Triplet formation

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The triplet formation is a pair formation , i.e. the formation of an electron - positron pair from a photon ( gamma radiation ), which takes place in the field of a shell electron instead of an atomic nucleus.

During pair formation, momentum is transferred from the photon to the impact partner (“recoil”). While this hardly has any effect on an atomic nucleus during pair formation in the field, the shell electron itself is strongly accelerated because of its much lower mass. The result shows three particles (two electrons and one positron), i.e. a triplet , which are rapidly moving apart.

As a process in competition with pair formation, triplet formation only becomes noticeable at photon energies of the order of 100 MeV.