1、Designation: E2971 14Standard Test Method forDetermination of Effective Boron-10 Areal Density inAluminum Neutron Absorbers using Neutron AttenuationMeasurements1This standard is issued under the fixed designation E2971; the number immediately following the designation indicates the year oforiginal
2、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 test method is intended for quantitative determina-tion of effe
3、ctive boron-10 (10B) areal density (mass per area of10B, usually measured in grams-10B/cm2) in aluminum neu-tron absorbers. The attenuation of a thermal neutron beamtransmitted through an aluminum neutron absorber is com-pared to attenuation values for calibration standards allowingdetermination of
4、the effective10B areal density. This test istypically performed in a laboratory setting. This method isvalid only under the following conditions:1.1.1 The absorber contains10B in an aluminum or alumi-num alloy matrix.1.1.2 The primary neutron absorber is10B.1.1.3 The test specimen has uniform thickn
5、ess.1.1.4 The test specimen has a testing surface area at leasttwice that of the thermal neutron beams surface cross-sectional area.1.1.5 The calibration standards of uniform compositionspan the range of areal densities being measured.1.1.6 The areal density is between 0.001 and 0.080 grams of10B pe
6、r cm2.1.1.7 The thermalized neutron beam is derived from afission reactor, sub-critical assembly, accelerator or neutrongenerator.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address
7、all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards2C1671 Practice for
8、Qualification and Acceptance of BoronBased Metallic Neutron Absorbers for Nuclear CriticalityControl for Dry Cask Storage Systems and TransportationPackagingE1316 Terminology for Nondestructive Examinations3. Terminology3.1 For definitions of terms used in this test method, refer toTerminology E1316
9、.4. Summary of Test Method4.1 In this test method, aluminum neutron absorbers areplaced in a thermal neutron beam and the number of neutronstransmitted through the material in a known period of time iscounted. The neutron count can be converted to10B arealdensity by performing the same test on a ser
10、ies of appropriatecalibration standards and comparing the results.4.2 This test method uses a beam of neutrons with theneutron energy spectrum thermalized by an appropriate mod-erator. Other methods such as neutron diffraction may be usedto generate a thermal neutron beam.4.3 A beam of thermal neutr
11、ons shall be derived from afission reactor, sub-critical assembly, accelerator or neutrongenerator.5. Significance and Use5.1 The typical use of this test method is determination of10B areal density in aluminum neutron absorber materials usedto control criticality in systems such as: spent nuclear f
12、uel drystorage canisters, transfer/transport nuclear fuel containers,spent nuclear fuel pools, and fresh nuclear fuel transportcontainers.1This test method is under the jurisdiction of ASTM Committee E07 onNondestructive Testing and is the direct responsibility of Subcommittee E07.05 onRadiology (Ne
13、utron) Method.Current edition approved June 1, 2014. Published July 2014. Originally approvedin 2014. DOI: 10.1520/E2971-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, r
14、efer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.2 Areal density measurements are also used in the inves-tigation of the uniformity in10B spatial distribution.5.3 The exp
15、ected users of this standard include designers,suppliers, neutron absorber users, testing labs, and consultantsin the field of nuclear criticality analysis.5.4 Another known method used to determine areal densityof10B in aluminum neutron absorbers is an analytical chemicalmethod as mentioned in Prac
16、tice C1671. However, the analyti-cal chemical method does not measure the “effective”10B arealdensity as measured by neutron attenuation.6. Interferences6.1 Counts not associated with attenuation by the sampleshall be accounted for by measuring and incorporating back-ground readings. Background read
17、ing will vary depending onthe set up of the electronics of the system and the presence/absence of high energy photons.6.2 Measured count rates approaching the background countrate may limit the abilities of a system to accurately measurehighly attenuating samples.6.3 Coincidence loss may occur in th
18、e10B detector(s) whenthe neutron count rate is too high.7. Apparatus7.1 The essential features required for areal density mea-surement are the following:7.1.1 Source of thermal neutrons of an appropriate intensityto obtain the desired counting statistics in a reasonable timeperiod while not saturati
19、ng the detector. If the counting rate istoo high, pulses can pile up, causing counts to be lost in whatis called “coincidence loss.” The detector time constant in mostmodern counting circuits is sufficiently small to accommodateupto2106CPM. However, checks should be made to assurethat the coincidenc
20、e loss is not excessive.7.1.2 A neutron beam intensity monitor for correction ofneutron intensity fluctuations.7.1.3 A collimator long enough to result in a thermalneutron beam with a minimal beam divergence that will reducescattering contributions and10B measurement variability withsample thickness
21、. The collimator may be evacuated, filled withair, or an inert gas.7.1.4 A physical support, preferably adjustable, to mountthe standard and the test specimens in the neutron beam.7.1.5 A neutron detector, usually a boron tri-fluoride (BF3)filled detector tube. In BF3detectors, the pulse amplitudes
22、fromneutrons are much larger than the pulses produced by gammaradiation. The pulse height discriminator is normally readilyable to bias out the gamma pulses.7.1.6 Electronic circuitry to count the number of neutronsdetected by the neutron detector(s). The electronics generallyconsist of a pre-amplif
23、ier, amplifier, pulse-height discriminator,counting circuits and an appropriate timer7.1.7 A thermal neutron beam with a cross-sectional areabetween 0.75 cm2and 6.0 cm2. The diameter of the beamshould not exceed the active area of the neutron detector.8. Hazards8.1 This test method does not address
24、radiation safety. It isthe responsibility of the user of this test method to establishappropriate safety procedures, if necessary.9. Calibration and Standardization9.1 A series of standards with uniform, homogenous, andaccurately known10B areal densities is necessary for quanti-tative interpretation
25、 of the counting data acquired in theattenuation measurements. If the standards are not chemicallyhomogenous, the user of this standard must demonstrate thatthe uniformity of the samples10B is sufficient to meet theintention of this standard. These standards shall include10Bareal densities spanning
26、the range of areal densities expected inthe test specimens. Calibration standards must have a testingsurface area at least twice that of the thermal neutron beamscross-sectional area9.2 The number of standards used shall take into consider-ation the magnitude and range of the samples target arealden
27、sity and required accuracy of the measurement.Aminimumof three standards shall be used. The facility, calibrationstandards, and the test samples areal densities should beconsidered when determining the spacing of the calibrationareal densities. For example, when using a poly-energeticbeam, the optim
28、al spacing of the calibration standards arealdensities will not be uniform.9.3 Aluminum shim plate(s) may be required with thestandards to simulate the aluminum in the test specimen.Because the absorption and scattering cross-sections of alumi-num are very small, exact replication of the aluminum in
29、 thetest specimens is not critical. Scattering plays a very minor rolein neutron attenuation measurements. The standards shall beshimmed to ensure an equivalent or larger scattering contribu-tion than the test specimen.9.4 If the material used for calibration standards containsneutron absorbing or s
30、cattering nuclides not present in the testspecimens, or vice versa, the effect of these nuclides on theaccuracy of the measurements shall be addressed.10. Procedure10.1 The following procedure describes the method used tomeasure the calibration standards as well as the samples.Calibration, backgroun
31、d, and beam intensity shall be measuredeach time a set of samples are undergoing investigation, so themeasurement of these values is also described as part of theprocedure. This particular approach measures all values ascounts per measurement period.10.2 Prepare the neutron source for use. Verify th
32、at calibra-tion standards and test specimens are available and ready foruse.10.3 Measure the counting rate for the direct beam (db) withany holders in place.10.4 Measure the background counting rate (bkg) with astrong absorber at the sample position sufficient to attenuate theneutrons responsible fo
33、r the measurement.E2971 14210.5 Position a calibration standard at the exposure locationensuring that its thinnest dimension is perpendicular to thebeam line and the beam will not extend past any edges of thecalibration standard.10.6 Use the apparatus to establish the count rate throughthe calibrati
34、on standard ensuring an exposure of sufficientduration to obtain a minimum number of counts. The minimumnumber of counts shall be established to ensure an acceptablelevel of uncertainty in calculated10B areal densities.10.7 Repeat steps 10.5 and 10.6 with all other selectedcalibration standards.10.8
35、 Record the values obtained from the measured calibra-tion standards.10.9 Position a sample at the exposure location ensuringthat the thinnest dimension of the sample is perpendicular tothe beam line and the beam will not extend past any edges ofthe sample.10.10 Use the apparatus to establish the co
36、unt rate throughthe sample ensuring an exposure of sufficient duration to obtaina minimum number of counts. The minimum number of countsshall be established to ensure an acceptable level of uncertaintyin calculated10B areal densities.11. Calculation or Interpretation of Results11.1 The effective10B
37、areal density of a sample is deter-mined from the measurements detailed in the procedure inSection 10.After correcting the measured counts of the sampleand calibration standards, the effective10B areal density isdetermined by mathematical or graphical methods (on the basisof the logarithmic attenuat
38、ion of neutrons) to establish theeffective10B areal density of the samples from the known10Bareal densities of the calibration standards.11.2 Count Rate11.2.1 The raw count rate for each data point must becorrected for fluctuations in neutron intensity and corrected forbackground radiation detection
39、s. The corrected count rate iscalculated by:Cci! 5Crawi!trawi!3Cpowerdb!tpowerdb!Cpoweri!tpoweri!2Crawbkg!trawbkg!3Cpowerdb!tpowerdb!Cpowerbkg!tpowerbkg!(1)where:i = a sample or calibration standard referenceidentifierCc(i) = corrected counts per second for the test part iCraw(i) = raw counts from t
40、he test part itraw(i) = count time from the test part iCpower(i) = power counts from the test part itpower(i) = power count time from the test part iCraw(bkg) = raw counts from the background calibrationtraw(bkg) = count time from the background calibrationCpower(bkg) = power counts from the backgro
41、und calibrationtpower(bkg) = power count time from the background cali-brationCpower(db) = power counts from the direct beamtpower(db) = power count time from the direct beamNOTE 1Eq 1 normalizes the count rates with the power counts fromthe direct beam measurement. Normalizing with any consistent c
42、alibrationpower count is valid.11.3 B10 Areal Density Determination11.3.1 The10B areal density is determined based on inter-polation from the calibration standard and test samples cor-rected count rates. This interpolation needs to take into accountthe exponential attenuation of neutrons. The mathem
43、aticalmethod to determine a test samples areal density, as describedbelow, uses the two calibration standards that bound the testsamples count rate. This is intended to reduce bias from beamhardening (a gradual increase in the energy spectrum of theneutron beam as it passes through the absorber in b
44、road energyspectrum beams) and the associated change in neutron attenu-ation that results from this change in the neutron energyspectrum. Alternative mathematical or graphical interpolationmethods using two or more calibration points may also beacceptable provided they have been properly validated.1
45、1.3.2 Interpolating between two calibration standards, asamples10B content can be determined as follows:NADi! 53lnCc(calib high)Cci!lnCc(calib high)Cc(calib low)43NADlow!2 NADhigh!1NADhigh!(2)where,Cc(calib high) = corrected counts per second for the calibra-tion part with10B areal density greater t
46、hanCc(i)Cc(calib low) = corrected counts per second for the calibra-tion part with10B areal density less thanCc(i)NAD(i)= nominal areal density of test part iNAD(high)= nominal areal density of calibration partchosen as Cc(calib high)NAD(low)= nominal area l density of calibration partchosen as Cc(c
47、alib low)12. Report12.1 Report the following information:12.1.1 The10B areal density calculated with the associateduncertainty,12.1.2 The number and10B areal density of the calibrationstandards used,12.1.3 The testing facility and apparatus, and12.1.4 The calculation method used.13. Precision and Bi
48、as13.1 An interlaboratory study of this test method is beingconducted and a complete precision statement is expected to beavailable in or before 2015.13.2 The precision is influenced by the counting uncertaintyand the uncertainty in the known areal density of the calibra-tion standards.13.3 Care sho
49、uld be exercised to assure that no other strongattenuators are present in the test specimen or referenceE2971 143standards. Strongly attenuating impurities in the test specimenmay be interpreted as10B and distort the10B areal density.13.4 Beam hardening of the thermal neutron beam canresult in somewhat non-exponential attenuation of neutrons. Toreduce bias, reduced spacing between the areal densities incalibration standards for poly energetic neutron beams may berequired.13.5 As10B areal densities approach the limits of a facilitysmeasurement capab
