|Message: Re: 9Be photoneutrons at low (<3 MeV) energies||Not Logged In (login)|
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First of all, it should be said that Geant4 gamma-nuclear models are quite rough at energies below, say, 10 MeV. These models treat nuclei as collections of nucleons rather than objects with discrete energy levels so in the formation stage there is no competition between channels.
The gamma is absorbed and the excited nucleus is sent straight to a precompound model and then to an evaporation model. At this stage a photo-evaporation database is used so specific nuclear levels do appear, but their strengths are not guaranteed to be correct. This is probably what you're seeing.
Second, I see you're using version 9.5, which uses the CHIPS model for photo-nuclear. Validation tests indicate that using Bertini cascade for photo-nuclear does a better job, and you get that automatically if you switch to Geant4 version 9.6. Note, however, that the same caveat of point 1 applies, so no guarantees.