Neutron energy spectrum with different optical detector issue

Dear all,

Please I am new to Geant4 and c++. I am following the manual to make a simple Geant4 simulation with Neutrons of energy 2.0MeV. Basically, in my detector construction I am shooting my neutrons onto a polythylene box, then I have an optical detectors(NaI and cherenkov detector) to detect the protons that comes from the interaction. I am scoring the energy depositions from these detectors but in my Energy Spectrum I see some difference that I do not understand. Can anyone help me deduce what I am doing wrong and why these energy spectrums. I am attaching my files. Thank you all in advance.


_Geant4 Version: geant4-v11.1.3
_Operating System: Ubuntu 20.04.6 LTS
_Compiler/Version: c++
_CMake Version: VERSION 2.6 FATAL_ERROR


event.cc (587 Bytes)
generator.cc (1.1 KB)
physics.cc (2.7 KB)
run.cc (1.1 KB)
stepping.cc (789 Bytes)
action.cc (697 Bytes)
construction.cc (8.3 KB)
detector.cc (1.6 KB)

What are these two histograms of?

the first histogram is from the cherenkov detector I created and the second histogram is from NaI scintillator. I am scoring the photons deposited in each of them.

By rough inspection, the NaI deposited energy spectrum does not look inconsistent with what I would expect: Na recoils (max energy~100keV), I recoils (max energy ~20 keV), a few capture gamma rays up to ~6-8 MeV.

Likewise the Aerogel (Cherenkov detector) spectrum is not inconsistent with what I would expect: recoils from the H in H2O with ~2MeV max energy, The recoils from O, Si, C would be buried in the H recoils, so seeing ther max energy edges would be unlikely. The low density would make observation of neutron captures unlikely.

Why do you think the spectra look wrong?

Hi,
You say you are “scoring the photons deposited in each of them”.

I cannot see where in your code you select only photons to score deposited energy. It looks like you are scoring deposited energy from whatever particles hit your sensitive detector.

Maybe I am missing something.

Hi,
you are right my idea was to do neutron to proton conversion. then detect the protons in the optical detects and finally reconstruct the positions. I think I got the physics wrong in the coding.