A CIGAR-SHAPED atom has demonstrated a novel kind of radioactive decay by spitting out two free protons at the same time.
Radioactive decay normally involves the emission of one of three types of particle: a helium nucleus consisting of two protons and two neutrons, an electron or a photon. Exotic atoms engineered to contain fewer neutrons than in the atom鈥檚 natural state were expected to break down by emitting protons, either one at a time or in pairs. But the two-proton decay had never been seen.
Sam Tabor, a nuclear physicist at Florida State University in Tallahassee, and his colleagues bombarded a thin film of nickel foil with a beam of calcium atoms, causing some nickel and calcium ions to coalesce to form silver atoms with fewer neutrons than normal. Most of these silver atoms decayed conventionally, but a few ejected two protons at once (Nature, vol 439, p 298).
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The deficit of neutrons in the silver had deformed the nuclei from spheres into fat cigar shapes. In some cases the proton pairs jumped out from the same end of the cigar, at other times from opposite ends, but they were always perfectly synchronised, says Tabor. 鈥淚t鈥檚 like there鈥檚 a captain on board telling them exactly when to dive.鈥�
