1、Designation: E722 091Standard Practice forCharacterizing Neutron Fluence Spectra in Terms of anEquivalent Monoenergetic Neutron Fluence for Radiation-Hardness Testing of Electronics1This standard is issued under the fixed designation E722; the number immediately following the designation indicates t
2、he year oforiginal adoption or, in the case 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.This standard has been approved for use by agencies of the De
3、partment of Defense.1NOTEEditorial changes were made throughout in October 2009.1. Scope1.1 This practice covers procedures for characterizing neu-tron fluence from a source in terms of an equivalent monoen-ergetic neutron fluence. It is applicable to neutron effectstesting, to the development of te
4、st specifications, and to thecharacterization of neutron test environments. The sources mayhave a broad neutron-energy range, or may be mono-energeticneutron sources with energies up to 20 MeV. This practice isnot applicable in cases where the predominant source ofdisplacement damage is from neutron
5、s of energy less than 10keV. The relevant equivalence is in terms of a specified effecton certain physical properties of materials upon which thesource spectrum is incident. In order to achieve this, knowl-edge of the effects of neutrons as a function of energy on thespecific property of the materia
6、l of interest is required. Sharpvariations in the effects with neutron energy may limit theusefulness of this practice in the case of mono-energeticsources.1.2 This practice is presented in a manner to be of generalapplication to a variety of materials and sources. Correlationbetween displacements (
7、1-3)2caused by different particles(electrons, neutrons, protons, and heavy ions) is beyond thescope of this practice. In radiation-hardness testing of elec-tronic semiconductor devices, specific materials of interestinclude silicon and gallium arsenide, and the neutron sourcesgenerally are test and
8、research reactors and californium-252irradiators.1.3 The technique involved relies on the following factors:(1) a detailed determination of the fluence spectrum of theneutron source, and (2) a knowledge of the degradation(damage) effects of neutrons as a function of energy on specificmaterial proper
9、ties.1.4 The detailed determination of the neutron fluence spec-trum referred to in 1.3 need not be performed afresh for eachtest exposure, provided the exposure conditions are repeatable.When the spectrum determination is not repeated, a neutronfluence monitor shall be used for each test exposure.1
10、.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 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
11、-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E170 Terminology Relating to Radiation Measurements andDosimetryE265 Test Method for Measuring Reaction Rates and Fast-Neutron Fluences by Radioactiv
12、ation of Sulfur-32E693 Practice for Characterizing Neutron Exposures in Ironand LowAlloy Steels in Terms of Displacements PerAtom(DPA), E 706(ID)E720 Guide for Selection and Use of Neutron Sensors forDetermining Neutron Spectra Employed in Radiation-Hardness Testing of ElectronicsE721 Guide for Dete
13、rmining Neutron Energy Spectra fromNeutron Sensors for Radiation-Hardness Testing of Elec-tronics1This practice is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.07 on Radiation Dosimetry for Radiation Effects on
14、 Materials and Devices.Current edition approved June 1, 2009. Published August 2009. Originallyapproved in 1980. Last previous edition approved in 2004 as E722 042. DOI:10.1520/E0722-09E01.2The boldface numbers in parentheses refer to a list of references at the end ofthis practice.3For referenced A
15、STM 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consho
16、hocken, PA 19428-2959, United States.E844 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)2.2 International Commission on Radiation Units andMeasurements (ICRU) Repor
17、ts:ICRU Report 13Neutron Fluence, Neutron Spectra, andKerma4ICRU Report 26Neutron Dosimetry for Biology andMedicine4ICRU Report 33Radiation Quantities and Units43. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 displacement damage function(FD,mat) an energy-dependent parameter p
18、roportional to the quotient of the ob-servable displacement damage per target atom and the neutronfluence. Different displacement-related damage functions mayexist, so the damage mode of interest and the observationprocedure shall be identified when the specific damage func-tion is defined. See, for
19、 example, Annexes A1.2.2 and A2.2.2.3.1.1.1 DiscussionObservable changes in a materialsproperties attributable to the atomic displacement process areuseful indices of displacement damage in that material. Incases where the observed displacement damage is not in linearproportion to the applied fluenc
20、e, the displacement damagefunction represents the quotient FD,mat(E)/dF in the limitingcase of zero fluence. Examples of suitable representations ofdisplacement damage functions are given in the annexes. In thecase of silicon, damage mode of interest is the change inminority-carrier recombination li
21、fetime in the bulk semicon-ductor material. While several procedures exist to directlymeasure the minority carrier lifetime in bulk material, sincethis lifetime is related to the gain of a bipolar junction transistor(BJT), one observable damage metric is the BJT gain degra-dation. For this damage mo
22、de, it has been shown that thedisplacement damage function may be successfully equatedwith the microscopic displacement kerma factor. This questionis discussed further in the annexes.3.1.2 microscopic displacement kerma factor(kD,mat(E)the energy-dependent quotient of the displacement kerma pertarge
23、t atom and the neutron fluence. kD,mat(E) is proportionalto KD,matA/F, where KD,matis the displacement kerma, Ais themean atomic mass of the material and F is the neutron fluencefrom a monoenergetic source of energy E.3.1.2.1 DiscussionThis quantity may be calculated fromthe microscopic neutron inte
24、raction cross sections, the kine-matic relations for each reaction and from a suitable partitionfunction which divides the total kerma into ionization anddisplacement kerma. The use of the term microscopic kermafactor in this standard is to indicate that energy times area peratom is used, instead of
25、 per unit mass, as in the term kermafactor defined in E170.3.1.3 fluence spectrum hardness parameter(Hmat= Feq,Eref,mat/F) this parameter is defined as the ratio ofthe equivalent monoenergetic neutron fluence to the totalfluence, Feq,Eref,mat/F. The numerical value of the hardnessparameter is also e
26、qual to the fluence of monoenergeticneutrons at the specific energy, Eref, required to produce thesame displacement damage in the specified material, mat, perunit fluence of neutrons of neutron spectrum F(E).3.1.3.1 DiscussionFor damage correlation, a convenientmethod of characterizing the shape of
27、an incident neutronfluence spectrum F(E), is in terms of a fluence spectrumhardness parameter. The hardness parameter in a particularneutron field depends on the displacement damage functionused to compute the damage (see annexes) and is thereforedifferent for different semiconductor materials.3.1.4
28、 equivalent monoenergetic neutron fluence(Feq,Eref-,mat) an equivalent monoenergetic neutron fluence, Feq,Eref,mat,characterizes an incident fluence spectrum, F(E), in terms ofthe fluence of monoenergetic neutrons at a specific energy Erefrequired to produce the same displacement damage in aspecifie
29、d irradiated material, mat, as F(E).3.1.4.1 DiscussionNote that Feq,Eref,matis equivalent toF(E) if, and only if, the specific device effect (for example,current gain degradation in silicon) being correlated is de-scribed by the displacement damage function used in thecalculation.3.1.5 fluence and f
30、luence spectrumsee neutron fluence andneutron fluence spectrum.3.1.6 kerma factor(kmat(E) the kerma per unit fluenceof particles of energy E present in a specified material, mat. SeeTerminology E170 for the definition of kerma, and a formulafor calculating the kerma factor.3.1.6.1 DiscussionWhen a m
31、aterial is irradiated by aneutron field, the energy imparted to charged particles in thematerial may be described by the kerma. The kerma may bedivided into two parts, ionization kerma and displacementkerma. See 3.1.2.1 for the distinction between kerma factor andmicroscopic kerma factor. Calculatio
32、ns of ionization and mi-croscopic displacement kerma in silicon and gallium arsenideas a result of irradiation by neutrons with energies up to 20MeV are described in Refs 5-8 and in the annexes.3.1.7 neutron fluence and neutron fluence spectrum are usedin this standard, and are special cases of part
33、icle fluence andparticle fluence spectrum as defined in E170.3.1.7.1 DiscussionIn cases where the context makes clearthat neutrons are referred to, the terms fluence and fluencespectrum are sometimes used.4. Summary of Practice4.1 The equivalent monoenergetic neutron fluence,Feq,Eref,mat, is given a
34、s follows:Feq,Eref,mat5*0FE!FD,matE!dEFD,Eref,mat(1)where:F(E) = incident neutron fluence spectrum,4Available from International Commission on Radiation Units and Measure-ments, 7910 Woodmont Avenue Suite 400 Bethesda, MD 20841-3095, http:/www.icru.org/E722 0912FD,mat= neutron displacement damage fu
35、nction forthe irradiated material (displacement dam-age per unit fluence) as a function of energy,andFD,Eref,mat= displacement damage reference value desig-nated for the irradiated material and for thespecified equivalent energy, Eref, as givenin the annexes.The energy limits on the integral are det
36、ermined in practiceby the incident neutron fluence spectrum and by the materialbeing irradiated.4.2 The neutron spectrum hardness parameter, Hmat,isgiven as follows:Hmat5*0FE!FD,matE!dEFD,Eref,mat *0FE!dE(2)4.3 Once the neutron fluence spectrum has been determined(for example, in accordance with Tes
37、t Method E721) and theequivalent monoenergetic fluence calculated, then a monitor(such as an activation foil) can be used in subsequent irradia-tions at the same location to determine the fluence; that is, theneutron fluence is then described in terms of the equivalentmonoenergetic neutron fluence p
38、er unit monitor response,Feq,Eref,mat/Mr. Use of a monitor foil to predict Feq,Eref,matisvalid only if the neutron spectrum remains constant.5. Significance and Use5.1 This practice is important in characterizing the radiationhardness of electronic devices irradiated by neutrons. Thischaracterizatio
39、n makes it feasible to predict some changes inoperational properties of irradiated semiconductor devices orelectronic systems. To facilitate uniformity of the interpretationand evaluation of results of irradiations by sources of differentfluence spectra, it is convenient to reduce the incident neutr
40、onfluence from a source to a single parameteran equivalentmonoenergetic neutron fluenceapplicable to a particularsemiconductor material.5.2 In order to determine an equivalent monoenergeticneutron fluence, it is necessary to evaluate the displacementdamage of the particular semiconductor material. I
41、deally, thisquantity is correlated to the degradation of a specific functionalperformance parameter (such as current gain) of the semicon-ductor device or system being tested. However, this correlationhas not been established unequivocally for all device types andperformance parameters since, in man
42、y instances, other effectsalso can be important. Ionization effects produced by theincident neutron fluence or by gamma rays in a mixed neutronfluence, short-term and long-term annealing, and other factorscan contribute to observed performance degradation (damage).Thus, caution should be exercised i
43、n making a correlationbetween calculated displacement damage and performancedegradation of a given electronic device. The types of devicesfor which this correlation is applicable, and numerical evalu-ation of displacement damage are discussed in the annexes.5.3 The concept of 1-MeV equivalent fluenc
44、e is widely usedin the radiation-hardness testing community. It has merits anddisadvantages that have been debated widely (9-12). For thesereasons, specifics of a standard application of the 1-MeVequivalent fluence are presented in the annexes.6. Procedure for Calculating Feq,Eref,mat6.1 To evaluate
45、 Eq 1 and 2, determine the energy limits Eminand Emaxto be used in place of zero and infinity in the integralsof (Eq 1) and (Eq 2) and the values of the displacement damagefunction FD,mat(E) for the irradiated material and perform theindicated integrations.6.1.1 Choose the upper limit Emaxto be at a
46、n energy abovewhich the integral damage falls to an insignificant level. ForGodiva- or TRIGA-type spectra, this limit is about 12 MeV.6.1.2 Choose the lower-energy limit Eminto be at an energybelow which the integral damage falls to an insignificant level.For silicon irradiated by Godiva-type spectr
47、a, this energy hasbeen historically chosen to be about 0.01 MeV. More highlymoderated spectra may require lower thresholds or specializedfiltering requirements such as a boron shield, or both.6.1.3 The values of the neutron displacement damage func-tion used in Eq 1 and 2 obviously depend on the mat
48、erial andthe equivalent energy chosen. For silicon, resonance effectscause large variations (by a factor of 20 or more) in thedisplacement damage function as a function of energy over therange from about 0.1 to 8 MeV (4, 5). Therefore, monoener-getic neutron sources with these energies may not be us
49、eful foreffects testing.Also, for a selected equivalent energy, the valueof FD,Eref,matat that specific energy may not be representativeof the displacement damage function at nearby energies. Insuch cases, a method of averaging the damage function over arange of energies around the chosen equivalent energy can beused. Such averaging is discussed in the annexes. Because theFD,mat(E) term is normalized by dividing by FD,Eref,matin Eq 1and 2, only the shape of the FD,mat(E) function versus energyis of primary importance. In such a case, precise knowl
