ASTM C1268-94(2008)
(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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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 (Reapproved2008)
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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope C1168PracticeforPreparationandDissolutionofPlutonium
Materials for Analysis
1.1 This test method covers the quantitative determination
E181Test Methods for Detector Calibration andAnalysis of
of americium 241 by gamma-ray spectrometry in plutonium
Radionuclides
nitratesolutionsamplesthatdonotcontainsignificantamounts
2.2 ANSI Standards:
of radioactive fission products or other high specific activity
ANSI N15.20Guide to Calibrating Nondestructive Assay
gamma-ray emitters.
Systems
1.2 This test method can be used to determine the ameri-
ANSI N15.35Guide to Preparing Calibration Material for
cium241insamplesofplutoniummetal,oxideandothersolid
NondestructiveAssaySystemsthatCountPassiveGamma
forms, when the solid is appropriately sampled and dissolved.
Rays
1.3 This standard does not purport to address all of the
ANSI N15.37Guide to the Automation of Nondestructive
safety concerns, if any, associated with its use. It is the
Assay Systems for Nuclear Material Control
responsibility of the user of this standard to establish appro-
2.3 U.S. Nuclear Regulatory Commission Regulatory
priate safety and health practices and determine the applica- 5
Guides:
bility of regulatory limitations prior to use.
Regulatory Guide 5.9,Rev. 2—Guidelines for Germanium
Spectroscopy Systems for Measurement of Special
2. Referenced Documents
Nuclear Materials
2.1 ASTM Standards:
Regulatory Guide 5.53,Rev. 1—Qualification, Calibration,
C758Test Methods for Chemical, Mass Spectrometric,
and Error Estimation Methods for NondestructiveAssay
Spectrochemical,Nuclear,andRadiochemicalAnalysisof
Nuclear-Grade Plutonium Metal
3. Summary of Test Method
C759Test Methods for Chemical, Mass Spectrometric,
3.1 An aliquot of the sample that contains about 10 to 100
Spectrochemical,Nuclear,andRadiochemicalAnalysisof
ng of americium 241 is analyzed by measuring the intensity of
Nuclear-Grade Plutonium Nitrate Solutions
the characteristic 59.5 keV gamma ray emitted by americium
C859Terminology Relating to Nuclear Materials
241.
C982 Guide for Selecting Components for Energy-
3.2 Multiple sample geometries may be used if an appro-
Dispersive X-Ray Fluorescence (XRF) Systems (With-
priate calibration for each geometry is made.
drawn 2008)
C1009Guide for Establishing a QualityAssurance Program
3.3 The sample geometry must be reproducible. This in-
forAnalytical Chemistry Laboratories Within the Nuclear cludes the physical characteristics of the sample container, the
Industry
positioningofthesample,andthevolumeofsampleviewedby
the gamma-ray detector.
3.4 Electronic corrections are made, if required, for the
ThistestmethodisunderthejurisdictionofASTMCommitteeC26onNuclear
effectsofpulsepile-upanddeadtimelossesduetotheactivity
Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of
of the sample. The necessity of dead time and pulse pile-up
Test.
Current edition approved Jan. 1, 2008. Published February 2008. Originally corrections can be reduced by sample dilution to control count
approved in 1994. Last previous edition approved in 2000 as C1268–94(2000).
rates.
DOI: 10.1520/C1268-94R08.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
3 5
The last approved version of this historical standard is referenced on Available from U.S. Nuclear Regulatory Commission, 1717 H ST., NW,
www.astm.org. Washington, DC 20555.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1268 − 94 (2008)
3.5 Acorrectionismadeforthecontributiontothe59.5keV 6. Apparatus
intensity due to gamma rays produced in the decay of uranium
6.1 High-Resolution Gamma Ray Counting System—Ahigh
237.
resolution gamma-ray counting system is required. General
guidelines for the selection of detectors and signal processing
3.6 The relationship between the measured gamma-ray
electronics are discussed in Guide C982 and NRC Regulatory
intensity and the americium 241 content is determined by the
Guide 5.9. Data acquisition systems are addressed in ANSI
use of appropriate standards.
15.37 and NRC Regulatory Guide 5.9. This system should
include the following items as a minimum.
4. Significance and Use
6.1.1 Germanium Photon Detector with Integral
4.1 Thistestmethodallowsthedeterminationofamericium
Preamplifier—A coaxial type detector should typically have a
241 in a plutonium solution without separation of the ameri-
fullwidthathalfmaximumresolutionof850eVorlessat122
cium from the plutonium. It is generally applicable to any
keV and 2.0 keV or less at 1332 keV. A planar type detector
solution containing americium 241.
should typically have a full width at half maximum resolution
4.2 Theamericium241insolidplutoniummaterialsmaybe of600eVorlessat122keV.Considerationshouldbegivento
the use of a high efficiency detector to enhance the ability to
determined when these materials are dissolved (see Practice
C1168). analyze low levels of americium.
6.1.2 High Voltage Power Supply—A high voltage power
4.3 When the plutonium solution contains unacceptable
supply with voltage range and current output compatible with
levels of fission products or other materials, this method may
the detector selected is required. It is desirable that the voltage
beusedfollowingatri-n-octylphosphineoxide(TOPO)extrac-
output be continuously adjustable.
tion, ion exchange or other similar separation techniques (see
6.1.3 Nuclear Spectroscopy Amplifier—Select a nuclear
Test Methods C758 and C759).
spectroscopyamplifierwithpulseshaping,baselinerestoration,
4.4 This test method is less subject to interferences from
and pulse pile-up rejection circuitry.
plutonium than alpha counting since the energy of the gamma 6.1.4 Multichannel Pulse Height Analyzer (MCA)—Select
ray used for the analysis is better resolved from other gamma
an MCAwith a minimum of 2048 channels. It is desirable that
rays than the alpha particle energies used for alpha counting.
the MCA be compatible with computerized operations so that
data acquisition and analysis may be automated.The analog to
4.5 The minimal sample preparation reduces the amount of
digital converter (ADC) associated with the MCAshould have
sample handling and exposure to the analyst.
aclockrateofatleast100MHzandthecapabilityofdigitizing
4.6 This test method is applicable only to homogeneous
the input voltage range into a minimum of 2048 channels
solutions. This test method is not suitable for solutions con-
(other types of ADC’s which provide equivalent capabilities
taining solids.
can be used). TheADC should also have dead time and pulse
−5
pile-up correction capabilities.
4.7 Solutionscontainingaslittleas1×10 g/Lamericium
241 may be analyzed using this method. The lower limit 6.2 Sample Holder, incorporating shielding to limit the
depends on the detector used and the counting geometry.
interferences from background radiation sources, is required.
Solutions containing high concentrations may be analyzed Collimation to restrict the view of the detector to a portion of
following an appropriate dilution.
the sample may be required. The sample holder may incorpo-
rate more than one sample position. The sample holder shall
5. Interferences provide reproducible positioning for each sample position so
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 of sufficient volume to contain the desired
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
7. Hazards
estimation of the amount of americium 241 present. This
interferenceisespeciallypronouncedinplutoniumfromwhich
7.1 Plutonium and americium bearing materials are radio-
the americium has recently been separated.
active and toxic. Adequate laboratory facilities, gloved boxes,
fume hoods, etc., along with safe techniques must be used in
5.3 The presence of radioactive materials in the vicinity of
handlingsamplescontainingthesematerials.Adetaileddiscus-
thegamma-raydetectorwhicharenotinthesamplemaycreate
sionofalltheprecautionsnecessaryisbeyondthescopeofthis
interferences if detector shielding is not adequate. These
test method; however, personnel who handle these materials
interferences may be due to the Compton scattering of high
should be familiar with such safe handling practices.
energy gamma rays which contribute to the background in the
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
C1268 − 94 (2008)
handling them.Appropriate sample shielding, sample handling
R (59) = 59.5 keV rate (gamma rays/s) due to americium
Am
procedures, and radiation monitoring should be employed to
241,
ensure personnel protection.
R (59) = measured 59.5 keV rate (counts/s),
obs
D(59) = detection efficiency (counts/gamma ray) at 59.5
8. Calibration and Standardization keV,
R (208) = measured 208 keV rate (counts/s),
obs
8.1 Calibrate the counting system for energy (eV/channel)
D(208) = detection efficiency (counts/gamma ray) at 208
intherange0to300keVusingaradioactivesourceorsources
keV,
which emit gamma rays with well known energies. A pluto-
B = 1.5668, and
U
nium source is an obvious choice. See Methods E181, ANSI
B = 45385.6.
Am
N15.20, and U.S. Regulatory Guide 5.53 for further guidance.
NOTE 1—B and B are dimensionless constants derived from the
U Am
half-lives of uranium 237 and americium 241 and the branching ratios of
8.2 Determine the relative detection efficiency (counts/
the 59.5 and 208 keV gamma rays. The factor (1− B /B ) may be
U Am
emittedgammaray)ofthecountingsysteminthe0to300keV
neglected for most applications.
range. Specifically, the efficiency at 59.5 keV and 208 keV
10.3 Calculate the amount of americium 241 present in the
needs to be determined. See Methods E181,ANSI N15.20 and
sample using the count rate from 10.2 and the factor in 8.3.
U.S. Regulatory Guide 5.53 for further guidance.
10.4 Using the dilution factor for the sample calculate the
8.3 The relationship between the mass of americium 241
amount of americium 241 in the original solution.
andthenumberof59.5keVgammaraysisestablishedthrough
fundamental physics and basic nuclear constants, that is, the
11. Measurement Control
number of 59.5 keV gamma rays/sec/gram americium
241=4.543×10 .
11.1 Establish a measurement control program for the
analyticalmethod.Section12ofGuideC1009providesfurther
9. Procedure
guidance in this area.
9.1 If necessary, prepare a plutonium solution from a solid
11.2 As a minimum, the following periodic checks should
sample following the procedure in Practice C1168 or other
be made.
dissolution procedure.
11.2.1 Make a daily check of all instrument settings and of
the energy calibration of the counting system prior to any
9.2 Determine the amount of solution and the dilution
measurement or series of measurements.
required to provide 10 to 100 ng of americium 241 in the
11.2.2 Make a daily measurement of the counting room
selected sample volume. The sample volume viewed by the
background. Ideally a measurement of the room background
detector should be consistent for the samples and standards
should be made both before and after any series of americium
used, regardless of the concentration.
determinations.
9.3 Determine the counting time necessary to achieve the
11.2.3 Makeadailymeasurementofanamericiumstandard
desired statistical counting precision. Samples which contain
or sample with a known concentration to provide a measure-
more americium will generally require less time to achieve the
ment bias check.
same statistical precision.
11.2.4 Make weekly replicate measurements of a standard
9.4 Quantitatively transfer the predetermined volume of
or sample to determine the precision of the measurement
solution from 9.2 into a sample vial and close.
method.
9.5 Place the vial in the counting system sample holder and
11.3 It is recommended that control charts and other peri-
acquire a spectrum. The detector should see a consistent
odic statistical analysis of the precision and bias data be used.
portion of the sample volume. The same counting geometry
and sample size as used for the standards must be used.
12. Precision and Bias
9.6 Record the sample counting time, sample volume,
12.1 The precision of the assay is a function of counting
dilutionfactor,andcountinggeometryusedifmorethanoneis
statistics. Precision may be improved with increased counting
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 Calculatethe59.5keVcountingrateduetoamericium
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
~ ! ~ ! ~ ! ~ !
obs U obs result in a bias.
R 59 5 (1)
~ !
Am
1 2 B
...
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