Calculation of Bias

Dear Experts,
I want to simulate muons production from electron beam interaction with Tungsten target.
I have three questions:
As I understand I must use PHOTONUC card.
But I am not sure about the number of Bias inter-landa, How can calculate it? because I test several numbers and each number returns very different results.
Also, I have another question when I set Bias that means my result is not real. Is it correct?
I found this topic:
but when I add a PHOTONUC card with an empty SDUM, my result of the number of muon production is zero.

Best regard.

2. No, what you say is not correct, otherwise what would be the interest in biasing?
With biasing you alter artificially the probability of an event, specifically in your case you increase the one of a rare event, in order to get a better statistics. But the results, as obtained by the FLUKA scoring cards, are automatically corrected by the use of respective statistical weights, compensating for the probability alteration.
3. You need indeed a PHOTONUC card with SDUM=MUMUPAIR, in order to switch on muon pair production by bremsstrahlung photons generated by the electron beam.
1. You should check the reliability of those results by looking at the respective statistical errors. Start with a biasing factor (in WHAT(2) of PHOTONUC with SDUM=MUMUPAIR) of the order of percent and possibly decrease it further.

3. I should add that another PHOTONUC card with SDUM=ELECTNUC, activating both electronuclear and photonuclear reactions in the indicated material (with WHAT(1)=1.0) and to be complemented by a LAM-BIAS card biasing the respective probabilities (for PHOTON and ELECTRON), enables the contribution to muon production from pion generation and decay.

Thanks so much, @ceruttif .
Now I think I understood how to handle it. But I am a little confused about the physics implement in Fluka for muon production.
In the manual: PHOTONUC is pair production from photons so If I want to add other physics that muon production from the interaction of the electron with High-Z target which card I must use?
Best regards,

I recalled above the different muon production mechanisms to be activated:
- one is muon pair production by high energy photons (generated in turn by your electron beam), by means of PHOTONUC with SDUM=MUMUPAIR and embedded biasing factor (WHAT(2));
- another is muon production by decay of mesons generated in photonuclear reactions, where the latter ones require both PHOTONUC with SDUM=ELECTNUC (activating both photonuclear and electronuclear reactions) and LAM-BIAS with SDUM empty and biasing factor to be input in WHAT(2).
You will be able to appreciate the respective roles.