We have added a source definition component to the Moritz geometry editing and display program. Gamma line emission can be imported from a library based on the Brookhaven National Laboratory Nuclear Data Center. The user can select one or more isotopes from a tree view list. The abundances can be corrected for radioactive decay between two times. The line emission is then converted to MCNP SDEF format. Tabulated data, such as an X-ray tube spectrum, can be read and converted to MCNP format. Interactive tools are available for defining source volumes, direction, cone source opening angle, and bias direction; these items can be shown together with the geometry. All source definition items can be entered exactly in dialog fields. Source definitions can be read from existing input files. The tools will expedite and verify source definition and ensure accuracy and do not require knowledge of the MCNP SDEF syntax.