1、Designation: E1297 08 (Reapproved 2013)Standard Test Method forMeasuring Fast-Neutron Reaction Rates by Radioactivationof Niobium1This standard is issued under the fixed designation E1297; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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,n
3、)93mNb.1.2 This 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 i
4、n fast-neutron fluences above about 1016cm2. 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 transmu
5、tation of93mNb 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 E261.1.5 Fast-neutron fluence rates can be determined from thereaction rates provided that the appropriate cross sectioninformation is available t
6、o meet the accuracy requirements.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.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 o
7、f 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:2D1193 Specification for Reagent WaterE170 Terminology Relating to Radiation Measurements andDosimetryE181 Test Meth
8、ods for Detector Calibration and Analysis ofRadionuclidesE185 Practice for Design of Surveillance Programs forLight-Water Moderated Nuclear Power Reactor VesselsE261 Practice for Determining Neutron Fluence, FluenceRate, and Spectra by Radioactivation TechniquesE262 Test Method for Determining Therm
9、al Neutron Reac-tion Rates and Thermal Neutron Fluence Rates by Radio-activation TechniquesE844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E 706 (IIC)E944 Guide for Application of Neutron Spectrum Adjust-ment Methods in Reactor Surveillance, E 706 (IIA)E1005 Test Method for
10、 Application and Analysis of Radio-metric Monitors for Reactor Vessel Surveillance, E 706(IIIA)E1006 Practice for Analysis and Interpretation of PhysicsDosimetry Results for Test Reactors, E 706(II)E1018 Guide for Application of ASTM Evaluated CrossSection Data File, Matrix E706 (IIB)3. Terminology3
11、.1 DefinitionsThe definitions stated in TerminologyE170 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,n)93mNb reac-tion. The metastable state decays to the ground state by thevirtual emiss
12、ion of 30 keV gamma rays that are all 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
13、 reaction rate, as defined in Practice E261,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 E261.1This test method is under the jurisdiction of
14、ASTM Committee E10 on NuclearTechnology and Applicationsand is the direct responsibility of SubcommitteeE10.05 on Nuclear Radiation Metrology.Current edition approved Jan. 1, 2013. Published January 2013. Originallyapproved in 1989. Last previous edition approved in 2008 as E1297 08. DOI:10.1520/E12
15、97-08R12.2For 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.Copyright ASTM International, 100 Barr Harbor Drive,
16、 PO Box C700, West Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 Refer to Practice E261 for a general discussion of thedetermination of decay rates, reaction rates, and neutronfluence rates with threshold detectors (1-29).3Refer to PracticeE1006, Practice E185 and Guide E1018
17、 for the use andapplication of results obtained by this test method.(34-36)5.2 The half-life of93mNb is 5730 6 220 days (30) and hasa K X-ray emission probability of 0.1099 6 0.0025 per decay(30). The Kand KX-rays of niobium are at 16.521316.152and 18.61818.953 keV, respectively. The recommended93Nb
18、(n,n)93mNb cross section comes from the IRDF-90 crosssection compendium (31), was drawn from the RRDF-98 crosssection evaluations (37) 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 consistent res
19、ults. 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 andappropriat
20、e 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 the c
21、urrent uncertainty in the cross section versus energyshape.5.5 The93Nb(n,n)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 steeland
22、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 handled as a
23、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 E844 for the selection, irradiation, andquality control of neutron dosimeters.6.2 There are some distinct advantages and l
24、imitations tothree measurement techniques identified in 5.3.Itistheresponsibility 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, stable long
25、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-ray spectrome
26、try 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, large X-ray
27、 source self-absorptioncorrections, larger corrections for interference fluorescence dueto the other radionuclides, and source geometry control.6.2.3 Liquid scintillation counting advantages include veryhigh detection efficiency, reproducible source preparation, andno source self absorption correcti
28、ons. Limitations includespecialized calibration techniques to reduce interference from3The 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 the93Nb(n,n)93mNb ReactionE1297 08 (2013)2other radionuclides, limit
29、ed 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 multichannel pulse-height analyzer. For moreinformation, refer to Test Methods E181 and E1005.7.2 Precision Balance, able to achi
30、eve the required accu-racy.7.3 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 MethodE181.7.5 Liquid Scintillation Counter.8. Reagents
31、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.4Other grade
32、s 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 Specificati
33、on D1193.8.3 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 with the93mN
34、bactivity 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 materialsho
35、uld 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 irradiation enviro
36、nment 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-form thick
37、ness (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 liquid as is
38、 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 the filte
39、rpaper 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 to accu-rately and reproducibly position the sources for the countinggeometry to be used. The source holder should be constructedof l
40、ow density materials such as aluminum or plastic.8.10 Liquid Scintillation MaterialsVials, emulsion scintil-lant (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 in handling
41、 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 the irradiati
42、on.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 filter materialif
43、 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 level versus t
44、ime,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-exposure to r
45、adiation 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 reactions (seeTes
46、t Method E262) 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:4“Reagent Chemicals,American Chemical Society Specifications,”Am. Chemi-cal Soc., Washington, DC. For suggestions on the test
47、ing of reagents not listed bytheAmerican Chemical Society, see “Reagent Chemicals and Standards,” by JosephRosin, D. Van Nostrand Co., Inc., New York, NY, and the “United StatesPharmacopeia.”E1297 08 (2013)39.7.1 If the metal is being dissolved and reduced to a lowmass-per-unit area source, dissolve
48、 the sample by placing 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 mLof HF).Addconcentrated nitric acid dropwise to start dissolution; asdissolution slows, add additional dro
49、ps to maintain a 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.Apreweighedpolyethylene pycnometer (weighing bottle) is 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
