The Three-Photon Annihilation of Positrons and Electrons [Thesis]

The three-photon annihilation of positrons and electrons has been investigated experimentally by means of a triple coincidence technique. Three Nal(Tl) scintillation counters in coincidence were used to study the occurrence of the triplet annihilation process when positrons annihilate against the electrons within solids, liquids, and liquefied gases. The annihilation rates in aluminum, liquid nitrogen, and liquid Freon-12 (CCl₂F₂) were compared with the theoretical predictions made under the assumption that free positron-electron pairs produced all annihilation events; experiment and theory agreed within the experimental error. The formation of stable ortho-positronium in Freon-12, SF₆, N₂, H₂, and He was verified and its comparative stability in these gases measured. The spectra of the annihilation rays from ortho-positronium were measured to demonstrate that energy and momentum are conserved in the three-photon annihilation process.