GEORGE S. BROWN

Professor of Physics Ph.D. Cornell University 1973 Fellow of the American Physical Society Office: 290 ISB Phone: (831) 459-2327 Email: gsbrown@ucsc.edu

RESEARCH INTERESTS

Synchrotron Radiation Research

Professor Brown's research program has been devoted to a broad range of interdisciplinary topics requiring intense, highly collimated beams of x-rays.

Starting as early as the late 1950's, electron storage rings have been developed by high energy physics researchers for studying the elementary constituents of nature. These particle accelerators, as it turns out, generate beams of electromagnetic radiation, from the infra-red to gamma-rays, that are many orders of magnitude brighter than conventional sources. The high intensity of these sources has transformed formerly "weak" physical phenomena into now standard probes of physical systems. Many particle accelerators, formerly utilized for high energy physics, are now fully dedicated to this multidisciplinary field, called "synchrotron radiation research." Even more importantly, entire new laboratories, in the United States, in Europe, and in Asia, are being constructed for this class of research.

Atomic physics: With synchrotron radiation, Professor Brown's group has for the first time been able to probe with exquisite detail the inner shells of atomic electrons. By bombarding atoms with photons of precisely determined energy, novel excited states of atoms have been produced where the photoelectron emerges on a slower time scale than the atomic relaxation, resulting in unstable atoms with unusual properties, and with important applications to fusion and to astrophysics.

Resonant nuclear scattering: With synchrotron radiation one can, for the first time, examine the scattering and diffraction of radiation by ordered arrays of resonant nuclei. Professor Brown's group has been the first to observe a host of unusual phenomena related to resonant nuclear superradiance, quantum oscillations, and dynamical diffraction. In addition, his group has been the first to observe resonant nuclear scattering in Ta and gaseous Xe.

Accelerator Physics: The particle accelerators that were designed for high energy physics have served as efficient sources of synchrotron radiation. However, with the advent of accelerators designed especially for synchrotron radiation research, opportunities have been available to develop accelerators and magnetic radiators (wigglers and undulators) extraordinarily well matched to the requirents of the particular experiments. Professor Brown's group has conducted investigations into the optimization of accelerators and undulator magnets for synchrotron radiation, and is now studying the feasibility of short wavelength free electron lasers illuminated by electrons from electron linear accelerators.

Diagnostic medical imaging: In early 1896, within months of the discovery of x-rays, physicians utilized the radiation for the diagnosis of broken bones, bullet wounds, and so forth. To this day x-ray imaging rains the most valuable tool for imaging human organs in vivo. Synchrotron radiation has pushed this frontier, by making it possible to non-invasively image human coronary arteries, bronchial passages, and so forth. Professor Brown's group has pioneered the development x-ray dichromography, and is developing novel diffractive and reflective x-ray optical systems for both medical and nonmedical imaging applications.

SELECTED PUBLICATIONS

"Undulators and the Properties of Synchrotron Radiation," G.S. Brown, Research Advances in Surface and Low Dimensional Science, Plenum Press, New York, 1992.

"MeV Generation with a Femtosecond Laser," J.D. Kmetec, C.L. Gordon, J.J. Macklin, B.E. Lemoff, G.S. Brown, and S.E. Harris, Phys. Rev. Lett. 68, 1527 (1992).

"Multielectron Inner-Shell Photoexcitation in Absorption Spectra of Kr: Theory and Experient," S.J. Schaphorst, A.F. Kodre, J. Ruscheinski, B. Crasemann, T. Aberg, J. Tulkki, M.H. Chen, Y. Azuma, and G.S. Brown, Phys. Rev. A 47, 1953 (1993).

"Nuclear scattering of Synchrotron Radiation by 181Ta," A.I. Chumakov, A.Q.R. Baron, J. Arthur, S.L. Ruby, G.S. Brown, G.V. Smirnov, U. van Burck, and G. Wortmann, Phys. Rev. Lett. 75, 549 (1995).

"Xenon K-edge dichromographic Bronchography: Synchrotron Radiation Based Medical Imaging," E. Rubenstein, J.C. Giacomini, H.J. Gordon, J.A.L. Rubenstein, G.S. Brown, Nuclear Instruments and Methods in Physics Research A 364, 360-361 (1995).