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Abstract

The accurate determination of the measuring volume is one of the most important conditions for the verification of the roentgen dose unit by means of a standard ionization chamber. The realization of this demand was discussed in detail and the importance of several controls of the size of the diaphragm cross section and the length of the electrode was pointed out, based on experiments made by the authors. It is possible that the beam used for the measurements is not homogeneous enough, making the results dependent on the size of the diaphragm and causing wrong results, when secondary standards or dosemeters are calibrated. This is particularly true if there are needed high dose rates with short focus distances. The authors' experiments also point out the importance of the diaphragm close to the focus. It was concluded that a standard chamber mast be equipped with diaphragms of different sizes of cross section and particularly chambers for the determination of soft radiation doses should also be equipped with electrodes of different lengths, both being easily interchangeable without changing the position of the chamber