Program DISIC, a new diode simulation code, has been developed to study the behavior of high ν/γ diodes. The code is based on a two-dimensional finite-size particle simulation model, and is designed to provide good resolution of small anode-cathode gaps. Results are shown which (i) compare with earlier calculations, (ii) compute electron trajectories in strongly self-pinched diodes, and (iii) compute electron trajectories for a diode having a conical cross section.