Moderator gratings for the generation of epithermal positive muons

We studied the effect of surface enlargement on the ef®ciency of a muon (m‡) moderator by comparing the ¯ux of epithermal m‡ emerging from a solid Ar (s-Ar) layer deposited on a ¯at Al substrate with the ¯uxes 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 20 mm depth and ridge distance of 30 mm on an area of 30 30mm2. We obtain a gain in epithermal m‡ ¯ux of 1.5 with respect to that of a ¯at moderator geometry. The 15% reduction with respect to the geometrical enlargement factor of 1.73 is due to m‡ absorption losses in the V-groove walls. The data imply a nearly isotropic angular distribution of epithermal m‡ inside the s-Ar moderator and a re¯ection coef®cient of about 80% for epithermal m‡ impinging on s-Ar. # 2001 Elsevier Science B.V. All rights reserved