Photon do not propagate to the axial direction of the fiber

Dear expert,
There is an isotropic neutron source outside the side surface of the scintillation fiber, and the photons generated in the fiber do not propagate to the axial direction of the fiber. How to solve this problem?
mixscint.flair (2.4 KB)

Look forward to your help.

Dear Xiong,

I ran your simulation with a modified scoring, you can find the .flair file attached so you can replicate the results. The problem is that given the low energy of neutrons, most of the light is generated in the outer layer (REGmix - LiFZnS). Given the very high absorption coefficient, most of the light does not reach the inner layer.

So what you are seeing are the optical photons generated in the REGmix that have not been absorbed and reached the inner layer. Since they arrive to the inner layer at angles close to 90°, there is no reason why they should propagate along the fiber axis.



mixscint.flair (2.8 KB)

I hope this helps

Dear@vojtech.stransky ,
I am sorry for late,it works,thank you!