1、Designation: E 722 04e2Standard Practice forCharacterizing Neutron Energy Fluence Spectra in Terms ofan Equivalent Monoenergetic Neutron Fluence forRadiation-Hardness Testing of Electronics1This standard is issued under the fixed designation E 722; the number immediately following the designation in
2、dicates 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 (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies
3、 of the Department of Defense.e1NOTETable A1.1 and A2.1 were corrected editorially in February 2005.e2NOTEAn = sign was added in Eq 1 in April 2007.1. Scope1.1 This practice covers procedures for characterizing aneutron fluence from a source in terms of an equivalentmonoenergetic neutron fluence. It
4、 is applicable to neutroneffects testing, to the development of test specifications, and tothe characterization of neutron test environments. The sourcesmay have a broad neutron-energy spectrum, or may be mono-energetic neutron sources with energies up to 20 MeV. Thispractice is not applicable in ca
5、ses where the predominantsource of displacement damage is from neutrons of energy lessthan 10 keV. The relevant equivalence is in terms of a specifiedeffect on certain physical properties of materials upon whichthe source spectrum is incident. In order to achieve this,knowledge of the effects of neu
6、trons as a function of energy onthe specific property of the material of interest is required.Sharp variations in the effects with neutron energy may limitthe usefulness of this practice in the case of mono-energeticsources.1.2 This practice is presented in a manner to be of generalapplication to a
7、variety of materials and sources. Correlationbetween displacements (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
8、and gallium arsenide, and the neutron sourcesgenerally are test and research reactors and californium-252irradiators.1.3 The technique involved relies on the following factors:(1) a detailed determination of the energy spectrum of theneutron source, and (2) a knowledge of the degradation(damage) eff
9、ects of neutrons as a function of energy on specificmaterial properties.1.4 The detailed determination of the neutron energy 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 repeate
10、d, a neutronfluence monitor shall be used for each test exposure.1.5 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 appl
11、ica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E 265 Test Method for Measuring Reaction Rates andFast-Neutron Fluences by Radioactivation of Sulfur-32E 693 Practice for Characterizing Neutron Exposures inIron and Low Alloy Steels in Terms of Displacement
12、s 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 for Radiation-Hardness Testing of Elec-tronicsE 844 Guide for Sens
13、or 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)1This practice is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibili
14、ty of SubcommitteeE10.07 on Radiation Dosimetry for Radiation Effects on Materials and Devices.Current edition approved Feb. 15, 2005. Published July 2004. Originallyapproved in 1980. Last previous edition approved in 2002 as E 722 94(2002).2The boldface numbers in parentheses refer to a list of ref
15、erences at the end ofthis practice.3For 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.1Copyright ASTM Internatio
16、nal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.2 International Commission on Radiation Units andMeasurements (ICRU) Reports:ICRU Report 13Neutron Fluence, Neutron Spectra, andKerma4ICRU Report 26Neutron Dosimetry for Biology andMedicine4ICRU Report 33Radia
17、tion Quantities and Units43. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 displacement damage function(FD,mat) an energyde-pendent parameter proportional to the quotient of the observ-able displacement damage per target atom and the neutronfluence.3.1.1.1 DiscussionObservable
18、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 fluence, the displacement damagefunction represents the quotient FD,mat
19、(E)/dF, in the limitingcase of zero fluence. Examples of suitable representations ofdisplacement damage functions are given in the annexes. In thecase of silicon, it has been shown that the displacement damagefunction may be successfully equated with the displacementkerma factor. This question is di
20、scussed further in the annexes.3.1.2 displacement kerma factor(KD,mat(E) the energydependent quotient of the displacement kerma per target atomand the neutron fluence.3.1.2.1 DiscussionThis quantity may be calculated fromthe microscopic neutron interaction cross sections, the kine-matic relations fo
21、r each reaction and from a suitable partitionfunction which divides the total kerma into ionization anddisplacement kerma.3.1.3 energy-spectrum hardness parameter(Hmat = Feq,Eref,mat/F) this parameter is defined as the ratio of theequivalent monoenergetic neutron fluence to the true totalfluence, Fe
22、q,Eref,mat/F. The numerical value of the hardnessparameter is also equal to the fluence of monoenergeticneutrons at the specific energy, Eref, required to produce thesame displacement damage in the specified material, mat unitfluence of neutrons of spectral distribution F(E).3.1.3.1 DiscussionFor da
23、mage correlation, a convenientmethod of characterizing the shape of an incident neutronenergy-fluence spectrum F(E), is in terms of an energyspectrum hardness parameter (4). The hardness parameter in aparticular neutron field depends on the displacement damagefunction used to compute the damage (see
24、 annexes) and istherefore different for different semiconductor materials.3.1.4 equivalent monoenergetic neutron fluence(Feq,Eref-,mat) an equivalent monoenergetic neutron fluence, Feq,Eref,mat,characterizes an incident energy-fluence spectrum, F(E), interms of the fluence of monoenergetic neutrons
25、at a specificenergy Eref required to produce the same displacement damagein a specified 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-
26、scribed by the displacement damage function used in thecalculation.3.1.5 kerma(Kmat(E) the sum of the initial kineticenergies of all the charged particles liberated by indirectlyionizing particles (for example, neutrons) in a volume elementcontaining a unit mass of the specified material (see ICRUre
27、ports 13 and 33).3.1.5.1 DiscussionWhen a material is irradiated by aneutron field, the energy imparted to the material may bedescribed by the quantity kerma. The total kerma may bedivided into two parts, ionization kerma and displacementkerma. Calculations of ionization and displacement kerma insil
28、icon and gallium arsenide as a result of irradiation byneutrons with energies up to 20 MeV are described in Refs 5-8and in the annexes.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) = incid
29、ent neutron energy-fluence spectral dis-tribution,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 e
30、quivalent energy, Eref, as givenin the annexes.The energy limits on the integral are determined in practiceby the incident-energy spectrum and by the material beingirradiated.4.2 The neutron energy spectrum hardness parameter, Hmat,is given as follows:Hmat5*0FE!FD,matE!dEFD,Eref,mat *0FE!dE(2)4.3 On
31、ce the neutron energy-fluence spectrum has beendetermined (for example, in accordance with Test MethodE 721) and the equivalent monoenergetic fluence calculated,then a monitor (such as an activation foil) can be used insubsequent irradiations at the same location to determine thefluence; that is, th
32、e neutron fluence is then described in termsof the equivalent monoenergetic neutron fluence per unitmonitor response, Feq,Eref,mat/Mr. Use of a monitor foil topredict Feq,Eref,matis valid only if the energy spectrum remainsconstant.4Available from International Commission on Radiation Units and Meas
33、ure-ments, 7910 Woodmont Ave., Bethesda, MD 20814.E72204e225. 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 of irradiated
34、 semiconductor devices orelectronic systems.To facilitate uniformity of the interpretationand evaluation of results of irradiations by sources of differentenergy spectra, it is convenient to reduce the incident neutronfluence from a source to a single parameteran equivalentmonoenergetic neutron flue
35、nceapplicable 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 functionalperfor
36、mance 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 produced by thei
37、ncident 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 performancedegradat
38、ion 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 merits anddisadv
39、antages 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 place of zero and
40、 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 level. ForGodiva-
41、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. More highlymoderate
42、d 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 effectscause large var
43、iations (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). Therefore, monoenergeticneutron sources with these energies may not be useful foreffects testing.Also, for a selected equivalent energy, the valueof FD,Eref,matat
44、 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
45、 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,matand Hmat.7. Determining Feq,Eref,matwith a Monitor Foil
46、7.1 At the same time that the energy spectrum, F(E), of thesource is determined (for example, with an activation foil set inaccordance with Guides E 720 or E 844, or both, and TestMethod E 721 or Practice E 944, or both, place a fast-neutronmonitor foil in the neutron field at an appropriate locatio
47、n.After Feq,Eref,matis determined and the monitor foil counted,calculate the ratio of the equivalent monoenergetic fluence tothe unit monitor response, Feq,Eref,mat/Mr.7.2 Use the response of the fast-neutron monitor foil, Mr,topredict Feq,Eref,matin subsequent routine device test irradia-tions. For
48、 this method to be valid, it is important to keep thesource-foil geometry essentially identical to that used forcalibrating the monitor foil. Moderate changes in source-to-foildistance are allowable. In addition, make sure the sourcelocation (of a Godiva-type reactor) with respect to scatteringmater
49、ials (walls, floor, etc.) is the same. Do not change ormove nearby scattering materials or moderators.7.3 Precautions in maintaining original calibration condi-tions are necessary to avoid altering the neutron energyspectrum significantly in subsequent irradiations. An appre-ciable change in the spectrum will invalidate the calibration ofthe monitor foil and, therefore, would necessitate a newmeasurement of F(E) and recalibration of the monitor foil.Whenever the neutron source configuration is changed, as forexample, if the core fuel elements are replaced o
