Dear Vasilis,
at least i can try. The detectors of my simulation are cylinders with a
thickness of 1cm (10 cylinders). With the help of those cylinders i am able
to track the neutron fluence inside of the cylinders depending on the energy
of the neutrons and the travelled distance of the neutrons.
All my simulation results for the materials PMMA, HDPE and Water (all
moderator mterials) are almost identically. The neutron fluence hits the
maximum at the energyspectrum of 2E-11 GeV, which is the energy level of
neutrons. This means, that the moderation of neutrons is good with those
materials and as the results the neutron fluence is rising in the energy
spectrum of thermal neutrons.
Only the results of graphite are different. The neutron fluence hits it‘s
maximum at the starting energy of my neutron source (0,003 GeV) and then
only decreases. No further maximums and especially no detectable neutron
fluence inside the thermal energy spectrum. Also the plots of my _tab.lis
files are normaly standardized in the range of 1E-12 to 1E-9 GeV on the
x-axis. But in the case of graphit i had to decrease the range to
1E-8 to 1E-2 GeV due to the lack of detectable neutron fluence in lower
energy ranges (e.g. 1E-11 GeV).
So i expected from the simulation with graphite results, which are
comparable to the results of PMMA, HDPE and Water. I hoped to see a increase
of the neutron fluence on the energy level of 1E-11 GeV. Therefore i
questioned myself, if graphite only moderates fast neutrons? Is there
another cross section for graphite, which allows me to simulate neutron
fluence in lower energy ranges, especially at 1E-11 GeV (thermal level)? Why
is there no detectable neutron fluence in the energy spectrum of 1E-12 to
1E-9 GeV?
I hope i could explain my problem a bit better for you!
Again thank you for your time effort!
Cheers,
Tom
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Received on Sun Jul 09 2017 - 14:08:02 CEST