Playing Games with Positrons
The positron research group is based around two beamlines providing sources of pulsed positrons, with tuneable energy. Positrons come from a 22-Na source, and are then conditioned in two stages, through moderation and trapping. Once trapped, the positrons can be used to form a beam with a variety of research applications.
One of the positron beams is used to study low energy atomic and molecular physics. Positrons are directed through a gas cell containing some target, and single interaction cross sections can be measured. This program of research has both fundamental and applied aims, studying basic quantum mechanical interactions, as well as investigating interactions that are relevant to a better understanding of the processes underlying Positron Emission Tomography (PET).
The second beamline is geared towards the study of material structure. In this case, positrons are temporally compressed before being injected into the target of choice. By measuring the time information associated with the positron annihilation inside the sample, information regarding the size and distribution of defects can be obtained.
This talk will outline the techniques we use for handling positrons to form high energy or time resolution positron beams. I will describe the analysis techniques that are used, including a focus on some of the detector technology, which overlaps with that used in nuclear physics experiments. Examples of measurements covering the various arms of our research program will also be presented. New developments will also be described, which aim to expand the capabilities of the materials beamline through the measurement of the Doppler spread induced in annihilation of positrons with atomically bound electrons.