I’ve got a simple model of a beryllium cylinder with a spherical proton source and then I’m scoring neutrons due to spallation. I’m comparing the FLUKA model with PHITS but I’m not getting agreement between the results so I just wanted to clarify that the source is being defined correctly in FLUKA to eliminate this as the source of error. I want to define a spherical proton source with the following parameters:
radius = 5cm
energy = 100MeV
direction = isotropic
sphere centre = (60.0, 0.0, 65.0) cm
I have defined this using a BEAM car and two BEAM-POS cards for the source position and SPHE-VOL definition. Here is my input file:
Your source definition looks correct to me. But please double-check your geometry definition in the Flair Geometry tab, for me, it contains errors in the blackhole region.
A full description of a physical model can be found here: Physics
At your energies, it will be using PEANUT.
My quick check with PHITS (I am a beginner) has shown reasonable agreement between obtained results. Probably it’s possible to adjust default parameters in PHITS to obtain better agreement.
Thank you for your quick response. Regarding the geometry errors, even though there’s a warning in the geometry tab, there isn’t any error under ‘Input’ or the output tab so I’m not sure what the issue is here
The results between PHITS and FLUKA have quite large percentage differences (>30%) but they are the same order of magnitude so I’m not sure if these discrepancies are acceptable given that the different codes use different models?
PHITS uses INCL model but according to some of the literature, the INCL and PEANUT should agree pretty well it seems.
Unfortunately, Input will not show this type of error. Although FLUKA accepts it as an input, it will result in unreliable output results. Please redefine your regions until your “Error Found” message disappears:
Edit: In Fluka, the peak is slightly higher but the difference is not as big as in your case and lies in another energy range. Could you make a neutron lethargy plot as I did?
Please also double-check that your FLUKA version supports pointwise low-energy neutron treatment.
Thank you. I have modified the geometry to use boxes instead of planes and it has removed the errors. I am using FLUKA version 4.3.4 which according to the manual includes point-wise neutron treatment. I have included the LOW-PWXS card in the input file so it should be using the point-wise treatment as far as I’m aware.
I’m not sure how to create the lethargy plots similar to the ones you have provided. Have you done this in Flair or externally?
I’ve followed the instructions to create the plot using FLUKA data but mine looks different to yours, so I’m not sure what I’m doing wrong. Sorry I haven’t really used plotting in Flair at all.
In USRBDX I was checking flux from the core region into the reflector region, reversed case to yours. Also, the energy range is different. my histogram for neutrons has a range (1e-11, 100) MeV.
Ah right, ok, I’m interested in the reflector->core flux but I’ve reversed the direction and changed the energy boundaries. It seems like my results are similar to yours now. I will look into importing the PHITS results.
