Intercomparison of Extrapolation Chamber Measurements of the Directional Absorbed Dose Rate for 204Tl Beta Radiation

Abstract

An intercomparison of directional absorbed dose rates, D'(0.07,α), at radiation protection levels in beta dosimetry was performed by five European laboratories in 1993 and 1994 using extrapolation chambers. For this purpose, a 204 Tl beta ray source with an activity of about 6 MBq, constituent of the PTB Beta Secondary Standard, was sent to the five laboratories for intercomparison measurements. The dose rates, without a beam flattening filter, were determined at a distance of 20 cm for angles of incidence of the radiation, α, of 0° and 60°. In the first stage of the intercomparison some unexpected differences of up to ±5% in the results were obtained. These could be explained by the different methods used by the participants for measuring depth-dose curves. After applying a consistent method, the results of all participants agreed to within ±2%.