Thursday, 9 June 2011

Cern, Alpha and antimatter storage: why antimatter should matter to us

Sixteen minutes is not a particularly long time. It's enough time for a cup of tea, or to run two miles, if you're in good shape. But if you have a few atoms of antimatter, it may be enough time to learn about the birth of the universe.
On Sunday, scientists at the European Organization for Nuclear Research (Cern) generated excited headlines worldwide when it was announced that they had created and stored antimatter – the elusive "mirror image" of everything we see around us – in a stable state for the first time. They have managed to keep atoms of antihydrogen – the antimatter equivalent of hydrogen, the simplest element – trapped for 1,000 seconds, or 16 minutes and 40 seconds. Their previous record stood at just 172 milliseconds, or rather less than a fifth of a second. It's an exciting breakthrough, but one that may have been hard to grasp for those of us without a physics degree.
To understand it, we first need to know what matter and antimatter really are. The universe is made of subatomic particles – electrons, protons and neutrons being the best known. In 1928, the English physicist Paul Dirac, a pioneer of quantum mechanics, created a detailed mathematical model of the subatomic world – but he realised that, for his equations to work, he required a particle with the same mass as an electron, but with the opposite, "positive" charge. In 1932, an American, Carl Anderson, observed such a particle, which became known as a positron. Later, it became clear to physicists that every particle of matter had an associated antiparticle. In 1955, researchers at the University of California at Berkeley identified an antineutron and antiproton.
But studying this antimatter was not easy. When an antiparticle of any kind meets its matter counterpart, the pair annihilate each other in a small but fierce burst of energy. An atom of antihydrogen, consisting of a positron and an antiproton, would instantly vanish upon contact with any matter. The only way to store antimatter, then, is to keep it in a magnetic field.
Until very recently, that meant that only subatomic antiparticles could be stored and studied because only charged antiparticles, antiprotons and positrons, can be manipulated by a magnetic field. Whole atoms do not have an electric charge and so magnets were of limited use.

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