Improvement of rare-gas solid moderators by using conical geometry

Abstract

A slow positron beam with narrow energy spread can be obtained by moderating the β+ decay of a radioactive source. We report here the improvement in the efficiency of the rare-gas solid positron moderators by using a different geometry. The efficiency for slow positrons, ε, was measured for the cylindrical and the cone configurations of the moderator with the latter yielding ε of (4.6±0.2)×10−3 for solid neon deposited on an encapsulated radioactive 22Na source deposited on a 5 μm Cu98/Be2 window. No corrections were applied for the attenuation caused by the window. The ε for the conical configuration is (2.7 ± 0.2) times higher than that for the cylindrical configuration. Other rare-gas solids (e.g., Ar, Xe, Kr) yielded lower ε as compared to that for the solid neon in agreement with the earlier measured efficiencies of Mills and Gullikson [Appl. Phys. Lett. 49, 1121 <usb>(1986)].