ASTM E1893-1997(2003) Standard Guide for Selection and Use of Portable Radiological Survey Instruments for Performing In Situ Radiological Assessments in Support of Decommissioning.pdf

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1、Designation: E 1893 97 (Reapproved 2003)Standard Guide forSelection and Use of Portable Radiological SurveyInstruments for Performing In Situ RadiologicalAssessments in Support of Decommissioning1This standard is issued under the fixed designation E 1893; the number immediately following the designa

2、tion indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This standard provides recommend

3、ations on the selec-tion and use of portable instrumentation that is responsive tolevels of radiation that are close to natural background. Theseinstruments are employed to detect the presence of residualradioactivity that is at, or below, the criteria for release fromfurther regulatory control of a

4、 component to be salvaged orreused, or a surface remaining at the conclusion of decontami-nation and/or decommissioning.1.2 The choice of these instruments, their operating charac-teristics and the protocols by which they are calibrated andused will provide adequate assurance that the measurements o

5、fthe residual radioactivity meet the requirements established forrelease from further regulatory control.1.3 This standard is applicable to the in situ measurement ofradioactive emissions that include:1.3.1 alpha1.3.2 beta (electrons)1.3.3 gamma1.3.4 characteristic x-rays1.3.5 The measurement of neu

6、tron emissions is not includedas part of this standard.1.4 This standard dose not address instrumentation used toassess residual radioactivity levels contained in air samples,surface contamination smears, bulk material removals, orhalf/whole body personnel monitors.1.5 This standard does not address

7、 records retention require-ments for calibration, maintenance, etc. as these topics areconsidered in several of the referenced documents.2. Referenced Documents2.1 ASTM Standards:E 170 Standard Terminology Relating to Radiation Mea-surements and Dosimetry2E 181 Standard General Methods for Detector

8、Calibrationand Analysis of Radionuclides2C 1215 Standard Guide for Preparing and InterpretingPrecision and Bias Statements in Test Method StandardsUsed in the Nuclear Industry32.2 ANSI Standards:ANSI N323 Radiation Protection Instrumentation Test andCalibration4ANSI N15.5 Statistical Terminology and

9、 Notation forNuclear Materials Management4ANSI N42.17A Performance Specifications for HealthPhysics Instrumentation-Portable Instrumentation for Usein Normal Environmental Conditions4ANSI N42.17C Performance Specifications for HealthPhysics Instrumentation-Portable Instrumentation for Usein Extreme

10、Environmental Conditions4ANSI N42.3 Standard Test Procedure for Geiger MuellerCounters42.3 National Council on Radiation Protection and Mea-surements:NCRP Report No. 57 Instrumentation and MonitoringMethods for Radiation Protection, National Council onRadiation Protection and Measurements, May 19785

11、NCRP Report No. 58 A Handbook of Radioactivity Mea-surement Procedures, National Council on Radiation Pro-tection and Measurements, 2nd Ed. February 19855NCRP Report No. 112 Calibration of Survey InstrumentsUsed in Radiation Protection for the Assessment ofIonizing Radiation Fields and Radioactive S

12、urface Con-tamination, National Council on Radiation Protection andMeasurements, December 199152.4 International Organization for Standardization (ISO):ISO-4037 X and Gamma Reference Radiations for Calibrat-ing Dosimeters and Dose-rate Meters and for Determiningtheir Response as a Function of Photon

13、 Energy, Interna-tional Organization for Standardization, 197961This guide is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.03 on Radiological Protection for Decontamination and Decommissioning ofNuclear Facilit

14、ies and Components.Current edition approved June 10, 1997. Published March 1998.2Annual Book of ASTM Standards, Vol 12.02.3Annual Book of ASTM Standards, Vol 12.01.4American National Standards Institute, 11 W. 42nd St., 13thFloor, New York,NY 100365National Council on Radiation Protection and Measur

15、ement, 7910 WodmontAve., Bethesda, MD 208146Available fromANSI Sales Department, 1430 Broadway, New York, NY 100181Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.ISO-6980 Reference Beta Radiations for Calibrating Do-simeters and Dose

16、-rate Meters and for Determining TheirResponse as a Function of Beta Radiation Energy, Inter-national Organization for Standardization, 19846ISO-8769 Reference Sources for the Calibration of SurfaceContamination Monitors Beta Emitters (Maximum BetaEnergy Greater than 0.15 MeV) and Alpha Emitters,Int

17、ernational Organization for Standardization, 19886ISO-75031 Evaluation of Surface Contamination - Part 1:Beta Emitters (Maximum Beta Energy Greater than 0.15MeV) and Alpha Emitters, International Organization forStandardization, 19886ISO-75032 Evaluation of Surface Contamination - Part 2:Tritium Sur

18、face Contamination, International Organiza-tion for Standardization, 19886ISO-75033 Evaluation of Surface Contamination - Part 3:Isomeric Transition and Electron Capture Emitters, LowEnergy Beta Emitters (Ebmax0.15 MeV) emitters - ISO7503-15.5.2.3 tritium - ISO 7503-25.5.2.4 beta (E 4 seconds.NOTE 4

19、Experiments using hidden sources (Co-57) with signal-to-background ratios from 0.6-6 resulted in approximately 75 % beinglocated based on ratemeter observation alone, compared to approximately90 % for audio response (10).6.4.5 Direct (fixed) Measurements. The estimate of the levelof residual radioac

20、tivity is based on a measurement with thesource-detector geometry fixed (stationary). When makingthese fixed measurements, the following requirements, as aminimum, should be complied with:6.4.5.1 The detector should be coupled to a scaler for thismeasurement.6.4.5.2 If a ratemeter is used with this

21、measurement, a longresponse time should be used ( 20 sec). The detector shall bekept in position for at least three times the time constant of theratemeter.6.4.5.3 The effects of the concavity of the surfaces beingmeasured on instrument efficiency shall be evaluated when thesurface is not flat (exam

22、ples are given in Appendix X5 for betaemissions).6.4.5.4 For conditions where a visible layer of dirt, oxida-tion, or other coating cannot be removed, the effect onsource-detector response shall be included for alpha and betameasurements (examples are given in Appendix X5 for betaemissions).6.5 Data

23、 Interpretation:6.5.1 Alpha and Beta Emissions:6.5.2 The evaluation of surface activity for alpha or betaemissions (in dpm/100 cm2) is given by the expression(ISO-7503-1)As5n 2 nB!ei3es3W100where:n = total count rate in cpmnB= background count rate in cpmei= instrument efficiency for alpha or beta r

24、adiation incpm per dpmW = total physical window area of the detector in cm2es= source correction factor to account for differencesbetween the calibration source and the residual activ-ity, such as backscatter, self absorption, source pro-tective coatings and/or surface coatings, geometry,etc. (unitl

25、ess)NOTE 5The factor eimay be defined for either a point source or asurface source. The point source efficiency should be used to quantify hotspots. The surface source efficiency should be used to evaluate surfaceswithout hot spots.NOTE 6Further explanation of the factor eiand its relative magnitude

26、are given in Appendix X5.6.5.3 Gamma Emissions:6.5.3.1 Gamma detection and subsequent interpretation isnormally employed to evaluate the levels of residual activitythat are distributed within a source matrix expressed aspCi/gm, Bq/kg, etc. For a uniformly distributed source, thevolumetric source ter

27、m is provided by the expressionSv5n 2 nBegwhere:Sv= volumetric source term in pCi/gmn = total count rate in cpmnB= background count rate in cpmeg= instrument efficiency for an infinitely distributedgamma source in cpm per pCi/gm.E 1893 97 (2003)5NOTE 7The gamma efficiency will normally be composed o

28、f twofactors; a dose conversion in units of cpm/(mR/hr) measured with a knowncalibration source, and a source conversion factor in units of (mR/hr)/(pCi/gm) based on shielding theory. In general, the dose conversion factorfor a particular detector is provided for a single photon energy, whereas,the

29、source conversion factor includes scattered photons (buildup) whichleads to an estimate of the gamma source strength that is conservative. Theresponse of various NaI detector geometries as a function of photonenergy is shown in Appendix X9.APPENDIXES(Nonmandatory Information)X1. MINIMUM DETECTABLE A

30、CTIVITY (MDA)X1.1 When measuring residual radioactivity at the comple-tion of a D t50.87 sec 0.015 min!Slow: us5 20 sec; t58.7 sec 0.15 min!X3.8 When ratemeter output is utilized, the minimumsensitivity may be derived for point source activity andconstant source/detector distance to account for the

31、change inapparent detector efficiency as a function of probe velocity bythe relationship.e V! 5e01 2 e2dp/vdt!# (X3.3)where:e (v) = “apparant” detector efficiency for detector velocity(v)e0= detector efficiency for steady state source responsedp= distance detector probe travels with source withineff

32、ective detection area (length of window in direc-tion of travel)vd= scanning velocity of the detector probet = electronic time constant of the ratemeterEquation Eq X1.5 would be modified for transient responseas follows:MSS 54.65 =B0/2te v! Ad/ 100!(X3.4)X3.9 Fig. X3.2 illustrates the effects of dif

33、ferent detectorprobe window sizes, and time responses on the transientresponse of the detector probe traveling at velocities up to6-inches per second. Note that recommended practice is to scanat a probe velocity of 2-inches per second (5 cm/sec).X3.10 When an audio output signal is used, experience

34、hasshown that a 25 % to 50 % increase may be easily identified atambient background levels of several thousand counts perminute (typical of gamma scintillators), but at ambient levelsof 12 counts per minute (typical of alpha meters) a two toFIG. X3.1 Area of DetectionE 1893 97 (2003)9FIG.X3.2Transie

35、ntResponseofVariousSurfactContaminationDetectorRatemeterCombinationsE 1893 97 (2003)10three fold increase in audible signal is required to be recog-nizable. These observations resulted in a conservative expres-sion, based upon 3 times background:MSS 53B0e0 Ad/ 100!(X3.5)Other observers (13) have emp

36、loyed a term defined asminimum detection level (MDL) to denote the calculatedminimum activity that can be detected using audio outputduring scanning. The MDL is based on the assumption that adoubling in the count rate can be recognized with the detectorover the source for one second. This expression

37、 is:MDL 5B0e0 Ad/ 100!(X3.6)Table X1.1 presents a summary of estimated minimumsensitivities for various sizes of instruments used for beta andalpha detection using Equation Eq X1.4 for scaler and Equa-tion Eq X1.5 for ratemeter. Minimum sensitivity is the termused to represent the “detection limit”

38、for the ratemeters orscalers using the above expressions. For comparison, TableX3.1 presents a summary of estimated minimum sensitivitiesfor these same instruments used with a ratemeter to performscan surveys.Method 1 2 MSS 54.65 =B0/2tev! Ad/ 100!(X3.7)Method 2 2 MSS 52B02 B0!e0 Ad/ 100!(X3.8)Metho

39、d 3 2 MSS 53B0e0 Ad/ 100!(X3.9)t = 0.87 sec (corresponds to a response time of 2 seconds)X4. EFFECTS OF SOURCE-DETECTOR GEOMETRYX4.1 The theoretical relationships that relate dose rate as afunction of source configuration, for both beta and photonparticles, are derived for a point in space at some d

40、istance fromthe source. In other words, the detector is assumed to be a pointin space. This is a reasonable assumption if the source-detectordistance is greater than five times the primary dimension of thedetector (h 5dpin Fig. X3.1). Conversely, a small source sizein relationship to the detector si

41、ze may be treated as a pointsource if the above relationship is true with respect to thedimensions of the source. This is shown for two differentdetector window geometries on Fig. X4.1.X4.2 A series of beta measurements were obtained fordifferent sizes at source-distances ranging from contact withth

42、e detector window to 2-inches for different source sizes (15,18). The detectors used for this test were:Pancake GM Ad= 15.5 cm2Large Area Ad= 128 cm2Floor Monitor Ad= 584 cm2X4.3 The sources used ranged in size from an active area of15 cm2to approximately 250 cm2. The results of thesemeasurements ar

43、e shown on Fig. X4.2 and Fig. X4.3.OnFig.X4.2, the results are compared to point source theory. Thisfigure confirms that point source theory is a valid relationshipfor detector/source area ratios 5. Note, however, the devia-tion from point source theory for the small detector probe areawith respect

44、to source size.X4.4 Fig. X4.3 has not been correlated with theory. Thecurves shown are simply an attempt to “fit” the measuredresponses. The curves do, however, illustrate the reduction inresponse to a source that is equivalent in size to the detector asthe detector distance from that source is chan

45、ged. This factor issignificant for small changes in scan height. For example, byincreasing the scan height from14 inch to12 inch, thefollowing reductions in scan efficiency could be anticipated:Pancake GM: ;15 %Large Area Probe: ;12 %Floor Monitor: ;5%TABLE X3.1 Typical Minimum Surface Sensitivities

46、 ScanningSurveyMinimum Surface Sensitivity(dpm/100cm2)Detector Area BackgroundStationary Transient Method 1 Method 2 Method 3(cpm) ResponseResponse(cpm/dpm)(cpm/dpm)Pancake 15.5 50 .30 .24 1660 1075 3225GMLargeArea128.0 300 .30 .28 425 260 780Floor 584.0 1000 .30 .29 160 570 1710MonitorAlpha 50.0 2

47、.15 .135 180 30 80ScintillatorE 1893 97 (2003)11FIG. X4.1 Instrument Response as Function of Distance from Point SourceE 1893 97 (2003)12FIG.X4.2ComparisonofDetectorResponsetoPointSourceTheoryforVariousProbeAreasandaSmallAreaSourceE 1893 97 (2003)13FIG.X4.3ComparisonofDetectorResponseforVariousProbe

48、AreastoaLargeAreaSourceE 1893 97 (2003)14X5. FACTORS AFFECTING THE MEASUREMENT OF ALPHA AND BETA SURFACE CONTAMINATIONX5.1 This appendix provides additional information onvarious characteristics of surface conditions that affect theevaluation of surface contamination level from an in situdetector re

49、sponse.GENERAL THEORYX5.2 The geometrical relationship between a particle de-tector and a source emitting those particles from a surface isshown on Fig. X5.1.X5.3 Define the following parameters:RD= Detector response (cpm)So= Total activity of source - (Bq, dpm)ST= Source emission rate - b/s or a/sSs=2p surface emission rate - b/s or a/s* = Location of particle interaction by scattering or finalabsorptionX5.4 The relationship between total source activity (Bq)and source emission rate (particles/sec) is given by:ST5edSo(X5.1)where:ed= the