We observe the emission of slow positive muons (${\mu }^{+}$) from solid neon, argon, krypton, and xenon moderators exposed to a 4.2-MeV incident ${\mu }^{+}$ beam. The time-of-flight spectra for all of the targets studied exhibit a narrow distribution with no delayed component. Energy spectra obtained from the time-of-flight data indicate a maximum below ∼10 eV with a tail extending to higher energies. The data suggest a slowly thermalizing muon emission mechanism, implying a long diffusion length for low-energy ${\mu }^{+}$ in these solids. Of the targets measured, argon was observed to produce the highest yield (∼${10}^{-5\mathrm{}}$ slow ${\mu }^{+}$ per incident ${\mu }^{+}$), providing a useful flux for further experimentation.

• Received 27 April 1987

DOI:https://doi.org/10.1103/PhysRevB.36.8850