Design of dual flattening filter for 4-MeV electron beam irradiation system

Abstract

A 4-MeV electron radio-frequency linear accelerator (RF linac) at the Plasma and Beam Physics Research Facility is used to irradiate electron beam on the natural rubber latex for vulcanization process. The irradiation area and uniformity of electron dose have significant influence on the vulcanization quality and throughput. This research focuses on the design of electron beam flattening filter to enlarge the transverse beam size with more uniform energy and dose distribution. The flattening filter system consists of two different filters. The primary one is used to increases the transverse beam size while the secondary one is used to modify the beam for achieving more uniform transverse distribution. Optimization of the filter system was performed for 4 MeV electron beam by using the GEANT4 Monte Carlo simulation program. The initial electron beam has a pencil shape with transverse Gaussian distribution and an RMS radius of 2 mm. The optimized parameters of the filters are thickness, shape and position. The results of the optimization suggest that the primary filter should have high atomic number. The tantalum (Ta) sheet with a thickness of 30 micron was chosen. The material and shape of the secondary filter were also studied. It is found that the aluminium (Al) plate with a shape of the truncated cone can smear the beam to uniformly distribute over the irradiating area. The output of this work can be used to construct the flattening filter system in the electron beam irradiation system for increasing the vulcanization throughput.