Solid neon moderator for producing slow positrons.

Slow positrons can be made by moderating the energetic beta (+) particles from a radioactive source. We find that solid Ne makes a more efficient moderator than any other material known to date. The efficiency, defined as the number of slow positrons per beta(+) emitted by the source, is 0.30% for a flat layer of Ne covering a (22)Na deposit. In a cylindrical geometry, epsilon is 0.70% more than twice the value obtained with the best tungsten moderator. The energy spectrum of the slow positrons has a full width at half maximum of 0.58eV.