Hello Georgios,
You are right, as nicely explained in last FLUKA beginner’s course lecture on RP calculations, the results you obtain will be expressed as the amount of nuclei per primary particle simulated [#nuclei / primary] since you did not specify a region volume or mass.
You could try to combine RESNUCLEi with EVENTBIN to get an event-by-event summary of the residual nuclei produced on a Region basis. However, I have no experience with this and the output might be difficult to process. To make things cleaner and to give you better flexibility, I’m afraid that the use of an mgdraw.f routine is the best way forward. Perhaps the best starting point would be this discussion where the full isotope information is extracted. You can then select with ICRES (= residual nucleus atomic number) and IBRES (= residual nucleus mass number) on the isotopes you would like to consider. In addition, you would need to update the mgdraw routine such as to filter on the primary number NCASE.
Let me know if it works!
Andreas