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None Low Energy Neutron Scattering from Cold Target 

Forum: Hadronic Processes
Date: 06 Jun, 2012
From: Edward Leggett <Edward Leggett>

I am attempting to simulate the scattering of low energy (~10^-3 eV) neutrons off of a cold acrylic target (Hydrogen should dominate the scattering). In order to verify that the scattering was correct, I performed a simulated measurement of the cross section for a block of Hydrogen and obtained a value that was consistent with what is in the G4NDL4.0 file (~20 barns). However, if you look at the attached plot, you can see that the cross section at this energy should be ~120 barns at 1e-9 MeV. This plot was obtained from the NNDC website.

Now, if you look in the ENDF file itself, you see that the cross section is ~20 barns, and this discrepency is explained on the NNDC forum by the fact that the plots are created from data that is processed with PREPRO, and the low energy rise is due to a "Temperature Effect". My understanding is that the data in the ENDF file is constant below thermal neutron energies because the data was obtained from room temperature targets where the nucleus always has some kinetic energy. Therefore, even though the incident neutron energy may be low, the CM energy between the neutron and target will never drop below some limit. However, when dealing with a cold target, the motion of the nucleus becomes negligible and the neutron should see this much larger cross section displayed in the plot (~120 barns).

My question is: Does Geant4 correctly modify the cross sections for scattering of low energy neutrons off of a cold target? If so, could you please explain why I should not see this low energy rise in cross section displayed in the plot?

Thanks for any help, Jed Leggett

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2012/06/06/14.59-53757-E4R5354_e4.pdf

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