A newly developed calculational model for nucleus-nucleus collisions has been applied to obtain secondary-neutron spectra from 100-MeV/nucleon alpha particles incident on 12C and from 100-MeV/nucleon 12C incident on 12C. These data can be used in estimating shielding requirements for medium-energy heavy-ion machines. Also included is a comparison between a previous model used only for calculating secondary-particle spectra from alpha-particle nuclear reactions and the new, more general nucleus-nucleus collision model.