Superdeformed Nuclei Rotate So Fast They Make Heads Spin

Spin a nucleus fast enough and it will stretch into an elongated shape. Spin it even faster and it will fission. But below the angular momentum at which fission can occur, some nuclei can be relatively stable, especially those whose lengths are twice their widths. Nuclear theory has long predicted such rapidly rotating, superdeformed states. Only recently, however, have experimenters been capable of producing such nuclei, through heavy‐ion collisions, and of observing them, with large arrays of highresolution germanium detectors. In 1986, a group working at the Daresbury Laboratory in Great Britain succeeded in measuring the largest angular momentum reported until then for a nucleus. They found dysprosium‐152 to be rotating with a spin of 60 ℏ—or about ${\text{2×10}}^{20}$ revolutions per second in a classical estimate. Several months ago the same team confirmed that this state of Dy¹⁵² has a superdeformed shape: It resembles a prolate ellipsoid rotating about a minor axis. (A prolate ellipsoid has one major and two equal minor axes, and the length ratio of the major to minor axes is 2:1 for superdeformed nuclei.)