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 ϳ2.5 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. [S0031-9007 (98)05357-5]

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