In general we have the reactions $$ \sum_i {^{N_i+Z_i}}i \rightarrow \sum_f {^{N_f+Z_f}}f $$ We require also that the number of protons and neutrons (the total number of nucleons) is conserved in the initial stage and final stage, unless we have processes which violate baryon conservation, $$ \sum_iN_i = \sum_f N_f \hspace{0.2cm}\mathrm{and} \hspace{0.2cm}\sum_iZ_i = \sum_f Z_f. $$