1、Designation: E722 091E722 14Standard 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 indi
2、cates 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
3、 the U.S. Department of Defense.1 NOTEEditorial changes were made throughout in October 2009.1. Scope1.1 This practice covers procedures for characterizing neutron fluence from a source in terms of an equivalent monoenergeticneutron fluence. It is applicable to neutron effects testing, to the develo
4、pment of test specifications, and to the characterization ofneutron test environments. The sources may have a broad neutron-energy range, or may be mono-energetic neutron sources withenergies up to 20 MeV. This practice is not applicable in cases where the predominant source of displacement damage i
5、s fromneutrons of energy less than 10 keV. The relevant equivalence is in terms of a specified effect on certain physical properties ofmaterials upon which the source spectrum is incident. In order to achieve this, knowledge of the effects of neutrons as a functionof energy on the specific property
6、of the material of interest is required. Sharp variations in the effects with neutron energy maylimit the usefulness of this practice in the case of mono-energetic sources.1.2 This practice is presented in a manner to be of general application to a variety of materials and sources. Correlation betwe
7、endisplacements (1-3)2 caused by different particles (electrons, neutrons, protons, and heavy ions) is beyond the scope of thispractice. In radiation-hardness testing of electronic semiconductor devices, specific materials of interest include silicon and galliumarsenide, and the neutron sources gene
8、rally are test and research reactors and californium-252 irradiators.1.3 The technique involved relies on the following factors: (1) a detailed determination of the fluence spectrum of the neutronsource, and (2) a knowledge of the degradation (damage) effects of neutrons as a function of energy on s
9、pecific material properties.1.4 The detailed determination of the neutron fluence spectrum referred to in 1.3 need not be performed afresh for each testexposure, provided the exposure conditions are repeatable. When the spectrum determination is not repeated, a neutron fluencemonitor shall be used f
10、or each test exposure.1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in thisstandard.standard, except for MeV, keV, eV, MeVmbarn, rad(Si)cm2, rad(GaAs)cm2.1.6 This standard does not purport to address all of the safety concerns, if any, a
11、ssociated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E170 Terminology Relating to Radiation Measurements and D
12、osimetryE265 Test Method for Measuring Reaction Rates and Fast-Neutron Fluences by Radioactivation of Sulfur-32E693 Practice for Characterizing Neutron Exposures in Iron and LowAlloy Steels in Terms of Displacements PerAtom (DPA),E 706(ID)1 This practice is under the jurisdiction of ASTM Committee E
13、10 on Nuclear Technology and Applicationsand is the direct responsibility of Subcommittee E10.07 onRadiation Dosimetry for Radiation Effects on Materials and Devices.Current edition approved June 1, 2009June 1, 2014. Published August 2009October 2014. Originally approved in 1980. Last previous editi
14、on approved in 20042009 asE722 04E722 09 21. DOI: 10.1520/E0722-09E01.10.1520/E0722-14.2 The boldface numbers in parentheses refer to a list of references at the end of this practice.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.o
15、rg. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit
16、 may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr H
17、arbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1E720 Guide for Selection and Use of Neutron Sensors for Determining Neutron Spectra Employed in Radiation-HardnessTesting of ElectronicsE721 Guide for Determining Neutron Energy Spectra from Neutron Sensors for Radiation-Hardn
18、ess Testing of ElectronicsE844 Guide for Sensor Set Design and Irradiation for Reactor Surveillance, E 706 (IIC)E944 Guide for Application of Neutron Spectrum Adjustment Methods in Reactor Surveillance, E 706 (IIA)2.2 International Commission on Radiation Units and Measurements (ICRU) Reports:4ICRU
19、Report 13Neutron13 Neutron Fluence, Neutron Spectra, and KermaICRU Report 26Neutron60 Dosimetry for Biology and MedicineFundamental Quantities and Units for Ionizing RadiationICRU Report 33Radiation85 Fundamental Quantities and Units for Ionizing Radiation (Revised)3. Terminology3.1 Definitions of T
20、erms Specific to This Standard:3.1.1 displacement damage function(FD,mat)(E) an energy-dependent parameter proportional to the quotient of the observabledisplacement damage per target atom and the neutron fluence. Different displacement-related damage functions may exist, so thedamage mode of intere
21、st and the observation procedure shall be identified when the specific damage function is defined. See, forexample, Annexes A1.2.2 and A2.2.2.3.1.1.1 DiscussionObservable changes in a materials properties attributable to the atomic displacement process are useful indices of displacementdamage in tha
22、t material. In cases where the observed displacement damage is not in linear proportion to the applied fluence, thedisplacement damage function represents the quotient Fd(observedD,mat(E)/d damage)/d in the limiting case of zero fluence.Examples of suitable representations of displacement damage fun
23、ctions are given in the annexes. In the case of silicon, damagemode of interest is the change in minority-carrier recombination lifetime in the bulk semiconductor material. While severalprocedures exist to directly measure the minority carrier lifetime in bulk material, since this lifetime is relate
24、d to the gain of abipolar junction transistor (BJT), one observable damage metric is the BJT gain degradation. For this damage mode, it has beenshown that the displacement damage function may be successfully equated with the microscopic displacement kerma factor. Thisquestion is discussed further in
25、 the annexes.3.1.2 microscopic displacement kerma factor(D,mat(E) the energy-dependent quotient of the displacement kerma per targetatom and the neutron fluence. D,mat(E) is proportional to KD,mat/, where KD,mat is the displacement kerma, is the mean atomicmass of the material and is the neutron flu
26、ence from a monoenergetic source of energy E.3.1.2.1 DiscussionThis quantity may be calculated from the microscopic neutron interaction cross sections, the kinematic relations for each reactionand from a suitable partition function which divides the total kerma into ionization and displacement kerma
27、. The use of the termmicroscopic kerma factor in this standard is to indicate that energy times area per atom is used, instead of per unit mass, as in theterm kerma factor defined in E170.3.1.3 fluence spectrum hardness parameter(HmatEref,mat = eq,Eref,mat/) this parameter is defined as the ratio of
28、 the equivalentmonoenergetic neutron fluence to the total fluence, eq,Eref,mat/. The numerical value of the hardness parameter is also equal tothe fluence of monoenergetic neutrons at the specific energy, Eref, required to produce the same displacement damage in thespecified material, mat, peras uni
29、t fluence of neutrons of neutron spectrum (E).3.1.3.1 DiscussionFor damage correlation, a convenient method of characterizing the shape of an incident neutron fluence spectrum (E), is in termsof a fluence spectrum hardness parameter.parameter (4). The hardness parameter in a particular neutron field
30、 depends on thedisplacement damage function used to compute the damage (see annexes) and is therefore different for different semiconductormaterials.3.1.4 equivalent monoenergetic neutron fluence(eq,Eref,mat) an equivalent monoenergetic neutron fluence, eq,Eref,mat,characterizes an incident fluence
31、spectrum, (E), in terms of the fluence of monoenergetic neutrons at a specific energy Erefrequired to produce the same displacement damage in a specified irradiated material, mat, as (E).4 Available from International Commission on Radiation Units and Measurements, 7910 Woodmont Avenue Suite 400 Bet
32、hesda, MD 20841-3095, http:/www.icru.org/E722 1423.1.4.1 DiscussionNote that eq,Eref,mat is equivalent to (E) if, and only if, the specific device effect (for example, current gain degradation in silicon)being correlated is described by the displacement damage function used in the calculation.3.1.5
33、fluence andfluence spectrumsee neutron fluence and neutron fluence spectrum.3.1.6 kerma factor(Kmat(E) the kerma per unit fluence of particles of energy E present in a specified material, mat. SeeTerminology E170 for the definition of kerma, and a formula for calculating the kerma factor.3.1.6.1 Dis
34、cussionWhen a material is irradiated by a neutron field, the energy imparted to charged particles in the material may be described by thekerma. The kerma may be divided into two parts, ionization kerma and displacement kerma. See 3.1.2.1 for the distinction betweenkerma factor and microscopic kerma
35、factor. Calculations of ionization and microscopic displacement kerma in silicon and galliumarsenide as a result of irradiation by neutrons with energies up to 20 MeV are described in Refs 4-5-78 and in the annexes.3.1.7 neutron fluence and neutron fluence spectrum are used in this standard, and are
36、 special cases of particle fluence andparticle fluence spectrum as defined in E170.3.1.7.1 DiscussionIn cases where the context makes clear that neutrons are referred to, the terms fluence and fluence spectrum are sometimes used.4. Summary of Practice4.1 The equivalent monoenergetic neutron fluence,
37、eq,Eref,mat, is given as follows:eq,Eref,mat5*0 E!FD,matE!dEFD,Eref,mat (1)eq,Eref,mat 5*0 E!FD,matE!dEFD,Eref,mat (1)where:(E) = incident neutron fluence spectrum,FD,mat(E) = neutron displacement damage function for the irradiated material (displacement damage per unit fluence) as afunction of ener
38、gy, andFD,Eref,mat = displacement damage reference value designated for the irradiated material and for the specified equivalent energy,Eref, as given in the annexes.The energy limits on the integral are determined in practice by the incident neutron fluence spectrum and by the material beingirradia
39、ted.4.2 The neutron spectrum hardness parameter, HmatEref,mat, is given as follows:Hmat5*0E!FD,matE!dEFD,Eref,mat*0 E!dE(2)HEref,mat 5*0E!FD,matE!dEFD,Eref,mat *0 E!dE(2)4.3 Once the neutron fluence spectrum has been determined (for example, in accordance with Test Method E721) and theequivalent mon
40、oenergetic fluence calculated, then a monitor (such as an activation foil) can be used in subsequent irradiations atthe same location to determine the fluence; that is, the neutron fluence is then described in terms of the equivalent monoenergeticneutron fluence per unit monitor response, eq,Eref,ma
41、t /Mr. Use of a monitor foil to predict eq,Eref,mat is valid only if the neutronspectrum remains constant.5. Significance and Use5.1 This practice is important in characterizing the radiation hardness of electronic devices irradiated by neutrons. Thischaracterization makes it feasible to predict som
42、e changes in operational properties of irradiated semiconductor devices orelectronic systems. To facilitate uniformity of the interpretation and evaluation of results of irradiations by sources of differentE722 143fluence spectra, it is convenient to reduce the incident neutron fluence from a source
43、 to a single parameteran equivalentmonoenergetic neutron fluenceapplicable to a particular semiconductor material.5.2 In order to determine an equivalent monoenergetic neutron fluence, it is necessary to evaluate the displacement damage ofthe particular semiconductor material. Ideally, this quantity
44、 is correlated to the degradation of a specific functional performanceparameter (such as current gain) of the semiconductor device or system being tested. However, this correlation has not beenestablished unequivocally for all device types and performance parameters since, in many instances, other e
45、ffects also can beimportant. Ionization effects produced by the incident neutron fluence or by gamma rays in a mixed neutron fluence, short-termand long-term annealing, and other factors can contribute to observed performance degradation (damage). Thus, caution shouldbe exercised in making a correla
46、tion between calculated displacement damage and performance degradation of a given electronicdevice. The types of devices for which this correlation is applicable, and numerical evaluation of displacement damage arediscussed in the annexes.5.3 The concept of 1-MeV equivalent fluence is widely used i
47、n the radiation-hardness testing community. It has merits anddisadvantages that have been debated widely (8-9-1112). For these reasons, specifics of a standard application of the 1-MeVequivalent fluence are presented in the annexes.6. Procedure for Calculating eq,Eref,mat6.1 To evaluate Eq 1 and 2,
48、determine the energy limits Emin and Emax to be used in place of zero and infinity in the integralsof (Eq 1) and (Eq 2) and the values of the displacement damage function FD,mat(E) for the irradiated material and perform theindicated integrations.6.1.1 Choose the upper limit Emax to be at an energy
49、above which the integral damage falls to an insignificant level. For Godiva-or TRIGA-type spectra, this limit is about 12 MeV.6.1.2 Choose the lower-energy limit Emin to be at an energy below which the integral damage falls to an insignificant level. Forsilicon irradiated by Godiva-type spectra, this energy has been historically chosen to be about 0.01 MeV. More highly moderatedspectra may require lower thresholds or specialized filtering requirements such as a boron shield, or both.6.1.3 The va
