1、Designation: E2059 151Standard 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 case of revision,
2、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.1NOTEIn paragraph 1.5, “three major limitations” was corrected editorially to “four major limitations” in March 2016.1
3、. Scope1.1 Nuclear Research Emulsions (NRE) have a long andillustrious history of applications in the physical sciences, earthsciences and biological sciences (1,2)2. In the physicalsciences, NRE experiments have led to many fundamentaldiscoveries in such diverse disciplines as nuclear physics,cosmi
4、c ray physics and high energy physics. In the appliedphysical sciences, NRE have been used in neutron physicsexperiments in both fission and fusion reactor environments(3-6). Numerous NRE neutron experiments can be found inother applied disciplines, such as nuclear engineering, environ-mental monito
5、ring and health physics. Given the breadth ofNRE applications, there exist many textbooks and handbooksthat provide considerable detail on the techniques used in theNRE method.As a consequence, this practice will be restrictedto the application of the NRE method for neutron measure-ments in reactor
6、physics and nuclear engineering with particu-lar emphasis on neutron dosimetry in benchmark fields (seeMatrix E706).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 ari
7、se with radiometric (RM) dosimeters (see TestMethod E1005). NRE provide permanent records, so thatoptical microscopy observations can be carried out any timeafter exposure. If necessary, NRE measurements can be re-peated at any time to examine questionable data or to obtainrefined results.1.3 Since
8、NRE measurements are conducted with opticalmicroscopes, high spatial resolution is afforded for 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
9、 detectors to provide such data because of in-situperturbations and finite-size effects (see Section 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
10、reactor environments have beenpredominantly based on this (n,p) reaction. NRE have alsobeen used to measure the6Li (n,t)4He and the10B(n,)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 (
11、n,p) reaction forneutron dosimetry in low power reactor environments (seeSection 4).As a consequence, 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 four majorlimitations for applicabilit
12、y in low power reactor environ-ments.1.5.1 Gamma-Ray SensitivityGamma-rays create a sig-nificant limitation for NRE measurements.Above a gamma-rayexposure of approximately 0.025 Gy, NRE can become foggedby gamma-ray induced electron events. At this level ofgamma-ray exposure, neutron induced proton-
13、recoil tracks canno longer be accurately measured. As a consequence, NREexperiments are limited to 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
14、, islimited.1.5.2 Low Energy LimitIn the measurement of tracklength for proton recoil events, track length decreases asproton-recoil energy decreases. Proton-recoil track length be-low approximately 3m in NRE can not be adequately mea-sured with optical microscopy techniques. As proton-recoiltrack l
15、ength decreases below approximately 3 m, it becomesvery difficult to measure track length accurately. This 3 mtrack length limit corresponds to a low energy limit ofapplicability in the range of approximately 0.3 to 0.4 MeV forneutron induced proton-recoil measurements in NRE.1This practice is under
16、 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 Oct. 1, 2015. Published November 2010. Originallyapproved in 2000. Last previous edition approved in 2010 as E
17、2059 - 06(2010).DOI: 10.1520/E2059-15.2The boldface numbers in parentheses refer to the list of references at the end ofthe text.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States11.5.3 High-Energy LimitsAs a consequence of finite-sizeli
18、mitations, fast-neutron spectrometry measurements are lim-ited to 15 MeV. The limit for in-situ spectrometry 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 dens
19、ity, a maze orlabyrinth of overlapping tracks is created, which precludes theuse of optical microscopy techniques. For manual scanning,this limitation arises above approximately 104tracks/cm2,whereas interactive computer based scanning systems canextend this limit up to approximately 105tracks/cm2.
20、Theselimits correspond to neutron fluences of 106107cm2,respectively.1.6 Neutron Spectrometry (Differential Measurements)Fordifferential neutron spectrometry measurements in low powerreactor environments, NRE experiments can be conducted intwo different modes. In the more general mode, NRE areirradi
21、ated in-situ in the low power reactor environment. Thismode of NRE experiments is called the 4 mode, since thein-situ irradiation creates tracks in all directions (see 3.1.1). Inspecial circumstances, where the direction of the neutron fluxis known, NRE are oriented parallel to the direction of then
22、eutron flux. In this orientation, one edge of the NRE faces theincident neutron flux, so that this measurement 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
23、).1.7 Neutron Dosimetry (Integral Measurements)NRE alsoafford integral neutron dosimetry through use of the (n,p)reaction in low power reactor environments. Two differenttypes of (n,p) integral mode dosimetry reactions are possible,namely the I-integral (see 3.2.1) and the J-integral (see 3.2.2)(10,
24、11). Proton-recoil track scanning for these integral reac-tions is conducted in a different mode than scanning fordifferential neutron spectrometry (see 3.2). Integral mode dataanalysis is also different than the analysis required for differ-ential neutron spectrometry (see 3.2). This practice will
25、em-phasize NRE (n,p) integral neutron dosimetry, because of theutility and advantages of integral mode measurements in lowpower benchmark fields.2. Referenced Documents2.1 ASTM Standards:3E706 Master Matrix for Light-Water Reactor PressureVesselSurveillance Standards, E 706(0) (Withdrawn 2011)4E854
26、Test Method for Application and Analysis of SolidState Track Recorder (SSTR) Monitors for ReactorSurveillance, E706(IIIB)E910 Test Method for Application and Analysis of HeliumAccumulation Fluence Monitors for Reactor VesselSurveillance, E706 (IIIC)E944 Guide for Application of Neutron Spectrum Adju
27、st-ment Methods in Reactor Surveillance, E 706 (IIA)E1005 Test Method for Application and Analysis of Radio-metric Monitors for Reactor Vessel Surveillance3. Alternate Modes of NRE Neutron Measurements3.1 Neutron Spectrum MeasurementsThe neutron energyrange of interest in reactors environments cover
28、s approxi-mately nine orders of magnitude, extending from thermalenergies up to approximately 20 MeV. No single high-resolution method of neutron spectrometry exists that cancompletely cover this energy range of interest (12). Work withproton-recoil proportional counters has not been extendedbeyond
29、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-sizeeffects can be non-negligible above 0.5 MeV (13). Finite-sizeeffects are much more manageable in NRE because of thereduced ra
30、nge 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 measurements up to 8.0 MeVare possible with very smallfinite-size corrections (14-16).3.1.1 4 ModeIt has been shown (3-6) that a ne
31、utronfluence-spectrum can be deduced from the integral relationshipME! 5 npV *E npE! E!EdE (1)where:(E) = neutron fluence in n/(cm2MeV),np(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 = v
32、olume 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 theform:E! 52EnpE!npVdMdE(2)Eq 2 reveals that the neutron fluence spectrum at energy Edepends upon the slope of the proton spectrum at e
33、nergy E.Asa consequence, approximately 104tracks must be measured togive statistical accuracies of the order of 10 % in the neutronfluence spectrum (with a corresponding energy resolution ofthe order of 10 %). It must be emphasized that spectralmeasurements determined with NRE in the 4 mode areabsol
34、ute.3.1.2 End-On ModeDifferential neutron spectrometrywith NRE is considerably simplified when the direction ofneutron incidence is 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 neutronene
35、rgy. Observation of proton-recoil direction and proton-recoil track length provide the angle of proton scatteringrelative to the incident neutron direction, , and the proton3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For A
36、nnual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4The last approved version of this historical standard is referenced onwww.astm.org.E2059 1512energy, Ep, respectively. In terms of these observations, theneutron energy, En, is simply:En5
37、Epcos2(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, namely:3.1.2.1 Benchmark field validation of the NRE
38、 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 from the neutron source, for example,neutron spectrum me
39、asurements 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). In contrast, NRE work in the integral mode is amore
40、 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 not utilized integral reaction rates based on NRE.The
41、 significance of NRE integral reaction rates stems from theunderlying response, which is based on the elastic scatteringcross section of hydrogen. This np(E) cross section isuniversally accepted as a standard cross section and is knownto an accuracy of approximately 1 %.3.2.1 The I Integral Relation
42、The first integral relationshipfollows directly from Eq 1. The integral in Eq 1 can be definedas:IET! 5 *ET E!EE! dE (4)Here I(ET) possesses units of proton-recoil tracks/MeV perhydrogen atom. Clearly I(ET) is a function of the lower protonenergy cut-off used for analyzing the emulsion data. Using E
43、q4 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 energy E in theNRE and dR/dE is known from the proton range-
44、energyrelation for the NRE. One need only determine M(R)intheneighborhood of R = RT. Here M(R) is the number of proton-recoil tracks/m observed in the NRE. Consequently, scanningefforts can be concentrated in the neighborhood of R=RTinorder to determine I(ET). In this manner, the accuracy attainedin
45、 I(ET) is comparable to the accuracy of the differentialdetermination of (E), as based on Eq 2, but with a signifi-cantly reduced scanning effort.3.2.2 The J Integral RelationThe second integral relationcan be obtained by integration of the observed proton spectrumM(ET). From Eq 1:*EminMET!dET5 npV
46、*EmindET*ET E!EE!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 E!EE! (9)has:FIG. 1 Geometrical Configuration for End-On Irradiation of NREE2059 1513JEmin! 5Emin!npV(10)Hence, th
47、e 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 the NRE. Consequently the integral J(Emin) possesses unitsof proton-r
48、ecoil tracks per hydrogen atom. The integral J(Emin)can be reduced to the form:JEmin! 5 *EminS1 2EminEDE!E!dE (11)In addition by using Eq 6, the observable (Emin) can beexpressed in the form:Emin! 5 *RminMR!dR (12)Hence, to determine the second integral relationship, oneneed only count proton-recoil
49、 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 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 s
