1、Designation: C1189 11Standard Guide toProcedures for Calibrating Automatic Pedestrian SNMMonitors1This standard is issued under the fixed designation C1189; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、 A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers calibrating the energy response of theradiation detectors and setting the discriminator and alarmthresholds used i
3、n automatic pedestrian special nuclear mate-rial (SNM) monitors.1.2 Automatic pedestrian SNM Monitors and their applica-tion are described in Guide C1112, which suggests that themonitors be calibrated and tested when installed and that,thereafter, the calibration should be checked and the monitortes
4、ted 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 helpboth to achieve dependable operation and obtain timely warn-ing of misoperation.1.4 T
5、his guide can be used in conjunction with other ASTMstandards. Fig. 1 illustrates the relationship between calibrationand other procedures described in standard guides, and it alsoshows how the guides relate to an SNM monitor user. Theguides below the user in the figure deal with routine proceduresf
6、or operational monitors. Note that Guide C993 is an in-plantperformance evaluation that is used to verify acceptabledetection of SNM after a monitor is calibrated. The guidesshown above the user in Fig. 1 give information on applyingSNM monitors (C1112) and on evaluating SNM monitors(C1169) to provi
7、de comparative information on monitor per-formance.2. Referenced Documents2.1 ASTM Standards:2C859 Terminology Relating to Nuclear MaterialsC993 Guide for In-Plant Performance Evaluation of Auto-matic Pedestrian SNM MonitorsC1112 Guide for Application of Radiation Monitors to theControl and Physical
8、 Security of Special Nuclear MaterialC1169 Guide for Laboratory Evaluation of Automatic Pe-destrian SNM Monitor PerformanceE876 Practice for Use of Statistics in the Evaluation ofSpectrometric Data33. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 calibrationa multistep procedur
9、e that uniformlyadjusts the energy response of a monitors detector array andsets the operating parameters of its detection circuits foroptimum performance. In a few monitors, an additional analogadjustment of a signal detection circuit is required.3.1.2 SNMspecial nuclear material: plutonium of anyi
10、sotopic composition,233U, or enriched uranium as defined inTerminology C859.3.1.2.1 DiscussionThis term is used here to describe bothSNM and strategic SNM, which is plutonium, uranium-233,and uranium enriched to 20% or more in the235U isotope.1This guide is under the jurisdiction of ASTM Committee C
11、26 on Nuclear FuelCycle and is the direct responsibility of Subcommittee C26.12 on SafeguardApplications.Current edition approved June 1, 2011. Published June 2011. Originallyapproved in 1991. Last previous edition approved in 2002 as C1189 02 which waswithdrawn January 2011 and reinstated June 2011
12、. DOI: 10.1520/C1189-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version
13、 of this historical standard is referencedon www.astm.org.FIG. 1 The Relationship of Calibration to Other ProceduresDescribed in Standard Guides for SNM Monitors1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.3 SNM Monitora radia
14、tion detection system that mea-sures ambient radiation intensity, determines an alarm thresh-old from the result, and then when it monitors, sounds an alarmif its measured radiation intensity exceeds the threshold.3.1.3.1 DiscussionThe automatic pedestrian SNM moni-tor discussed here is a walk-throu
15、gh or wait-in portal ormonitoring booth.4. Summary of Guide4.1 This guide covers various instructions for calibratingSNM pedestrian monitors for optimum performance in normaloperation. The order of procedures is as follows.4.1.1 The energy response of inorganic or organic scintilla-tion detectors or
16、 of neutron proportional counters, is calibratedto produce appropriate signal pulse heights for SNM radiation(see Section 10).4.1.2 The monitors pulse height discriminators are cali-brated to form a region of interest containing SNM radiationfrom highly enriched uranium or low-burnup plutonium (seeS
17、ections 9 and 11), or for detecting neutrons in proportionalcounters (see Section 9).4.1.3 The monitors transient signal detection logic is ad-justed for appropriate response to walk-through or wait-inmonitoring (see Section 12).4.2 This guide covers adjusting various thresholds used inSNM monitors.
18、4.2.1 This guide describes setting background alarm thresh-olds that may be used to announce loss of detection sensitivityor detector failure (see Section 13).4.2.2 This guide discusses setting the lowest practical dis-criminator levels for the radiation detectors (see Section 11).4.3 When calibrati
19、on is complete, the monitor should betested using in-plant evaluation procedures described in GuideC993.5. Significance and Use5.1 SNM monitors are an effective means to search pedes-trians for concealed SNM. Maintaining monitor effectivenessrests on appropriate calibration and adjustment being part
20、 of acontinuing maintenance program.5.2 The significance of this guide for monitor users whomust detect SNM is to describe calibration and adjustmentprocedures for the purpose.5.3 The significance of this guide for monitor manufacturersis to describe calibration procedures, particularly for detectin
21、gforms of SNM that may not be readily available to them.6. Interferences6.1 The monitor should be in proper operating conditionwhen calibrated. Any indication that the monitor does not stayin calibration or that it drifts substantially during the intervalbetween calibration checks is cause for repai
22、r or renovationand then recalibration.7. Apparatus7.1 SNM Automatic Pedestrian Monitors, having arrays ofradiation detectors that form a portal through which pedestrianspass or that surround a pedestrian as he waits in a booth forclearance to pass.7.2 Radiation Detectors, used in SNM monitors may de
23、tectgamma rays, neutrons, or both. One of three types of detectorlisted is usually used. All of types of detector operate in apulse-counting mode to obtain good sensitivity for detectingsmall changes in radiation intensity.7.2.1 Inorganic Scintillation Detectors, such as sodiumiodide NaI(T1), detect
24、 gamma rays but have little response toneutrons from SNM. This detector is useful for detectingunshielded SNM.7.2.2 Neutron Proportional Counters, containing BF3or3He as a converter gas, detect thermal neutrons and are usedwith a moderator to thermalize fast neutrons from SNM. Thisdetector is useful
25、 for detecting unshielded or shielded pluto-nium.7.2.3 Organic Scintillators, detect both gamma rays and fastneutrons from SNM. This detector is useful for detectingunshielded SNM and shielded plutonium.7.3 Oscilloscope or Multi-Channel Analyzer, for viewingreference detector pulses produced by a sp
26、ecific radiationsource during energy calibration.7.3.1 Gamma-Ray Detectors, reference pulses from 662-keV gamma rays emitted by a137Cs source with a nominal8-microCurie (0.3-kBq) activity are used for calibration.7.3.2 Neutron Proportional Counters, reference pulses fromneutrons emitted by a252Cf ne
27、utron source with less than2 3 104neutron/s (0.009-g) source strength can be used forcalibration.NOTE 1Acquisition, storage, and use of sources should be under theguidance of a responsible radiation safety officer (see Section 8 onhazards).7.4 Manufacturers or Designers Operation and Mainte-nance Ma
28、nual, essential for quick and efficient monitor cali-bration. The manufacturers suggested calibration scheme is agood starting place, if not the best approach to calibration.Calibration requires knowledge of test point and adjustmentlocations that should be described in the manuals.8. Hazards8.1 Mak
29、e sure that the use of radioactive materials is underthe guidance of a responsible radiation safety officer who canprovide any needed radiation safety training, personnel dosim-etry, and handling procedures for radiation sources.8.2 The radiation detectors in SNM monitors all operate athigh voltages
30、 that may be hazardous. Although a person is notusually exposed to high voltage during calibration, make surethat the work is performed with the approval of a responsiblesafety officer with proper attention given to electrical safetytraining and reading any warnings of high voltage exposure inmanual
31、s or posted on equipment.9. Pulse-Height Analysis Calibration9.1 Once a monitors detector array is adjusted to uniformpulse height, the pulse-height analysis circuitry can be ad-justed. The point is to set a lower-level discriminator to excludeelectronic noise and pulses from radiation below the SNM
32、energy range. Most often a second-level discriminator orwindow is also set to discriminate energy above the SNMradiation, thus forming an SNM energy region of interest.C1189 1129.2 Discriminator Settings for SNMThe lower-level dis-criminator setting and the window or upper-level discriminatorsetting
33、, if used, may depend on the type of SNM to be detectedand the type of detector used for the following reasons.9.2.1 The two types of SNM, highly enriched uranium(HEU) and low-burnup plutonium, differ in their intrinsicgamma-ray spectra.9.2.2 Inorganic and organic scintillators respond differentlyto
34、 gamma rays. Inorganic scintillators produce pulse heightsthat are proportional to the detected gamma-ray energy. How-ever, organic scintillators do not, as Fig. 2 illustrates. At lowgamma-ray energies, a smaller fraction of the incident gamma-ray energy is deposited in an organic scintillator, and
35、itproduces a proportionately smaller pulse height. Hence, inor-ganic and organic scintillators calibrated to the same referencepulse height will have different upper and lower discriminatorvoltage levels for an SNM region of interest. The examplesfollowing illustrate the differences.9.3 Gamma-Ray Re
36、gions of Interest for SNM:9.3.1 HEUThe HEU gamma-ray region extends from 60to 220 keV (1).4The corresponding deposited energy range inan organic scintillator is 11.4 to 102 keV. The resultingdiscriminator levels for calibrations using 2 and 3.3 V for137Cspulse height are as follows:(a) Calibration u
37、sing 2 V in a NaI(Tl) detector: 0.18 to 0.66V,(b) Calibration using 3.3 V in a NaI(Tl) detector: 0.3 to 1.10V,(c) Calibration using 2 V in a plastic detector: 0.05 to 0.43V, and(d) Calibration using 3.3 V in a plastic detector: 0.08 to 0.70V.9.3.2 Low-Burnup PlutoniumThe optimum region of in-terest
38、for low-burnup plutonium extends from 0 to 450 keV (1).The value 0 means the lowest practical value achieved by oneof the means discussed in Section 11. The correspondingdeposited energy range in an organic scintillator is 0 to 287keV. The resulting discriminator levels for calibrations using 2and 3
39、.3 V for137Cs pulse height are as follows:(a) Calibration using 2 V in a NaI(Tl) detector: 0 to 1.36 V,(b) Calibration using 3.3 V in a NaI(Tl) detector: 0 to 2.24V,(c) Calibration using 2 V in a plastic detector: 0 to 1.20 V,and(d) Calibration using 3.3 V in a plastic detector: 0 to 1.97 V.9.3.3 In
40、 case of other gamma-ray pulse-height calibrationsfor137Cs gamma rays than are given here, use values directlyscaled from the listed values for the same type of detector.9.4 Optimum Neutron Analysis Windows, for proportionalcounters are given here.NOTE 2For organic scintillators, adequate fast neutr
41、on response forpresent-day SNM monitoring applications is usually achieved using theplastic detector discriminator levels for gamma rays given in 9.3.2.9.4.1 Neutron proportional counters detect moderated neu-trons from plutonium and each type of proportional counter hasits own pulse-height spectrum
42、 for detected neutrons.9.4.2 The upper level is unimportant in this case becausethere is no high level background. Only a lower-level discrimi-nator may be available in some monitors. Suggested operatingranges are as follows:(a) For BF3calibrated to 2 V, from 0.3 to 10 V;(b) For3He calibrated to 2 V
43、, from 0.4 to 10 V;(c) For BF3calibrated to 8 V, from 1.2 to 10 V; and(d) For3He calibrated to 8 V, from 1.6 to 10 V.9.4.3 In case another neutron pulse height than given here isused, the values can be directly scaled from the listed valuesfor the same type of detector.9.5 Setting the Discriminators
44、:9.5.1 Set the appropriate values in the monitors discrimi-nators or single-channel analyzers (SCA) noting the followingspecial cases:9.5.1.1 Interpreting Window Discriminator VoltageLevelsMonitors having both a level discriminator and awindow discriminator float the window voltage level on top ofth
45、e level-discriminator voltage level. Hence, the upper dis-criminator value, which is the upper limit of the operatingranges just tabulated, is the sum of the monitors leveldiscriminator and window values.9.5.1.2 Zero Discriminator ValuesThe value 0 means thelowest practical value. It will be determi
46、ned later using aprocedure described in Section 11.9.5.1.3 Backlash in Potentiometer AdjustmentsWhen set-ting multiturn potentiometers, adopt a convention for thedirection of rotation so that settings can be made reproducibly.9.5.1.4 Uncalibrated AdjustmentsIf a calibrated multiturnpotentiometer dia
47、l is not provided, the designer or manufac-turer will have to indicate how to make these adjustments withthe aid of a voltmeter or oscilloscope.10. Procedures10.1 Detector Energy Calibration:10.1.1 Detector energy calibration sets the SNM detectorresponse to a particular reference pulse height for g
48、amma raysor neutrons from a calibration source. The reference pulseheight recommendations of designers and manufacturers for4The boldface numbers in parentheses refer to the list of references at the end ofthis guide.FIG. 2 The Relationship Between Incident Gamma-Ray Energyand Energy Deposited in Na
49、I(Tl) and Plastic ScintillatorsC1189 113different detectors range from 2 to 8 V. Particular values foreach detector type are provided, and the corresponding energyregions for different types of SNM are listed in the followingprocedures.10.1.2 Put the monitor into operation using the manufactur-ers instructions. Pay particular attention to checking or settingthe detector high voltage to the recommended value usingproper electrical safety practice (see 8.2).10.1.3 With the detectors operating at an appropriate highvoltage, proceed with energy calibration b
