A simple filter method for measuring peak voltage and inherent filtration of pulsating potential X-ray machines

A simple filter method is described for determining peak tube voltage and inherent filtration of single- and two-pulse X-ray units. Because this method is for use in the routine control of dental X-ray machines, low voltages must be measured and aluminium was chosen as a filter material. An ionization chamber is fixed to the filter holder behind the changeable Al filter discs. The ratio of dose rates measured without an additional absorber and with a 3.2 mm Al absorber yields the inherent filtration if the voltage is known. The voltage is deduced from the ratio of dose rates measured with 3.2 mm and 9.6 mm Al absorbers. Calibration curves were measured using a self-rectified X-ray unit with a Be-window that has virtually no inherent filtration and adding Al discs in front of the exit window. The tube voltage was measured with a Ge(Li) detector and multichannel analyzer. The use of these curves to evaluate voltage and inherent filtration from the measured dose rate ratios is described. (author)