IMPROVEMENT OF ELECTRON-BEAM SHAPE CONTROL IN RADIATION PROCESSING

The development of radiation processing using electron accelerators re quires good control of the treatment parameters to improve the dosimet ry quality. Especially, the analysis of the shape of the scanned elect ron beam that interacts with the product, is of prime necessity. A Mul tiwire Beam Shape Analyser (MBSA) has been developed by the AERIAL Lab oratory in order to insure good monitoring of the scanning length and uniformity. This device consists of an aluminum beam-stop covered with a mesh of individually insulated stainless steel wires, placed under the scanning cone. The current generated by the impact of the electron beam on each wire is converted into voltage. After pulse shaping and multiplexing of the different channels, the beam profile can be displa yed on an oscilloscope or on a PC screen. A prototype is now operating on an experimental irradiation plant based on a 2.5 MeV/300 W Van de Graaff electron accelerator. It allows almost continuous visualization of the beam profile (between two conveyor passes) and its response wa s compared to classical film dosimeters (Gafchromic, FWT 60.00). Consi dering FWHM and homogeneous treatment regions of the profiles, MBSA an d the dosimeters give similar responses and variations remain lower th an +/- 12%. The acquisition of an electrical signal corresponding to t he beam profile in air constitutes the original aspect of the MBSA and is in keeping with the general pattern of continuous control and auto mation of the irradiation processes. Hereafter, much work has to be do ne to adapt this device to an industrial use (higher energy, high powe r electron beams, non-destructive measurements...).