ASTM C1268-94(2000)
(Test Method)Standard Test Method for Quantitative Determination of Americium 241 in Plutonium by Gamma-Ray Spectrometry
Standard Test Method for Quantitative Determination of Americium 241 in Plutonium by Gamma-Ray Spectrometry
SIGNIFICANCE AND USE
This test method allows the determination of americium 241 in a plutonium solution without separation of the americium from the plutonium. It is generally applicable to any solution containing americium 241.
The americium 241 in solid plutonium materials may be determined when these materials are dissolved (see Practice C 1168).
When the plutonium solution contains unacceptable levels of fission products or other materials, this method may be used following a tri-n-octylphosphine oxide (TOPO) extraction, ion exchange or other similar separation techniques (see Test Methods C 758 and C 759).
This test method is less subject to interferences from plutonium than alpha counting since the energy of the gamma ray used for the analysis is better resolved from other gamma rays than the alpha particle energies used for alpha counting.
The minimal sample preparation reduces the amount of sample handling and exposure to the analyst.
This test method is applicable only to homogeneous solutions. This test method is not suitable for solutions containing solids.
Solutions containing as little as 1 × 10 −5 g/L americium 241 may be analyzed using this method. The lower limit depends on the detector used and the counting geometry. Solutions containing high concentrations may be analyzed following an appropriate dilution.
SCOPE
1.1 This test method covers the quantitative determination of americium 241 by gamma-ray spectrometry in plutonium nitrate solution samples that do not contain significant amounts of radioactive fission products or other high specific activity gamma-ray emitters.
1.2 This test method can be used to determine the americium 241 in samples of plutonium metal, oxide and other solid forms, when the solid is appropriately sampled and dissolved.
1.3 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.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:C1268–94 (Reapproved 2000)
Standard Test Method for
Quantitative Determination of Americium 241 in Plutonium
by Gamma-Ray Spectrometry
This standard is issued under the fixed designation C1268; 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 2.2 ANSI Standards:
ANSI N15.20 Guide to Calibrating Nondestructive Assay
1.1 This test method covers the quantitative determination
Systems
of americium 241 by gamma-ray spectrometry in plutonium
ANSI N15.35 Guide to Preparing Calibration Material for
nitratesolutionsamplesthatdonotcontainsignificantamounts
NondestructiveAssaySystemsthatCountPassiveGamma
of radioactive fission products or other high specific activity
Rays
gamma-ray emitters.
ANSI N15.37 Guide to the Automation of Nondestructive
1.2 This test method can be used to determine the ameri-
Assay Systems for Nuclear Material Control
cium 241 in samples of plutonium metal, oxide and other solid
2.3 U.S. Nuclear Regulatory Commission Regulatory
forms, when the solid is appropriately sampled and dissolved.
Guides:
1.3 This standard does not purport to address all of the
Regulatory Guide 5.9, Rev. 2—Guidelines for Germanium
safety concerns, if any, associated with its use. It is the
Spectroscopy Systems for Measurement of Special
responsibility of the user of this standard to establish appro-
Nuclear Materials
priate safety and health practices and determine the applica-
Regulatory Guide 5.53, Rev. 1—Qualification, Calibration,
bility of regulatory limitations prior to use.
and Error Estimation Methods for NondestructiveAssay
2. Referenced Documents
3. Summary of Test Method
2.1 ASTM Standards:
3.1 An aliquot of the sample that contains about 10 to 100
C758 Test Methods for Chemical, Mass Spectrometric,
ng of americium 241 is analyzed by measuring the intensity of
Spectrochemical, Nuclear, and RadiochemicalAnalysis of
the characteristic 59.5 keV gamma ray emitted by americium
Nuclear-Grade Plutonium Metal
241.
C759 Test Methods for Chemical, Mass Spectrometric,
3.2 Multiple sample geometries may be used if an appro-
Spectrochemical, Nuclear, and RadiochemicalAnalysis of
priate calibration for each geometry is made.
Nuclear-Grade Plutonium Nitrate Solutions
2 3.3 The sample geometry must be reproducible. This in-
C859 Terminology Relating to Nuclear Materials
cludes the physical characteristics of the sample container, the
C982 Guide for Selecting Components for Energy Disper-
2 positioningofthesample,andthevolumeofsampleviewedby
sive X-ray Fluorescence (XRF) Systems
the gamma-ray detector.
C1009 Guide for Establishing a Quality Assurance Pro-
3.4 Electronic corrections are made, if required, for the
gram for Analytical Chemistry Laboratories Within the
effects of pulse pile-up and dead time losses due to the activity
Nuclear Industry
of the sample. The necessity of dead time and pulse pile-up
C1168 Practice for Preparation and Dissolution of Pluto-
corrections can be reduced by sample dilution to control count
nium Materials for Analysis
rates.
E181 Methods for Detector Calibration and Analysis of
3.5 Acorrectionismadeforthecontributiontothe59.5keV
Radionuclides
intensity due to gamma rays produced in the decay of uranium
237.
ThistestmethodisunderthejurisdictionofASTMCommitteeC26onNuclear
Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of
Test. Available from American National Standards Institute, 11 W. 42nd St., 13th
Current edition approved June 10, 2000. Published June 1994. Floor, New York, NY 10036.
2 5
Annual Book of ASTM Standards, Vol 12.01. Available from U.S. Nuclear Regulatory Commission, 1717 H ST., NW,
Annual Book of ASTM Standards, Vol 12.02.
Washington, DC 20555.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1268–94 (2000)
3.6 The relationship between the measured gamma-ray 15.37 and NRC Regulatory Guide 5.9. This system should
intensity and the americium 241 content is determined by the include the following items as a minimum.
use of appropriate standards. 6.1.1 Germanium Photon Detector with Integral
Preamplifier—Acoaxial type detector should typically have a
4. Significance and Use full width at half maximum resolution of 850 eVor less at 122
keV and 2.0 keV or less at 1332 keV. A planar type detector
4.1 This test method allows the determination of americium
should typically have a full width at half maximum resolution
241 in a plutonium solution without separation of the ameri-
of 600 eVor less at 122 keV. Consideration should be given to
cium from the plutonium. It is generally applicable to any
the use of a high efficiency detector to enhance the ability to
solution containing americium 241.
analyze low levels of americium.
4.2 Theamericium241insolidplutoniummaterialsmaybe
6.1.2 High Voltage Power Supply—A high voltage power
determined when these materials are dissolved (see Practice
supply with voltage range and current output compatible with
C1168).
the detector selected is required. It is desirable that the voltage
4.3 When the plutonium solution contains unacceptable
output be continuously adjustable.
levels of fission products or other materials, this method may
6.1.3 Nuclear Spectroscopy Amplifier— Select a nuclear
beusedfollowingatri-n-octylphosphineoxide(TOPO)extrac-
spectroscopyamplifierwithpulseshaping,baselinerestoration,
tion, ion exchange or other similar separation techniques (see
and pulse pile-up rejection circuitry.
Test Methods C758 and C759).
6.1.4 Multichannel Pulse Height Analyzer (MCA)—Select
4.4 This test method is less subject to interferences from
an MCAwith a minimum of 2048 channels. It is desirable that
plutonium than alpha counting since the energy of the gamma
the MCA be compatible with computerized operations so that
ray used for the analysis is better resolved from other gamma
data acquisition and analysis may be automated.The analog to
rays than the alpha particle energies used for alpha counting.
digital converter (ADC) associated with the MCAshould have
4.5 The minimal sample preparation reduces the amount of
aclockrateofatleast100MHzandthecapabilityofdigitizing
sample handling and exposure to the analyst.
the input voltage range into a minimum of 2048 channels
4.6 This test method is applicable only to homogeneous
(other types of ADC’s which provide equivalent capabilities
solutions. This test method is not suitable for solutions con-
can be used). TheADC should also have dead time and pulse
taining solids.
−5
pile-up correction capabilities.
4.7 Solutionscontainingaslittleas1 310 g/Lamericium
6.2 Sample Holder, incorporating shielding to limit the
241 may be analyzed using this method. The lower limit
interferences from background radiation sources, is required.
depends on the detector used and the counting geometry.
Collimation to restrict the view of the detector to a portion of
Solutions containing high concentrations may be analyzed
the sample may be required. The sample holder may incorpo-
following an appropriate dilution.
rate more than one sample position. The sample holder shall
provide reproducible positioning for each sample position so
5. Interferences
that a consistent volume or portion of the sample is viewed by
5.1 Thepresenceofotherradioactivenuclidesinthesample
the detector.
or in the vicinity of the detector may produce interferences.
6.3 Sample Vials ofsufficientvolumetocontainthedesired
These may be due to the Compton scattering of high energy
sample as described in 9.2 are required. The sample vials
gamma rays which contribute to the background in the region
shouldbemadeoflowdensitymaterialsandhavereproducible
of interest or from gamma rays with energies close to the
dimensions such as wall thickness and internal diameter. Vials
energies used for the analysis.
with identical dimensions should be used for samples and
5.2 The presence of uranium 237 will interfere if a correc-
standards.
tion is not applied. This interference will lead to an over
estimation of the amount of americium 241 present. This
7. Hazards
interferenceisespeciallypronouncedinplutoniumfromwhich
7.1 Plutonium and americium bearing materials are radio-
the americium has recently been separated.
active and toxic. Adequate laboratory facilities, gloved boxes,
5.3 The presence of radioactive materials in the vicinity of
fume hoods, etc., along with safe techniques must be used in
thegamma-raydetectorwhicharenotinthesamplemaycreate
handlingsamplescontainingthesematerials.Adetaileddiscus-
interferences if detector shielding is not adequate. These
sionofalltheprecautionsnecessaryisbeyondthescopeofthis
interferences may be due to the Compton scattering of high
test method; however, personnel who handle these materials
energy gamma rays which contribute to the background in the
should be familiar with such safe handling practices.
region of interest or from gamma rays with energies close to
7.2 Solutions and solids containing radioactive materials
the energies used for the analysis.
represent a potential for high radiation exposure to personnel
handling them.Appropriate sample shielding, sample handling
6. Apparatus
procedures, and radiation monitoring should be employed to
6.1 High-Resolution Gamma Ray Counting System—Ahigh
ensure personnel protection.
resolution gamma-ray counting system is required. General
8. Calibration and Standardization
guidelines for the selection of detectors and signal processing
electronics are discussed in Guide C982 and NRC Regulatory 8.1 Calibrate the counting system for energy (eV/channel)
Guide 5.9. Data acquisition systems are addressed in ANSI intherange0to300keVusingaradioactivesourceorsources
C1268–94 (2000)
NOTE 1—B and B are dimensionless constants derived from the
which emit gamma rays with well known energies. A pluto-
U Am
half-lives of uranium 237 and americium 241 and the branching ratios of
nium source is an obvious choice. See Methods E181,
the 59.5 and 208 keV gamma rays. The factor (1− B /B ) may be
U Am
ANSIN15.20, and U.S. Regulatory Guide 5.53 for further
neglected for most applications.
guidance.
8.2 Determine the relative detection efficiency (counts/ 10.3 Calculate the amount of americium 241 present in the
emittedgammaray)ofthecountingsysteminthe0to300keV sample using the count rate from 10.2 and the factor in 8.3.
range. Specifically, the efficiency at 59.5 keV and 208 keV
10.4 Using the dilution factor for the sample calculate the
needstobedetermined.SeeMethodsE181,ANSIN15.20and
amount of americium 241 in the original solution.
U.S. Regulatory Guide 5.53 for further guidance.
8.3 The relationship between the mass of americium 241
11. Measurement Control
andthenumberof59.5keVgammaraysisestablishedthrough
11.1 Establish a measurement control program for the
fundamental physics and basic nuclear constants, that is, the
analytical method. Section 12 of Guide C1009 provides
number of 59.5 keV gamma rays/sec/gram americium
further guidance in this area.
241=4.543 310 .
11.2 As a minimum, the following periodic checks should
9. Procedure
be made.
11.2.1 Make a daily check of all instrument settings and of
9.1 If necessary, prepare a plutonium solution from a solid
the energy calibration of the counting system prior to any
sample following the procedure in Practice C1168 or other
measurement or series of measurements.
dissolution procedure.
9.2 Determine the amount of solution and the dilution
11.2.2 Make a daily measurement of the counting room
required to provide 10 to 100 ng of americium 241 in the background. Ideally a measurement of the room background
selected sample volume. The sample volume viewed by the
should be made both before and after any series of americium
detector should be consistent for the samples and standards determinations.
used, regardless of the concentration.
11.2.3 Makeadailymeasurementofanamericiumstandard
9.3 Determine the counting time necessary to achieve the
or sample with a known concentration to provide a measure-
desired statistical counting precision. Samples which contain
ment bias check.
more americium will generally require less time to achieve the
11.2.4 Make weekly replicate measurements of a standard
same statistical precision.
or sample to determine the precision of the measurement
9.4 Quantitatively transfer the predetermined volume of
method.
solution from 9.2 into a sample vial and close.
11.3 It is recommended that control charts and other peri-
9.5 Place the vial in the counting system sample holder and
odic statistical analysis of the precision and bias data be used.
acquire a spectrum. The detector should see a consistent
portion of the sample volume. The same counting geometry
12. Precision and Bias
and sample size as used for the standards must be used.
9.6 Record the sample counting time, sample volume, 12.1 The precision of the assay is a function of counting
statistics. Precision may be improved with increased counting
dilutionfactor,andcountinggeometryusedifmorethanoneis
available. time.
12.2 Variationsinsamplevialgeometryandpositioningwill
10. Calculation
affect the precision of the measurement.
10.1 Using the same methods as used for the calibration,
12.3 Differences in the plutonium and acid concentration
determinethebackgroundcorrectednetcountratesforthe59.5
between the sample and the calibration standards may cause a
keVgammarayandthe208keVgammarayusingthespectral
bias due to self attenuation in the sample.
data acquired in 9.5.
12.4 The calibration of standard sources, including errors
10.2 Calculate the 59.5 keVcounting rate due to americium
introduced in using a standard radioactive solution or aliquot
241 in the sample.
thereof, to prepare a working standard for bias correction may
R ~59!/ D~59! 2 B R ~208!/ D~208!
result in a bias.
obs U obs
R ~59! 5 (1)
Am
1 2 B / B
U Am
12.5 The full energy peak efficiency at a given energy
determined from the calibration function may introduce a bias.
where:
12.6 Errorsinpreparationincludingsampledilution,sample
R (59) = 59.5 keV rate (gamma rays/s) due to ameri-
Am
transfer by pipetting, etc. can result in a bias.
cium 241,
R (59) = measured 59.5 keV rate (counts/s),
12.7 Samples producing high count rates may cause a bias
obs
D (59) = detection efficiency (counts/gamma ray) at
due to dead time losses and pulse pileup. This bias will be
59.5 keV,
dependent on the adequacy of the corrections provided by the
R (208) = measured 208 keV rate (counts/s),
obs pulse p
...
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