Correct the sampling of discrete interactions for energy loss #209
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sethrj
reviewed
Apr 11, 2021
whokion
approved these changes
Apr 12, 2021
sethrj
approved these changes
Apr 15, 2021
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For energy loss processes the post-step energy will be different from the pre-step energy, so the assumption that the cross section is constant along the step is no longer valid. To correctly sample the interaction length, Geant4 uses the "integral approach", which uses MC integration to sample from the exact distribution. At the start of the step, the maximum cross section over the step
xs_maxis estimated and used for the process instead of the cross section at the pre-step energyE. At the end of the step, if that process is selected, the cross section is recalculated at the post-step energyE'and the discrete interaction occurs with probabilityxs(E') / xs_max.