With the investment in the new QUADRA7 X-ray inspection system, the question of the limits of what can be detected was posed. It would have been easiest to take the manufacturer’s specifications from the marketing documents, but this did not meet our own quality requirements. Research showed that there is no valid international standard available for the measurement of very small focal spot sizes in X-ray tubes. The current standard for industrial X-ray machines, DIN EN 12543-5:1999-12, is only valid for focal spot sizes down to a minimum of 5µm.
Why does the size of the focal spot matter at all ? The resolution of X-ray machines depends, among other things, on the size of the focal spot (see below). Thus, X-ray images show areas of blurring due to the finite extension of the focal spot. If two objects come closer and closer to each other, these areas of blurring will eventually prevent the two objects from being clearly detected as separate objects.
In order to measure the focal spot size in the new QUADRA7, tests were therefore carried out together with specialists from the Federal Institute for Materials Research and Testing (BAM, Berlin), using the new NanoXSpot target (see below) which represents the basis of the new draft for the standard. The evaluation of these measurements and its results will be discussed in one of the next contributions.