INSTALLATION OF A KR MODERATOR IN THE HIGH-BRIGHTNESS BEAM AT BRANDEIS

A solid Kr moderator has been installed in the high-brightness beam at Brandeis. Its raw moderation efficiency for the an encapsulated Na-22 source has been found to be as high as 4.0 X 10(-4). The longitudinal energy spread of the re-emitted slow positrons has been measured by a high-resolution (0.1 eV) parallel plane geometry retarding field anal yser comprised of the source plane and a parallel grid and is found to be 2.5 +/- 0.1 eV. This value can be regarded as intrinsic to the pos itron moderation by solid Kr and not an artifact of the energy analyse r. Implications of these measurements with regard to electrostatic foc using of positron beams are discussed.