A Positronium Beam and Positronium Reflection from LiF

Abstract

At the Brookhaven National Laboratory we have constructed a positronium (Ps) beam by transmitting monoenergetic, low energy positrons through a gas cell containing either Ar or He which provide an electron to form positronium. A description of the positron beam and of the Ps formation mechanisms are found in these Proceedings (see M. Weber, et al. and B. L. Brown). The positrons were obtained by magnetically deflecting positrons in the straight section of the positron beamline (see Fig. 1) into a beamline which contained the gas cell and a Ps detection chamber. By having two beamlines we are able to switch from an experiment which uses positrons (a study of the angular correlation of annihilating radiation--ACAR) to one which uses Ps atoms without breaking vacuum, nor moving equipment. This, however, put a constraint on the placement of the Ps beamlíne because it could not interrupt the annihilation gamma ray in its long flight from the target chamber to a gamma ray position imaging detector (Anger camera). At present this constraint has resulted in a degradation of the positron beam intensity and energy resolution in the Ps beamline. Efforts are presently underway to eliminate this problem.