Moderator Gratings for the Generation of Epithermal Positive Muons

We studied the effect of surface enlargement on the efficiency of a muon (μ+) moderator by comparing the flux of epithermal μ+ emerging from a solid Ar (s-Ar) layer deposited on a flat Al substrate with the fluxes from an Ar layer deposited on gratings manufactured in Si and Ag substrates. We developed a simple replication technique to emboss a Si grating into a thin Ag foil, where the gratings consist of V-shaped grooves with 20μm depth and ridge distance of 30μm on an area of 30×30mm2. We obtain a gain in epithermal μ+ flux of 1.5 with respect to that of a flat moderator geometry. The 15% reduction with respect to the geometrical enlargement factor of 1.73 is due to μ+ absorption losses in the V-groove walls. The data imply a nearly isotropic angular distribution of epithermal μ+ inside the s-Ar moderator and a reflection coefficient of about 80% for epithermal μ+ impinging on s-Ar.