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Physics news update 608

2002 Nobel Prize, 3-D ink, new object in solar system

American Institute of Physics

THE 2002 NOBEL PRIZE FOR PHYSICS recognizes work that led to the establishment of two new branches of astrophysics, those involving x rays and neutrinos. The award will be presented to Raymond Davis (University of Pennsylvania and Brookhaven Natl. Lab), Masatoshi Koshiba (University of Tokyo), and Riccardo Giacconi (Associated Universities Inc.). In the 1960s Davis was the first to detect neutrinos coming from the sun. The number of nu's recorded fell short of predictions made by John Bahcall (Institute for Advanced Study) and thus was born the "solar neutrino problem." Later detector experiments, such as SAGE and Gallex, also failed to observe the expected number of neutrinos from the sun. The best explanation for the shortfall was that electron neutrinos made in the solar core, as products of nuclear fusion reactions, might be transforming while in flight toward Earth into other types of neutrino such as muon neutrinos, which could not be recorded in terrestrial detectors.

This hypothesis was put to the test in the Kamiokande detector, which had earlier sought to find evidence for proton decay. Koshiba and his collaborators enlarged the detector (Super-Kamiokande) and finally affirmed (by observing asymmetries in cosmic-ray-engendered nu's coming through the Earth to the detector or directly into the detector from Earth's atmosphere) that nu's were indeed transforming, or "oscillating." Still more proof for the oscillation principle arrived this past spring when the Sudbury Neutrino Observatory (SNO), capable of directly detecting all three types of neutrino, reported that all solar nu's (albeit not the same mix as was produced in the sun) were accounted for.

Neutrinos are important in astrophysics since they might have played a considerable role in shaping or herding early galaxies; they are the form of energy coming directly from the solar core (photons scatter around inside the sun for up to a million years before escaping); and they account of the largest share of energy released during supernovas; indeed, after the 1987A supernova, a dozen or so nu's from the event were observed in terrestrial detectors.

As for x-ray astrophysics, Giacconi was the first to employ an x-ray telescope in space (1962) and observe specific x-ray sources outside our solar system. There followed decades of new orbiting x-ray telescopes (e.g., ASCA, RXTE, ROSAT, Einstein, Yokhoh, Chandra) and notable x-ray discoveries, such as the detection of an x-ray background, resolving that background mostly into point sources, and the detection of x rays from a variety of sources, such as comets, black holes, quasars, and neutron stars.

(Background articles in Physics Today, August 98, Kamiokande oscillation results; July 02, SNO results; May 00, x-ray background; Nov 00, Chandra results. Some useful websites:SNO website: www.sno.phy.queensu.ca/; US-Kamiokande: www.phys.washington.edu/~superk/; Beamline, Winter '99: www.slac.stanford.edu/pubs/beamline/pdf/99iii.pdf;Swedish Academy: www.nobel.se/physics/laureates/2002/phyreading.html; historic APS journal articles, www.aps.org/media/; Chandra X-Ray Telescope: www.chandra.harvard.edu. Some past Update items include: solar neutrino problem: www.aip.org/enews/physnews/1990/split/pnu003-1.htm; x rays from a supernova: www.aip.org/enews/physnews/1995/split/pnu250-2.htm; x-ray background: www.aip.org/enews/physnews/1994/split/pnu175-2.htm; background pt. sources: www.aip.org/enews/physnews/2000/split/pnu467-1.htm; Chandra: www.aip.org/enews/physnews/1999/split/pnu441-1.htm; quark stars: www.aip.org/enews/physnews/2002/split/585-1.html; nu oscillation: www.aip.org/enews/physnews/1998/split/pnu375-1.htm; nu mass limits: www.aip.org/enews/physnews/2002/split/600-2.html; recent SNO: www.aip.org/enews/physnews/2002/split/586-1.html)

3-DIMENSIONAL INK. Most people are familiar with three-dimension drawings, which are of course rendered on two dimensional surfaces in a way that gives the illusion of depth. Jennifer Lewis (jalewis@ux1.cso.uiuc.edu, 217-244-4973) and colleagues at the University of Illinois, however, are developing techniques to draw truly 3-D structures. The researchers are perfecting "inks" that carry tiny particles made of metals, ceramics, plastics, or a variety of other materials instead of pigments. The inks are deposited with a machine similar to an ink jet printer. But unlike most inks, the fluid that the printer deposits is a gel that can be built up, layer by layer, into three-dimensional structures. The gel must be thick enough to support itself as it spans empty space. (Imagine, for instance, squeezing out a stream of toothpaste across your fingers. The line of toothpaste can, at least for a little while, support itself across a small gap between two fingers.) It also must be designed to retain its shape without significant shrinking or sagging as it hardens. The manufacturing technique may soon lead to novel structures woven of inky threads only tens of microns in diameter (see image at www.aip.org/mgr/png). Lewis will present recent studies of 3-D inks (http://www.rheology.org/sor02a/abstract.asp?PaperID=243) on October 14 at the 74th annual Society of Rheology Meeting (http://www.rheology.org/sor/annual_meeting/2002Oct/), in Minneapolis.

QUAOAR is the name for a planet-like inhabitant of the Kuiper Belt debris zone lying beyond Neptune. Spotted first as a mere dot of light, it has now been imaged by the Hubble Space Telescope. It is a plum for students of the solar system: with a diameter of 1300 km and a distance of 4 billion miles from Earth, Quaoar is the largest solar-system object to be measured since Pluto was discovered in the 1930s and the farthest-out to be resolved by a telescope. The finding was announced yesterday by Caltech scientists at the meeting of the Division for Planetary Sciences of the American Astronomical Society in Alabama.

SLAC IS 40 YEARS OLD. On October 2 the anniversary of SLAC's founding was observed at a large gathering (http://www-conf.slac.stanford.edu/40years/ ) The Stanford Linear Acceleration Center has been the scene of many notable strides in physics, including the deep inelastic scattering of electrons from a hydrogen target (helping to establish the existence of quarks inside protons and neutrons), the discovery of the Psi meson (helping to establish the existence of charm quarks; similar research was performed simultaneously at Brookhaven), the discovery of the tau lepton, studies of the Z boson (suggesting a limit on the number of quarks and leptons), and most recently studies of B meson decay (exhibiting a violation of CP conservation).

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by Phillip F. Schewe, Ben Stein, and James Riordon

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