Department of Physics and Astronomy

Research Group: Professors Volker Oberacker and Sait Umar

Research summary

One basic problem that is common to many areas of physics -- and other natural sciences such as chemistry -- is the quantum many-particle problem. Theorists working in atomic, molecular, and condensed matter physics, in nuclear physics and in some areas of astrophysics face a similar challenge: how to describe the features of interacting quantum many-particle systems in terms of suitable constituent particles and the fundamental interactions between them. Such theories are referred to as "microscopic theories".

The aim of nuclear theory is to study the quantum many-particle aspects of the strong interaction, which is one of the four fundamental forces of nature. Because of the large coupling constant of the strong interaction, the vast majority of nuclear phenomena cannot be treated in perturbation theory and require large-scale numerical calculations. At relatively low energy, an atomic nucleus may be viewed as a system of N point-like protons and neutrons which interact via two-body Coulomb potentials and via two-body / three-body strong nuclear potentials. Most of our work uses "nuclear mean-field theories" such as static Hartree-Fock (HF) and Hartree-Fock-Bogoliubov (HFB) to describe individual nuclei. Reactions between two heavy nuclei are described by the Time-Dependent Hartree-Fock (TDHF) theory.

One of the fundamental questions of nuclear structure physics is: what are the limits of nuclear stability? How many neutrons can we add to a given nuclear isotope before it becomes unstable against spontaneous neutron emission (neutron radioactivity)? If one connects the isotopes with zero neutron separation energy, Sn=0, in the nuclear chart one obtains the neutron dripline. Similarly, the proton dripline is defined by the condition Sp=0. Another limit to stability is the superheavy element region around Z=124 and N=184.

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    A nuclear quantum many-body problem: 3-D TDHF calculation for 48Ca + 132Sn   

The nuclear chart shows less than 300 stable nuclear isotopes, and about 2700 additional isotopes have been created in heavy-ion accelerators. Nuclei in between the proton and neutron driplines are unstable against beta-decay. Nuclei outside the driplines decay by spontaneous neutron emission or proton radioactivity. The neutron-rich side, in particular, exhibits thousands of nuclear isotopes still to be explored ('terra incognita'). Some of these exotic nuclei can be studied with existing first-generation Radioactive Ion Beam Facilities (e.g. HRIBF at Oak Ridge National Laboratory). Several countries are constructing new 'second generation' RIB facilities (RIKEN in Japan, FAIR in Germany, GANIL in France). In the United States, construction has begun of FRIB (Facility for Rare Isotope Beams) at Michigan State University.

Theories predict profound differences between the known isotopes near stability and the exotic nuclei at the driplines: for neutron-rich nuclei, as the Fermi level approaches the particle continuum at E=0, weakly bound neutron states couple strongly to the continuum giving rise to neutron halos and neutron skins. Theories also expect large pairing correlations and new types of collective modes (giant mutipole resonances), a weakening of the spin-orbit force leading to a quenching of the shell gaps, and perhaps new magic numbers. Furthermore, Radioactive Ion Beam Facilities will allow us to address fundamental questions in nuclear astrophysics: more than half of all elements heavier than iron are thought to be produced in supernovae explosions by the rapid neutron capture process (r-process). The r-process path contains many exotic neutron-rich nuclei which can only be studied with these new heavy-ion accelerators.

Specifically, our research concentrates on the following topics:
1. Fusion, capture, and deep-inelastic reactions of neutron-rich nuclei in the vicinity of the Coulomb barrier.
2. Hot and cold fusion reactions leading to superheavy elements.
3. Microscopic dynamic calculation of nuclear excitation energies during heavy-ion collisions.
4. Microscopic study of clusters (e.g. triple-alpha reaction).
5. Microscopic description of nuclear fission dynamics.

External research funding

The Vanderbilt Nuclear Theory group has been funded since 1984 by the U.S. Department of Energy, Division of Nuclear Physics.

Prof. Oberacker's Research Honors and Awards

1) Award for " The best Ph. D. thesis written at the Goethe University of Frankfurt in 1977 " (awarded in 1978 by the Association of Friends and Supporters of the Goethe - University in Frankfurt am Main, Germany)

2) DOE Grand Challenge Award, High-Performance Computing and Communications Program, project entitled "The Quantum Structure of Matter", Vanderbilt - ORNL - Univ. Tennessee collaboration, 1992

PowerPoint presentations

"Fusion and other applications of density-constrained TDDFT",
V.E. Oberacker, invited talk at the INT 13-3 Program on
Quantitative Large Amplitude Shape Dynamics: fission and heavy ion fusion,
Institute for Nuclear Theory, Seattle, WA (Oct. 6-12, 2013)
 (PDF, 2.9 MB)

TDHF animations (produced by Volker Oberacker and Sait Umar)

The reaction 48Ca + 132Sn at Ecm = 130 MeV for two different impact parameters

Heavy-ion fusion at b = 4.45 fm (MPEG4 movie, 120 kb)

Deep-inelastic reaction at b = 4.60 fm (MPEG4 movie, 72 kb)

Current and former graduate students

David Pigg (Ph.D. in Aug. 2012, 'First Ab-Initio, Coupled-Cluster Solution of the Time-Dependent Schroedinger Equation for Atomic Nuclei', Adviser: Prof. Umar); Research Associate, Oak Ridge National Laboratory (2012-13), Assistant Professor of Physics, Lee University, Cleveland, TN (Fall 2013 - )

Nikolaus Loebl (March - June 2011); visiting graduate student from Universitaet Frankfurt, Germany

Artur Blazkiewicz (Ph.D. in December 2005, '2D Coordinate Space Hartree-Fock-Bogoliubov Calculations for Neutron-Rich Nuclei in the A~100 Mass Region', Adviser: Prof. Oberacker); software designer, Glasgow, KY (2006-)

Edgar Teran (Ph.D. in May 2003, 'Hartree-Fock-Bogoliubov Calculations for Nuclei far from Stability', Adviser: Prof. Umar), postdoc at San Diego State University (2003-2006); Associate Scientist, PROS software company in Houston, TX (Sep. 2006 - )

Jun Chen, (1998 -2001, Adviser: Prof. Oberacker); Computational Analyst at Bloomberg Financial Services, New York City

Alan C. Calder, (Ph.D. 1997, 'Multidimensional simulations of core collapse supernovae using multigroup neutrino transport', Adviser: Prof. Umar); Research Associate, U. Illinois (Urbana); Research Associate, U. Chicago; Senior Scientist, U. Chicago Flash Center for Astrophysics. Recipient of the Gordon Bell prize. Assistant Professor at SUNY Stony Brook.

D. Russell Kegley, (Ph.D. 1996, 'Spline techniques for modeling weakly bound nuclear systems' , Adviser: Prof. Oberacker); currently RF Engineering Manager at Teledyne Electronic Manufacturing Services, Lewisburg, Tennessee.

Mehmet Cem Guclu, (Ph.D. 1995, 'Monte-Carlo Calculations of Lepton-Pair Production in Relativistic Heavy-Ion Collisions', Adviser: Prof. Umar); currently Associate Professor, Istanbul Technical University, Turkey

Dr. Jack Wells, (Ph.D. 1994, 'Electromagnetic Lepton-Pair Production with Capture in Relativistic Heavy-Ion Collisions', Adviser: Prof. Oberacker); Research Associate, Harvard-Smithsonian Center for Astrophysics; Wigner Fellow and Staff Member at ORNL; first recipient at ORNL of the "Computing and Computational Sciences Fellow" award (2004); Group Leader of the Computational Materials Sciences Group and Group Leader of the Nanomaterials Theory Institute (2008-2009); Director of Institutional Planning at ORNL (2009 - present).

Dr. David Dean, (Ph.D. 1991, 'The String-Parton Model', Adviser: Prof. Umar); Research Associate, Caltech; Wigner Fellow, Staff Member, Oak Ridge National Laboratory, DOE Young Scientist Award, and a Presidential Early Career Award (1997); Group Leader, Nuclear Physics Theory Program at ORNL; Senior Advisor to the Under Secretary for Science, Department of Energy (August 2009-present).

Dwight P. Russell (1983-1986); Asst. and Assoc. Professor, University of Texas at El Paso; currently Assoc. Professor at Baylor University, Waco, Texas.

Mohammad W. Katoot (1983 - 1986), Chairman and CEO, MK Industries, Tucker, GA; deceased Aug. 2000

Current and former postdocs

Dr. Recep Keser (April 2011 - April 2012), Ph.D. Rize University, Turkey

Dr. Clayton R. Chinn (1994-1996), Ph.D. University of Maryland; currently Senior Scientist at Arete Associates (Arlington, VA)

Dr. Guenter Plunien (1992), Ph.D. Universitaet Frankfurt, Germany; currently Privatdozent at Technische Universitaet Dresden, Germany

Dr. Martin Greiner (1988), Ph.D. Universitaet Frankfurt, Germany

Last update: Oct. 2, 2013
Volker Oberacker
Vanderbilt University