Positronium deuteride and hydride in MgO crystals

Abstract

Low-temperature positron lifetime and Doppler broadening measurements were made in MgO crystals containing D⁻ or H⁻ ions in order to investigate the temperature dependence of the positron trapping by D⁻ and H⁻ ions and elucidate the possible formation of PsD (PsH) states. Positrons are trapped at D⁻ and H⁻ ions once the oxygen vacancies, which are more effective positron traps, are eliminated by annealing the crystals at high temperatures in a reducing atmosphere. From the temperature dependence of the annihilation parameters the positron trapping coefficients for D⁻ and H⁻ centers were shown to increase with temperature between 100–300 K. The lifetime of the PsD (PsH) state is (650±30) ps and temperature independent. The dissociation rate of the PsD (PsH) state into D (H) and Ps is also temperature independent. No isotopic effect was observed.