The Effect of Accumulated Charge on Depth Dose Profile in Poly(Methylmethacrylate) Irradiated with Fast Electron Beam

The reduction of the electron penetration length induced by space charge accumulation in solid insulator during exposure of the fast electron beam of the current density below 1 ¿A/cm2 was found by depth-dose measurement in red-dyed poly(methylmethacrylate) plate. The reduction rate depends on charge fluence, the current density and the irradiation temperature. The experimental results are well explained by the calculation of the space charge density and the consequent field strength; these are obtained from a consideration of the deformation of depth-dose profile and the deposition function of thermalized electrons due to the increase of charge accumulation.