Detection of High Altitude Nuclear Detonations Using the VLF Phase Shift Technique

High altitude nuclear detonations can affect the ionization of the lower ionosphere through a number of mechanisms. Three of the more important ones listed in their order of occurrence and in order of increasing time of onset are: (1) Prompt effect created by the prompt x-rays, gamma rays and neutrons from the bomb. The horizontal extent of this effect can range from rather limited regions resulting from sub-ionospheric burst heights to a hemisphere for a space burst. Registration of the rapid onset times of the prompt effects appears to afford a useful method for distinguishing between bomb-induced and natural effects. (2) Neutron-beta decay effects can affect up to one-half the earth, depending upon burst height. The onset time is rapid and also affords a basis for discrimination from natural events. (3) Delayed debris effects can result from gammas or betas radiated from the debris cloud in the region of the burst. The horizontal extent of the ionization depends upon the size of the debris cloud and the travel distance of the ionizing radiations. Enhanced ionization can also be created in regions magnetically conjugate in the Northern and Southern hemispheres. In the first two cases the ionization will decay (seconds to minutes)4 but in the last case the effect may persist for several days.