Number 133, June 17, 1993 by Phillip F. Schewe and Ben Stein
THE WAVELIKE NATURE OF ELECTRONS at the surface of a copper crystal
has been imaged with a scanning tunneling microscope (STM) by Donald Eigler
and his colleagues at IBM Almaden. Looking like photos of the criss-crossing
water waves arising from pebbles dropped in a pond, the STM images actually
correspond to the patterns of quantum mechanical standing waves set up
when an essentially two-dimensional electron gas (electrons trapped between
a very high vacuum and a chilled, clean metal surface) scatters from a
small number of imperfections in the crystal surface. (M.F. Crommie et
al., Nature, 10 June 1993.)
COMET SHOEMAKER-LEVY 9 has been torn by Jupiter's gravity into a string
of fragments, and worse is to come: according to Brian Marsden of Harvard-Smithsonian,
the train of comets will strike Jove itself in July 1994. If the collision
were to occur on the front side of the planet (which it will not), the
resulting explosion would be visible from Earth by day. The impact will
be comparable in energy to the dinosaur-killing KT impact on Earth. (Nature,
10 June 1993.)
THE LARGE MAGELLANIC CLOUD orbits the Milky Way with a transverse speed
of 220 km/sec. With photos of the LMC (and its attendant stream of hydrogen
gas streaming behind) taken 15 years apart, Douglas Lin of UC Santa Cruz
not only calculates the satellite galaxy's speed (the first time another
galaxy's motion across the sky has been measured) but also arrives at a
rough estimate of the distribution and density of matter (including dark
matter) in the Milky Way needed to produce such a motion. (Science News,
12 June, reporting on last week's Berkeley meeting of the American Astronomical
Society.)
WHERE DOES THE NEUTRON GET ITS SPIN? Two experiments address this issue.
At CERN the Spin Muon Collaboration (SMC) scatters polarized muons from
a target of polarized deuterons, while at Stanford the E142 collaboration
scatters polarized electrons from a target of polarized helium-3 atoms.
In both cases the study of deep inelastic scattering events---inelastic
because some of the collision energy is converted into extra particles
and "deep" because the lepton probes the neutron at a very small
distance scale---allows scientists to determine how much of the neutron's
spin can be ascribed to its constituent quarks. The CERN result, 6% (with
an uncertainty of 25%), is quite different from the Stanford result, 57%
(with an uncertainty of 11%). New experiments at both labs may resolve
the issue. (Nature, 13 May 1993.)
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