The electric charge accumulation in the dielectric insulation materials under an electron beam irradiation (40 keV and 60 keV) was measured by using the pressure wave propagation (PWP) method. These insulation materials were polar polymeric films such as polycarbonate (PC), polyethylene-naphthalate (PEN), polyimide (PI) and polyethylene-terephthalate (PET), and non-polar polymeric films such as polystyrene (PS), polypropylene (PP), polyethylene (PE) and polytetra-fluoroethylene (PTFE).The PE and PTFE (non-polar polymers) showed the properties of large amount of electric charge accumulation more than 50 C/m 3 and took the time of arrival to saturation of charge accumulation over 80 minutes. On the other hand, it was found the peculiar effect that the charge accumulatuin in PTFE did not observe for the period of 20 minutes after starting electron beam irradiation, as shown Fig. 1 (PTFE). After the period of 20 minutes, the irradiated electric charge was gardually accumulated in PTFE.The PC, PEN, PI and PET (polar polymers) showed properties that smaller amount of charge accumulation about -6 to -14C/m 3 were saturated within the short time about 1.0 minutes after starting beam irradiation as shown Fig. 1 (PC, PI). The PP and PS (non-polar polymer) showed the properties of middle amount of charge accumulation about 20 C/m 3 and took the middle saturation time about 1 to 20 minutes. The PC, PEN, PI and PET (polar polymers) have the benzene ring in principal chain, and have the functional groups of carbonyl group, ester bond, ketone group. These functional groups possess the electrical dipole moment field for trapping an excess electron carrier by irradiation.The PE and PTFE (non-polar polymers) have a carbon-carbon principal chain. And the hydrogen atom was attached to a side chain of PE, the fluorine atom was attached to a side chain of PTFE. There is basically not a trapp site for the excess electron carrier by electron beam irradiation, because these polymers are not a functional group.This paper summarizes the relationship between the properties of irradiated electron charge accumulation and chemical structural formula. Futher more, this paper compares between the electro static potential distribution with negative charged polymer and its chemical structural formula.

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Charge accumulations in electron-beam (e-beam)-irradiated polymers are investigated by observing them using the pressure wave propagation method. The purpose of our research work is to measure the charge distribution in e-beam-irradiated dielectric materials for spacecrafts. We have been developing a system for measuring such a charge distribution in dielectric materials. Using this system, we tried to measure the charge distribution in various typical polymers (poly(ethylene terephthalate), polystyrene, low-density polyethylene) under e-beam irradiation. As a result, it is found that charging characteristics of insulating material is strongly influenced by the existence of benzene ring in the molecular architecture. 

In order to investigate the different properties of electric charge accumulation by electron beam irradiation between a saturated hydrocarbon and an aromatic hydrocarbon, an electron affinity and a trap depth for both hydrocarbons were calculated by using Molecular Orbital method. From calculated results, the relationship among a vacuum level, a conduction level, an ionization level, an electron affinity and a trap depth were drawn in an energy diagram for both saturated and aromatic hydrocarbons.

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