[en] The effects of radiation source fluctuations and void distributions and fluctuations on void fraction determinations in two-phase-flow systems employing the radiation transmission technique are presented. These fluctuations and distributions result in an error which varies in a different manner with the amplitudes of the fluctuations. The variance of the probability density function of the error is independent of void fluctuations, but decreases with measurement time-intervals while the peak is determined by the distribution pattern but shifts with void fluctuation. (author)