Production and use of low-energy,monoenergetic positron beams from electron LINACS

Low-energy intense positron beams derived from pair production can be made at high-energy electron linacs and such beams are in operation or under installation at several linac facilities. Using a pulsed position beam made at a 100 MeV electron linac, we have measured the intensity and velocity distribution of positronium emitted from materials by measuring the time-of-flight of annihilating positronium. The time-of-flight data are augmented by positron lifetime and angular correlation measurements performed with the beam. Positronium spectra have been measured for a number of metallic samples. Several new observations have been made including details of the energy distribution of positronium emission formed by a thermalized positron and a conduction electron and the production of positronium from energetic positrons scattered out of the sample.This paper is based upon an invited talk given by R.H.H. at the International Symposium Production of Low-Energy Positrons with Accelerators and Applications Justus-Liebig-Universität Giessen, FRG (25–27 September, 1986)