Time-of-flight spectroscopy of positronium emission from quartz and magnesium oxide

Abstract

The energy distribution of Ps emitted from ${\mathrm{SiO}}_{2}$ and MgO single crystals bombarded by 500--900-eV positrons was measured. For ${\mathrm{SiO}}_{2}$ a nearly monoenergetic component at 3.27(4) is observed and is consistent with a bulk excitonlike Ps emitted from the surface. A broader component of \ensuremath{\sim}1.5 eV full width at half maximum is also observed. For MgO the Ps spectrum is characterized by a high-energy tail extending up to 6--7 eV. Possible models which would explain the MgO results are discussed.