I am writing to ask your help in setting the damage energy threshold for alloys. I am evaluating the DPA induced in multiple metals, including Cr, Ni, Ti, Al, V and the alloys CrMnV (atom percentage: 33% for each metal), CrMnVTi (31% atom percentage for the first three mental and 7% atom percentage for Ti). I can find the threshold energy for each single metal in FLUKA material database, and your slides (RADIATE4_FLUKA (kek.jp)) mentioned that it is not applicable to estimate the threshold by the mass percentage. I am wondering, do you have any possible experience to estimate the threshold for the alloys?
As you indeed correctly read in the mentioned slides, FLUKA uses an averaged, single displacement damage threshold energy over all crystallographic directions set by the user to his/her best knowledge. This is fully inherent to the fact that FLUKA is a Monte Carlo code where the materials are fully static, isotropic and homogeneous, i.e. no lattice or crystal structure is present and defect migration and
recombination of Frenkel pairs cannot be taken into account at runtime. FLUKA relies on separate data and models for this. By consequence this is automatically extended to compounds and there is not really an easy answer to your question.
I suggest to look at the literature which shed some light on the FLUKA implementation (such as the review article by Nordlund et al.). In addition to the FLUKA database you can also search the literature on experimental verifications of the displacement damage threshold obtained for the elements you consider. These data can also often show very different values.
Then my best suggestion would be to perform a kind of ‘sensitivity’ study where you assume a threshold that corresponds to the highest value you can find for either of the compound’s constituents vs. the lowest value. You assume these to be the average displacement damage threshold energy for the full compound in the FLUKA simulation and check how different the outcome of the simulation is and by consequence, what the extent of the uncertainty is on the result. For now, averageing by percentages of the compounds constituents would still be the best guess but is up to the user’s responsibility. Improvements in the code are being considered which could tackle these shortcomings (such as multiple damage thresholds for each of the compound’s constituent and implementation of the Nordlund arc-dpa).
Thank you very much for your great advice. The sensitivity study would be a good idea.
I did find different threshold values for the same material, will try some simulations for that.