Abstract :
Two methods are under study for bunching 15 ns pulses of slow positrons produced by the Oak Ridge electron linear accelerator (ORELA). The first method involves the application of a time-dependent potential to a remoderating foil during the time positrons are being emitted from it. Lifetime spectra of polymer films have been collected with a resolution of 500 ps. The positron flux into the specimen during the pulse was about 3.9 × 1011 /s. A molybdenum moderator foil was used with an ORELA power of 3 kW. The quadratic potential bunching technique is also being considered. In this method a voltage is applied to a string of lenses, such that the potential experienced by positrons contained within the lenses varies as the square of the distance from a point that is defined at ground potential. Calculations indicate that a time resolution of about 200 ps can be achieved with this method.
