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Number 382, July 17, 1998 by Phillip F. Schewe and Ben Stein
BOSE EINSTEIN CONDENSATION OF HYDROGEN ATOMS has been achieved by Daniel Kleppner and Tom Greytak (greytak@mit.edu) and their colleagues at MIT. Unlike conventional condensates of atoms, a Bose Einstein condensate (BEC) is essentially an amalgamation of many atoms (which have been chilled to nearly absolute zero temperatures) into a single quantum state. In the past few years researchers had reached the BEC state with alkali atoms but not yet with the simplest of elements, hydrogen, partly because the energy levels within the H atom are more widely spaced (the transitions corresponding to ultraviolet light, for which no suitable laser source is available) making it harder to manipulate and probe the sample with lasers. But with a modified evaporative cooling technique, in which the hotter atoms are ejected from their atom trap (as with alkali atoms) by blasts of radio waves, and by probing the hydrogen atoms with two photons at once, the BEC state was observed at last. The MIT researchers are presently gathering more data before submitting papers to a journal, but their preliminary results (reported indirectly last week at the Conference on Precision Measurement in Washington, DC) are as follows: the transition to BEC occurred at a temperature of about 40 micro-kelvins and the number of atoms involved was about 100 million, 10 times more than in any previous condensate. The difficult (but high-precision) form of spectroscopy used to probe the H atoms (involving two photons simultaneously) has the virtue of (1) causing a narrow beam of atoms to be ejected from the condensate (useful for any future atom laser) and (2) permitting the study of some condensate properties not yet examined in the alkali work. (See figure at Physics News Graphics)
A SUN-EARTH CONNECTION EVENT, in which a gust of plasma particles (a coronal mass ejection) detaches from the Sun and travels all the way to our planet, where it causes electromagnetic disturbances and atmospheric auroras, has been monitored from start to stop for the first time. The International Solar-Terrestrial Physics Observatory, a network of ground-based and satellite detectors, watched the drama play out over the period January 6- 11, 1997. The absence then of notable surface features on the Sun, such as flares, reinforces the notion that coronal rather than surface activity is more important for determining near- Earth space storms. (Several articles in the 15 July 1998 issue of Geophysical Research Letters.)
THE INTERNATIONAL PHYSICS OLYMPIAD, the annual competition which sets tough problems to some of the best high school students in the world, was held this year in Iceland. As befits the fire-and-ice locale, some of the problems involved finding the pressure under an ice cap, determining the results of lava intrusions into icefields, and the motion of superluminal radio jets, which can be thought of as the astrophysical equivalent of lava flows. The national teams with the greatest number of gold medals were China (5), Russia (3), and Korea, Poland, and Iran with one each. The U.S. team earned one silver medal (Andrew Lin, Wallingford, CT) and one bronze (Peter Onyisi, Exeter, NH). (See the upcoming issue of the Announcer, published by the American Association of Physics Teachers.)
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