Prompt air fluorescence induced by a high-altitude nuclear explosion

A high-altitude (>100) nuclear explosion emits a large fraction of its energy yield in the form of x rays, approximately half of which are deposited in the atmospheric layers {approximately}50--90 km, exciting prompt fluorescence. This paper examines four of the N{sub 2}{sup +} first negative bands that fluorescence strongly: {lambda}{lambda} 3914(0,0), 4278(0,1), 4709(0,2), and 5228(0,3) {Angstrom}. We developed both forward'' and backward'' Monte Carlo procedures and performed calculations using Los Alamos CRAY computers to simulate the physical problem for the variety of situations that are possible. We include the time-dependent treatment of x-ray energy deposition, both local and nonlocal excitation of fluorescence, multiple scattering and transmission of fluorescent photons with the resulting enhancement of the longer wavelength N{sub 2}{sup +} bands, and chemical reactions. A realistic atmospheric model is defined up to 800 km, including the troposphere and a Lambert reflecting ground surface with given albedo. To expedite such computations we use separate spatial meshes in which to carry out the x-ray deposition and fluorescence light scattering. Examples of our calculated results illustrate the effects of explosion yield, geometry, tropospheric scattering, ground albedo, and temperature of the fluorescing layer. 41 refs., 38 figs., 12 tabs.