An attempt to detect the positronium Lyman alpha spectral line

Abstract

The possibility of optical radiation from the 2 p states of positronium is discussed, and an experimental attempt to detect the positronium Lyman α line is described. Photomultipliers were used in the attempted detection. Initially filters, and later a quartz monochromator, were employed as the dispersive elements. Positrons from a radioactive source were stopped in various inert gases, and the total optical signal was recorded by counting circuitry with an automatic system that eliminated background and sensitivity variations. It was estimated that if 1 in 1000 of the positrons stopped in the gas gave rise to a Lyman α emission, then a signal would have been obtained which would be about four times the observed standard deviation in the background counting rate. This peak was not observed, although light from excitation of the target gas was detected. These results are compared with the findings of other workers, and the possible reasons for these negative results are examined.