Low-energy positron scattering from atoms and molecules using positron accumulation techniques
نویسندگان
چکیده
Positron scattering from atoms and molecules is studied at low values of incident positron energy. The experiments use a cold magnetized positron beam formed in a positron accumulator. A discussion of positron scattering in a magnetic ®eld is presented along with dierential cross-sections (DCS) for positron±atom collisions and positron± molecule total vibrational excitation cross-sections. Absolute values of the DCS for elastic scattering from argon and krypton are measured at energies ranging from 0.4 to 2.0 eV. The ®rst low-energy positron±molecule vibrational excitation cross-sections have been measured (i.e., for carbon tetra ̄uoride at energies ranging from 0.2 to 1 eV). Using information gained from these experiments a second generation scattering apparatus is described, which was designed and built speci®cally for scattering experiments using a magnetized positron beam. This apparatus has a number of improvements, including an order of magnitude higher throughput, better energy separation between elastic and inelastic scattering events, and improved measurement of the absolute pressure of the test-gases. Analysis techniques for the data taken in these experiments using a retarding potential energy analyzer and possible extensions of these experiments are also discussed. Ó 2000 Elsevier Science B.V. All rights reserved. PACS: 34.85.+x; 41.75.Fr; 34.50.-s; 34.50.Ez
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