One of the consequences of the interaction of high energy particles (neutrons, ions or electrons) with crystalline materials is the formation of lattice defects resulting from the energy transfer towards the atoms. A very useful and widely used standard has been proposed by Norget, Torrens and Robinson in 1975 to evaluate the number of Frenkel pairs formed for a given energy transferred to the primary knocked on atom, and therefore the number of "displacements per atom", or so-called NRT-dpa (or just dpa in short). This evaluation of the primary damage suffers a number of limitations. First, it does not account for the recombination of atoms occurring during the cascade process. Molecular Dynamics simulations have shown for more than a decade that the number of defects remaining after the cascade is only about a third of the NRT rule. Second, this simple standard does not account for the nature and spatial distribution of the defects, which are also very important for the subsequent time evolution of the defect population. Third, the dpa value is inversely proportional to the displacement threshold energy; but this quantity is itself not very robust. The consequences of these limitations are that it becomes very difficult to compare the primary damage resulting from different irradiation conditions (nature of damaging particles and their energy spectra), or different materials.
The main objectives of this expert group are:
Last updated: 29 May 2013