I am having problems with the scoring of neutrons with USRTRACK. While trying to score the number of neutrons in different regions of my detector I am not being able to perform simulations with a thinner bin in the low energy range and the number of neutrons keeps piling up and showing an unrealistic number of neutrons, for example: 35 neutrons per primary with a 13.8 MeV proton beam.
The question is: How is it possible to get a thinner binning in that low energy region in order to have the real number of neutrons? Or is there any other way to go around the problem?
You can see the simulation and the output from the USRTRACK in these two files (The problematic histograms are NDET and NPM):
Hallo Duarte. The simulation is not meant to yield an unrealistic number of neutrons in any case, and it doesn’t. The problem may rather be the interpretation of USRTRACK results, which do not give the number of neutrons, rather differential neutron fluence (GeV^-1 cm^-2).
I’m not sure where you read that 35 neutrons are generated per primary proton (nor how you can expect that a different energy binning may change such an integral value).
I read in the output file (Number of secondaries generated in inelastic interactions per beam particle) that 0.00025 (!) neutrons per primary proton are generated in inelastic interactions (by beam protons). Then, low energy neutron re-interactions can further contribute, if the number of produced neutrons actually exceeds the number of interacting neutrons. But we are orders of magnitude below your estimate.
On the other hand, looking at the integral neutron fluence scored by USRTRACK and printed in the geom_detect_42_sum.lis file, I read for NDET something like 10^-7 cm^-2 per beam proton.
So, the pre-defined (and not alterable) energy binning applying to low energy neutrons is not responsible here for any anomalous result.
Best