Hi Sergio @szpigel, it is possible, but it requires some coding in dedicated user routines.
To this purpose, I’d advertise the use of mdstck.f, to be compiled and linked into your own executable after implementing a suitable logic. This should discard irrelevant gammas (and other secondary particles) by setting their weight WEI (IP) to ZERZER (i.e. zero), where IP runs from 1 to NP (the relevant variables are available through the included genstk.inc file). Such a weight zeroing should be done unless JTRACK (available through trackr.inc) is equal to -5 (i.e. the projectile is 3He) and IBRES = 18 and IZRES = 9 or 10 (IBRES and IZRES are the mass and atomic numbers of the residue and are available through resnuc.inc, which has to be INCLUDEd in mdstck.f as the other include files are). Also, if the target material is not monoisotopic (16O), you should check whether IBTAR = 16 and ICHTAR = 8. You may want to add some printout, into a file unit of your choice (larger than 20 and not used in any scoring card of your input), to make sure that the logic makes sense (in particular, the secondary particle identity is given by KPART (IP)). I did not have the time to run a relevant test myself, so you are especially welcome to keep us posted in case of issues.