Production of a fully spin-polarized ensemble of positronium atoms

Long-lived |m|=1 positronium (Ps) atoms are produced in vacuum when high density bursts of positrons with net polarization p{0} are implanted into a porous silica film in a 2.3 T magnetic field. We observe a decrease in the |m|=1 population as the density of the incident positron beam is increased due to quenching interactions between oppositely polarized Ps atoms within the target. Saturation of this density dependent quenching indicates that the initial positron spin polarization p{0}=28+/-1%, and demonstrates the long term (10{2} s) survival of positron polarization in a Surko-type buffer gas trap. We conclude that, at high Ps densities, the minority spin component is essentially eliminated and the remaining Ps is almost entirely (approximately 96%) polarized, as required for the formation of a Ps Bose-Einstein condensate.