A technique used in atomic physics to study the structure and dynamics of atomic ions of any element in any state of ionization. For this purpose, a beam of fast ions is sent through a very thin foil. The ion-foil interaction shakes up the electronic shells of the projectile and, after leaving the foil, the ions shed surplus energy by emitting photons, and sometimes electrons. The energies and intensities of these particles yield spectral information on the projectile.