ON THE CURRENT STATUS OF AN ISO WORKING DOCUMENT ON THE CALIBRATION AND TYPE TESTING OF RADIATION PROTECTION DOSIMETERS FOR PHOTONS

In October 1992, Working Group 2 'Reference Radiations' of ISO TC85/SC 2 'Nuclear Energy/Radiation Protection' officially prepared a first dr aft of a document with the working title: 'The Calibration of Individu al and Area Dosimeters for Photon Radiation and the Determination of t heir Response as a Function of Photon Energy and Angle of Incidence'. On the basis of existing ISO Standards 4037 'X and gamma Reference Rad iations ...' and ISO 8963 'Dosimetry of X and gamma Reference Radiatio ns ...' and the recent updating of these standards, a first draft of t he new working document has been prepared. An overview of its contents is presented, an account of some of the topics as yet open is given a nd some new data pertinent to this future standard are included. While area monitoring instruments are generally calibrated without a phanto m, individual dosemeters usually require a phantom which, in terms of its radiation transport properties, simulates the human body. Phantoms are now available whose backscatter factor over the relevant photon e nergy range is within 1 or 2% of that of the reference phantom made of four-component ICRU tissue substitute material. This lends support to the idea of stipulating certain physical properties for a suitable ph antom without explicity laying down suitable phantom materials. With r espect to the calibrations free in air practised up to now, the introd uction of a phantom into future calibration procedures gives rise to a number of additional sources of uncertainty. These are considered in some detail and an attempt is made to give a realistic estimate of the magnitude of these uncertainties. Upper limits for an acceptable over all uncertainty will be presented for discussion. A question as yet un resolved is incomplete electronic build-up for H(0.07) in the energy r ange above about 70 keV and for H(10) for the 4-9 MeV photon radiation s. This issue cannot only be dealt with in a standard on the procedure s for calibration. In some cases it may be desirable to perform calibr ations or a determination of response under simplified conditions such as a reduced field size on the phantom surface or by irradiating seve ral dosemeters simultaneously. Criteria on the acceptability of such s implified procedures are presented.