BetheHeitlerProzess

Bethe-Heitler process, named after Hans Bethe and Walther Heitler, is the production of an electron-positron pair when a high-energy photon interacts with the electromagnetic field of a nucleus. It is a fundamental gamma-ray interaction in matter described by quantum electrodynamics. The reaction requires photon energy above 1.022 MeV (twice the electron rest mass) and results in an electron, a positron, and a recoiling nucleus. The probability grows with the square of the nuclear charge Z and depends on energy, with corrections from screening by atomic electrons and from nuclear recoil.

In the simplest case the photon converts to a pair in the field of the nucleus, preserving overall energy and momentum with the nucleus absorbing the recoil. The cross section increases roughly logarithmically with photon energy and is enhanced for high-Z materials. There are related processes, such as triplet production, where the interaction occurs with an atomic electron instead of a nucleus, producing an additional recoil electron.

Historically, Bethe and Heitler formulated the cross section for this process in 1934, with subsequent refinements to account for screening effects, higher-order quantum electrodynamics corrections, and nuclear recoil. The Bethe-Heitler process is of practical importance in many contexts: it is a dominant gamma interaction mechanism in dense detectors and calorimeters for MeV to GeV photons, and it plays a key role in the interpretation of astrophysical gamma-ray spectra and in simulations of particle transport in matter.