Number 221 (Story #4), April 10, 1995 by Phillip F. Schewe and Ben Stein THE ADVANCED PHOTON SOURCE (APS) is nearing completion at Argonne. The $811 million synchrotron light source uses 7-GeV positrons to produce short pulses of hard x rays. One of the chief functions of the APS will be as an x-ray camera, taking still photos of proteins and movies of molecules on the move. APS's chief rivals are the 6-GeV European Synchrotron Radiation Facility (ESRF) in Grenoble, France (finished last year) and an 8-GeV machine in Japan, to be finished in 1998. (Science, 31 March.)