Surface interactions of muonium in oxide powders at low temperatures

Abstract

Measurements of muonium (${\ensuremath{\mu}}^{+}{e}^{\ensuremath{-}}$) spin relaxation in finely powdered samples of ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, MgO, and Si${\mathrm{O}}_{2}$ indicate that the muonium atoms escape the powder grains with a high efficiency, regardless of the ambient temperature of the powder. In ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ powder in a pure He (or Ne) atmosphere at low temperature ($T<30$ K), the muonium spin relaxation rate is proportional to the fraction of the powder surface area not covered by adsorbed He (Ne); it is postulated that a He (Ne) film on the powder surfaces protects muonium against depolarizing collisions with the bare ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ surfaces.