1、Designation: E 1297 02Standard Test Method forMeasuring Fast-Neutron Reaction Rates by Radioactivationof Niobium1This standard is issued under the fixed designation E 1297; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year o
2、f 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 describes procedures for measuringreaction rates by the activation reaction93Nb(n,n8)93mNb.1.2 Thi
3、s activation reaction is useful for monitoring neu-trons with energies above approximately 0.5 MeV and forirradiation times up to about 30 years.1.3 With suitable techniques, fast-neutron reaction rates forneutrons with energy distribution similar to fission neutronscan be determined in fast-neutron
4、 fluences above about1016cm2. In the presence of high thermal-neutron fluence rates(1012cm2s1), the transmutation of93mNb due to neutroncapture should be investigated. In the presence of high-energyneutron spectra such as are associated with fusion and spalla-tion sources, the transmutation of93mNb
5、by reactions such as(n,2n) may occur and should be investigated.1.4 Procedures for other fast-neutron monitors are refer-enced in Practice E 261.1.5 Fast-neutron fluence rates can be determined from thereaction rates provided that the appropriate cross sectioninformation is available to meet the acc
6、uracy requirements.1.6 The values stated in SI units are to be regarded as thestandard.1.7 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
7、and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 1193 Specification for Reagent Water2E 170 Terminology Relating to Radiation Measurementsand Dosimetry3E 181 Test Methods for Detector Calibration and Analysisof Radionuclides3E 185 Pr
8、actice for Conducting Surveillance Tests for Light-Water Cooled Nuclear Power Reactor Vessels, E706 (IF)3E 261 Practice for Determining Neutron Fluence Rate, Flu-ence, and Spectra by Radioactivation Techniques3E 262 Test Method for Determining Thermal Neutron Re-action and Fluence Rates by Radioacti
9、vation Techniques3E 844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E706 (IIC)3E 944 Practice for Application of Neutron Spectrum Adjust-ment Methods in Reactor Surveillance3E 1005 Test Method for Application and Analysis of Radio-metric Monitors for Reactor Vessel Surveilla
10、nce, E706(IIIA)3E 1006 Practice for Analysis and Interpretation of PhysicsDosimetry Results for Test Reactors, E706 (II)3E 1018 Guide for Application of ASTM Evaluated CrossSection Data File (ENDF/A)Cross Section and Uncer-tainty File, E706 (IIB)33. Terminology3.1 DefinitionsThe definitions stated i
11、n TerminologyE 170 are applicable to this test method.4. Summary of Test Method4.1 High purity niobium is irradiated in a neutron fieldproducing radioactive93mNb from the93Nb(n,n8)93mNb reac-tion. The metastable state decays to the ground state by thevirtual emission of 30 keV gamma rays that are al
12、l internallyconverted giving rise to the actual emission of orbital electronsfollowed by X rays.4.2 Sources of the irradiated niobium are prepared for X rayor liquid scintillation counting.4.3 The X rays emitted as a result of the decay of93mNb arecounted, and the reaction rate, as defined in Practi
13、ce E 261, iscalculated from the decay rate and irradiation conditions.4.4 The neutron fluence rate may then be calculated fromthe appropriate spectral-weighted neutron activation crosssection as defined by Practice E 261.5. Significance and Use5.1 Refer to Practice E 261 for a general discussion of
14、thedetermination of decay rates, reaction rates, and neutron1This 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, 2002. Published
15、September 2002. Originallypublished as E 1297 89. Last previous edition E 1297 96.2Annual Book of ASTM Standards, Vol 11.01.3Annual Book of ASTM Standards, Vol 12.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.fluence rates with
16、threshold detectors (1-29).4Refer to PracticeE 1006 and Guide E 1018 for the use and application of resultsobtained by this test method.(34-36)5.2 The half-life of93mNb is 5890 6 50 days (30) and hasa K X-ray emission probability of 0.1104 6 0.0035 per decay(30). The Kaand KbX-rays of niobium are at
17、 16.5216.62 and18.619.07 keV, respectively. The recommended93Nb(n,n8)93mNb cross section comes from the IRDF-90 crosssection compendium (31) and is shown in Fig. 1.5.3 Chemical dissolution of the irradiated niobium to pro-duce very low mass-per-unit area sources is an effective way toobtain consiste
18、nt results. The direct counting of foils or wirescan produce satisfactory results provided appropriate methodsand interpretations are employed. It is possible to use liquidscintillation methods to measure the niobium activity providedthe radioactive material can be kept uniformly in solution andappr
19、opriate corrections can be made for interfering activities.5.4 The measured reaction rates can be used to correlateneutron exposures, provide comparison with calculated reac-tion rates, and determine neutron fluences. Reaction rates canbe determined with greater accuracy than fluence rates becauseof
20、 the current uncertainty in the cross section versus energyshape.5.5 The93Nb(n,n8)93mNb reaction has the desirable proper-ties of monitoring neutron exposures related to neutron damageof nuclear facility structural components. It has an energyresponse range corresponding to the damage function of st
21、eeland has a half-life sufficiently long to allow its use in very longexposures (up to about 40 years). Monitoring long exposures isuseful in determining the long-term integrity of nuclear facilitycomponents.6. Interferences6.1 Pure niobium in the forms of foil and wire is availableand easily handle
22、d as a metal. When thin niobium is irradiated,it may become brittle and fragile, thus requiring carefulhandling or encapsulation to prevent damage or loss of theniobium. Refer to Guide E 844 for the selection, irradiation,and quality control of neutron dosimeters.6.2 There are some distinct advantag
23、es and limitations tothree measurement techniques identified in 5.3. It is theresponsibility of the user to evaluate these and determine theoptimum technique for the situation.6.2.1 Low mass source X-ray spectrometry advantagesinclude sufficient energy resolution to eliminate other X-rayemissions, s
24、table long life sources, reduced interference fluo-rescence due to other radionuclides, small and precise back-ground corrections, and minimal X-ray source self-absorptioncorrections. Limitations are low counting efficiency, complexsource preparation, and use of hazardous chemicals.6.2.2 Direct X-ra
25、y spectrometry of metal (foil or wire)sources has the advantages of simple source preparation, stablelong life sources, sufficient energy resolution to eliminate otherX-ray emissions, small and precise background corrections,and no use of hazardous chemicals. Limitations are lowcounting efficiency,
26、large X-ray source self-absorption correc-tions, larger corrections for interference fluorescence due to theother radionuclides, and source geometry control.6.2.3 Liquid scintillation counting advantages include veryhigh detection efficiency, reproducible source preparation, andno source self absorp
27、tion corrections. Limitations includespecialized calibration techniques to reduce interference fromother radionuclides, limited source stability, use of hazardouschemicals, and disposal of hazardous chemical waste.7. Apparatus7.1 X-ray Spectrometer, using a Si(Li) detector or a Gedetector and a mult
28、ichannel pulse-height analyzer. For moreinformation, refer to Test Methods E 181 and E 1005.7.2 Precision Balance, able to achieve the required accu-racy.4The boldface numbers in parentheses refer to the list of references at the end ofthis test method.FIG. 1 IRDF-90 Cross Section Versus Energy for
29、the93Nb(n,n*)93mNb ReactionE12970227.3 Beakers, 50 mL polyethylene; pycnometer (weighingbottle), 50 mL polyethylene; volumetric pipets, 10 L to 5 mL.7.4 Gamma Ray Spectrometer, using a Ge detector and amultichannel pulse-height analyzer. Refer to Test MethodE 181.7.5 Liquid Scintillation Counter.8.
30、Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society, wheresuch specifications are available.5Ot
31、her grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.8.2 Purity of WaterUnless otherwise indicated, any waterused shall be understood to mean reagent water as defined byType I of Sp
32、ecification D 1193.8.3 Hydrofluoric AcidConcentrated (32M) hydrofluoricacid (HF).8.4 Nitric AcidConcentrated (16M) nitric acid (HNO3).8.5 Niobium MetalThe purity of the niobium is importantin that no impurities (such as tantalum) should be present toproduce long-lived radionuclides that interfere wi
33、th the93mNbactivity determination. To avoid problems from tantalum, theniobium should have the lowest tantalum content possible.Niobium metal in the form of foil and wire with tantalumcontent of about 5 ppm (parts per million) or less is obtainableand can be used under most conditions. The niobium m
34、aterialshould be tested for interfering radioactivity by neutron acti-vation techniques.8.6 Encapsulation MaterialThe encapsulation material(such as quartz, stainless steel, aluminum, etc.) should beselected to prevent corrosion of the niobium during irradiationand to be compatible with the irradiat
35、ion environment andpost-irradiation handling. If thermal and epithermal neutronfilters or shrouds are used, these materials (such as cadmium,tantalum, gadolinium, etc.) must also be compatible with theencapsulation and irradiation environment.8.7 Analytical PaperAnalytical grade filter paper of uni-
36、form thickness (about 0.076 cm) and density (about 8 mgcm2). The paper can be cut or obtained precut to the desiredsize (usually between 0.5 and 1.5 cm diameter) that iscompatible with the activity concentration of the solution andthe counting conditions. The paper should be able to absorb asmuch li
37、quid as is necessary and not decompose from the acid.TFE-fluorocarbon rings with an inside diameter matching theoutside diameter of the filter paper disks so they fit togetherwith light contact.8.8 Support and Cover MaterialsThin plastic film andplastic tape materials are useful to support and cover
38、 the filterpaper sources. They should be strong enough to contain thesources and thin enough to minimize attenuation of the X rays.8.9 Source HolderA source holder must be used toaccurately and reproducibly position the sources for the count-ing geometry to be used. The source holder should be con-s
39、tructed of low density materials such as aluminum or plastic.8.10 Liquid Scintillation MaterialsVials, emulsion scin-tillant (xylene-based), chelating agent (di-2-ethylhexyl phos-phoric acid).9. Procedure9.1 Determine the size and shape of the niobium samplebeing irradiated. Consider the convenience
40、 in handling andavailable irradiation space. Ensure that sufficient93mNb activ-ity will be produced to permit accurate radioassay. Typically,samples of 0.2 to 20 mg of niobium may be used, but apreliminary calculation of the expected production of93mNbwill aid in selecting the appropriate mass for t
41、he irradiation.9.2 Accurately weigh the niobium sample being irradiated.9.3 Encapsulate the niobium sample so that it can beretrieved and identified following the irradiation. Record thesample identification, sample weight, and exact details of theencapsulation. Shroud the niobium with neutron filte
42、r materialif necessary. If the thermal-to-fast neutron fluence rate ratio ishigh (greater than 5) or the tantalum impurity is high (greaterthan 10 ppm), use neutron filter materials, if possible.9.4 Irradiate the niobium samples. Keep an accurate recordof the irradiation history including neutron le
43、vel versus time,starting and ending time of the irradiation, and the periodswhen the neutron level is zero. Record the spatial position ofthe sample in the irradiation facility.9.5 After the irradiation, retrieve and identify the irradiatedsample. Take necessary precautions to avoid personnel over-e
44、xposure to radiation and the spread of radioactive contamina-tion.9.6 A waiting time between the end of irradiation and thestart of counting may be necessary to allow92mNb or95Nb, orboth, to decay to an insignificant level. Check the samples foractivity from contamination by other materials or react
45、ions (seeTest Method E 262) and for any material adhering to thesample. Check the weight of the sample. If necessary, cleanand reweigh the sample.9.7 X-Ray Source Preparation and Counting:9.7.1 If the metal is being dissolved and reduced to a lowmass-per-unit area source, dissolve the sample by plac
46、ing it ina preweighed 50 mL polyethylene or TFE-fluorocarbon (non-wettable) beaker and adding enough concentrated hydrofluoricacid to cover the sample (usually about 1 to 10 mL of HF). Addconcentrated nitric acid dropwise to start dissolution; asdissolution slows, add additional drops to maintain a
47、controlledslow rate of dissolution until the entire sample dissolves. Afterdissolution is complete, bring the final volume of solution tothe desired amount by adding distilled water. Weigh thesolution in the beaker if mass aliquoting is used. A preweighedpolyethylene pycnometer (weighing bottle) is
48、recommendedfor mass aliquoting. The ratio of the niobium mass to thesolution mass determines the concentration of niobium in thesolution. When transferring the solution from one container toanother, ensure that all of the solution is transferred by usingmultiple rinses. Use accurately calibrated pip
49、ets if volumetricaliquoting is performed.5“Reagent Chemicals, American Chemical Society Specifications,” Am. Chemi-cal Soc., Washington, DC. For suggestions on the testing of reagents not listed bythe American Chemical Society, see “Reagent Chemicals and Standards,” by JosephRosin, D. Van Nostrand Co., Inc., New York, NY, and the “United StatesPharmacopeia.”E12970239.7.2 Deposit the desired amount of the solution on a filterpaper disk surrounded by a TFE-fluorocarbon ring to producea counting source. Deposit the solution on the paper drop-by-drop so the paper does
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