A monitor for measuring X-ray beam intensities

Measurements of the intensity of diffracted X-rays are usually expressed as a fraction of the intensity of the incident beam. Such measurements become difficult when fluctuations of the mains voltage and frequency cause variations in the intensity of the incident X-ray beam. This problem is solved by the use of the present monitor in which the incident X-rays produce ionization in a short length of their normal path and the ions so produced are used to measure the intensity of the X-rays at the same time as they are being diffracted. The ionization current operates a Wheatstone bridge circuit and the indicating galvanometer operates a photocell system so that the steady rate of movement of the galvanometer is recorded. This is taken as the measure of the incident X-ray intensity and the accuracy of the measurement is about 1%.