Editing Pair production (section)

=== Cross section ===
{{See also|Gamma ray cross section}}
[[File:Electron-Positron nuclear Pair production Feynman Diagram.svg|thumb|[[Feynman diagram]] of electron–positron pair production. One must calculate multiple diagrams to get the net cross section]]

The exact analytic form for the cross section of pair production must be calculated through [[quantum electrodynamics]] in the form of [[Feynman diagram]]s and results in a complicated function. To simplify, the cross section can be written as:
: <math>\sigma = \alpha \, r_\text{e}^2 \, Z^2 \, P(E,Z)</math>
where <math>\alpha</math> is the [[fine-structure constant]], <math>r_\text{e}</math> is the [[classical electron radius]], <math>Z</math> is the [[atomic number]] of the material, and <math>P(E,Z)</math> is some complex-valued function that depends on the energy and atomic number. Cross sections are tabulated for different materials and energies.

In 2008 the [[Titan laser]], aimed at a 1&nbsp;millimeter-thick [[gold]] target, was used to generate positron–electron pairs in large numbers.<ref>{{cite news|title=Laser technique produces bevy of antimatter|url=https://www.nbcnews.com/id/wbna27998860|website=[[MSNBC]]|year=2008|access-date=2019-05-27}}</ref>