Number 68, 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.)
ELECTRON MICROSCOPY WITH 1-ANGSTROM RESOLUTION has been achieved by a Glasgow-Cambridge-Arizona State-Berkeley-Stockholm collaboration of scientists, who were imaging a crystal of the radiation-resistant molecule perchlorocoronene. The best resolution at the Cambridge electron microscope one could have expected, 0.32 nm, was extended to 0.1 nm in this case through the manipulation of phase information using "search tree" algorithms similar to those used in game-playing computer programs. The researchers hope to modify their method so that it can be used in the study of other organic molecules less resistant to electron beam damage. (W. Dong et al., Nature, 13 Feb. 1992.)
THE HEAVIEST KNOWN PROTON EMITTERS , radioactive rhenium-160 and tantalum-156, have been discovered in an experiment at the Daresbury accelerator in the United Kingdom. In the experiment, conducted by a Daresbury-Edinburgh-Darmstadt-Liverpool collaboration, nickel ions were smashed into a cadmium target, creating at times rare nuclei which could be detected in a special mass separator device. Proton emission is a rare form of radioactivity, observed for the first time only in the early 1980's. It is of interest because it offers information on the structure of rare neutron-deficient nuclides. (R.D. Page et al., Physical Review Letters, 2 Mar. 1992.)
SUPERNOVAS PRODUCE DIAMOND DUST . Donald Clayton of Clemson University has calculated that as much as one-thousandth of a solar mass of diamond may have been produced in Supernova 1987A. Clayton came to this conclusion after studying the relative abundance of diamonds and other elements, such as the heavy isotopes of rare gases, in meteorites. (New Scientist, 8 Feb. 1992.)
10 GIGABITS OF DATA can now be transmitted, largely without errors, over distances of 11,000 km. Linn Mollenauer of AT&T Bell Labs encoded the data in the form of solitons, pulses that retain their shape, which traveled through special erbium-doped optical fibers. Mollenauer reported this new work at the Conference on Optical Fiber Communications last week in San Jose, CA.