Jul-2015

Overview

ASTM C1832-23, "Standard Test Method for Determination of Uranium Isotopic Composition by Modified Total Evaporation (MTE) Method Using Thermal Ionization Mass Spectrometer," establishes procedures for accurately measuring uranium isotope ratios in nitrate solutions using the Modified Total Evaporation (MTE) method and Thermal Ionization Mass Spectrometry (TIMS). This standard plays a crucial role in nuclear fuel quality control, material verification, and nuclear safeguards, ensuring that uranium materials meet strict specifications required for use in nuclear reactors and other regulated applications.

Key Topics

• Uranium Isotopic Composition: Provides procedures to determine isotope ratios (e.g., 235U/238U, 234U/238U, 236U/238U) in uranium nitrate solutions.
• MTE Method Advantages:
  • Enhances accuracy for minor isotope ratios compared to the classical total evaporation (TE) method.
  • Intermittent evaporation allows for regular background corrections and internal calibrations, reducing measurement uncertainties and improving data reliability.
• Sample Preparation and Range:
  • Capable of analyzing very low uranium amounts (as little as 2–6 µg, with recommendations to load at least 3 µg per filament for optimal signal stability).
  • Uranium hexafluoride samples must be converted to nitrate solutions before analysis.
• Instrument Requirements:
  • Developed for and validated on the TRITON™ TIMS platform.
  • Requires precise vacuum, high-purity reagents and filaments, and a robust multi-collector detection system (Faraday cups and secondary electron multipliers).
• Calibration and Quality Control:
  • Emphasizes the use of certified reference materials (CRMs) for calibration and mass fractionation corrections.
  • Outlines the need for regular equipment checks, environmental controls, and contamination prevention for reliable isotopic readings.
• Extensibility: MTE method applicability is confirmed for other elements, such as plutonium and calcium, broadening its value in analytical laboratories.

Applications

• Nuclear Fuel Cycle:
  • Ensures uranium materials used in reactors comply with specifications outlined in related ASTM standards (e.g., C753, C767, C787).
  • Assists in the verification of uranium enrichment levels, critical for both regulatory compliance and reactor safety.
• Nuclear Safeguards and Forensics:
  • Supports precise material characterization necessary for international safeguards, non-proliferation monitoring, and forensic investigations.
• Quality Control Laboratories:
  • Provides standardized methods for laboratory accreditation and inter-laboratory consistency.
• Analytical Chemistry & Research:
  • Enables high-precision isotopic measurements essential for geochemical studies, environmental monitoring, and advanced research into actinide behavior.

Related Standards

When implementing or referencing ASTM C1832-23, it may be necessary to consider the following related standards for a holistic approach to uranium analysis and nuclear material handling:

• ASTM C753: Specification for Nuclear-Grade, Sinterable Uranium Dioxide Powder
• ASTM C776: Specification for Sintered Uranium Dioxide Pellets for Light Water Reactors
• ASTM C787: Specification for Uranium Hexafluoride for Enrichment
• ASTM C833: Specification for Sintered (Uranium-Plutonium) Dioxide Pellets for Light Water Reactors
• ASTM C967: Specification for Uranium Ore Concentrate
• ASTM C996: Specification for Uranium Hexafluoride Enriched to Less Than 5% U-235
• ASTM C1672: Test Method for Determination of Uranium or Plutonium Isotopic Composition or Concentration by the Total Evaporation Method Using a Thermal Ionization Mass Spectrometer
• ASTM C1871: Test Method for Determination of Uranium Isotopic Composition by the Double Spike Method Using Thermal Ionization Mass Spectrometer
• ASTM C1411: Practice for Ion Exchange Separation of Uranium and Plutonium Prior to Isotopic Analysis
• ASTM D1193: Specification for Reagent Water

Implementing ASTM C1832-23 ensures high-quality, standardized uranium isotopic analysis, underpinning critical nuclear operations, regulatory compliance, and advanced scientific research.

Standards Content (Sample)

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:C1832 −23
Standard Test Method for
Determination of Uranium Isotopic Composition by Modified
Total Evaporation (MTE) Method Using Thermal Ionization
Mass Spectrometer
This standard is issued under the fixed designation C1832; 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 priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.1 This test method describes the determination of the
1.6 This international standard was developed in accor-
isotope amount ratios of uranium material as nitrate solutions
dance with internationally recognized principles on standard-
by the modified total evaporation (MTE) method using a
ization established in the Decision on Principles for the
thermal ionization mass spectrometer (TIMS) instrument.
Development of International Standards, Guides and Recom-
1.2 The analytical performance in the determination of the
mendations issued by the World Trade Organization Technical
235 238
U/ U major isotope amount ratio by MTE is similar to the
Barriers to Trade (TBT) Committee.
(“classical”) total evaporation (TE) method as described in
C1672. However, in the MTE method, the evaporation process
2. Referenced Documents
is interrupted on a regular basis to allow measurements and 2
2.1 ASTM Standards:
subsequent corrections for background from peak tailing,
C753Specification for Nuclear-Grade, Sinterable Uranium
perform internal calibration of a secondary electron multiplier
Dioxide Powder
(SEM) detector versus the Faraday cups, peak centering, and
C776SpecificationforSinteredUraniumDioxidePelletsfor
ion source refocusing. Performing these calibrations and cor-
Light Water Reactors
rections on a regular basis during the measurement, improves
C787Specification for Uranium Hexafluoride for Enrich-
precision, and significantly reduces uncertainties for the minor
ment
234 238 236 238
isotope amount ratios U/ U and U/ U as compared to
C833Specification for Sintered (Uranium-Plutonium) Diox-
the TE method.
ide Pellets for Light Water Reactors
1.3 In principle, the MTE method may yield major isotope C859Terminology Relating to Nuclear Materials
C967Specification for Uranium Ore Concentrate
amount ratios without the need for mass fractionation correc-
tion. However, depending on the measurement conditions, C996Specification for Uranium Hexafluoride Enriched to
Less Than 5% U
small variations are observed between sample turrets.
Therefore, a small correction based on measurements of a C1008 Specification for Sintered (Uranium-Plutonium)
DioxidePellets—Fast Reactor Fuel (Withdrawn 2014)
certified reference material is recommended to improve con-
sistency.Theuncertaintyaroundthemassfractionationcorrec- C1068Guide for Qualification of Measurement Methods by
a Laboratory Within the Nuclear Industry
tion factor usually includes unity.
C1128Guide for Preparation of Working Reference Materi-
1.4 Units—The values stated in SI units are to be regarded
als for Use in Analysis of Nuclear Fuel Cycle Materials
as standard. The values given in parentheses after SI units are
C1156Guide for Establishing Calibration for a Measure-
providedforinformationonlyandarenotconsideredstandard.
ment Method Used toAnalyze Nuclear Fuel Cycle Mate-
1.5 This standard does not purport to address all of the
rials
safety concerns, if any, associated with its use. It is the
C1347Practice for Preparation and Dissolution of Uranium
responsibility of the user of this standard to establish appro-
Materials for Analysis
1 2
ThistestmethodisunderthejurisdictionofASTMCommitteeC26onNuclear For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Test. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Jan. 1, 2023. Published January 2023. Originally the ASTM website.
approved in 2016. Last previous edition approved in 2022 as C1832–22. DOI: The last approved version of this historical standard is referenced on
10.1520/C1832-23. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1832−23
C1411Practice for The Ion Exchange Separation of Ura- 3.3.9 ICPMS—Inductively Coupled Plasma Mass Spec-
nium and Plutonium Prior to Isotopic Analysis trometry
C1625Test Method for Uranium and Plutonium Concentra-
3.3.10 IRMM—Institute for Reference Materials and Mea-
tions and Isotopic Abundances by Thermal Ionization
surements
Mass Spectrometry
3.3.11 ITU—Institute for Transuranium Elements
C1672Test Method for Determination of Uranium or Pluto-
nium Isotopic Composition or Concentration by the Total 3.3.12 JRC—Joint Research Centre of the European Union
Evaporation Method Using a Thermal Ionization Mass
3.3.13 JRC-G.2—Unit for Standards for Nuclear Safety,
Spectrometer
SecurityandSafeguardsofJRC(newnameforthenuclearpart
C1871Test Method for Determination of Uranium Isotopic
of the former IRMM)
Composition by the Double Spike Method Using a Ther-
3.3.14 JRC-G.II.6—UnitforNuclearSafeguardsandForen-
mal Ionization Mass Spectrometer
sics of JRC (part of the former ITU)
D1193Specification for Reagent Water
3.3.15 LEU—Low Enriched Uranium
E2586Practice for Calculating and Using Basic Statistics
E2655Guide for Reporting Uncertainty of Test Results and
3.3.16 MTE—Modified Total Evaporation
Use of the Term Measurement Uncertainty inASTM Test
3.3.17 NBL—New Brunswick Laboratory
Methods
3.3.18 RSD—Relative Standard Deviation; SD (see below)
3. Terminology divided by the mean value of the observations in repeated
sampling
3.1 Terminology C859 contains terms, definitions, descrip-
3.3.19 RSE—Relative Standard Error; SE (see below) di-
tions of terms, nomenclature, and explanations of acronyms
vided by the mean value of the observations in repeated
and symbols specifically associated with standards under the
sampling
jurisdiction of Committee C26 on Nuclear Fuel Cycle.
3.3.20 SD—Standard Deviation; according to Practice
3.2 Definitions:
E2586, 3.1.30, the square root of the sum of the squared
3.2.1 abundance sensitivity, n—in isotope amount ratio
deviations of the observed values in the sample divided by the
measurements, the ratio of the measured intensity of an ion
sample size minus one
beam at a mass m, to the measured intensity from the same
isotope measured at one mass unit difference (for example, m
3.3.21 SE—Standard Error; according to Practice E2586,
6 1).
3.1.29, standard deviation of the population of values of a
3.2.1.1 Discussion—Abundance sensitivity is a measure of sample statistic (that is, the mean value) in repeated
the magnitude of the peak tailing correction. For measuring measurements, or an estimate of it.
uranium on thermal ionization mass spectrometer (TIMS) and
3.3.21.1 Discussion—According to Practice E2586, 3.1.30,
inductively coupled plasma mass spectrometry (ICP-MS)
if the standard error (SE, see above) of a statistic is estimated,
instruments,theabundancesensitivityistypicallycalculatedas
it will itself be a statistic with some variance that depends on
the ratio of the measured signal intensities at masses 237 and
the sample size, that is, the number of observed values in the
238 using a suitable uranium sample.
sample (Practice E2586, 3.1.26).
3.3.21.2 Discussion—According to Guide E2655, 5.8.4.1,
3.2.2 dark noise, n—observed count rate on an ion counting
fromstatisticaltheory,a95%confidenceintervalforthemean
detector measured without incident ion beam
of a normal distribution, given n independent observations x ,
3.2.3 total evaporation, TE, n—analytical method for deter-
x , ., x drawn from the distribution is, x 6 t×SD/ √ n,
2 n mean
mination of isotope amount ratios of uranium or plutonium, as
where x is the sample mean, SD is the standard deviation
mean
described in Test Method C1672, also called “classical” total
oftheobservations(seeabove),and tisthe0.975percentileof
evaporation in this test method.
the Student’s t distribution with n-1 degrees of freedom.
3.2.4 turret, n—holder for sample filaments.
Because Student’s t distribution approaches the Normal as n
3.2.4.1 Discussion—Alternate names for turret are carousel,
increases,thevalueof tapproaches1.96as nincreases.Thisis
magazine, wheel. the basis for using the (coverage) factor 2 for expanded
uncertainty. The standard error (SE) of the mean value of a
3.3 Acronyms and Abbreviations:
series of n independent repeated measurements can be derived
3.3.1 cpm—counts per minute
from that by using t = 1, so the standard error (SE) is given by
3.3.2 cps—counts per second
SD/√n.
3.3.3 CRM—Certified Reference Material
3.3.22 SEM—Secondary Electron Multiplier
3.3.4 DS—Double Spike 3.3.22.1 Discussion—Inthescientificliteraturetheacronym
SEM is also used for Scanning Electron Microscope, but
3.3.5 DU—Depleted Uranium
within this document SEM represents Secondary Electron
3.3.6 FAR—Faraday Cup
Multiplier.
3.3.7 HEU—High Enriched Uranium
3.3.23 SGAS—Safeguards Analytical Services Laboratory
3.3.8 IAEA—International Atomic Energy Agency of the IAEA
C1832−23
3.3.24 TIMS—thermal ionization mass spectrometry controlfeaturethroughmanipulationofthetargetsumintensity
depending on the actual measurement conditions.
4. Summary of Test Method
4.2 The sample amount to be loaded for MTE analyses is
4.1 The modified total evaporation method has been devel-
limited to a range of about 2µg to 6 µg to achieve ion beam
opedonthebasisofthe“classical”totalevaporationtechnique
signals of about 20V to 30V for the major isotope ( U for
(1-4), alsodescribedinTestMethodC1672.Byusingthetotal
DU, NU, and LEU samples and U for HEU samples)
evaporation technique, the mass fractionation is minimized by
corresponding to a U intensity of 1mV to 10 mV. This
evaporating the entire sample amount loaded on the filament,
causes the U ion beam to be suitable for an internal cross
incontrasttothe“conventional”techniqueasdescribedinTest
calibration of the SEM versus the Faraday cups through the
236 238
Method C1625. The MTE method has already been described
entire measurement time. This also allows the U/ U
in detail in Refs (5) and (6). If necessary, uranium is separated
isotope amount ratio to be measured in a wide dynamic range
-2 -10
from plutonium and other elements (to eliminate isobaric
from 10 down to 10 using a Faraday cup or an SEM in
interferences) by selective extraction, anion exchange (see
combination with an energy filter for improved abundance
234 238
Practice C1411), or extraction chromatography. The purified
sensitivity. For all samples with minor ratios U/ U and
236 238 -5
uranium fraction as nitrate solution is loaded onto a degassed
U/ U higher than3×10 , which also includes HEU
filament (made of metals such as rhenium, zone-refined
samples, the minor isotopes are only measured using Faraday
12 13
rhenium, or tungsten) with high evaporation temperature and
cups, with amplifier resistors of 10 Ω or 10 Ω yielding a
converted to an oxide by controlled heating of the filament
favorable signal-to-noise ratio.
under atmospheric conditions. For the MTE method, the
4.3 Similar to the TE analysis, the isotope ion beams of the
uranium load is in the range of about 2µg to 6 µg, which is
235 238
major isotopes U and U are integrated over the course of
aboutonetotwoordersofmagnitudehigherthanthattypically
the analysis, and the summed intensity for U is divided by
usedforthe“classical”totalevaporationmethodbyTIMS.The
the summed intensity for U to yield the major isotope
sample filament is mounted on the sample turret using a
amount ratio. The result of the major isotope amount ratio is
double-filament configuration. This configuration consists of
corrected for mass fractionation using the measurement of a
an evaporation filament (Re or W) on which the sample is
CRM analyzed on the same sample turret.
loaded, and an ionization filament (Re filament with no
4.4 The minor isotope amount ratios are corrected for mass
sample). For a measurement in the mass spectrometer, the
fractionation for each integration step individually. This is
ionizationfilamentisheatedtoatemperatureofabout1700°C
accomplishedinaninternalmanner;themagnitudeofthemass
to 1900 °C, sufficient to generate Re ion beam signals of
fractionation for the minor ratios is calculated from the
150mV to 400 mV (corresponding to ion currents of 1.5 ×
-12 -12 11
measured mass fractionation of the major ratio. The peak
10 Ato4×10 A using an amplifier resistor of 10 Ω).
tailing contributions are determined at two positions, slightly
The intensity of the optimized Re signal depends on the Re
below and slightly above the isotope masses of interest. If
material (zone-refined or non-zone-refined), thickness and the
applicable, the SEM-versus-Faraday calibration is also per-
measurement conditions, but it is expected to be similar for all
formed for each integration step individually.
filaments on the same sample turret. The Re ion current is
also used for the initial ion beam focusing. The evaporation
5. Significance and Use
filament is heated next. After ion beam re-focusing and mass
re-adjustment initially using a small sum intensity (sum of
5.1 Uranium material is used as a fuel in certain types of
234 235 236 238
U, U, U, and U) of about 1V to 4V, the data
nuclear reactors. To be suitable for use as nuclear fuel, the
acquisition begins usually under computer control to yield a
starting material shall meet certain specifications such as those
predefinedtargetsumintensityof20Vto30V(corresponding
described in Specifications C753, C776, C787, C833, C967,
-10 -10
to ion currents of 2 × 10 Ato3×10 Ausing an amplifier
C996,andC1008,orasspecifiedbythepurchaser.Theisotope
resistorof10 Ω).Thistargetvaluedependsontheamountof
amount ratios of uranium material can be measured by mass
uranium loaded on a filament. The MTE analysis takes
spectrometry following this test method to ensure that they
between2and5hpersamplefilamentandisaboutthreetoten
meet the specification.
times longer than (“classical”) TE analyses in spite of the
5.2 The MTE method can be used for a wide range of
higher intensities at which the analyses are performed. To
sample sizes even in samples containing as low as 20 µg of
ensure that the whole sample is completely evaporated and
uranium. If the uranium sample is in the form of uranium
analyzed before the ionization filament breaks as a result of
hexafluoride, it has to be converted into a uranium nitrate
overheating, the MTE analysis routine is programmed to
solution for measurement by the MTE method. The concen-
increase the target sum intensity during the course of the
tration of the loading solution for MTE has to be in the range
analysis if necessary. The occurrences of outliers due to
of 1 mg/g to 6 mg/g to allow a sample loading of 2µg to 6 µg
technical glitches, for example, as a result of termination
of uranium.Aminimum loading of 3 µg uranium per filament
beforecompletesampleevaporationorbecauseofearlysample
is strongly recommended. This is needed to have a sufficient
exhaustion, are minimized by a dynamic target intensity
and stable ion signal especially for the two minor isotopes
234 236
( U and U) thus enabling the internal calibration of SEM
versus the Faraday cups using the U ion beam signal during
The boldface numbers in parentheses refer to a list of references at the end of
this standard. the measurement.
C1832−23
5.3 Until now, the instrument capabilities for the MTE 7.1.3 Amultiple Faraday collector system to allow simulta-
+
method have only been implemented on theTRITON™TIMS neousdetectionofisotopebeamsfrom m/z=233to238forU
instrument. Therefore, all recommendations for measurement ions.
parameters in this test method are specified for the TRITON 7.1.4 For the Faraday cups used to measure the major ion
235 238
instrument. The manufacturers of other TIMS instruments (for beams of U and U, there shall be current amplifiers
example, IsotopX and Nu Instruments) have indicated plans to equippedwith10 Ωresistorsand,fortheminorionbeamsof
234 236
implementthemodificationsneededintheirinstrumentstouse U and U, there shall be current amplifiers equipped with
11 12 13
the MTE method. atleast10 Ω,andpreferably10 Ω(oreven10 Ω)resistors
to improve the signal-to-noise ratio.
5.4 The MTE method described here can also be extended
7.1.5 The detection system shall include at least one sec-
to measurement of elements other than uranium. Note that the
ondary electron multiplier (SEM) operated in ion counting
MTEmethodhasalreadybeenimplementedforplutoniumand
mode or a Daly detector, or similar detector, with a dark noise
calcium.
<0.2 cps. The SEM shall be equipped with an energy filter to
improve the abundance sensitivity, which shall be better than
6. Interferences
-8 238 +
2×10 at mass 237 for ions from U with the energy filter
6.1 Isobaric nuclides such as Pu interfere in the uranium
in operation.
measurements. The removal of interferences is generally ac-
7.1.6 A sample turret with at least ten filament positions to
complished by chemical separation leading to ionization of
allow automatic measurement sequences of at least five repli-
uranium only and improved precision of measured isotope
cate filament loadings per sample and at least five replicate
amount ratios.
filament loadings for a calibration standard (preferentially a
6.2 It has to be ensured that samples are not contaminated
CRM).
by environmental uranium. The level of effort required to
7.1.7 A pumping system that is able to attain a vacuum of
-5 -7
minimize contamination shall be based upon the sample size
<4.0 × 10 Pa (3 × 10 torr) in the ion source, the analyzer,
and the levels of contamination present in the analytical
and the detector is required. Tailing corrections are dependent
facility. For extremely small samples or extremely low U
on the vacuum levels inside the mass spectrometer. Analyzer
-7 -9
abundances, residual uranium from chemicals used for sample
pressures below 7.0 × 10 Pa (5 × 10 torr) are preferred.
dissolution and sample preparation are possible sources for
7.1.8 Amechanism to scan masses by varying the magnetic
bias in the isotopic data.
field or the accelerating voltage, or both.
7.1.9 An optical pyrometer for determining the tempera-
6.3 Samples shall be chemically purified to assure reliable
tures of the filaments.
analyses by TIMS. Impurities, especially alkali elements,
7.1.10 A computer for control of the data acquisition ac-
produce unstable ion emission leading to poor precision in the
cording to a predefined sequence.
isotopeamountratios.Organiccontaminantsoroxidelayerson
the filaments also adversely influence TIMS analyses. Isobaric
7.2 Special MTE Capabilities—Themassspectrometersoft-
interferences, if not removed, will bias the isotope amount
ware must be flexible enough to implement a user-defined
ratios.Contaminantsinreagents,labware,orfilamentmaterial
filament-heating program for MTE.
are also sources for bias in the isotope amount ratios.
7.3 Aseparate filament degassing device for cleaning of the
6.4 The performance of the instrument can be adversely
filaments before sample loading is recommended.
affected by changes in the environmental conditions of the
7.4 Microsyringe or Micropipette—Syringe to transfer mi-
laboratory, that is, temperature and humidity. For this reason,
crolitre volumes of solutions.
controlled laboratory environmental conditions should be
maintained (within the manufacturer’s specifications) during
8. Reagents and Materials
instrument operation.
8.1 Purity of Reagents—Reagent-grade chemicals shall be
7. Apparatus used in all sample preparations. Unless otherwise indicated, it
isintendedthatallreagentsconformtothespecificationsofthe
7.1 Thesuitabilityofthemassspectrometerforcarryingout
Committee onAnalytical Reagents of theAmerican Chemical
measurements by the MTE method shall be evaluated by
Society where such specifications are available. Other grades
means of performance tests. The relevant instrument charac-
may be used, provided it is first ascertained that the reagent is
teristics are as follows:
7.1.1 Athermal ionization source for using double filament
assemblies with rhenium or tungsten filaments, or both.
The sole source of supply of the apparatus known to the committee at this time
7.1.2 A mass analyzer sufficient to resolve adjacent masses
is Thermo Fisher Scientific Inc., 81 Wyman St., Waltham, MA 02451. If you are
inthemass-to-chargerangebeingstudied, m/z=233to238for aware of alternative suppliers, please provide this information to ASTM Interna-
+
tional Headquarters.Your comments will receive careful consideration at a meeting
U . Resolution shall be greater than 350 (full width at 1% of
of the responsible technical committee, which you may attend.
peakheight)andtheabundancesensitivityatmass237forions
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
238 -6
of U less than5×10 .
Standard-Grade Reference Materials, American Chemical Society, Washington,
DC. For suggestions on the testing of reagents not listed by theAmerican Chemical
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
TheTRITON™(Plus)MulticollectorThermalIonizationMassSpectrometeris U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
a trademark product of Thermo Fisher Scientific, http://www.thermoscientific.com. copeial Convention, Inc. (USPC), Rockville, MD.
C1832−23
of sufficiently high purity and low uranium concentration to 10.2 Uraniumsamplestobemeasuredandisotopereference
permit its use without lessening the accuracy of the MTE materials used for estimation of the mass fractionation correc-
measurements. tionfactor(K-factor)orforqualitycontrolpurposesshallbein
the same medium and in the same oxidation state. The
8.2 Ultra-high purity reagents are necessary for processing
solutions for loading onto the filaments are 1 M nitric acid
smallsampleamountsorsampleswithextremelysmallisotope
solutions. The uranium concentrations of these solutions shall
amount ratios. The level of uranium contamination from
be similar. The loading and drying sequence of the filaments
chemicals, water, and the sample handling environments shall
shall also be similar.
bedeterminedtoensurethatthematerialsandtheenvironment
are sufficiently pure for the samples being analyzed. 10.3 Inthecaseofcharacterizationstudiesoftestmaterials,
possible inhomogeneity between test units shall be evaluated
8.3 Nitric Acid (HNO , 15.8 M)—Concentrated nitric acid.
statistically and included in the uncertainty calculations of the
8.4 Nitric Acid (HNO,1M)—One volume of concentrated
isotope amount ratios assigned.
nitric acid (HNO , 15.8 M) brought to 15.8 volumes with
water.
11. Preparation of Apparatus
8.5 Purity of Water—Unless otherwise indicated, references
11.1 Filament Degassing—Degass all filaments before us-
to water shall be understood to mean laboratory accepted
ing them for MTE measurements. It is recommended to use a
demineralized or deionized water as described by Type I of
separate apparatus (see 7.3) for performing this. Start the
-4
Specification D1193.
degassingprocedurewhenavacuumpressureof<4.0×10 Pa
-6
(3×10 torr) is reached. Recommended filament currents for
8.6 Filaments—High-purity filaments, for example, zone
degassing are in the range of 4.0Ato 5.0A, corresponding to
refined Re, are required. The size and configuration of the
temperatures in the range of 1700°C to 2000°C. Perform the
filamentisinstrumentdependent.Tungstenmightbeusedwith
degassing for a duration of at least 30 min.
minormodificationstotheheatingscript.Allfilamentsmustbe
degassedbeforeuse.Formeasurementofuraniumpresentonly
11.2 “Initialization” of Sample Turret—Adjust, if needed,
at the trace levels in the sample, contamination of the samples the position of the sample turret in the ion source and verify
by interferences from elemental or molecular species within
proper electrical connections for both the evaporation and
the m/z=233to238rangeneedtobedeterminedtoensurethat ionizationfilamentforeachsampleloadingposition.Itshallbe
biases due to contributions from the filament material will not
ensured that the electrical contact is not interrupted in case the
bias the analysis results. In case a significant count rate >1 cps turret is slightly moved for the purpose of ion beam focusing.
is determined at m/z = 236, a correction has to be applied for
11.3 Amplifier Signal Decay Adjustment—Adjust the signal
236 238 -6
U/ U ratios < 10 (6, 7).
decay characteristics of the current amplifiers of the Faraday
cups. This is important for measuring isotope amount ratios
9. Hazards
with a large dynamic range, especially for the minor isotope
9.1 TIMS instruments operate at 8 to 10 kV electrical
amount ratios of uranium. Depending on the combination of
potential. Ensure that the high-voltage is switched off before
the capacitance and resistance of the current amplifier, the
insertion or removal of the sample turret into/from the
responsetimeforasuddenchangeintheionbeamsignaltothe
instrument,andworkingwiththeionsource,oraccessingother
Faradaycupcanreachupto5s.Forresistanceshigherthanthe
electronic components. 11 12 13
10 Ω, for example, 10 Ω, and in particular 10 Ω, longer
9.2 The filaments reach temperatures in excess of 2000°C. response times of about 15 s can be expected. The MTE
The filament holders, sample wheel, and ion source parts are
method is designed by taking into consideration the required
expected to be hot. Ensure that a sufficient time has lapsed response times. The amplifier response can be checked either
since the last filament heating before accessing the filaments, using a custom-made software module within the operating
sample turrets, and ion source. software (when available) or “manually” by means of a large
ion beam that is abruptly directed into a Faraday cup to check
9.3 Wear eye protection and suitable gloves when filling
the signal ingrowth time, or away from a Faraday cup (for
coldtrapswithliquidnitrogen.Protecthands,torso,andfeetin
example, by closing a valve between ion source and analyzer)
the event of splashing or spilling of the liquid nitrogen.
to check the signal decay time.
9.4 Handle radioactive materials with appropriate attention
11.4 SEM Plateau Voltage—The SEM plateau voltage, that
to radiological safety.
is,thedependencyofthecountrateontheappliedhighvoltage
10. Sampling, Test Specimens, and Test Units to the SEM, shall be measured on a regular basis, as recom-
mended by the manufacturer of the SEM or the operator’s
10.1 Isotope Reference Materials—Uranium reference ma-
quality system. Typical SEM plateau voltages range between
terials used in the analysis should be prepared from certified
1700V to 3000 V. The SEM plateau voltage drifts to higher
reference materials (CRMs) traceable to SI units. Examples
values with use and shall be readjusted to restore the original
include the NBL U-Series CRMs (for example, U010 and
efficiency. The efficiency should be higher than 90%.
U500), IRMM uranium standards IRMM 184-187, IRMM
019-029 (to be converted from UF ), IRMM-074, IRMM-075, 11.5 SEM Dark Noise—SEM detectors are usually operated
and IRMM-3100. See Guide C1128 for additional guidance on inioncountingratherthananaloguemodetoavoidtheresistor
preparation of traceable working reference materials. noiseofthecurrentamplifier.Theioncountingmoderesultsin
C1832−23
much smaller uncertainties encountered for measurements of normally performed by sequentially applying a stable calibra-
-19 -16
very low intensity ion beams (10 Ato10 A, equivalent to tion current to the input of each Faraday cup amplifier and the
0.6cps to 600 cps). However, the dark noise, that is, the output is then normalized to a reference value to generate a
observed count rate measured without incident ion beam, shall gain calibration factor for each amplifier. A gain calibration
bemeasuredbeforeanautomatedMTEmeasurementsequence shall be performed prior to each automatic MTE sequence.
to enable corrections to the isotope amount ratios and their Historical gain calibration data can be used to evaluate the
uncertainties (7). The dark noise shall be below 0.5 cps. stability of the amplifiers.
11.6 Ion Source and Analyzer Pressure—It is important to 12.5 Faraday Cup Effıciency Test—The response of indi-
achieve a certain level of vacuum before the isotope amount vidual Faraday cups depends on several factors, for example,
ratio measurements can begin. See 7.1.7 for the recommended extent of usage, manufacturing variability, and can also be
pressure. The peak tailing depends strongly on the vacuum affected by an insufficient electron suppression voltage. The
pressure in the detector system since the number of ion relative response of the Faraday cups, therefore, shall be
collisionswithgasmoleculesinsidethemassspectrometerisa determined periodically. Usually, the Faraday cups of a multi-
directfunctionoftheambientpressure.Increaseinthepressure collector system are only intercalibrated for the current ampli-
within the ion source caused by the heating of the ionization fiersconnectedtothem(see12.4)butnotforthedifferencesin
and evaporation filaments can be subdued, to a certain extent,
the efficiencies of the Faraday cups themselves. The efficien-
by using a cold trap filled with liquid nitrogen. cies of the Faraday cups are expected to be similar to each
other,whichmeansthattherelativeefficiencies(relativetoone
12. Calibration and Standardization
reference cup) are normally close to unity. Note that an
NOTE 1—The measurement method may be qualified following Guide
(electronic) amplifier gain calibration (see 12.4) shall be
C1068 and calibrated following Guide C1156. Additional information
performedpriortotheFaradaycupefficiencytest.TheFaraday
regarding mass spectrometer calibrations with regard to the MTE method
cup efficiency test can be performed in several ways, as
may be found in Refs (5, 6).
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
known atomic masses and the magnetic field necessary to
stable ion beam of Re (from a blank filament) between each
direct the isotope beams into the detectors shall be updated on
Faraday cup and a reference Faraday cup. In case a relative
aregularbasis.Masscalibrationshallbeperformedatintervals
efficiency between the detectors is significantly different from
specified by the manufacturer or the user’s quality assurance
unity, this result can be used to correct for differences in the
program.
detector response. This procedure can be performed with a
12.2 Peak Centering—Thepeakcenteringroutineisusedas
relative uncertainty at the level of <0.1%.
afineadjustmenttoensurethattheionbeamiscenteredwithin
12.5.2 Aseries of peak-jumping measurements between all
the detector. Peak centering usually occurs by means of fine
Faraday cups and a reference cup to be checked can also be
adjustments of the accelerating voltage, and any difference
performed using a sufficiently large uranium sample and one
between the value optimized during peak centering from the
largestableionbeam,forexample,a10Vto20Vionbeamof
defaultacceleratingvoltagerequiresareadjustmentofthemass
U from an LEU or natural uranium sample. The drift of the
calibrationcurve.Peakcenteringshallbeperformedforatleast
signal intensity shall be corrected for using the operating
three uranium masses as part of the mass calibration and also
software. This procedure can be performed with a relative
before the start of each MTE measurement sequence. During
uncertainty at the level of <0.01%.
the MTE measurement, peak centering is performed on a
12.5.3 A series of comparative neodymium (Nd) isotope
regular basis.
amount ratio measurements can be performed in two different
modes such as the multi-dynamic mode and the static mode
12.3 Amplifier Baseline Calibration—The baselines of the
Faraday cup amplifiers, that is, the amplifier responses without with “amplifier rotation” (only for TRITON TIMS, also called
“virtual amplifier”: each Faraday cup is connected to each
incoming ion beam to the cup, shall be measured on a regular
basisandcheckedforstability.DuringtheMTEmeasurements, amplifier for regular time intervals during the measurement).
This procedure can be performed with a relative uncertainty at
baseline measurements are performed on a regular basis. Note
that the integration time for the baseline measurement has a the level of few ppm (5). It shall be repeated until all Faraday
cups of interest for MTE measurements have been included.
significant influence on the uncertainty of Faraday cup
measurements, particularly at lower ion beam intensities. 12.5.4 A series of static measurements can be performed
Therefore, the integration time of the baseline (within a using special “multi-isotope” reference materials, such as
233 235 236 238
measurement) shall be comparable to the integration time of IRMM-3100a ( U/ U/ U/ U = 1/1/1/1) (8), IRMM-
233 235 238
072/1, IRMM-074/1, or IRMM-199 ( U/ U/ U = 1/1/1)
theactualionbeamsignalintegration.Thelong-termhistorical
baseline data shall be regularly reviewed by the user to assure (9), to include all Faraday cups. This procedure can be
performed with relative uncertainties of about 0.03%.
that the system performance is within manufacturer specifica-
tions and quality system requirements.
12.6 Linearity Test—There are various procedures to check
12.4 Amplifier Gain Calibration—The stability and re- the linearity of an isotope mass spectrometer detection system.
sponse of individual Faraday detector amplifiers shall be The procedures described in 12.6.1 and 12.6.2 are mainly
measured and differences between amplifiers corrected by applicable for Faraday multi-collector systems (for SEM cali-
means of the amplifier gain calibration. Gain calibration is bration and linearity, see 12.8 and 12.9).
C1832−23
12.6.1 The linearity of the mass spectrometer is determined only source of nonlinearity of a SEM system, the value can be
over the working range of the Faraday cups by measuring the determined in various ways (9) using CRMs, as described in
235 238
12.8.1 and 12.8.2.
U/ U ratios of various reference materials under identical
12.8.1 Forthisprocedure,theIRMM-072/8orIRMM-074/3
conditions. The mass spectrometer system is linear if the
238 235
235 238
(9) reference materials, characterized by a U/ U ratio of
K-factor, that is, the ratio of the certified U/ U ratio to the
233 235
235 238
≈1 and a U/ U ratio of ≈0.01, or the NBL CRM U500,
measured U/ U ratio, is independent of the isotopic
238 235 234 235
characterized by a U/ U ratio of ≈1 and a U/ U ratio
composition of the material. For this procedure, the NBL
of ≈0.01 (using new data published in Ref (5)), can be used.
U-seriesofreferencematerials(U005atoU970,0.5%to97%
Peak-jumping measurements are performed for count rates
of U)isidealandcanbecombinedwiththeIRMM-183-187
4 5 235 238
between5×10 cpsand5×10 cpsfor U(similarfor U).
series (0.3% to 5% of U) and the IRMM 019-029 (0.17%
233 235 234 235
235 The U/ U ratios ( U/ U in case of NBL CRM U500)
to5%of U.Thisprocedureshallbeperformedsequentially
238 235
are internally normalized using the U/ U ratios of >1 and
for all Faraday cups of the multi-collector system needed for
plotted versus the U count rate. If the data show a linear
the MTE analyses.
relationship with no significant intercept, a linear regression is
12.6.2 The IRMM-072 and IRMM-074 series of reference
calculated with the intercept being zero. The slope of the
238 235
materials are characterized by U/ U ratios of ≈1 and
regression line can be used to calculate the dead time using:
233 235 -6
U/ U ratios ranging from ≈1 down to ≈10 for the 15 or
U
10units,respectively,oftheusedseries.Foreachunit,thebias
τ 5 $slope% ⁄ 1 2 (1)
S S D D
238 235
U
ofthemeasured U/ Uratiosfromthecertifiedonescanbe CERT
used for internal mass fractionation correction of the measured
where:
233 235 233 235
U/ U ratios. The comparison of the corrected U/ U
τ = dead time,
ratios with the certified ones allows the linearity of the
slope = slope of linear regression calculation
233 235
detection system to be checked over a dynamic range of six
based on measured U/ U ratios ver-
orders of magnitude for the ion beam intensity. A detailed
sus the U count rate, and
233 235
descriptionoftheprocedureisgiveninRef (9).Thisprocedure
( U/ U) = certified isotope amount ratio of used
CERT
shallbeperformedsequentiallyforallFaradaycupsneededfor
CRM.
the MTE analyses.
In case NBLCRM U500 is used instead of IRMM-072/8 or
233 235
IRMM-074/3, the ( U/ U) in Eq 1 has to be replaced
12.7 Peak Overlap—When a Faraday multi-collector sys- CERT
234 235
by ( U/ U) .
temforthesimultaneousdetectionofseveralmassesisused,it CERT
12.8.1.1 Incasethedatadonotindicatealinearrelationship
needstobeensuredthatthepeakoverlapisacceptable.Amass
with a non-significant intercept, the SEM detection system is
scan, usually by scanning the magnetic field, shall be per-
likely to be affected by other sources of nonlinearity, which
formed by which all ion beams are simultaneously moved
shall be investigated.
through the respective cups. The measured intensities for all
12.8.2 For an “external check” of the linearity of the SEM
detectors shall be plotted versus the mass of a reference
detection system, a series of reference materials can be
detector to make the peak overlap visible.All peaks shall have
measured by MTE, for example, the NBL U-series (5), the
a symmetric shape with a common flat region in the center,
IRMM-183-187 series, the IRMM-019-029 series, or the
withthepeakcentersreasonablyclosetogether,asspecifiedby
gravimetrically prepared IRMM-075 series (6, 10) with U/
themanufacturerortheuserqualitysystem.Afterasatisfactory
238 -4 -5 -6 -7 -8 -9
U rations of 10 ,10 ,10 ,10 ,10 , and 10 .
peak overlap is realized (by moving cups relative to one
another if necessary), the positions of all detectors shall be 12.9 SEM Versus Faraday Cup Inter-calibration—Sincethe
inter-calibration between a SEM detector with a Faraday cup
saved, for example, as a Faraday cup configuration file. The
positionsshallbecheckedandpossiblyreadjusted,manuallyor depends on the ion source focusing and ion beam shape, this
calibrationshallbeperformedinaninternalmannerduringthe
using stepping motors, as needed before a new automatic
course of each measurement for MTE measurements. For this
measurement sequence.
internal calibration, the ion beam of one of the uranium
12.8 SEM Linearity Check and Correction—Thelinearityof
isotopes present in the sample is switched between the SEM
SEM systems shall be checked carefully on a regular basis
and one Faraday cup within each integration step during the
accordingtomanufacturer’sspecificationsortheuser’squality
entire measurement. To allow such an internal calibration,
assurance program. It is emphasized that there can be more
there shall be at least one suitable ion beam available for this
than one reason for nonlinearity of a SEM detector. For SEM
purpose. This ion beam shall be within a certain intensity
detectors operated in ion counting mode, the dead time of the
range, between the lower limit of reasonable Faraday cup
pulse-counting electronic system is always one source of
measurements (typically 1 mV on an amplifier with 10 Ω,
nonlinearity, but this can be easily corrected.As pointed out in
which is affected by about the same noise as 0.5 mV on an
Ref (9), there is also the possibility of an intrinsic nonlinearity
amplifier with 10 Ω) and the upper limit for reasonable SEM
forSEMdetectors,possiblydependingonthedesignoftheion
measurements(typically1.0×10 cps,equivalentto16mVon
optics, the dynode surfaces, or the electronics, which could
an amplifier with 10 Ω). The isotope used for the internal
causethelinearityinvestigationandcorrectiontobecomemore
calibration within MTE measurements is for most samples
234 236
complicated. But in case the dead time is confirmed to be the U, in few cases U instead.As a consequence, the sample
C1832−23
amount to be loaded is limited to a certain range as well. For 12.10 Mass Fractionation Correction:
typical TIMS conditions, the sample amount for MTE mea- 12.10.1 Intheory,the“classical”totalevaporation(TE)and,
surements is about 2 to 6 µg, which provides ion beam signals
therefore, also the MTE methods are expected to yield isotope
of about 20V to 30 V for the sum of the main isotopes U amount ratios that do not need correction for mass fraction-
and U. The choice of the isotope used for the inter-
ation. In practice, measurable mass fractionation for uranium
calibration depends on the isotopic composition of the sample measurements has been observed. To be consistent in the
(based on process knowledge or sample supplier information, evaluation of the data and the associated uncertainties, it is
or estimated by a mass scan in the m/z=233 to 238 mass recommended to perform a mass fractionation correction also
range), in the following way: formeasurementsequencesinwhichtheratiosseemtobemass
12.9.1 Mainly for DU, NU, and LEU samples with U/ fractionation free, that is, where the K-factor (see 12.10.2)is
238 -5 -4 236 238
U ratios between3×10 and5×10 and with U/ U equaltounitywithinitsuncertainty.ForMTEmeasurementsit
-5 234
ratiosbelow3×10 ,the Uionbeamisusedfortheinternal is recommended to perform the mass fractionation correction
calibration. bymeasuringacertifiedisotopereferencematerialinsequence
12.9.2 Mainly for DU (in principle also in case of NU and with the samples, and calculate a mass fractionation correction
234 238 -5
LEU) samples with U/ U ratios below3×10 and with factor based upon the deviation of the measured major ratio
236 238 -5 236
U/ Uratioshigherthan3×10 ,the Uionbeamisused
from the certified ratio. The mass fractionation correction
for the internal calibration (also called “reverse” MTE, (6)). factor, adjusted for isotope mass difference, is then applied to
Due to the availability and frequent use of amplifiers with
all measured sample ratios. It is important that the reference
12 13
resistors of 10 Ω and 10 Ω, this “reverse” MTE procedure materialsarepreparedandmeasuredinthesamemannerasthe
235 238
has become obsolete and is therefore not described in this
samples. For the MTE method, the major ratio U/ Uis
revision any more. used to calculate a correction factor, known as the K-factor,
234 238
12.9.3 In the rare case that both the U/ U and the
which is then applied also for performing corrections for the
236 238 -5 234 234 238 236 238
U/ U ratios are below3×10 , the larger one of U and minorratios U/ Uand U/ Uinternally(fordetailssee
U shall be used. This might only apply to quite highly
Section 14).
235 238
enriched Uor U materials, for example, for spike 12.10.2 The mass fractionation correction factor, K,is
materials. In this case, an internal calibration using a suitable
calculated as follows:
ion beam from an added U spike (11) is another option,
K 5 R ⁄ R (2)
~ !
c m
which would require isobaric corrections because of the
234 236 233
where:
possible U and U contents of the U spike.As another
option, if amplifiers with a resistor of 10 Ω are available for
K = mass fractionation correction factor,
234 236 234 238
R = average measured isotope amount ratio for the CRM,
measuring U and U, a MTE measurement of U/ U
m
236 238 -5 -5
and U/ U ratios between1×10 and3×10 using only and
R = certified isotope amount ratio value for the CRM.
Faraday cups is recommended over using the SEM.
c
12.9.4 Forallsamples,thatis,DU,NU,LEU,orHEU,with
12.10.3 To correct individual measured isotope amount
234 238 236 238
any values for the U/ U and U/ U ratios, an MTE
ratios, calculate the appropriate mass fractionation correction
measurement can always be performed using Faraday cup
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C1832 − 22 C1832 − 23
Standard Test Method for
Determination of Uranium Isotopic Composition by Modified
Total Evaporation (MTE) Method Using Thermal Ionization
Mass Spectrometer
This standard is issued under the fixed designation C1832; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method describes the determination of the isotope amount ratios of uranium material as nitrate solutions by the
modified total evaporation (MTE) method using a thermal ionization mass spectrometer (TIMS) instrument.
235 238
1.2 The analytical performance in the determination of the U/ U major isotope amount ratio by MTE is similar to the
(“classical”) total evaporation (TE) method as described in C1672. However, in the MTE method, the evaporation process is
interrupted on a regular basis to allow measurements and subsequent corrections for background from peak tailing, perform
internal calibration of a secondary electron multiplier (SEM) detector versus the Faraday cups, peak centering, and ion source
refocusing. Performing these calibrations and corrections on a regular basis during the measurement, improves precision, and
234 238 236 238
significantly reduces uncertainties for the minor isotope amount ratios U/ U and U/ U as compared to the TE method.
1.3 In principle, the MTE method may yield major isotope amount ratios without the need for mass fractionation correction.
However, depending on the measurement conditions, small variations are observed between sample turrets. Therefore, a small
correction based on measurements of a certified reference material is recommended to improve consistency. The uncertainty
around the mass fractionation correction factor usually includes unity.
1.4 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided
for information only and are not considered standard.
1.5 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
C753 Specification for Nuclear-Grade, Sinterable Uranium Dioxide Powder
This test method is under the jurisdiction of ASTM Committee C26 on Nuclear Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of Test.
Current edition approved Feb. 1, 2022Jan. 1, 2023. Published March 2022January 2023. Originally approved in 2016. Last previous edition approved in 20212022 as
C1832 – 21.C1832 – 22. DOI: 10.1520/C1832-22.10.1520/C1832-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1832 − 23
C776 Specification for Sintered Uranium Dioxide Pellets for Light Water Reactors
C787 Specification for Uranium Hexafluoride for Enrichment
C833 Specification for Sintered (Uranium-Plutonium) Dioxide Pellets for Light Water Reactors
C859 Terminology Relating to Nuclear Materials
C967 Specification for Uranium Ore Concentrate
C996 Specification for Uranium Hexafluoride Enriched to Less Than 5 % U
C1008 Specification for Sintered (Uranium-Plutonium) DioxidePellets—Fast Reactor Fuel (Withdrawn 2014)
C1068 Guide for Qualification of Measurement Methods by a Laboratory Within the Nuclear Industry
C1128 Guide for Preparation of Working Reference Materials for Use in Analysis of Nuclear Fuel Cycle Materials
C1156 Guide for Establishing Calibration for a Measurement Method Used to Analyze Nuclear Fuel Cycle Materials
C1347 Practice for Preparation and Dissolution of Uranium Materials for Analysis
C1411 Practice for The Ion Exchange Separation of Uranium and Plutonium Prior to Isotopic Analysis
C1625 Test Method for Uranium and Plutonium Concentrations and Isotopic Abundances by Thermal Ionization Mass
Spectrometry
C1672 Test Method for Determination of Uranium or Plutonium Isotopic Composition or Concentration by the Total
Evaporation Method Using a Thermal Ionization Mass Spectrometer
C1871 Test Method for Determination of Uranium Isotopic Composition by the Double Spike Method Using a Thermal
Ionization Mass Spectrometer
D1193 Specification for Reagent Water
E2586 Practice for Calculating and Using Basic Statistics
E2655 Guide for Reporting Uncertainty of Test Results and Use of the Term Measurement Uncertainty in ASTM Test Methods
3. Terminology
3.1 Terminology C859 contains terms, definitions, descriptions of terms, nomenclature, and explanations of acronyms and
symbols specifically associated with standards under the jurisdiction of Committee C26 on Nuclear Fuel Cycle.
3.2 Definitions:
3.2.1 abundance sensitivity, n—in isotope amount ratio measurements, the ratio of the measured intensity of an ion beam at a mass
m, to the measured intensity from the same isotope measured at one mass unit difference (for example, m 6 1).
3.2.1.1 Discussion—
Abundance sensitivity is a measure of the magnitude of the peak tailing correction. For measuring uranium on thermal ionization
mass spectrometer (TIMS) and inductively coupled plasma mass spectrometry (ICP-MS) instruments, the abundance sensitivity
is typically calculated as the ratio of the measured signal intensities at masses 237 and 238 using a suitable uranium sample.
3.2.2 dark noise, n—observed count rate on an ion counting detector measured without incident ion beam
3.2.3 total evaporation, TE, n—analytical method for determination of isotope amount ratios of uranium or plutonium, as
described in Test Method C1672, also called “classical” total evaporation in this test method.
3.2.4 turret, n—holder for sample filaments.
3.2.4.1 Discussion—
Alternate names for turret are carousel, magazine, wheel.
3.3 Acronyms and Abbreviations:
3.3.1 cpm—counts per minute
3.3.2 cps—counts per second
3.3.3 CRM—Certified Reference Material
3.3.4 DS—Double Spike
3.3.5 DU—Depleted Uranium
The last approved version of this historical standard is referenced on www.astm.org.
C1832 − 23
3.3.6 FAR—Faraday Cup
3.3.7 HEU—High Enriched Uranium
3.3.8 IAEA—International Atomic Energy Agency
3.3.9 ICPMS—Inductively Coupled Plasma Mass Spectrometry
3.3.10 IRMM—Institute for Reference Materials and Measurements
3.3.11 ITU—Institute for Transuranium Elements
3.3.12 JRC—Joint Research Centre of the European Union
3.3.13 JRC-G.2—Unit for Standards for Nuclear Safety, Security and Safeguards of JRC (new name for the nuclear part of the
former IRMM)
3.3.14 JRC-G.II.6—Unit for Nuclear Safeguards and Forensics of JRC (part of the former ITU)
3.3.15 LEU—Low Enriched Uranium
3.3.16 MTE—Modified Total Evaporation
3.3.17 NBL—New Brunswick Laboratory
3.3.18 RSD—Relative Standard Deviation; SD (see below) divided by the mean value of the observations in repeated sampling
3.3.19 RSE—Relative Standard Error; SE (see below) divided by the mean value of the observations in repeated sampling
3.3.20 SD—Standard Deviation; according to Practice E2586, 3.1.30, the square root of the sum of the squared deviations of the
observed values in the sample divided by the sample size minus one
3.3.21 SE—Standard Error; according to Practice E2586, 3.1.29, standard deviation of the population of values of a sample
statistic (that is, the mean value) in repeated measurements, or an estimate of it.
3.3.21.1 Discussion—
According to Practice E2586, 3.1.30, if the standard error (SE, see above) of a statistic is estimated, it will itself be a statistic with
some variance that depends on the sample size, that is, the number of observed values in the sample (Practice E2586, 3.1.26).
3.3.21.2 Discussion—
According to Guide E2655, 5.8.4.1, from statistical theory, a 95 % confidence interval for the mean of a normal distribution, given
n independent observations x , x , ., x drawn from the distribution is, x 6 t × SD / √ n, where x is the sample mean, SD
1 2 n mean mean
is the standard deviation of the observations (see above), and t is the 0.975 percentile of the 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 for using the (coverage) factor 2 for expanded uncertainty. The standard error (SE) of the mean value of a series
of n independent repeated measurements can be derived from that by using t = 1, so the standard error (SE) is given by SD/√n.
3.3.22 SEM—Secondary Electron Multiplier
3.3.22.1 Discussion—
In the scientific literature the acronym SEM is also used for Scanning Electron Microscope, but within this document SEM
represents Secondary Electron Multiplier.
3.3.23 SGAS—Safeguards Analytical Services Laboratory of the IAEA
C1832 − 23
3.3.24 TIMS—thermal ionization mass spectrometry
4. Summary of Test Method
4.1 The modified total evaporation method has been developed on the basis of the “classical” total evaporation technique (1-4),
also described in Test Method C1672. By using the total evaporation technique, the mass fractionation is minimized by evaporating
the entire sample amount loaded on the filament, in contrast to the “conventional” technique as described in Test Method C1625.
The MTE method has already been described in detail in Refs (5) and (6). If necessary, uranium is separated from plutonium and
other elements (to eliminate isobaric interferences) by selective extraction, anion exchange (see Practice C1411), or extraction
chromatography. The purified uranium fraction as nitrate solution is loaded onto a degassed filament (made of metals such as
rhenium, zone-refined rhenium, or tungsten) with high evaporation temperature and converted to an oxide by controlled heating
of the filament under atmospheric conditions. For the MTE method, the uranium load is in the range of about 22 μg to 6 μg, which
is about one to two orders of magnitude higher than that typically used for the “classical” total evaporation method by TIMS. The
sample filament is mounted on the sample turret using a double-filament configuration. This configuration consists of an
evaporation filament (Re or W) on which the sample is loaded, and an ionization filament (Re filament with no sample). For a
measurement in the mass spectrometer, the ionization filament is heated to a temperature of about 17001700 °C to 1900 °C,
187 -12 -12
sufficient to generate Re ion beam signals of 150150 mV to 400 mV (corresponding to ion currents of 1.5 × 10 A to 4 × 10
11 187
A using an amplifier resistor of 10 Ω). The intensity of the optimized Re signal depends on the Re material (zone-refined or
non-zone-refined), thickness and the measurement conditions, but it is expected to be similar for all filaments on the same sample
turret. The Re ion current is also used for the initial ion beam focusing. The evaporation filament is heated next. After ion beam
234 235 236 238
re-focusing and mass re-adjustment initially using a small sum intensity (sum of U, U, U, and U) of about 11 V to 4
V, 4 V, the data acquisition begins usually under computer control to yield a predefined target sum intensity of 2020 V to 30 V
-10 -10 11
(corresponding to ion currents of 2 × 10 A to 3 × 10 A using an amplifier resistor of 10 Ω). This target value depends on
the amount of uranium loaded on a filament. The MTE analysis takes between 2 and 5 h per sample filament and is about three
to ten times longer than (“classical”) TE analyses in spite of the higher intensities at which the analyses are performed. To ensure
that the whole sample is completely evaporated and analyzed before the ionization filament breaks as a result of overheating, the
MTE analysis routine is programmed to increase the target sum intensity during the course of the analysis if necessary. The
occurrences of outliers due to technical glitches, for example, as a result of termination before complete sample evaporation or
because of early sample exhaustion, are minimized by a dynamic target intensity control feature through manipulation of the target
sum intensity depending on the actual measurement conditions.
4.2 The sample amount to be loaded for MTE analyses is limited to a range of about 22 μg to 6 μg to achieve ion beam signals
238 235
of about 2020 V to 30 V for the major isotope ( U for DU, NU, and LEU samples and U for HEU samples) corresponding
234 234
to a U intensity of 11 mV to 10 mV. This causes the U ion beam to be suitable for an internal cross calibration of the SEM
236 238
versus the Faraday cups through the entire measurement time. This also allows the U/ U isotope amount ratio to be measured
-2 -10
in a wide dynamic range from 10 down to 10 using a Faraday cup or an SEM in combination with an energy filter for improved
234 238 236 238 -5
abundance sensitivity. For all samples with minor ratios U/ U and U/ U higher than 3 × 10 , which also includes HEU
12 13
samples, the minor isotopes are only measured using Faraday cups, with amplifier resistors of 10 Ω or 10 Ω yielding a favorable
signal-to-noise ratio.
235 238
4.3 Similar to the TE analysis, the isotope ion beams of the major isotopes U and U are integrated over the course of the
235 238
analysis, and the summed intensity for U is divided by the summed intensity for U to yield the major isotope amount ratio.
The result of the major isotope amount ratio is corrected for mass fractionation using the measurement of a CRM analyzed on the
same sample turret.
4.4 The minor isotope amount ratios are corrected for mass fractionation for each integration step individually. This is
accomplished in an internal manner; the magnitude of the mass fractionation for the minor ratios is calculated from the measured
mass fractionation of the major ratio. The peak tailing contributions are determined at two positions, slightly below and slightly
above the isotope masses of interest. If applicable, the SEM-versus-Faraday calibration is also performed for each integration step
individually.
5. Significance and Use
5.1 Uranium material is used as a fuel in certain types of nuclear reactors. To be suitable for use as nuclear fuel, the starting
The boldface numbers in parentheses refer to a list of references at the end of this standard.
C1832 − 23
material shall meet certain specifications such as those described in Specifications C753, C776, C787, C833, C967, C996, and
C1008, or as specified by the purchaser. The isotope amount ratios of uranium material can be measured by mass spectrometry
following this test method to ensure that they meet the specification.
5.2 The MTE method can be used for a wide range of sample sizes even in samples containing as low as 20 μg of uranium. If
the uranium sample is in the form of uranium hexafluoride, it has to be converted into a uranium nitrate solution for measurement
by the MTE method. The concentration of the loading solution for MTE has to be in the range of 1 mg/g to 6 mg/g to allow a
sample loading of 22 μg to 6 μg of uranium. A minimum loading of 3 μg uranium per filament is strongly recommended. This is
234 236
needed to have a sufficient and stable ion signal especially for the two minor isotopes ( U and U) thus enabling the internal
calibration of SEM versus the Faraday cups using the U ion beam signal during the measurement.
5.3 Until now, the instrument capabilities for the MTE method have only been implemented on the TRITON™ TIMS instrument.
Therefore, all recommendations for measurement parameters in this test method are specified for the TRITON instrument. The
manufacturers of other TIMS instruments (for example, IsotopX and Nu Instruments) have indicated plans to implement the
modifications needed in their instruments to use the MTE method.
5.4 The MTE method described here can also be extended to measurement of elements other than uranium. Note that the MTE
method has already been implemented for plutonium and calcium.
6. Interferences
6.1 Isobaric nuclides such as Pu interfere in the uranium measurements. The removal of interferences is generally accomplished
by chemical separation leading to ionization of uranium only and improved precision of measured isotope amount ratios.
6.2 It has to be ensured that samples are not contaminated by environmental uranium. The level of effort required to minimize
contamination shall be based upon the sample size and the levels of contamination present in the analytical facility. For extremely
small samples or extremely low U abundances, residual uranium from chemicals used for sample dissolution and sample
preparation are possible sources for bias in the isotopic data.
6.3 Samples shall be chemically purified to assure reliable analyses by TIMS. Impurities, especially alkali elements, produce
unstable ion emission leading to poor precision in the isotope amount ratios. Organic contaminants or oxide layers on the filaments
also adversely influence TIMS analyses. Isobaric interferences, if not removed, will bias the isotope amount ratios. Contaminants
in reagents, lab ware, or filament material are also sources for bias in the isotope amount ratios.
6.4 The performance of the instrument can be adversely affected by changes in the environmental conditions of the laboratory, that
is, temperature and humidity. For this reason, controlled laboratory environmental conditions should be maintained (within the
manufacturer’s specifications) during instrument operation.
7. Apparatus
7.1 The suitability of the mass spectrometer for carrying out measurements by the MTE method shall be evaluated by means of
performance tests. The relevant instrument characteristics are as follows:
7.1.1 A thermal ionization source for using double filament assemblies with rhenium or tungsten filaments, or both.
+
7.1.2 A mass analyzer sufficient to resolve adjacent masses in the mass-to-charge range being studied, m/z = 233 to 238 for U .
Resolution shall be greater than 350 (full width at 1 % of peak height) and the abundance sensitivity at mass 237 for ions of U
-6
less than 5 × 10 .
+
7.1.3 A multiple Faraday collector system to allow simultaneous detection of isotope beams from m/z = 233 to 238 for U ions.
235 238
7.1.4 For the Faraday cups used to measure the major ion beams of U and U, there shall be current amplifiers equipped with
11 234 236 11
10 Ω resistors and, for the minor ion beams of U and U, there shall be current amplifiers equipped with at least 10 Ω,
12 13
and preferably 10 Ω (or even 10 Ω) resistors to improve the signal-to-noise ratio.
The TRITON™ (Plus) Multicollector Thermal Ionization Mass Spectrometer is a trademark product of Thermo Fisher Scientific, http://www.thermoscientific.com.
C1832 − 23
7.1.5 The detection system shall include at least one secondary electron multiplier (SEM) operated in ion counting mode or a Daly
detector, or similar detector, with a dark noise <0.2 cps. The SEM shall be equipped with an energy filter to improve the abundance
-8 238 +
sensitivity, which shall be better than 2 × 10 at mass 237 for ions from U with the energy filter in operation.
7.1.6 A sample turret with at least ten filament positions to allow automatic measurement sequences of at least five replicate
filament loadings per sample and at least five replicate filament loadings for a calibration standard (preferentially a CRM).
-5 -7
7.1.7 A pumping system that is able to attain a vacuum of <4.0 × 10 Pa (3 × 10 torr) in the ion source, the analyzer, and the
detector is required. Tailing corrections are dependent on the vacuum levels inside the mass spectrometer. Analyzer pressures
-7 -9
below 7.0 × 10 Pa (5 × 10 torr) are preferred.
7.1.8 A mechanism to scan masses by varying the magnetic field or the accelerating voltage, or both.
7.1.9 An optical pyrometer for determining the temperatures of the filaments.
7.1.10 A computer for control of the data acquisition according to a predefined sequence.
7.2 Special MTE Capabilities—The mass spectrometer software must be flexible enough to implement a user-defined
filament-heating program for MTE.
7.3 A separate filament degassing device for cleaning of the filaments before sample loading is recommended.
7.4 Microsyringe or Micropipette—Syringe to transfer microlitre volumes of solutions.
8. Reagents and Materials
8.1 Purity of Reagents—Reagent-grade chemicals shall be used in all sample preparations. Unless otherwise indicated, it is
intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society
where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently
high purity and low uranium concentration to permit its use without lessening the accuracy of the MTE measurements.
8.2 Ultra-high purity reagents are necessary for processing small sample amounts or samples with extremely small isotope amount
ratios. The level of uranium contamination from chemicals, water, and the sample handling environments shall be determined to
ensure that the materials and the environment are sufficiently pure for the samples being analyzed.
8.3 Nitric Acid (HNO , 15.8 M)—Concentrated nitric acid.
8.4 Nitric Acid (HNO , 1 M)—One volume of concentrated nitric acid (HNO , 15.8 M) brought to 15.8 volumes with water.
3 3
8.5 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean laboratory accepted
demineralized or deionized water as described by Type I of Specification D1193.
8.6 Filaments—High-purity filaments, for example, zone refined Re, are required. The size and configuration of the filament is
instrument dependent. Tungsten might be used with minor modifications to the heating script. All filaments must be degassed
before use. For measurement of uranium present only at the trace levels in the sample, contamination of the samples by
interferences from elemental or molecular species within the m/z = 233 to 238 range need to be determined to ensure that biases
due to contributions from the filament material will not bias the analysis results. In case a significant count rate >1 cps is
236 238 -6
determined at m/z = 236, a correction has to be applied for U/ U ratios < 10 (6, 7).
The sole source of supply of the apparatus known to the committee at this time is Thermo Fisher Scientific Inc., 81 Wyman St., Waltham, MA 02451. If you are aware
of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsible
technical committee, which you may attend.
ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference Materials, American Chemical Society, Washington, DC. For
suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and
the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
C1832 − 23
9. Hazards
9.1 TIMS instruments operate at 8 to 10 kV electrical potential. Ensure that the high-voltage is switched off before insertion or
removal of the sample turret into/from the instrument, and working with the ion source, or accessing other electronic components.
9.2 The filaments reach temperatures in excess of 2000 °C. The filament holders, sample wheel, and ion source parts are expected
to be hot. Ensure that a sufficient time has lapsed since the last filament heating before accessing the filaments, sample turrets, and
ion source.
9.3 Wear eye protection and suitable gloves when filling cold traps with liquid nitrogen. Protect hands, torso, and feet in the event
of splashing or spilling of the liquid nitrogen.
9.4 Handle radioactive materials with appropriate attention to radiological safety.
10. Sampling, Test Specimens, and Test Units
10.1 Isotope Reference Materials—Uranium reference materials used in the analysis should be prepared from certified reference
materials (CRMs) traceable to SI units. Examples include the NBL U-Series CRMs (for example, U010 and U500), IRMM
uranium standards IRMM 184-187, IRMM 019-029 (to be converted from UF ), IRMM-074, IRMM-075, and IRMM-3100. See
Guide C1128 for additional guidance on preparation of traceable working reference materials.
10.2 Uranium samples to be measured and isotope reference materials used for estimation of the mass fractionation correction
factor (K-factor) or for quality control purposes shall be in the same medium and in the same oxidation state. The solutions for
loading onto the filaments are 1 M nitric acid solutions. The uranium concentrations of these solutions shall be similar. The loading
and drying sequence of the filaments shall also be similar.
10.3 In the case of characterization studies of test materials, possible inhomogeneity between test units shall be evaluated
statistically and included in the uncertainty calculations of the isotope amount ratios assigned.
11. Preparation of Apparatus
11.1 Filament Degassing—Degass all filaments before using them for MTE measurements. It is recommended to use a separate
-4 -6
apparatus (see 7.3) for performing this. Start the degassing procedure when a vacuum pressure of <4.0 × 10 Pa (3 × 10 torr)
is reached. Recommended filament currents for degassing are in the range of 4.04.0 A to 5.0 A, corresponding to temperatures in
the range of 17001700 °C to 2000 °C. Perform the degassing for a duration of at least 30 min.
11.2 “Initialization” of Sample Turret—Adjust, if needed, the position of the sample turret in the ion source and verify proper
electrical connections for both the evaporation and ionization filament for each sample loading position. It shall be ensured that
the electrical contact is not interrupted in case the turret is slightly moved for the purpose of ion beam focusing.
11.3 Amplifier Signal Decay Adjustment—Adjust the signal decay characteristics of the current amplifiers of the Faraday cups.
This is important for measuring isotope amount ratios with a large dynamic range, especially for the minor isotope amount ratios
of uranium. Depending on the combination of the capacitance and resistance of the current amplifier, the response time for a sudden
11 12
change in the ion beam signal to the Faraday cup can reach up to 5 s. For resistances higher than the 10 Ω, for example, 10
Ω, and in particular 10 Ω, longer response times of about 15 s can be expected. The MTE method is designed by taking into
consideration the required response times. The amplifier response can be checked either using a custom-made software module
within the operating software (when available) or “manually” by means of a large ion beam that is abruptly directed into a Faraday
cup to check the signal ingrowth time, or away from a Faraday cup (for example, by closing a valve between ion source and
analyzer) to check the signal decay time.
11.4 SEM Plateau Voltage—The SEM plateau voltage, that is, the dependency of the count rate on the applied high voltage to the
SEM, shall be measured on a regular basis, as recommended by the manufacturer of the SEM or the operator’s quality system.
Typical SEM plateau voltages range between 17001700 V to 3000 V. The SEM plateau voltage drifts to higher values with use
and shall be readjusted to restore the original efficiency. The efficiency should be higher than 90 %.
C1832 − 23
11.5 SEM Dark Noise—SEM detectors are usually operated in ion counting rather than analogue mode to avoid the resistor noise
of the current amplifier. The ion counting mode results in much smaller uncertainties encountered for measurements of very low
-19 -16
intensity ion beams (10 A to 10 A, equivalent to 0.60.6 cps to 600 cps). However, the dark noise, that is, the observed count
rate measured without incident ion beam, shall be measured before an automated MTE measurement sequence to enable
corrections to the isotope amount ratios and their uncertainties (7). The dark noise shall be below 0.5 cps.
11.6 Ion Source and Analyzer Pressure—It is important to achieve a certain level of vacuum before the isotope amount ratio
measurements can begin. See 7.1.7 for the recommended pressure. The peak tailing depends strongly on the vacuum pressure in
the detector system since the number of ion collisions with gas molecules inside the mass spectrometer is a direct function of the
ambient pressure. Increase in the pressure within the ion source caused by the heating of the ionization and evaporation filaments
can be subdued, to a certain extent, by using a cold trap filled with liquid nitrogen.
12. Calibration and Standardization
NOTE 1—The measurement method may be qualified following Guide C1068 and calibrated following Guide C1156. Additional information regarding
mass spectrometer calibrations with regard to the MTE method may be found in Refs (5, 6).
12.1 Mass Calibration—The relationship between the known atomic masses and the magnetic field necessary to direct the isotope
beams into the detectors shall be updated on a regular basis. Mass calibration shall be performed at intervals specified by the
manufacturer or the user’s quality assurance program.
12.2 Peak Centering—The peak centering routine is used as a fine adjustment to ensure that the ion beam is centered within the
detector. Peak centering usually occurs by means of fine adjustments of the accelerating voltage, and any difference between the
value optimized during peak centering from the default accelerating voltage requires a readjustment of the mass calibration curve.
Peak centering shall be performed for at least three uranium masses as part of the mass calibration and also before the start of each
MTE measurement sequence. During the MTE measurement, peak centering is performed on a regular basis.
12.3 Amplifier Baseline Calibration—The baselines of the Faraday cup amplifiers, that is, the amplifier responses without
incoming ion beam to the cup, shall be measured on a regular basis and checked for stability. During the MTE measurements,
baseline measurements are performed on a regular basis. Note that the integration time for the baseline measurement has a
significant influence on the uncertainty of Faraday cup measurements, particularly at lower ion beam intensities. Therefore, the
integration time of the baseline (within a measurement) shall be comparable to the integration time of the actual ion beam signal
integration. The long-term historical baseline data shall be regularly reviewed by the user to assure that the system performance
is within manufacturer specifications and quality system requirements.
12.4 Amplifier Gain Calibration—The stability and response of individual Faraday detector amplifiers shall be measured and
differences between amplifiers corrected by means of the amplifier gain calibration. Gain calibration is normally performed by
sequentially applying a stable calibration current to the input of each Faraday cup amplifier and the output is then normalized to
a reference value to generate a gain calibration factor for each amplifier. A gain calibration shall be performed prior to each
automatic MTE sequence. Historical gain calibration data can be used to evaluate the stability of the amplifiers.
12.5 Faraday Cup Effıciency Test—The response of individual Faraday cups depends on several factors, for example, extent of
usage, manufacturing variability, and can also be affected by an insufficient electron suppression voltage. The relative response of
the Faraday cups, therefore, shall be determined periodically. Usually, the Faraday cups of a multi-collector system are only
intercalibrated for the current amplifiers connected to them (see 12.4) but not for the differences in the efficiencies of the Faraday
cups themselves. The efficiencies of the Faraday cups are expected to be similar to each other, which means that the relative
efficiencies (relative to one reference cup) are normally close to unity. Note that an (electronic) amplifier gain calibration (see 12.4)
shall be performed prior to the Faraday cup efficiency test. The Faraday cup efficiency test can be performed in several ways, as
described in 12.5.1 – 12.5.4.
12.5.1 The calibration may be performed by switching a stable ion beam of Re (from a blank filament) between each Faraday
cup and a reference Faraday cup. In case a relative efficiency between the detectors is significantly different from unity, this result
can be used to correct for differences in the detector response. This procedure can be performed with a relative uncertainty at the
level of <0.1 %.
12.5.2 A series of peak-jumping measurements between all Faraday cups and a reference cup to be checked can also be performed
C1832 − 23
using a sufficiently large uranium sample and one large stable ion beam, for example, a 1010 V to 20 V ion beam of U from
an LEU or natural uranium sample. The drift of the signal intensity shall be corrected for using the operating software. This
procedure can be performed with a relative uncertainty at the level of <0.01 %.
12.5.3 A series of comparative neodymium (Nd) isotope amount ratio measurements can be performed in two different modes such
as the multi-dynamic mode and the static mode with “amplifier rotation” (only for TRITON TIMS, also called “virtual amplifier”:
each Faraday cup is connected to each amplifier for regular time intervals during the measurement). This procedure can be
performed with a relative uncertainty at the level of few ppm (5). It shall be repeated until all Faraday cups of interest for MTE
measurements have been included.
12.5.4 A series of static measurements can be performed using special “multi-isotope” reference materials, such as IRMM-3100a
233 235 236 238 233 235 238
( U/ U/ U/ U = 1/1/1/1) (8), IRMM-072/1, IRMM-074/1, or IRMM-199 ( U/ U/ U = 1/1/1) (9), to include all
Faraday cups. This procedure can be performed with relative uncertainties of about 0.03 %.
12.6 Linearity Test—There are various procedures to check the linearity of an isotope mass spectrometer detection system. The
procedures described in 12.6.1 and 12.6.2 are mainly applicable for Faraday multi-collector systems (for SEM calibration and
linearity, see 12.8 and 12.9).
12.6.1 The linearity of the mass spectrometer is determined over the working range of the Faraday cups by measuring the
235 238
U/ U ratios of various reference materials under identical conditions. The mass spectrometer system is linear if the K-factor,
235 238 235 238
that is, the ratio of the certified U/ U ratio to the measured U/ U ratio, is independent of the isotopic composition of the
material. For this procedure, the NBL U-series of reference materials (U005a to U970, 0.50.5 % to 97 % of U) is ideal and can
235 235
be combined with the IRMM-183-187 series (0.3(0.3 % to 5 % of U) and the IRMM 019-029 (0.17(0.17 % to 5 % of U. This
procedure shall be performed sequentially for all Faraday cups of the multi-collector system needed for the MTE analyses.
238 235 233 235
12.6.2 The IRMM-072 and IRMM-074 series of reference materials are characterized by U/ U ratios of ≈1 and U/ U
-6
ratios ranging from ≈1 down to ≈10 for the 15 or 10 units, respectively, of the used series. For each unit, the bias of the measured
238 235 233 235
U/ U ratios from the certified ones can be used for internal mass fractionation correction of the measured U/ U ratios.
233 235
The comparison of the corrected U/ U ratios with the certified ones allows the linearity of the detection system to be checked
over a dynamic range of six orders of magnitude for the ion beam intensity. A detailed description of the procedure is given in Ref
(9). This procedure shall be performed sequentially for all Faraday cups needed for the MTE analyses.
12.7 Peak Overlap—When a Faraday multi-collector system for the simultaneous detection of several masses is used, it needs to
be ensured that the peak overlap is acceptable. A mass scan, usually by scanning the magnetic field, shall be performed by which
all ion beams are simultaneously moved through the respective cups. The measured intensities for all detectors shall be plotted
versus the mass of a reference detector to make the peak overlap visible. All peaks shall have a symmetric shape with a common
flat region in the center, with the peak centers reasonably close together, as specified by the manufacturer or the user quality system.
After a satisfactory peak overlap is realized (by moving cups relative to one another if necessary), the positions of all detectors
shall be saved, for example, as a Faraday cup configuration file. The positions shall be checked and possibly readjusted, manually
or using stepping motors, as needed before a new automatic measurement sequence.
12.8 SEM Linearity Check and Correction—The linearity of SEM systems shall be checked carefully on a regular basis according
to manufacturer’s specifications or the user’s quality assurance program. It is emphasized that there can be more than one reason
for nonlinearity of a SEM detector. For SEM detectors operated in ion counting mode, the dead time of the pulse-counting
electronic system is always one source of nonlinearity, but this can be easily corrected. As pointed out in Ref (9), there is also the
possibility of an intrinsic nonlinearity for SEM detectors, possibly depending on the design of the ion optics, the dynode surfaces,
or the electronics, which could cause the linearity investigation and correction to become more complicated. But in case the dead
time is confirmed to be the only source of nonlinearity of a SEM system, the value can be determined in various ways (9) using
CRMs, as described in 12.8.1 and 12.8.2.
238 235
12.8.1 For this procedure, the IRMM-072/8 or IRMM-074/3 (9) reference materials, characterized by a U/ U ratio of ≈1 and
233 235 238 235 234 235
a U/ U ratio of ≈0.01, or the NBL CRM U500, characterized by a U/ U ratio of ≈1 and a U/ U ratio of ≈0.01 (using
new data published in Ref (5)), can be used. Peak-jumping measurements are performed for count rates between 5 × 10 cps and
5 235 238 233 235 234 235
5 × 10 cps for U (similar for U). The U/ U ratios ( U/ U in case of NBL CRM U500) are internally normalized using
238 235 235
the U/ U ratios of >1 and plotted versus the U count rate. If the data show a linear relationship with no significant intercept,
a linear regression is calculated with the intercept being zero. The slope of the regression line can be used to calculate the dead
time using:
C1832 − 23
U
τ 5 $slope% ⁄ 1 2 (1)
S S D D
U
CERT
where:
τ = dead time,
233 235 235
slope = slope of linear regression calculation based on measured U/ U ratios versus the U count rate, and
233 235
( U/ U) = certified isotope amount ratio of used CRM.
CERT
233 235
In case NBL CRM U500 is used instead of IRMM-072/8 or IRMM-074/3, the ( U/ U) in Eq 1 has to be replaced by
CERT
234 235
( U/ U) .
CERT
12.8.1.1 In case the data do not indicate a linear relationship with a non-significant intercept, the SEM detection system is likely
to be affected by other sources of nonlinearity, which shall be investigated.
12.8.2 For an “external check” of the linearity of the SEM detection system, a series of reference materials can be measured by
MTE, for example, the NBL U-series (5), the IRMM-183-187 series, the IRMM-019-029 series, or the gravimetrically prepared
236 238 -4 -5 -6 -7 -8 -9
IRMM-075 series (6, 10) with U/ U rations of 10 , 10 , 10 , 10 , 10 , and 10 .
12.9 SEM Versus Faraday Cup Inter-calibration—Since the inter-calibration between a SEM detector with a Faraday cup depends
on the ion source focusing and ion beam shape, this calibration shall be performed in an internal manner during the course of each
measurement for MTE measurements. For this internal calibration, the ion beam of one of the uranium isotopes present in the
sample is switched between the SEM and one Faraday cup within each integration step during the entire measurement. To allow
such an internal calibration, there shall be at least one suitable ion beam available for this purpose. This ion beam shall be within
a certain intensity range, between the lower limit of reasonable Faraday cup measurements (typically 1 mV on an amplifier with
11 12
10 Ω, which is affected by about the same noise as 0.5 mV on an amplifier with 10 Ω) and the upper limit for reasonable SEM
6 11
measurements (typically 1.0 × 10 cps, equivalent to 16 mV on an amplifier with 10 Ω). The isotope used for the internal
234 236
calibration within MTE measurements is for most samples U, in few cases U instead. As a consequence, the sample amount
to be loaded is limited to a certain range as well. For typical TIMS conditions, the sample amount for MTE measurements is about
235 238
2 to 6 μg, which provides ion beam signals of about 2020 V to 30 V for the sum of the main isotopes U and U. The choice
of the isotope used for the inter-calibration depends on the isotopic composition of the sample (based on process knowledge or
sample supplier information, or estimated by a mass scan in the m/z = 233 to 238 mass range), in the following way:
234 238 -5 -4 236 238
12.9.1 Mainly for DU, NU, and LEU samples with U/ U ratios between 3 × 10 and 5 × 10 and with U/ U ratios below
-5 234
3 × 10 , the U ion beam is used for the internal calibration.
234 238 -5 236 238
12.9.2 Mainly for DU (in principle also in case of NU and LEU) samples with U/ U ratios below 3 × 10 and with U/ U
-5 236
ratios higher than 3 × 10 , the U ion beam is used for the internal calibration (also called “reverse” MTE, (6)). Due to the
12 13
availability and frequent use of amplifiers with resistors of 10 Ω and 10 Ω, this “reverse” MTE procedure has become obsolete
and is therefore not described in this revision any more.
234 238 236 238 -5 234 236
12.9.3 In the rare case that both the U/ U and the U/ U ratios are below 3 × 10 , the larger one of U and U shall
235 238
be used. This might only apply to quite highly enriched U or U materials, for example, for spike materials. In this case, an
internal calibration using a suitable ion beam from an added U spike (11) is another option, which would require isobaric
234 236 233 13
corrections because of the possible U and U contents of the U spike. As another option, if amplifiers with a resistor of 10
234 236 234 238 236 238 -5
Ω are available for measuring U and U, a MTE measurement of U/ U and U/ U ratios between 1 × 10 and 3 ×
-5
10 using only Faraday cups is recommended over using the SEM.
234 238 236 238
12.9.4 For all samples, that is, DU, NU, LEU, or HEU, with any values for the U/ U and U/ U ratios, an MTE
measurement can always be performed using Faraday cups only, thus without using the SEM and without the need for a SEM
intercalibration. This shall be carefully considered in view of the associated uncertainties originating on one hand from the SEM
calibration and SEM linearity correction (see 12.8) and on the other hand from the higher relative amplifier noise in case of low
234 238 236 238 -4
signals on the Faraday cups. In case both ratios U/ U and U/ U are higher than 5 × 10 , the SEM cannot be used for
236 238 -5 236
MTE, only Faraday cups
...