Dear Fatima,
You don’t need to manipulate the NPFLKA variable in the source_newgen.f routines, but you need to call the set_primary() subroutine multiple times to push each particle to the stack. See the following small example:
npflka_example.flair (2.5 KB)
source_npflka_example.f (4.5 KB)
By the way, the (Anti)Coincidence option of the DETECT card is for two separate detector regions. In a single region, if multiple particles deposit energy, you will get the sum of energy deposition by default.
Cheers,
David