Positronium in low temperature mesoporous films
Abstract
We investigate the formation and annihilation of ortho-positronium atoms (o-Ps), the spins parallel electron (e-) -positron (e+) bound state, in mesoporous films from 400to50K . At room temperature up to 20% of the implanted e+ end up as o-Ps which self-annihilates (the bound e+ and e- annihilate); this is 50% of the formed o-Ps. One would expect self-annihilation to be suppressed at lower temperatures since, although o-Ps trapped in pores of diameter ϕ>1nm , found in these films, is more likely to self-annihilate, several effects could decrease o-Ps formation and/or o-Ps trapping in a pore. Instead we find that at 50K the amount of e+ ending up as self-annihilating o-Ps is up to 19% greater than predicted if no suppressing effects played a role. Copious amounts of o-Ps atoms self-annihilate at 50K (up to 30% of implanted e+ , 75% of formed o-Ps). This amount was found to increase even further down to 10K making these films ideal substrates in which to confine large amounts of collisionally cooled, self-annihilating o-Ps for the eventual realization of an o-Ps Bose Einstein condensate (BEC).
- Publication:
-
Physical Review B
- Pub Date:
- May 2005
- DOI:
- 10.1103/PhysRevB.71.180102
- Bibcode:
- 2005PhRvB..71r0102F
- Keywords:
-
- 61.72.Qq;
- 78.70.Bj;
- 82.30.Gg;
- Microscopic defects;
- Positron annihilation;
- Positronium chemistry