Moderator gratings for the generation of epithermal positive muons

We studied the effect of surface enlargement on the efficiency of a muon (mu (+)) moderator by comparing the flux of epithermal mu (+) emerging from a solid Ar (s-Ar) layer deposited on a Rat 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 g-rating into a thin Ag foil, where the gratings consist of V-shaped grooves with 20 mum depth and ridge distance of 30 mum on an area of 30 x 30 mm(2), We obtain a gain in epithermal mu (+) flux of 1.5 with respect to that of a Rat moderator geometry. The 15% reduction with respect to the geometrical enlargement factor of 1.73 is due to mu (+) absorption losses in the V-groove walls. The data imply a nearly isotropic angular distribution of epithermal mu (+) inside the s-Ar moderator and a reflection coefficient of about 80% for epithermal mu (+) impinging on s-Ar. (C) 2001 Elsevier Science B.V. All rights reserved.