Positron production in tungsten crystals by 1.2-GeV channeling electrons

The efficiency of positron production by a 1.2-GeV electron beam incident on a tungsten single crystal oriented in an axially channeling condition has been experimentally studied. Positron yields from a 1.2-mm-thick crystal have been measured to be similar to 2.5-3.0 times larger than those from amorphous targets with the same thickness. A simple model simulation of the positron production process shows that coherent bremsstrahlung, as well as channeling radiation, contributes to the enhancement of the positron yields.