Pohang Light Source: A Major Source of Scientific Discovery

Nan Chen (ATIP Technology Analyst)

Light from synchrotron sources has very high intensity and can span a very wide range of frequencies. There are eight so-called third-generation synchrotron light sources in the world, with a few others under construction. The Pohang Light Source (PLS), which was commissioned in 1994, is one of them. Its operating voltage of 2.5 GeV places it mid-range among the eight (at 8 GeV, Japan's SPring-8 is the highest) and offers access to a wide range of studies in biological and physical sciences. PLS's frequencies range from infrared to gamma rays/hard X-rays. Its physical size is also mid-range for a large modern synchrotron: 160 m linear accelerator; diameter of storage-ring building of 144 m.

PLS is a national users facility for basic and applied science research and is on the campus of the Pohang University of Science and Technology (POSTECH), which is ranked each year among Asia's top technical institutions of higher learning. POSTECH was founded in 1986, with strong financial support provided by an endowment from the Pohang Iron and Steel Company (POSCO). About 60% of the $190M needed to construct the PLS was also provided by POSCO. The remaining 40% and most of the operating funds to date were provided by Korea's Ministry of Science and Technology.

Third-generation synchrotrons feature wigglers and undulators, providing very bright light (millions of times more intense than medical X-rays) that can be focused with high precision. Light of many frequencies is available simultaneously. Beamlines tap into the storage ring's supply of photons. PLS now has 26 beamlines in use or under construction and can eventually accommodate nearly double that amount. Experiments at the various beamlines range from static determinations of the structure of matter to nanosecond-by-nanosecond analyses of, for example, chemical reactions or responses of protein molecules. Each beamline has a limited number of missions. Studies in progress at the beamlines include X-ray microprobe and microscopy, various types of X-ray scattering, photoemission spectroscopy, high-resolution crystallography and diffraction, electrochemistry, macromolecule characterization, lithography, and various surface studies. A recent exciting result from measurements made at PLS and SPring-8 was featured on the cover of the 4 September 2003 issue of Nature. A team of scientists used synchrotron radiation to determine the three-dimensional structures of phosphodiesterase-5 complex with various inhibitors in current clinical use. The results elucidate important aspects of bonding and will assist in discovery of new selective inhibitors with improved pharmacological effects.

Synchrotron radiation has become an indispensable tool for medical, biological, environmental, chemical, materials, and physics research. Studies can be made down to very small length scales, if need be, in real time. Synchrotrons are one of the key tools being used in nanotechnology research and those countries without adequate access to a synchrotron have been constrained in their goals and expectations for development and application of new nanotechnologies.