Beam scanning for dose uniformity

A low max/min ratio of absorbed dose is a prime objective in any industrial irradiation process. The IMPELA electron beam irradiator has been further developed to deliver a beam distribution that can be tailored to match the required dose uniformity for specific products and applications. Thus, for the first time, the beam source can be readily adjusted to create an acceptable max/min ratio. Prior knowledge of product geometry and density anisotropy, together with off-line dosimetry measurements, are used to specify the beam distribution necessary to provide a uniform absorbed dose. The characteristics of two scanning methods are examined: deflection of the beam across the product width within each beam pulse, and a slow scan covering the width with many beam pulses. Product-specific distributions are achieved by reducing the duration of individual pulses and tailoring the scan waveform during a slow scan. Examples will be given of irradiations carried out on the 10 MeV, 50 kW accelerator at Chalk River Laboratories. (author)