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

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1、Designation: E 1893 08Standard 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 follo

2、wing 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 pro

3、vides 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 regulato

4、ry 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 the

5、 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 mea

6、surement 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 d

7、oes not address records retention require-ments for calibration, maintenance, etc. as these topics areconsidered in several of the referenced documents.2. Referenced Documents2.1 ASTM Standards:2C 998 Practice for Sampling Surface Soil for RadionuclidesC 999 Practice for Soil Sample Preparation for

8、the Deter-mination of RadionuclidesC 1000 Test Method for Radiochemical Determination ofUranium Isotopes in Soil by Alpha SpectrometryC 1133 Test Method for Nondestructive Assay of SpecialNuclear Material in Low-Density Scrap and Waste bySegmented Passive Gamma-Ray ScanningE 170 Terminology Relating

9、 to Radiation Measurementsand DosimetryE 181 Test Methods for Detector Calibration and Analysisof RadionuclidesC 1215 Guide for Preparing and Interpreting Precision andBias Statements in Test Method Standards Used in theNuclear Industry2.2 ANSI Standards:ANSI N323B Radiation Protection Instrumentati

10、on Test andCalibration, Portable Survey Instrumentation for NearBackground Operation3ANSI N42.17A Performance Specifications for HealthPhysics Instrumentation-Portable Instrumentation for Usein Normal Environmental Conditions3ANSI N42.17C Performance Specifications for HealthPhysics Instrumentation-

11、Portable Instrumentation for Usein Extreme Environmental Conditions32.3 National Council on Radiation Protection and Mea-surements:NCRP Report No. 57 Instrumentation and Monitoring1This guide is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications and is the direct resp

12、onsibility of SubcommitteeE10.03 on Radiological Protection for Decontamination and Decommissioning ofNuclear Facilities and Components.Current edition approved June 1, 2008. Published July 2008. Originally approvedin 1997. Last previous edition approved in 2003 as E 1893-97(2003).2For referenced AS

13、TM 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.3American National Standards Institute, 11 W. 42nd St., 13thFloor, New York,NY

14、100361Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Methods for Radiation Protection, National Council onRadiation Protection and Measurements, May 19784NCRP Report No. 58 A Handbook of Radioactivity Mea-surement Procedures, Nationa

15、l Council on Radiation Pro-tection and Measurements, 2nd Ed. February 19854NCRP Report No. 112 Calibration of Survey InstrumentsUsed in Radiation Protection for the Assessment ofIonizing Radiation Fields and Radioactive Surface Con-tamination, National Council on Radiation Protection andMeasurements

16、, December 199142.4 International Organization for Standardization (ISO):ISO-4037-4 : 2004 X and Gamma Reference Radiations forCalibrating Dosimeters and Dose-rate Meters and forDetermining their Response as a Function of PhotonEnergy, International Organization for Standardization,19795ISO-6980-2 :

17、 2005 Nuclear energy Reference beta particleradiation - Part 2: Calibration fundamentals related tobasic quantities characterizing the radiation field5ISO-8769 Reference Sources for the Calibration of SurfaceContamination Monitors Beta Emitters (Maximum BetaEnergy Greater than 0.15 MeV) and Alpha Em

18、itters,International Organization for Standardization, 19885ISO 8769-2 : 1996 Reference sources for the calibration ofsurface contamination 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 Emit

19、ters (Maximum Beta Energy Greater than 0.15MeV) and Alpha Emitters, International Organization forStandardization, 19885ISO-7503-2 Evaluation of Surface Contamination - Part 2:Tritium Surface Contamination, International Organiza-tion for Standardization, 19885ISO-7503-3 : 2003 Evaluation of Surface

20、 Contamination -Part 3: Isomeric Transition and Electron Capture Emitters,Low Energy Beta Emitters (Ebmax0.15 MeV) emitters - ISO7503-15.5.2.3 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 7

21、5 % beinglocated based on ratemeter observation alone, compared to approximately90 % for audio response (6).6.4.5 Direct (fixed) Measurements. The estimate of the levelof residual radioactivity is based on a measurement with thesource-detector geometry fixed (stationary). When makingthese fixed meas

22、urements, 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 measurement, a longresponse time should be used ( 20 sec). The detector shall bekept in position for at least thr

23、ee 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 (examples are given in Appendix X5 for betaemissions).6.4.5.4 For conditions where a visible layer of dirt, oxida-tion

24、, 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 Interpretation:6.5.1 Alpha and Beta Emissions:6.5.2 The evaluation of surface activity for alpha or betaemission

25、s (in dpm/100 cm2) is given by the expression(ISO-7503-1)E 1893 085As5n 2 nB!i3s3W100where:n = total count rate in cpmnB= background count 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

26、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. (unitless)NOTE 5The factor imay be defined for either a point source or asurface source. The point source efficie

27、ncy should be used to quantify hotspots. The surface source efficiency should be used to evaluate surfaceswithout hot spots.NOTE 6Further 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 isnormal

28、ly 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 term is provided by the expressionSv5n 2 nBgwhere:Sv= volumetric source term in pCi/gmn = total count rate in cp

29、mnB= background count rate in cpmg= instrument efficiency for an uniformly distributedgamma source in cpm per pCi/gm.NOTE 7The gamma efficiency 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 i

30、n 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 source conversion factor includes scattered photons (buildup) whichleads to an estimate of the gamma source strength that is cons

31、ervative. Theresponse of various NaI detector geometries as a function of photonenergy is shown in Appendix X9.APPENDIXES(Nonmandatory Information)X1. MINIMUM DETECTABLE ACTIVITY (MDA)X1.1 When measuring residual radioactivity that must bewithin limits or guidelines that are very near to the levels

32、thatare present from natural background, the minimum amount ofradioactivity that may be detected by a particular measurementsystem must be determined. With radiation measurement, thephysical amount of the residual radiation source (pCi, dpm, Bq,etc.) is not directly measurable, but is observed as a

33、measure-ment instrument response (digital counts, voltmeter deflection,etc.). Because radioactive decay follows statistical relation-ships, the statistics of detection and determination applydirectly to the observed (or observable) signal (meter reading)and its associated random fluctuations. When m

34、easuring for thepresence of low residual activity, one must distinguish betweentwo fundamental aspects of the detection problem (6).X1.2 Given 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 detec

35、ted? (The“false positive” or Type I error)X1.3 Given a completely specified measurement process,what is the minimum “real” activity that will 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)

36、decision based upon the net signal(s) and a definedcriterion for detection. This leads to the establishment of a“critical level” (Lc) for 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).

37、Con-versely, the second aspect relates to making an a priori (beforethe fact) estimate of the detection capabilities of the measure-ment process 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 valu

38、e such that realresidual radioactive material greater than LDwill be interpretederroneously as background with a probability less than b.Mathematically 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

39、 normallydistributed eventsThe relationships between Lcand LDare shown on Fig.X1.1.X1.5 The quantity Lcis used to test an experimental result,whereas LDrefers to the capability of the measurement processitself (6). The concept of “detection limit” (LD) has also beenidentified as “limit of detection”

40、 (8) and “minimum detectableactivity” (MDA) (4). The term minimum detectable activity isE 1893 086most commonly encountered in radiation 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:C

41、o= proportionally constant relating the detector responseto an activitys0= standard deviation of the backgroundFor purposes of this discussion, 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

42、. The concept of detection limit for distributedactivity will be expressed using the “minimum surface sensi-tivity” (MSS) of the detector, which will incorporate thedetector area as a function that will allow values of minimumsurface sensitivity to be compared directly to surface activityregulatory

43、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 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 effic

44、iency in counts/disintegration (includesall source surface and self attenuation effects - seeAppendix X5)t = scaler count time (min)t = ratemeter 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 c

45、ommon detector types are shown in Table X1.1.FIG. X1.1 Hypothesis TestingErrors of the First and Second KindE 1893 087X2. DETECTION OF LOW-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

46、dependent on both the electromechanicalcharacteristics of the detector system and upon the protocols bywhich the detector system is employed. For assessing theresidual radioactive condition of a surface to support anunrestricted release determination, the accepted protocol is toemploy a detector, co

47、upled to a scaler, to obtain measurementson a fixed set of grid locations. For this type of measurement,one must know the minimum sensitivity of the detector systemfor comparison to guidelines that must be met. However, thistechnique is only representative for uniformly distributedactivity. It will

48、not be effective for “hot” spot activity, particu-larly beta or alpha. For example, five measurements using a100 cm2probe to characterizea1m3 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

49、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.X3. SCANNING EFFECTS - CONTAMINATION MONITORSX3.1 The most common survey protocol utilized forsurface release measurement is scanning for the presence ofresidual radioactivity. This is accomplished by moving theradiation detector over the surface of interest. For radioactivesource levels very close to natural back