CR particle spectrum

[amrit.p.nayak (Amrit Nayak)]

Hello,
This is a followup question from the previous topic

@amrit.p.nayak

Hello,
I have concentric sphere geometry to study the CR interaction . For reference, please look at the attached figure of the geometry.
Using SPECSOUR and GCR-SPE, I created a source at certain radius(indicated by the dotted line). Then, I set a USRBDX scoring between (REGION3,REGION2) and (REGION3, Outer blackbody). Region 3 is vaccum thus no interaction in that region. I am scoring the fluence in both cases. Also, I have taken into account the difference in the surface area in both cases. The 1D plot of both the USRBDX scoring is quite identical.

Does this mean that the particles from the generation sphere can have momentum either inward or outward? I am very new to fluka, so I want to understand these small setups before proceeding further.
Also, is there a way to dump the information of all the primary particles(coordinates, intial momentum direction, energy, etc) generated into a file(preferably csv or some file that can be analyzed in python).

Thanks a lot!

I am using USRBDX scoring between Region 3 and Region 2 to score the primary particle. Since I a new to FLUKA, I am rying to understand the impact of varying the parameter of GCR-SPE through SPECSOUR card.

1. The WHAT(5) card is used to specify the spectral index for sampling. So, If I choose it to be zero, I would expect a flat spectrum from USRBDX scoring(below the transition energy i.e- WHAT(6)). But that is not the case.

2. The spectral shape does not change for the negative values of spectral index. Please see the attached plot for the same.

3. Next, for a given spectral index, if the transition energy [WHAT(6)] is changed, it has no impact on the spectral shape. Please see the attached plots

Am I missing something or my choice of parameters for sampling the particle energy is bit vague?
Any help regarding this regard would be much appreciated.

Thanks
Best Wishes
Amrit

[ceruttif (Francesco Cerutti)]

You are missing the fact that the spectral index is not meant to arbitrarily change the shape of the spectrum, which is given in the spc files, rather to alter the energy sampling along the input range, while assigning anyway the proper weight to the sampled energy.
Moreover, SPECSOUR expects the absolute value of the spectral index (gamma, for E^(-gamma) sampling), as in the provided example. Therefore, the negative values you input, disable the E^(-gamma) sampling and imply the 1/E sampling adoption over the full range, making the variation of the spectral index value as well as of the transition energy of no effect at all.