Measurement of the Decay Rate of the Positronium Negative Ion

Abstract

Positronium negative ions ${\mathrm{Ps}}^{-}$ are formed by a beam of 420-eV positrons impinging on a thin carbon film in vacuum. Measurements of the number of ions reaching a grid under different acceleration conditions are used to determine both the ${\mathrm{Ps}}^{-}$ decay rate $\Gamma =2.09\mathrm{}\left(9\right)\mathrm{}$ ${\mathrm{nsec}}^{-1\mathrm{}}$ and its initial kinetic energy $T={13}_{-10\mathrm{}}^{+19\mathrm{}}$ eV. The decay rate is in good agreement with a recent calculation by Ho.