Annihilation gamma-ray spectra from positron-molecule interactions

Abstract

We report measurements of annihilation gamma-ray spectra from the isolated two-body interaction of room-temperature positrons with a range of chemical species. The Doppler broadening of these spectra provides information about the wave functions of the annihilating particles. For a variety of hydrocarbons, we observe linewidths of approximately 2.2 keV (FWHM), while for perfluorocarbons the widths are approximately 2.8 keV, as compared with 1.7 keV for molecular hydrogen. The implications of these results for a number of physical problems are discussed.