Protons with energy under PART-THR minimum appearing in spectrum

Dear FLUKA experts,

I am trying to score the proton spectra in a water phantom at several depths using USRYIELD. For my study, I need to set up a proton transport threshold of 15 MeV, which I do using the PART-THR card.

When I graph these spectra, I still find protons under this energy of 15 MeV. Why is this the case?

I am aware that (as per the manual): “for thresholds lower than 100 MeV, the particle is not stopped, but is ranged out to rest in an approximate way”, do these contribute to the scorer?

If so, can you raise the production threshold so that no protons with energies higher than 15 MeV are produced?

I attach the flair file and a couple of examples of the spectra. Thank you very much for your time in advance!

Best regards,
Daniel
boxwater.flair (39.1 KB)
spectra-codes-z=3.9867549668874176.eps|attachment (118.9 KB)
spectra-codes-z=10.963576158940398.eps|attachment (110.0 KB)

Dear @danipuerta ,

Thank you for your question. I will review your inquiry and respond as soon as possible.

Best regards,
Tommaso

Dear Daniel,

Yes, in your plots, you still see protons because they are not drastically removed from the simulation. Instead, they are ranged out to rest in an approximate way (as noted in the manual under Note 4, PART-THRes card, which you have already identified).

Based on what I see in your input file, I believe that adjusting the protons production thresholds would surely affect the physics of your transport problem.
This thread (and related links on the page) offers some considerations about a similar issue and may help provide an overview. In short, handling this in a detailed way would likely require advanced user-written routines, possibly intercepting the secondary particle stack (introduction in this advanced lecture).

Depending on your needs, another option would be to adjust the scoring. A straightforward approach could be to set different energy ranges in your USRYIELD cards or filter particles below a certain energy at scoring time using advanced scoring techniques, such as fluscw.f ).

A side note about neutron transport:
- PART-THRes: the energy threshold is in GeV. Currently, your neutrons have a cutoff at 1E-5 GeV, but you might be interested in the full transport down to 1E-14 GeV.

I hope this gives you a good starting point.
Best of luck with your simulation.

Tommaso

Dear Tommaso,

Thank you very much for your detailed response. I think that the best solution is to simply limit the scorer as you point out.

With respect to neutron transport, I need to limit the transport to this energy for this study but thank you for the advice.

Best regards,
Daniel

A pleasure.
Best regards,

Tommaso