Thermal neutron detection using MCNP

[Islam Nabil]

How can i detect the thermal neutron, E = 0.025 Ev, by MCNP using CUToff Or PHYS:N cards?

 

[Alex A]

Unless there is a specific reason not to, I'd use an energy bin card for the tally. For example,
F4:n 3
e4 5e-7 0.1 3 $ Energy bins
Results in 3 tallies for cell 3, everything under half an eV, everything between half an eV and 0.1MeV and everything between 0.1 and 3 MeV.

Don't expect any neutrons at exactly 0.025 of course, it's a distribution, so take the range you are calling thermal neutrons and put them into the energy bins.

 

[Islam Nabil]

Unless there is a specific reason not to, I'd use an energy bin card for the tally. For example,
F4:n 3
e4 5e-7 0.1 3 $ Energy bins
Results in 3 tallies for cell 3, everything under half an eV, everything between half an eV and 0.1MeV and everything between 0.1 and 3 MeV.

Don't expect any neutrons at exactly 0.025 of course, it's a distribution, so take the range you are calling thermal neutrons and put them into the energy bins.

No, the energy bins will be below the energy cutoff. 0.025 ev will not be detected. The cutoff or phys:n must be in the input file to handle the low energy bin E= 0.025ev

 

[Alex A]

Respectfully, I believe you are mistaken. Photons and electrons traditionally cut off at 1kev. I do not think there is any default low energy cut off for neutrons.

I understand the lower energy bound for the ACE data tables is traditionally ten micro eV. I don't know what the limits are for the newer tables.

If you are running an input file that isn't working we would be happy to look at it if you can share it, or a simplified input you can share with the same problem.