Standardization of reference radiations

The response of a radiation measuring device as a function of energy is a convolution of the absolute response as a function of energy and the spectral characteristics of the radiation used for calibration. Therefore, a direct inter-comparison between measurements made at different laboratories requires the radiation qualities to identical and the dosimetry of the radiations to be performed under precisely known and reproducible conditions. Radiation beams may be characterized by their attenuation properties (half-value layer in a specified material) or better still spectral distributions. Unfortunately, similarity of attenuation characteristics does not necessarily guarantee similarity of spectral distribution. Additional measurements of successive half-value layers will provide further information, but the quantitative differences between radiation beams may remain elusive. In fact the same half-value thickness characteristic (but different spectral composition) can be produced by beams of entirely different applied potentials and filtration. The filtration can be quite different in both thickness and type of material. In some cases experimental data is presented without any reference to the half-value layer equivalence, spectral distribution or method of production. This makes comparison of experimental results impossible and produces disagreement between manufacturers published data and the results obtained by testing laboratories. Therefore, irrespective of the subsequent methods used to characterize the beams by measurements, in order to achieve identity, agreement should be reached on the parameters of beam production