Characterization of a 1.5 MeV electron beam irradiator using a homemade diode-based dosimetry system

Abstract

The characterization of an industrial-scale electron beam irradiator using an online diode-based dosimetry system, previously developed and calibrated for routine processes control, is presented in this work. The investigation is focused on the dose per pass and beam length operating parameters of the EB facility, which most take advantage of the online dosimetry performance based on an unbiased diode with linear dose response and stable current signal proportional to the dose rate. The dose per pass values are obtained through integrating the current signals delivered by the diode irradiated at a constant dose rate (4 kGy/s) under (2–6 m/min) conveyor speeds. The integration time of the electrometer on the current signal shape is also investigated from 0.05 to 0.55 s. All dose per pass results perfectly match those assessed with reference standard alanine dosimeters, regardless of the integration time. However, the most precise dose per pass data, quantified through the lowest residues to the alanine measurements, is obtained at 0.1 s, where Gaussian current signals with well-defined centroid and FWHM parameters are achieved. It enables applying the straightforward method to assess the beam length through a current signal, provided it realistic traduces the dose rate variations as a function of the time while the diode passes through the beam. The validity of this approach is checked by measuring the beam length at 4 kGy/s, 6 m/min speed conveyor, and 17 cm from the scan window, which are the conditions mostly used in routine processes conducted in this EB facility. A good agreement is found among the FWHM of beam profiles, assessed with the diode (9.7 cm), CTA film (6.6 cm), a standard dosimeter for this type of measurement, and alanine dosimeters (7.1 cm). The differences between the spatial resolution of the dosimeters perfectly justify the small discrepancies found in the FWHM values. It is noteworthy that the overall results presented herein, benchmarked against those assessed with reference standard passive dosimeters for radiation processing dosimetry, not only validate the approach to measure the dose per pass and beam length parameters, but also endorses the reliable performance of this diode-based system as an inexpensive and reliable dosimeter for routine process control.