Dear @Jungle,
Thanks for the clearly stated questions. Let’s tackle them:
1 and 2: This is an indirect way of looking at the number of reactions, which should be ok assuming that you do not expect protons and/or tritons to appear as a result of any other reaction.
Probably the most direct way is to count the number of reactions using the mgdraw.f routine. But in this case you will need to code the logic yourself. This post may help you to do so: (p.n) reaction position-MGDRAW - #5 by qding
3: The reason why you don’t see them in the USRBIN is because these secondaries are not transported but their energy is deposited at the point of interaction. This is the general approach for charged secondaries produced in low energy neutron reactions, although there are some exceptions. This is why your USRBINs, which are trying to score track-length of protons and tritons see nothing.
Kind regards,
Francisco