1、Designation: E2059 06 (Reapproved 2010)Standard Practice forApplication and Analysis of Nuclear Research Emulsions forFast Neutron Dosimetry1This standard is issued under the fixed designation E2059; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase of revision, 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 Nuclear Research Emulsions (NRE) have a long andillustrious history of applications in th
3、e physical sciences, 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 ne
4、utron physics experimentsin 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 an
5、d handbooks that 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 f
6、ields (see MatrixE706).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 E1005). NRE provide permanent records, so
7、 thatoptical 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 fo
8、r fine struc-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 S
9、ection 11).1.4 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 us
10、ed to measure 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 cons
11、equence, this 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-nifi
12、cant limitation 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 t
13、o low power environments 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, tra
14、ck length decreases 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.
15、This 3 tracklength limit corresponds to a low energy limit of applicabilityin the range of approximately 0.3 to 0.4 MeV for neutroninduced proton-recoil measurements in NRE.1This practice is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications , and is the direct respon
16、sibility of SubcommitteeE10.05 on Nuclear Radiation Metrology.Current edition approved Oct. 1, 2010. Published November 2010. Originallyapproved in 2000. Last previous edition approved in 2006 as E2059 - 06. DOI:10.1520/E2059-10.2The boldface numbers in parentheses refer to the list of references at
17、 the end ofthe text.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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 spectrometr
18、y in reactorenvironments is #8MeV.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
19、 manual scanning, thislimitation arises 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 Measure
20、ments)For differential neutron spectrometry 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 i
21、n-situ irradiation creates tracks 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
22、mode is calledthe end-on mode. Scanning 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,
23、p)reaction in low power reactor environments. 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 s
24、pectrom-etry (see 3.2). Integral mode 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
25、fields.2. Referenced Documents2.1 ASTM Standards:3E706 Master Matrix for Light-Water Reactor Pressure Ves-sel Surveillance Standards, E 706(0)E854 Test Method for Application and Analysis of SolidState Track Recorder (SSTR) Monitors for Reactor Sur-veillance, E706(IIIB)E910 Test Method for Applicati
26、on and Analysis of HeliumAccumulation Fluence Monitors for Reactor Vessel Sur-veillance, E706 (IIIC)E944 Guide for Application of Neutron Spectrum Adjust-ment Methods in Reactor Surveillance, E 706 (IIA)E1005 Test Method for Application and Analysis of Radio-metric Monitors for Reactor Vessel Survei
27、llance, E706(IIIA)3. Alternate Modes 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
28、 neutron spectrometry exists that 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 prop
29、ortional counters for such finite-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 spectrome
30、try in reactor environments,NRE measurements 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
31、),snp(E) = neutron-proton scattering 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
32、be derived from Eq 1 and takes theform: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 neutron
33、fluence spectrum (with a corresponding 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 i
34、s known, such as for irradiations 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 i
35、ncident neutron direction, u, and the protonenergy, Ep, respectively. In terms of these observations, theneutron energy, En, is simply:3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume inf
36、ormation, refer to the standards Document Summary page onthe ASTM website.E2059 06 (2010)2En5Epcos2u(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
37、 two types of benchmark fieldexperiments, 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 spe
38、ctra at suffi-ciently large distances from 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
39、carried out in the differentialmode (3-6). 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. Bef
40、ore these recent efforts, suchcodes have 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 stand
41、ard cross section and is knownto an accuracy 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
42、 (ET) is a function of the lower protonenergy 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)wh
43、ere: R (E) is the proton-recoil range at 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 co
44、ncentrated in the neighbor-hood of R=RTin 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 integr
45、al relationcan be obtained by integration 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!E
46、FE! (9)has:JEmin! 5Emin!npV(10)FIG. 1 Geometrical Configuration for End-On Irradiation of NREE2059 06 (2010)3Hence, 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 p
47、er hydrogen atom observed above an energy Eminin 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
48、 the form:Emin! 5*RminMR!dR (12)Hence, to determine 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
49、that an accuratelower bound Rmincan be effectively 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
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