Number 35, May 22, 1991 by Phillip F. Schewe and Ben Stein|
ATOM INTERFEROMETRY has been demonstrated by scientists at MIT and at Konstanz University in Germany. Interferometry is a phenomenon in which a wave (light waves from a laser, for example) is split and made to interfere with itself, resulting in a characteristic pattern of constructive and destructive interference. Previously, electrons and neutrons---which according to quantum mechanics have wavelike properties---have been subjected to interferometry. Now this process has been extended to atoms. At MIT (David E. Pritchard, 617-253-6812) a highly collimated beam of sodium atoms with a de Broglie wavelength (the wavelength of sodium "matter waves") of 16 nm passes through three sets of diffraction gratings, the first two to establish an interference pattern and the third to sample the pattern. In the German experiment (O. Carnal and J. Mlynek) a beam of atomic helium with a de Broglie wavelength of from 0.56 to 1.03 angstroms passes through a system of slits, creating an interference pattern at a detection plane 64 cm away. Atom interferometry will permit certain new studies of quantum mechanics and may be useful in testing general relativity. (Both groups report in Physical Review Letters, 27 May 1991.)
STUDIES OF GLOBULAR CLUSTERS indicate that it may have taken 3 billion years (rather than 1 billion years as was previously thought) for the material which formed our galaxy to collapse into a disk. A Rutherford-New South Wales-Maryland team of astronomers has measured the abundance of Fe, C, N, and O atoms in two clusters, NGC288 and NGC362, and found them to be the same. This, combined with previous plots of color-versus-luminosity for stars in the two clusters, shows that NGC288 and NGC362 differ in age by 3 billion years. (Nature, 16 May 1991.)
SUPERCONDUCTIVITY AT A TEMPERATURE OF 28 K has been observed in carbon-60 doped with rubidium by the same group at AT&T Bell Labs (Arthur F. Hebard, 201-582-4944) that last month discovered superconductivity in C-60 at 18 K. The 28-K transition temperature is the highest for any material except Ba-K-Bi-O and the cuprate superconductors. (Physical Review Letters, 27 May 1991.)
BAND TWINNING is the name for a curious similarity in the energy spectra of certain superdeformed nuclei, nuclei that are oblate or stretched out and quickly rotating as a result of high-energy collisions. Marie-Anne Deleplanque of LBL (415-486-5384) reported at last month's APS meeting in Washington, D.C. that the sequence (or band) of gamma rays emitted by superdeformed dysprosium-152 and terbium-151 are surprisingly like the pattern observed for nuclei (such as mercury) in the atomic mass range of 190. According to Deleplanque, "There is no explanation for any of these properties based on our present knowledge of nuclear structure." (Science 10 May.)
FUNDS FOR THE SPACE STATION were essentially eliminated by a House Appropriations Subcommittee in a vote taken on May 16. The matter will be taken up again on May 30 when the full House Committee meets. The Subcommittee also deleted most of the funds for the proposed Laser Interferometry Gravitational Observatory (LIGO).