Generation of slow positive muons from solid rare-gas moderators

Abstract

We observe the emission of slow positive muons (${\ensuremath{\mu}}^{+}$) from solid neon, argon, krypton, and xenon moderators exposed to a 4.2-MeV incident ${\ensuremath{\mu}}^{+}$ 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 \ensuremath{\sim}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 ${\ensuremath{\mu}}^{+}$ in these solids. Of the targets measured, argon was observed to produce the highest yield (\ensuremath{\sim}${10}^{\ensuremath{-}5}$ slow ${\ensuremath{\mu}}^{+}$ per incident ${\ensuremath{\mu}}^{+}$), providing a useful flux for further experimentation.