In this paper we reexamine an old idea of using an electric-field-assisted moderator (FAM) based on a rare-gas solid (RGS) to form intense low-energy positron beams. Contrary to common belief, the main body of a successful FAM should consist of a dirty (a high level of molecular impurities) RGS which will allow for a high e(+) drift velocity. On top of this layer is condensed a thin layer of a highy-purity RGS. When the e(+) enters this latter region its energy will heat up, and e(+) emission into vacuum will become possible despite a positive e(+) affinity of the RGS. Simple calculations show that the e(+) intensity can be increased by a factor of 100 over what can be achieved using a RGS moderator without an applied electric field and, equally important, the e(+) transverse energy is reduced to less than 0.3 eV. This leads to a gain in brightness by a factor of 1000. [References: 19]
展开▼
