Paris

A facility for probing the fleeting existence of highly unstable atomic nuclei began operating at the GANIL heavy-ion accelerator in Caen, northwest France, last week. Researchers say that the device, known as SPIRAL, could help to overthrow existing models of nuclear structure.

Mystery machine: researchers hope that SPIRAL will reveal the secrets of short-lived exotic nuclei. Credit: J.-M. ENGUERRAND/GANIL

SPIRAL will produce a beam of 'exotic ions' — charged atoms with an unusual balance of protons and neutrons in their nuclei. Most decay into more stable nuclei in fractions of a second. Exotic nuclei are created in extreme environments such as supernovae, and do not occur naturally on Earth.

SPIRAL fires a beam of stable ions at a carbon target held at temperatures of around 2,000 °C. The nuclei of the stable ions fragment on impact, creating a beam of exotic ions. These ions are sorted and then captured by detectors which can, for example, identify them by their decay products.

In most nuclei, protons and neutrons are packed into a ball. But the nucleus of one lithium isotope, for example, seems to consist of a dense centre surrounded by a cloud of neutrons. SPIRAL will aid the search for other such 'halo' nuclei. “We will probably need two or three of this type of facility in Europe to satisfy the demand,” says William Gelletly, of GANIL's advisory committee.

Marek Lewitowicz, GANIL's deputy director, says the lab is already seeking to supplement SPIRAL's construction budget of 18 million euros (US$15.7 million), to boost the range and intensity of its beams.

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