Development of a cone-geometry positron moderator

Abstract

Results are presented on a new cone-shaped positron moderator which shows a high moderator efficiency (i.e., conversion of beta decay to emitted slow positrons). The moderator efficiencies for the cone moderators studied were found to be up to 0.14% compared to thin-foil measurements of 0.06% in the same experimental system including identical source and holder. These moderators are rugged and easily fabricated, however, they have a lower brightness than single-crystal foil moderators. Comparison of various geometries is presented as well as suggestions for further improvements to increase the total efficiencies.

Spatial profiles of positrons injected at low energies into water: influence of cross section models

“…Even in a device perfectly engineered for CF 4 trapping, some advantage might be gained by using a tungsten moderator, which provides much narrower positron energy distributions than solid neon [2,38,57]. Increasing the trapping efficiency in this way comes at the cost of the primary beam intensity, so one must consider several parameters simultaneously when evaluating such options.…”

Energy distribution and adiabatic guiding of a solid-neon-moderated positron beam

“…As shown in in figure 1, the sealed 22 Na radioactive source (activity ∼6 mCi 2 ) is placed next to a gold-plated Cu coneshaped cap (figure 2). The cone and source are attached to the second stage (∼8 K) of a cryo-cooler by a sapphire washer which provides good thermal conductivity and electrical insulation.…”

“…tungsten, copper or nickel) [9][10][11][12] and thin layers of a rare-gas solid at cryogenic temperatures [13][14][15][16][17]. The major difference between metal and rare-gas moderators is that metals provide better energy resolution than the solid rare gases [18], but rare gases are more efficient [19][20][21][22]. Solid neon has been found to have the highest efficiency of any moderator developed to date.…”

“…The combination of a 22 Na radioisotope source and solidneon moderator is very well suited for operation with buffer-gas positron traps (BGT). In this case, positrons with appreciable energy spread (e.g.…”

High resolution positron-annihilation spectroscopy with a new positron microprobe

“…Further efforts will concentrate on the improvement of the alignment and the reduction of the diameter of the positron beam. An additional improvement is expected by the use of a cone shaped hole in the tungsten plate as proposed by Lynn et al 18 An appreciable increase of the beam intensity is expected from both activities. Moreover, a more brilliant source of a positron emitter with a shorter halflife ͑e.g., 74 As͒ may be used.…”