Determination of the radiation chemical yield (G) for the Fricke chemical dosimetry system in photon and electron beams

Historical data for the Fricke G-value in photon and electron beams are reviewed and the results of recent measurements carried by the Ionizing Radiation Standards group at the National Research Council are reported. Good repeatability was obtained for G(Fe3+) in a Co-60 beam compared to the previously\u2013obtained value at the NRC (agreement within the combined standard uncertainty for results obtained more than ten years apart). The first data reported in decades have been obtained for kV x-rays beams, and these show a significantly higher value than given in the literature. Measurements for two kV x-ray beams at NRC (different effective energies and kerma rates) were consistent within their combined standard uncertainties Based on the Co-60 and kV x-ray results, a value for G(Fe3+) for the mean energy of Ir- 192 was determined to be 1.589 \ub1 0.009 \u3bcmol J-1 (at a reference temperature of 25 \ub0C) and this will be used in the development of a Fricke-based standard of absorbed dose to water for HDR brachytherapy. The G-value for high energy electron beams (> 15 MeV) was measured to be 1.620 \ub1 0.006 \u3bcmol J-1 (@ 25 \ub0C), which was found to be consistent with literature values and also with NRC data for high-energy photon beams. This electron beam G-value is required to develop an absorbed dose to water standard for megavoltage (linac) electron beams.Peer reviewed: YesNRC publication: Ye