1、Designation: E 722 09Standard 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 E 722; the number immediately following the designation indicates
2、the 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 D
3、epartment of Defense.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 test specifications, and to thecharacterization of neutron te
4、st 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 neutrons of energy less than 10keV. The relevant equivalence is in
5、 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 material of interest is required. Sharpvariations in the effects w
6、ith 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 (1-3)2caused by different particles(electrons, neutrons, pro
7、tons, 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 research reactors and californium-252irradiators.1.3 The te
8、chnique 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 properties.1.4 The detailed determination of the neutron fluence
9、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.1.5 The values stated in SI units are to be regarded asstand
10、ard. 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-priate safety and health practices and determine the appli
11、ca-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E 170 Terminology Relating to Radiation Measurementsand DosimetryE 265 Test Method for Measuring Reaction Rates andFast-Neutron Fluences by Radioactivation of Sulfur-32E 693 Practice for Characterizing Neutro
12、n Exposures inIron and Low Alloy Steels in Terms of Displacements PerAtom (DPA), E 706(ID)E 720 Guide for Selection and Use of Neutron Sensors forDetermining Neutron Spectra Employed in Radiation-Hardness Testing of ElectronicsE 721 Guide for Determining Neutron Energy Spectra fromNeutron Sensors fo
13、r Radiation-Hardness Testing of Elec-tronicsE 844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E 706(IIC)E 944 Guide for Application of Neutron Spectrum Adjust-ment Methods in Reactor Surveillance, E 706 (IIA)2.2 International Commission on Radiation Units andMeasurements (IC
14、RU) Reports:1This 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 Materials and Devices.Current edition approved June 1, 2009. Published August 2009.
15、Originallyapproved in 1980. Last previous edition approved in 2004 as E 722 042.2The boldface numbers in parentheses refer to a list of references at the end ofthis practice.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For
16、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 Conshohocken, PA 19428-2959, United States.ICRU Report 13Neutron Fluence, Neutron Spectra, andKerma4ICRU Report 26N
17、eutron 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 proportional to the quotient of the ob-servable displacement damage per targ
18、et 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 example, Annexes A1.2.2 and A2.2.2.3.1.1.1 DiscussionObservable changes in
19、 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 fluence, the displacement damagefunction represents the quotient FD,mat(E)/dF, in
20、 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 lifetime in the bulk semicon-ductor material. While several procedures exist
21、 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 mode, it has been shown that thedisplacement damage function may be successf
22、ully 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 pertarget atom and the neutron fluence. KD,mat(E) is proportionalto KD,mat.A/F, wh
23、ere KD,matis the displacement kerma, Aisthe mean atomic mass of the material and F is the neutronfluence from a monoenergetic source of energy E.3.1.2.1 DiscussionThis quantity may be calculated fromthe microscopic neutron interaction cross sections, the kine-matic relations for each reaction and fr
24、om 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 per unit mass, as in the term kermafactor defined in E 170.3.1.3 fluence
25、 spectrum hardness parameter(Hmat = Feq,Eref,mat/F) this parameter is defined as the ratio of theequivalent monoenergetic neutron fluence to the total fluence,Feq,Eref,mat/F. The numerical value of the hardness parameteris also equal to the fluence of monoenergetic neutrons at thespecific energy, Er
26、ef, required to produce the same displace-ment damage in the specified material, mat, per unit fluence ofneutrons of neutron spectrum F(E).3.1.3.1 DiscussionFor damage correlation, a convenientmethod of characterizing the shape of an incident neutronfluence spectrum F(E), is in terms of a fluence sp
27、ectrumhardness 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 equivalent monoenergetic neutron fluence(Feq,Eref-,mat) an equivalen
28、t 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 aspecified irradiated material, mat, as F(E).3.1.4.1 DiscussionNote that Feq,E
29、ref,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 fluence spectrumsee neutron fluence andneutron fluence spectrum.3.1.6
30、kerma factor(Kmat(E) the kerma per unit fluenceof particles of energy E present in a specified material, mat. SeeTerminology E 170 for the definition of kerma, and a formulafor calculating the kerma factor.3.1.6.1 DiscussionWhen a material is irradiated by aneutron field, the energy imparted to char
31、ged 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. Calculations of ionization and mi-croscopic displacement kerma in silicon and
32、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 particle fluence andparticle fluence spectrum as defined in E 170.3.1.7.
33、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 as follows:Feq,Eref,mat5*0FE!FD,matE!dEFD,Eref,mat(1)where:F(E) = in
34、cident neutron fluence spectrum,FD,mat= neutron displacement damage function 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,
35、Eref, as givenin the annexes.4Available from International Commission on Radiation Units and Measure-ments, 7910 Woodmont Avenue Suite 400 Bethesda, MD 20841-3095, http:/www.icru.org/E722092The energy limits on the integral are determined in practiceby the incident neutron fluence spectrum and by th
36、e 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 Test Method E 721) and theequivalent monoenergetic fluence calculated, t
37、hen 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 per unit monitor response,Feq,Eref,mat/Mr. Use of a monitor foil to p
38、redict 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. Thischaracterization makes it feasible to predict some changes inoperational properties
39、 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 neutronfluence from a source to a single parameteran equivalentmonoenerge
40、tic 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. Ideally, thisquantity is correlated to the degradation of a specific
41、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 many instances, other effectsalso can be important. Ionization effects
42、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 in making a correlationbetween calculated displacement damage and per
43、formancedegradation 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 fluence is widely usedin the radiation-hardness testing community. It has
44、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 Eq 1 and 2, determine the energy limits Eminand Emaxto be used in p
45、lace 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 an energy abovewhich the integral damage falls to an insignificant le
46、vel. 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 spectra, this energy hasbeen historically chosen to be about 0.01 MeV. Mor
47、e 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 material andthe equivalent energy chosen. For silicon, resonance effect
48、scause 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, monoenergeticneutron sources with these energies may not be useful foreffects testing.Also, for a selected equivalent energy, the valu
49、eof 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 knowledge ofthe absolute values of FD,mat(E) is not required in evaluatingFeq,Eref
