Search for Positronium Lyman α-Radiation from Positrons Stopped in Inert Gases

Abstract An attempt to detect the positronium Lyman α-radiation at 2430 A is reported. Positrons from an intense 64Cu source (20 Ci) were stopped in high purity A, Ne, and He at pressures ranging from 0.01 to 3.0 atm. Light from the stopping region was collected by a large solid-angle light pipe and directed to a photomultiplier. Spectra were obtained by inserting a series of optical interference filters in front of the photomultiplier. Identical spectra were obtained with an intense electron emitter replacing the 64Cu source. These results indicate that any Lyman α-radiation present at the photomultiplier is masked by a large background continuum associated with gas excitation processes. The data were employed to set an upper limit of 1 in 2000 on those positrons stopping in the gas which result in Lyman α-radiation.