Hello Egemen,
looking into more details into your request of simulation, I reached a critical aspect: in FLUKA, the gamma coming from the de-excitation of a nucleus is emitted instantly (without delays). Therefore I don’t think is possible to retrieve from the results of a simulation the information you are interested in.
On another side, the life of a nucleus’ exited state is known a priori, and if it is not, it surely cannot be obtained from a simulation.
If you still want to reproduce in FLUKA the experimental setup, you can use as source of your simulation an isomer of a specific isotope with the ISOTOPE entry in the BEAM card associated with HI-PROPE where WHAT(3) represents the isomeric state you are interested in. You can find some references on the forum and on the manual. I also suggest to have a look to the course slide to correctly set up a radioactive isotope as source.
Generally for the scoring, coincidence capability are included in the DETECT card. It will need to be correctly set once defined which signals are you looking for.
Otherwise, the gamma generated from the de-excitation of the isomer could be intercepted and scored through the use of the mgdraw.f routine.
Hope you will find this useful,
Giuseppe