1、Designation: E2971 14E2971 16Standard 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 ofo
2、riginal 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. Scope Scope*1.1 This test method is intended for quantitative determi
3、nation of effective boron-10 (10B) areal density (mass per area of 10B,usually measured in grams-10B/cm2 ) in aluminum neutron absorbers. The attenuation of a thermal neutron beam transmittedthrough an aluminum neutron absorber is compared to attenuation values for calibration standards allowing det
4、ermination of theeffective 10B areal density. This test is typically performed in a laboratory setting. This method is valid only under the followingconditions:1.1.1 The absorber contains 10B in an aluminum or aluminum alloy matrix.1.1.2 The primary neutron absorber is 10B.1.1.3 The test specimen ha
5、s uniform thickness.1.1.4 The test specimen has a testing surface area at least twice that of the thermal neutron beams surface cross-sectional area.1.1.5 The calibration standards of uniform composition span the range of areal densities being measured.1.1.6 The areal density is between 0.001 and 0.
6、080 grams of 10B per cm2.1.1.7 The thermalized neutron beam is derived from a fission reactor, sub-critical assembly, accelerator or neutron generator.1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does
7、not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standard
8、s2C1671 Practice for Qualification andAcceptance of Boron Based Metallic NeutronAbsorbers for Nuclear Criticality Control forDry Cask Storage Systems and Transportation PackagingE1316 Terminology for Nondestructive Examinations3. Terminology3.1 For definitions of terms used in this test method, refe
9、r to Terminology E1316.4. Summary of Test Method4.1 In this test method, aluminum neutron absorbers are placed in a thermal neutron beam and the number of neutronstransmitted through the material in a known period of time is counted. The neutron count can be converted to 10B areal densityby performi
10、ng the same test on a series of appropriate calibration standards and comparing the results.4.2 This test method uses a beam of neutrons with the neutron energy spectrum thermalized by an appropriate moderator. Othermethods such as neutron diffraction may be used to generate a thermal neutron beam.4
11、.3 A beam of thermal neutrons shall be derived from a fission reactor, sub-critical assembly, accelerator or neutron generator.1 This test method is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.05 on Radiology(Neutron) Me
12、thod.Current edition approved June 1, 2014June 1, 2016. Published July 2014June 2016. Originally approved in 2014. Last previous edition approved in 2014 as E2971-14.DOI: 10.1520/E2971-14.10.1520/E2971-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Se
13、rvice at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previ
14、ous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Chan
15、ges section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 The typical use of this test method is determination of 10B areal density in aluminum neutron absorber materials
16、 used tocontrol criticality in systems such as: spent nuclear fuel dry storage canisters, transfer/transport nuclear fuel containers, spentnuclear fuel pools, and fresh nuclear fuel transport containers.5.2 Areal density measurements are also used in the investigation of the uniformity in 10B spatia
17、l distribution.5.3 The expected users of this standard include designers, suppliers, neutron absorber users, testing labs, and consultants in thefield of nuclear criticality analysis.5.4 Another known method used to determine areal density of 10B in aluminum neutron absorbers is an analytical chemic
18、almethod as mentioned in Practice C1671. However, the analytical chemical method does not measure the “effective” 10B arealdensity as measured by neutron attenuation.6. Interferences6.1 Counts not associated with attenuation by the sample shall be accounted for by measuring and incorporating backgro
19、undreadings. Background reading will vary depending on the set up of the electronics of the system and the presence/absence of highenergy photons.6.2 Measured count rates approaching the background count rate may limit the abilities of a system to accurately measure highlyattenuating samples.6.3 Coi
20、ncidence loss may occur in the 10B detector(s) when the neutron count rate is too high.7. Apparatus7.1 The essential features required for areal density measurement are the following:7.1.1 Source of thermal neutrons of an appropriate intensity to obtain the desired counting statistics in a reasonabl
21、e time periodwhile not saturating the detector. If the counting rate is too high, pulses can pile up, causing counts to be lost in what is called“coincidence loss.” lost. The detector time constant in most modern counting circuits is sufficiently small to accommodate up to2 106 CPM. However, checks
22、should be made to assureensure that the coincidence loss system resolving time is not excessive.7.1.2 A neutron beam intensity monitor for correction of neutron intensity fluctuations.7.1.3 A collimator long enough to result in a thermal neutron beam with a minimal beam divergence that will reduce s
23、catteringcontributions and 10B measurement variability with sample thickness. The collimator may be evacuated, filled with air, or an inertgas.7.1.4 A physical support, preferably adjustable, to mount the standard and the test specimens in the neutron beam.7.1.5 A neutron detector, usually a boron t
24、ri-fluoride (BF3) filled detector tube. In BF3 detectors, the pulse amplitudes fromneutrons are much larger than the pulses produced by gamma radiation. The pulse height discriminator is normally readily ableto bias out the gamma pulses.7.1.6 Electronic circuitry to count the number of neutrons dete
25、cted by the neutron detector(s). The electronics generally consistof a pre-amplifier, amplifier, pulse-height discriminator, counting circuits and an appropriate timer7.1.7 A thermal neutron beam with a cross-sectional area between 0.75 cm2 and 6.0 cm2. The diameter of the beam should notexceed the
26、active area of the neutron detector.8. Hazards8.1 This test method does not address radiation safety. It is the 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,
27、 and accurately known 10B areal densities is necessary for quantitativeinterpretation of the counting data acquired in the attenuation measurements. If the standards are not chemically homogenous, theuser of this standard must demonstrate that the uniformity of the samples 10B is sufficient to meet
28、the intention of this standard.These standards shall include 10B areal densities spanning the range of areal densities expected in the test specimens. Calibrationstandards must have a testing surface area at least twice that of the thermal neutron beams cross-sectional area9.2 The number of standard
29、s used shall take into consideration the magnitude and range of the samples target areal density andrequired accuracy of the measurement.Aminimum of three standards shall be used. The facility, calibration standards, and the testsamples areal densities should be considered when determining the spaci
30、ng of the calibration areal densities. For example, whenusing a poly-energetic beam, the optimal spacing of the calibration standards areal densities will not be uniform.9.3 Aluminum shim plate(s) may be required with the standards to simulate the aluminum in the test specimen. Because theabsorption
31、 and scattering cross-sections of aluminum are very small, exact replication of the aluminum in the test specimens is notcritical. Scattering plays a very minor role in neutron attenuation measurements. The standards shall be shimmed to ensure anequivalent or larger scattering contribution than the
32、test specimen.E2971 1629.4 If the material used for calibration standards contains neutron absorbing or scattering nuclides not present in the testspecimens, or vice versa, the effect of these nuclides on the accuracy of the measurements shall be addressed.10. Procedure10.1 The following procedure d
33、escribes the method used to measure the calibration standards as well as the samples.Calibration, background, and beam intensity shall be measured each time a set of samples are undergoing investigation, so themeasurement of these values is also described as part of the procedure. This particular ap
34、proach measures all values as counts permeasurement period.10.2 Prepare the neutron source for use. Verify that calibration standards and test specimens are available and ready for use.10.3 Measure the counting rate for the direct beam (db) with any holders in place.10.4 Measure the background count
35、ing rate (bkg) with a strong absorber at the sample position sufficient to attenuate theneutrons responsible for the measurement.10.5 Position a calibration standard at the exposure location ensuring that its thinnest dimension is perpendicular to the beamline and the beam will not extend past any e
36、dges of the calibration standard.10.6 Use the apparatus to establish the count rate through the calibration standard ensuring an exposure of sufficient durationto obtain a minimum number of counts. The minimum number of counts shall be established to ensure an acceptable level ofuncertainty in calcu
37、lated 10B areal densities.10.7 Repeat steps 10.5 and 10.6 with all other selected calibration standards.10.8 Record the values obtained from the measured calibration standards.10.9 Position a sample at the exposure location ensuring that the thinnest dimension of the sample is perpendicular to the b
38、eamline and the beam will not extend past any edges of the sample.10.10 Use the apparatus to establish the count rate through the sample ensuring an exposure of sufficient duration to obtain aminimum number of counts. The minimum number of counts shall be established to ensure an acceptable level of
39、 uncertainty incalculated 10B areal densities.11. Calculation or Interpretation of Results11.1 The effective 10B areal density of a sample is determined from the measurements detailed in the procedure in Section 10.After correcting the measured counts of the sample and calibration standards, the eff
40、ective 10B areal density is determined bymathematical or graphical methods (on the basis of the logarithmic attenuation of neutrons) to establish the effective 10B arealdensity of the samples from the known 10B areal densities of the calibration standards.11.2 Count RateRate11.2.1 The raw count rate
41、 for each data point must be corrected for fluctuations in neutron intensity and corrected forbackground radiation detections. The corrected count rate is calculated by:Cci!5Crawi!trawi! 3Cpowerdb!tpowerdb!Cpoweri!tpoweri!2Crawbkg!trawbkg! 3Cpowerdb!tpowerdb!Cpowerbkg!tpowerbkg!(1)where:i = a sample
42、 or calibration standard reference identifierCc(i) = corrected counts per second for the test part iCraw(i) = raw counts from the 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 f
43、rom the background calibrationtraw(bkg) = count time from the background calibrationCpower(bkg) = power counts from the background calibrationtpower(bkg) = power count time from the background calibrationCpower(db) = power counts from the direct beamtpower(db) = power count time from the direct beam
44、NOTE 1Eq 1 normalizes the count rates with the power counts from the direct beam measurement. Normalizing with any consistent calibration powercount is valid.11.3 B10 Areal Density DeterminationDeterminationE2971 16311.3.1 The 10B areal density is determined based on interpolation from the calibrati
45、on standard and test samplescorrected countrates. This interpolation needs to take into account the exponential attenuation of neutrons. The mathematical method to determinea test samples areal density, as described below, uses the two calibration standards that bound the test samples count rate. Th
46、isis intended to reduce bias from beam hardening (a gradual increase in the energy spectrum of the neutron beam as it passes throughthe absorber in broad energy spectrum beams) and the associated change in neutron attenuation that results from this change inthe neutron energy spectrum. Alternative m
47、athematical or graphical interpolation methods using two or more calibration pointsmay also be acceptable provided they have been properly validated.11.3.2 Interpolating between two calibration standards, a samples 10B content can be determined as follows:NADi!53lnCc (calib high)Cci!lnCc(calib high)
48、Cc(calib low)4 3NADlow! 2 NADhigh!1NADhigh! (2)where,Cc(calib high) = corrected counts per second for the calibration part with 10B areal density greater than Cc(i)Cc(calib low) = corrected counts per second for the calibration part with 10B areal density less than Cc(i)NAD(i) = nominal areal densit
49、y of test part iNAD(high) = nominal areal density of calibration part chosen as Cc(calib high)NAD(low) = nominal area l density of calibration part chosen as Cc(calib low)12. Report12.1 Report the following information:12.1.1 The 10B areal density calculated with the associated uncertainty,12.1.2 The number and 10B areal density of the calibration standards used,12.1.3 The testing facility and apparatus, and12.1.4 The calculation method used.13. Precision and Bias13.1 PrecisionAn interlaboratory study The repeatability standard deviation from a
