Determination of x-ray tube focal spot position

In x-ray spectral measurement using a semiconductor detector system, accurate positioning of the detector in front of the anode is very important. This needs accurate determination of the focal spot position on the target in an x-ray tube. We present a simple technique to determine the focal spot position accurately. Using a pinhole technique, the focal image made by x rays is overlapped on the target image made by visible rays emitted when filament heating takes places. Both images are made in the same geometry with the tube diaphragm and filter removed.