Background:

• Postdoctoral Fellow, University of California, 1961-62
• NSF and Ford Postdoctoral Fellow, Centre Europeénne pour la Recherche Nucléaire, Geneva, Switzerland, 1963-64
• Research Associate, Argonne National Laboratory, 1964-66
• ACS Award for Nuclear Chemistry, 1986
• Chairman, Division of Nuclear Chemistry and Technology, American Chemical Society, 1980
• Guggenheim Fellow, 1980-81
• Fellow, American Physical Society, 1986
• Fellow, American Association for the Advancement of Science, 1987
• Indiana University Teaching Excellence Recognition Award, 1998
• Tracy M. Sonneborn Award, 2000

Determining the properties of nuclear matter as a function of density, temperature, and composition is one of the fundamental goals of nuclear science. The resulting nuclear equation of state is essential, not only for understanding terrestrial experiments with nuclei, but also for describing astrophysical systems—for example, the aggregation of nuclear matter to form stars, and their subsequent evolution into supernovae, neutron stars, or black holes. In order to address this problem, our group is currently investigating the formation dynamics and decay mechanisms of hot nuclear matter. Such systems are formed in the collision of energetic nuclear projectiles with complex target nuclei, and are studied using nuclear particle accelerators.

At sufficiently high bombarding energies, one observes multiple cluster formation in nuclear matter, or multifragmentation, signaling a "nuclear phase transition." Recently, we have performed studies that suggest the heating effects of pi mesons and antiprotons cause the nucleus to undergo a liquid - gas phase transition. Our measurements permit us to examine the dynamics of the collisional heating process and the time evolution of the hot multifragmenting system. Recent theoretical studies have also demonstrated that the data are in excellent agreement with general theory of phase transitions and critical behavior.

In order to study these phenomena, our group constructed and successfully implemented a large 500-detector array (the Indiana Silicon Sphere) that permitted simultaneous measurement of the angular and energy relationships of all charged nuclei emitted in these reactions. A new, more complex array based on silicon chip technology has recently been funded and will be used in studies with radioactive nuclear beams.

	Schematic diagram of the collision stages in reactions between a 5 GeV hydrogen ion and a gold nucleus. In the initial stage, heat is deposited in the nucleus, accompanied by the knockout of several fast particles. The hot nucleus then thermalizes and expands, eventually undergoing a "soft explosion, or multifragmentation.

Selected Publications:

Transition from Surface to Bulk Emission in Thermal Multifragmentation, L. Beaulieu, K. Kwiatkowski, W.-c. Hsi, T. Lefort, R. de Souza, G. Wang, D.S. Bracken, E. Cornell, D.S. Ginger, V.E. Viola, L. Pienkowski, R.G. Korteling, R. Laforest, E. Martin, E. Ramakrishnan, D. Rowland, A. Ruangma, E. Winchester, S.J. Yennello, S. Gushue, L.P. Remsberg, H. Breuer, and B. Back, Phys. Rev. Lett. 84, 5971 (2000)

Thermal Excitation-Energy Deposition in 5-15 GeV/C Hadron-Induced Reactions with 197Au I. Reconstruction of Thermal Source Properties, T. Lefort, L. Beaulieu, K. Kwiatkowski, W.-c. Hsi, V.E. Viola, R. Laforest, E. Martin, E. Ramakrishnan, D. Rowland, A. Ruangma, E. Winchester, S.J. Yennello, L. Pienkowski, R.G. Korteling, and H. Breuer, Phys. Rev. C, 64, 064603-1-064603-12 (2001).

Thermal Excitation-Energy Deposition in 5-15 GeV/c Hadron-Induced Reactions with 197Au. II. Relation between Excitation Energy and Reaction Variables, L. Beaulieu, T. Lefort, , K. Kwiatkowski, W.c. Hsi, G. Wang, D.S. Bracken, E. Cornell, D.S. Ginger, K.B. Morley, V.E. Viola, F. GimenoNogues, R. Laforest, E. Martin, E. Ramakrishnan, D. Rowland, A. Ruangma, E. Winchester, S.J. Yennello, R.G. Korteling, L. Pienkowski, H. Breuer, B. Back, S. Gushue, L.P. Remsberg, Phys. Rev. C 64, 064604-1-064604-11 (2001).

The Liquid to Vapor Phase Transition in Excited Nuclei, J.B. Elliott, L.G. Moretto, L. Phair, G.J. Wozniak, L. Beaulieu, H. Breuer, R.G. Korteling, K. Kwiatkowski, T. Lefort, L. Pienkowski, A. Ruangma, V.E. Viola and S.J. Yennello, Phys. Rev. Lett. 88, 042901 (2002).

Event-by-Event Analysis of Proton-Induced Nuclear Multifragmentation: Determination of Phase Transition Universality-Class in System with Extreme Finite-Size Constraints, M. K. Berkenbusch, W. Bauer, K. Dillman, S. Pratt, T. Lefort, K. Kwiatkowski, V.E. Viola, L. Beaulieu, A. Ruangma, S.J. Yennello, R.G. Korteling, L. Pienkowski, Phys. Rev. Lett. 88, 022701 (2002).