Test puts pedal to heavy metal

From Tampa, at a meeting of the American Physical Society

FICKLE NICKEL. Decays of nickel ions in this 4.5-meter-diameter cyclotron—shown from the inside and open—suggest that supernovas manufacture heavy elements faster than predicted. B. Mitcham/Michigan State University

Cosmic atom factories crank out gold and other heavy elements faster than scientists had suspected. So say physicists who have made the first measurement ever of the half-life of the isotope nickel-78.

Scientists consider stellar explosions, called supernovas, the blast furnaces in which about half of all heavy elements found in nature today were, and continue to be, forged. In a supernova, light nuclei pack on extra neutrons and then become heavier elements when some of the neutrons decay into protons. Every additional proton moves the evolving nucleus up one place in the Periodic Table of the Elements. However, many aspects of the process, called rapid neutron capture, remain poorly understood.

Every heavy nucleus formed in a supernova briefly becomes nickel-78 along the way, says Hendrik Schatz of Michigan State University in East Lansing. “If [nickel-78] decays quickly, you can build up heavy elements quickly,” he says.

Using a particle accelerator to bombard a beryllium target with 100 billion krypton ions per second for about a week, Schatz and his colleagues produced exactly 11 nickel-78 nuclei. Few as they were, those nuclei were enough to reveal that the isotope’s half-life is only 110 milliseconds, about a fourth of what theorists had predicted, Schatz says. The implication, he notes, is that elements heavier than nickel in the periodic table form faster in supernovas than physicists have predicted.

Scientists are now using the result to refine models of the cosmos’ element-making processes, Schatz says.

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