1、Designation: E 2059 06Standard Practice forApplication and Analysis of Nuclear Research Emulsions forFast Neutron Dosimetry1This standard is issued under the fixed designation E 2059; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 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 Nuclear Research Emulsions (NRE) have a long andillustrious history of applications in the physical scie
3、nces, earthsciences and biological sciences (1,2)2. In the physical sci-ences, NRE experiments have led to many fundamental dis-coveries in such diverse disciplines as nuclear physics, cosmicray physics and high energy physics. In the applied physicalsciences, NRE have been used in neutron physics e
4、xperimentsin both fission and fusion reactor environments (3-6). Numer-ous NRE neutron experiments can be found in other applieddisciplines, such as nuclear engineering, environmental moni-toring and health physics. Given the breadth of NRE applica-tions, there exist many textbooks and handbooks tha
5、t provideconsiderable detail on the techniques used in the NRE method.As a consequence, this practice will be restricted to theapplication of the NRE method for neutron measurements inreactor physics and nuclear engineering with particular empha-sis on neutron dosimetry in benchmark fields (see Matr
6、ixE 706).1.2 NRE are passive detectors and provide time integratedreaction rates. As a consequence, NRE provide fluence mea-surements without the need for time-dependent corrections,such as arise with radiometric (RM) dosimeters (see TestMethod E 1005). NRE provide permanent records, so thatoptical
7、microscopy observations can be carried out anytimeafter exposure. If necessary, NRE measurements can be re-peated at any time to examine questionable data or to obtainrefined results.1.3 Since NRE measurements are conducted with opticalmicroscopes, high spatial resolution is afforded for fine struc-
8、ture experiments. The attribute of high spatial resolution canalso be used to determine information on the angular anisot-ropy of the in-situ neutron field (4,5,7). It is not possible foractive detectors to provide such data because of in-situperturbations and finite-size effects (see Section 11).1.
9、4 The existence of hydrogen as a major constituent ofNRE affords neutron detection through neutron scattering onhydrogen, that is, the well known (n,p) reaction. NRE mea-surements in low power reactor environments have beenpredominantly based on this (n,p) reaction. NRE have alsobeen used to measure
10、 the6Li (n,t)4He and the10B(n,a)7Lireactions by including6Li and10B in glass specks near themid-plane of the NRE (8,9). Use of these two reactions doesnot provide the general advantages of the (n,p) reaction forneutron dosimetry in low power reactor environments (seeSection 4).As a consequence, this
11、 standard will be restricted tothe use of the (n,p) reaction for neutron dosimetry in low powerreactor environments.1.5 LimitationsThe NRE method possesses three majorlimitations for applicability in low power reactor environ-ments.1.5.1 Gamma-Ray SensitivityGamma-rays create a sig-nificant limitati
12、on for NRE measurements.Above a gamma-rayexposure of approximately 3R, NRE can become fogged bygamma-ray induced electron events. At this level of gamma-ray exposure, neutron induced proton-recoil tracks can nolonger be accurately measured. As a consequence, NREexperiments are limited to low power e
13、nvironments such asfound in critical assemblies and benchmark fields. Moreover,applications are only possible in environments where thebuildup of radioactivity, for example, fission products, islimited.1.5.2 Low Energy LimitIn the measurement of tracklength for proton recoil events, track length dec
14、reases asproton-recoil energy decreases. Proton-recoil track length be-low approximately 3 in NRE can not be adequately measuredwith optical microscopy techniques. As proton-recoil tracklength decreases below approximately 3, it becomes verydifficult to measure track length accurately. This 3 track1
15、This practice 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 Jan. 1, 2006. Published February 2006. Originallyapproved in 2000. Last previous editio
16、n approved in 2005 as E 2059 - 05.2The boldface numbers in parentheses refer to the list of references at the end ofthe text.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.length limit corresponds to a low energy limit of applicabil
17、ityin the range of approximately 0.3 to 0.4 MeV for neutroninduced proton-recoil measurements in NRE.1.5.3 High-Energy LimitsAs a consequence of finite-sizelimitations, fast-neutron spectrometry measurements are lim-ited to #15 MeV. The limit for in-situ spectrometry in reactorenvironments is #8MeV.
18、1.5.4 Track Density LimitThe ability to measure protonrecoil track length with optical microscopy techniques dependson track density. Above a certain track density, a maze orlabyrinth of tracks is created, which precludes the use ofoptical microscopy techniques. For manual scanning, thislimitation a
19、rises above approximately 104tracks/cm2, whereasinteractive computer based scanning systems can extend thislimit up to approximately 105tracks/cm2. These limits corre-spond to neutron fluences of 106107cm2, respectively.1.6 Neutron Spectrometry (Differential Measurements)For differential neutron spe
20、ctrometry measurements in lowpower reactor environments, NRE experiments can be con-ducted in two different modes. In the more general mode, NREare irradiated in-situ in the low power reactor environment.This mode of NRE experiments is called the 4p mode, sincethe in-situ irradiation creates tracks
21、in all directions (see 3.1.1).In special circumstances, where the direction of the neutronflux is known, NRE are oriented parallel to the direction of theneutron flux. In this orientation, one edge of the NRE faces theincident neutron flux, so that this measurement mode is calledthe end-on mode. Sca
22、nning of proton-recoil tracks is differentfor these two different modes. Subsequent data analysis is alsodifferent for these two modes (see 3.1.1 and 3.1.2).1.7 Neutron Dosimetry (Integral Measurements)NREalso afford integral neutron dosimetry through use of the (n,p)reaction in low power reactor en
23、vironments. Two differenttypes of (n,p) integral mode dosimetry reactions are possible,namely the I-integral and the J-integral (10,11). Proton-recoiltrack scanning for these integral reactions is conducted in adifferent mode than scanning for differential neutron spectrom-etry (see 3.2). Integral m
24、ode data analysis is also different thanthe analysis required for differential neutron spectrometry (see3.2). This practice will emphasize NRE (n,p) integral neutrondosimetry, because of the utility and advantages of integralmode measurements in low power benchmark fields.2. Referenced Documents2.1
25、ASTM Standards:3E 706 Master Matrix for Light-Water Reactor PressureVessel Surveillance Standards, E 706(0)E 854 Test Method for Application and Analysis of SolidState Track Recorder (SSTR) Monitors for Reactor Sur-veillance, E706(IIIB)E 910 Test Method for Application and Analysis of HeliumAccumula
26、tion Fluence Monitors for Reactor Vessel Sur-veillance, E706 (IIIC)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, E706(IIIA)3. Alternate Mo
27、des of NRE Neutron Measurements3.1 Neutron Spectrum MeasurementsThe neutron energyrange of interest in reactors environments covers approxi-mately nine orders of magnitude, extending from thermalenergies up to approximately 20 MeV. No single high-resolution method of neutron spectrometry exists that
28、 cancompletely cover this energy range of interest (12). Work withproton-recoil proportional counters has not been extendedbeyond a few MeV, due to the escape of more energetic protonsfrom the finite sensitive volume of the counter. In fact,correction of in-situ proportional counters for such finite
29、-sizeeffects can be non-negligible above 0.5 MeV (13). Finite-sizeeffects are much more manageable in NRE because of thereduced range of recoil protons. As a consequence, NRE fastneutron spectrometry has been applied at energies up to 15MeV (3). For in-situ spectrometry in reactor environments,NRE m
30、easurements up to 8.0 MeVare possible with very smallfinite-size corrections (14-16).3.1.1 4p ModeIt has been shown (3-6) that a neutronfluence-spectrum can be deduced from the integral relationshipME! 5 npV*E snpE! FE!EdE (1)where:F(E) = neutron fluence in n/(cm2MeV),snp(E) = neutron-proton scatter
31、ing cross section (cm2)atneutron energy, E,E = neutron or proton energy (MeV),np= atomic hydrogen density in the NRE (atoms/cm3),V = volume of NRE scanned (cm3), andM (E) = proton spectrum (protons/MeV) observed in theNRE volume V at energy E.The neutron fluence can be derived from Eq 1 and takes th
32、eform:FE! 5 EsnpE!npVdMdE(2)Eq 2 reveals that the neutron fluence spectrum at energy Edepends upon the slope of the proton spectrum at energy E.Asa consequence, approximately 104tracks must be measured togive statistical accuracies of the order of 10 % in the neutronfluence spectrum (with a correspo
33、nding energy resolution ofthe order of 10 %). It must be emphasized that spectralmeasurements determined with NRE in the 4p mode areabsolute.3.1.2 End-On ModeDifferential neutron spectrometrywith NRE is considerably simplified when the direction ofneutron incidence is known, such as for irradiations
34、 in colli-mated or unidirectional neutron beams. In such exposures, thekinematics of (n,p) scattering can be used to determine neutronenergy. Observation of proton-recoil direction and proton-recoil track length provide the angle of proton scatteringrelative to the incident neutron direction, u, and
35、 the proton3For 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.E2059062energy, Ep, respectively. In terms of thes
36、e observations, theneutron energy, En, is simply:En5Epcos2u(3)In collimated or unidirectional neutron irradiations, theemulsion is exposed end-on as depicted in Fig. 1. The end-onmode can be used to advantage in media where neutronscattering is negligible for two types of benchmark fieldexperiments,
37、 namely:3.1.2.1 Benchmark field validation of the NRE method orcharacterization of point neutron sources, for example, thestandard252Cf neutron field at the National Institute of Stan-dards and Technology (NIST) (17).3.1.2.2 Measurement of leakage neutron spectra at suffi-ciently large distances fro
38、m the neutron source, for example,neutron spectrum measurements at the Little Boy Replica(LBR) benchmark field (18).3.2 Integral ModeIt is possible to use emulsion data toobtain both differential and integral spectral information.Emulsion work is customarily carried out in the differentialmode (3-6)
39、. In contrast, NRE work in the integral mode is amore recent concept and, therefore, a fuller explanation of thisapproach is included below. In this integral mode, NREprovide absolute integral reaction rates, which can be used inspectral adjustment codes. Before these recent efforts, suchcodes have
40、not utilized integral reaction rates based on NRE.The significance of NRE integral reaction rates stems from theunderlying response, which is based on the elastic scatteringcross section of hydrogen. This snp(E) cross section isuniversally accepted as a standard cross section and is knownto an accur
41、acy of approximately 1 %.3.2.1 The I Integral RelationThe first integral relationshipfollows directly from Eq 1. The integral in Eq 1 can be definedas:IET! 5*ET s E!EFE! dE (4)Here I (ET) possesses units of proton-recoil tracks/MeV perhydrogen atom. Clearly I (ET) is a function of the lower protonen
42、ergy cut-off used for analyzing the emulsion data. Using Eq4 in Eq 1, one finds the integral relation:IET! 5MET!npV(5)I (ET) is evaluated by using a least squares fit of the scanningdata in the neighborhood of E=ET. Alternatively, since:MET! 5 MRT!dRE!dE(6)where: R (E) is the proton-recoil range at
43、energy E in theNRE and dR/dE is known from the proton range-energyrelation for the NRE. One need only determine M (R)intheneighborhood ofR=RT. Here M(R) is the number ofproton-recoil tracks/micron observed in the NRE. Conse-quently, scanning efforts can be concentrated in the neighbor-hood of R=RTin
44、 order to determine I (ET). In this manner, theaccuracy attained in I (ET) is comparable to the accuracy of thedifferential determination of F(E), as based on Eq 2, but witha significantly reduced scanning effort.3.2.2 The J Integral RelationThe second integral relationcan be obtained by integration
45、 of the observed proton spectrumM (ET). From Eq 1:*EminMET!dET5 npV*EmindET *ET sE!EFE!dE (7)where: Eminis the lower proton energy cut-off used inanalyzing the NRE data. Introducing into Eq 7 the definitions:Emin! 5*EminMET!dET(8)and:JEmin! 5*EmindET *ET sE!EFE! (9)has:FIG. 1 Geometrical Configurati
46、on for End-On Irradiation of NREE2059063JEmin! 5Emin!npV(10)Hence, the second integral relation, namely Eq 10, can beexpressed in a form analogous to the first integral relation,namely Eq 5. Here (Emin) is the integral number of proton-recoil tracks per hydrogen atom observed above an energy Eminin
47、the NRE. Consequently the integral J (Emin) possesses unitsof proton-recoil tracks per hydrogen atom. The integral J(Emin) can be reduced to the form:JEmin! 5*EminS1EminEDsE!FE!dE (11)In addition by using Eq 6, the observable (Emin) can beexpressed in the form:Emin! 5*RminMR!dR (12)Hence, to determi
48、ne the second integral relationship, oneneed only count proton-recoil tracks above R=Rmin. Tracksconsiderably longer than Rminneed not be measured, butsimply counted. However, for tracks in the neighborhood of R=Rmin, track length must be measured so that an accuratelower bound Rmincan be effectivel
49、y determined.4. Significance and Use4.1 Integral Mode DosimetryAs shown in 3.2, two differ-ent integral relationships can be established using proton-recoilemulsion data. These two integral reactions can be obtainedwith roughly an order of magnitude reduction in scanningeffort. Consequently this integral mode is an important comple-mentary alternative to the customary differential mode of NREspectrometry. The integral mode can be applied over extendedspatial regions, for example, perhaps up to as many as tenin-situ locati
