Hope explanation for SPECSOUR/GCR-ION

Dear all

I would like to find out SPECSOUR card clearly, which may be a little vague for me in manual.
Could you help me with any one of the following, please?

  1. How does the spectral index for sampling work? why set 1.75 is approprite?
    I see the real specrum index is 2.75. (SPECSOUR/GCR-ION WHAT(5))

  2. Does the transition energy for sampling has recommended value ? What should I set it according to? (SPECSOUR/GCR-ION WHAT(6))

  3. What’s the number of the energy point in the spectra refer to? If I increase it value, what benefit will happen?(SPECSOUR/GCR-ION WHAT(9))

  4. What’s the meaning of the possibilities used for the various ions? (SPECSOUR/GCR-ION WHAT(11))
    If I use zzphi0465.spc of 28 files totally and set 5000 primary/cycle, how does the sample work among the different ions? Is the component percent of sampling results same as the real CR? set WHAT(11) or not, which is more reasonable?

  5. In SPECSOUR/GCR-ION, when and why choose the WHAT(12)< 0, i.e.make the ions are split instead of treating them as real one?
    In additon, what’s the meaningful of the ALL-Nucleon spectrum existing ? I’m not sure what it’s advantage is and when I need to use.

  6. General question: what’s the difference of benefit of increasing the number of primary/cycle and cycles?

Just list my confusions here, please take it easy.
even one of them being answered would help me a lot.

Thank you and best

Dear @YUYI

The difference between the set of 28 *.spc files and the ALL-Nucleon is the way in which the source spectra are treated. For a detailed explanation, see Chapter 16 of the FLUKA manual.
Quoting the manual:

“Two options are available: with the first one the actual ion composition
of the flux is used (All-Particle Spectrum), while with the second option
the primary flux is treated as a sum of nucleons (All-Nucleon Spectrum).”

In the first case, you have the different spectra (which considers all elemental groups from Z = 1 to Z = 28) ; in the second case you have a fit of the All-Particle Spectrum (please refer to the manual for the detailed bibliographic references).

With regard to the number of primary & cycles, generally speaking, both can be used to improve your statistics, i.e. getting close to the expectation value and reduce the variance. The suggested value of 5 cycles, is a good starting point (but you can have more). With regard to the number of primaries, that depends from the statistical uncertainty you want to achieve. You can check at the scoring outputs to see if you need to simulate more histories to reduce the statistical uncertainty.

Hope this can help.