Heavy Ion Reactions

The availability of energetic, light- and heavy-ion beams from the K500 provides many possibilities for exploring new aspects of nuclear behavior. Using a wide variety of projectiles and bombarding energies, one can hope to achieve a more detailed understanding of the dynamics of nuclear collisions, casting new light onto the temporal evolution of quantal systems under a broad range of conditions and yielding fertile testing grounds for theories of many body systems, chaotic regime dynamics and the statistical mechanics of strongly interacting, finite systems. At the same time, one can investigate the properties and the decay modes of nuclear systems up to their very limits of thermal and rotational stability. Advanced instrumentation plays a key role in these investigations. A 4p neutron and charged particle detection system, NIMROD, is used to select collisions according to their violence. Dynamic and thermodynamic information is derived from the observed multiplicities, energies and angular distributions of the particles and fragments produced.

Besides the obvious implications of an improved understanding of nuclear behavior, reaction mechanism studies can profoundly impact other areas of science. In particular, thermodynamic information concerning the behavior of nuclear systems derived from these investigations can shed light on the nuclear equation of state. This yields important input relevant to problems in nuclear astrophysics, such as the big bang, stellar evolution and the dynamics of supernova explosions.

In other types of measurements, the emission of energetic photons is used to explore nuclear properties and dynamics. These studies involve the detection of light charged particles and heavier fragments in coincidence with so-called Giant Dipole Resonance gamma rays. A
Giant Dipole Resonance is a vibration of the nucleus in which the protons and the neutrons move in opposite directions causing the nucleus to acquire a transient dipole moment. The energy spectrum of the photons emitted from the de-excitation of this mode carry information on the deformation of the decaying system.

Moreover, the yield of these photons offers insights into the time scale of the decay process. Experiments are currently in process to utilize this phenomenon to explore the lifetime of fission and other processes.