Characterization of ion chambers set for different metrological applications

Abstract

In this work, the standard dosimeters for radiotherapy, protection and X-ray dosimetry of the National Institute of Standards (NIS)-Egypt were standardized for metrological application. A set of standard dosimeters composed of 0.3, 0.6 and 30 cm3 ion chambers and NPL, Unidose electrometer was used for charge collection within the used chambers. Different beam qualities such as 60Co, 137Cs and X-ray machines were used as reference beams. The ion chambers and electrometers are traceable to SI units through the calibration at the BIPM every five years. The calibration factor drift of each chamber in air and water was determined and the full uncertainty budget of gamma doses at the reference condition was reported in accordance with the international protocols. Commissioning of the 60Co machine was performed and a comparison between the measured doses and the calculated doses was obtained for one half-life of 60Co. The data showed the high performance of the secondary standard dosimeter of NIS for calibration and metrological application in radiation therapy, protection and the X-ray range. The drift in the ion chamber calibration factor over the course of 2 decades is 0.12, 0.001 and 0.11 respectively, which extracted a ratio of 20%, 0.12% and 10.6% from the combined uncertainty.