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Nuclear Physics Research
Introduction
Nuclear physics is a broad area of science pursued by four active research
groups at the University of Tennessee. Two research groups, one experimental
and one theoretical, are engaged in the studies of nuclear structure. Another
group is active in the study of collisions of heavy ions at ultra-relativistic
energies, a regime suitable for the study of nuclear matter as it might
have existed before the formation of nuclei. A fourth area of endeavor is
in the modeling of explosive astrophysical occurrences, with a goal of understanding
the details of the energy release and the formation of elements in such
explosions.
Nuclear Structure Physics
 Nuclear
structure research is led by Carrol Bingham
and Lee Riedinger in experiment and Witek
Nazarewicz, Thomas Papenbrock and David
Dean in theory. Both programs include the work of postdocs, graduate
students, visitors, and research faculty. This research program has wide
overlap with people and facilities in the Oak Ridge National Laboratory
Physics Division. The strengths and mutual interests of the experimental
and theoretical efforts have led to a combined program that is among the
world's strongest university programs in nuclear structure physics. Even
though research in this branch of nuclear physics has been conducted in
some form for 40 years, the evolution of new ideas, directions, and tools
has led to interesting new physics in recent years. Perhaps the two most
visible aspects of nuclear structure research are the studies of nuclei
at extremes of high angular momentum and at extremes of neutron/proton imbalance.
These are exactly the two major areas of experimental and theoretical programs
at UT.
In order to study nuclei far from stability, our faculty have in the past
utilized isotope separators at Oak Ridge and CERN in Geneva, Switzerland,
and more recently, the Fragment Mass Analyzer at Argonne National Laboratory,
where UT has formed a collaboration to study the decay mechanism of proton
radioactivity. To facilitate the study of nuclear structure and reaction
properties far from stability, the U.S. Nuclear Science Advisory Committee
recommends the construction of a large radioactive-nuclear-beam (RNB) accelerator
facility as the next major building project for DOE in nuclear physics.
Oak Ridge is well positioned to be the site for this next generation RNB
facility, since the Holifield Radioactive Ion Beam Facility (HRIBF) at ORNL
is the DOE first-generation RNB accelerator with radioactive beams for experiments.
Our experimental group has been approved for three of the first six experiments
at this national user facility, and is actively involved in building and
testing the experimental equipment for these studies. Our theory work, under
the leadership of Dr. Nazarewicz, has led to the strong justifications for
this facility.
The other major thrust in UT's nuclear structure physics program is the
study of nuclei at high angular momentum and in extremes of shape deformation.
The discovery of superdeformation has led to intense studies of nuclear
collective modes with ever increasing arrays of gamma-ray detectors. Both
our experimental and theoretical groups are extremely active in high-spin
physics. At present, the world's best detector for nuclei in extreme spin
modes is called GAMMASPHERE, composed of 110 Compton-suppressed Ge counters.
This detector is stationed at the Lawrence Berkeley National Laboratory
and is a prime source of experimental data for the UT research group.
Studies of Hot and Dense Nuclear Matter
This research is led by Soren Sorensen
and Ken Read and involves several postdocs,
graduate students and computer programming assistants. Because of the construction
of the Relativistic Heavy-Ion Collider
(RHIC) at Brookhaven National Laboratory, and our faculty's strong involvement
in the construction of one of the large detectors (PHENIX) to be used in
this facility, the group is in a prime position to do forefront measurements
in this emerging field.
 The
main goal in this exciting new field of high energy nuclear physics is to
study nuclear matter at extremely high temperatures and energy densities.
Today our researchers have a much better understanding of the complicated
reaction mechanisms involved in ultra-relativistic heavy-ion collisions
than in the past due to experiments at the SPS at CERN and the AGS at Brookhaven.
However, there are still many open questions, some so elementary as the
discovery of the most important degrees of freedom in hot dense nuclear
matter. For example, can a hadronic scenario based on baryon and meson resonances
give the best description or is it necessary to invoke a quark-gluon plasma?
Charting unknown territory in this relatively new field of endeavor requires
that the signatures used to answer the most intriguing questions be developed
in the initial stages of the work. New experimental beams at CERN and especially
at Brookhaven should raise the energy density to the level where the critical
questions can be addressed. The next several years will be an exciting time
for this research.
Nuclear Astrophysics
Mike Guidry
and Mike Strayer are actively involved with other colleagues at Oak Ridge
in the study of explosive events in the universe such as novae and supernovae,
through which all heavy nuclei were initially formed from lighter nuclei.
This field involves modeling the explosions and involves a wide range of
physics, from a mixture of strong nuclear reactions and massive gravitational
fields to energy and matter propagation during the course of the explosion.
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