Number 185, June 28, 1994 by Phillip F. Schewe and Ben Stein
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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