I was wondering if, in calculating activation/residual products, FLUKA takes into account sequential activation. e.g. I’m interested in He-production in the 58-Ni (n,gamma), 59-Ni(n,alpha),56-Fe reaction.
Specifically here, does the production model take into account the 59-Ni produced in the first reaction?
no, since normally the possibility that a neutron interacts with another reaction product is safely negligible. This is one of the main simulation postulates: material properties (i.e. composition) do not change (residual nuclei are not considered as target nuclei in turn). This holds unless a macroscopic amount of additional nuclear species develops with time, as in nuclear reactors.
To get the 59-Ni(n,alpha)56-Fe reaction simulated, you need to model a material containing in advance some 59Ni fraction. But, as first mentioned, normally the single nuclei generated by the 58-Ni(n,gamma)59-Ni reaction can be safely ignored to the 56-Fe (and alpha) production purposes, since in reality they have no role.