Progress with Positron Beams for Atomic Collisions

Abstract

Positron collision studies at low energies using beams of slow positrons below 1 keV appear to have been limited to the following: an unpublished thesis by Cherry1 on secondary electron emission from surfaces under positron bombardment; and two published papers on the e+ - He scattering cross sections by Costello et al.2 and ourselves3. In a second publication of Costello et al.4 they discuss experimental evidence in favour of postulating a negative work function for slow positrons escaping from a metal surface. In the period 1965 to the present there have been several other attempts by various groups to produce slow positron beams, most of them unsuccessful and unpublished. The more recent work by McGowan and his coworkers and by ourselves has all been directed at obtaining a satisfactory beam of slow positrons for atomic collisions or at studying the characteristics of the beam, partly with a view to obtaining a better beam, and partly so as to understand the slow positron emission process about which we shall make some statements in what follows.