Generation of Thermal Muonium in Vacuum

Abstract

We find that thermal-energy muonium atoms are emitted from a clean hot tungsten foil in which positive muons are stopping near the surface. The temperature dependence of the thermal-muonium signal yields a surprisingly low activation energy of 0.66(4) eV, suggesting that we are observing the thermionic emission of muonium from the solid. The total muonium yield at 2300 K is about 0.04 per stopped muon of 23 MeV/c initial muon momentum. A number of new experiments should be possible using this unique source of thermal muonium in vacuum.