Near-threshold structure in the atomic K-shell spectra for ionisation by photons or fast charged particles

Spectra of the optical and generalised oscillator strength for the K-shell ionisation of all free atoms with Z or=8. This is in sharp contrast to the hydrogenic result, according to which the spectral strength for every shell monotonically decreases with the kinetic energy. The magnitude of the near-threshold structure sometimes amounts to 30%. A partial interpretation of the structure is given and consequences of these results to applications such as electron energy-loss spectroscopy and stopping-power calculations are pointed out.