Why is the fluence suddenly dropped, is it because of Ny size in scoring?

Dear Fluka experts,

I want to find the penetration depth of x-rays into silicon.
I am using a USRBIN card (Part: Beampart). But as you can see, it suddenly drops. Could you please help me to fix it?

Are the number of Nx, Ny, and Nz in scoring, kind of mesh sizes?
When I enter more than 10,000 it gives an error.
Fluence.flair (4.2 KB)
Fluence.inp (2.0 KB)

I really appreciate your kind help,
Best regards,


I could not reproduce your plot because the USRBIN writing to unit 53 is apparently not in the .flair or .inp you provide.

Nevertheless, your beam definition looks weird. In the BEAM card you are defining a rectangular profile (in X and Y) and then applying a divergence (on Z), but yet in BEAMPOS you appear to shoot essentially along the Y axis. To make the BEAM card parameters apply to a custom beam direction you should use the BEAMAXES card.

Note also that putting 10000 bins to cover a stretch of 0.5 um is asking for 0.5 A resolution (half the size of an atom!!) which is too far fetched and may by the way coincide with particle step sizes.


Dear Francesc,

I appreciate your quick response.
As for the beam definition, the beam is irradiated at (0,0,0) at 4mrad (the angle between the incident beam and the surface). Could you please tell me which part I made a mistake on?

Best regards,

Since your beam is not pencil-like, but has a transverse size and a divergence, in order to change its direction you have to use BEAMAXES and not BEAMPOS.

I really appreciate your kind help.
Thank you very much.