Imagining left- or right-handed nuclei is a little like trying to pat your head, rub your stomach and tap dance all at the same time. Instead of being spherical, they are shaped like elongated cigars, having three axes of different lengths. And instead of having all of their protons and neutrons paired up and moving as a central unit, they have oddball nucleons that orbit the core independently. In fact, one nucleon orbits the longest axis, one orbits the shortest axisand the core spins around the third axis. It is because there are two ways to pull this trick off that these nuclei are said to be "handed."

Until now no one was sure they even existed. Stefan Frauendorf of the University of Notre Dame and the Rossendorf Research Center in Germany and his colleagues showed that handedness was theoretically possible for these odd-odd triaxial nuclei a few years back. But in the February 5 issue of Physical Review Letters, Frauendorf's teamin collaboration with Krzysztof Starosta of the State University of New York and othersoffers experimental proof.

The scientists aimed beams of heavy ions at targets of certain elements to produce nuclei with 75 neutrons and 55, 57, 59 or 61 protons in a wide range of spin states. Then they detected gamma rays emitted by the nuclei and measured the energies of each spin state. What they found were doublets. These pairs of closely spaced energy states had the same amounts of angular momentum and corresponded to seemingly identical nucleifacts that the physicists took as evidence of handedness. The discovery, researchers say, could shed light on our most basic knowledge of nuclear structure.