ASTM E1893-2008a Standard Guide for Selection and Use of Portable Radiological Survey Instruments for Performing In Situ Radiological Assessments to Support Unrestricted Release fr.pdf

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1、Designation: E 1893 08aStandard Guide forSelection and Use of Portable Radiological SurveyInstruments for Performing In Situ RadiologicalAssessments to Support Unrestricted Release from FurtherRegulatory Controls1This standard is issued under the fixed designation E 1893; the number immediately foll

2、owing the designation 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This standard pr

3、ovides recommendations 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 regulat

4、ory control of a 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 th

5、e measurements ofthe 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 me

6、asurement of neutron 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

7、does not address records retention require-ments for calibration, maintenance, etc. as these topics areconsidered in several of the referenced documents.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.2. Referenced Documents

8、2.1 ASTM Standards:2C 998 Practice for Sampling Surface Soil for RadionuclidesC 999 Practice for Soil Sample Preparation for the Deter-mination of RadionuclidesC 1000 Test Method for Radiochemical Determination ofUranium Isotopes in Soil by Alpha SpectrometryC 1133 Test Method for Nondestructive Ass

9、ay of SpecialNuclear Material in Low-Density Scrap and Waste bySegmented Passive Gamma-Ray ScanningE 170 Terminology Relating to Radiation Measurementsand DosimetryE 181 Test Methods for Detector Calibration and Analysisof RadionuclidesC 1215 Guide for Preparing and Interpreting Precision andBias St

10、atements in Test Method Standards Used in theNuclear Industry2.2 ANSI Standards:ANSI N323B Radiation Protection Instrumentation Test andCalibration, Portable Survey Instrumentation for NearBackground Operation3ANSI N42.17A Performance Specifications for HealthPhysics Instrumentation-Portable Instrum

11、entation for Usein Normal Environmental Conditions3ANSI N42.17C Performance Specifications for HealthPhysics Instrumentation-Portable Instrumentation for Usein Extreme Environmental Conditions32.3 National Council on Radiation Protection and Mea-surements:NCRP Report No. 57 Instrumentation and Monit

12、oring1This 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 Facilities and Components.Current edition approved Nov. 1, 2008.

13、Published March 2009. Originallyapproved in 1997. Last previous edition approved in 2008 as E 1893-08.2For 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

14、Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Methods for Radia

15、tion Protection, National Council onRadiation Protection and Measurements, May 19784NCRP Report No. 58 A Handbook of Radioactivity Mea-surement Procedures, National Council on Radiation Pro-tection and Measurements, 2nd Ed. February 19854NCRP Report No. 112 Calibration of Survey InstrumentsUsed in R

16、adiation Protection for the Assessment ofIonizing Radiation Fields and Radioactive Surface Con-tamination, National Council on Radiation Protection andMeasurements, December 199142.4 International Organization for Standardization (ISO):ISO-4037-4 : 2004 X and Gamma Reference Radiations forCalibratin

17、g Dosimeters and Dose-rate Meters and forDetermining their Response as a Function of PhotonEnergy, International Organization for Standardization,19795ISO-6980-2 : 2005 Nuclear energy Reference beta particleradiation - Part 2: Calibration fundamentals related tobasic quantities characterizing the ra

18、diation field5ISO-8769 Reference Sources for the Calibration of SurfaceContamination Monitors Beta Emitters (Maximum BetaEnergy Greater than 0.15 MeV) and Alpha Emitters,International Organization for Standardization, 19885ISO 8769-2 : 1996 Reference sources for the calibration ofsurface contaminati

19、on monitors-Part 2: Electrons of en-ergy less than 0.15 MeV and photons of energy less than1.5 MeVISO-7503-1 Evaluation of Surface Contamination - Part 1:Beta Emitters (Maximum Beta Energy Greater than 0.15MeV) and Alpha Emitters, International Organization forStandardization, 19885ISO-7503-2 Evalua

20、tion of Surface Contamination - Part 2:Tritium Surface Contamination, International Organiza-tion for Standardization, 19885ISO-7503-3 : 2003 Evaluation of Surface Contamination -Part 3: Isomeric Transition and Electron Capture Emitters,Low Energy Beta Emitters (Ebmax0.15 MeV) emitters - ISO7503-15.

21、5.2.3 tritium - ISO 7503-25.5.2.4 beta (E 4s.NOTE 4Experiments 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 (6).6.4.5 Direct (fixed) Measurem

22、ents. The estimate of the levelof residual radioactivity 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 thismea

23、surement.6.4.5.2 If a ratemeter is used with this measurement, a longresponse time should be used ( 20 s). 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 shal

24、l be evaluated when thesurface is not flat (examples 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

25、given in Appendix X5 for betaemissions).6.5 Data 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)E 1893 08a5As5n 2 nB!i3s3W100where:n = total count rate in cpmnB= background count

26、 rate in cpmi= instrument efficiency for alpha or beta radiation incpm per dpmW = total physical window area of the detector in cm2s= source correction factor to account for differencesbetween the calibration source and the residual activ-ity, such as backscatter, self absorption, source pro-tective

27、 coatings and/or surface coatings, geometry,etc. (unitless)NOTE 5The factor imay 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

28、explanation of the factor iand its relative magnitudeare 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 u

29、niformly distributed source, thevolumetric source term is provided by the expressionSv5n 2 nBgwhere:Sv= volumetric source term in pCi/gmn = total count rate in cpmnB= background count rate in cpmg= instrument efficiency for an uniformly distributedgamma source in cpm per pCi/gm.NOTE 7The gamma effic

30、iency will normally be composed of 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 s

31、ingle photon energy, whereas,the 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 Inf

32、ormation)X1. MINIMUM DETECTABLE ACTIVITY (MDA)X1.1 When measuring residual radioactivity that must bewithin limits or guidelines that are very near to the levels thatare present from natural background, the minimum amount ofradioactivity that may be detected by a particular measurementsystem must be

33、 determined. With radiation measurement, thephysical amount of the residual radiation source (pCi, dpm, Bq,etc.) is not directly measurable, but is observed as a measure-ment instrument response (digital counts, voltmeter deflection,etc.). Because radioactive decay follows statistical relation-ships

34、, the statistics of detection and determination applydirectly to the observed (or observable) signal (meter reading)and its associated random fluctuations. When measuring for thepresence of low residual activity, one must distinguish betweentwo fundamental aspects of the detection problem (6).X1.2 G

35、iven a net signal that is greater in value than asimilar signal that has been established as defining background,has a “real” activity above background been detected? (The“false positive” or Type I error)X1.3 Given a completely specified measurement process,what is the minimum “real” activity that w

36、ill produce anobserved signal that will be detected? (The “false negative” orType II error)X1.4 The first aspect relates to making an a posterior (afterthe fact) decision based upon the net signal(s) and a definedcriterion for detection. This leads to the establishment of a“critical level” (Lc) for

37、which a signal exceeding this level willbe interpreted as a residual activity with a probability a, whenin fact it is only background, (error of the first kind). Con-versely, the second aspect relates to making an a priori (beforethe fact) estimate of the detection capabilities of the measure-ment p

38、rocess that yields a signal exceeding the critical levelthat is in fact from a “real” residual source of activity. This“detection limit” (LD) is the smallest value such that realresidual radioactive material greater than LDwill be interpretederroneously as background with a probability less than b.M

39、athematically these concepts are given as (7):Lc5 Kas01 B0(X1.1)LD5 Lc1 Kbs0(X1.2)where:s = standard deviationK = statistical constant based error probability for normallydistributed eventsThe relationships between Lcand LDare shown on Fig.X1.1.X1.5 The quantity Lcis used to test an experimental res

40、ult,whereas LDrefers to the capability of the measurement processitself (6). The concept of “detection limit” (LD) has also beenidentified as “limit of detection” (8) and “minimum detectableactivity” (MDA) (4). The term minimum detectable activity isE 1893 08a6most commonly encountered in radiation

41、measurement reports,and will be utilized here. The basic relationship for estimatingthe MDA at the 95% confidence level is (9):MDA 5 Co3.0 1 4.65 so! (X1.3)where:Co= proportionally constant relating the detector responseto an activitys0= standard deviation of the backgroundFor purposes of this discu

42、ssion, MDA will be defined inunits of activity expressed as dpm or pCi. This mathematicalrelationship for MDA will be applied to point source or “hotspot” residual. The concept of detection limit for distributedactivity will be expressed using the “minimum surface sensi-tivity” (MSS) of the detector

43、, which will incorporate thedetector area as a function that will allow values of minimumsurface sensitivity to be compared directly to surface activityregulatory guidelines.X1.6 For time integrated measurements using a scalerreadout:MSS 53.0 1 4.65 =Bo*tt0 Ad/100!(X1.4)For measurements involving a

44、ratemeter signal, the relation-ship is:MSS 54.65 =Bo/2t0 Ad/100!(X1.5)where:Bo= background count rate (cpm)Ad= window area of detector probe (cm2)0= detector efficiency in counts/disintegration (includesall source surface and self attenuation effects - seeAppendix X5)t = scaler count time (min)t = r

45、atemeter time constant (min) = 0.438 uu = time for meter to reach 90 % of steady state (X3.5)X1.7 Typical minimum sensitivities for scalers and rateme-ters using common detector types are shown in Table X1.1.FIG. X1.1 Hypothesis TestingErrors of the First and Second KindE 1893 08a7X2. DETECTION OF L

46、OW-LEVEL RESIDUAL ACTIVITYX2.1 The ability to evaluate the existence and amount oflow-level residual activity in the presence of natural radioac-tive background is dependent on both the electromechanicalcharacteristics of the detector system and upon the protocols bywhich the detector system is empl

47、oyed. For assessing theresidual radioactive condition of a surface to support anunrestricted release determination, the accepted protocol is toemploy a detector, coupled to a scaler, to obtain measurementson a fixed set of grid locations. For this type of measurement,one must know the minimum sensit

48、ivity of the detector systemfor comparison to guidelines that must be met. However, thistechnique is only representative for uniformly distributedactivity. It will not be effective for “hot” spot activity, particu-larly beta or alpha. For example, five measurements using a100 cm2probe to characteriz

49、ea1m3 1 m area will cover 5percent of the surface being assessed. Even when applied atpredetermined systematic or biased locations, it will onlydetect hot spots in a hit or miss fashion. Scanning, using thedetector coupled to a ratemeter is the most effective method forlocating “hot” spot activity. This technique however, is limitedby the transient response characteristics of the detector and theratemeter. The effects of scanning protocol on hot spot detec-tion has been quantified for several commonly used instru-ments (10,11).X3. SCANNING EFFECTS - CON