1.Scope 1.1This practice describes a standard procedure for characterizing charged-particle irradiations of materials in terms of non-ionizing energy loss. 1.2Although 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. 1.3Procedures analogous to this one are used for calculation of dpa in charged particle irradiations (see E521) or neutron irradiations (see E693). 1.4Procedures related to this one are used for calculation of 1-MeV equivalent neutron fluence in electronic materials (see Practice E722), but in that Standard Practice the concept of damage efficiency, based on correlation of observed damage effects, is included. 1.5The application of this standard requires knowledge of the total particle fluence and energy distribution. 1.6The correlation of radiation effects data is beyond the scope of this standard.
4.Significance and Use 4.1A 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. 4.2A 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). 4.3Each 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. 4.4No 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 4.5Since NIEL is a construct that depends on a model of the particle interaction processes in a material, as well as the cross section for each type of interaction, the calculated value of NIEL depends on the details of the model used and on the cross section data file. It is essential, when using NIEL as a correlation parameter, to ensure that consistent modeling parameters and nuclear data are used to calculate the NIEL value for each irradiation.
KeywordsDisplacement; kerma; kerma factor; hardness factor; damage equivalence
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top