ASTM C1133/C1133M-10(2018)

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: C1133/C1133M − 10 (Reapproved 2018)
Standard Test Method for
Nondestructive Assay of Special Nuclear Material in Low-
Density Scrap and Waste by Segmented Passive Gamma-
Ray Scanning
ThisstandardisissuedunderthefixeddesignationC1133/C1133M;thenumberimmediatelyfollowingthedesignationindicatestheyear
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 determine system detection efficiency vs. gamma energy and
thereby calibrate for all gamma-emitting radionuclides of
1.1 This test method covers the transmission-corrected non-
interest (12).
destructive assay (NDA) of gamma-ray emitting special
235 239 1.2.1.1 Efficiency Curve Calibration, over the energy range
nuclear materials (SNMs), most commonly U, Pu,
241 for which the efficiency is defined, has the advantage of
and Am, in low-density scrap or waste, packaged in cylin-
providing calibration for many gamma-emitting nuclides for
drical containers. The method can also be applied to NDA of
which half-life and gamma emission intensity data are avail-
other gamma-emitting nuclides including fission products.
able.
High-resolution gamma-ray spectroscopy is used to detect and
measure the nuclides of interest and to measure and correct for 1.3 Theassaytechniquemaybeapplicabletoloadingsupto
gamma-ray attenuation in a series of horizontal segments several hundred grams of nuclide in a 208-L [55-gal] drum,
(collimated gamma detector views) of the container. Correc- with more restricted ranges to be applicable depending on
tions are also made for counting losses occasioned by signal specific packaging and counting equipment considerations.
processing limitations (1-3).
1.4 Measured transmission values must be available for use
1.2 There are currently several systems in use or under incalculationofsegment-specificattenuationcorrectionsatthe
development for determining the attenuation corrections for energies of analysis.
NDA of radioisotopic materials (4-8). A related technique,
1.5 A related method, SGS with calculated correction fac-
tomographic gamma-ray scanning (TGS), is not included in
tors based on item content and density, is not included in this
this test method (9, 10, 11).
standard.
1.2.1 This test method will cover two implementations of
1.6 The values stated in either SI units or inch-pound units
theSegmentedGammaScanning(SGS)procedure:(1)Isotope
are to be regarded separately as standard. The values stated in
Specific (Mass) Calibration, the original SGS procedure, uses
each system may not be exact equivalents; therefore, each
standards of known radionuclide masses to determine detector
system shall be used independently of the other. Combining
response in a mass versus corrected count rate calibration that
values from the two systems may result in non-conformance
applies only to those specific radionuclides for which it is
with the standard.
calibrated, and (2) Efficiency Curve Calibration, an alternative
1.7 This standard does not purport to address all of the
method, typically uses non-SNM radionuclide sources to
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
ThistestmethodisunderthejurisdictionofASTMCommitteeC26onNuclear
priate safety, health, and environmental practices and deter-
Fuel Cycle and is the direct responsibility of Subcommittee C26.10 on Non
mine the applicability of regulatory limitations prior to use.
Destructive Assay.
Current edition approved April 1, 2018. Published April 2018. Originally
Specific precautionary statements are given in Section 10.
approved in 1996. Last previous edition approved in 2010 as C1133/C1133M–10.
1.8 This international standard was developed in accor-
DOI: 10.1520/C1133_C1133M-10R18.
dance with internationally recognized principles on standard-
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this test method. ization established in the Decision on Principles for the
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1133/C1133M − 10 (2018)
Development of International Standards, Guides and Recom- rate-relatedlossesandattenuationbytheitem.Theappropriate
mendations issued by the World Trade Organization Technical mass or efficiency calibration then provides the relationship
Barriers to Trade (TBT) Committee. between observed gamma-ray intensity and nuclide content.
4.2 Either of two distinct calibration methods can be used:
2. Referenced Documents
4.2.1 Isotope Specific Calibration provides assay results for
2.1 ASTM Standards:
only those radionuclides for which the SGS is specifically
C1030TestMethodforDeterminationofPlutoniumIsotopic
calibrated.Calibrationisperformedusingstandardscontaining
Composition by Gamma-Ray Spectrometry
the radionuclides to be assayed.
C1128Guide for Preparation of Working Reference Materi-
4.2.2 Effıciency Curve Calibration entails determination of
als for Use in Analysis of Nuclear Fuel Cycle Materials
the system detection efficiency as a function of gamma ray
C1156Guide for Establishing Calibration for a Measure-
energy. Analysis of assay data consists of using the energy of
ment Method Used toAnalyze Nuclear Fuel Cycle Mate-
a peak to infer the emitting radionuclide, and then calculating
rials
theradionuclidemassfromthespecificactivityandthegamma
C1207Test Method for Nondestructive Assay of Plutonium
emission intensity of the radionuclide, and the corrected count
in Scrap and Waste by Passive Neutron Coincidence
rate and detector efficiency at the peak energy.
Counting
4.3 The assay item is rotated about its vertical axis and
C1210Guide for Establishing a Measurement System Qual-
scanned segment by segment along that axis, thereby reducing
ity Control Program for Analytical Chemistry Laborato-
the effects of nonuniformity in both matrix density and nuclide
ries Within the Nuclear Industry
distribution (see Fig. 1).
C1215Guide for Preparing and Interpreting Precision and
Bias Statements in Test Method Standards Used in the 4.4 Count rate-dependent losses from pulse pile-up and
Nuclear Industry
analyzer dead time are corrected for by electronic modules, a
C1316Test Method for Nondestructive Assay of Nuclear radioactive source, a pulser, or a combination of these.
Material in Scrap and Waste by Passive-Active Neutron
4.5 The average linear attenuation coefficient of each hori-
Counting Using Cf Shuffler
zontalsegmentiscalculatedbymeasurementofthetransmitted
C1458Test Method for NondestructiveAssay of Plutonium,
intensity of an appropriate external gamma-ray source. The
Tritium and Am by Calorimetric Assay
sourceismounteddirectlyoppositethegamma-raydetector,on
C1490GuidefortheSelection,TrainingandQualificationof
the far side of the assay item (see Fig. 1).
Nondestructive Assay (NDA) Personnel
4.6 Two conditions must be met to optimize SGS assay
C1592/C1592MGuide for Making Quality Nondestructive
results as follows:
Assay Measurements (Withdrawn 2018)
C1673Terminology of C26.10 NondestructiveAssay Meth-
ods
E181Test Methods for Detector Calibration andAnalysis of
Radionuclides
2.2 ANSI Standards:
ANSI/IEEE 325Test Procedures for Germanium Gamma-
Ray Detectors
ANSI N15.36 Measurement Control Program—
Nondestructive Assay Measurement Control and Assur-
ance
3. Terminology
3.1 Refer to Terminology C1673 for terminology defini-
tions.
4. Summary of Test Method
4.1 The assay of the nuclides of interest is accomplished by
measuring the intensity of one or more characteristic gamma
rays from each nuclide. Corrections are made for count
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
the ASTM website.
The last approved version of this historical standard is referenced on
www.astm.org.
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St., FIG. 1 Typical Arrangement for Segmented Gamma-Ray Scan-
4th Floor, New York, NY 10036, http://www.ansi.org. ning
C1133/C1133M − 10 (2018)
4.6.1 The particles containing the nuclides of interest must measurementmethodused.Also,processknowledgeshouldbe
besmallenoughtominimizeself-absorptionofemittedgamma used, when available, as part of a waste management program
radiation (13).
to complement information on item parameters, container
4.6.1.1 Under specific conditions, particles large enough to properties, and the appropriateness of calibration factors.
provide significant self absorption (lumps) may be assayed
5.4 To obtain the lowest detection levels, a two-pass assay
accurately. These conditions include use of specific nuclide
should be used. The two-pass assay also reduces problems
differential peak calibration and calibration using mass stan-
related to potential interferences between transmission peaks
dards that have the same attenuation characteristics over the
and assay peaks. For items with higher activities, a single-pass
energy range used for quantitative measurements as the mate-
assay may be used to increase throughput.
rials to be assayed.
4.6.1.2 An alternative approach to mass calibration with
6. Interferences
standards that contain the same sized particles is to apply
correctionalgorithmsthatarebasedonthedifferentialresponse
6.1 Radionuclides may be present in the assay item that
of two or more peaks at different energies from the same
produce gamma rays with energies that are the same or very
nuclide. For example, the 129 and 414 keV peaks of Pu or
nearly the same as the gamma rays suggested for nuclide or
the 144 and 186 keV peaks of U could be used (see 7.7).
transmission measurement. The areas of the closely spaced
4.6.1.3 The presence of lumps in material being assayed
peaks that are produced in the gamma-ray spectrum cannot be
also can be detected using differential peak response algo-
calculated by simple spectroscopic procedures. Peak fitting
rithms.
software routines may be able to resolve closely spaced peaks
4.6.2 The mixture of material within each item segment
in some cases; alternatively, the nuclide of interest may
must be sufficiently uniform to apply an attenuation correction
produce other gamma rays that may be used for analysis.
factor, generally computed from a measurement of gamma-ray
6.1.1 Thepeakproducedbythe661.6-keVgammarayfrom
transmission through the segment.
Cs would interfere with calculation of the area of the
4.7 Thecorrectedgamma-raycountratesforthenuclidesof
Am peak produced by its 662.4-keV gamma ray. The
interest are determined on a segment-by-segment basis. The
721.9-keV gamma ray of Am may be a useful alternative.
precision of the measured count rate of each gamma ray used
6.1.2 Thepeakproducedbythe765.8-keVgammarayfrom
for analysis is also estimated on a segment-by-segment basis.
95 238
Nb would interfere with calculation of the area of the Pu
At the completion of the measurement of all segments,
peak produced by its 766.4-keV gamma ray. The 786.3-keV
corrected count rates are summed, and mass values for the
gamma ray of Pu may be a useful alternative.
nuclides of interest in the entire container are calculated based
6.1.3 Occasionally, Np is found in the presence of pluto-
either on comparisons to appropriate calibration materials or
237 233
nium. The Np daughter, Pa, emits a gamma ray at 415.8-
from the gamma emission rates determined from the segment
keV along with several gamma rays in the range from 300 to
efficienciesdeterminedovertheenergyrangeofinterest.Based
400 keV. Peaks from these gamma rays would interfere with
on counting statistics for individual segments, precision values
calculation of the area of the Pu peak produced by its
arepropagatedtoobtaintheestimatedprecisionoftheanalysis.
413.7-keV gamma ray and several other often used peaks
4.8 In the event that a single nuclide of an element is
from Pu. In this case, the peak produced by the 129.3-keV
measured and the total element mass is required (for ex-
gamma ray of Pu may be the only reasonable alternative.
ample, Pu and total plutonium), it is common practice to
6.1.4 The peak produced by the 63.1-keV gamma ray
apply a known or estimated nuclide/total element ratio to the
from Yb, sometimes used as the transmission source
nuclide assay value to determine the total element content.
for U assays, may interfere with calculation of the area of
4.8.1 Isotope ratios can be determined using gamma isoto-
the peak produced by the 59.5-keV gamma ray of Am,
pic analysis techniques such as those described inTest Method
which is used as the count rate correction source. The Yb
C1030.
gammaraycanbesufficientlyattenuatedbyplacingacadmium
absorber over the transmission source or the problem can be
5. Significance and Use
avoided altogether by using a two-pass assay. In a two-pass
5.1 Segmented gamma-ray scanning provides a nondestruc-
assay, the first measurement pass measures the intensity of the
tivemeansofmeasuringthenuclidecontentofscrapandwaste
transmission source for each segment. The second measure-
where the specific nature of the matrix and the chemical form 239
ment pass measures the intensity of the 413.7-keV Pu
and relationship between the nuclide and matrix may be
gamma-ray emission from each segment with the transmission
unknown.
source shutter closed.
5.2 The procedure can serve as a diagnostic tool that
6.1.5 Transmission source peaks may have errors intro-
provides a vertical profile of transmission and nuclide concen-
duced by the presence of a radionuclide in the assay material
tration within the item.
that emits gamma rays at or near one or more of the measured
transmission energies. The affected measurements will then be
5.3 Item preparation is generally limited to good waste/
scrap segregation practices that produce relatively homoge- higher than the actual transmissions through the item, leading
neous items that are required for any successful waste/ to calculation of a lower than actual correction factor and
inventory management and assay scheme, regardless of the quantity of measured radionuclide.
C1133/C1133M − 10 (2018)
239 75
6.2 In the case of Pu assays using Se as a transmission fixed absorbers, typically cadmium, tin, or lead, between the
source, random coincident summing of the 136.00 and 279.53- assay item and the detector (see Fig. 1 and 8.2.7).
keV gamma-ray emissions from Se produces a low-intensity
7.4 Radionuclides emitting high-energy radiation will con-
peakat415.5-keVthatinterfereswithcalculationoftheareaof
tribute Compton-continuum under peaks to be used for the
the Pu peak produced by its 413.7-keV gamma ray. The
assay. The Compton-continuum will worsen the estimated
effects of this sum-peak can be reduced by attenuating the
precision calculated from the counting statistics. The assay
radiation from the transmission source to the lowest intensity
235 169
of U is normally performed using Yb as the transmission
required for transmission measurements of acceptable preci-
source. This source provides 177- and 198-keV gamma rays
sion. This problem also can be avoided by making a two-pass
that allow accurate calculation of the transmission at 185.7-
assay. 235
keV,theenergyofthegammarayfrom Unormallyusedfor
6.3 Peaks may appear at the gamma-ray energies used for
assays. The problem of added Compton-continuum from the
analysis when there is no nuclide present on the turntable. The Yb source can be avoided by making a two-pass assay. If the
likely cause is excessive amounts of nuclide stored in the
high-energy gamma rays are from the assay item itself, but not
vicinity of the detector. The preferred solution to this problem from the nuclide of interest, it may be possible to eliminate
is removal of the nuclide from the vicinity and restraint of
them from future assay items by scrap and waste segregation
nuclidemovementsaroundthesystemduringmeasurements.If
procedures.
these conditions cannot be met, sufficient shielding must be
7.5 Ifthetransmissionsourcenuclideoraradionuclidewith
provided to eliminate these peaks. Shielding opposite the
one or more gamma rays of similar energy is in the assay
detector,onthefarsideoftheitemtobeassayed,willalsohelp
material, a two-pass assay allows the passive scan data to be
to reduce the amount of ambient radiation seen by the detector
used as the background for the transmission measurement.
(see Fig. 1).
7.6 Variations in item composition and density within a
7. Sources of Error
segmentleadtoindeterminateerrors.Suchvariationsshouldbe
minimized through appropriate scrap and waste segregation
7.1 Sources of error specifically applicable to segmented
and packaging procedures.
gamma-ray scanning are discussed in this section. General
descriptions of sources of error encountered in gamma-ray
7.7 Some matrix forms may be unsuitable for segmented
nondestructive assay systems can be found in Guide C1592/
gamma-ray analysis procedures.
C1592M and Refs (1, 2, 11, 14, 15, 16, and 17).
7.7.1 Such forms may contain lumps of nuclide, that is,
7.2 The bias in an assay is strongly dependent on how well nuclide contained in small volumes having a localized density
substantially different from the bulk density of the rest of the
theattenuationforeachsegmenthasbeendetermined.Inorder
to determine the attenuation, a radioactive source with a container.The dimensions of nuclide particles that constitute a
lump vary with the energy of the emitted radiation used for the
gamma ray of nearly the same energy as the gamma ray of the
nuclide of interest is positioned directly opposite the gamma- analytical measurement. The possible magnitude of the prob-
lem may be estimated from the following examples. A pluto-
ray detector, on the far side of the assay item (see Table 1 for
suggestednuclide/transmissionsourcecombinationsandFig.1 nium metal sphere 0.02 cm [0.008 in.] in diameter will absorb
approximately 4% of the 414-keV Pu gamma rays pro-
for geometry). At lower energies, where the mass attenuation
duced. Approximately 15% of the 186-keV U gamma rays
coefficient varies rapidly, it is useful to find a source that
produces gamma rays with energies that bracket the energy of will be absorbed in a uranium metal sphere of the same
diameter (13).
thegammarayfromthenuclideofinterest.Athigherenergies,
where the mass attenuation coefficient varies more slowly, a
7.7.2 The presence of lumps of plutonium may be detected
transmission source with a single gamma ray of nearly the and, in some cases, a correction may be made using various
same energy as the nuclide of interest may provide a suffi-
algorithms. The techniques use transmission-corrected assay
ciently accurate determination of attenuation. results for multiple gamma-ray energies from a single nuclide
and a weighting function to account for self-absorption by
7.3 Radionuclides emitting low-energy radiation, espe-
241 lumps. This approach has been used primarily for the analysis
cially Am, may contribute a large fraction of the total count
of Pu,wherethenuclideofinterestsemitsgammaraysover
rate. The low-energy radiation may be reduced by the use of
a range of several hundred keV. The success of the lump
correction calculations is not universal (6-8), however, and the
TABLE 1 Suggested Nuclide/Source Combinations for
technique must be evaluated for specific material streams prior
Segmented Gamma-Ray Assay
to implementation.
Peak Trans- Peak Count Rate Peak
Nuclide Energy, mission Energy, Correction Energy, 7.7.3 Another condition that will cause measurement prob-
keV Source keV Source keV
lems is presented by containers with radically heterogeneous
235 169 241
U 185.7 Yb 177.2, 198.0 Am 59.5
contents having highly variable densities and non-uniform
238 54 137
U 1001.1 Mn 834.8 Cs 661.6
60 activity distributions, that prevent the calculation of a valid
Co 1173.2, 1332.5
237 203 235
Np 311.9 Hg 279.2 U 185.7 attenuation correction based on the transmission measurement.
238 137 133
Pu 766.4 Cs 661.6 Ba 356.3
In the case of such a condition, an analytical method less
239 75 133
Pu 413.7, 129.3 Se 400.1 Ba 356.3
241 75 133 sensitive to nuclide and matrix densities should be used. See
Am 662.4 Se 400.1 Ba 356.3
Test Methods C1207, C1458, and C1316, for example.
C1133/C1133M − 10 (2018)
7.8 Thenatureofthesegmentingprocessleadstoendeffect either a large number of rotations (ten or more) or a small
problems. During counting, the detector’s field of view in the integral number of rotations during the counting period for
vertical direction is larger than the horizontal extensions of the each segment.
top and bottom planes of the collimator (see Fig. 1). Through-
8.2.4 Detector Collimator—Collimator constructed of lead
out most of the item, the results of this overview present no
or tungsten serves to define the detector’s horizontal and
particular problem since calibration procedures effectively
verticalviewinganglesandtoshieldthedetectorfromambient
account for it. However, the top and bottom segments present
radiation. A deep collimator (front to back), along with close
particular problems. If the limits of the scan are set to match
coupling of the collimator and assay item, reduces the vertical
thetopandbottomoftheitemtostraightlineextensionsofthe
viewing angle and improves segmentation. The reduced view-
collimator’s top and bottom planes, the nuclide material in the
ing angle decreases the bias of the attenuation correction and
top and bottom segments is viewed for a period of time 65 to
decreases the severity of end effects. Collimator slit height
1 1
80% as long as nuclide toward the center of the assay item.
should be chosen to be in the range ⁄8 to ⁄16 of the height of
Scanning beyond the end of the item is likely to overestimate
the assay item. The horizontal field of view must include the
the nuclide content of the bottom segment due to the high
entire diameter of the item. Lining the inside of the collimator
density of the turntable itself and underestimate the nuclide
with appropriately-thick sheets of cadmium or tin and copper
contentofthetopsegmentasthedetectorlooksoverthetopof
will eliminate collimator lead X-rays from the spectrum.
the item. One way to decrease this problem involves the
8.2.4.1 Forlargeitems,wherehighefficiencyisrequiredfor
placement of a hollow cylindrical pedestal with high transmis-
reasonable count times, the height of the collimator slit should
sion between the item and the turntable (see Fig. 1), combined
be approximately equal to the diameter of the detector crystal.
with scanning beyond the end of the item on both ends.
In practice, collimator depth/height ratios of two to four for
Another option, more difficult to implement, involves the
208-L [55-gal] drum-sized items are reasonable.
previous two steps along with application of the measured
8.2.4.2 Smalleritemsrequirenarrower(vertical)collimators
attenuation from the nearest item segment, to the appropriate,
to maintain the benefits of accurate attenuation corrections and
overscanned segments (1, 7).
to minimize end effects.Acollimator depth/height ratio of six
to ten is reasonable.
8. Apparatus
8.2.5 Count-Rate Correction Source—Correction source is
8.1 The following considerations apply specifically to seg-
chosen to have gamma-ray emission energies that are lower
mented gamma-ray scanners. General guidelines for the selec-
than the energy of the characteristic gamma ray from the
tion of detectors and signal processing electronics are dis-
nuclideofinterestandthetransmissionsourceinordertoavoid
cussed in Ref (14).
Compton interferences. These sources can be obtained as 5 to
10 µCi, flat plastic wafer, sealed sources, for easy attachment
8.2 Complete hardware and software systems for high-
close to the detector. Recommended sources are listed in Table
resolution, segmented gamma-ray scanning of both large and
1.Acombination of cadmium or tin and copper (closest to the
small items of waste and scrap containing SNM are commer-
detector) foils positioned under the source reduce the effect of
cially available. It is recommended that the system have the
abundantlow-energygammaraysthatarepresentwithsomeof
following components:
thesuggestedcount-ratecorrectionsources.Thepositionofthe
8.2.1 Germanium Detector, with appropriate electronics to
source is adjusted to produce a count rate providing sufficient
handle the required count rates.The choice of optimal detector
precision for the assay times used and then fixed in place.
depends on the application. A detector with diameter greater
235 239
Alternatively, an electronic pulser can be used for count rate
than length is more useful for measurements of Uor Pu.
correction.
Measurements that involve higher energy gamma rays require
a detector with greater length.Adetector that subtends a larger
8.2.6 Transmission Source—Transmissionsourcestrengthis
solid angle around the measurement item is more useful for
selected so the gamma rays penetrate the measurement item
low level waste measurements since it will have larger detec-
and provide reasonable counting precision; consequently it is
tion efficiency. typically considerably stronger than the count-rate correction
8.2.2 Computer—Computer appropriate for control of the source to perform effectively. Ten to 50 mCi sources for small
assay hardware, performance of analysis computations, and item counters and 50 to 300 mCi sources for barrel size
display and storage of the data and results. counters,intheshapeofsmalldiameterrods,arewellsuitedto
8.2.3 Motorized, Vertical Scanning Turntable—Turntable useincylindricalleadortungstenshields.Theseshieldsreduce
capable of accommodating the largest size and weight contain- radiation exposure to workers and collimate the radiation from
ers to be measured is required. For normal analyses, segment the transmission source to a narrow region containing the
sizes between the height of the collimator and one-half the detector. If an assay system is to be calibrated for multiple
collimator height provide sufficient segmentation. The system radionuclides, it may be useful to select a transmission source
should provide acceptable detector-assay item positioning having multiple gamma ray energies (with appropriate relative
accuracy and repeatability (6 0.5% of the range of travel is intensities), and use a suitable method to determine transmis-
commercially available). Both helical or fixed-segment count- sions at the radionuclide analysis energies. Table 1 provides a
ing schemes are acceptable, and either the assay item or the listing of suggested nuclides for use as transmission sources,
detector-collimator and transmission source shield assemblies with the listed nuclides of interest. Because an otherwise
can be moved. The turntable rotational speed should provide appropriate source isotope can be relatively short-lived, it may
C1133/C1133M − 10 (2018)
be necessary to obtain one with an activity considerably above ation and rate-related losses) and summed over all segments of
the optimum to provide for a useful working life. The count an item. The sum is adjusted by the specific activity and
rate of a new source may be attenuated by collimation, gamma ray intensity to determine the radionuclide mass. For
absorbers directly in front of the source, source-to-detector this method, the radioisotopes in the calibration standards are
spacing, or some combination thereof. For the most accurate chosen based on their half-lives and gamma energies and
assaysincasesinwhichthehalf-lifeofthetransmissionsource typically are not the same as the isotopes for which the
isotope is short, a mathematical decay calculation to determine calibration is used. See 11.3.2 through 11.3.11 and 11.3.13
current source strength should be made for each measurement. through 11.3.15.
In the case of assays where gamma-ray peaks from the
9.1.3 Perform calibrations using the same procedures and
transmission source interfere with determination of the area of
conditions that will be used for the assays of actual waste
the gamma-ray peak used for nuclide analysis, peak fitting
items. These include, but are not limited to, electronic
software may be able to resolve overlapping peaks or a
components, peak area determination procedures, procedures
two-pass assay may be used. In cases that employ a two-pass
for the determination of counting losses, segment sizes, ab-
assay, equip the transmission source collimator with a shutter,
sorber foil combinations, collimator arrangements, and mea-
preferably tungsten, to block the transmission source from the
surement geometries. Alternatively, differences between cali-
gamma-ray detector during one of the passes (see Fig. 1).As a
bration and assay geometries can be corrected for by
safety consideration, design such shutters so that, in the event
appropriately calculated correction factors (5).
of a power failure, the shutter will shield the radiation beam
9.1.4 Ref (5)andGuideC1128provideusefulguidelinesfor
automatically.
the preparation and characterization of calibration materials
and calibration procedures and the statistical analysis of data.
8.2.7 Absorber Foils—Foils must generally be used to
reduce the contribution of low-energy gamma rays to the Where there are conflicts among the documents, Ref (5)
reflects information most specific to SGS requirements. Mod-
overall count rate, especially in the assay of Pu. As
mentioned in 7.3, cadmium or tin foils serve to absorb the eling is often used to support the calibration effort.
low-energy gamma rays from the item. For Pu assay, a
9.2 Reference Materials for Isotope Specific Calibration:
series of 0.5-mm [approximately 0.020-in.] cadmium or tin
9.2.1 Prepare calibration items for small item types by
foils can serve for sensitivity versus interference optimization.
uniformly dispersing known masses of stable chemical com-
The use of lead foil is likely to require the additional use of
poundswithaknownisotopicmassfractionoftheradionuclide
cadmium or tin and copper foils as secondary absorbers
of interest throughout a stable diluting medium such as
(closest to the detector) to reduce the intensity of the fluores-
graphite,diatomaceousearth,orcastablesiliconcompounds.It
cent X rays produced in the lead foil.Asingle 1-mm cadmium
is desirable that the gamma-ray transmission through the
or tin foil may be appropriate for U assay. Once a
reference material at the energies of interest be uniform. The
combination is chosen, it cannot be changed without instru-
radioactive material should have a particle size small enough
ment recalibration.
so that the effects of self-attenuation within each particle are
negligible. With this requirement satisfied, choose the best
9. Calibration and Reference Materials
particle size range to form a stable, homogenous mixture with
9.1 Calibration: the diluting material. Although the segmentation procedure
usedbytheinstrumentusuallycompensatesforstratificationof
9.1.1 Isotope Specific (Mass) Calibration of a segmented
the components of the mixture over time, some mixing,
gamma-ray scanning instrument involves using a series of
provided by gently shaking or rolling the container prior to
calibration items to determine the relationship between the
each measurement, may be useful for calibration items con-
observed, corrected count rate of a nuclide’s characteristic
taining powder.
gamma ray and the mass of nuclide known to be present. For
this method, the radioisotope calibrated for is actually present 9.2.2 Construct calibration items for larger item types such
in the calibration standards. With the correction of individual as 208-L[55-gal] drums from modules of matrix material such
segment count rates for rate-related losses and the attenuation as filter paper, fiberglass, etc., wetted with known quantities of
of each segment, a direct proportionality between count rate, solutions containing the nuclide of interest at a known concen-
summedoverallsegmentsofanitem,andtotalnuclidemassis tration. Dry the modules and pack them in plastic bags. Place
obtained. Guide C1156 provides background information use- the modules into the drum in a uniform manner until the drum
ful in developing a calibration plan. See 10.3.2 through is filled. Modules with varying nuclide loadings and varying
10.3.12, 10.3.14, and 10.3.15 for details.
combinationsofmodulesproducearangeofitemloadings.For
purposes of the initial calibration process, the mass of nuclide
9.1.2 Effıciency Calibration of a segmented gamma-ray
in individual modules should be limited so as not to create
scanning instrument involves using calibration standards to
self-attenuating lumps. Where possible, eliminate voids and
determineforeachsegmenttheratiooftheobserved,corrected
small volumes containing high concentrations of nuclide (18,
count rate of each of a number of gamma rays from the
19).
standard to its known emission rate within the segment, and
use these ratios (efficiencies) to define the system detection 9.2.3 For each item geometry, prepare a set of three cali-
efficiency as a function of energy. A detector efficiency value bration items of differing nuclide mass.The mass loadings and
appropriate to the gamma ray energy is then applied to each the gamma-ray transmissions through the calibration items
individual segment corrected count rate (corrected for attenu- should span the ranges expected in the unknowns.
C1133/C1133M − 10 (2018)
9.2.4 In order to evaluate the magnitude of biases that will 10. Precautions
becausedbythedeviationofrealitemsfromidealdistributions
10.1 Safety:
of matrix and nuclide, prepare representative items from
10.1.1 Transuranic materials are both radioactive and toxic.
segregated varieties of scrap and waste materials typical of
Adequate laboratory facilities and safe operating procedures
expected assay items. Vary the spatial distribution of the
must be considered to protect operators from both unnecessary
nuclide from widely dispersed to concentrated in various
exposure to ionizing radiation and contamination while han-
extreme dimensions of the container volume. Comparison of
dling assay items (22).
the assay results for such representative items with the known
10.1.2 The recommended analytical procedures call for the
nuclide masses will indicate the possible range of bias caused
use of radioisotope sources, some with high levels of ionizing
byheterogeneityofnuclideandmatrixmaterialandthatcaused
radiation. Consult a qualified health physicist or radiation
by nuclide location within the item.
safetyprofessionalconcerningexposureproblemsandleaktest
9.2.5 Nuclide particle sizes in assay items may vary from
requirements before handling discrete radioactive sources.
those in the calibration standards, causing variations in the
count rate per gram of nuclide and yielding biased results.An 10.2 Technical:
acceptable alternative to the preparation of special representa-
10.2.1 Prevent counting conditions that may produce spec-
tive standards for calibration and uncertainty estimation mea-
tral distortions. Use pulse pile-up rejection techniques if high
surements is the assay of real items (actual process materials)
count rates are encountered. Use absorbers when appropriate,
by analytical methods less sensitive to particle size problems.
to reduce the intensity of low-energy gamma rays such as the
Theseanalyticalmethodsmaybetotaldissolutionandsolution
59.54-keVemissionof Am(see7.3and8.2.7).Temperature
quantification after completion of the segmented gamma-ray
and humidity fluctuations in the measurement environment
measurements (20), or combined gamma-ray isotopic (Test
may cause gain and zero-level shifts in the gamma-ray spec-
Method C1030) with either calorimetric (Test Method C1458)
trum. Use environmental controls or digital stabilization to
or neutron (Test Methods C1207 and C1316) assay for pluto-
prevent shifts, or use software to monitor the changes in gain
nium materials. In either case, the determination of biases and
and zero level, and adjust the regions of interest accordingly.
total measurement uncertainty (TMU) for these items will
Failure to isolate electronic components from other electrical
require special attention.
equipment or the presence of noise in the ac power also may
produce spectral distortions.
9.3 Reference Materials for Effıciency Curve Calibration:
10.2.2 Locate the instrument in an area with as low a
9.3.1 Radionuclide sources for determining an efficiency
gamma-ray radiation background as possible. Prohibit the
curve are typically multi-isotope sources having multiple
movement of containers of radioactive material in the vicinity
gamma ray energies spanning a broad energy range. The
of the instrument while an assay is underway.
available gamma ray energies should be sufficient to appropri-
ately define the efficiency function over the energy range of
11. Procedure
interest, generally 50 to 2000 keV.
11.1 Optimization of System Physical Parameters:
9.3.2 Line sources prepared by radioisotope source vendors
are often used. Line source uncertainties are generally in the 11.1.1 Adjust the instrument controls to optimize signal
rangeofafewpercentat1standarddeviation.Uncertaintiesin processing and peak analysis functions. Choose the shaping
the data for radionuclide half-lives and gamma ray emission time constant or filter parameter to optimize the trade-off
intensities also contribute to the measurement uncertainty. between improved resolution with longer time constants and
Each of these uncertainties must be included in an uncertainty decreaseddeadtimelosseswithshortertimeconstants.Choose
propagation to determine the total measurement uncertainty of the system gain so that a sufficient number of channels will be
an instrument. The TMU should be determined for each included in peaks to allow visual inspection of peak shapes,
container and material type. without including so many channels that peaks do not develop
into recognizable shapes with expected count rates in planned
9.3.3 Line sources are used by inserting them into
count times.
appropriately-located holes in a cylinder of non-radioactive
matrix material (21). The holes should be small relative to the
11.1.2 Choose collimator sizes that are appropriate to the
size of the cylinder and the cylinder should be rotated during item type to be assayed, using the criteria described in 8.2.4.
counting.
11.1.3 Choose scanning segment sizes that match the item
9.3.3.1 Several methods of source placement and measure- and previously chosen collimator sizes. For normal analyses,
ment can be used: A single measurement using multiple line when stepped segments are used, limit the segment sizes to
sources in a matrix drum, multiple measurements with a single betweentheheightofthecollimatorslitandone-halftheheight
source in a different location for each count with the resulting of the collimator slit. When helically scanned segments are
spectra summed, or multiple sets of sources, each providing used, segments considerably larger than the collimator slit
different gamma ray lines. Each of these methods is used so as height may be used if the transmission does not vary signifi-
tosimulateahomogeneousdistributionofsourceactivityinthe cantly.
matrix (22).
11.1.4 Choose absorber combinations for the detector that
9.3.4 Calibration sources also can be fabricated using tech- match the expected spectral properties of assay items to the
niques described in 9.2. desired conditions for the counting system (see 8.2.7).
C1133/C1133M − 10 (2018)
11.1.5 Select the segment count time to obtain the sensitiv- straight line background subtraction formula given in Eq 1.If
ity and precision required while still allowing practical a different peak calculation method is used, an appropriate
throughput. variance calculation will be required.
11.1.6 Ensure that the turntable rotational speed provides 2 2
NP NP
σ A 5 P1 3B 1 3B (2)
either a large number of rotations (ten or more) or a small ~ ! FS D G FS D G
1 2
2 3NB 2 3NB
1 2
integral number of rotations during the counting period for
where:
each segment.
11.1.7 Position and attenuate the transmission and count- σ (A) = estimated variance of peak area due to counting
rate correction sources to provide sufficient precision for the statistics. All other terms are the same as in Eq 1.
count time chosen.
11.3.4 For each segment, i, correct the nuclide and trans-
11.2 Measurement of Initial System Parameters:
mission net peak areas for count rate-related losses (deadtime
11.2.1 Measure and store for later use, the following basic
andpulsepile-up)basedontheobservedactivitychangeinthe
parameters for system sources and assay item containers:
count-rate correction source. The activity of the count-rate
11.2.1.1 Count-rate correction source intensity and the date
correctionsourcewillbeunaffectedbytheassayofthenuclide.
of measurement.
Any observed decrease in the source count rate during the
11.2.1.2 Unattenuated transmission source intensity, cor-
assay, compared with the count rate when no other sources are
rected for count-rate related losses, and the date of measure-
present, is used to calculate a correction factor to be applied to
ment.
all other peaks used for the analysis.
11.2.1.3 Empty container transmission.
LT
o
11.2.1.4 Establish the minimum acceptable transmission
A ' 5 A 3 (3)
i i
LT
i
source count rate for assays, based on the transmission source
strength and acceptable precision. where:
th
11.2.1.5 Determine the degree of interference between
A ʹ = net nuclide or transmission peak area for the i
i
transmission and nuclide peaks and the need for two-pass
segment corrected for rate-related losses,
assays (most likely to be required for the assay of U, also
A = observednetnuclideortransmissionpeakareaforthe
i
th
possibly with plutonium at low mass loadings).
i segment,
LT = measured net peak area of the count rate correction
o
11.3 Calibration of System:
source with no other sources present, normalized to a
11.3.1 Measure a series of appropriate calibration items
collection time equal to that of A, and
i
containing known quantities of nuclide, prepared as described
LT = observed net peak area of the count rate correction
i
in 9.2.1 through 9.2.3. In some applications, modeling can be
th
source for the i segment.
helpful when insufficient variety of standards is available (23).
11.3.2 While rotating standards, count each, segment by 11.3.5 For each segment, convert the net peak area to a
segment. Net peak areas for nuclide, transmission source, and
countrateandcorrectthenuclidepeakcountratetoaccountfor
count-rate correction source usually may be calculated using
item attenuation. This correction has two components, one
the most basic peak area determination technique, that is, accounting for container attenuation, and the second account-
channel summation and straight line Compton continuum
ing for attenuation due to the container contents (5, 15):
background subtraction, as shown in Eq 1. In this procedure,
A '
i
the background regions should be located, one on each side of CC 5 3CF ~T '! 3CF (4)
i i i can
t
the peak, as near the peak as possible, in areas where the
where:
spectrum is relatively flat.The peak region of interest must not
overlap either of the background regions of interest. CC = totally corrected nuclide peak count rate of the
i
th
the i segment,
NP B B
1 2
th
A 5 P 2 1 (1) A ʹ = net peak area of the i segment, corrected for
F S DG
i
2 NB NB
1 2
rate-related losses (from Eq 3),
th
where:
t = counting time for the i segment,
th
CF(T ʹ) = attenuation correction factor for the i segment
A = net peak area (counts) for nuclide,
i i
due to attenuation by the container contents, and
transmission, and count-rate correction
peaks,
CF = attenuation correction factor due to attenuation
P = total counts in peak region of interest for can
by the container wall.
nuclide, transmission, and count-rate cor-
rection peaks,
11.3.6 Theattenuationcorrectionfactorduetothecontainer
NP =
...