PHYSICS NEWS UPDATE A digest of physics news items by Phillip F. Schewe, American Institut

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PHYSICS NEWS UPDATE A digest of physics news items by Phillip F. Schewe, American Institute of Physics Number 185 June 28, 1994 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.) - END OF FILE - ==========


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