The effect of adsorbed noble gas atoms on muonium formation at the silica surface

Muonium formation on a silica powder surface has been studied while films of noble gases up to a monolayer thickness covered the surface of the powder grains. The fraction of muons stopped in the powder that formed muonium was found to decrease as the surface coverage increased for all the gases investigated. This has enabled muonium formation in the bulk, and at the surface of the grains, to be distinguished and provided the first direct evidence for the formation of muonium atoms at the surface of an insulator.