# ASTM E3084-17

Designation: E3084 − 17Standard Practice forCharacterizing Particle Irradiations of Materials in Terms ofNon-Ionizing Energy Loss (NIEL)1This standard is issued under the fixed designation E3084; the number immediately following the designation indicates 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.1. Scope1.1 This practice describes a procedure for characterizingparticle irradiations of materials in terms of non-ionizingenergy loss (NIEL). NIEL is used in published literature tocharacterize both charged and neutral particle irradiations.1.2 Although the methods described in this practice apply toany particles and target materials for which displacement crosssections are known (see Practice E521), this practice isintended for use in irradiations in which observed damageeffects may be correlated with atomic displacements. This istrue of some, but not all, radiation effects in electronic andphotonic materials.1.3 Procedures analogous to this one are used for calcula-tion of displacements per atom (dpa) in charged particleirradiations (see Practice E521) or neutron irradiations (seePractice E693).1.4 Guidance on calculation of dpa from NIEL is provided.1.5 Procedures related to this one are used for calculation of1-MeV equivalent neutron fluence in electronic materials (seePractice E722), but in that practice the concept of damageefficiency, based on correlation of observed damage effects, isincluded.1.6 Guidance on conversion of NIEL in silicon to monoen-ergetic neutron fluence in silicon (see Practice E722), and viceversa, is provided.1.7 The application of this standard requires knowledge ofthe particle fluence and energy distribution of particles whoseinteraction leads to displacement damage.1.8 The correlation of radiation effects data is beyond thescope of this standard. A comprehensive review (1)2ofdisplacement damage effects in silicon and their correlationwith NIEL provides appropriate guidance that is applicable tosemiconductor materials and electronic devices.2. Referenced Documents2.1 ASTM Standards3E170 Terminology Relating to Radiation Measurements andDosimetryE521 Practice for Investigating the Effects of Neutron Ra-diation Damage Using Charged-Particle IrradiationE693 Practice for Characterizing Neutron Exposures in Ironand Low Alloy Steels in Terms of Displacements PerAtom (DPA), E 706(ID)E722 Practice for Characterizing Neutron Fluence Spectra inTerms of an Equivalent Monoenergetic Neutron Fluencefor Radiation-Hardness Testing of Electronics3. Terminology3.1 Definitions of some terms used in this practice can befound in Terminology E170.3.2 Definitions:3.2.1 tracked particles—those particles whose position-dependent fluence spectra are calculated in a particle transportcalculation for a specific target geometry.3.2.1.1 Discussion—In calculating displacement damageenergy and NIEL, the tracked particles should includeneutrons, photons, protons and ions up to Z=2, unless theircontributions are known to be negligible. Heavier ions mayalso be tracked in some Monte Carlo codes. Except in the caseof neutrons, particles below a specified minimum energy arenot tracked, and are treated as non-tracked particles.3.2.2 tracked-particle fluence spectrum, Φp(E)—the fluencespectrum of particles, of species p and at particle energy E, thatare tracked in a particle transport calculation. For each speciesof tracked particle other than neutrons there is a specifiedminimum energy. Particles at lower energy are non-trackedparticles.3.2.3 secondary particles—those particles produced in amaterial by interaction with the tracked particles. Secondaryparticles may include tracked particles and non-tracked par-ticles.1This test method 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 Feb. 1, 2017. Published March 2017. DOI: 10.1520/D3084-17.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.4 non-ionizing energy loss, NIELp(E)—the quotient ofdɛ¯dby Φp(E).dE.dm, where Φp(E)dE is the tracked-particlefluence in the energy interval E to E+dE of particle species pin a volume element containing material of mass dm, and dɛ¯dis that part of the mean energy imparted to matter by thetracked particle radiation which produces atomic displace-ments and lattice phonons (that is, excluding the part thatproduces ionization and excitations of electrons).NIELp~E! 5 dε¯d⁄ Φp~E!dEdm (1)Unit: MeV·m2·kg-1. (also used are keV·cm2·g-1, andMeV·cm2·g-1)3.2.4.1 Discussion—For silicon, using the atomic mass28.086 g/mol, a displacement kerma cross section 100MeV·mbarn is equivalent to 2.144 MeV·cm2/g (2). Micro-scopic displacement kerma cross sections (See Practice E722)having units with dimensions equal to the product of energyand area (for example, MeV·mbarn) are sometimes used, toapply to single target atoms, and may be thought of as themicroscopic version of NIEL. For 1-MeV neutrons the refer-ence value of the displacement damage function in silicon isdefined in Practice E722 as equal to 95 MeV·mbarn, equivalentto a NIEL value of 2.037 MeV·cm2/g (0.2037 Mev·m2·kg-1).3.2.4.2 Discussion—In Eq 1, NIELp(E) is to be interpretedas a function dependent on the particle energy, on the speciesof particle, and on the material in which the particle fluence ispresent. Its use requires knowledge of NIEL for all energiesand tracked-particle species that contribute significantly to thetotal displacement damage energy in a given material.3.2.4.3 Discussion—In the definition, Eq 1, the volumeelement in which the tracked-particle fluence Φpis presentdoes not necessarily contain all of the atomic displacementsproduced by the energy transferred, dɛ¯d. The quantity iscalculated as if the extended volume, dependent on the particleenergy, in which displacements occur is homogeneous and ofthe same composition as the volume element in which thetracked-particle fluence is present. This assumption is justifiedin cases in which secondary particle equilibrium applies for thenon-tracked particles: the number and energy distribution ofsecondary particles entering a volume element is the same asfor those leaving that element. See the analogous description of“charged particle equilibrium” in the definition of kerma,E170.3.2.4.4 Discussion—Damage energy per unit mass, dɛ¯d/dmis calculated from NIEL by integrating the product of the NIELwith the tracked-particle fluence spectrum over all energies,and summing over all species of tracked particle:dε¯d⁄ dm 5 Σp*0`NIELp~E!Φp~E!dE (2)3.2.4.5 Discussion—The 1 MeV equivalent neutron fluence(cm-2) in silicon may be calculated by dividing the damageenergy per unit mass (MeV/g) in Eq 2 by 2.037 MeV cm2/g(see 3.2.4.1).3.2.4.6 Discussion—The dpa may be calculated from thedamage energy per unit mass by multiplying by the averageatomic mass of the target and by β/2Td, where β is an atomicscattering correction factor equal to 0.8 and Tdis the displace-ment threshold. This approximation to the Norgett, Robinsonand Torrens (3) model is consistent with the method recom-mended in Practice E521 (14.5.2.1).3.2.4.7 Discussion—In cases where secondary particle equi-librium does not apply, due to inhomogeneities in the targetmaterial, the damage energy that can be calculated from NIELvalues is not necessarily equivalent to the local value of theabsorbed dose that leads to displacements. The scale of therelevant inhomogeneities depends on the energies and actualranges of the non-tracked secondary particles. Detailed MonteCarlo modeling in which tracked particles include all thosesecondary particles whose range is comparable with or greaterthan the scale of the material inhomogeneity in the targetgeometry is necessary. Suitable codes include MCNP6, Geant,and SRIM (4-9).4. Significance and Use4.1 A radiation-hardness assurance program requires amethodology for relating radiation induced changes in materi-als exposed to a variety of particle species over a wide range ofenergies, including those encountered in spacecraft and interrestrial environments as well as those produced by particleaccelerators and nuclear fission and fusion reactors.4.2 A major source of radiation damage in electronic andphotonic devices and materials is the displacement of atomsfrom their normal lattice site. An appropriate exposure param-eter for such damage is the damage energy calculated fromNIELby means of Eq 2. Other analogous measures, which maybe used to characterize the irradiation history that is relevant todisplacement damage, are damage energy per atom or per unitmass (displacement kerma, when the primary particles areneutral), and displacements per atom (dpa). See TerminologyE170 for definitions of those quantities.4.3 Each of the quantities mentioned in the previous para-graph should convey similar information, but in a differentformat. In each case the value of the derived exposureparameter depends on approximate nuclear, atomic, and latticemodels, an on measured or calculated cross sections. Ifconsistent comparisons are to be made of irradiation effectscaused by different particle species and energies, it is essentialthat these approximations be consistently applied.4.4 No correspondence should be assumed to exist betweendamage energy as calculated from NIEL and a particularchange in a material property or device parameter. Instead, thedamage energy should be used as a parameter which describesthe exposure. It may be a useful correlation variate, even whendifferent particle species and energies are included. NIELshould not be reported as a measure of damage, however,unless its correlation with a particular damage modality hasbeen demonstrated in that material or device.4.5 NIEL is a construct that depends on a model of theparticle interaction processes in a material, as well as the crosssection for each type of interaction. It is essential, when usingNIEL as a correlation parameter, to ensure that consistentmodeling parameters and nuclear data are used to calculate theNIEL value for each irradiation.4.6 Damage energy deposited in materials can be calculateddirectly, without the use of NIEL, using the Monte Carlo codesE3084 − 172mentioned in 3.2.4.7, if all the particles involved in atomicdisplacement are tracked. The utility of the NIEL conceptarises in cases where some particles, especially recoiling heavyions, do not need to be tracked. In the NIEL representation,these are treated instead by means of infinite homogeneousmedium solutions of the type originated by Lindhard et al. (10).5. Calucation of NIEL5.1 The method of calculating NIEL used in this practice isbased on that originally proposed for proton irradiation ofsilicon by Burke (11). Similar NIEL calculations and compari-sons to experiment have since been done for other particles andother targets (12-17).5.2 The basic formula for the calculation of NIEL is:NIELp~E! 5 ΣiNiΣk*0`Tkdσpik~E , Tk!dTkL~Tk!dTk(3)where:Ni=wi,Nav/Ai= the number of target atoms of isotope i perunit mass,wi= the weight fraction of isotope i in thetarget,NAv= is Avogadro’s number/mole,Ai= the molar mass for isotope i,Tk= the energy of a non-tracked secondaryparticle, k,dσpik(E,Tk)/dTk= the differential cross section for collisionsof tracked particle, p, in isotope i throughall reaction channels resulting in produc-tion of non-tracked secondary particle, k,of energy Tk.L(Tk) = the Lindhard partition function (10) de-scribing the fraction of the energy ofsecondary particle, k, that results inatomic displacements and phonons. Theform of the function L(Tk) depends on thespecies of particle, p, and on the targetmaterial.NOTE 1—Published NIEL calculations have often used Tdas the lowerlimit of the integral in Eq 3, where Tdis the displacement threshold energy(defined in Terminology E170). It is not used here because damage energybelow the displacement threshold contributes to phonons and is non-ionizing. This also maintains consistency with other ASTM standards(E521 and E722). The inclusion of Tdin the calculation has negligibleeffect in cases of practical interest for irradiation effects in electronicdevices.5.3 Most authors who have used formulae analogous to Eq3 have followed the precedent of Burke (11), but excludinglight ions with masses up to and including He-4 from thesecondary particles that contribute to NIEL. This is equivalentto treating such particles as tracked particles whose contribu-tions to displacement were ignored.5.4 Radiation induced damage to the lattice of solid mate-rials arises from elastic collisions and nuclear reactions result-ing in high energy recoils. These cause ionization and excita-tion of the atoms in the irradiated material as well as elastic andinelastic scattering which produce displacement of the atomsfrom their sites in the lattice. Ionization is a transient effect inmany semiconductors and does not contribute to permanentdamage in, for example, bulk silicon (2). Elastic collisions andinlastic reactions can generate permanent stable lattice defectsvia what are called displacement cascades. Cascade dynamicsare best described by molecular dynamics simulations (18)although energy partitioning can also be obtained from MonteCarlo simulations (4-9) and other transport calculations.5.5 The partition of the secondary particle energy Tkbe-tween electronic excitation and atomic displacements is re-flected in the partition function L(Tk), sometimes called thedamage efficiency. Various approximations to the partitionfunction have been used, based on the Lindhard screenedpotential scattering theory (LSS) (10), using the Thomas-Fermimodel. An approximation based on the LSS model is given bythe Robinson fit (19), used also in the NRT model (3) forcalculating dpa:L~Tk! 5111FL~3.4008 ε1⁄61 0.40244 ε3⁄41 ε!(4)where ε5TkEL, withEL5 30.724 ZkZL~Zk2⁄31 ZL2⁄3!1⁄2~Ak1 AL!⁄AL,and (5)FL0.0793Zk2⁄3ZL1⁄2~Ak1 AL!3⁄2~Zk2⁄31 ZL2⁄3!3⁄4Ak3⁄2AL1⁄2(6)A and Z are mass numbers and atomic numbers and the sub-scripts L and k stand for lattice atom and recoil parti