1、Designation: E 523 07Standard Test Method forMeasuring Fast-Neutron Reaction Rates by Radioactivationof Copper1This standard is issued under the fixed designation E 523; 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers procedures for measuring reac-tion rates by the activation reaction63Cu(n,a)60Co. The crosssec
3、tion for60Co produced in this reaction increases rapidlywith neutrons having energies greater than about 5 MeV.60Codecays with a half-life of 1925.28 days (60.5 days)(1)2andemits two gamma rays having energies of 1.1732228 and1.332492 MeV(2). The isotopic content of natural copper is69.17 %63Cu and
4、30.83 %65Cu (1). The neutronreaction,63Cu(n,g)64Cu, produces a radioactive product thatemits gamma rays which might interfere with the counting ofthe60Co gamma rays.1.2 With suitable techniques, fission-neutron fluence ratesabove 109cm2s1can be determined. The63Cu(n,a)60Coreaction can be used to det
5、ermine fast-neutron fluences forirradiation times up to about 15 years (for longer irradiations,see Practice E 261).1.3 Detailed procedures for other fast-neutron detectors arereferenced in Practice E 261.1.4 This standard does not purport to address all of thesafety concerns, if any, associated wit
6、h 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 Standards:3E 170 Terminology Relating to Radiation Measurementsand DosimetryE
7、181 Test Methods for Detector Calibration and Analysisof RadionuclidesE 261 Practice for Determining Neutron Fluence, FluenceRate, and Spectra by Radioactivation TechniquesE 844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E 706(IIC)E 944 Guide for Application of Neutron Spec
8、trum Adjust-ment Methods in Reactor Surveillance, E 706 (IIA)E 1005 Test Method forApplication andAnalysis of Radio-metric Monitors for Reactor Vessel 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
9、Refer to Terminology E 170.4. Summary of Test Method4.1 High-purity copper (1 g/g), thereported possible thermal component of the (n,a) reaction, andthe possibly significant cross sections for thermal neutrons for63Cu and60Co (that is 4.5 and 2.0 barns, respectively),(4) whichwill require burnout co
10、rrections at high fluences.6. Apparatus6.1 NaI(Tl) or High Resolution Gamma-RaySpectrometerBecause of its high resolution, the germaniumdetector is useful when contaminant activities are present orwhen it is necessary to analyze before the 12.7 h64Cu hasdecayed.6.2 Precision Balance, able to achieve
11、 the required accu-racy.7. Materials7.1 Copper MetalPure copper metal in the form of wire orfoil is available.7.1.1 The metal should be tested for impurities by a neutronactivation technique. If the measurement is to be made in athermal-neutron environment, there must be no cobalt impurity(1 g/g) be
12、cause the reaction59Co(n,g)60Co produces thesame product as produced in the subject reaction. To reducethis interference, the use of a thermal-neutron shield duringirradiation would be advisable if cobalt impurity is suspected.7.2 Encapsulating MaterialsBrass, stainless steel, copper,aluminum, quart
13、z, 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 E 844).8. Procedure8.1 Decide on th
14、e size and shape of the copper sample to beirradiated, taking into consideration the size and shape of theirradiation space. The mass and exposure time are parametersthat can be varied to obtain a desired disintegration rate for agiven neutron fluence rate level (see Guide E 844).8.2 Weigh the sampl
15、e.8.3 Irradiate the sample for the predetermined time period.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.8.4 A waiting period of about 6 days is recomm
16、endedbetween termination of the exposure and analyzing the samplefor60Co content. This allows the 12.7 h64Cu to decay so thatthere is no interference from the gamma rays emitted by64Cu,that is, the 0.511 and 1.34577 MeV gamma rays.(2) However,analysis may be performed sooner if a suitable gamma-ray
17、orpeak analysis technique is used.8.5 Check the sample for activity from cross-contaminationby other irradiated materials. Clean, if necessary and reweigh.8.6 Analyze the sample for60Co content in disintegrationsper second using the gamma-ray spectrometer (see Test Meth-ods E 181 and E 1005).8.7 Dis
18、integration of60Co nuclei produces 1.173228 MeVand 1.332492 MeV gamma rays with probabilities per decay of0.9985 and 0.999826 respectively.(2) When analyzing eitherpeak in the gamma-ray spectrum, a correction for coincidencesumming may be required if the sample is placed close to thedetector (10 cm
19、or less) (see Test Methods E 181).9. Calculations9.1 Calculate the saturation activity As, as follows:FIG. 163Cu(n,a)60Co Cross SectionE523072As5 A/1 2 exp 2 lti#! exp 2 ltw#!#(1)where:A =60Co disintegrations per second measured by count-ing,l = decay constant for60Co = 4.167 3 109s1,ti= irradiation
20、 duration s,tw= elapsed time between the end of irradiation andcounting, s.NOTE 2The equation for Asis valid if the reactor operated atessentially constant power and if corrections for other reactions (forexample, impurities, burnout, etc.) are negligible. Refer to Practice E 261for more generalized
21、 treatments.9.2 Calculate the reaction rate, Rs, as follows:Rs5 As/No(2)where:As= saturation activity, andNo= number of63Cu 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
22、.11. Precision and BiasNOTE 3Measurement 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 Organization for Standardization
23、(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 a bias of 6 3 % (1S %) and with aprecision of 61 % (1S %).12. Keywords12.1 activation; activation reaction; cop
24、per; cross section;dosimetry; fast-neutron monitor; neutron metrology; pressurevessel surveillance; reaction rateREFERENCES(1) Tulti, J. K. “Nuclear Wallet Cards,” National Nuclear Data Center,Brookhaven National Laboratory, Upton, New York, January 2000.(2) Evaluated Nuclear Structure Data File (EN
25、SDF), a computer file ofevaluated nuclear 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 Nu
26、clear Data Section of the International Atomic EnergyAgency (IAEA). The URL is http;/www.nndc.bnl.gov/ensdf. The dataquoted here comes from the database as of January 1, 2002.(3) “ENDF-201, ENDF/B-VI Summary Documentation,” edited by P.F.Rose, Brookhaven National Laboratory Report BNL-NCS-1741, 4the
27、d., October 1991. Cross section data is taken from ENDF/B-VIversion 8.(4) Atlas of Neutron Resonances: Resonance Parameters and ThermalCross Sections, Z +1 100. S. Mughabghab, Elservier Press,April 17,2006. This document was formerly known as BNL-325.(5) Taylor, B. N,. Kuyatt, C. E., Guidelines for
28、Evaluating and Expressingthe Uncertainty of NIST Measurement Results, NIST Technical Note1297, National Institute of Standards and Technology, Gaithersburg,MD, 1994.(6) Guide in the Expression of Uncertainty in Measurement, InternationalOrganization for Standardization, 1995, ISBN 9267101889. Avail-
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