ASTM E526-1997(2002) Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Titanium《用钛的放射性测定快速中子反应率的试验方法》.pdf

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1、Designation: E 526 97 (Reapproved 2002)Standard Test Method forMeasuring Fast-Neutron Reaction Rates by Radioactivationof Titanium1This standard is issued under the fixed designation E 526; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev

2、ision, the year of 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 for measuring reac-tion rates by the activation reactions46Ti (

3、n, p)46Sc +47Ti (n,np)46Sc.NOTE 1Since the cross section for the (n,np) reaction is relativelysmall for energies less than 12 MeV and is not easily distinguished fromthat of the (n,p) reaction, this test method will refer to the (n,p) reactiononly.1.2 The reaction is useful for measuring neutrons wi

4、thenergies above approximately 4.4 MeV and for irradiationtimes up to about 250 days (for longer irradiations, see PracticeE 261).1.3 With suitable techniques, fission-neutron fluence ratesabove 109cm2s1can be determined. However, in the pres-ence of a high thermal-neutron fluence rate,46Sc depletio

5、nshould be investigated.1.4 Detailed procedures for other 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 sa

6、fety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 170 Terminology Relating to Radiation Measurementsand Dosimetry2E 181 Test Methods for Detector Calibration and Analysisof Radionuclides2E 261 Practice for De

7、termining Neutron Fluence Rate, Flu-ence, and Spectra by Radioactivation Techniques2E 262 Test Method for Determining Thermal Neutron Re-action and Fluence Rates by Radioactivation Techniques2E 844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E 706 (IIC)2E 944 Guide for Appli

8、cation of Neutron Spectrum Adjust-ment Methods in Reactor Surveillance, (IIA)2E 1005 Test Method for Application and Analysis of Radio-metric Monitors for Reactor Vessel Surveillance, E 706(IIIA)2E 1018 Guide for Application of ASTM Evaluated CrossSection Data Files, Matrix E 706 (IIB)23. Terminolog

9、y3.1 Definitions:3.1.1 Refer to Terminology E 170.4. Summary of Test Method4.1 High-purity titanium is irradiated in a fast-neutron field,thereby producing radioactive46Sc from the46Ti (n, p)46Scactivation reaction.4.2 The gamma rays emitted by the radioactive decay of46Scare counted in accordance w

10、ith Methods E 181 and the reactionrate, as defined by Test Method E 261, is calculated from thedecay rate and the irradiation conditions.4.3 The neutron fluence rate above about 4.4 MeV can thenbe calculated from the spectral-weighted neutron activationcross section as defined by Test Method E 261.5

11、. Significance and Use5.1 Refer to Guide E 844 for the selection, irradiation, andquality control of neutron dosimeters.5.2 Refer to Test Method E 261 for a general discussion ofthe determination of fast-neutron fluence rate with thresholddetectors.5.3 Titanium has good physical strength, is easily

12、fabri-cated, has excellent corrosion resistance, has a melting tem-perature of 1675C, and can be obtained with satisfactorypurity.5.446Sc has a half-life of 83.81 days.3The46Sc decay4emitsa 0.8893 MeV gamma 99.984 % of the time and a secondgamma with an energy of 1.1205 MeV 99.987 % of the time.1Thi

13、s test method is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.05 on Nuclear Radiation Metrology.Current edition approved June 10, 1997. Published May 1998. Originallypublished as E 526 76. Last previous edition

14、 E 526 92.2Annual Book of ASTM Standards, Vol 12.02.3Nuclear Wallet Cards, National Nuclear Data Center, prepared by Jagdish K.Tuli, July 1990.4Evaluated Nuclear Structure Data File (ENSDF), maintained by the NationalNuclear Data Center (NNDC), Brookhaven National Laboratory, on behalf of theInterna

15、tional Network for Nuclear Structure Data Evaluation.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.5 The isotopic content of natural titanium recommendedfor46Ti is 8.012 %.55.6 The radioactive products of the neutronreactions47Ti

16、(n,p)47Sc(T12= 3.35 d) and48Ti(n,p)48Sc(T12 =1.82 d), might interfere with the analysis of46Sc.5.7 Contaminant activities (for example,65Zn and182Ta)might interfere with the analysis of46Sc. See Section 7.1.2 and7.1.3 or more details on the182Ta and65Zn interference.5.846Ti and46Sc have cross sectio

17、ns for thermal neutrons of0.6 and 8 barns, respectively;6therefore, when an irradiationexceeds a thermal-neutron fluence greater than about 23 1021cm2, provisions should be made to either use a thermal-neutron shield to prevent burnup of46Sc or measure thethermal-neutron fluence rate and calculate t

18、he burnup.5.9 Fig. 1 shows a plot of cross section versus neutronenergy for the fast-neutron reactions of titanium whichproduce46Sc (that is,NatTi(n,X)46Sc). Included in the plot isthe46Ti(n,p) reaction7and the47Ti(n,np) contribution to the46Scproduction,8normalized (to 14.7 MeV)9per46Ti atom. Thisf

19、igure is for illustrative purposes only to indicate the range ofresponse of the46Ti(n,p) reaction. Refer to Guide E 1018 fordescriptions of recommended tabulated dosimetry cross sec-tions.6. Apparatus6.1 NaI(Tl) or High Resolution Gamma-Ray Spectrometer.Because of its high resolution, the germanium

20、detector isuseful when contaminant activities are present. See MethodsE 181 and E 1005.6.2 Precision Balance, able to achieve the required accu-racy.6.3 Digital Computer, useful for data analysis (optional).7. Materials7.1 Titanium MetalHigh-purity titanium metal in the formof wire or foil is availa

21、ble.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, scandium impurity must be lowbecause of the reaction,45Sc (n,g)46Sc. To reduce this interfer-ence, the use of a thermal-neutron shield during irradi

22、ationwould be advisable if scandium impurity is suspected. As anexample, when a titanium sample containing 6 ppm scandiumhas been irradiated in a neutron field with equal thermal andfast-neutron fluence rates about 1 % of the46Sc in the sample isdue to the reaction45Sc (n,g)46Sc.7.1.2 Tantalum impur

23、ities can also cause a problem. Thelow-energy response of the181Ta(n,g)182Ta reaction producesgamma activity that interferes with the measurement of46Scradioactivity produced from the46Ti(n,p)46Sc high-energythreshold reaction. The radioactive182Ta isotope has a half-lifeof t1/2= 114.43 d and emits

24、a 1121.302 keV photon 34.7 % ofthe time. This photon is very close in energy to one of the twophotons emitted by46Sc (889.3 keV and 1120.5 keV). More-over, during the46Sc decay, the 1120.5 keV and 889.3 keVphotons are emitted in true coincidence and the randomcoincidence between the 1121.302 keV pho

25、tons from182Ta andthe 889.3 keV photons from46Sc can affect the application ofsumming corrections when the counting is done in a closegeometry and the46Sc activity is being monitoring with 889.3keV photon.7.1.3 Zinc contamination can lead to the production of65Znvia the64Zn(n,g)65Zn reaction. The ra

26、dioactive65Zn isotope hasa half-life of t1/2= 244.26 d and emits a 1115.518 keV photon50.75 % of the time. These 1115.518 keV photons can interferewith the 1120.5 keV line from46Sc and require a multi-peakresolution. For a small contaminant level the65Zn line may behidden in the background of the la

27、rger46Sc peak. There is noother high probability65Zn decay gamma with which to moni-tor or correct for the presence of zinc in the titanium sample.7.1.4 Impurity problems in titanium are a particular concernfor applications to reactor pressure vessel surveillance dosim-etry because the46Ti(n,p)46Sc,

28、 along with the63Cu(n,a)60Coreaction, are the two highest-energy dosimetry reactions usedto detect spectrum differences in reactor neutron environments.Incorrect radioactivity measurements of these two reactionscan alter the high-energy end of the derived spectrum, andresult in the incorrect predict

29、ion of neutron irradiation damage.7.2 Encapsulating MaterialsBrass, stainless steel, copper,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 open

30、ed easily, especially if themonitors must be removed remotely (see Guide E 844).8. Procedure8.1 Decide on the size and shape of the titanium sample tobe irradiated, taking into consideration the size and shape of5Isotopic Compositions of the Elements 1983, International Union of Pure andApplied Chem

31、istry, Vol. 56, Pergamon Press, 1984.6Chart of the Nuclides, Knolls Atomic Power Laboratory, 14th Ed, April 1988.7“International Reactor Dosimetry File (IRDF-90),” assembled by N. P.Kocherov, et al., International Atomic Energy Agency, Nuclear Data Section,IAEANDS141, Rev 0, August 1990.8ENDF/B-V Do

32、simetry Tape 531-G, Mat. No. 6427 (22-Ti-46), October 1979.9J. W. Meadows, D. L. Smith, M. M. Bretscher, and S. A. Cox, “Measurementof 14.7 MeV Neutron-Activation Cross Sections for Fusion,” Annals of NuclearEnergy, Vol 1, No. 9, 1987.FIG. 1NatTi(n,X)46Sc Cross Section (Normalized per Ti-46 Atom)E 5

33、262the irradiation space. The mass and exposure time are param-eters that can be varied to obtain a desired disintegration ratefor a given neutron-fluence rate level. (See Guide E 844.)8.2 Weigh the sample.8.3 Irradiate the sample for the predetermined time period.Record the power level and any chan

34、ges in power during theirradiation, the time at the beginning and end of each powerlevel and the relative position of the monitors in the irradiationfacility.8.4 If the counting procedure available requires that theactivity be pure46Sc, a waiting period of about 20 days isrecommended between termina

35、tion of the exposure and ana-lyzing the samples for46Sc content. This allows the 44-h48Sc todecay so that there is no interference from the gamma raysemitted by48Sc, that is, the 0.175, 0.983, 1.037, and 1.312-MeVgamma rays. If the 0.159-MeV gamma ray emitted by 3.35-day47Sc interferes with counting

36、 conditions, a longer decaytime may be necessary. The 5.75-min51Ti will usually havedecayed by count time. However, gamma-ray spectra may betaken with germanium detectors soon after irradiation, if countrates are not excessive.8.5 Check the sample for activity from cross-contaminationby other irradi

37、ated materials. Clean, if necessary, and reweigh.8.6 Analyze the sample for46Sc content in disintegrationsper second using the gamma-ray spectrometer (see MethodsE 181 and E 1005).8.7 Disintegrations of46Sc nuclei produces 0.8893-MeV and1.1205-MeV gamma rays with probabilities per decay of0.99984 an

38、d 0.99997, respectively.4When analyzing eitherpeak in the gamma-ray system, a correction for coincidencesumming may be required if the sample is placed close to thedetector (10 cm or less) (see Methods E 181).9. Calculation9.1 Calculate the saturation activity, As, as follows:As5 A/1 exp lti#! exp l

39、tw#!# (1)where:A =46Sc disintegrations per second measured by counting,l = decay constant for46Sc = 9.570 3 108s1,ti= irradiation 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 c

40、orrections for other reactions (forexample, impurities, burnout, etc.) are negligible. Refer to Test MethodE 261 for more generalized treatments.9.2 Calculate the reaction rate, Rs, as follows:Rs5 As/No(2)where:As= saturation activity, andNo= number of46Ti atoms.9.3 Refer to Test Method E 261 and Pr

41、actice E 944 for adiscussion of fast-neutron fluence rate and fluence.10. Report10.1 Test Method E 261 describes how data should bereported.11. Precision and BiasNOTE 3Measurement uncertainty is described by a precision and biasstatement in this standard. Another acceptable approach is to use Type A

42、and B uncertainty components.10,11This Type A/B uncertainty specifica-tion is now used in International Organization 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 ra

43、tes canbe determined with a bias of 63 % (1S %) and with a precisionof 61 % (1S %). For a fission spectrum, the typical uncertaintyin the spectrum-averaged cross section12is 2.4 %.12. Keywords12.1 activation reaction; cross section; dosimetry; nuclearmetrology; pressure vessel surveillance; reaction

44、 rate; titaniumASTM 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 of the validity of any such patent rights, and the riskof infringement of s

45、uch 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 withdrawn. Your comments are invited either for revision of this standard or for add

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47、he 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 or multiple copies) of this standard may be obtained by contacting ASTM at th

48、e aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).10B. N. Taylor, C. E. Kuyatt, Guidelines for Evaluating and Expressing theUncertainty of NIST Measurement Results, NIST Technical Note 1297, NationalInstitute of Stan

49、dards and Technology, Gaithersburg, MD, 1994.11Guide in the Expression of Uncertainty in Measurement, International Orga-nization for Standardization, 1993, ISBN 92-67-10188-9.12P. J. Griffin, “Comparison of Uncertainty Metrics for Calculated DosimetryActivities,” American Nuclear Society Proceedings of the 1996 Topical MeetingRadiation Protection and Shielding, held in No. Falmouth, Massachusetts, April2125, 1996, Vol. 1, pp. 2735.E 5263