Trouble scoring fluence of alpha particles using USRTRACK. Questions regarding the USRBIN card

Dear experts,

I have problems using the USRTRACK card for scoring particle fluence of alpha particles in a material. My code involved the study of a neutron capture reaction, more specifically 10B(n, alfa)7Li, occuring in several Boron plates (defined as cartesian meshes), placed above a neutron source (submerged in a partially filled water tank) at different distances. Previously I used the USRTRACK card for scoring photon fluence through the plates with no problem whatsoever. The resulting graphs in the case of alpha particles, however, showed zero fluence along their thickness. I have included the simulation files below. What exactly is wrong with my code?
Another question more or less related, regarding the USRBIN card (used here in order to visualise energy distribution of neutrons inside tank). By modifying the normalisation factor, the energy varies as well. How is the real energy determined if it’s dependent on the normalisation factor?
One more problem I have encountered is not being able to visualise the energy distribution of alpha particles with USRBIN in said plates. Output shows a single-coloured rectangle regardless of the axes selected. While their range would be indeed too small, I wanted to know if there is a way to still obtain a transverse view of the plate.
12mai.flair (6.4 KB)

Thanks in advance.

1-. You miss an empty LOW-PWXS card. Also, you may want to lower the alpha transport threshold from the default value of 100 keV, by means of a PART-THR card (the minimum allowed value is 1 keV). Moreover, if you ask for a spectrum resolution at keV level (1024 (?) bins up to 5 MeV), you would need a FLUKAFIX card to reduce the fraction of the kinetic energy to be lost in a step.

2-3. USRBIN is not meant at all for visualizing the energy distribution (spectrum) of particles [for this there is USRTRACK, referring to a whole geometry region], but gives an energy-integrated 3D fluence map. The USRBIN normalization factor has nothing to do with the particle energy, rather scales the resulting fluence, which is provided by FLUKA per source particle, according to your source intensity.

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Dear @ceruttif

Thank you for the answer. However, after including the LOW-PWXS together with the JEFF-3.3 database, PART-THR with a threshold of 10 keV, as well as the FLUKAFIX card set at 0.002, I’m encountering the same problem. I have attached the modified code below.
P.S: Also, I don’t know exactly if it’s relevant, but I’m mentioning that the version of Flair that I’m using is 3.2-4.5.
1iunie.flair (4.7 KB)

You do not see any alpha most likely because in your setup the number of neutrons reaching the boron regions is too low (for crosscheck, change WATER into BORON, and you should see them).
RADDECAY and DCYSCORE have no point, since you are dealing with prompt particles, and not radioactive decay products.
FLUKAFIX has to be applied to a material (range).
The Flair version is irrelevant.