School Seminar Program

Studies of positron scattering processes from simple targets

Ms Tamara Babij
Plasma Research Laboratory, RSPE, ANU

Positron scattering is useful in the investigation of positron interactions with atoms and molecules, which in turn helps with the classification of fundamental quantum processes. Methods for measuring absolute positron scattering cross sections on the ANU positron beamline are discussed, as well as measurements made at the University College London positronium beamline. By measuring these cross sections for simple targets and comparing to theory, the hope is to provide benchmark cross sections that can be expanded to experimentally inaccessible targets.

This talk will focus on three key experimental topics, the first of these is positron and positronium scattering from neon with an emphasis on absolute cross section measurements for comparison to the latest theory.

The second topic concerns quantum correlations in the scattering process. The Wannier law predicts a strict escape geometry for low energy positron and electron escape from a residual ion, allowing for a classical theoretical treatment dependent only on the long range Coulomb interactions of the particles. This Wannier law has been confirmed for the electron impact case, In this talk I will present the first near threshold ionization results for positron impact ionization.

Also discussed will be the development of a positron reaction microscope apparatus. This experiment aims to obtain measurements resolvable in both energy and angle, in order to reconstruct the momentum distribution of the scattering event, providing a fully kinematic reconstruction.  This type of measurement has not been successfully performed for positron impact to date, despite notable successes with electron and photo projectiles, due (mostly) to a lack of sufficiently intense and mono-energetic positron beams. The latest results using the apparatus at ANU will be presented.

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