ASTM C1672-23

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: 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
This standard is issued under the fixed designation C1672; 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 eliminate or diminish peak tailing effects. Measurement of the
abundance sensitivity of the instrument may be used to ensure
1.1 This method describes the determination of the isotopic
that such biases are negligible, or may be used to bias correct
composition, or the concentration, or both, of uranium,
the minor isotope ratios.
plutonium, and americium as nitrate solutions by the total
evaporation method using a thermal ionization mass spectrom- 1.4 The values stated in SI units are to be regarded as
eter (TIMS) instrument. Purified uranium, plutonium, or am- standard. When non-SI units are provided in parentheses, they
ericium nitrate solutions are deposited onto a metal filament are for information only.
and placed in the mass spectrometer. Under computer control,
1.5 This standard may involve the use of hazardous mate-
ion currents are generated by heating of the filament(s). The ion
rials and equipment. This standard does not purport to address
currents are continually measured until the whole deposited
all the safety concerns, if any, associated with its use. It is the
solution sample is exhausted. The measured ion currents are
responsibility of the user of this standard to establish appro-
integrated over the course of the measurement and normalized
priate safety, health, and environmental practices and to
to a reference isotope ion current to yield isotope ratios.
determine the applicability of regulatory limitations prior to
use.
1.2 In principle, the total evaporation method should yield
1.6 This international standard was developed in accor-
isotope ratios that do not require mass bias correction. In
dance with internationally recognized principles on standard-
practice, samples may require this bias correction. Compared
ization established in the Decision on Principles for the
to the conventional TIMS method described in Test Method
Development of International Standards, Guides and Recom-
C1625, the total evaporation method is approximately two
mendations issued by the World Trade Organization Technical
times faster, improves precision of the isotope ratio measure-
Barriers to Trade (TBT) Committee.
ments by a factor of two to four, and utilizes smaller sample
sizes. Compared to the C1625 method, the total evaporation
235 238 240
2. Referenced Documents
method provides “major” isotope ratios U/ U, Pu/
239 241 243
Pu, and Am/ Am with improved accuracy.
2.1 ASTM Standards:
C753 Specification for Nuclear-Grade, Sinterable Uranium
1.3 The total evaporation method is prone to biases in the
233 238 234 238 236 238
Dioxide Powder
“minor” isotope ratios ( U/ U, U/ U, and U/ U
238 239 241 239
C757 Specification for Nuclear-Grade Plutonium Dioxide
ratios for uranium materials and Pu/ Pu, Pu/ Pu,
242 239 244 239
Powder for Light Water Reactors
Pu/ Pu, and Pu/ Pu ratios for plutonium materials)
C776 Specification for Sintered Uranium Dioxide Pellets for
due to peak tailing from adjacent major isotopes. The magni-
Light Water Reactors
tude of the absolute bias is dependent on measurement and
C787 Specification for Uranium Hexafluoride for Enrich-
instrumental characteristics. The relative bias, however, de-
ment
pends on the relative isotopic abundances of the sample. The
C833 Specification for Sintered (Uranium-Plutonium) Diox-
use of an electron multiplier equipped with an energy filter may
ide Pellets for Light Water Reactors
C859 Terminology Relating to Nuclear Materials
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. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Dec. 1, 2023. Published January 2024. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2007. Last previous edition approved in 2017 as C1672 – 17. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/C1672-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1672 − 23
C967 Specification for Uranium Ore Concentrate 3.3.6 JRC—Joint Research Centre
C996 Specification for Uranium Hexafluoride Enriched to
3.3.7 LEU—Low Enriched Uranium
Less Than 5 % U
3.3.8 NBL—New Brunswick Laboratory
C1068 Guide for Qualification of Measurement Methods by
3.3.9 NU—Natural Uranium
a Laboratory Within the Nuclear Industry
C1156 Guide for Establishing Calibration for a Measure- 3.3.10 TIMS—Thermal Ionization Mass Spectrometry
ment Method Used to Analyze Nuclear Fuel Cycle Mate-
3.3.11 WRM—Working Reference Material
rials
C1168 Practice for Preparation and Dissolution of Plutonium 4. Summary of Test Method
Materials for Analysis
4.1 Uranium, plutonium, and americium are separated from
C1347 Practice for Preparation and Dissolution of Uranium
each other and purified from other elements by selective anion
Materials for Analysis
exchange chromatography (such as in Practice C1411 or Test
C1411 Practice for The Ion Exchange Separation of Ura-
Method C1415 or Practice C1816). The purified uranium or
nium and Plutonium Prior to Isotopic Analysis
plutonium or americium samples as nitrate solutions are
C1415 Test Method for Pu Isotopic Abundance By Alpha
drop-deposited or otherwise loaded on a refractory metal
Spectrometry
filament (typically rhenium, tungsten, or tantalum) and con-
C1625 Test Method for Uranium and Plutonium Concentra-
verted to a solid chemical form via controlled heating of the
tions and Isotopic Abundances by Thermal Ionization
filament under atmospheric conditions. The sample filament is
Mass Spectrometry
mounted on the sample turret, often in the double filament
C1816 Practice for The Ion Exchange Separation of Small
configuration. This configuration consists of an evaporation
Volume Samples Containing Uranium, Americium, and
filament (Re or W) on which the sample is loaded, and an
Plutonium Prior to Isotopic Abundance and Content
ionization filament (Re filament with no sample). The filaments
Analysis
are heated to yield a small ion current suitable for lens focusing
C1832 Test Method for Determination of Uranium Isotopic
and peak centering. Following focusing and peak centering,
Composition by Modified Total Evaporation (MTE)
data acquisition begins, with the filaments heated under com-
Method Using Thermal Ionization Mass Spectrometer
puter control to yield a pre-defined major isotope ion current
235 238 239 240
D1193 Specification for Reagent Water
( U or U for uranium, Pu or Pu for plutonium and
D3084 Practice for Alpha-Particle Spectrometry of Water 241 243
Am or Am for americium) or a predefined sum total for
all measured ion currents. Data acquisition and filament
3. Terminology
heating continues until the sample is exhausted or the ion
3.1 For definitions of terms used in this test method but not
current reaches a pre-defined lower limit. Ion intensity of each
defined herein, refer to Terminology C859. isotope is integrated over the course of the analysis, and the
summed intensity for each isotope is divided by the summed
3.2 Definitions of Terms Specific to This Standard:
intensity of a common isotope (typically the most abundant
3.2.1 isotopic equilibration, n—series of chemical steps
isotope) to yield isotope amount ratios. The isotopic composi-
performed on a mixture of two samples (for example, a
tion of the sample (formatted as amount fraction or mass
uranium sample and a uranium spike) to ensure identical
fraction) may be calculated from the isotope amount ratios.
valency and chemical form prior to purification of the mixture.
Additional information on the total evaporation method may be
Failure to perform isotopic equilibration of a sample-spike
found in Refs (1-5).
mixture may result in partial separation of the sample from the
spike during the purification procedure, causing a bias in the 4.2 The isotope dilution mass spectrometry (IDMS) method
results of isotope dilution mass spectrometry measurements. may be used to determine the uranium, plutonium, or ameri-
235 238
cium concentrations. In this method, a spike of known isotopic
3.2.2 major ratio, n—alternate expression for U/ U (or
238 235 240 239 243 241
composition and element concentration is added to a sample
U/ U), Pu/ Pu, and Am/ Am isotope ratios.
prior to chemical separation. Typical spike materials in-
233 238
3.2.3 minor ratios, n—alternate expression for U/ U,
233 235 238 239 242
clude U, U, or U for uranium samples, Pu, Pu,
234 238 236 238 234 235 236 235 238 239
U/ U, U/ U, U/ U, and U/ U or Pu/ Pu,
244 243
or Pu for plutonium samples, and Am for americium
241 239 242 239 244 239
Pu/ Pu, Pu/ Pu, and Pu/ Pu isotope ratios.
samples. Samples containing both uranium and plutonium (for
3.2.4 turret, n—holder for sample filaments, other words
example, mixed oxide fuels or fuel reprocessing materials)
used: wheel, magazine.
may be mixed with a combined U/Pu spike prior to separation.
When using a spike containing significant quantities of one or
3.3 Abbreviations:
more of the isotopes present in the sample, the isotopic
3.3.1 CRM—Certified Reference Materials
composition of the sample must be known in advance. The
3.3.2 DU—Depleted Uranium
spike-sample mixture undergoes a valency adjustment,
3.3.3 HEU—High Enriched Uranium
purification, and is then loaded onto a filament and the isotopic
3.3.4 IDMS—Isotope Dilution Mass Spectrometry
composition of the mixture is determined. Using the measured
3.3.5 IRMM—Institute for Reference Materials and Mea-
surements (IRMM is now known as European Commission
The boldface numbers in parentheses refer to the list of references at the end of
Joint Research Centre, JRC-Geel, see 3.3.6) this standard.
C1672 − 23
isotope ratios of the spike-sample mixture, the known isotopic interfere in the measurement of each other, and Am and
composition and amount of spike added to the mixture, and the Pu interfere in the measurement of each other, thereby
isotopic composition of the sample, the elemental concentra- requiring chemical separation. Removal of impurities provides
tion of the sample may be calculated. The IDMS method yield uniform ionization of uranium, plutonium, or americium,
results that are directly traceable to the SI unit of mole, hence improved precision, and reduces the interference from
provided the spike is SI traceable. molecular species of the same mass number as the uranium or
plutonium or americium isotopes being measured. Isotopic
5. Significance and Use
analysis of plutonium should be completed within a reasonable
time after the separation of americium to minimize interference
5.1 The total evaporation method is used to measure the
241 241
isotopic composition of uranium, plutonium, and americium due to Am in-growth from Pu. An example of a pre-
scribed interval limiting the time between sample purification
materials, and may be used to measure the elemental concen-
trations of these elements when employing the IDMS tech- and isotopic analysis is 20 days. For NBL CRMs 136, 137, and
241 239
138 the Pu/ Pu ratio changes by about 0.092 % per week
nique.
because of Pu decay. Instrument users are responsible for
5.2 Uranium and plutonium compounds are used as nuclear
determining a maximum interval between purification and
reactor fuels. In order to be suitable for use as a nuclear fuel the
mass spectrometric analysis, based on an evaluation of Am
starting material must meet certain criteria, such as found in
in-growth from decay of Pu and the accuracy and precision
Specifications C757, C833, C753, C776, C787, C967, C996, or
targets consistent with the data quality objectives of the facility
as specified by the purchaser. The uranium concentration,
241 239
for the Pu/ Pu isotope amount ratio. Other atomic and
plutonium concentration, or both, and isotope abundances are
molecular species may interfere with total evaporation
measured by TIMS following this method.
analyses, particularly if they cause a change in the ionization
5.3 Americium-241 is the decay product of Pu isotope.
efficiency of the analyte during an analysis. Presence of carbon
The abundance of the Am isotope together with the abun-
may disturb total evaporation measurements. It is recom-
dance of the Pu parent isotope can be used to estimate
mended that instrument users perform validation tests on
radio-chronometric age of the Pu material for nuclear forensic
unique or complex samples by mixing known pure standards
applications Ref (6). The americium concentration and isotope
with other constituents to create matrix-matched standards.
abundances are measured by TIMS following this method.
6.2 Precautionary steps must be taken to avoid contamina-
5.4 The total evaporation method allows for a wide range of
tion of the sample by environmental uranium, plutonium, or
sample loading with no significant change in precision or
americium from the analytical laboratory environment. The
accuracy. The method is also suitable for trace-level loadings
level of effort needed to minimize the effect of contamination
with some loss of precision and accuracy. The total evaporation
of the sample should be based upon the sample size, planned
method and modern instrumentation allow for the measure-
handling and processing of the sample, and knowledge of the
ment of minor isotopes using ion counting detectors, while the
levels of contamination present in the laboratory. For very
major isotope(s) is(are) simultaneously measured using Fara-
small uranium, plutonium, or americium samples, extreme
day cup detectors.
measures are often warranted to ensure that the sample is not
5.5 The new generation of miniaturized ion counters allow contaminated. For these samples, residual uranium, plutonium,
or americium in the mass spectrometer and trace uranium in
extremely small samples, in the picogram range, to be mea-
sured via the total evaporation method. The method may be chemicals or containers used for sample storage and processing
employed for measuring environmental or safeguards inspec- or the filaments may bias measurement data.
tion samples containing nanogram quantities of uranium or
6.3 The total evaporation method may generate biases in the
plutonium. Very small loadings require special sample han-
minor isotope ratios, especially when measuring trace amounts
dling and careful evaluation of measurement uncertainties. 234 235
of U in a HEU (highly enriched uranium, U abundance >
5.6 Typical uranium analyses are conducted using sample
20 %) material, or trace amounts of U in a LEU (low
loadings between 50 nanograms and 800 nanograms. For enriched uranium, 1 % < U abundance < 20 %), NU (natural
uranium isotope ratios the total evaporation method had been
or normal uranium, 0.3 % < U abundance < 1 %), or DU
used in several recent NBL isotopic certified reference material (depleted uranium, U abundance < 0.3 %) material with
238 238 239
(CRM) characterizations (for example (2, 3)). A detailed
U, or Pu in the presence of Pu. Biases in the minor
comparison of the total evaporation data on NBL uranium isotope data can occur due to peak tailing from the major
TM
CRMs analyzed by the MAT 261 and TRITON instruments
isotopes. The magnitude of the peak tailing correction is a
is provided in Ref (5). For total evaporation, plutonium function of the design of the instrument and spread in the ion
analyses are generally conducted using sample loads in the
beam due to source design and particle collisions in the
range of 20 to 200 nanograms of plutonium. instrument. The peak tailing may be quantified by measuring
the abundance sensitivity under experimental conditions simi-
6. Interferences
lar to those at which samples are analyzed. A bias correction
6.1 Ions with atomic masses in the uranium, plutonium, and may then be applied based upon the measured abundance
americium ranges cause an interference if they have not been sensitivity. Additionally, the use of an energy filter in conjunc-
removed or if they are generated as part of the chemical tion with an ion counting detector can significantly reduce or
238 238
handling or analysis of the samples. Both U and Pu eliminate peak tailing and allow for accurate measurement of
C1672 − 23
minor isotopes. The use of an energy filter, ultra-high-purity in a multi-collector design. Very small samples may be
filaments and chemicals, effective sample purification, and low measured utilizing a multi-ion counting array.
ionization and evaporation temperatures to minimize U 7.1.6 A pumping system to attain a vacuum of less than 400
-6
interferences can allow for the accurate measurement of μPa (3 × 10 torr) in the source, the analyzer, and the detector
small Pu abundances by this technique. Another commonly regions. The ability to accurately measure minor isotopes is
used method for low abundance Pu measurement is the directly related to analyzer pressure. Analyzer pressures below
-8
alpha-spectrometry technique, following Test Method C1415 approximately 7 μPa (5 × 10 torr) are preferable.
or Practice D3084. 7.1.7 A mechanism to scan masses by varying the magnetic
field and the accelerating voltage.
6.4 The modified total evaporation method, following Test
7.1.8 A computer to automate the instrument operation and
Method C1832, was developed to correct for the peak tailing
to collect and process data produced by the instrument.
interferences at the minor isotopes. It utilizes total evaporation
of larger sample loads of uranium, sample loads of up to 5 7.2 An optical pyrometer is recommended for determining
micrograms are analyzed (7). In this method, the total evapo- filament temperatures.
ration process is interrupted on a regular basis to perform
7.3 Filament preheating/degassing unit for cleaning fila-
measurement of the peak tail intensities for all isotopes of
ments.
interest and for peak centering, focusing, baseline
measurements, inter-calibration of the detectors, etc. As a result
8. Reagents and Materials
of the ability to perform the tailing corrections on the minor
8.1 Purity of Reagents—Reagent grade chemicals shall be
isotopes during the measurement, the precision and accuracy of
used in all tests. Unless otherwise indicated, it is intended that
the minor ratio data from modified total evaporation are
all reagents conform to the specifications of the Committee on
improved without compromising the quality of the major
Analytical Reagents of the American Chemical Society where
isotope ratio data. The modified total evaporation method had
such specifications are available. Other grades may be used,
been used in several recent characterization measurements at
provided it is first ascertained that the reagent is of sufficiently
NBL (2, 3, 8) and IRMM (9) (IRMM is now known as
high purity to permit its use without lessening the accuracy of
JRC-Geel) and shown to yield major isotope data of compa-
the determination. Ultra-high purity reagents may be necessary
rable precision and accuracy as the total evaporation method.
for small samples, samples with extreme ratios, or samples
6.5 Chemical interferences like organics in the sample do
otherwise susceptible to isotope ratio biases from cross-
not directly interfere with the uranium or plutonium isotope
contamination.
ratio measurements. These, however, adversely affect the
8.1.1 For small samples, or samples with extreme ratios, or
precision and accuracy of the runs by changing the ionization
samples otherwise susceptible to biases from cross-
efficiency. To minimize the impact of this factor, samples and
contamination, the level of uranium or plutonium
standards are processed through the same preparation process
contamination, or both, in chemicals, water, and the sample
and are analyzed in similar matrices.
handling environment should be determined to ensure that the
materials used and analytical environment are sufficiently pure
7. Apparatus
for the samples being analyzed.
7.1 Mass Spectrometer—The suitability of mass spectrom-
8.2 Purity of Water—Unless otherwise indicated, references
eters for use with this method of analysis shall be evaluated by
to water shall be understood to mean laboratory accepted
means of performance tests described in this method. The mass
demineralized or deionized water as described by Type I of
spectrometer used should possess the following characteristics:
Specification D1193.
7.1.1 A thermal ionization source capable of analyzing
8.3 Rhenium Filaments—High purity ribbons shall be used,
single or double filaments, or both, of rhenium; tungsten or
the size and configuration are instrument dependent. Tungsten
tantalum may be substituted with minor modifications in the
or tantalum may be substituted with minor modifications to the
procedure.
procedure. Tungsten filaments have been reported to yield
7.1.2 An analyzer radius sufficient to resolve adjacent
higher precision analyses via the total evaporation method.
masses in the mass-to-charge range being studied, that is, m/z
+ + Degassed filaments are preferred. For small samples, the
= 233 to 238 for U or 238 to 244 for Pu or 241 to 243 for
+ amount of uranium in the filaments should be measured to
Am . Resolution greater than 360 (full width at 1 % of peak
-5 ensure that the uranium content of the filament material will
height) and an abundance sensitivity of less than 10 are
not bias sample results. Carburized filaments have been re-
recommended. For minor isotope ratio measurements, lower
ported to yield higher precision using the total evaporation
abundance sensitivity is preferable.
method.
7.1.3 An instrument capable of monitoring ion beam inten-
NOTE 1—The purity of the filaments should be confirmed with each
sity and adjusting filament currents during ion beam integration
is recommended. This reduces the sample loss between inte-
grations due to the time necessary to adjust the filament
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
Standard-Grade Reference Materials, American Chemical Society, Washington,
current.
DC. For suggestions on the testing of reagents not listed by the American Chemical
7.1.4 A mechanism for changing samples.
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
7.1.5 Multiple direct-current detectors (Faraday cups) or a
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
combination of Faraday cups and electron multiplier detector copeial Convention, Inc. (USPC), Rockville, MD.
C1672 − 23
new batch received. Zone refined filaments should be used for low-level
within glove boxes to prevent ingestion/inhalation. After
analyses.
dissolution, smaller aliquots of the americium solutions can be
safely handled in a fume hood or glovebox with filtered air and
9. Reference Materials
use of personal protective equipment.
9.1 Isotopic Reference Materials—Uranium, plutonium, or
10.4 Thermal ionization mass spectrometers operate at elec-
americium standard reference solutions, of varying isotopic
trical potentials of up to 10 kV. Care must be taken to ensure
composition depending on sample. The standard solutions
that high voltage electronics are switched off prior to handling
should preferably be made from CRMs traceable to a national
5 the source or accessing electronic components.
standard body. Examples for uranium isotope reference ma-
10.5 The filaments can reach temperatures in excess of
terials include the NBL U-series CRM’s (for example, U005A,
U010, U030A, U045, U200, U350, U500, U630, U750, U800, 2000 °C, with consequent heating of the filament holders and
of the source region. Allow the turret and source parts to cool
U900, U930, U970), and IRMM materials series IRMM
184–187, the IRMM-074 series, the IRMM-2019-2029 series before handling and exercise caution when adding or removing
filaments/turrets.
(based on UF materials IRMM-019-029) and the IRMM-
3000, IRMM-3000a series. Plutonium isotope reference mate-
10.6 Liquid nitrogen is used in cryogenic cold traps. Shield
rials include the NBL plutonium standards CRM 128, CRM
eyes and face when filling cold traps, and protect hands, torso,
136, CRM 137, and CRM 138, and the IRMM-290, IRMM-
and feet in the event of splashing or spilling of the liquid
290a, and IRMM-290b series. Americium isotope reference
nitrogen.
materials include the IRMM-0243.
9.2 Elemental Concentration and Isotopic Reference Mate- 11. Calibration and Standardization
rials (IDMS Spikes)—Materials of known isotopic and chemi-
11.1 The measurement method may be qualified following
cal composition, preferably CRMs traceable to a national
Guide C1068 and calibrated following Guide C1156. Addi-
standard body, for use in the determination of elemental
tional information regarding calibration of the mass spectrom-
concentration by IDMS. Examples for uranium include NBL
eter in relation to the total evaporation method may be found in
233 238
CRM 111-A ( U spike), CRM 112–A or CRM 115 ( U
Ref (10).
233 235
spike), IRMM 040a ( U spike), and IRMM 054 ( U spike).
11.2 Electronic Performance Check—Modern mass spec-
For plutonium commonly used spike materials are NBL CRM
242 244
trometer instruments normally offer an automated routine
130 ( Pu spike), CRM 131 ( Pu spike), the IRMM 049c/
242 244
which tests the stability and performance of the electronic
d/e/f series ( Pu spikes), IRMM-042a ( Pu spike), the
233 242
systems of the instrument and reports results, flagging systems
IRMM 046b/c series (mixed U and Pu spikes) or IRMM-
or components which are out of specification. Instrument users
0243 ( Am spike).
should perform routine electronic performance checks to
ensure that the instrument meets manufacturer’s specifications
10. Precautions
for stability and performance. The interval between the elec-
10.1 Appropriate precautions should be taken when han-
tronic performance checks should be established based upon
dling radioactive materials. A detailed discussion of the nec-
manufacturer’s recommendation and instrument history.
essary precautions is beyond the scope of this test method.
Personnel involved in the handling of radioactive material 11.3 Mass Calibration—The relationship between the
atomic masses and the magnetic field necessary to direct the
analyses should be familiar with safe handling practices for
these materials and be trained appropriately. The safe handling isotope beam into the detectors shall be updated on a periodic
basis. The interval between mass calibrations is determined by
practices, at a minimum, shall include use of glove boxes or
fume hoods with filtered air and use of personnel protective the instrument manufacturer. The stability of the mass calibra-
tion curve is dependent on the laboratory conditions and may
equipment.
vary between different instruments. It is recommended that a
10.2 Because of the toxicity of plutonium, all operations
mass calibration check be performed prior to each day’s
involving plutonium in the solid state should be performed
analyses.
within glove boxes to prevent ingestion/inhalation of pluto-
11.4 Peak Centering—The peak centering routine is used as
nium. After dissolution, plutonium samples can be handled in
a fume hood or glovebox with filtered air and use of personal a fine adjustment to ensure that the ion beam is centered within
the detector. Peak centering occurs via fine adjustments of the
protective equipment.
accelerating high voltage. Peak centering should be performed
10.3 Because of the toxicity of americium, all operations
as part of the mass calibration, and at the start of each sample
involving americium in the solid state should be performed
analysis.
11.5 Amplifier Gain Calibration—The stability and re-
The sole source of supply of the standards known to the committee at this time
sponse of each Faraday detector amplifier system should be
are: (1) New Brunswick Laboratory Program Office, National Nuclear Security
measured, and differences between amplifier systems compen-
Administration, https://www.energy.gov/nnsa/nbl-program-office and (2) European
Commission Joint Research Centre, Retiesweg 111, B-2440 Geel, Belgium, http://
sated for, via a gain calibration. The gain calibration is
ec.europa.eu/jrc. If you are aware of alternative suppliers, please provide this
normally performed by sequentially applying a stable calibra-
information to ASTM International Headquarters. Your comments will receive
tion signal to the inputs of the different detector channels. The
careful consideration at a meeting of the responsible technical committee, which
you may attend. output of each channel is then normalized to a reference
C1672 − 23
channel to generate a gain calibration factor for each channel. uncertainties. At a minimum, the electronic dead time should
Depending upon the stability of the amplifier system, a gain be performed once per year.
calibration may be performed on a weekly basis or as often as
11.10 Mass Bias Calibration—Even though the sum inte-
prior to each sample analysis. Instrument users may use
grated major isotope ratio data using the total evaporation
historical gain calibration data to evaluate the stability of the
method is minimally biased compared to the certified ratio of
amplifiers to determine appropriate gain calibration frequen-
the CRMs, the major and minor isotope ratios evolve through-
cies.
out the evaporation process (5) due to preferential release of
the lighter isotopes in the early stages of the filament heating
11.6 Amplifier Baseline Calibration—The baselines of the
process. All isotope ratios, major and minor, are affected by
Faraday detector amplifiers, that is, the amplifier response
this process. In theory, if the ionization efficiency and ion
without ion beam to the detector, shall be measured on a
transmission are constant, the total evaporation method should
regular basis and checked for stability. The integration time for
yield mass bias-free ratios. In practice, small mass biases have
the baseline measurement influences the uncertainty of Faraday
been reported for uranium and plutonium isotope ratio mea-
detector measurements, particularly at the lower ion beam
surements using TIMS instruments (2-5, 7-9). Therefore in
intensities. The long-term historical baseline data shall be
several laboratories a mass bias correction on the total evapo-
regularly reviewed by the user to assure that the system
ration data for uranium, plutonium, and americium is per-
performance is within manufacturer specifications and facility
formed. In this case, additional components are included in the
specific quality requirements. Amplifier baseline calibration
uncertainty evaluation to account for the mass bias calibration
should be performed before each analysis day.
uncertainties. When a mass bias correction is performed, a
11.7 Faraday Detector Calibration—The response of indi-
commonly employed method is to measure multiple filament
vidual Faraday cups may differ depending on history of use,
loadings of a certified isotopic reference material in sequence
manufacturing variability or other factors. The relative re-
with replicate loadings for the samples, and calculate a mass
sponse of the Faraday cups should be determined periodically,
bias correction factor based on the deviation of the measured
or at frequencies established based on the data quality objec-
major ratio of the reference material from the certified ratio. A
tives of the facility. The calibration may be performed by mass bias correction factor is then applied to the measured
switching a stable ion beam (the use of Re is suggested due sample ratios. Regardless of the method used, it is important
to ease of generating a very stable ion beam from a blank that the reference materials are treated, prepared, and measured
in exactly the same manner as the samples. For uranium
filament) between a Faraday cup and a reference cup. The
relative gain between detectors can be used to compensate for samples hydrolyzed from uranium hexafluoride, it is recom-
mended that the samples be converted to U O prior to
differences in detector response, or the test can be used to
3 8
dissolution and analysis. Mass bias calibrations are, generally,
ensure that individual detector responses are within appropriate
performed on a turret-by-turret basis.
limits to allow for the necessary level of accuracy for sample
measurements. In either case, the precision and accuracy of the 11.10.1 Calculate the mass bias correction factor, K, for the
detector calibration should be evaluated to ensure that the major ratio as follows:
calibration factor or detector response is of sufficient accuracy
K 5 ~R ⁄ R ! (1)
c m
for sample measurement. A gain calibration should be per-
where:
formed immediately prior to Faraday detector calibration.
K = mass bias correction factor,
11.8 Electron Multiplier/Faraday Intercalibration—When
R = average measured atom ratio for CRM, and
m
using an electron multiplier to measure minor isotopes, a
R = certified atom ratio for the CRM.
c
calibration factor shall be determined to correct for differences
11.10.2 To correct major and minor individual sample
in detector responses. This calibration factor may be deter-
ratios, calculate the appropriate mass bias correction factor
mined by switching a stable beam repeatedly between the ion
based upon the mass difference between isotopes in the
counter and a reference Faraday detector. The measurement
numerator and denominator, and multiply the sample ratio by
uncertainty of this factor should be determined and incorpo-
the applicable mass bias correction factor.
rated into the uncertainty estimates for the sample results. The
frequency at which this calibration should be performed may
11.11 In case a mass bias correction is not performed on the
be established based on the data quality objectives of the
total evaporation data, it is recommended to measure quality
specific task at hand.
control samples, certified reference materials, on a predefined
frequency to ensure that any bias from mass fractionation is
11.9 Electron Multiplier Calibration—Recommended for
insignificant or within the limits specified in the user’s quality
the most accurate measurements of minor isotopes. When
system. See Fig. A1.1 and Fig. A1.2 for examples of control
using an electron multiplier, the electronic dead time and the
charts for U and Pu total evaporation measurements of certified
multiplier linearity should be accounted for. The multiplier
reference materials.
linearity, a function of count rate, may be determined at the
time of multiplier installation, or for the most accurate correc-
11.12 It is emphasized that precision and accuracy achieved
tions should be determined immediately prior to sample in a total evaporation analysis without mass bias correction
analyses. Non-linearity in the electron multiplier should be using an SI traceable CRM is dependent on the method
compensated for when calculating isotope ratios and their parameters such as sample loading, filament heating, etc. and
C1672 − 23
cannot be considered SI-traceable. SI-traceable total evapora- 12.1.2 Prepare the sample and any standard solutions as
tion data can only be obtained through the use of an SI purified nitrates, using identical chemical preparation and
traceable, that is, gravimetrically prepared, CRM for perform- handling steps. The solution concentrations should allow
ing the mass bias correction. convenient filament loading (for example, a 0.1 mg U/mL
solution yields 100 ng of uranium in a 1 μL drop).
11.13 In case a mass bias correction is performed on the
12.1.3 Sample Purification—Use Practice C1411 or similar
total evaporation data according to Eq 1, it is recommended to
procedure to separate uranium and plutonium from each other
measure additional quality control samples, different certified
and from other impurities.
reference materials, on a predefined frequency to ensure that
the mass bias correction applied is correct and under control.
12.2 Filament Loading—Samples may either be directly
See Fig. A1.3 for an example of a control chart for mass bias
loaded on the filament by drop deposition, electroplated onto
corrected Pu total evaporation measurements of a certified
the filament, or loaded onto a resin bead for subsequent
reference material.
mounting on the filament. Samples and standards should be
prepared for analysis by the same method at similar mass
11.14 In cases when no reference materials as mentioned in
loadings. Drop deposition onto the filament can be accom-
9.1 are available, working reference materials (WRM) can be
plished with the use of a microsyringe fitted with a plastic tip
used for quality control purposes, as described in 11.11 and
or with pipettes fitted with disposable tips. The tips should be
11.13.
changed between sample loadings to prevent cross-
11.15 During conventional analyses routinely utilized for
contamination. Typically, 1 μL drops are loaded.
uranium and plutonium isotope ratio measurements (Test
12.3 Sample Conditioning—For filaments loaded by drop
Method C1625), only a portion of the uranium or plutonium
deposition, the solution should be evaporated by passing
released from the sample is utilized for analysis. The mass
sufficient electrical current through the filament to cause gentle
biases at the minor isotope ratios are estimated assuming that
drying without splattering. After the initial drying, a stepped-
the deviations of the major ratio from certified values are due
heating program can be employed to convert samples to
to mass bias effects. Thus, the major ratio values, by definition,
suitable chemical forms. Care should be taken to avoid
are identical to certified ratios. This is explained in detail in (2,
evaporation of the sample or melting of the filament. The use
3) for NBL characterization measurements on isotopic stan-
of an optical pyrometer or salt crystals of varying melting
dards.
points can help to establish the current-to-temperature relation-
11.16 Linearity—The linearity of the mass spectrometer
ship appropriate for the sample loading. Once a suitable
may be determined over the working ratio range by measuring
heating program is established, a programmable power supply
235 238
the U/ U, under identical conditions, of appropriate
may be used to ensure that the conditioning regimens for all
CRMs. The system is linear if the ratio of the certified U/
samples and standards are applied consistently. At different
238 235 238
U ratio to the experimental U/ U is independent of
facilities, different loading and conditioning practices have
isotope ratio. Under ideal conditions, deviations from constant
been established and validated. Each practice shall be applied
values are likely due to nonlinearity. Uranium CRMs are
in a consistent manner for all samples and standards. An
typically used for linearity checks because the range of isotopic
example of sample conditioning program is shown below
compositions observed in safeguards measurements. See Test
(steps 12.3.1 through 12.3.4):
Method C1832 for details on how to perform the linearity test
12.3.1 Ramp electrical current to 0.5 A to 0.7 A and hold
using U CRMs.
until the drop disappears. The aim is to evaporate the liquid
gently without causing splattering.
12. Procedure
12.3.2 Ramp current to 1 A and hold for 2 minutes.
12.1 Sample Preparation:
12.3.3 Ramp current to 1.5 A and hold for 10 s.
12.1.1 Sample Dissolution—Dissolve an appropriate
12.3.4 Ramp current to 2.0 A and hold for 10 s.
amount of the sample to obtain solutions suitable for filament
12.4 Isotopic Ratio Measurement:
loading. See Practice C1347 for the dissolution of uranium or
12.4.1 Insert the filament assembly into the mass spectrom-
Practice C1168 for the dissolution of plutonium. If performing
eter.
isotope dilution mass spectrometry, add the appropriate amount
12.4.2 Seal the source and evacuate to the manufacturer’s
of spike, by weight or volume as appropriate to sample size and
recommended minimum pressure.
desired accuracy, to the previously weighed sample. Spike
12.4.3 Add liquid nitrogen to the cryogenic trap, if desired.
addition and equilibration must be performed prior to chemical
12.4.4 Steps 11.3 through 11.6 may be performed automati-
purification if determining concentration by IDMS.
cally under computer control, depending upon instrument. Very
NOTE 2—Independent of whether known amount of sample is added to
small samples may require manual control to avoid sample
the vial in which known spike amounts are stored or known weights/
loss.
volumes of spike is added to container in which known weights/volumes
of sample are stored, quantitative transfer is critical to avoid biases in the 12.4.5 Perform a gain calibration if desired (see 11.5).
concentration results. Measures to ensure quantitative transfer are rinsing
12.4.6 Perform a baseline (amplifier noise) measurement
the caps of the container in which the sample or spike was stored and
(see 11.6).
transferring the rinsate to the mixture and rinsing the walls of the container
12.4.7 If using the double filament technique, heat the
by slowly adding drops of 8 M nitric acid and transferring the rinsate to
the mixture. ionization filament to a temperature sufficient to provide
C1672 − 23
adequate ionization. Recommended temperature range for
I~ U!
235 (
U
ALL_INTEGRATIONS
uranium is ~1800 °C to 2000 °C, for plutonium is ~1750 °C to
S 238 D
U
I U
TE ~ !
1850 °C, and for Am is 1700 °C to 1800 °C (current required (
ALL_INTEGRATIONS
will depend on the filament material and even for the same type
I U
~ !
of filaments will vary from batch to batch; typical currents ·I~ U!
FS D G
( 238
I~ U!
ALL_INTEGRATIONS
required for U analysis is in the range of 5 A to 5.8 A). In the 5 (2)
I U
187 ~ !
(
absence of an optical pyrometer, the Re beam may be used
ALL_INTEGRATIONS
as an indication of filament temperature. The Re intensity
where:
may provide a more reproducible indication of temperature
235 238 235
I( U) and I( U) = signal intensities (in volt) for U and
than the optical pyrometer.
U measured on Faraday cups, cor-
12.4.8 Slowly heat the sample filament to a temperature
rected for the Faraday cup amplifier
sufficient to yield a small ion beam suitable for focusing and
gains and baselines.
peak centering. Typical temperatures are 1100 °C to 1300 °C
235 238
for americium, 1200 °C to 1400 °C for plutonium, and 1400 °C
13.1.1 According to Eq 2, the U per U ratio is
to 1600 °C for uranium. If available, the ion counter may be calculated as the sum of all U ion beam intensity integra-
used to minimize sample loss during the focusing and peak
tions during the measurement divided by the respective sum of
centering steps. Typical ion intensities for these purposes are a the U ion beam intensity integrations. This is the same as the
235 238
few thousands of counts per second when using the ion
average of all measured I( U) per I( U) signal intensity
counter, or 10 mV to 30 mV when using Faraday cup detectors
ratios during the measurement, weighted by the U ion signal
(connected to 10 Ω amplifiers). Alternatively, the use of the
intensities.
Re beam for focusing purposes is generally acceptable. The use
13.2 For mass spectrometer instruments, measured quanti-
of carburized filaments is recommended if the U (or Pu) beams
ties are isotope ratios. Therefore, control limits for monitoring
are quite high even when the evaporation filament current is
the performance of the analytical method are generally set by
zero.
evaluating the accuracy and precision of isotopic standards
12.4.9 Perform peak centering and focusing of the major
traceable to the
...