POSITRONIUM FORMATION IN LIQUID-NITROGEN AS A FUNCTION OF ELECTRIC-FIELD

The intensity of the orthopositronium component and its lifetime have been measured in liquid nitrogen as a function of electric field. Whil e the lifetime remains constant at about 12.5 ns, the fraction of posi tronium formed is about 20% at zero field and monotonically to an asym ptotic value near 6% as the field is raised to 3.2 MV m-1. The is roug hly exponential with a drop off rate of 2.0 MV m-1. The results are a further indication of the importance of Mogensen's spur mechanism in t he positronium formation process.