Forward Emission of Positronium from Nanochanneled Silicon Membranes

Positronium beam formation and manipulation are required in several fundamental experiments. Efficient positron/positronium conversion in transmission configuration would offer important geometrical advantages over the reflection one for these applications. A novel type of transmission positron/positronium converters, which consists of silicon membranes with pass-through nanochannels, was produced and tested. The amount of forward emitted positronium was studied as a function of the thickness of the membranes and the nanochannel size. A maximum of, at least, (16 +/- 4)% of positrons implanted in (3.5 +/- 0.5)-mu m-thick membrane with a nanochannel size of 5-8 nm were found to be forward emitted as positronium. A similar maximum amount of, at least, (16 +/- 5)%, was found to be emitted from a membrane (7.7 +/- 1.3)-mu m-thick with a nanochannel size of 7-10 nm. A preliminary evaluation shows that the maximum amount of forward emitted positronium with the entire kinetic energy distribution below 1 eV is, at least, 9% of the positrons implanted in the (3.5 +/- 0.5)-mu m-thick membrane.