Estimating Transmission Fraction with usrbdx

I’m currently engaged in determining the mass attenuation coefficient (μ) for specific materials, such as water.

The simulation setup involves a transmission geometry comprising a NaI detector within a lead collimator, a sample, and a pencil beam source of 3 mm in diameter. In this simulation, the photon interactions are defined by Lambert law (I = I0e−μt) for transmitted intensity through a medium.

I implemented the usrbdx scorer to track the transmitted fraction, but I only have zero in the tab.lis and sum.lis files

Could you offer guidance on estimating the transmission fraction (I/I0) using the usrbdx scorer in this scenario ?
I seek clarification on the appropriate utilization of usrbdx for this purpose.

Your expertise and assistance in resolving this matter would be immensely valuable to my study.

I have included my input file below:

Best regards,
mass_23_tab.lis (2.1 KB)
mass_23_sum.lis (4.2 KB)
mass.flair (3.7 KB)

Dear @assia.arectout,

I’ve run your input just adding a USRBIN scoring to show where the photons are going.
The result is visible in the picture:

You can see two things:
1-the photon are emitted isotropically, therefore you’re spending most of the simulation time tracking particles that are of no interest to you. Only a handful of particles enter the collimator;
2-the particles in the collimator lose their energy in the air inside the collimator.