Transit dose measurements using alanine and diode-based dosimeters

Abstract

The growing interest in low-dose (< 100 Gy) radiation processing applications has raised concerns about accurately measuring the absorbed dose in irradiated materials. Depending on the irradiator design, the transit time due to the radioactive source movement (or the product itself) until the stable irradiation position might affect the predicted absorbed dose. This work aims to evaluate the transit dose in a 60Co Gammacell 220-Nordion irradiator, which has radioactive sources settled at the bottom of a lead shielding. When the facility is on, the product and the dosimeter are mechanically guided down to the irradiation position, and hereafter the selected exposure time starts to be counted. At the end of irradiation, both product and dosimeter rise to the initial position enabling them to be gathered by the operator. The product is continuously irradiated at different dose rates during its fall and rise movement, preventing the transit dose from being obtained straightforward. The experimental approach adopted is to assess the transit time, and thus the transit dose, using an online diode-based dosimetry system previously calibrated against reference standard alanine dosimeters. The agreement between the transit doses attained with the diode (0.41 ± 0.02) Gy and alanine (0.38 ± 0.01) Gy validates the method herein proposed.