Positron and Positronium in Al_2O_3 nanopowders

摘要

Software that allows fitting positron lifetime (LT) and coincidence Doppler broadened (CDB) positron annihilation spectra of nanodispersed dielectric powders is developed. Computer program takes into account following effects: possibility of e~+ trapping by vacancy-type defects, formation of the surface-bound e~+ states, formation and thermalization of Ps atoms in inter-granular space. In order to test the developed software, lifetime and coincident Doppler broadened spectra of Al_2O_3 nanopowders with different grain sizes are acquired. Suggested physical model of the processes involved gives self-consistent interpretation of the spectra. Parameters of the thermalization kinetics of Ps and its ortho-para conversion due to presence of O_2 molecules adsorbed on the crystallite surface are obtained.