ASTM C1189-95(2001)
(Guide)Standard Guide to Procedures for Calibrating Automatic Pedestrian SNM Monitors
Standard Guide to Procedures for Calibrating Automatic Pedestrian SNM Monitors
SCOPE
1.1 This guide covers calibrating the energy response of the radiation detectors and setting the discriminator and alarm thresholds used in automatic pedestrian special nuclear material (SNM) monitors.
1.2 Automatic pedestrian SNM Monitors and their application are described in Guide C 1112, which suggests that the monitors be calibrated and tested when installed and that, thereafter, the calibration should be checked and the monitor tested with SNM at three-month intervals.
1.3 Dependable operation of SNM monitors rests, in part, on an effective program to test, calibrate, and maintain them. The procedures and methods described in this guide may help both to achieve dependable operation and obtain timely warning of misoperation.
1.4 This guide can be used in conjunction with other ASTM standards. illustrates the relationship between calibration and other procedures described in standard guides, and it also shows how the guides relate to an SNM monitor user. The guides below the user in the figure deal with routine procedures for operational monitors. Note that Guide C 993 is an in-plant performance evaluation that is used to verify acceptable detection of SNM after a monitor is calibrated. The guides shown above the user in give information on applying SNM monitors (C 1112) and on evaluating SNM monitors (C 1169) to provide comparative information on monitor performance.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: C 1189 – 95 (Reapproved 2001)
Standard Guide to
Procedures for Calibrating Automatic Pedestrian SNM
Monitors
This standard is issued under the fixed designation C 1189; 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
1.1 This guide covers calibrating the energy response of the
radiation detectors and setting the discriminator and alarm
thresholds used in automatic pedestrian special nuclear mate-
rial (SNM) monitors.
1.2 Automatic pedestrian SNM Monitors and their applica-
tion are described in Guide C 1112, which suggests that the
monitors be calibrated and tested when installed and that,
thereafter, the calibration should be checked and the monitor
tested with SNM at three-month intervals.
1.3 Dependable operation of SNM monitors rests, in part,
on an effective program to test, calibrate, and maintain them.
The procedures and methods described in this guide may help
both to achieve dependable operation and obtain timely warn-
ing of misoperation.
1.4 This guide can be used in conjunction with other ASTM
standards. Fig. 1 illustrates the relationship between calibration
FIG. 1 The Relationship of Calibration to Other Procedures
and other procedures described in standard guides, and it also
Described in Standard Guides for SNM Monitors
shows how the guides relate to an SNM monitor user. The
guides below the user in the figure deal with routine procedures
for operational monitors. Note that Guide C 993 is an in-plant
E 876 Practice for Use of Statistics in the Evaluation of
performance evaluation that is used to verify acceptable
Spectrometric Data
detection of SNM after a monitor is calibrated. The guides
3. Terminology
shown above the user in Fig. 1 give information on applying
SNM monitors (C 1112) and on evaluating SNM monitors
3.1 Definitions of Terms Specific to This Standard:
(C 1169) to provide comparative information on monitor
3.1.1 calibration—a multistep procedure that uniformly
performance.
adjusts the energy response of a monitor’s detector array and
sets the operating parameters of its detection circuits for
2. Referenced Documents
optimum performance. In a few monitors, an additional analog
2.1 ASTM Standards:
adjustment of a signal detection circuit is required.
C 859 Terminology Relating to Nuclear Materials
3.1.2 SNM—special nuclear material: plutonium of any
C 993 Guide for In-Plant Performance Evaluation of Auto-
isotopic composition, U, or enriched uranium as defined in
matic Pedestrian SNM Monitors
Terminology C 859.
C 1112 Guide for Application of Radiation Monitors to the
3.1.2.1 Discussion—This term is used here to describe both
Control and Physical Security of Special Nuclear Material
SNM and strategic SNM, which is plutonium, uranium-233,
C 1169 Guide for Laboratory Evaluation of Automatic Pe-
and uranium enriched to 20% or more in the U isotope.
destrian SNM Monitor Performance
3.1.3 SNM Monitor—a radiation detection system that mea-
sures ambient radiation intensity, determines an alarm thresh-
old from the result, and then when it monitors, sounds an alarm
This guide is under the jurisdiction of ASTM Committee C–26 on Nuclear Fuel
Cycle and is the direct responsibility of Subcommittee C26.12 on Safeguard if its measured radiation intensity exceeds the threshold.
Applications.
Current edition approved Sept. 10, 1995. Published November 1995. Originally
published as C 1189 – 91. Last previous edition C 1189 – 91.
2 3
Annual Book of ASTM Standards, Vol 12.01. Annual Book of ASTM Standards, Vol 03.06.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 1189
3.1.3.1 Discussion—The automatic pedestrian SNM moni- 7.2.1 Inorganic Scintillation Detectors, such as sodium
tor discussed here is a walk-through or wait-in portal or iodide [NaI(T1)], detect gamma rays but have little response to
monitoring booth. neutrons from SNM. This detector is useful for detecting
unshielded SNM.
4. Summary of Guide
7.2.2 Neutron Proportional Counters, containing BF
4.1 This guide covers various instructions for calibrating
or He as a converter gas, detect thermal neutrons and are used
SNM pedestrian monitors for optimum performance in normal
with a moderator to thermalize fast neutrons from SNM. This
operation. The order of procedures is as follows.
detector is useful for detecting unshielded or shielded pluto-
4.1.1 The energy response of inorganic or organic scintilla-
nium.
tion detectors or of neutron proportional counters, is calibrated
7.2.3 Organic Scintillators, detect both gamma rays and fast
to produce appropriate signal pulse heights for SNM radiation
neutrons from SNM. This detector is useful for detecting
(see Section 10).
unshielded SNM and shielded plutonium.
4.1.2 The monitor’s pulse height discriminators are cali-
7.3 Oscilloscope or Multi-Channel Analyzer, for viewing
brated to form a region of interest containing SNM radiation
reference detector pulses produced by a specific radiation
from highly enriched uranium or low-burnup plutonium (see
source during energy calibration.
Sections 9 and 11), or for detecting neutrons in proportional
7.3.1 Gamma-Ray Detectors, reference pulses from 662-
counters (see Section 9).
keV gamma rays emitted by a Cs source with a nominal
4.1.3 The monitor’s transient signal detection logic is ad-
8-microCurie (0.3-kBq) activity are used for calibration.
justed for appropriate response to walk-through or wait-in
7.3.2 Neutron Proportional Counters, reference pulses from
monitoring (see Section 12).
neutrons emitted by a Cf neutron source with less than
4.2 This guide covers adjusting various thresholds used in
2 3 10 neutron/s (0.009-μg) source strength can be used for
SNM monitors.
calibration.
4.2.1 This guide describes setting background alarm thresh-
NOTE 1—Acquisition, storage, and use of sources should be under the
olds that may be used to announce loss of detection sensitivity
guidance of a responsible radiation safety officer (see Section 8 on
or detector failure (see Section 13).
hazards).
4.2.2 This guide discusses setting the lowest practical dis-
7.4 Manufacturer’s or Designer’s Operation and Mainte-
criminator levels for the radiation detectors (see Section 11).
nance Manual, essential for quick and efficient monitor cali-
4.3 When calibration is complete, the monitor should be
bration. The manufacturer’s suggested calibration scheme is a
tested using in-plant evaluation procedures described in Guide
good starting place, if not the best approach to calibration.
C 993.
Calibration requires knowledge of test point and adjustment
5. Significance and Use
locations that should be described in the manuals.
5.1 SNM monitors are an effective means to search pedes-
trians for concealed SNM. Maintaining monitor effectiveness 8. Hazards
rests on appropriate calibration and adjustment being part of a
8.1 Make sure that the use of radioactive materials is under
continuing maintenance program.
the guidance of a responsible radiation safety officer who can
5.2 The significance of this guide for monitor users who
provide any needed radiation safety training, personnel dosim-
must detect SNM is to describe calibration and adjustment
etry, and handling procedures for radiation sources.
procedures for the purpose.
8.2 The radiation detectors in SNM monitors all operate at
5.3 The significance of this guide for monitor manufacturers
high voltages that may be hazardous. Although a person is not
is to describe calibration procedures, particularly for detecting
usually exposed to high voltage during calibration, make sure
forms of SNM that may not be readily available to them.
that the work is performed with the approval of a responsible
safety officer with proper attention given to electrical safety
6. Interferences
training and reading any warnings of high voltage exposure in
6.1 The monitor should be in proper operating condition
manuals or posted on equipment.
when calibrated. Any indication that the monitor does not stay
in calibration or that it drifts substantially during the interval
9. Pulse-Height Analysis Calibration
between calibration checks is cause for repair or renovation
9.1 Once a monitor’s detector array is adjusted to uniform
and then recalibration.
pulse height, the pulse-height analysis circuitry can be ad-
7. Apparatus
justed. The point is to set a lower-level discriminator to exclude
7.1 SNM Automatic Pedestrian Monitors, having arrays of electronic noise and pulses from radiation below the SNM
radiation detectors that form a portal through which pedestrians energy range. Most often a second-level discriminator or
pass or that surround a pedestrian as he waits in a booth for window is also set to discriminate energy above the SNM
clearance to pass. radiation, thus forming an SNM energy region of interest.
7.2 Radiation Detectors, used in SNM monitors may detect 9.2 Discriminator Settings for SNM—The lower-level dis-
gamma rays, neutrons, or both. One of three types of detector criminator setting and the window or upper-level discriminator
listed is usually used. All of types of detector operate in a setting, if used, may depend on the type of SNM to be detected
pulse-counting mode to obtain good sensitivity for detecting and the type of detector used for the following reasons.
small changes in radiation intensity. 9.2.1 The two types of SNM, highly enriched uranium
C 1189
(HEU) and low-burnup plutonium, differ in their intrinsic (d) Calibration using 3.3 V in a plastic detector: 0 to 1.97 V.
gamma-ray spectra. 9.3.3 In case of other gamma-ray pulse-height calibrations
9.2.2 Inorganic and organic scintillators respond differently for Cs gamma rays than are given here, use values directly
to gamma rays. Inorganic scintillators produce pulse heights scaled from the listed values for the same type of detector.
that are proportional to the detected gamma-ray energy. How- 9.4 Optimum Neutron Analysis Windows, for proportional
ever, organic scintillators do not, as Fig. 2 illustrates. At low counters are given here.
gamma-ray energies, a smaller fraction of the incident gamma-
NOTE 2—For organic scintillators, adequate fast neutron response for
ray energy is deposited in an organic scintillator, and it
present-day SNM monitoring applications is usually achieved using the
produces a proportionately smaller pulse height. Hence, inor-
plastic detector discriminator levels for gamma rays given in 9.3.2.
ganic and organic scintillators calibrated to the same reference
9.4.1 Neutron proportional counters detect moderated neu-
pulse height will have different upper and lower discriminator
trons from plutonium and each type of proportional counter has
voltage levels for an SNM region of interest. The examples
its own pulse-height spectrum for detected neutrons.
following illustrate the differences.
9.4.2 The upper level is unimportant in this case because
9.3 Gamma-Ray Regions of Interest for SNM:
there is no high level background. Only a lower-level discrimi-
9.3.1 HEU—The HEU gamma-ray region extends from 60
4 nator may be available in some monitors. Suggested operating
to 220 keV (1). The corresponding deposited energy range in
ranges are as follows:
an organic scintillator is 11.4 to 102 keV. The resulting
137 (a) For BF calibrated to 2 V, from 0.3 to 10 V;
discriminator levels for calibrations using 2 and 3.3 V for Cs
(b) For He calibrated to 2 V, from 0.4 to 10 V;
pulse height are as follows:
(c) For BF calibrated to 8 V, from 1.2 to 10 V; and
(a) Calibration using 2 V in a NaI(Tl) detector: 0.18 to 0.66
(d) For He calibrated to 8 V, from 1.6 to 10 V.
V,
9.4.3 In case another neutron pulse height than given here is
(b) Calibration using 3.3 V in a NaI(Tl) detector: 0.3 to 1.10
used, the values can be directly scaled from the listed values
V,
for the same type of detector.
(c) Calibration using 2 V in a plastic detector: 0.05 to 0.43
9.5 Setting the Discriminators:
V, and
9.5.1 Set the appropriate values in the monitor’s discrimi-
(d) Calibration using 3.3 V in a plastic detector: 0.08 to 0.70
nators or single-channel analyzers (SCA) noting the following
V.
special cases:
9.3.2 Low-Burnup Plutonium—The optimum region of in-
9.5.1.1 Interpreting Window Discriminator Voltage
terest for low-burnup plutonium extends from 0 to 450 keV (1).
Levels—Monitors having both a level discriminator and a
The value 0 means the lowest practical value achieved by one
window discriminator float the window voltage level on top of
of the means discussed in Section 11. The corresponding
the level-discriminator voltage level. Hence, the upper dis-
deposited energy range in an organic scintillator is 0 to 287
criminator value, which is the upper limit of the operating
keV. The resulting discriminator levels for calibrations using 2
137 ranges just tabulated, is the sum of the monitor’s level
and 3.3 V for Cs pulse height are as follows:
discriminator and window values.
(a) Calibration using 2 V in a NaI(Tl) detector: 0 to 1.36 V,
9.5.1.2 Zero Discriminator Values—The value 0 means the
(b) Calibration using 3.3 V in a NaI(Tl) detector: 0 to 2.24
lowest practical value. It will be determined later using a
V,
procedure described in Section 11.
(c) Calibration using 2 V in a plastic detector: 0 to 1.20 V,
9.5.1.3 Backlash in Potentiometer Adjustments—When set-
and
ting multiturn potentiometers, adopt a convention for the
direction of rotation so that settings can be made reproducibly.
The boldface numbers in parentheses refer to the list of references at the end of
9.5.1.4 Uncalibrated Adjustments—If a calibrated multiturn
this guide.
potentiometer dial is not provided, the designer or manufac-
turer will have to indicate how to make these adjustments with
the aid of a voltmeter or oscilloscope.
10. Procedures
10.1 Detector Energy Calibration:
10.1.1 Detector energy calibration sets the SNM detector
response to a particular reference pulse height for gamma rays
or neutrons from a calibration source. The reference pulse
height recommendations of designers and manufacturers for
different detectors range from 2 to 8 V. Particular values for
each detector type are provided, and the corresponding energy
regions for different types of SNM are listed in the following
procedures.
10.1.2 Put the monitor into operation using the manufactur-
er’s instructions. Pay particular attention to checking or setting
FIG. 2 The Relationship Betwee
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