Number 83, June 8, 1992 by Phillip F. Schewe and Ben Stein|
IONS IN STORAGE RINGS can form ordered structures such as linear, zig-zag, helical, or concentric-ring arrangements. Experimenters at the Max Planck Institute for Quantum Optics in Garching, Germany use a ring-shaped ion trap (11.5 cm diameter) to store laser-cooled magnesium ions. Drawing on the technology of previous (essentially one-dimensional) traps that confine a relatively small number of ions to a pointlike space (the center of the trap), the Garching scientists store thousands of ions in a (two-dimensional) space with a ring geometry. The advent of ordered structures in storage rings would help atomic physicists conducting high-precision spectroscopy and would benefit accelerator physicists by making possible beams with higher luminosity and smaller momentum spread. (Nature, 28 May 1992.)
THE MT. PINATUBO ERUPTION in the Philippines in 1991 "produced the largest climate-modifying cloud since Krakatau erupted in Indonesia in 1883, "says a new report by the American Geophysical Union (AGU). The report, "Volcanism and Climate Change, "asserts that volcanic sulphur aerosols cause significant depletion of the ozone layer. The report also concludes that "the sulphur content of an eruptive cloud, and not dust or ash, is the essential variable responsible for altering climate, at lease in explosive eruptions."
BEAMS OF RADIOACTIVE NUCLEI help scientists to study short-lived nuclides in a way that was not possible before. A great deal of what we know about nuclei comes from high-energy collisions at accelerators, where necessarily the beam or target particles are themselves stable nuclei. In recent years, however, it has been possible to collect short-lived nuclei (created in reactions involving a primary beam) and re-inject them for acceleration, after which they can participate in high-energy collisions of their own. For example, at the Louvain-la-Neuve cyclotron lab in Belgium, a primary proton beam strikes a carbon-13 target. The nitrogen-13 nuclei produced in the process are extracted and accelerated up to an energy of 8.2 MeV and then shot into a polyethylene target. The ensuing collisions provide an important insight into reactions presumed to take place in certain extreme astrophysical environments, such as white dwarfs and neutron stars. (Physics Today, June 1992.)
THE MOST ABUNDANT MINERAL ON EARTH , silicate perovskite, has, ironically, been of more interest to materials scientists than to geologists, according to Alexandra Novrotsky of the Princeton Materials Institute. Perovskite, a class of ceramic crystal (e.g., MgSiO3) in which three chemical elements in the ratio 1:1:3 form a cubic structural unit, makes up 80 to 100% (by volume) of the lower mantle. Materials scientists eagerly study artificially made perovskite, hoping to synthesize, among other things, high-temperature superconductors. By contrast, the perovskite samples geologist want to study lie 670 km underfoot. Increasingly, however, geologists are able to study perovskites under conditions resembling those of deep Earth interior using high-pressure diamond-anvil cells. (Materials Research Society Bulletin, May 1992.)