Firm Evidence for Existence of Positronium

The same group that had the initial evidence for the formation of positronium (a "molecule" of 2 electrons and 2 positrons) has now presented more convincing evidence (link may only be open to non-subscribers for a limited time).

The clinching data come from looking at how the intensity of the gamma-rays changes as the temperature is altered. Electron-positron annihilation should be more rapid in Ps2 than in lone positronium atoms, because the binding increases the chance of collision. And the positronium mix should have a greater proportion of molecules at lower temperatures, since the cold makes molecules more stable. So the gamma-rays should become more intense when the mixture is cooled. That's exactly what the researchers saw, they report in Nature.

The exact citation for this paper is:

D. B. Cassidy and A. P. Mills, Jr., Nature v.449, p.195 (2007).

Nice going!

Zz.