Pulsed Electron Beam Energy Deposition Profiles Using Solid Radiation Sensitive Plastics

The deposition profiles for the pulsed electron beams in solid radiation sensitive plastics have been measured and indicate a pronounced range shortening at charge fluences greater than 0.5 microcoulombs/cm2. This range shortening, due to charge trapping and the attendant internal field, reaches a constant value in the absence of apparent breakdown which is independent of charge fluence at current densities greater than about 33 amps/cm2 for mean electron energies of 1.35 MeV. The dose depth profiles at charge fluences greater than 0.5 microcoulomb/ cm2 exhibit a linearly decreasing back edge which extrapolates to approximately 35% of the low fluence range and a low intensity tail extending to greater than 55% of this range. As the charge fluence increases, the tail of the dose profile decreased in relation to the forward portion. These phenomena are interpreted in terms of a charge deposition model including radiation induced conductivity.