Positronium deuteride and hydride in MgO crystals

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. (author)