PHYSICS NEWS UPDATE A digest of physics news items prepared by Phillip F. Schewe, AIP Publ

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PHYSICS NEWS UPDATE A digest of physics news items prepared by Phillip F. Schewe, AIP Public Information Number 167 March 3, 1994 CORONAL MASS EJECTIONS VS. SOLAR FLARES. John Gosling of Los Alamos believes that many strong solar phenomena such as geomagnetic storms and shock waves in the solar wind are actually a result of coronal mass ejections (CME's) and not solar flare activity. During a CME up to 10**16 grams of matter from the corona (the very hot region above the sun's surface) are thrown out into space at speeds up to 1200 km/sec. The appearance of CME's, like that of other solar phenomena, is related to the 11-year solar cycle, and indeed some CME's and flares (and other eruptions) appear at nearly the same time. Gosling contends, however, that a careful analysis of the intensity, energy, and temporal characteristics of many prominent events in the solar-terrestrial environment shows that they are caused by CME's, not by flares. CME's are poorly understood, Gosling says, because they are difficult to measure, particularly Earth-bound ejections (those which would have the greatest effect on the near-Earth space environment) which proceed amid the glare of sunlight. (Nature, 17 Feb. 1994.) SEARCHING FOR ANTIPROTON DECAY is harder than searching for proton decay. Proton stability can be studied by using vast underground tanks of fluids; such experiments have pushed the proton's measured lifetime to at least 10**32 years. Antiprotons, in contrast, must be created artificially at accelerators and can be stored in comparatively small numbers. The most stringent previous antiproton lifetime limit was 3.4 months. Now scientists at Fermilab has established new higher limits for a variety of possible decay modes, such as 1848 years for antiproton decay into a positron plus a photon and 554 years for decay into a positron and a pion. Theorists expect that the lifetime of the proton and antiproton would be identical, but this has to be confirmed experimentally. (S. Geer et al., UPCOMING ARTICLE in Physical Review Letters, 14 Mar. 1994.) DETERMINING THE NATURE OF CHEMICAL BONDS AT NEAR-ATOMIC RESOLUTION in the interfaces of inorganic solids is now possible using a combination of electron microscopy techniques. First, columns of atoms at an interface are imaged at sub-nm resolution using scanning transmission electron microscopy (STEM). Then information about the electronic states of atoms in the column are obtained through a technique known as electron energy-loss spectroscopy (EELS), in which a beam of electrons is sent down a specified column, after which the energy spectrum of the scattered electrons is measured. Philip Batson of IBM images layers of silicon atoms at a silicon-silicon dioxide interface and can deduce the chemical bonding states for silicon atoms from layer to layer. Meanwhile, David Muller at Cornell maps columns of carbon atoms between a diamond film and a silicon substrate. He finds that the carbon bonding states change between columns over a distance of less than 1 nm and that the diamond grows on an amorphous carbon layer, ruling out other proposed scenarios. This technique is likely to be a useful tool for studying and controlling properties of inorganic thin films as well as grain boundaries in metals and ceramics (Nature, 23/30 Dec. 1993). Furthermore, the combined use of STEM and EELS should result in the ability to map the presence of trace elements at a level of 10 parts per million in 10-nm-wide regions. (Science News, 26 Feb. 1994.)


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