A technique for measuring the variation of photon spectrum from X-ray generators over the mains voltage cycle

The variation in current and accelerating voltage across an X-ray tube, that occurs over the mains voltage waveform cycle, produces changes in photon flux and spectrum shape. A knowledge of these changes is required to provide an understanding of the parameters affecting X-ray output. Variation in the photon flux will cause distortion of a measured 'mean' spectrum if the dead time of the spectrometry system employed varies over the waveform cycle. A system has been developed that enables the spectrometer to be synchronized to the mains voltage cycle so that variations in photon flux and the instantaneous spectra at selected parts of this cycle can be measured. The variation in photon flux is dependent upon the type of power supplies (both high and low tension). the tube current and the degree of filtration employed. Examples are given of the ripple of photon output due to the voltage and current ripple for a nominally constant potential generator and a half-wave rectified type. The way in which they interact to produce the measured variation is shown.