MCNP neutron energy deposition in water

[oksuz_]

Hi,

I did an MCNP simulation to see the neutron energy deposition in water. I used 14-MeV neutrons, and big enough water body to make sure all the neutrons stay in the water and give all their energies to water. I used F6 tally. However, I got energy deposition of around 10.3 MeV, not 14 MEV. I suspected that maybe when a proton captures a neutron, MCNP does not score neutron's energy. And I included energy deposition of Deuteron and got ~20 KeV, Which is so small. I wanted to try the same thing for Oxygen, but MCNP does not track O individually ( as far as I know). Can anyone give me some suggestion? Maybe I am missing something.

 

[Astronuc]

Does the tracking of the 14.1 MeV neutron have a cutoff energy below which it is not counted?

If the neutron is absorbed, there is both recoil of the resulting nuclide, as well as radiative capture (gamma ray). When a proton captures a neutron, the exited deuteron emits a 2.2235 MeV gamma, which is slightly less than the gamma energy required to separate the neutron from the proton (photo-dissociation). This gamma would deposit energy by Compton scattering or photo-absorption. Similarly, oxygen would emit a gamma ray when it absorbs a neutron. With respect to H₂O, the cross-section is weighted according to the number of atoms in the molecule. Neutron scattering off water involves the protons, the oxygen to a lesser extent, and the whole molecule, at thermal energies.

 

[raining Pete]

Hi there,

It sounds like you have done a thorough simulation and have some interesting results. Have you considered checking your input parameters to make sure everything is set up correctly? It's possible that there may be a mistake in your input that is causing the discrepancy in the energy deposition.

Also, have you tried reaching out to the MCNP community for assistance? They may have some insights or suggestions for you to try. You can also try posting your question on forums or discussion boards specific to MCNP to see if anyone else has encountered a similar issue.

Lastly, have you consulted any literature or resources on MCNP to see if there are any known limitations or known issues with tracking oxygen specifically? It may be worth looking into to see if there are any known workarounds or solutions.

I hope this helps and good luck with your simulation!