Transmitted positron reemission from a thin single-crystal Ni(100) foil.

We have investigated the reemission of positrons from a 1500 angstroms thick unsupported Ni(100) foil irradiated with a collimated beam of positrons of variable energy 0 to 6 KeV. At 5keV (19+-3)% of the positrons emerge with low energy from the transmission side of the foil; ~~55% of the slow positron spectrum is concentrated in a 0.2eV wide peak at 1.1eV. The Ni(100) foil remoderator is as efficient as the W(100) foils investigated by Chen et al. Foils of this type will thus be very useful for brightness enhancement stages using transmission remoderation.