Number 68 (Story #1), February 21, 1992 by Phillip F. Schewe and Ben Stein ULTRACOLD NEUTRONS (UCN) , neutrons with energies of less than a millionth of an electron volt, can be produced by sending a beam of neutrons (originally from a reactor) into a sample of superfluid helium-4. Although this technique had been proposed 15 years ago (other UCN schemes use neutron baffles and guides), only now have scientists been able to demonstrate that ultracold neutron production greatly increases when neutrons incident on a sample of superfluid helium have a characteristic wavelength of 8.78 angstroms, just as the original theory had suggested. The researchers, a collaboration of scientists at Tohoku University, Kyoto University, and the National Laboratory for High Energy Physics, believe that use of helium as a cooling medium may be preferable to some other schemes since neutrons can enter the cooling chamber from all directions. UCN research may lead to a more accurate measurement of the neutron lifetime or facilitate the search for a nonzero neutron electric dipole moment. (H. Yoshiki et al., Physical Review Letters, 2 Mar. 1992.)