[en] In recent years, a new technique to detect the characteristic X-ray from projectile ions in accelerator mass spectrometry has been developed. When bombarding a target with heavy ions, characteristic X-ray from these ions and from the target element(s) are emitted, from which it is possible to analyse the element of the projectile ions. If the mass of the ions are known, the isobars can be identified, which is important for heavy isotope analysis and ion beam impurity analysis. To optimize the X-ray yield, the ion velocity and target composition must be well chosen. This can be achieved if the experiment is done in the velocity domain where the formation of quasi-molecules is the main process for X-ray production