A NEW THEORY OF NMR FOR EXTENDED OBJECTS. Nuclear magnetic resonance (NMR) isn't just an imaging technique, but a valuable spectroscopic tool for deducing the chemical environment and structural layout of atoms in different environments. This is because the NMR spectrum of an atom (or to be more precise, the spectrum of the atom's nuclear magnetic states) is different depending on the local geometry, just as an atom's allowed electron energies will be different if the atom is suddenly lodged in a crystal with many other atoms. Previous NMR theories have been able to explain accurately what the NMR spectrum ought to be only for atoms or atom clusters in isolation. Now, physicists at UC Berkeley (Steven Louie, louie@jungle.berkeley.edu, 510-642-1709) have devised a method which for the first time makes possible rigorous calculations of the NMR spectra of extended systems such as crystals, surfaces, polymers, or even amorphous materials; given the coordinates of the atoms, the Berkeley researchers were able to predict the spectrum. They tried out their theory on an industrially important material---synthetic diamond films used, for example, as coatings for tools and engine parts. The prediction of the NMR spectrum for carbon atoms in the diamond films was in close agreement with the observed spectrum. (Francesco Mauri et al., Physical Review Letters, 22 Sept. 1997.)

PARTICLE IDENTIFICATION WITH PROBE MICROSCOPY. Scanning tunneling microscopes (STM) provide pretty pictures of atoms and can even be used to pluck single atoms from the sample surface. But often the identity of that atom (especially if it is an impurity) remains unknown. Physicists at Arizona State (John Spence, Uwe Weierstall, weierstall@asu.edu) have addressed this problem. First, they use a small voltage to remove a surface atom or molecule with an STM probe; then a larger voltage launches the object from the probe toward a distant detector. A measurement of the time of flight (TOF) supplies a mass-to-charge ratio for the mystery particle, which in most cases will supply the identity of the unknown species. The best resolution achieved by other methods of chemical identification on surfaces is about 2 nm. This new STM + TOF identification, with essentially atomic-level resolution, should be handy in a number of research areas, such as catalysis and the study of the role of foreign atoms at kinks and steps in crystal growth. This work will be reported in a session (NS-TuA, Oct. 21) at the upcoming meeting of the American Vacuum Society (Oct. 20-24 in San Jose). The program for this meeting can be viewed on the Internet at this address: www.vacuum.org/symposium/program.html. (General press contact at the meeting: 408- 271-6000.)

FISSION HELPS SUPERCONDUCTIVITY. One of the problems of using high temperature superconductors as wires in magnets is that the bundles of magnetic field lines that normally stay put in the presence of low currents start to move around (dissipating energy thereby) when larger currents are sent through the wire sample. Scientists working at Los Alamos have now used a proton beam to induce nuclear fission in mercury atoms in a mercury/copper oxide superconductor. The defects caused by the fissioning atoms splay out in all directions in the superconductor crystal and help to snag the wayward field lines. This permits the sample to carry much more current. (Nature, 18 Sept.)