The annihilation of positrons in pure elements and chemical compounds

The angular correlation between annihilation quanta due to the decay of positrons in eleven different materials has been measured with anthracene scintillation counters. The materials studied were, the pure elements, Mg, S, Cu, Sn, Pt, and Hg, and the chemical compounds LiCl, KCl, CsCl, KF, and KI. Calculations were performed to determine the effect of the geometry on the shape of the angular correlation curves. The effects of scattering were also investigated. The apparatus was tested by means of measurements on the γ-rays of Co⁶⁰ and Zn⁶⁵. The centre of mass momentum distributions of annihilating pairs in copper, platinum and possibly mercury were found to be exponential in character and the mean centre of mass momentum obtained for copper was found to be in reasonable agreement with the results obtained by DeBenedetti and coworkers and by P. E. Argyle. The momentum distributions for the other materials were not found to be of a simple exponential form. The results suggest that there is a relation between the shape of the distribution curve and the outer electronic structure of an atom.Science, Faculty ofPhysics and Astronomy, Department ofGraduat