Number 126, April 28, 1993 by Phillip F. Schewe and Ben Stein
A NEW VERSION OF YOUNG'S INTERFERENCE EXPERIMENT , using not a pair of
slits in a screen but instead a pair of mercury ions in an atom trap to
scatter light waves and produce interference fringes, has been performed
by a group at NIST in Boulder, Colorado. The researchers used a single
laser beam both to cool (to mK temperatures) the ions, which are held in
the inhomogeneous electric fields of a Paul trap, and to serve as a light
source for producing interference effects. Stable fringe patterns were
produced for several relative spacings (typically a few microns) for the
ions. The fringe pattern, in turn, may be used as a diagnostic for measuring
the temperature or spacing of ions in various trap experiments. (Phys.
Rev. Lett., 19 April 1993; contact Ulli Eichmann of NIST at 303-497-7374).
THE RATE OF HELIUM BURNING IN MASSIVE STARS , particularly the ratio
of two reactions---three helium nuclei fusing to form carbon-12 and helium
and carbon fusing to form oxygen-16---determines the sequence by which
heavy elements build up in stellar cores and the fateful chronology by
which massive stars approach a supernova condition. The rate at which oxygen
is produced, the so called S factor, has now been measured in two separate
experiments. (The carbon production rate had been previously measured.)
Speaking at the April APS meeting, Moshi Gai of Yale and Lothar Buchmann
of TRIUMPH (British Columbia) described their respective studies of the
decay of oxygen-16 into carbon and helium. It was necessary to measure
this reverse reaction because the fusion rate for carbon and helium, at
least under lab conditions on Earth, was prohibitively small. The two experimental
results were rather similar and largely in agreement with theoretical calculations.
(Science, 2 April; Science News, 24 April 1993.)
THE EXTREME ULTRAVIOLET (EUV) waveband (10-100 nm wavelength) is one
of the least studied spectral ranges in astronomy. One reason for this
is that EUV is absorbed by interstellar gas, which is mostly hydrogen and
helium. So it came as something of a surprise that the Rosat and the Extreme
Ultraviolet Explorer (EUVE) satellite telescopes could see as far as they
do. In this case EUV measurements are benefitting from the fact that our
solar system seems to sit in a bubble at least partially cleared of interstellar
matter, perhaps by past supernovas. This allows the telescopes to see objects
(mostly hot white dwarfs) hundreds of light years away. In certain directions
viewing conditions are so good that faraway galaxies can be seen. (Science
News, 17 April 1993.)
A BIPOLAR SPIN SWITCH , a transistor-like device developed by Mark Johnson
of Bellcore, consists of a sandwich of metal---not semiconductor---films,
two outer ferromagnetic films with a paramagnetic gold film in between.
This device operates as a closed or open switch depending on whether the
magnetizations of the magnetic layers are parallel or anti-parallel. According
to Johnson, his switch would benefit from further miniaturization; the
device's gain increases with decreasing size, and even with nanometer proportions,
the all-metal structure would have plenty of electrons to work with. (Science,
16 April 1993.)
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