PHYSICS NEWS UPDATE
A digest of physics news items by Phillip F. Schewe, American
Institute of Physics
Number 185  June 28, 1994                   physnews@aip.org

BARE URANIUM IONS HAVE BEEN TRAPPED using an electron beam.  Uranium atoms
stripped of all or most of their 92 electrons have been produced before, in
accelerator beams moving at nearly the speed of light. To produce stationary
ions, a Livermore team uses a 198-keV electron beam to attract a sample of
uranium ions stripped of 2 or 3 electrons each. The beam ionizes the uranium
atoms further, producing bare (0-electron) and hydrogenlike (1-electron)
uranium ions.  A set of electrodes confines the ions along a 2-cm segment of
the 70-micron-diameter electron beam.  Measurements of these stationary ions
can stringently test predictions of special relativity and quantum
electrodynamics, because uranium's heavy nucleus makes relativistic and QED
effects very pronounced, and the absence of all or most of the electrons
prevents these effects from being muddled by electron-electron interactions.
(R.E. Marrs et al, Phys. Rev. Lett, 27 June 1994).

THE POSSIBILITY OF PLANETS ORBITING THE STAR BETA PICTORIS is inferred by
French astronomers from infrared images of the dust disk around the star.
The discovery of this circumstellar disk ten years ago supported the idea
that planetary systems, including our own solar system, form when a broad
band of dust coalesces around planetesimals, which further sweep up dust as
they evolve into planets.  New images, recorded in the 10-micron portion of
the infrared spectrum with a spatial resolution of 5 astronomical units
(about the size of Jupiter's orbit), reveal a depletion of dust within 40 AU
of the star.  Pierre-Olivier Lagage and Eric Pantin believe that the missing
dust was swept up by at least one planet.  (P.O. Lagage and E. Pantin,
Nature, 23 June 1994.)

MAGNETIC RESONANCE FORCE MICROSCOPY represents the attempted marriage of
atomic force microscopy (AFM) and nuclear magnetic resonance (NMR)
techniques.  Scientists at IBM Almaden have devised a microscope which
employs a force-sensing cantilever arm, whose minute motions are observed
through interferometry, just as in AFM.  But in this case the force measured
is not the repulsive force between probe and sample but the magnetic force
between the sample (mounted on the arm) and a nearby magnet.  As in NMR an
external radiofrequency coil causes magnetic nuclei in the sample to
oscillate, a process that provides information about the composition and
distribution of atoms in the sample.  So far the device can detect
subfemtonewton forces and has a spatial resolution of 2.6 microns in one
dimension, much better than with conventional NMR.  (D. Rugar et al.,
Science, 10 June 1994.)

A 75-NANOMETER-WIDE ELECTRON BEAM has been produced at the Stanford Linear
Accelerator Center. With the next generation of linear colliders moving from
the GeV to TeV energy range, more tightly focused beams are crucial so as to
maximize the likelihood of high-energy collision events between particles.
The narrow beam, demonstrated at the SLAC's Final Focus Test Beam (FFTB)
facility just a month after it became operational, already approaches the
FFTB group's goal of a beam with vertical width of 60 nanometers and
horizontal width of a micron. (Physics Today, July 1994.)

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