Number 198, October 12, 1994 by Phillip F. Schewe and Ben Stein
THE 1994 PHYSICS NOBEL PRIZE goes to Bertram N. Brockhouse of McMaster
University in Ontario, Canada and to Clifford G. Shull of MIT for their
pioneering work in neutron scattering experiments during the 1940s and
1950s. Quantum mechanics holds that at the atomic level matter has both
particle and wavelike properties. Slow-moving neutrons, considered as waves,
are particularly valuable as a means of studying the structure and energy
properties of crystals. Partly this is because the equivalent wavelength
of the neutrons can be adjusted to match the spacing between the atoms
in the crystal, or because the energies of the neutrons can be selected
to match those of the characteristic vibrations of the crystal. Shull is
being recognized for his work on experiments in which neutron waves fall
on the crystal and scatter elastically (they lose no energy) in a process
called diffraction. By detecting the scattered neutrons, the positions
of the atoms in the lattice can be deduced. The neutrons can also scatter
inelastically; that is, the neutrons lose energy by creating modes of vibration
(phonons) in the crystal. In this case an analysis of the energies of the
scattered neutrons provides information about the energy states of the
crystal. Brockhouse won his half of the award for spectroscopic work of
this type. Neutron diffraction has an important advantage over x-ray diffraction
in that neutrons interact with (and therefore probe) the crystal's magnetic
structure, while x rays cannot. To this day, the use of neutrons at many
labs around the world (where, for example, neutrons can be produced at
fission reactors) is an important way of studying diverse materials, such
as biological samples and high-temperature superconductors. Contact Brockhouse
at 416-648-6329; Shull at 617-862-8627. Magazine references: Scientific
American, June 1979 (an article on cold neutrons) and Physics Today, January
1985 (a special issue on neutrons.)
PERHAPS THE MOST CHEMICALLY ACTIVE FORM OF MATTER IN NATURE are the
bare uranium (U92+) ions recently made by scientists at Lawrence Livermore
National Laboratory (see Update #185). The electrical attraction between
such a heavy ion and electrons on surfaces is immense. The Livermore researchers
(contact Ross Marrs, 510-422-3890) invented a tabletop device known as
the electron beam ion trap (EBIT) to make U92+ and many other highly charged
ions such as Xe44+. Although EBIT was originally developed for trapping
heavy ions, its mode of operation can be modified to provide an efficient
source of very slow, very highly charged ions for collisions with surfaces.
For instance, single-ion impacts on insulators have led to the creation
of nm-sized blister-like defects. The volume of the defects can be controlled
by varying the charge of the incident ion. These properties may eventually
lead to applications in nanotechnology such as extremely high-density data
storage, nanoscale electronic circuit patterns, and micromachining. (Physics
Today, October 1994.)
ELEMENTS HEAVIER THAN ZINC have been detected in an interstellar gas
for the first time. Astronomers used the Hubble Space Telescope to observe
such elements as lead, arsenic, and krypton in a gas cloud 400 light years
away, a feat made difficult by the tiny trace amounts of the elements in
comparison to lighter elements. (Sky & Telescope, Nov.)
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