Comparison of graphite-to-water absorbed-dose transfers for Co photon beams using ionometry and Fricke dosimetry

To derive the absorbed dose to water from a standard of absorbed dose to graphite, the metrology laboratories which apply such a method usually make use of cavity ionization chambers as transfer instruments. In addition, the BNM-LPRI has tested, as such instruments, two types of Fricke dosimeter in its cobalt-60 beam. The two procedures are compared and their results are found to be in good agreement (the difference is less than 0.1%). Both procedures are then taken into account for the calculation of the reference value of absorbed dose to water.