Recent Results of Experiments with Slow Muons

Abstract

The ratio n₁/n₂ of measured spectral flux densities and, thus, inverse stopping powers S₂/S₁ of negative muons emerging from a MgF₂ and a Au moderator is larger than S₂ ^a/S₁ ^a for a muon energy T less than 10 keV, with S^a obtained from proton atomic S data which are combined in case of MgF₂. Furthermore, n₁/n₂ is larger than the relation of calculated spectral flux densities using S^a values. The deviation increases with decreasing T. This is caused by the lack of decelerating electrons in the MgF₂ insulator which has an energy gap of 11 eV. Negative muons can be used as a surface probe for elemental analysis. An about monoatomic oxygen layer on a Si surface has been detected by characteristic X rays of μ 0 atoms which were formed by the capture of µ with T ≈ 20 eV in 0.