Number 165, February 17, 1994 by Phillip F. Schewe and Ben Stein LEPTOQUARKS HAVE NOT BEEN FOUND at the Tevatron. Certain theories seeking to unify the electromagnetic, weak, and strong forces hold that in addition to the known families of elementary particles---the quarks and the leptons---there should exist another family, the leptoquarks, which would have both lepton and quark-like attributes. Scientists using the D0 detector at the Tevatron proton-antiproton collider have sought in vain for evidence of leptoquarks in interactions at the highest energy available at any accelerator, 1.8 TeV. If they had existed within an accessible mass range, leptoquarks would have been produced in pairs; each would have decayed into an electron and a quark. From the data, the Tevatron scientists estimate a lower limit on the leptoquark mass of 133 GeV. As if to illustrate the massiveness of the undertaking of finding a new class of fundamental particles, the published paper bears the names of 351 authors. (S. Abachi et al., 14 February 1994, Physical Review Letters.) A SCANNING MAGNETIC FLUX MICROSCOPE , a device that can map magnetic fields with a spatial resolution of about 80 microns and a field sensitivity of 7 pico-Tesla-Hz**-1/2, has been developed by a Maryland-Berkeley collaboration (contact Frederick Wellstood, 301-405-7649). The detector uses a 77-K superconducting quantum interference device to sense tiny magnetic fields from a sample which moves back and forth beneath the SQUID in 1-micron steps. For practice, the scientists made a picture of the face of George Washington as it appears on the one- dollar bill. The accurate likeness is composed of the measurements of the enhanced fields in the vicinity of the tiny droplets of magnetic ink used on all greenbacks. The scientific uses of the magnetic microscope include prospecting for the characteristic fields emanating from microscopic nuggets of superconductor buried inside otherwise non-superconducting samples. The microscope can also be used to image poorly-magnetic materials such as thin copper patterns on printed circuit boards by measuring the faint magnetic fields that arise from eddy currents induced in the copper. (R.C. Black et al., 3 January 1994, Applied Physics Letters.) MYSTERIOUS ATMOSPHERIC RADIO BURSTS have been measured by the ALEXIS satellite, which patrols the sky for evidence of nuclear detonations. The radio bursts are much stronger than those associated with lightning bolts and only seem to occur over Africa and South America. The best explanation given so far is that the radio signals may be linked with equally mysterious light flashes seen above certain thunderstorms. (Science News, 12 Feb.) THE GLOBAL POSITIONING SYSTEM (GPS) can determine latitude and longitude for any spot on Earth with an uncertainty of only 10 meters; the distance between two points hundreds of km apart can be determined to within 1 cm. GPS does this by relaying timing signals from a network of satellites, each carrying an atomic clock, to a receiver (sometimes a hand-held device) which calculates the position from the relative time delay of the signals. In an essay in the January 1994 Physics Today, MIT physicist Daniel Kleppner uses GPS as a case study for demonstrating why science is a good investment. He recounts the slow, painstaking march of scientific and technological advances---e.g., hydrogen-maser clocks, microelectronics, high- speed data processing---that culminated in GPS.