ASTM C1221-92(1998)
(Test Method)Standard Test Method for Nondestructive Analysis of Special Nuclear Materials in Homogeneous Solutions by Gamma-Ray Spectrometry
Standard Test Method for Nondestructive Analysis of Special Nuclear Materials in Homogeneous Solutions by Gamma-Ray Spectrometry
SCOPE
1.1 This test method is applicable to the determination of the concentration of gamma-ray emitting special nuclear materials dissolved in homogeneous solutions. The test method corrects for gamma-ray attenuation by the sample and its container by measurement of the transmission of a beam of gamma rays from an external source (Refs. (1), (2), and (3)).
1.2 Two sample geometries, slab and cylinder, are considered. The sample container that determines the geometry may be either a removable or a fixed geometry container. This test method is limited to sample containers having walls or a top and bottom of equal transmission through which the gamma rays from the external transmission correction source must pass.
1.3 This test method is typically applied to radionuclide concentrations ranging from a few mg/L to several hundred g/L. The assay range will be a function of the specific activity of the nuclide of interest, the physical characteristics of the sample container, counting equipment considerations, assay gamma-ray energies, sample matrix, gamma-ray branching ratios, and interferences.
1.4 This standard does not purport to address all of the safety problems, 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. For specific hazards, see Section 8.
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Designation: C 1221 – 92 (Reapproved 1998)
Standard Test Method for
Nondestructive Analysis of Special Nuclear Materials in
Homogeneous Solutions by Gamma-Ray Spectrometry
This standard is issued under the fixed designation C 1221; 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 1168 Practice for Preparation and Dissolution of Pluto-
nium Materials for Analysis
1.1 This test method is applicable to the determination of
E 181 General Methods for Detector Calibration and Analy-
the concentration of gamma-ray emitting special nuclear ma-
sis of Radionuclides
terials dissolved in homogeneous solutions. The test method
2.2 ANSI Standards:
corrects for gamma-ray attenuation by the sample and its
ANSI N15.20 Guide to Calibrating Nondestructive Assay
container by measurement of the transmission of a beam of
Systems
gamma rays from an external source (Refs. (1), (2), and (3)).
ANSI N15.35 Guide to Preparing Calibration Material for
1.2 Two sample geometries, slab and cylinder, are consid-
Nondestructive Assay Systems that Count Passive Gamma
ered. The sample container that determines the geometry may
Rays
be either a removable or a fixed geometry container. This test
ANSI N15.37 Guide to the Automation of Nondestructive
method is limited to sample containers having walls or a top
Assay Systems for Nuclear Material Control
and bottom of equal transmission through which the gamma
ANSI/IEEE 645 Test Procedures for High-Purity Germa-
rays from the external transmission correction source must
nium Detectors for Ionizing Radiation
pass.
2.3 U.S. Nuclear Regulatory Commission Regulatory
1.3 This test method is typically applied to radionuclide
Guides:
concentrations ranging from a few mg/L to several hundred
Regulatory Guide 5.9, Rev. 2, Guidelines for Germanium
g/L. The assay range will be a function of the specific activity
Spectroscopy Systems for Measurement of Special
of the nuclide of interest, the physical characteristics of the
Nuclear Materials
sample container, counting equipment considerations, assay
Regulatory Guide 5.53, Rev. 1, Qualification, Calibration,
gamma-ray energies, sample matrix, gamma-ray branching
and Error Estimation Methods for Nondestructive Assay
ratios, and interferences.
1.4 This standard does not purport to address all of the
3. Terminology
safety problems, if any, associated with its use. It is the
3.1 For definitions of terms used in this test method, refer to
responsibility of the user of this standard to establish appro-
Terminology C 859.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. For specific
4. Summary of Test Method
hazards, see Section 9.
4.1 Many nuclear materials spontaneously emit gamma rays
with energies and intensities characteristic of the decaying
2. Referenced Documents
nuclide. The analysis for these nuclear materials is accom-
2.1 ASTM Standards:
3 plished by selecting appropriate gamma rays and measuring
C 859 Terminology Relating to Nuclear Materials
their intensity to identify and quantify the nuclide.
C 982 Guide for Selecting Components for Energy Disper-
3 4.1.1 The gamma-ray spectrum of a portion of solution is
sive X-Ray Fluorescence (XRF) Systems
obtained with a collimated, high resolution gamma-ray detec-
C 1133 Test Method for Nondestructive Assay of Special
tor.
Nuclear Material in Low Density Scrap and Waste by
4.1.2 Count-rate-dependent losses are determined and cor-
Segmented Passive Gamma-Ray Scanning
rections are made for these losses.
4.1.3 A correction factor for gamma-ray attenuation in the
This test method is under the jurisdiction of ASTM Committee C-26 on Nuclear sample and its container is determined from the measurement
Fuel Cycle and is the direct responsibility of Subcommittee C26.10 on Non-
Destructive Assay.
Current edition approved Nov. 15, 1992. Published July 1993. Annual Book of ASTM Standards, Vol 12.02.
2 5
The boldface numbers in parentheses refer to the list of references at the end of Available from American National Standards Institute, 11 W. 42nd St., 13th Fl.,
this test method. New York, NY 10036.
3 6
Annual Book of ASTM Standards, Vol 12.01. Available from U.S. Nuclear Regulatory Commission, Washington, DC 20555.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 1221
of the transmitted intensity of an external gamma-ray source.
The gamma rays from the external source have energies close
to those of the assay gamma rays emitted from the sample.
Figs. 1 and 2 illustrate typical transmission source, sample, and
detector configurations. Gamma rays useful for assays of U
and Pu are listed in Table 1.
4.1.4 The relationship between the measured gamma-ray
intensity and the nuclide concentration (the calibration con-
stant) is determined by use of appropriate standards (ANSI
N15.20, ANSI N15.35, USNRC Regulatory Guide 5.53, Rev.
1).
4.2 In the event that the total element concentration is
desired and only one isotope of an element is determined (for
example, Pu), the isotopic ratios must be measured or
estimated.
NOTE 1—The sample geometry in this case is a slab. (Not to scale.)
5. Significance and Use FIG. 2 Schematic of an Uplooking Configuration
5.1 This test method is a nondestructive means of determin-
TABLE 1 Suggested Nuclide/Source Combinations
ing the nuclide concentration of a solution for special nuclear
Count
material accountancy, nuclear safety, and process control.
Peak Peak Peak
Transmission Rate
5.2 It is assumed that the nuclide to be analyzed is in a Nuclide Energy Energy Energy
Source Correction
(keV) (keV) (keV)
homogeneous solution (Practice C 1168).
Source
5.3 The transmission correction makes the test method 235 169 241
U 185.7 Yb 177.2 Am 59.5
198.0
independent of matrix and useful over several orders of
239 75 133
Pu 413.7 Se 400.1 Ba 356.3
magnitude of nuclide concentrations. However, a typical con-
239 57 109
Pu 129.3 Co 122.1 Cd 88.0
figuration will normally span only two to three orders of
136.5
magnitude.
5.4 The test method assumes that the sample-detector ge-
nearly the same as the gamma rays suggested for nuclide
ometry is the same for all measured items. This can be
measurement, count rate correction, or transmission correction.
accomplished by requiring that the liquid height in the side-
Thus, the corresponding peaks in the gamma-ray spectrum may
looking geometry exceeds the detector field of view defined by
be unresolved and their areas may not be easily determined
the collimator. For the uplooking geometry, a fixed sample fill
unless multiplet fitting techniques are used. In some cases the
height must be maintained and vials of identical radii must be
nuclide of interest may emit other gamma rays which can be
used unless the vial radius exceeds the field of view defined by
used for analysis or alternative transmission or count rate
the collimator.
correction sources may be used.
5.5 Since gamma-ray systems can be automated, the test
6.1.1 Occasionally, a significant amount of Np is found in
method can be rapid, reliable and not labor intensive.
237 233
a plutonium sample. The Np daughter, Pa, emits a gamma
5.6 This test method may be applicable to in-line or off-line
ray at 415.8 keV as well as other gamma rays in the 300 to 400
situations.
keV region. These Pa gamma rays may interfere with the
6. Interferences
analysis of Pu at 413.7 keV and at several other normally
useful Pu gamma-ray energies. In this case, the Pu gamma
6.1 Radionuclides may be present in the sample which
ray at 129.3 keV may be a reasonable alternative. In addition,
produce gamma rays with energies that are the same or very
the 398.7 keV gamma ray from Pa may interfere with the
transmission corrections based on the 400.7 keV Se gamma-
ray measurements. Multiplet fitting techniques can resolve
these problems.
169 235
6.1.2 Yb, used as the transmission source for U assays,
emits a 63.1 keV gamma ray which may interfere with the
measurement of the area of the peak produced by the 59.5 keV
gamma ray of Am, which is commonly used as the count
rate correction source. The 63.1 keV Yb gamma ray should
be attenuated by placing a cadmium absorber over the trans-
mission source. Cd may be a suitable alternative count rate
correction source.
239 75
6.1.3 In the special case of Pu assays using Se as a
transmission source, random coincident summing of the 136.0
NOTE 1—The sample geometry may be either cylindrical or a slab. (Not
and 279.5 keV gamma-ray emissions from Se produces a low
to scale.)
FIG. 1 Schematic of a Sidelooking Configuration intensity sum peak at 415.5 keV that interferes with the peak
C 1221
area calculation for the peak produced by the 413.7 keV creased count rate losses and sum peak interferences. An
gamma ray from Pu. The effects of this sum peak interfer- absorber should be fixed between the source and detector to
ence can be reduced by using absorbers to attenuate the reduce the number of low energy X-rays detected.
radiation from the Se to the lowest intensity required for
transmission measurements of acceptable precision. The prob-
7. Apparatus
lem can be avoided entirely by making two separate measure-
7.1 General guidelines for selection of detectors and signal-
ments on each sample; first, measure the peak area of the
processing electronics are discussed in Guide C 982 and NRC
transmission source with the sample in place and second,
Regulatory Guide 5.9, Rev. 2. Data acquisition systems are
measure the peak area of the assay gamma ray while the
considered in ANSI N15.37 and NRC Regulatory Guide 5.9,
detector is shielded from the transmission source.
Rev. 2. It is recommended that the system have the following
239 241
6.1.4 In Pu solutions with high activities of Am or
components:
237U, or both, the Compton continuum from intense 208.0 keV
7.1.1 High Resolution, Germanium, Gamma-Ray
gamma rays may make the 129.3 keV gamma ray from Pu
Detector—A coaxial-type detector with full width at half
unusable for assays. Also, the 416.0 keV sum peak that results
maximum (FWHM) resolution typically less than 850 keV at
from pileup of the 208.0 keV gamma rays may interfere with
122 keV and less than 2.0 keV at 1333 keV may be used for the
the 413.7 keV gamma ray from Pu. Use an absorber (for
analysis. A planar-type detector with resolution typically less
example, 0.5 to 0.8 mm of tungsten) between the detector and
than 600 keV FWHM at 122 keV may also be used. The stated
sample to attenuate the 208.0 keV gamma rays. This will
resolutions are for guidance only. The selection of detector
attenuate the intensity of the lower energy gamma rays and also
type, coaxial or planar, should be based on the usual consid-
reduce the sum peak interference. The resulting Pu assay
erations of efficiency and resolution required for the specific
will be based on the 413.7 keV gamma ray.
application. Test procedures for detectors are given in Method
6.1.5 X-rays of approximately 88 keV from lead in the
E 181 and ANSI/IEEE 645.
shielding may interfere with the measurement of the 88.0 keV
7.1.2 Nuclear Spectroscopy Amplifier—The amplifier capa-
gamma-ray peak when Cd is used as the count rate correc-
bilities should include selectable pulse shaping time constants,
tion source. Graded shielding (4) is required to remove the
pole zero adjustment, active gated baseline restoration, and
interference.
pulse pileup rejection. A discussion of these functions is found
6.2 Peaks may appear in the spectrum at gamma-ray ener-
in Guide C 982.
gies used for analysis when there is no sample present. This
7.1.3 Oscilloscope, required for proper adjustment of the
may be caused by excessive amounts of radioactive material
various amplifier controls and troubleshooting the electronics.
stored in the vicinity of the detector or by contamination of the
The oscilloscope should have selectable time bases ranging
instrument. This can cause variable and unacceptably high
from 1 ms/cm to 0.5 μs/cm (20 MHz) and selectable vertical
backgrounds leading to poor measurement quality.
sensitivities ranging from 5 V/cm to 10 mV/cm.
6.2.1 Remove unnecessary radioactive material from the
7.1.4 High Voltage Bias Supply, equipped with continuously
vicinity and also restrain movement of radioactive material
adjustable voltage control with a voltage range compatible with
around the assay area during measurements. Shielding should
the requirements of the above detector.
be provided that completely surrounds the detector with the
7.1.5 Count-Rate Meter, to monitor the total electronic
exception of the collimator opening. Shielding opposite the
pulse rate in the system for acceptable rate. It should be
detector on the far side of the sample will also reduce the
compatible with the output of the above amplifier.
amount of ambient radiation incident on the detector.
7.1.6 Multichannel Analyzer (MCA)—An MCA with a
6.2.2 Use sample containers that are free of outer surface
minimum of 4096 data channels is recommended. The analyzer
contamination. Remove any contamination from the instru-
should operate using a Wilkinson type analog-to-digital con-
ment which may interfere with analyses. It may not be possible
verter (ADC) with a minimum ADC clock rate of 100 MHz, or
to completely decontaminate in-line instrumentation. In this
a fixed conversion time ADC with a maximum conversion time
case the contamination should be minimized to the extent
of 10 μs. Anti-coincidence gating for pulse-pile-up rejection,
practical.
compatible with the above amplifier, and signal level discrimi-
6.2.3 The measurement of background should be made at
nation may be required. Analyzer control, data transfer, and
various times during the day. Varying backgrounds can be
data analysis by computer are recommended. Spectrum display
caused by process activities which often occur on regular
may be provided by the analyzer or computer.
schedules. These time-dependent backgrounds might not be
7.1.7 Digital Spectrum Stabilizer—The stabilizer monitors
detected if the background is checked at the same time each
two separate gamma rays, one at low energy and one at high
day.
energy, to control changes in both zero intercept and energy
6.3 High energy gamma rays from fission products in the
gain. The stabilizer must be compatible with the ADC/MCA
sample will increase the Compton background and d
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