1、Designation: E266 11Standard Test Method forMeasuring Fast-Neutron Reaction Rates by Radioactivationof Aluminum1This standard is issued under the fixed designation E266; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast 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 covers procedures measuring reactionrates by the activation reaction27Al(n,a)24Na.1.2 This activation
3、reaction is useful for measuring neutronswith energies above approximately 6.5 MeV and for irradiationtimes up to about 2 days (for longer irradiations, see PracticeE261).1.3 With suitable techniques, fission-neutron fluence ratesabove 106cm2s1can be determined.1.4 Detailed procedures for other fast
4、 neutron detectors arereferenced in Practice E261.1.5 This standard does not purport to address 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 r
5、egulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E170 Terminology Relating to Radiation Measurements andDosimetryE181 Test Methods for Detector Calibration andAnalysis ofRadionuclidesE261 Practice for Determining Neutron Fluence, FluenceRate, and Spectra by Radioactivati
6、on TechniquesE844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E 706(IIC)E944 Guide for Application of Neutron Spectrum Adjust-ment Methods in Reactor Surveillance, E 706 (IIA)E1005 Test Method for Application and Analysis of Radio-metric Monitors for Reactor Vessel Surveilla
7、nce, E706(IIIA)E1018 Guide for Application of ASTM Evaluated CrossSection Data File, Matrix E706 (IIB)3. Terminology3.1 Definitions:3.1.1 Refer to Terminology E170.4. Summary of Test Method4.1 High-purity aluminum is irradiated in a neutron field,thereby producing radioactive24Na from the27Al(n,a)24
8、Naactivation reaction.4.2 The gamma rays emitted by the radioactive decay of24Na are counted (see Test Methods E181) and the reactionrate, as defined by Practice E261, is calculated from the decayrate and irradiation conditions.4.3 The neutron fluence rate above about 6.5 MeV can thenbe calculated f
9、rom the spectral-weighted neutron activationcross section as defined by Practice E261.5. Significance and Use5.1 Refer to Guide E844 for the selection, irradiation, andquality control of neutron dosimeters.5.2 Refer to Practice E261 for a general discussion of thedetermination of fast-neutron fluenc
10、e rate with threshold de-tectors.5.3 Pure aluminum in the form of foil or wire is readilyavailable and easily handled.27Al has an abundance of 100 %(1)3.5.424Na has a half-life of 14.9574 h (2) and emits gammarays with energies of 1.368626 and 2.754007 MeV (2).5.5 Fig. 1 shows a plot of cross sectio
11、n versus neutronenergy for the fast-neutron reaction27Al(n,a)24Na (3) alongwith a comparison to the current experimental database (4).1This test method is under the jurisdiction ofASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.05 on Nucle
12、ar Radiation Metrology.Current edition approved June 1, 2011. Published June 2007. Originallyapproved in 1965. Last previous edition approved in 2007 as E266 07. DOI:10.1520/E0266-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.
13、org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to a list of References at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken
14、, PA 19428-2959, United States.This figure is for illustrative purposes only to indicate the rangeof response of the27Al(n,a) reaction. Refer to Guide E1018 fordescriptions of recommended tabulated dosimetry cross sec-tions.5.6 Two competing activities,28Al and27Mg, are formed inthe reactions27Al(n,
15、g)28Al and27Al(n,p)27Mg, respectively,but these can be eliminated by waiting 2 h before counting.6. Apparatus6.1 NaI(T1) or High Resolution Gamma-Ray Spectrometer.Because of its high resolution, the germanium detector isuseful when contaminant activities are present (see Test Meth-ods E181 and E1005
16、).6.2 Precision Balance, able to achieve the required accu-racy.7. Materials7.1 The purity of the aluminum is important. No impuritiesshould be present that produce long-lived gamma-ray-emittingradionuclides having gamma-ray energies that interfere withthe24Na determination. Discard aluminum that co
17、ntains suchimpurities or that contains quantities of23Na sufficient tointerfere, through thermal-neutron capture, with24Na determi-nation. The presence of these impurities should be determinedby activation analysis since spectrographically pure aluminummay contain a contaminant not detectable by the
18、 emissionspectrograph. If the24Na content of the irradiated samples isdetermined from the emission rate of the 2.754007 MeVgamma ray, the probability of interference from contaminantgamma rays is much less than if the 1.368626 MeV gamma rayis used.7.2 Encapsulating MaterialsBrass, stainless steel, c
19、opper,aluminum, quartz, or vanadium have been used as primaryencapsulating materials. The container should be constructedin such a manner that it will not create significant fluxperturbation and that it may be opened easily, especially if thecapsule is to be opened remotely (see Guide E844).8. Proce
20、dure8.1 Decide on the size and shape of aluminum sample to beirradiated. This is influenced by the irradiation space and theexpected production of24Na. Calculate the expected productionrate of24Na from the activation equation described in Section9, and adjust sample size and irradiation time so that
21、 the24Namay be accurately counted.Atrial irradiation is recommended.8.2 Determine a suitable irradiation time (see 8.1).Since24Na has a 14.9574 h half-life, the24Na activity willapproach equilibrium after a day of irradiation.8.3 Weigh the sample.8.4 Irradiate the sample for the predetermined time p
22、eriod.Record the power level and any changes in power during theirradiation, the time at the beginning and end of the irradiation,and the relative position of the monitors in the irradiationfacility.8.5 After irradiation, the sample should be thoroughlyrinsed in warm water. This will remove any24Na
23、surfacecontamination produced during irradiation.8.6 Check the sample for activity from cross-contaminationby other irradiated materials. Clean, if necessary, and reweigh.8.7 Analyze the sample for24Na content in disintegrationsper second using the gamma-ray spectrometer after the28Aland27Mg have de
24、cayed (1 to 2 h will usually suffice) or until thecontaminant activities, if any, have decayed (see Test MethodsE181 and E1005).8.8 Disintegration of24Na nuclei produces 1.368626-MeVand 2.754007-MeVgamma rays with probabilities per decay of0.999935 and 0.99872, respectively (2). When analyzing eithe
25、rgamma-ray peak, a correction for coincidence summing maybe required if the sample is placed close to the detector (10 cmor less) (see Test Methods E181).8.9 If any question exists as to the purity of the gamma raybeing counted, the sample should be counted periodically todetermine if the decay foll
26、ows the 14.9574-h half-life of24Na(2).9. Calculations9.1 Calculate the saturation activity As, as follows:As5 A/1 2 exp 2 lti#! exp 2 ltw#!# (1)where:A =24Na disintegrations per second measured by count-ing,l = decay constant for24Na = 1.287262 3 105s1,ti= irradiation duration, s, andtw= elapsed tim
27、e between the end of irradiation andcounting, s.NOTE 1The equation Asis valid if the reactor operated at essentiallyconstant power and if corrections for other reactions (for example,impurities, burnout, etc.) are negligible. Refer to Practice E261 for moregeneralized treatments.9.2 Calculate the re
28、action rate, Rs, as follows:Rs5 As/No(2)where:As= saturation activity, andNo= number of27Al atoms.9.3 Refer to Practice E261 and Guide E944 for a discussionof fast-neutron fluence rate and fluence.FIG. 127Al(n,a)24Na Cross Section with EXFOR ExperimentalDataE266 11210. Report10.1 Practice E261 descr
29、ibes how data should be reported.11. Precision and BiasNOTE 2Measurement uncertainty is described by a precision and biasstatement in this standard. Another acceptable approach is to use Type Aand B uncertainty components (5,6). This Type A/B uncertainty specifi-cation is now used in International O
30、rganization for Standardization (ISO)standards and this approach can be expected to play a more prominent rolein future uncertainty analyses.11.1 General practice indicates that disintegration rates canbe determined with bias of 6 3 % (1S %) and with a precisionof 6 1 % (1S %).11.2 The energy-depend
31、ent uncertainty, expressed as a per-centage of the baseline cross section, for the27Al(n,a)24Nacross section is shown in Fig. 2.(3)11.3 Test results have been reported in neutron benchmarkfields.11.3.1 In the252Cf spontaneous fission reference neutronfield, the measured cross section is 1.016 b 6 1.
32、47 % (7) andthe calculated cross section using the RRDF-2008 cross sectionis 1.0182 b with a spectrum integrated cross section under-tainty of 0.336 % (3) and a spectrum characterization uncer-tainty of 1.609 %. This results in a calculated-to-experimental(C/E) ratio of 1.0022 6 2.21 %.11.3.2 In the
33、235U thermal neutron field, the measured crosssection is 0.7007 b 6 1.28 % (7) and the calculated crosssection using the RRDF-2008 cross section is 0.7173 b with aspectrum integrated cross section uncertainty of 0.287 % (3)and a spectrum characterization uncertainty of 6.951 %. Thisresults in a calc
34、ulated-to-experimental (C/E) ratio of 1.024 67.08 %.12. Keywords12.1 activation; activation reaction; aluminum; cross sec-tion; dosimetry; fast-neutron monitor; neutron metrology; pres-sure vessel surveillance; reaction rateREFERENCES(1) Nuclear Wallet Cards, compiled by J. K. Tuli, National Nuclear
35、 DataCenter, April 2005.(2) Update of X-ray and Gamma Ray Decay Data Standards for DetectorCalibration and Other Applications: Vol 1: Reommended Decay Data,High Energy Gamma Ray Standards and Anular Correlation Coeffi-cients, International Atomic Energy Agency, Vienna, report STI/PUB/1287, 2007.(3)
36、Zolotarev, K. I., Ignatyuk, A. V., Mahokhin, V. N., Pashchenco, A. B.,“RRDF-98 Russian Reactor Dosimetry File”, report IAEA-NDS-193,March 1999. The last full release was in 1998. Updated versionsreferenced here corresponding to the RRDF-2008 library.(4) “EXFOR Formats Description for Users (EXFOR Ba
37、sics)”, reportIAEA-NDS-206, International Atomic Energy Agency, Vienna, Aus-tria, June 2008. On-line database available at URL: http:/www-nds.iaea.org/indg_nexp.html. Data here as present on January 3, 2011.(5) Guide to the Expression of Uncertainty in Measurement, InternationalOrganization for Stan
38、dardization,1995, ISBN 92-67-10188-9.(6) Taylor, B. N., Kuyatt, C. E., Guidelines for Evaluating and Expressingthe Uncertainty of NIST Measurement Results, NIST Technical Note1297, National Institute of Standards and Technology, Gaithersbrug,MD, 1994.(7) Mannhart, W., Validation of Differential Cros
39、s Sections with IntegralData, Report INDC(NDS)-435, pp. 59-64, IAEA, Vienna, September2002.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination
40、 of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdraw
41、n. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your co
42、mments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single o
43、r multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).FIG. 2 Energy-dependent undertainty (%) for the27Al(N,a)24NaCross SectionE266 113
