In furtherance to improving agreement between calculated and experimental nuclear data, the nuclear reaction code GAMME was used to calculate the multistep compound ( MSC) nucleus double differential cross sections (DDCs) for proton-induced neutron emission reactions using the Feshbach-Kerman-Koonin (FKK) formalism. The cross sections were obtained for reactor structural materials involving Cr-52(p, n) Mn-52, Fe-56(p, n)Co-56, and 60 Ni(p, n)Cu-60 reactions at 22.2 MeV incident energy using the zero-range reaction mechanism. Effective residual interaction strength was 28 MeV, and different optical potential parameters were used for the entrance and exit channels of the proton-neutron interactions. The calculated DDCs were fitted to experimental data at the same backward angle of 150 degrees, where the MSC processes dominate. The calculated and experimental data agree well in the region of pre-equilibrium (MSC) reaction dominance against a weaker fit at the lower emission energies. We attribute underestimations to contributions from the other reaction channels and disagreement at higher outgoing energies to reactions to collectively excited states. Contrary to the FKK multi-step direct calculations, contributions from the higher stages to the DDCs are significant. Different sets of parameters resulted in varying levels of agreement of calculated and experimental data for the considered nuclei.
