  A new software package, the Fission Induced Electromagnetic Response (FIER)
code, has been developed to analytically predict delayed $\gamma$-ray spectra
following fission. FIER uses evaluated nuclear data and solutions to the
Bateman equations to calculate the time-dependent populations of fission
products and their decay daughters resulting from irradiation of a fissionable
isotope. These populations are then used in the calculation of $\gamma$-ray
emission rates to obtain the corresponding delayed $\gamma$-ray spectra. FIER
output was compared to experimental data obtained by irradiation of a $^{235}$U
sample in the Godiva critical assembly. This investigation illuminated
discrepancies in the input nuclear data libraries, showcasing the usefulness of
FIER as a tool to address nuclear data deficiencies through comparison with
experimental data. FIER provides traceability between $\gamma$-ray emissions
and their contributing nuclear species, decay chains, and parent fission
fragments, yielding a new capability for the nuclear science community.
