  Nuclear deexcitation associated with neutrino interactions and nucleon decays
has a significant impact on a recent key observable for neutrino detectors:
neutron multiplicity. However, most existing neutrino Monte Carlo event
generators do not consider this process. For a comprehensive prediction of the
neutron multiplicity, a nuclear deexcitation simulator based on TALYS named
NucDeEx is developed. NucDeEx can be used for neutrino interactions and nucleon
decayes for $^{12}\text{C}$ and $^{16}\text{O}$. The author provides the
NucDeEx codes and sample codes for applying the NucDeex to widely-used neutrino
Monte Carlo event generators, NEUT, NuWro, and GENIE.
