ASTM E266-2007 Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Aluminum《用铝的放射性测量快速中子反应速率的标准试验方法》.pdf

1、Designation: E 266 07Standard Test Method forMeasuring Fast-Neutron Reaction Rates by Radioactivationof Aluminum1This standard is issued under the fixed designation E 266; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of

2、 last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 activati

3、on reaction is useful for measuring neutronswith energies above approximately 6.5 MeV and for irradiationtimes up to about 2 days (for longer irradiations, see PracticeE 261).1.3 With suitable techniques, fission-neutron fluence ratesabove 106cm2s1can be determined.1.4 Detailed procedures for other

4、fast neutron detectors arereferenced in Practice E 261.1.5 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

5、 of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 170 Terminology Relating to Radiation Measurementsand DosimetryE 181 Test Methods for Detector Calibration and Analysisof RadionuclidesE 261 Practice for Determining Neutron Fluence, FluenceRate, and Spectra by Radi

6、oactivation TechniquesE 844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E 706(IIC)E 944 Guide for Application of Neutron Spectrum Adjust-ment Methods in Reactor Surveillance, E 706 (IIA)E 1005 Test Method forApplication andAnalysis of Radio-metric Monitors for Reactor Vessel

7、 Surveillance, E706(IIIA)E 1018 Guide for Application of ASTM Evaluated CrossSection Data File, Matrix E 706 (IIB)3. Terminology3.1 Definitions:3.1.1 Refer to Terminology E 170.4. Summary of Test Method4.1 High-purity aluminum is irradiated in a neutron field,thereby producing radioactive24Na from t

8、he27Al(n,a)24Naactivation reaction.4.2 The gamma rays emitted by the radioactive decay of24Na are counted (see Test Methods E 181) and the reactionrate, as defined by Practice E 261, is calculated from the decayrate and irradiation conditions.4.3 The neutron fluence rate above about 6.5 MeV can then

9、be calculated from the spectral-weighted neutron activationcross section as defined by Practice E 261.5. Significance and Use5.1 Refer to Guide E 844 for the selection, irradiation, andquality control of neutron dosimeters.5.2 Refer to Practice E 261 for a general discussion of thedetermination of f

10、ast-neutron fluence rate with threshold de-tectors.5.3 Pure aluminum in the form of foil or wire is readilyavailable and easily handled.5.424Na has a half-life of 14.951 h (1)3and emits gammarays with energies of 1.368.633 and 2.754028 MeV (2).5.5 Fig. 1 shows a plot of cross section versus neutrone

11、nergy for the fast-neutron reaction27Al(n,a)24Na from theIRDF2002 dosimetry cross section library(3). This figure is forillustrative purposes only to indicate the range of response ofthe27Al(n,a) reaction. Refer to Guide E 1018 for descriptionsof recommended tabulated dosimetry cross sections.5.6 Tw

12、o competing activities,28Al and27Mg, are formed inthe reactions27Al(n,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 is1This test

13、 method is under the jurisdiction ofASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.05 on Nuclear Radiation Metrology.Current edition approved June 1, 2007. Published June 2007. Originallyapproved in 1965. Last previous edition approved in

14、 2002 as E 266 02.2For 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 Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer

15、to a list of References at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.useful when contaminant activities are present (see Test Meth-ods E 181 and E 1005).6.2 Precision Balance, able to achieve the require

16、d 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 contains suchimpurities or that contains quantities of

17、23Na 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 emissionspectrograph. If the24Na content of the irr

18、adiated samples isdetermined from the emission rate of the 2.754028 MeVgamma ray, the probability of interference from contaminantgamma rays is much less than if the 1.368.6333 MeV gammaray is used.7.2 Encapsulating MaterialsBrass, stainless steel, copper,aluminum, quartz, or vanadium have been used

19、 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 E 844).8. Procedure8.1 Decide on the size and shape of aluminum

20、sample to beirradiated. This is influenced by the irradiation space and theexpected production of24Na. Calculate the expected produc-tion rate of24Na from the activation equation described inSection 9, and adjust sample size and irradiation time so thatthe24Na may be accurately counted. A trial irra

21、diation isrecommended.8.2 Determine a suitable irradiation time (see 8.1).Since24Na has a 14.951 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 period.Record the power level and any changes in

22、 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 surfacecontamination produced during irradiatio

23、n.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 decayed (1 to 2 h will usually suffice) or until

24、thecontaminant activities, if any, have decayed (see Test MethodsE 181 and E 1005).8.8 Disintegration of24Na nuclei produces 1.368.633-MeVand 2.754028-MeVgamma rays with probabilities per decay of0.9999 and 0.9986, respectively (2). When analyzing eithergamma-ray peak, a correction for coincidence s

25、umming maybe required if the sample is placed close to the detector (10 cmor less) (see Test Methods E 181).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 follows the 14.9512-h half-life of24Na.9. Calculat

26、ions9.1 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 = 1.2878 3 105s1,ti= irradiation duration, s, andtw= elapsed time between the end of irradiation andcounting, s.NOT

27、E 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 E 261 for moregeneralized treatments.9.2 Calculate the reaction rate, Rs, as follows:Rs5 As/No(2)where:As=

28、saturation activity, andNo= number of27Al atoms.9.3 Refer to Practice E 261 and Guide E 944 for a discus-sion of fast-neutron fluence rate and fluence.10. Report10.1 Practice E 261 describes how data should be reported.11. Precision and BiasNOTE 2Measurement uncertainty is described by a precision a

29、nd biasstatement in this standard. Another acceptable approach is to use Type Aand B uncertainty components (4,5). This Type A/B uncertainty specifi-cation is now used in International Organization for Standardization (ISO)standards and this approach can be expected to play a more prominent rolein f

30、uture uncertainty analyses.FIG. 127Al(n,a)24Na Cross SectionE26607211.1 General practice indicates that disintegration rates canbe determined with bias of 6 3 % (1S %) and with a precisionof 6 1 % (1S %).12. Keywords12.1 activation; activation reaction; aluminum; cross sec-tion; dosimetry; fast-neut

31、ron monitor; neutron metrology; pres-sure vessel surveillance; reaction rateREFERENCES(1) Tulti, J. K., “Nuclear Wallet Cards,” National Nuclear Data Center,Brookhaven National Laboratory, Upton, New York, April 2005.(2) Evaluated Nuclear Structure Data File (ENSDF), a computer file ofevaluated nucl

32、ear structure and radioactive decay data, which ismaintained by the National Nuclear Data Center (NNDC), BrookhavenNational Laboratory (BNL), on behalf of the International Network forNuclear Structure Data Evaluation, which functions under the auspicesof the Nuclear Data Section of the Internationa

33、l Atomic EnergyAgency (IAEA). The URL is http:/www.nndc.bnl.gov/nndc/ensdf. Thedata quoted here comes from the database as of April 2, 2007.(3) International Reactor Dosimetry File 2002 (IRDF200), TechnicalReport Series 452, InternationalAtomic EnergyAgency, Vienna, 2006.(4) Taylor, B. N., Kuyatt, C

34、. E., Guidelines for Evaluating and Expressingthe Uncertainty of NIST Measurement Results, NIST Technical Note1297, National Institute of Standards and Technology, Gaithersbrug,MD, 1994.(5) Guide in the Expression of Uncertainty in Measurement, InternationalOrganization for Standardization, 1995, IS

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