Muonium emission andreaction on platinum and gold powder surfaces revealed by MuSR

Muonium has been observed in powdered platinum (30 nm diameter) andgold (100 nm diameter), respectively, placed in vacuum by the muonium spin rotation (MuSR) technique at ambient temperature. Upon introducing gaseous oxygen up to 23 Torr into platinum powder, the muonium signal was eliminated, indicating that the observed muonium stays outside the platinum particles. The result on the platinum surface treated by hydrogen but exposed to oxygen gas suggests a reactive collision between muonium andoxygen adsorbed atomically on the surface.