Editing X-ray (section)

===Production by fast positive ions===
X-rays can also be produced by fast protons or other positive ions. The proton-induced X-ray emission or [[particle-induced X-ray emission]] is widely used as an analytical procedure. For high energies, the production [[cross section (physics)|cross section]] is proportional to ''Z''<sub>1</sub><sup>2</sup>''Z''<sub>2</sub><sup>−4</sup>, where ''Z''<sub>1</sub> refers to the [[atomic number]] of the ion, ''Z''<sub>2</sub> refers to that of the target atom.<ref>{{Cite journal|doi = 10.1016/0370-1573(86)90149-3|title = Review of experimental cross sections for K-shell ionization by light ions|journal = Physics Reports|volume = 135|issue = 2|pages = 47–97|date= 1986| vauthors = Paul H, Muhr J |bibcode = 1986PhR...135...47P}}</ref> An overview of these cross sections is given in the same reference.