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Radiation Protection Dosimetry 54:267-272 (1994)
© 1994 Oxford University Press
On the Current Status of an ISO Working Document on the Calibration and Type Testing of Radiation Protection Dosemeters for Photons
In October 1992, Working Group 2 'Reference Radiations' of ISO TC85/SC2 'Nuclear Energy/Radiation Protection' officially prepared a first draft of a document with the working title: 'The Calibration of Individual and Area Dosimeters for Photon Radiation and the Determination of their Response as a Function of Photon Energy and Angle of Incidence'. On the basis of existing ISO Standards 4037 'X and gamma Reference Radiations...' and ISO 8963 'Dosimetry of X and gamma Reference Radiations...' and the recent updating of these standards, a first draft of the 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 and some new data pertinent to this future standard are included. While area monitoring instruments are generally calibrated without 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 energy 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 phantom without explicitly laying down suitable phantom materials. With respect to the calibrations free in air practised up to now, the introduction 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 overall uncertainty will be presented for discussion. A question as yet unresolved is incomplete electronic build-up for H(0.07) in the energy range above about 70 keV and for H(10) for the 4-9 MeV photon radiations. This issue cannot only be dealt with in a standard on the procedures for calibration. In some cases it may be desirable to perform calibrations or a determination of response under simplified conditions such as a reduced field size on the phantom surface or by irradiating several dosemeters simultaneously. Criteria on the acceptability of such simplified procedures are presented.