FLUKA experts,
I am doing some comparative analysis of some results from mcnp and fluka, mainly about neutron flux. When I was writing the card, I found that mcnp has a reflecting surface. The explanation is as follows: A particle track that hits a reflecting surface is reflected specularly. (See Note 1.). (Note 1: Detectors and DXTRAN (next-event estimators) usually should not be used in problems that have reflecting surfaces or white boundaries. Also, tallies in problems with reflecting surfaces will need to be normalized differently as discussed in the MCNP6 Theory Manual[X-503a], Sections 2.6.3 and 5.5.4.2.)
I searched the fluka manual and did not find this definition. I would like to ask each experts if fluka has such a geometry？
Thanks 
Dear 一巍 王,
unfortunately, FLUKA doesn’t have a simple way to create reflective surfaces like in MCNP.
However, it is possible to use the lattice feature in conjunction with the lattic.f user routine to make a reflective surface. While it is not very well documented, you will find examples in the default user routine.
Cheers,
David
Dear Dávid Horváth:
Thanks for your reply. I will find this file to learn. Actually, I searched FLUKA user forum, and I found the usrmed.f file.
Its typical applications include simulating reflection (albedo) at a boundary. The direction cosines must be modified according to some reflection law or albedo angular distribution, and NEWREG must be set = MREG.
Can I use this card? My geometry includes multiple infinitely long cylinders cutting by two surfaces which are reflection surfaces. Maybe I need to set each region or set these two surfaces?
Dear 一巍 王,
you are correct, usrmed.f can indeed be used to create reflections. This could be easier to set up than lattices, but you need to manually filter the surfaces where you want to apply the reflection.
Cheers,
David