Non physical peak in the Lithium spectrum in Hadr03 example

Dear users,
I studied example Hadr03 with the neutron.mac macro, which is proposed in the example, as input.
This macro focus on the neutron capture of Boron-10.
This reaction generate a 7Li and a 4He, accompanied by a gamma in 94% of the cases.
The secondaries energies are respectively 1.01 MeV and 840 keV for the 7Li, 1.47 MeV and 1.78 MeV for the 4He and 480 keV for the gamma.
On the macro I changed the initial energy of the neutron from 1 MeV to 1 eV in order to see only the initial energy of the secondaries (neutron could be assimilated at rest).
I ploted the Lithium spectrum.
The lower energy lithium peak at 840 keV appears as a door, which is not physical.
I was expecting a peak with a gaussian fit, as obtained for the higher energy peak of the lithium and both the peaks of the alpha particle.
Is it a problem in the source code itself? Does someone knows how to solve this?
Thank you for your help,


From simple kinematics with a 1eV incident neutron, I would expect the energy of the excited 7Li nucleus to extend from 839 to 840 keV. Your simulation energy extends from ~832 to 846 keV. That’s 14 times more spread, which is puzzling since the incident neutron energy is approximately 0 compared to the Q value.

Thank you for your reply.
The 1.01 MeV energy peak of the lithium seems correct with a few keV spread, as well as the 1.47 MeV & 1.78 MeV peaks in the alpha spectrum.
I found in the librairies G4NDL the XS for this reaction but not the informations on the secondaries initial energies.
Do you know where is assigned the initial energy of the secondaries particles in the code for an inelastic process?

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