ASTM C1207-97

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: C 1207 – 97
Standard Test Method for
Nondestructive Assay of Plutonium in Scrap and Waste by
Passive Neutron Coincidence Counting
This standard is issued under the fixed designation C 1207; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope C 986 Guide for Developing Training Programs in the
Nuclear Fuel Cycle
1.1 This test method describes the nondestructive assay of
C 1009 Guide for Establishing a Quality Assurance Pro-
scrap or waste for plutonium content using passive thermal-
gram for Analytical Chemistry Laboratories Within the
neutron coincidence counting. This test method provides rapid
Nuclear Industry
results and can be applied to a variety of carefully sorted
C 1030 Test Method for Determination of Plutonium Isoto-
materials in containers as large as 208-L drums. The test
238 240 242
pic Composition by Gamma-Ray Spectrometry
method applies to measurements of Pu, Pu, and Pu and
C 1068 Guide for Qualification of Measurement Methods
has been used to assay items whose total plutonium content
by a Laboratory Within the Nuclear Industry
ranges from 0.01 to 6000 g (1).
C 1128 Guide for the Preparation of Working Reference
1.2 This test method requires knowledge of the relative
Materials for Use in the Analysis of Nuclear Fuel Cycle
abundances of the plutonium isotopes to determine the total
Materials
plutonium mass.
C 1133 Standard Test Method for NDA of Special Nuclear
1.3 This test method may not be applicable to the assay of
Material in Low Density Scrap and Waste by Segmented
scrap or waste containing other spontaneously fissioning nu-
Passive Gamma-Ray Scanning
clides.
C 1156 Guide for Establishing Calibration for a Measure-
1.3.1 This test method may give biased results for measure-
ment Method Used to Analyze Cycle Materials
ments of containers that include large amounts of hydrogenous
C 1210 Guide for Establishing a Measurement System
materials.
Quality Control Program for Analytical Chemistry Labo-
1.3.2 The techniques described in this test method have
ratories within the Nuclear Industry
been applied to materials other than scrap and waste (2, 3).
C 1215 Guide for Preparing and Interpreting Precision and
1.4 This test method assumes the use of shift-register-based
Bias Statements in Test Method Standards Used in the
coincidence technology (4).
Nuclear Industry
1.5 Several other techniques that are related to passive
2.2 ANSI Standards:
neutron coincidence counting are under development. These
ANSI 15.20 Guide to Calibrating Nondestructive Assay
include neutron multiplicity counting (5,6), add-a-source
Systems
analysis (7), and cosmic-ray rejection (8). Discussions of these
ANSI 15.35 Guide to Preparing Calibration Materials for
techniques are not included in this method.
NDA Systems that Count Passive Gamma-Rays
1.6 This standard does not purport to address all of the
ANSI 15.36 Nondestructive Assay Measurement Control
safety concerns, if any, associated with its use. It is the
and Assurance
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3. Terminology
bility of regulatory limitations prior to use.
The following definitions are needed in addition to those
presented in ASTM C 859.
2. Referenced Documents
3.1 Definitions:
2.1 ASTM Standards:
3 3.1.1 (a,n) reactions—occur when energetic alpha particles
C 859 Terminology Relating to Nuclear Materials
collide with low atomic number nuclei, such as O, F, or Mg,
producing single neutrons.
3.1.2 coincidence Gate Length—the time interval following
This practice is under the jurisdiction of ASTM Committee C-26 on Nuclear
Fuel Cycle and is the direct responsibility of Subcommittee C26.10 on Nondestruc-
the detection of a neutron during which additional neutrons are
tive Assay.
considered to be in coincidence with the original neutron.
Current edition approved June 10, 1997. Published August 1998. Originally
published as C 1207–91. Last previous edition C 1207–91.
The boldface numbers in parentheses refer to the list of references at the end of
4 nd th
this test method. Available from American National Standards Institute, 11 W. 42 St., 13
Annual Book of ASTM Standards, Vol 12.01. Floor, New York, NY 10036.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 1207
3.1.3 coincident neutrons—two or more neutrons emitted the probability of detecting a neutron as a function of time and
simultaneously from a single event, such as from a nucleus illustrates the time intervals discussed.
during fission. 3.1.9.1 Shift-register-based coincidence circuit—an elec-
3.1.4 Die–away time—the average life time of the neutron tronic circuit for determining totals t, reals plus accidentals (r
population as measured from the time of emission to detection, + a), and accidentals (a) in a selected count time t (9, 10). Shift
escape, or absorption. The average life time is the time required register-based circuitry was developed to reduce dead times in
for the neutron population to decrease by a factor of 1/e. It is thermal neutron coincidence counters. This technique permits
a function of several parameters including chamber design, improved measurement precision and operation at higher count
detector design, assay item characteristics, and neutron energy. rate ($ 100kHz).
3.1.5 item—an item refers to the entire scrap or waste 3.1.9.2 totals t—the total number of neutrons detected
container being measured and its contents. during the count time. This is a measured quantity.
3.1.6 matrix—the material which comprises the bulk of the 3.1.9.3 reals plus accidents, (r + a)—the number of neu-
item, except for the special nuclear material and the container. trons detected in the (r+a) gate period (Fig. 1) following the
This is the material in which the special nuclear material is initial detection of each neutron. This is a measured quantity
embedded. during the count time (4, 9).
3.1.6.1 benign matrix—a matrix that has negligible effects 3.1.9.4 accidentals, (a)—the number of neutrons detected in
on neutron transport. A benign matrix includes very little the (a) gate period (Fig. 1) following the initial detection of
neutron moderator. each neutron during the selected count time t. This is a
3.1.6.2 matrix–specific calibration—uses a calibration ma- measured quantity (4, 9).
trix similar to the matrix to be measured. No matrix correction 3.1.9.5 Reals, (r)—This quantity is the difference between
factors are used. This calibration is generally not appropriate the (r+a) and (a) quantities (4,9). It is proportional to the
for other matrices. number of fissions in the sample.
3.1.7 neutron absorbers—materials which have relatively 3.1.10 Neutron multiplication—Multiplication takes place
large thermal-neutron absorption cross sections. Absorbers when a neutron interaction yields more than one neutron as a
with the largest cross sections are commonly known as neutron product. Induced fission is the primary mechanism for neutron
poisons. Some examples are lithium, boron, cadmium, and multiplication, however (n,2n) interactions are also multiplica-
gadolinium. tion events.
3.1.8 neutron moderators—materials which slow down 3.1.11 poisson assumption—For passive neutron coinci-
neutrons through elastic scattering. Materials containing large dence measurements, it is assumed that the net counts in a fixed
amounts of low atomic weight materials, e.g. hydrogen are period of time follow a Poisson distribution. This assumption
highly moderating. can be verified by comparing the observed standard deviation
3.1.9 passive neutron coincidence counting—a technique of a series of measurements on an item with the square root of
used to measure the rate of coincident neutron emission in the the average number of counts. If the Poisson assumption is
assay item. The terminology used in this test method refers correct, these numbers should be equal within random error.
specifically to shift-register electronics (9, 10). Fig. 1 shows 3.1.12 Precision—The precision of a measurement is taken
NOTE 1—Curve (a) is a simplified probability distribution showing the approximately exponential decay, as a function of time, for detecting a second
neutron from a single fission event. The probability for detecting a random neutron is constant with time. Typical coincidence timing parameters are shown
in (b).
FIG. 1 Probability of Detection as a Function of Time
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 1207
to be the standard deviation or (percent) relative standard should be uniform with respect to size, shape, and composition
deviation of a series of measurements taken on the same item of the container. Each material category will require calibration
under essentially the same conditions. standards and may have different plutonium mass limits.
3.1.13 Pre-delay—the coincidence circuit has a pre-delay 5.4 Bias in passive neutron coincidence measurements is
immediately after a neutron has been detected to allow the related to item size and density, the homogeneity and compo-
amplifiers to recover and prepare to detect subsequent neu- sition of the matrix, and the quantity and distribution of the
trons. This principle is shown in Fig. 1. nuclear material. The precision of the measurement results is
240 240
Pu effective mass, m —is the mass of Pu that would related to the quantity of nuclear material, the (a,n) reaction
eff
produce the same coincident neutron response in the instru- rate, and the count time of the measurement.
ment as the assay item. It is correlated to the quantity of even 5.4.1 For both benign matrix and matrix specific measure-
mass isotopes of plutonium in the assay item (11). ments, the method assumes the calibration reference materials
3.1.15 transuranic waste (TRU waste)—as defined in DOE match the items to be measured with respect to the homoge-
Order 5820.2 (12), transuranic waste is radioactive waste neity and composition of the matrix, the neutron moderator and
containing alpha-emitting isotopes with atomic number greater absorber content, and the quantity of nuclear material, to the
than 92 and half-life greater than 20 years, and with activity extent they affect the measurement.
concentrations greater than 100 nCi per gram of waste at the 5.4.2 Measurements of smaller containers containing scrap
time of the measurement. and waste are generally more accurate than measurements of
208-L (55-gal) drums.
4. Summary of Test Method
5.4.3 It is recommended that measurements be made on
4.1 The even mass isotopes of plutonium fission spontane- items with homogeneous contents. Heterogeneity in the distri-
ously. On the average, two or more neutrons are emitted per
bution of nuclear material, neutron moderators, and neutron
fission event. The number of these coincident neutrons de- absorbers have the potential to cause biased results.
tected by the instrument is correlated to the quantity of even
5.5 The coincident neutron production rates measured by
mass isotopes of plutonium in the assay item, m . The total this test method are proportional to the mass of the even
eff
plutonium mass is determined from the known plutonium
number isotopes of plutonium. If the relative abundances of
isotopic ratios and the measured quantity of even mass these isotopes are not accurately known, biases in the total
isotopes.
plutonium assay value will result.
4.2 The shift register technology is intended to correct for
5.6 A typical count time is 1000 seconds.
the effects of accidental neutrons.
5.7 Reliable results from the application of this method
4.3 Other factors which may affect the assay are multipli-
require training of the personnel who package the scrap and
cation and matrix components with large (a, n) reaction rates,
waste prior to measurement and of personnel who perform the
neutron absorbers, or moderators. Corrections for these effects
measurements. Training guidance is available from ANSI
are often not possible from the measurement data alone,
15.20, ASTM C 1009, ASTM C 986, and ASTM C 1068.
consequently assay items are sorted into material categories or
6. Interferences
additional information is used to obtain the best assay result.
6.1 Conditions affecting measurement uncertainty include
4.4 Corrections are typically made for electronic deadtime
neutron background, moderators, multiplication, large (a,n)
and neutron background.
rates, absorbers, matrix and nuclear material heterogeneity, and
4.5 Calibrations are based on measurements of well docu-
other sources of coincident neutrons. It is usually not possible
mented and appropriate reference materials.
to detect these problems or to calculate corrections for these
4.6 This method includes measurement control tests to
effects from the measurement data alone. Consequently, assay
verify reliable and stable performance of the instrument.
items are sorted into material categories defined on the basis of
5. Significance and Use
these effects.
5.1 This test method is useful for determining the plutonium 6.2 Neutron background levels from external sources should
content of scrap and waste in containers as large as 208-L be kept as low and as constant as practical. Corrections can be
(55-gal) drums. Total plutonium content ranges from 10 mg to made for the effects of high-neutron background levels, but
6kg (1). The upper limit may be restricted to smaller mass these will adversely affect measurement precision and detec-
values depending on specific matrix, calibration material, tion limits.
criticality safety, or counting equipment considerations. 6.3 Neutron moderation by low atomic mass materials will
5.2 This test method is applicable for U.S. Department of not only increase thermal-neutron absorption effects, but will
Energy shipper/receiver confirmatory measurements (13), also increase multiplication effects. Consequently, the mea-
nuclear material diversion detection, and International Atomic sured neutron rates may be either smaller or larger than those
Energy Agency attributes measurements (14). for a nonmoderating matrix. Hydrogenous matrices contribute
5.3 This test method should be used in c
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