Thermally desorbed positronium from a clean and oxygen-covered Mo(110) surface

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Abstract
In a study of neutron-irradiated Mo containing voids, Schultz et al. [Phys. Rev. Lett. 44, 1629 (1980)] presented data which showed a small fraction of positronium atoms being formed in the voids and decaying by three photons. This effect was observable at temperatures above ≊650 K. It was stated at that time that the positronium may be forming through the same type of high-temperature positron desorption mechanism that had previously been observed for various metallic surfaces with the use of low-energy positron beams. In this Brief Report we show that the temperature at which thermal positronium is activated from a clean Mo(110) surface is 1000 K, which decreases significantly with adsorbed oxygen contamination. These results are consistent with the previous conclusions if the Mo voids were covered with oxygen.