Virtual detector

Dear Experts,
I want to calculate background noise around an area, which means I want to add some parts to a special area but I want to know about the spectrum energy of particles before adding this part.
when I try to use USRBDX, it depends on material in this area( I checked it with Air and other light z material)
Is there any virtual detector in Fluka for getting the spectrum energy of particles for any area?
thanks in advance,

Dear @rezaei.m.p,

I struggle to understand your question and your study case. Could you please provide some more details and also some image of your experimental set up in order to better understand?
Thank you.