Dear FLUKA experts,
I am working on a basic PGNAA problem where a 14.1 MeV neutron beam is directed at Silicon, assigned to the C4 region. I am measuring the photons generated from the neutron-Silicon interaction using a NaI detector in the C100 region. However, the resulting spectra do not match the expected standard, and I am unsure where the issue lies. I am seeking guidance from experts to help identify what I might be doing wrong. Below is the output I am currently obtaining.
I simplified your model to a neutron beam and a simple thin Silicon target and checked the spectra afterwards. Thus, I avoid spectra contamination with other lines and minimize the energy loss.
In the full simulation, you will see the modified original spectra by all possible gamma lines from other materials in the geometry, via USRBDX. Change these scoring cards to be from C4 to C100 region, and you will see something like this:
Your DETECT instead will show the energy deposition spectra in the NaI detector for these gammas and other secondary particles crossing the requested region
Thank you for @vorodin for your considerations. But what if I only want to consider the spectra from only C4 region and not from others? Is it possible? Moreover will it work for other materials too? Also can you please share the modified input files?
Thanks alot
@vorodin I have tried with your instructions but I am not getting the same plot as you are getting. what I am getting is attached here with the input files pgnaa.flair (7.9 KB) pgnaa.inp (9.0 KB)
I am sorry for sending to many messages in a short period. I can now get the spectra but the peaks are not at the standard energy values. For example here in the case of Hydrogen the standard peak is at 2.223MeV but I am getting at 4.45MeV. The peaks are not at their correct energy position. I even tested for other materials but getting similar results @vasilis is it the problem in the flair/fluka or I am doing something wrong @vorodin .
I had attached the updated files
Here are the input files, I defined variable “simple” which assigns most of the regions to Vacuum and sets Si thickness to 1 mm:
It results in this picture for USRBDX22 and DETECT17:
Thank you for your input, but I don’t understand the reasoning behind assigning vacuum material to the majority of the geometry regions. Won’t this affect the results when we conduct/compare the simulated results with real-time experimental ones?
Thus, I avoid spectra contamination with other (gamma) lines and minimize the energy loss.
It helps to see that FLUKA works correctly, and shows what peaks you need to look for
In the full simulation, you will see the modified original spectra by all possible gamma lines from other materials in the geometry, via USRBDX (and DETECT cards)
Further, I will revert to the original (simulation) complexity to understand how it changes deposition spectra in the NaI detector
You should do it step by step, checking what kind of background signal it brings to your NaI detector
I think I wasn’t able to clear my problem. Actually I’m looking for a capture neutron spectra where a themal neutron wilo be captured by a material, say Si, then the gammas emitted by the capture neutron interaction with material will be recorded by the NaI. For mcnp I got a similar spectra
Where the top left graph is for capture neutron whereas the below this one is inelastic. What we’re getting is also inelastic but I’m more interested in capture neutron plot.
That’s what I want to get using fluka.
Thanks
In FLUKA you will obtain spectra from a combination of both processes, capture and inelastic. You can separate them by looking into reaction fragments using mgdraw subroutine:
Commenting out the “simple” variable in the input which I shared with you, will revert the setup to the original complexity
