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I am using the QMD model in an application that is simulating Fe56 transport through materials for space (GCR) boundary conditions.
It appears that for hydrogen targets, the QMD model predicts a large number of reactions that usually produce 2 or 3 protons and gammas (all low energy) and a high energy Fe56 (displayed as a secondary product in the code). In fact, the number of reactions of this type seem to be almost the same as the expected reaction wherein the primary particle is fragmented into a high energy heavy ion (with lower mass) along with several nucleons and other products.
There are enough of the proton/gamma production reactions happening that the primary beam is actually amplified when compared to the first order analytic solution one obtains when only considering atomic slowing down and nuclear absorption. The amplification is occuring because there is a Fe56 secondary being produced and tracked that would otherwise not exist if the usual fragmentation reaction would have occured. This behavior does not seem to be occuring in other materials (aluminum, oxygen, nitrogen, carbon).
Admittedly, I am using the QMD model well beyond 10 GeV. However, for most of the comparisons I've done so far, particle energy spectra behind shielding agree well with other MC codes (FLUKA and PHITS) and simple analytic solutions. The one exception is for targets with hydrogen.
Is this a material-dependence problem/bug in the model, or does it just happen that the results turn out like this for hydrogen beyond 10 GeV for the QMD model?
Any help or guidance would be most appreciated.
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