P11. Dose verification for high-dose bulk industrial 60Co irradiators with chemical dosimeters and gafchromic media

Abstract

Introduction Dosimetry and dose verification at bulk industrial irradiator facilities is subject to numerous challenges, most notably due to their high volume, high throughput design and operations. Industries such as the Sterile Insect Technique (SIT), a biological control practice for the management of insect pests of agricultural and medical or veterinary significance, rely on annually derived output factors to deliver sterilization doses to organisms within strict parameters. Routine dose verification should therefore constitute an integral part of the quality control system. Materials and methods Two distinct dosimeter types were employed in this study. Firstly a chemical solution, Fricke’s solution made up of 1 mM Fe(NH4)2(SO4)2, 0.8 N H 2 SO 4 , 1 mM NaCl high purity chemicals, decanted in 2 ml ampules, secondly enveloped 1 cm 2 EBT2 radiochromic media sections. Dosimeters were exposed in a reference 60Co field under charged particle equilibrium conditions to incremental doses up to 100 Gy. Dosimeter absorbance measurements were conducted with a diode array spectrophotometer, resolution of 1 nm, at 304 nm and 676 nm for the Fricke and EBT2 dosimeters respectively. Results Dosimeter absorbance unit (AU) readings for the Fricke (0.06–0.35) and EBT2 (0.05–1.36) dosimetry systems were recorded for the dose range 0–100 Gy. Linear dose response relationships were noted for both the Fricke (dose range 20–100 Gy, r 2 = 0.9992 ) and EBT2 (2–100 Gy, r 2 = 0.9868 ) dosimetry systems. The dose–response relationship of the Fricke dosimetry system ( 3.6 × 10 - 3 ± 2.42 × 10 - 5 ) is roughly one order of magnitude lower compared to the EBT2 ( 1.35 × 10 - 2 ± 3.67 × 10 - 4 ) system. Conclusion Both dosimetry systems prove to be reliable dose verification tools for bulk industrial irradiator applications. The Fricke dosimetry system, a primary dosimeter, remains the preferred dosimeter due to its superior linear dose response and higher dose range capabilities.