Romualdo T. de Souza

Background:

• National Superconducting Cyclotron Laboratory Fellow, Michigan State University, 1988-91
• IU Teaching Excellence Recognition Award (three times)
• IU Distinguished Teaching Award (President's Award)
• Gill Fellow, Indiana University College of Arts and Sciences
• Alfred P. Sloan Fellow

Nuclei are interesting systems which manifest both macroscopic (collective) and microscopic (quantal) properties. The focus of our research is the response of nuclear matter to extreme conditions of temperature, density, shape, and N/Z. We prepare nuclear matter away from equilibrium by bombarding target nuclei with energetic light-ions (Z < 2) or heavy-ions (Z > 3) and then observe how the excited, compressed, and deformed nuclear matter decays. By studying the details of how the system disintegrates through emission of both light particles (protons, neutrons, etc.) and heavier clusters (Z=3-20) on a very fast time scale ('10-22 sec.), we can learn about the system's thermodynamic (temperature, density, N/Z, etc.) and kinetic properties (particle emission rates).

Understanding the thermodynamic properties (i.e., equation-of-state) of nuclear matter is important in understanding the synthesis of the heavy elements as it occurs in explosive stellar environments (e.g., supernovae) or the existence of objects such as neutron stars. It has recently been realized that it is essential to know the dependence of the nuclear equation-of-state on the neutron-to-proton ratio (N/Z). Recent development of accelerators dedicated to producing nuclei with extreme N/Z now allows us to address this question.

To probe these highly excited systems, we design, build, and utilize high-efficiency, low-threshold detectors with state-of-the-art analog and digital electronics coupled to a high-speed real-time data acquisition system. Powerful workstation clusters are used for subsequent data analysis and theoretical modeling.

Investigating the N/Z of the decaying system requires isotopically identifying the products. Our recent development of LASSA (Large Area Silicon Strip Array) represents a significant advance in our ability to study the isotopic composition of fragments with Z < 8 and thus characterize the short-lived nuclear systems of interest.

Selected Publications:

"Resolving multiple particles in a highly segmented silicon array," with T. Paduszynski, Nucl. Instr. Meth A547, 464 (2005).

"Comparison of midvelocity fragment formation with projectilelike decay", with S. Hudan Phys. Rev. C71, 054604 (2005).

"Interplay of initial deformation and Coulomb proximity on nuclear decay" , with S. Hudan, Phys. Rev. C 70 031601 (2004).

"Isospin diffusion and the nuclear symmetry energy in heavy-ion reactions", with M.B. Tsang, Phys. Rev. Lett. 92 062701 (2004).

"Spin determination of particle unstable levels with particle correlations" , with W. P. Tan Phys. Rev. C 69 061304 (2004).

"Isotope Yields from central 112,124Sn 112,124Sn collisions: Dynamical emission?" with T. X. Liu Phys. Rev. C 69, 014603 (2004).

"Excitation and decay of projectilelike fragments formed in dissipative peripheral collisions at intermediate energies" with R. Yanez Phys. Rev. C 68, 011602 (2003).

"Temperature and n-p asymmetry dependencies of the level density parameter in Ni Mo fusion reactions" with R.J. Charity, Phys. Rev. C. 67, 044611 (2003).