1、Designation: E 263 05Standard Test Method forMeasuring Fast-Neutron Reaction Rates by Radioactivationof Iron1This standard is issued under the fixed designation E 263; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method describes procedures f
3、or measuringreaction rates by the activation reaction54Fe(n,p)54Mn.1.2 This activation reaction is useful for measuring neutronswith energies above approximately 2.2 MeV and for irradiationtimes up to about 3 years (for longer irradiations, see PracticeE 261).1.3 With suitable techniques, fission-ne
4、utron fluence ratesabove 108cm2s1can be determined. However, in the pres-ence of a high thermal-neutron fluence rate (for example, 2 31014cm2s1)54Mn depletion should be investigated.1.4 Detailed procedures describing the use of other fast-neutron detectors are referenced in Practice E 261.1.5 This s
5、tandard 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 regulatory limitations prior to use.2. Referenced Documents2.
6、1 ASTM Standards:2D 1193 Specification for Reagent WaterE 170 Terminology Relating to Radiation Measurementsand DosimetryE 181 Test Methods for Detector Calibration and Analysisof RadionuclidesE 261 Practice for Determining Neutron Fluence Rate, Flu-ence, and Spectra by Radioactivation TechniquesE 8
7、44 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 Surveillance,E 706(IIIA)E
8、 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 for definitions of termsrelating to radiation measurements and neutron dosimetry.4. Summary of Test Method4.1 High-purity iron is irradiated in a neut
9、ron field, therebyproducing radioactive54Mn from the54Fe(n,p)54Mn activationreaction.4.2 The gamma rays emitted by the radioactive decay of54Mn are counted in accordance with Test Methods E 181. Thereaction rate, as defined by Practice E 261, is calculated fromthe decay rate and irradiation conditio
10、ns.4.3 Radioassay of the54Mn activity may be accomplishedby directly counting the irradiated iron dosimeter, or by firstchemically separating the54Mn activity prior to counting.4.4 The neutron fluence rate above about 2.2 MeV can thenbe calculated from the spectral-weighted neutron activationcross s
11、ection as defined by Practice E 261.5. Significance and Use5.1 Refer to Guide E 844 for guidance on the selection,irradiation, and quality control of neutron dosimeters.5.2 Refer to Practice E 261 for a general discussion of thedetermination of fast-neutron fluence rate with threshold de-tectors.5.3
12、 Pure iron in the form of foil or wire is readily availableand easily handled.5.4 Fig. 1 shows a plot of cross section as a function ofneutron energy for the fast-neutron reaction54Fe(n,p)54Mn(1).3This figure is for illustrative purposes only to indicate therange of response of the54Fe(n,p)54Mn reac
13、tion. Refer to1This test 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 Jan. 1, 2005. Published February 2005. Originallyapproved in 1965 as E 2
14、63 65 T. Last previous edition approved in 2000 asE 263 00.2For 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.3T
15、he boldface numbers in parentheses refer to the list of references located at theend of this test method.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Guide E 1018 for descriptions of recommended tabulateddosimetry cross sections.5
16、.554Mn has a half-life of 312.11 days (2) and emits agamma ray with an energy of 834.848 keV. (3)45.6 Interfering activities generated by neutron activationarising from thermal or fast neutron interactions are 2.58-h56Mn, 44.5-d59Fe, and 5.271-y60Co. (Consult Ref (2) for moreprecise values currently
17、 accepted for the half-lives.) Interfer-ence from56Mn can be eliminated by waiting 48 h beforecounting. Although chemical separation of54Mn from theirradiated iron is the most effective method for eliminating59Fe and60Co, direct counting of iron for54Mn is possibleusing high-resolution detector syst
18、ems or unfolding or strip-ping techniques, especially if the dosimeter was covered withcadmium or boron during irradiation. Altering the isotopiccomposition of the iron dosimeter is another useful techniquefor eliminating interference from extraneous activities whendirect sample counting is to be em
19、ployed.5.7 The vapor pressures of manganese and iron are such thatmanganese diffusion losses from iron can become significant attemperatures above about 700C. Therefore, precautions mustbe taken to avoid the diffusion loss of54Mn from irondosimeters at high temperature. Encapsulating the iron dosim-
20、eter in quartz or vanadium will contain the manganese attemperatures up to about 900C.5.8 Sections 6, 7 and 8 that follow were specifically writtento describe the method of chemical separation and subsequentcounting of the54Mn activity.When one elects to count the irondosimeters directly, those port
21、ions of Sections 6, 7 and 8 thatpertain to radiochemical separation should be disregarded.NOTE 1The following portions of this test method apply also to directsample-counting methods: 6.1-6.3, 7.4, 7.9, 7.10, 8.1-8.5, 8.18, 8.19, and9-12.6. Apparatus (Note 1)6.1 HighResolution Gamma-Ray Spectrometer
22、, because ofits high resolution, the germanium detector is useful whencontaminant activities are present. See Test Methods E 181 andE 1005.6.2 Precision Balance, able to achieve the required accu-racy.6.3 Digital Computer, useful for data analysis (optional).6.4 Chemical Separation Cylinder, borosil
23、icate glass, about25-mL capacity, equipped with stopcock and funnel. Thisapparatus is illustrated in Fig. 2.6.5 Beakers, borosilicate glass, 50 mL; volumetric flasks, 25and 50 mL, and volumetric pipets, 1 mL.7. Reagents and Materials (Note 1)7.1 Purity of ReagentsReagent-grade chemicals shall beused
24、 in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.5Other grades may beused, provided it is first ascertained that the reagent
25、 is ofsufficiently high purity to permit its use without lessening theaccuracy of the activity determination.7.2 Purity of Water Unless otherwise indicated, refer-ences to water shall be understood to mean reagent-grade waterconforming to Specification D 1193.7.3 Anion Exchange Resin, strongly basic
26、 type, 100 to 200mesh size.4Ref (3) gives a value of 834.848 keV as the most precise value currentlyaccepted for the54Mn decay gamma-ray energy.5“Reagent Chemicals,American Chemical Society Specifications,”Am. Chemi-cal Soc., Washington, DC. For suggestions on the testing of reagents not listed byth
27、e American Chemical Society, see “Analar Standards for Laboratory Chemicals,”BDH Ltd., Poole, Dorset, U.K., and the “United States Pharmacopeia.”FIG. 154Fe(n,p)54Mn Cross SectionFIG. 2 Ion-Exchange Separation ApparatusE2630527.4 Iron Foil or Wire, high purity.7.5 Hydrochloric Acid (sp gr 1.19, 1190
28、kg/m3)Concentrated hydrochloric acid (HCl).7.6 Hydrochloric Acid (1 + 3)Mix 1 volume of concen-trated HCl (sp gr 1.19) with 3 volumes of water.7.7 Manganese Carrier Solution (10 mg MnCl2/cm3).7.8 Nitric Acid (sp gr 1.42, 1420 kg/m3)Concentratednitric acid (HNO3).7.9 Encapsulating MaterialsBrass, sta
29、inless 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 a significant fluxperturbation and that it may be opened easily, especially if thecapsule is to be opened remotely. (See Gu
30、ide E 844.)7.10 The purity of the iron is important in that no impuritiesshould be present which produce long-lived radionuclides thatinterfere with the54Mn radioassay. This condition includesspecies that will accompany54Mn through the separationscheme and that have gamma rays, of energy 0.6 MeV orh
31、igher. The presence of impurities may be determined either byemission spectroscopy or by activation analysis.8. Procedure (Note 1)8.1 Decide on the size and shape of the iron sample to beirradiated. Consider convenience in handling and availableirradiation space when making this selection, but it is
32、 moreimportant to ensure that sufficient54Mn activity will beproduced to permit accurate radioassay. A preliminary calcu-lation of the expected production of54Mn, using the activationequation described in Section 9, will aid in selecting the massof iron required.8.2 Determine a suitable irradiation
33、time.8.3 Weigh the iron sample. The chemical manipulationsdescribed below function best with an iron dosimeter weighing10 to 20 mg.NOTE 2It is necessary to avoid a high iron concentration in thesolutions that are to be used for separation so that the efficiency of theion-exchange resin will not be s
34、eriously lowered. For the columndescribed herein the amount of iron let onto the resin should not exceed1 mg.8.4 Irradiate the samples 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
35、 relative position of the monitors in the irradiationfacility.8.5 A waiting period of 2 days is recommended betweentermination of the exposure and the start of counting. Thisallows 2.58-h56Mn, produced by fast-neutron reactions with56Fe and also by thermal-neutron activation of impurity man-ganese,
36、to decay below levels at which it may cause error in the54Mn assay. Check the samples for activity from cross con-tamination by other monitors or material irradiated in thevicinity, and for any foreign substance adhering to the sample.Clean, if necessary, and reweigh. If direct-counting techniquesar
37、e used, disregard the remaining procedures to step 8.18.8.6 After irradiation, dissolve the sample in 10 mL ofconcentrated hydrochloric acid to which 2 drops of nitric acidhave been added. The solution may be heated gently to hastendissolution.8.7 After dissolution is complete, transfer the solution
38、 withwashing to a 25-mL volumetric flask. Wash only with concen-trated hydrochloric acid and use this also in diluting to thecalibration mark on the volumetric flask.8.8 Prepare a slurry of anion exchange resin with distilled ordeionized water and pour it into the ion exchange columnapparatus (see F
39、ig. 2) to a height of 100 mm. Place aglass-wool plug above the resin and keep the column underliquid at all times.8.9 Prepare the ion exchange column for use by passingconcentrated hydrochloric acid through until it completelydisplaces the water used to form the resin slurry.8.10 Transfer an aliquot
40、 of the sample solution by volumet-ric pipet to the empty funnel above the column. This aliquotshould be of sufficient volume so that accurate counting datacan be obtained.8.11 Run the sample onto the column.8.12 Immediately pour a few millilitres from a premeasured50-mL volume of hydrochloric acid
41、(1+3) into the funnel towash any remaining sample solution onto the column.8.13 Place a 50-mL volumetric flask, to which 1 mL ofMnCl2carrier solution has been added, under the tip of thecolumn and open the column stopcock.8.14 Add the remaining hydrochloric acid (1+3) to thefunnel and adjust the sto
42、pcock to obtain a flow rate of about 1drop in 5 to 10 s. This will allow elution of a 50-mL volume inabout 2 h.8.15 Elute from the column until the solution reaches thecalibration mark on the volumetric flask.NOTE 3To prepare the ion exchange resin for further separations, runabout 50 mL of distille
43、d or deionized water through the column. This willremove iron and cobalt from the resin. Regenerate the column as before bypassing concentrated hydrochloric acid through until the acid completelydisplaces the water.NOTE 4The54Mn recovery should be checked by passing a known54Mn spike solution and ir
44、on carrier through the column.8.16 Stopper the flask and invert several times to mix thecontents thoroughly.8.17 Remove an accurately measured aliquot from thevolumetric flask for radioassay.A1-mLsample is convenient ifthe counting is to be done with a well-type scintillationdetector. If assay is to
45、 be made using a solid crystal, the aliquotcan be deposited into a cup planchet and dried under a heatlamp.8.18 Analyze the samples for54Mn content in disintegra-tions per second using the gamma ray spectrometer (see TestMethods E 181 and E 1005).8.19 Disintegration of an54Mn nucleus produces onegam
46、ma ray with a probability per decay of 0.9998 (4)6.9. Calculation9.1 Calculate the saturation activity As, as follows:As5A exp ltw#1 2 exp 2lti#!(1)6Ref (4) gives a value of 0.99976 as the most precise value currently acceptedfor the emission probability of the 834.848-keV gamma-ray emitted from the
47、nuclear decay of54Mn.E263053where:A =54Mn disintegrations per second measured by count-ing, s1,l = decay constant for54Mn = 2.570 3 108,s1,ti= irradiation duration, s, andtw= elapsed time between the end of irradiation andcounting, s.NOTE 5The equation for Asis valid if the reactor is operated atcon
48、stant 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= saturation activity, andNo= number of54Fe atoms.9.3 Refer to Method
49、E 261 and Practice 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 Bias11.1 General practice indicates that54Mn decay rate can bedetermined with a bias of 63%(1s) and with a precision of61%(1s). Measurement of54Mn activity produced from the54Fe(n,p)54Mn reaction in a235U thermal fission standardneutron field can be accomplished with an uncertainty of2.86 % (5), where the uncertainty component attributed toknowledge of the cross section is 2.12 % (6). Meas
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