Skyshine - material

Respected FLUKA experts,
I am performing simulations using FLUKA where I want tosimulation of skyshine according to this paper :“EVALUATION OF SKYSHINE FROM AN ACCELERATOR FACILITY: DEPENDENCE ON DISTANCE AND ANGLE”
How can i simulate skyshine after the black hole in FLUKA? beacuse black hole stops particle tracking.
but in the paper said :
“The electron beam direction is from left-to-right at a height of X = I 13 cm. A perfectly absorbing medium (a black hole in FLUKA) was implemented in the upstream and downstream tunnel directions. This technique removed the neutrons (generated from 4 Ge V electron beam loss on the copper target) that were streaming inside the accelerator tunnel from reaching the scoring detectors outside the tunnel.
Thus, only the neutrons escaping the tunnel’s roof and side walls remained in the simulation.”

Dear @yashar86shahoo,

In my understanding, the authors of the work have used black hole to stop any direct contribution the tunnel to the location of interest (i.e. at the same height of the tunnel and the location from interest).
They did not put a black hole all around the source of the radiation, therefore the radiation can go “up to the sky” and then be scattered back toward the location of interest.

Dear amario
Thank you very much for your detailed response.
Kind regards,