Matter-antimatter molecules in lab

Scientists at the University of California at Riverside have created molecular positronium, in which two positrons – antimatter siblings of electrons – are bound together by electrons, in the laboratory.

They say as electrons and positrons have equal and opposite charges, they can become bound together by their electrical attraction, just as a positively charged proton is orbited by an electron in ordinary hydrogen atoms.

In theory, positronium atoms – electron-positron pairs – should also be able to pair up to form molecules, just as two hydrogen atoms form H2, they said.

However, as physicist Clifford Surko of the University of California in San Diego, said, the hybrid molecule positronium, denoted as Ps2, is peculiar stuff.

“Rather than being two well-defined atoms stuck together, the four particles “do a merry dance around each other in a fuzzy, lump-less soup,” said Surko.

He, however, said these molecules are very hard to see because matter and antimatter annihilate each other, releasing a burst of energy in the form of gamma-rays.

When isolated in a vacuum, positronium atoms typically survive for less than a millionth of a second before they self-destruct, Sarko said.

”Almost as soon as they are made, they disappear again with a puff and a flash of light,” said Surko.

During their study, David Cassidy and Allen Mills at the University of California at Riverside, found, that if they could capture enough positronium, some of the pseudo-atoms might combine before they vanish.

If that happened, the positronium molecules would release a characteristic gamma-ray signature when annihilation eventually occurred.

So the researchers fired a beam of positrons (made with a technique developed by Surko) into porous silica glass, in an attempt to pick up electrons and make Ps2. They estimated a one-in-ten chance of two positronium atoms combining.

The clinching data, the researchers said, came from looking at how the intensity of the gamma rays changed, as the temperature was altered.

The pair now believes 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 we saw,” the researchers wrote in their study in the journal Nature. (ANI)

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