Low energy electron beam accelerator design for surface sterilization of aseptic food packaging materials

A low energy, compact size, and low cost electron beam accelerator has been developed to investigate the feasibility of using low energy electrons (55-65 keV) for surface sterilization of food packaging materials. An electromagnetic field analysis code SIMION was used to model the beam focusing system. Based on the findings of the SIMION modeling, a filament-off-center technique was used to simplify the inner structure of the accelerator. The energy delivery mechanism of the accelerator was characterized. The relationship between the absorbed dose rates and the thickness of the air gap was obtained experimentally. Experimental results showed that air gap should be minimized for low energy electrons in order to effectively irradiate food packaging materials. Microbiological experiments using Bacillus pumilus spores were conducted to measure the deactivation characteristics of low energy electrons.; A Monte Carlo analysis of the dose-depth distribution of 55 {dollar}sim{dollar} 65 keV electrons in the surface of food packaging materials was conducted. Theoretical predictions of both the penetration depth of electrons in the packaging materials, and the absorbed dose received by the surface of the packaging materials, were obtained. The penetration depth of electrons was observed experimentally by examining 50 micron thick slices of irradiated dose films under a microscope. Both measured dose rates and penetration depths are consistent with the results of the theoretical analysis.; A finite element analysis code ANSYS was used to model the heat transfer behavior of the accelerator chamber to find the steady state temperature of the extraction window. The accelerator undergoes thermal radiation from the filament, electron energy conversion into thermal energy to heat the window, forced air convection outside the chamber, and thermal conduction inside the metal wall of the chamber. Both the modeling and experiments showed that the steady state temperatures of the extraction window cooled by an air flow of 4.7 m/s were well below the melting temperatures of the window materials even under some extreme conditions.