Dependance of the Biological Effect on Radiation Frequency
For the purpose of radiation protection it may be sufficient to calculate the relative biological efficiency (RBE) of fast electrons as 1. Numerous investigations, however, indicate that biological effect of fast electrons produced by modern particle accelerators (e. g. Betatron, linear accelerator) in most cases is lower than the effects of conventional X-rays or 60Cogamma-rays. The difference varies between the biological objects and according to the reaction involved. Some authors try to explain the lower RBE of electrons by the difference of the spatial distribution of ionizations produced within the cells. Others consider that the lower RBE is caused by the fact that electrons of the accelerators mentioned are produced in the form of short radiation pulses of some microseconds (ultrafractionation) followed by relatively long pauses. Several experiments were carried out to investigate the influence of ultrafractionation. However, in some of these publications the various physical parameters were not always correctly interpreted: for example the frequency of radiation pulses, the pulse/pause-ratio, the dose per single pulse, the total absorbed dose, the average dosage rate and the time of irradiation respectively. The greater part of the ultrafractionation experiments mentioned is based on “stroboscopc” methods.
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