1. Scope
1. Scope 1.1 This practice describes a standard procedure for characterizing charged-particle irradiations of materials in terms of non-ionizing energy loss. 1.2 Although the methods described in this practice apply to any charged particles and target materials for which displacement cross sections are known (see Practice E521), this practice is intended for use in irradiations in which observed damage effects may be correlated with atomic displacements. This is true of some, but not all, radiation effects in electronic and photonic materials. 1.3 Procedures related to this one are used for calculation of 1-MeV equivalent neutron fluence in electronic materials (see Practice E722) and for calculation of dpa in charged particle irradiations (see E521) or neutron irradiations (see E693). 1.4 The application of this standard requires knowledge of the total particle fluence and energy distribution. 1.5 The correlation of radiation effects data is beyond the scope of this standard. 4. Significance and Use 4.1 A radiation-hardness assurance program requires a methodology for relating radiation induced changes in materials exposed to a variety of particle species over a wide range of energies, including those encountered in spacecraft and in terrestrial environments, such as those produced by particle accelerators and nuclear fission and fusion reactors. 4.2 A major source of radiation damage in electronic and photonic devices and materials is the displacement of atoms from their normal lattice site. An appropriate exposure parameter for such damage is NIEL. Other analogous measures, each used to characterize the irradiation history that is relevant to displacement damage, are displacement energy per atom or per unit mass (displacement kerma), and displacements per atom (dpa). 4.3 Each of the quantities mentioned in the previous paragraph should convey the same information, but in a different format. In each case the value of the derived exposure parameter depends on approximate nuclear, atomic, and lattice models, and on measured cross sections. If consistent comparisons are to be made between irradiation effects of different particle species and energies, it is essential that these approximations be consistently applied. 4.4 No correspondence should be assumed to exist between NIEL and a particular change in a material property or device parameter. Instead NIEL should be viewed as a parameter describing the exposure that may be a useful correlation variate, even when different particle species and energies are included. NIEL should not be reported as a measure of damage, however, unless its correlation with a particular damage modality has been demonstrated in that material or device. 4.5 1-MeV equivalent neutron fluence, as defined in Practice E722, is intended as a measure of observable displacement damage, restricted to materials and damage modalities for which its correlation with damage has been demonstrated. Therefore neutron induced NIEL and 1-MeV equivalent neutron fluence are not necessarily equivalent to each other.
The standard is needed because of the already prevalent use of NIEL by researchers, industry, and government agencies in assessment of radiation damage effects. Some of these assessments may be providing misleading results because of the lack of standardization of the methods.
Keywords
NIEL; radiation damage; radiation hardness; displacement kerma
The title and scope are in draft form and are under development within this ASTM Committee.
Citing ASTM Standards
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