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Positron and positronium scattering from atoms and molecules

Loreti, A; (2017) Positron and positronium scattering from atoms and molecules. Doctoral thesis , UCL (University College London).

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Abstract

This thesis is concerned with cross section measurements of positron (e+) and positronium (Ps) collisions with atoms and molecules. Total cross sections for (e+ + Kr) and (e+ + H2O) have been measured in the energy range (10 - 300) eV, for the first time in field-free interaction and detection regions, and therefore with a high angular discrimination against forward-elastic scattered particles (FSP) , 2o. The results for Kr show a marginal disagreement in comparison with previous measurements. Above 15 eV, these discrepancies are ascribable to forward elastic scattering, whereas, below 15 eV, additional systematics must be considered. Concerning H2O, the total cross sections are found to be (50 – 100)% higher than previous results obtained with poorer angular resolution. However, agreement between current and previous measurements is obtained once allowance is made for the angular acceptance against FSP of each experiment using theoretical models for the (e+ + H2O) differential elastic cross sections. The Ps beam production efficiency from He, Ar and N2, has been measured in the Ps energy range (1.5 - 65) eV, the main goal of this study being to probe Ps formation, for the first time, at energies below 9 eV for He, 30 eV for N2 and 2.6 eV for Ar. The total cross section measurements for (Ps + He) scattering are also presented and compared with former experiments and theoretical predictions in the energy range (1.9 - 44) eV. This range of energy covers the interval between (2 - 10) eV where outstanding questions remain among theories and where no other measurements are available. The differential positronium formation cross sections near 0o have been extracted, for He and N2 using current and previous available data for Ps beam production and total cross sections. The results are compared with theories, when available and others experiments.

Type: Thesis (Doctoral)
Title: Positron and positronium scattering from atoms and molecules
Event: UCL
Language: English
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: http://discovery.ucl.ac.uk/id/eprint/1554718
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