1、Designation: E721 11E721 16Standard 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 t
2、he 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 U.S. Department of Defense.1. Scope1.1
3、 This guide covers procedures for determining the energy-differential fluence spectra of neutrons used in radiation-hardnesstesting of electronic semiconductor devices. The types of neutron sources specifically covered by this guide are fission or degradedenergy fission sources used in either a stea
4、dy-state or pulse mode.1.2 This guide provides guidance and criteria that can be applied during the process of choosing the spectrum adjustmentmethodology that is best suited to the available data and relevant for the environment being investigated.1.3 This guide is to be used in conjunction with Gu
5、ide E720 to characterize neutron spectra and is used in conjunction withPractice E722 to characterize damage-related parameters normally associated with radiation-hardness testing of electronic-semiconductor devices.NOTE 1Although Guide E720 only discusses activation foil sensors, any energy-depende
6、nt neutron-responding sensor for which a response functionis 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 as standard. No other units of measurement are included in this standard.1.5 This standard does not
7、purport to address all of the safety concerns, if any, associated 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:3E
8、170 Terminology Relating to Radiation Measurements and DosimetryE261 Practice for Determining Neutron Fluence, Fluence Rate, and Spectra by Radioactivation TechniquesE262 Test Method for Determining Thermal Neutron Reaction Rates and Thermal Neutron Fluence Rates by RadioactivationTechniquesE263 Tes
9、t Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of IronE264 Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of NickelE265 Test Method for Measuring Reaction Rates and Fast-Neutron Fluences by Radioactivation of Sulfur-32E266 Test Method for Measuring Fa
10、st-Neutron Reaction Rates by Radioactivation of AluminumE393 Test Method for Measuring Reaction Rates by Analysis of Barium-140 From Fission DosimetersE523 Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of CopperE526 Test Method for Measuring Fast-Neutron Reaction Rates by
11、Radioactivation of TitaniumE704 Test Method for Measuring Reaction Rates by Radioactivation of Uranium-238E705 Test Method for Measuring Reaction Rates by Radioactivation of Neptunium-2371 This guide is under the jurisdiction of ASTM Committee E10 on Nuclear Technology and Applicationsand is the dir
12、ect responsibility of Subcommittee E10.07 onRadiation Dosimetry for Radiation Effects on Materials and Devices.Current edition approved Nov. 1, 2011Dec. 1, 2016. Published November 2011December 2016. Originally approved in 1980. Last previous edition approved in 20072011as E721 07.E721 11. DOI: 10.1
13、520/E0721-11.10.1520/E0721-16.2 The boldface numbers in parentheses refer to the list of references at the end of this guide.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, r
14、efer 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 may not be technically possible to adequately depict all
15、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 Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959
16、. United States1E720 Guide for Selection and Use of Neutron Sensors for Determining Neutron Spectra Employed in Radiation-HardnessTesting of ElectronicsE722 Practice for Characterizing Neutron Fluence Spectra in Terms of an Equivalent Monoenergetic Neutron Fluence forRadiation-Hardness Testing of El
17、ectronicsE844 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)E1018 Guide for Application of ASTM Evaluated Cross Section Data File, Matrix E706 (IIB)E1297 Test Meth
18、od for Measuring Fast-Neutron Reaction Rates by Radioactivation of NiobiumE1855 Test Method for Use of 2N2222A Silicon Bipolar Transistors as Neutron Spectrum Sensors and Displacement DamageMonitors3. Terminology3.1 Definitions: The following list defines some of the special terms used in this guide
19、:3.1.1 effectthe characteristic which changes in the sensor when it is subjected to the neutron irradiation. The effect may bethe reactions in an activation foil.3.1.2 responsethe magnitude of the effect. It can be the measured value or that calculated by integrating the response functionover the ne
20、utron fluence spectrum. The response is an integral parameter. Mathematically, the response, R5(iRi, where Ri is theresponse in each differential energy region at Ei of width Ei.3.1.3 response functionthe set of values of Ri in each differential energy region divided by the neutron fluence in thatdi
21、fferential energy region, that is, the set fi = Ri/(Ei)Ei).3.1.4 sensoran object or material (sensitive to neutrons) the response of which is used to help define the neutron environment.A sensor may be an activation foil.3.1.5 spectrum adjustmentthe process of changing the shape and magnitude of the
22、 neutron energy spectrum so that quantitiesintegrated over the spectrum agree more closely with their measured values. Other physical constraints on the spectrum may beapplied.3.1.6 trial functiona neutron spectrum which, when integrated over sensor response functions, yields calculated responses th
23、atcan be compared to the corresponding measured responses.3.1.7 prior spectruman estimate of the neutron spectrum obtained by transport calculation or otherwise and used as input toa least-squares adjustment.3.2 Abbreviations:3.2.1 DUTdevice under test.3.2.2 ENDFevaluated nuclear data file.3.2.3 NND
24、CNational Nuclear Data Center (at Brookhaven National Laboratory).3.2.4 RSICCRadiation Safety Information Computation Center (at Oak Ridge National Laboratory).3.2.5 TREEtransient radiation effects on electronics.4. Significance and Use4.1 It is important to know the energy spectrum of the particula
25、r neutron source employed in radiation-hardness testing ofelectronic devices in order to relate radiation effects with device performance degradation.4.2 This guide describes the factors which must be considered when the spectrum adjustment methodology is chosen andimplemented. Although the selectio
26、n of sensors (foils) and the determination of responses (activities) is discussed in Guide E720,the experiment should not be divorced from the analysis. In fact, it is advantageous for the analyst conducting the spectrumdetermination to be closely involved with the design of the experiment to ensure
27、 that the data obtained will provide the mostaccurate spectrum possible. These data include the following : (1) measured responses such as the activities of foils exposed inthe environment and their uncertainties, (2) response functions such as reaction cross sections along with appropriate correlat
28、ionsand uncertainties, (3) the geometry and materials in the test environment, and (4) a trial function or prior spectrum and itsuncertainties obtained from a transport calculation or from previous experience.5. Spectrum Determination With Neutron Sensors5.1 Experiment Design:5.1.1 The primary objec
29、tive of the spectrum characterization experiment should be the acquisition of a set of response values(activities) from effects (reactions) with well-characterized response functions (cross sections) with responses which adequatelydefine (as a set) the fluence values at energies to which the device
30、to be tested is sensitive. For silicon devices in fission-drivenenvironments the significant neutron energy range is usually from 10 keV to 15 MeV. Lists of suitable reactions along withapproximate sensitivity ranges are included in Guide E720. Sensor set design is also discussed in Guide E844. The
31、foil set mayE721 162include the use of responses with sensitivities outside the energy ranges needed for the DUT to aid in interpolation to other regionsof the spectrum. For example, knowledge of the spectrum below 10 keV helps in the determination of the spectrum above thatenergy.5.1.2 An example o
32、f the difficulty encountered in ensuring response coverage (over the energy range of interest) is thefollowing: If fission foils cannot be used in an experiment because of licensing problems, cost, or radiological handling difficulties(especially with 235U, 237Np or 239Pu), a large gap may be left i
33、n the foil set response between 100 keV and 2 MeVa regionimportant for silicon and gallium arsenide damage (see Figs. A1.1 and A2.3 of Practice E722). In this case two options areavailable. First, seek other sensors to fill the gap (such as silicon devices sensitive to displacement effects (see Test
34、 MethodE1855), 93Nb(n,n) 93mNb (see Test Method E1297) or 103Rh(n,n)103mRh. Second, devote the necessary resources to determinea trial function that is close to the real spectrum. In the latter case it may be necessary to carry out transport calculations to generatea prior spectrum which incorporate
35、s the use of uncertainty and covariance information.5.1.3 Other considerations that affect the process of planning an experiment are the following:5.1.3.1 Are the fluence levels low and of long duration so that only long half-life reactions are useful? This circumstance canseverely reduce the respon
36、se coverage of the foil set.5.1.3.2 Are high gamma-ray backgrounds present which can affect the sensors (or affect the devices to be tested)?5.1.3.3 Can the sensors be placed so as to ensure equal exposure? This may require mounting the sensors on a rotating fixturein steady-state irradiations or pe
37、rforming multiple irradiations with monitor foils to normalize the fluence between runs.5.1.3.4 DoesDo the DUT or the spectrum sensors perturb the neutron spectrum?5.1.3.5 Are response functions available that account for self-shielding for all sensors using (n,) or non-threshold (n,f)reactions, unl
38、ess the material is available in a dilute form of certified composition?5.1.3.6 Can the fluence and spectrum seen in the DUT test later be directly scaled to that determined in the spectrumcharacterization experiment (by monitors placed with the tested device)?5.1.3.7 Can the spectrum shape and inte
39、nsity be characterized by integral parameters that permit simple intercomparison ofdevice responses in different environments? Silicon is a semiconductor material whose displacement damage function is wellestablished. This makes spectrum parameterization for damage predictions feasible for silicon.5
40、.1.3.8 What region of the spectrum contributes to the response of the DUT? In other words, is the spectrum well determinedin all energy regions that affect device performance?5.1.3.9 How is the counting system set up for the determination of the activities? For example, are there enough countersavai
41、lable to handle up to 25 reactions from a single exposure? (This may require as many as six counters.) Or can the availablesystem only handle a few reactions before the activities have decayed below detectable limits?5.1.4 Once the experimental opportunities and constraints have been addressed and t
42、he experiment designed to gather the mostuseful data, a spectrum adjustment methodology must be chosen.5.2 Spectrum Adjustment Methodology:5.2.1 After the basic measured responses, response functions, and trial or prior spectrum information have been assembled,apply a suitable spectrum adjustment pr
43、ocedure to reach a “solution” that is as compatible as possible with that information.solution that satisfies the criteria of the chosen procedure. It must also meet other constraints such as, the fluence spectrum mustbe positive and defined for all energies. The solution is the energy-dependent spe
44、ctrum function, (E), which approximatelysatisfies the series of Fredholm equations of the first kind represented by Eq 1 as follows:Rj 5*0jE!E! dE 1#j#n (1)where:Rj = measured response of sensor j,j(E) = neutron response function at energy E for sensor j,(E) = incident neutron fluence versus energy,
45、 andn = number of sensors which yield n equations.One important characteristic of this set of equations is that with a finite number of sensors, n, which yield n equations, there isno unique solution. With certain restrictions, however, the range of physically reasonable solutions can be limited to
46、an acceptabledegree.NOTE 3Guides E720 and E844 provide general guidance on obtaining a suitable set of responses (activities) when foil monitors are used. PracticeE261 and Test Method E262 provide more information on the data analysis that generally is part of an experiment with activation monitors.
47、 Specificinstructions for some individual monitors can be found in 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 (niobium).5.2.2 One important characteri
48、stic of the set of equations (Eq 1) is that with a finite number of sensors, n, which yield nequations, there is no unique solution. Exact solutions to equations (Eq 1) may be readily found, but are not generally considereduseful. When the least squares adjustment method is used, equations (Eq 1) ar
49、e supplemented by the constraint that the solutionspectrum must be approximately equal to the prior spectrum. This additional constraint guarantees that the set of equation isoverdetermined and that a unique least squares solution does exist. The tolerances of the approximations are dependent on theE721 163specified variances and covariances of the prior spectrum, the response functions, and the measured responses. When otheradjustment methods are used it must be assumed that the range of physically reasonable solutions can be limited to an acce
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