How to score the GCR spectra similar to the figure from slide 2 of AdvancedCosmicRays2019.pdf

Dear Experts,

I would like to know how the GCR spectra from the slide 2 of AdvancedCosmicRays2019.pdf is calculated. I use the primary cosmic rays as specsour and all the region are assigned to be vacuum, but the calculated GCR spectra (using USRBDX) differs a lot from this one. I am not sure if I have set the right specsour.
Thanks in advance.

Dear @chenchcc ,

You don’t need to run a simulation to get this image. The image is produce directly from the *.spc files for solar minimum (see slide 6 of the presentation), i.e. xxphi0465.spc.

See the image I (re)produced by just plotting the *.spc files.


Please see also the note in the slide, quoting:

These spectra are without geomagnetic cutoff. They are used together with analytical calculations of the rigidity cutoff, according to different descriptions of the Earth geomagnetic field

Please note that you have selected NO-NORM in GCR-SPE. I think this may have an effect on the final output since no normalization factors are applied by default.

Hope this can help.



Dear @ainfanti,

Thank you for your response.

I want to verify that I have set the GCR source term correctly by comparing it with the energy spectrum form the *.spc file, as you said. I think that if both have the same distribution, then it can indicate the correctness of my subsequent calculations.

Regarding the normalization factor, I am a bit confused. Because in your answer, GCR extended layers and scoring through mgdraw file - #3 by ainfanti also uses NO-NORM selection, and its normalization factor can be calculated by fluxst/flux in the output file. Is it something to do with my model? I want to calculate the secondary neutrons produced under GCR irradiation and their distribution. The model is mostly composed of cylindrical and hexagonal prisms and within the radius of the GCR-IONF. If this calculation of the normalization factor does not apply, is there another way?

Dear @chenchcc ,

From your first post I understood you were interested in reproducing the figure of the course presentation for which it is not really necessary to run a full simulation or, on the other hand, if you want to reproduce from simulation it needs to properly set up the GCR-SPE card, your scoring and to apply proper normalization in post (e.g. including the scoring surface if not specified in the USRBDX, energy in MeV/amu, etc).

Now I see a different question, related to a specific geometry. In this case you may indeed use the NO-NORM and re-normalize everything in post. Once more, make sure that all relevant normalization factors (fluxst/flux, volume/surface depending if you request USRTRACK/USRBDX, etc) are properly applied in post.



Dear @ainfanti ,

Thank you for your quick response.

Regarding the first question, after divided by the atomic mass number of the ion for both x and y axes, I got a similar figure similar to the one in the presentation.

For the second one, my understanding is that each FLUKA transport calculation is a random sampling of primary particles on a sphere with r=WHAT(2), a process that has nothing to do with the geometry of my specific model. And the normalization of this sampling process is reflected in the result (fluxst/flux). For the tallies, the results depending on the USRTRACK/USRBDX cards selected and the corresponding volume/surface value is used. Then multiplied these tallies results by (fluxst/flux), I can get the final result.

Dear @chenchcc

Indeed, that was the point.

The NO-NORM option is indeed helpful when you want to get rid of the default normalization factors (which are applied only to the standard atmosphere shells) and you want to have full control of the normalization in post.