Mathematical models, including a generalized diffusion equation with time varying coefficients, are developed which approximate the propagation of both the initial neutron and the initial gamma radiation from nuclear weapon detonations. Typical plots of neutron and gamma pulse shapes obtained from these models are compared and show that for many cases the gamma spike, or unscattered components of gamma radiation, is predominant. Therefore, it is concluded that for most cases the simplified gamma spike formula commonly used in calculating the radiation environment is appropriate for use in predicting the effects of nuclear weapon detonations upon electronic equipment.