2009 Advanced Laboratories Conference Abstract Detail Page
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||This experiment attempts to explore several features of positron-electron annihilation. One of the attractive aspects of e+-e- annihilation is the relative simplicity of the interaction. To first order, the two-body system decays into two back-to-back photons, each carrying an energy of mec2. This feature has provided the basis for a medical imaging technique called Positron Emission Tomography (PET). PET is often used in conjunction with other tomographic techniques, such as MRI, to image potentially cancerous tumors in which exploratory surgery is particularly hazardous. In condensed matter, the interactions between positronium and the substrate can provide information about the details of the substrate structure via the effects on the momentum distribution at the instant of annihilation. The angular distributions measured in this experiment will be used to estimate the typical momenta associated with these systems. This is not quite trivial because the angles are typically of the order of a few milliradians(fractions of a degree).
The source for positrons in this experiment is a radioactive source, Na-22, with an activity of about 5 µCi. Na-22 has a half-life of 2.6019 years and decays with the release of 2,842.3 keV of energy. In 90.3% of the decays a ß+ is emitted with a 545.7 keV maximum kinetic energy followed by a 1,274.5 keV gamma-ray transition to the Ne-22 ground state. Approximately 0.06% of the time, the ß+ emission bypasses the excited state and directly transitions to the Ne-22 ground state. About 10% of all decays proceed by electron capture instead. The total energy budget is satisfied by including the 511.0 keV rest mass energy carried off by the sodium valence electron that is now unbound.
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||Session V - Parallel Workshops
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University of Michigan