Positron scattering from atoms and molecules at low energies

Elastic and inelastic scattering of positrons by atoms and molecules are st udied experimentally in a new range of positron energies, using a novel tec hnique involving a magnetized beam of cold positrons. Differential cross-se ction measurements are presented for Ar and Kr at energies from 0.4 to 2.0 eV, and they compare well with theoretical predictions. The first low-energ y measurements of the vibrational excitation of molecules by positrons is p resented (i.e., CF4 at energies from 0.2 to 1 eV), and comparison with elec tron scattering data is discussed.