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I'm using Geant3 for some neutron interactions in xenon gas, using GCALOR since my neutrons are fairly low energy (.1-10 MeV). I thought I had everything worked out, but when I look at the recoil energy spectrum I'm getting some strange results. I'm finding spikes in my spectrum spaced evenly every 8.19 keV. These spikes appear once I get to a input energy of 1.1 MeV. The number of events in the spike is typically an order of magnitude higher than the number of events on either side of the spike. Also all of these events are inelastic collisions.
My suspicion is that GCALOR/MICAP is somehow not producing secondaries correctly and instead is using a hadronic shower approximation and the spikes correspond to neutron capture events. I think this is what is going on because even in other inelastic events where I should see gammas produced, and where the energy loss is consistent with the separation of energy levels in the nucleus, the program is not tracking any gammas from the events. Also to get a 8.19keV recoil from a capture event you need an input energy of just under 1.1 MeV so that seems to match up.
I'm hoping that there is some flag or something I can set to change how GCALOR deals with these events. I tried changing the IHADR flag (from 1 to 2) but that had no effect. I also tried calling MICAP directly but that didn't fix the problem either.