Low-energy photoionization cross sections from proton-induced x-ray spectroscopy

It is shown that photoionization cross sections in the soft-x-ray region can be determined accurately with proton-induced x-ray spectroscopy. A film of the absorber is evaporated onto a substrate. The characteristic substrate radiation, generated with a proton beam, is measured with and without the absorber. The ionization cross section can then be calculated after a small and often negligible correction is made for the intensity change of the substrate radiation due to the energy loss of the proton beam passing through the absorber.