Number 64 (Story #4), January 20, 1992 by Phillip F. Schewe and Ben Stein THE SMALLEST SUPERFLUID OBJECTS IN THE UNIVERSE are atomic nuclei, with their tightly-packed protons and neutrons able to slide over one another without friction. Scientists have tried to learn more about the superfluid nature of nuclei by studying the phenomenon of "backbending," which occurs when an excited nucleus, shedding its energy by emitting gamma rays, suddenly speeds up its spin for a brief time before slowing down. Recent experiments with heavy-ion colliders and nanosecond-resolution gamma detectors in Australia show evidence that the outermost neutron pair in the tungsten-179 nucleus becomes unpaired, aligns with the rotation of the nucleus, and causes a sort of phase change in which neutron pairs become uncoupled. As a result, the neutrons in the atoms lose their superfluidity and yet co-exist with protons still in a superfluid state. The researchers believe that similar effects may also be responsible for the periodic "glitches" in the rotation of pulsars, the largest known superfluid objects in the universe. (New Scientist, 11 January 1992.)