This thesis documents a new approach to investigate the gamma radiation activity of the fission products of three different fuels (U-235, U-238, and U-239) exposed to three different incident neutron energy spectra (thermal, fast spectrum, and high energies). An application of the exponential moments function is used with a transmutation matrix in the calculation of complex radioactive decay chains to achieve greater precision than can be attained through current methods. The result of this research is a code which can calculate the decay products from complex radioactive decay chains with a high degree of precision while quantifying the uncertainty in gamma activity due to uncertainties in the isotope properties
