A RECTIFYING TUNGSTEN-MOLYBDENUM FOIL FOR POSITRON REMODERATION

We report the use of a layered foil as a positron rectifying device fo r transmission geometry positron moderation and remoderation, thereby increasing the efficiency of such devices, Positron transmission throu gh foils consisting of a 10 nm W layer on top of a 100 nm Mo foil has been measured. The measurements are compared with similar results for a 100 nm W foil. A strong rectifying effect with a forward to reverse current ratio of more than 10 is observed making this type of; well ma tched layered foils an, obvious candidate for positron remoderation, R etarding energy spectra of the transmitted positrons were obtained and measurements of Doppler broadening and surface branching ratios were performed to further characterize the foils, The obtained transmission results again reveal the discrepancy in positron implantation profile s for thin foils between experiments and existing theory. (C) 1997 Ame rican Institute of Physics.