Positron re-emission from electro-deposited NiW

Measurements on re-emitted positrons from electro-deposited NiW show the al loy to be an excellent candidate for the positron moderator in a new genera tion of position beam systems in which hitherto unattainable geometries can be used either to accommodate novel beam designs and/or to generate mole i ntense beams of positrons, After annealing at 1350 degreesC the moderation efficiency of the NiW is found to be similar to8 x 10(-4), comparable to th at commonly reported for polycrystalline W. It emits positrons of energies up to similar to3 eV, a value characteristic of the work-function emission of positrons from W. The re-emitted positron energy spectrum contains featu res characteristic of both Ni and W, suggesting that a degree of surface se gregation takes place on annealing. The remoderation efficiency of the allo y is stable after a decline of approximately 10% in the first two days afte r annealing in situ.