1、Designation: E721 11Standard Guide forDetermining Neutron Energy Spectra from Neutron Sensorsfor Radiation-Hardness Testing of Electronics1This standard is issued under the fixed designation E721; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 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 Department of Defense.1. Scope1.1 This guide
3、covers procedures for determining theenergy-differential fluence spectra of neutrons used inradiation-hardness testing of electronic semiconductor devices.The types of neutron sources specifically covered by this guideare fission or degraded energy fission sources used in either asteady-state or pul
4、se mode.1.2 This guide provides guidance and criteria that can beapplied during the process of choosing the spectrum adjust-ment methodology that is best suited to the available data andrelevant for the environment being investigated.1.3 This guide is to be used in conjunction with Guide E720to char
5、acterize neutron spectra and is used in conjunction withPractice E722 to characterize damage-related parameters nor-mally associated with radiation-hardness testing of electronic-semiconductor devices.NOTE 1Although Guide E720 only discusses activation foil sensors,any energy-dependent neutron-respo
6、nding sensor for which a responsefunction is known may be used (1).2NOTE 2For terminology used in this guide, see Terminology E170.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address
7、 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 applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E170 Terminology
8、Relating to Radiation Measurements andDosimetryE261 Practice for Determining Neutron Fluence, FluenceRate, and Spectra by Radioactivation TechniquesE262 Test Method for Determining Thermal Neutron Reac-tion Rates and Thermal Neutron Fluence Rates by Radio-activation TechniquesE263 Test Method for Me
9、asuring Fast-Neutron ReactionRates by Radioactivation of IronE264 Test Method for Measuring Fast-Neutron ReactionRates by Radioactivation of NickelE265 Test Method for Measuring Reaction Rates and Fast-Neutron Fluences by Radioactivation of Sulfur-32E266 Test Method for Measuring Fast-Neutron Reacti
10、onRates by Radioactivation of AluminumE393 Test Method for Measuring Reaction Rates by Analy-sis of Barium-140 From Fission DosimetersE523 Test Method for Measuring Fast-Neutron ReactionRates by Radioactivation of CopperE526 Test Method for Measuring Fast-Neutron ReactionRates by Radioactivation of
11、TitaniumE704 Test Method for Measuring Reaction Rates by Radio-activation of Uranium-238E705 Test Method for Measuring Reaction Rates by Radio-activation of Neptunium-237E720 Guide for Selection and Use of Neutron Sensors forDetermining Neutron Spectra Employed in Radiation-Hardness Testing of Elect
12、ronicsE722 Practice for Characterizing Neutron Fluence Spectrain Terms of an Equivalent Monoenergetic Neutron Fluence1This guide is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.07 on Radiation Dosimetry for Rad
13、iation Effects on Materials and Devices.Current edition approved Nov. 1, 2011. Published November 2011. Originallyapproved in 1980. Last previous edition approved in 2007 as E721 07. DOI:10.1520/E0721-11.2The boldface numbers in parentheses refer to the list of references at the end ofthis guide.3Fo
14、r 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 International, 100 Barr Harbor Drive, PO Box C70
15、0, West Conshohocken, PA 19428-2959, United States.for Radiation-Hardness Testing of ElectronicsE844 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)E1018 Guide for
16、Application of ASTM Evaluated CrossSection Data File, Matrix E706 (IIB)E1297 Test Method for Measuring Fast-Neutron ReactionRates by Radioactivation of NiobiumE1855 Test Method for Use of 2N2222A Silicon BipolarTransistors as Neutron Spectrum Sensors and Displace-ment Damage Monitors3. Terminology3.
17、1 Definitions: The following list defines some of thespecial terms used in this guide:3.1.1 effectthe characteristic which changes in the sensorwhen it is subjected to the neutron irradiation. The effect maybe the reactions in an activation foil.3.1.2 responsethe magnitude of the effect. It can be t
18、hemeasured value or that calculated by integrating the responsefunction over the neutron fluence spectrum. The response is anintegral parameter. Mathematically, the response, R =(iRi,where Riis the response in each differential energy region at Eiof width DEi.3.1.3 response functionthe set of values
19、 of Riin eachdifferential energy region divided by the neutron fluence in thatdifferential energy region, that is, the set fi= Ri/(F(Ei)DEi).3.1.4 sensoran object or material (sensitive to neutrons)the response of which is used to help define the neutronenvironment. A sensor may be an activation foi
20、l.3.1.5 spectrum adjustmentthe process of changing theshape and magnitude of the neutron energy spectrum so thatquantities integrated over the spectrum agree more closely withtheir measured values. Other physical constraints on thespectrum may be applied.3.1.6 trial functiona neutron spectrum which,
21、 when inte-grated over sensor response functions, yields calculated re-sponses that can be compared to the corresponding measuredresponses.3.1.7 prior spectruman estimate of the neutron spectrumobtained by transport calculation or otherwise and used asinput to a least-squares adjustment.3.2 Abbrevia
22、tions:3.2.1 DUTdevice under test.3.2.2 ENDFevaluated nuclear data file.3.2.3 NNDCNational Nuclear Data Center (atBrookhaven National Laboratory).3.2.4 RSICCRadiation Safety Information ComputationCenter (at Oak Ridge National Laboratory).3.2.5 TREEtransient radiation effects on electronics.4. Signif
23、icance and Use4.1 It is important to know the energy spectrum of theparticular neutron source employed in radiation-hardness test-ing of electronic devices in order to relate radiation effects withdevice performance degradation.4.2 This guide describes the factors which must be consid-ered when the
24、spectrum adjustment methodology is chosen andimplemented. Although the selection of sensors (foils) and thedetermination of responses (activities) is discussed in GuideE720, the experiment should not be divorced from the analysis.In fact, it is advantageous for the analyst conducting thespectrum det
25、ermination to be closely involved with the designof the experiment to ensure that the data obtained will providethe most accurate spectrum possible. These data include thefollowing : (1) measured responses such as the activities offoils exposed in the environment and their uncertainties, (2)response
26、 functions such as reaction cross sections along withappropriate correlations and uncertainties, (3) the geometryand materials in the test environment, and (4) a trial function orprior spectrum and its uncertainties obtained from a transportcalculation or from previous experience.5. Spectrum Determi
27、nation With Neutron Sensors5.1 Experiment Design:5.1.1 The primary objective of the spectrum characteriza-tion experiment should be the acquisition of a set of responsevalues (activities) from effects (reactions) with well-characterized response functions (cross sections) with re-sponses which adequ
28、ately define (as a set) the fluence values atenergies to which the device to be tested is sensitive. Forsilicon devices in fission-driven environments the significantneutron energy range is usually from 10 keV to 15 MeV. Listsof suitable reactions along with approximate sensitivity rangesare include
29、d in Guide E720. Sensor set design is also discussedin Guide E844. The foil set may include the use of responseswith sensitivities outside the energy ranges needed for the DUTto aid in interpolation to other regions of the spectrum. Forexample, knowledge of the spectrum below 10 keV helps in thedete
30、rmination of the spectrum above that energy.5.1.2 An example of the difficulty encountered in ensuringresponse coverage (over the energy range of interest) is thefollowing: If fission foils cannot be used in an experimentbecause of licensing problems, cost, or radiological handlingdifficulties (espe
31、cially with235U,237Np or239Pu), a large gapmay be left in the foil set response between 100 keV and 2MeVa region important for silicon and gallium arsenidedamage (see Figs.A1.1 andA2.3 of Practice E722). In this casetwo options are available. First, seek other sensors to fill thegap (such as silicon
32、 devices sensitive to displacement effects(see Test Method E1855),93Nb(n,n8)93mNb (see Test MethodE1297)or103Rh(n,n8)103mRh. Second, devote the necessaryresources to determine a trial function that is close to the realspectrum. In the latter case it may be necessary to carry outtransport calculation
33、s to generate a prior spectrum whichincorporates the use of uncertainty and covariance information.5.1.3 Other considerations that affect the process of plan-ning an experiment are the following:5.1.3.1 Are the fluence levels low and of long duration sothat only long half-life reactions are useful?
34、This circumstancecan severely reduce the response coverage of the foil set.5.1.3.2 Are high gamma-ray backgrounds present which canaffect the sensors (or affect the devices to be tested)?E721 1125.1.3.3 Can the sensors be placed so as to ensure equalexposure? This may require mounting the sensors on
35、 a rotatingfixture in steady-state irradiations or performing multipleirradiations with monitor foils to normalize the fluence be-tween runs.5.1.3.4 Does the DUT perturb the neutron spectrum?5.1.3.5 Can the fluence and spectrum seen in the DUT testlater be directly scaled to that determined in the s
36、pectrumcharacterization experiment (by monitors placed with thetested device)?5.1.3.6 Can the spectrum shape and intensity be character-ized by integral parameters that permit simple intercomparisonof device responses in different environments? Silicon is asemiconductor material whose displacement d
37、amage functionis well established. This makes spectrum parameterization fordamage predictions feasible for silicon.5.1.3.7 What region of the spectrum contributes to theresponse of the DUT? In other words, is the spectrum welldetermined in all energy regions that affect device perfor-mance?5.1.3.8 H
38、ow is the counting system set up for the determi-nation of the activities? For example, are there enough countersavailable to handle up to 25 reactions from a single exposure?(This may require as many as six counters.) Or can theavailable system only handle a few reactions before theactivities have
39、decayed below detectable limits?5.1.4 Once the experimental opportunities and constraintshave been addressed and the experiment designed to gather themost useful data, a spectrum adjustment methodology must bechosen.5.2 Spectrum Adjustment Methodology:5.2.1 After the basic measured responses, respon
40、se func-tions, and trial spectrum information have been assembled,apply a suitable spectrum adjustment procedure to reach a“solution” that is as compatible as possible with that informa-tion. It must also meet other constraints such as, the fluencespectrum must be positive and defined for all energi
41、es. Thesolution is the energy-dependent spectrum function, F(E),which approximately satisfies the series of Fredholm equationsof the first kind represented by Eq 1 as follows:Rj5*0sjE!FE! dE 1#j#n (1)where:Rj= measured response of sensor j,sj(E) = neutron response function at energy E for sensorj,F(
42、E) = incident neutron fluence versus energy, andn = number of sensors which yield n equations.One important characteristic of this set of equations is thatwith a finite number of sensors, n, which yield n equations,there is no unique solution. With certain restrictions, however,the range of physical
43、ly reasonable solutions can be limited toan acceptable degree.NOTE 3Guides E720 and E844 provide general guidance on obtaininga suitable set of responses (activities) when foil monitors are used.Practice E261 and Test Method E262 provide more information on thedata analysis that generally is part of
44、 an experiment with activationmonitors. Specific instructions for some individual monitors can be foundin Test Methods E263 (iron), E264 (nickel), E265 (sulfur-32), E266(aluminum), E393 (barium-140 from fission foils), E523 (copper), E526(titanium), E704 (uranium-238), E705 (neptunium-237), E1297 (n
45、io-bium).5.2.2 Neutron spectra generated from sensor response datamay be obtained with either of two types of spectrum adjust-ment codes. One type is the iterative method, an example ofwhich is SAND II (2). The second is least squares minimiza-tion used by codes such as LSL-M2 (3). If used properly
46、andwith sufficient, high-quality data, the two methods will usuallyyield nearly the same values (610 to 15 %) for the primaryintegral parameters discussed in E722.NOTE 4Another class of codes often referred to as Maximum Entropymay also prove useful for this type of analysis. These have historically
47、 notbeen used to estimate spectra for radiation-damage purposes.5.2.3 Appendix X1 and Appendix X2 discuss in some detailthe implementation and the advantages and disadvantages ofthe two approaches as represented by SAND II and LSL-M2.5.3 Iterative Code Characteristics:5.3.1 The “iterative” codes use
48、 a trial function supplied bythe analyst and integrate it over the response functions of thesensors exposed in the unknown environment to predict a set ofcalculated responses for comparison with the measured values.The calculated responses are obtained from Eq 1. The codeobtains the response functio
49、ns from a library. See Guide E1018for the recommendations in the selection of dosimetry-qualitycross sections.5.3.2 The code compares the measured and calculatedresponses for each effect and invokes an algorithm designed toalter the trial function so as to reduce the deviations betweenthe measured and calculated responses. The process is repeatedwith code-altered spectra until the standard deviation dropsbelow a specified valueat which time the code declares thata solution has been obtained and prepares a table of the lastspectrum. This should not be the end of
