ASTM C1514-02
(Test Method)Standard Test Method for Measurement of 235U Fraction using the Enrichment Meter Principle
Standard Test Method for Measurement of <sup>235</sup>U Fraction using the Enrichment Meter Principle
SIGNIFICANCE AND USE
The enrichment meter principle provides a nondestructive measurement of the 235U fraction of uranium-bearing items. Sampling is not required and no waste is generated, minimizing exposure to hazardous materials and resulting in reduced sampling error.
Use of a low resolution detector (e.g., NaI detector) to measure uranium with 235U fraction approximately 10 % which is contained in a thin-walled container can provide a rapid (typically 100 s), easily portable measurement system with precision of 0.6 % and bias of less than 1 %.
Use of a high resolution detector (e.g., high-purity germanium) can provide measurement with a precision better than 0.2 % and a bias less than 1 % within a 300-sec measurement time when measuring uranium with 235U fraction in the range of 0.711 % to 4.46 % which is contained in thin-walled containers.
In order to obtain optimum results using this method, the chemical composition of the item must be well known, the container wall must permit transmission of the 185.7 keV gamma ray, and the uranium-bearing material within the item must be infinitely thick with respect to the 185.7 keV gamma ray.
Items must be homogeneous with respect to both 235U fraction and chemical composition.
The uranium-bearing materials in the measured items and calibration reference materials used for calibration must fill the detector field of view.
When measuring items, using low-resolution detectors, in thin-walled containers that have not reached secular equilibrium, either the method should not be used, additional corrections should be made to account for the age of the uranium, or high-resolution measurements should be performed.
The method is typically used as a verification technique, not to establish enrichment.
SCOPE
1.1 This test method covers the quantitative determination of the fraction of 235U in uranium using measurement of the 185.7 keV gamma ray produced during the decay of 235U.
1.2 This test method is applicable to items containing homogeneous uranium-bearing materials of known chemical composition in which the compound is considered infinitely thick with respect to 185.7 keV gamma rays.
1.3 This test method can be used for the entire range of 235U fraction, from depleted (0.2 % 235U) to very highly enriched (97.5 % 235U).
1.4 Measurement of items that have not reached secular equilibrium between 238U and 234Th, may not produce the stated bias when low-resolution detectors are used with the computational method listed in Appendix B.
1.5 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:C1514–02
Standard Test Method for
Measurement of U Fraction using the Enrichment Meter
Principle
This standard is issued under the fixed designation C1514; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.4 Weight Percent—The ratio of the weight of a given
isotope (e.g., U) to the total weight of an element (e.g.,
1.1 This test method covers the quantitative determination
uranium), expressed as a percentage.
of the fraction of U in uranium using measurement of the
185.7 keV gamma ray produced during the decay of U.
4. Summary of Test Method
1.2 This test method is applicable to items containing
4.1 The test method consists of measuring the emission rate
homogeneous uranium-bearing materials of known chemical
of 185.7 keV gamma rays from an item and correlating that
composition in which the compound is considered infinitely
emission rate with the enrichment of the uranium contained in
thick with respect to 185.7 keV gamma rays.
235 the item.
1.3 Thistestmethodcanbeusedfortheentirerangeof U
4.2 Calibration is achieved using reference materials of
fraction, from depleted (0.2% U) to very highly enriched
known enrichment. Corrections are made for attenuating ma-
(97.5% U).
terials present between the uranium-bearing material and the
1.4 Measurement of items that have not reached secular
238 234
detector and for chemical compounds different from the
equilibrium between U and Th, may not produce the
calibration reference materials used for calibration.
stated bias when low-resolution detectors are used with the
4.3 The measured items must completely fill the field of
computational method listed in Appendix B.
view of the detector, and must contain a uranium-bearing
1.5 This standard may involve hazardous materials, opera-
material which is infinitely thick with respect to the 185.7 keV
tions, and equipment. This standard does not purport to
gamma ray.
address all of the safety concerns, if any, associated with its
use. It is the responsibility of the user of this standard to
5. Significance and Use
establish appropriate safety and health practices and deter-
5.1 The enrichment meter principle provides a nondestruc-
mine the applicability of regulatory limitations prior to use.
tive measurement of the U fraction of uranium-bearing
items. Sampling is not required and no waste is generated,
2. Referenced Documents
minimizing exposure to hazardous materials and resulting in
2.1 ASTM Standards:
reduced sampling error.
C 982 Standard Guide for Selecting Components for
5.2 Use of a low resolution detector (e.g., NaI detector) to
Energy-Dispersive X-Ray Fluorescence (XRF) Systems
measure uranium with U fraction approximately 10%
3. Terminology which is contained in a thin-walled container can provide a
rapid (typically 100 s), easily portable measurement system
3.1 Infinite thickness—The thickness of a material which is
with precision of 0.6% and bias of less than 1%.
at least seven mean free paths for 185.7 keVgamma rays (i.e.,
5.3 Use of a high resolution detector (e.g., high-purity
the minimum thickness which will attenuate 99.9% of 185.7
germanium) can provide measurement with a precision better
keV gamma rays incident on the compound).
than 0.2% and a bias less than 1% within a 300-sec measure-
3.2 Enrichment—The fraction of U relative to total ura-
ment time when measuring uranium with U fraction in the
nium in an item, typically expressed as a weight percentage.
range of 0.711% to 4.46% which is contained in thin-walled
3.3 Atom Percent—The ratio of the number of atoms of a
containers.
given isotope (e.g., U) to the total number of atoms of an
5.4 In order to obtain optimum results using this method,
element (e.g., uranium), expressed as a percentage.
the chemical composition of the item must be well known, the
container wall must permit transmission of the 185.7 keV
ThistestmethodisunderthejurisdictionofASTMCommitteeC26onNuclear
gamma ray, and the uranium-bearing material within the item
Fuel Cycle and is the direct responsibility of Subcommittee C26.10 on Non
must be infinitely thick with respect to the 185.7 keV gamma
Destructive Assay.
ray.
Current edition approved Jan. 10, 2002. Published May 2002.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1514
5.5 Items must be homogeneous with respect to both U include detector backshielding, an ultrasonic thickness gauge,
fraction and chemical composition. an oscilloscope, a spectrum stabilizer, a computer, and a
printer.
5.6 The uranium-bearing materials in the measured items
andcalibrationreferencematerialsusedforcalibrationmustfill 7.1 A high-resolution detector system or a low-resolution
detectorsystemshouldbeselected,dependingonprecisionand
the detector field of view.
5.7 When measuring items, using low-resolution detectors, bias requirements for the measurements. Additional detector
selection considerations are measurement time, cost, and ease
in thin-walled containers that have not reached secular equi-
librium, either the method should not be used, additional of use. Because they are cooled using liquid nitrogen, high-
resolution detector systems are larger, heavier, and somewhat
corrections should be made to account for the age of the
uranium, or high-resolution measurements should be per- more difficult to use than low-resolution detector systems. In
addition, the cost of high-resolution detectors is significantly
formed.
higher (roughly an order of magnitude) than the cost of
5.8 Themethodistypicallyusedasaverificationtechnique,
low-resolution detectors. High-resolution systems, however,
not to establish enrichment.
provide better results than low-resolution systems, and elimi-
nate some interferences.
6. Interferences
7.1.1 High-resolution detector. A high-resolution detector
6.1 Appropriate corrections must be made for attenuating
with a resolution of 2000 eV or better, full width at half
materials present between the uranium-bearing material and
maximum, at 122 keV is recommended. Either a planar or
the detector. Inappropriate correction for this effect can result
coaxialdetectorcanbeused,althoughexcessivedeadtimecan
in significant biases.
resultifacoaxialdetectorwithhigh(>15%)efficiencyisused.
6.2 Incorrect knowledge of chemical form of the uranium-
The selected detector should be of sufficient size (including a
bearing materials can result in a bias.
combination of surface area and thickness) to provide the
6.3 Depending on the dead-time correction method used,
desired counting-statistics based uncertainty within a reason-
excessive dead time can cause errors in live time correction
able counting time.
and, thus, result in a measurement bias. Excessive dead time
7.1.2 Low-resolution detector. A low-resolution detector
can usually be eliminated by modifications to the detector
with the following specifications is recommended: a 5-cm
collimator and aperture.
diam, 1.25-cm thick or larger detector with a resolution of
6.4 Background gamma rays near 185.7 keV can result in a
15% or better at 122 keV.
bias. Table 1 is a list of interfering gamma rays which may
7.1.3 Other system components. Specifications for ampli-
cause an interference.
fier, high-voltage bias supply, multi-channel analyzer, and
6.5 Any impurities present in the measured items must be
other components of the system are provided in C982.
homogeneously distributed and well characterized. The pres-
7.1.4 Collimator and Shield Assembly. The detector colli-
ence of impurities, at concentrations which can measurably
mator and shield assembly must be of sufficient thickness to
attenuate the 185.7 keV gamma ray and which are not
attenuate in excess of 99.9% of the 185.7 keV gamma rays
accounted for will result in a bias.
incident upon it. The detector collimator must also block in
6.6 The presence of radioactive impurities can affect the
excess of 99.9% of the gamma rays incident upon it and the
determination of the 185.7 keV peak area. This type of
aperture must restrict the field of view of the detector so that
interference is most often encountered in low-resolution mea-
the uranium in the measured items and calibration reference
surement, but can affect high-resolution measurements.
materials used for calibration completely fill the detector field
of view. A filter (typically fabricated from cadmium or tin)
7. Apparatus
may, optionally, be included to reduce the intensity of gamma-
Gamma-Ray Detector System. General guidelines for selec-
induced X rays from the collimator and shield assembly.
tion of detectors and signal-processing electronics are dis- 7.2 Preparation of Apparatus
cussed in Guide C982 and NRC Regulatory Guide 5.9, Rev. 2
7.2.1 Pole zero. Prior to the use of the detector system, the
(1). This system typically consists of a gamma-ray detector,
pole zero should be adjusted per manufacturer’s instructions.
spectroscopy grade amplifier, high-voltage bias supply, multi-
7.2.2 Gain. After setting the pole zero, set the gain so that
channelanalyzer,anddetectorcollimator.Thesystemmayalso
the 185.7 keV peak is well within the observable spectrum.
Depending on the software used for analysis, peak position
may not be arbitrary.
TABLE 1 Interfering Gamma Rays 7.2.3 Other parameters. Other detection parameters (e.g.,
threshold, zero level) should be configured as described in
Isotope Parent Gamma-Ray Energy (keV) Measurement Affected
Ra N/A 185.9 High Resolution, Low C982.
Resolution
212 232
Pb U 238.6 Low Resolution 8. Hazards
224 232
Ra U 241.0 Low Resolution
8.1 Gamma-raydetectorsmayusepower-supplyvoltagesas
233 237
Pa Np 300.1 Low Resolution
high as 5 kV. Appropriate precautions should be taken when
233 237
Pa Np 311.9 Low Resolution
234 238 using, assembling, and disassembling these systems.
Th U Bremsstrahlung Low Resolution
8.2 Collimators and shielding may use materials (e.g., lead
Tc N/A Bremsstrahlung Low Resolution
and cadmium) which are considered hazardous and/or toxic
C1514
and can be physically heavy and difficult to maneuver. Proper 10. Procedure
care in their use and disposal are required.
10.1 Measurement Control. Prior to the measurement of
8.3 Uranium-bearing materials present both chemical and
unknown items, local measurement control procedures should
radiological hazards. The analyst should be aware of these
be followed. Good measurement practice includes, at a mini-
hazards and take appropriate precautions.
mum, the measurement of an item used as a control source at
the start and end of each day of measurements.The source can
9. Calibration
be a calibration reference material or an item which is
maintained in inventory for the purpose of measurement
9.1 Two types of reference materials are typically used for
control, and does not change. The results of these measure-
performing calibration measurements (1) certified reference
ments should be evaluated each day of measurement, using a
materials, and (2) reference materials. Certified reference
valid statistical technique (e.g., control charting) to assess
materials are preferred for calibration of high resolution
control.
measurement systems. Containers in the same configuration as
10.2 Place the detector collimator in contact with the
the items to be measured are preferred for low resolution
container of the item to be measured, with the item in front of
measurements.
the detector. The uranium-bearing material within the mea-
9.1.1 Certified reference materials are available which have
sureditemmustcompletelyfillthefieldofviewofthedetector.
been fabricated for the primary purpose of calibration of
10.3 Measure the item for a sufficient amount of time to
gamma-ray systems for enrichment measurements using the
obtainthedesiredprecisionforthenetpeakarea.Theprecision
enrichment meter principle. These materials are available in
for the net peak area should be smaller than the target overall
the range of U fraction from 0.31% to 4.46%. High
measurement system uncertainty.
resolution measurement systems are typically calibrated using
10.4 Obtain the wall thickness and material type of the
these reference materials.
item’s container.
9.1.2 Secondary reference materials can be fabricated by
10.5 Recordtheidentifierforthemeasureditem,thetypeof
analyzing for enrichment using destructive analysis techniques
uranium-bearing material contained in the item, the counting
which have been calibrated with NIST traceable reference
time used, the net peak area and its uncertainty (or the
materials. Low-resolution measurement systems are typically
information needed to compute the net peak area and its
calibrated using these secondary reference materials.
uncertainty), and the wall thickness and material. Other infor-
9.2 Place the container to be used for calibration in contact
mation can be recorded as desired. The area for the 185.7 keV
with the detector collimator, with the uranium in the reference
peak must be determined using the same method as was used
material filling the detector field of view.
for calibration (peak fitting or regions of interest).
9.3 Measure the reference material for a sufficient amount
10.6 Compute the attenuation correction factor and its
of time to obtain the desired precision for the net peak area.
uncertainty using equations shown in Annex A1.
The precision for the net peak area should be smaller (a factor
10.7 Compute the enrichment and the measurement uncer-
of ten is recommended) than the target overall measurement
tainty using equations shown in Annex A1 or Annex A2, as
system uncertainty.
appropriate.
9.4 Record the identifier for the measured item, the type of
uranium-bearing material contained in the item, the counting
11. Precision and Bias
time used, the net peak area and its uncertainty (or the
Precision and bias are dependent on several factors, includ-
information needed to compute the net peak area and its
ing (but not limited to): measurement time, accuracy of wall
uncertainty), and the wall thickness and material. Other infor-
thickness correction factor determination, wall thickness, pu-
mation can be recorded as desired. The area for the 185.7 keV
rity of the measured items, collimation, and calibration uncer-
peakcanbedeterminedusingpeakfittingorregionsofinterest.
tainty. Because measurement precision is closely related to
Ifregionsofinterestareusedtodeterminetheareaofthe185.7
counting statistics, to a large degree, the measurement tech-
keV peak,
...
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