Dear @gamze,
The linear attenuation coefficient is a value which is tabulated and can be accessed using mgdraw, as done in the post. This will provide you with the value used by FLUKA as a function of the energy and the material. Answering some of your questions about this option:
- To use the mgdraw, you will have to recompile FLUKA with FLAIR, adding this user routine. Afterwards, you can run the simulation with the new executable.
- IREG defines the region whose material will be used to obtain the coefficient. The region number is set based on the order in which you define the regions in the input file.
- In the mgdraw file you can also set the range of energies of interest to obtain the coefficients.
On the contrary, if you want to simulate your experiment and compare it with your experimental results, then you can use something equivalent to your setup. The input file you have uploaded in your last post can serve as a good toy model. What you calculate with the two USRBDX cards is the flux [1/cm2/pp/GeV] entering the target from the left (Io) and the flux leaving the target from the right (I), respectively. Also, some answers:
- The integrated flux over the solid angle can be found in the tab file.
- USRBDX can output either the flux or the intensity over the surface. If you are interested in the flux, I suggest you use Phi1,LinE,LinTheta
- You will obtain only one value since you request only one bin for the energy and solid angle. Also note that the Emax you define is lower than the primary energy, what means you will not include most of the particles.
- You already add the normalisation factor (surface), but if you are interested in the ratio (
I/Io) this should not play a role. - If you find high error bars, try using more primaries to improve the statistics. Many photons do not interact if the material is thin.
I hope this helps.
Mario