Problem with MT=52 inelastic interaction

Physics Processes, Models and Cross Sections
1

Dear Geant4 team
Working with GEANT4.10.07 including the patch for elastic scattering Elastic bug with neutrons, I am simulating neutron transport (HP) in a U235/U238 sphere.
I noticed some discrepancies by comparing energies before and after inelastic processes for MT 52 in U235 between GEANT4 and MCNP.

image
image908×860 49.4 KB

As can be seen above, there is a deviation between the two codes.
All is happening in GEANT4 like if there is a problem in the sampling of the output energy after inelastic reactions.

At energies below 0.1 MeV, the energy entering and leaving the inelastic interaction is the same while it should be different (it is a straight line).

I have also tried to look at other MT numbers between 51 and 91 and for U238 as well. For the other MT and for U238, all seem to be correct.

Could you please clarify what is happening in MT52 for U235?
Thank you,
Thomas Frosio

2

Here is an example of what I found for U-238 MT=52 (other MT in U8 and U5 give similar results):
image

4

According to ENDF/BVIII, exictation energy in MT=52 with U235 is 13.04 keV.

ENDF/BVIII

In the source code of G4ParticleHPInelasticCompFS.cc, when excitation energy is below 20 keV, it is set to 0:

image
image1118×762 151 KB

Could this be responsible of the behavior observed in my first post?
Should I just comment the red squares in the figure above to solve the problem?

Thank you in advance,
Thomas Frosio

5

Please find attached a patch suggestionG4.patch.txt (1.6 KB)

Thomas Frosio