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The Best of Both Worlds

Three Wigner fellows divide their time between the laboratory and the classroom.

As a young researcher, Sean Agnew gained a competitive edge when he was named a Wigner fellow in 1999. Three years ago, after he had left ORNL to serve as an assistant professor at the University of Virginia (UVa), he retained his competitive edge by becoming the first former ORNL employee to win a joint faculty appointment at ORNL and an out-of-state university.

UVa is one of UT-Battelle's core universities.*

star cluster
Star cluster.

Agnew teaches in UVa's Materials Science and Engineering Department, serves as the thesis advisor for five graduate students, and conducts research on magnesium alloys in collaboration with ORNL researchers Craig Blue, Joe Horton, and Phil Sklad.

Agnew began working on magnesium alloys when he was encouraged to start a new program by his group leader in ORNL's Metals and Ceramics Division as part of his Wigner Fellowship program. "It was a dealmaker for me," Agnew says, noting that he passed up offers from a corporation and other national labs. "The fellowship's good salary, prestige, and freedom to work on what interests me were definitely incentives for me to come to Oak Ridge."

As a Wigner fellow, Agnew wrote a successful seed money proposal that started a growing program at ORNL to study the mechanical behavior of magnesium alloys. These alloys, which are approximately 4 times lighter than steel, are of interest to DOE and the automotive industry because they may be useful as structural materials for cars and trucks to help reduce their use of fuel.

DOE later funded Agnew to apply a technique he had studied for his Ph.D. thesis at Northwestern University—severe plastic deformation—to the processing of wrought magnesium. Agnew and his collaborators continue developing new magnesium alloys and fabrication processes so that wrought magnesium (rather than cast magnesium) can be used in vehicles more easily and cheaply. Part of that work has involved fundamental scientific studies of deformation mechanisms such as "mechanical twinning," which allows a material to deform by producing a structure in which the crystals on either side of the "twin" boundary resemble a mirror image of each other.

"Young faculty members know it's a real struggle to get funding for a new research program," Agnew says. "I appreciate my joint faculty appointment and the Wigner Fellowship because they have smoothed the way for me to establish my research program."

Agnew comes to ORNL periodically for review meetings and to make use of the Laboratory's special research capabilities—things that UVa cannot easily afford, such as the ability to make and process alloys. "This summer, a student and I will come to ORNL for an extended stay to get some research done," he says. "I plan to come to ORNL in a few years to conduct research using neutron scattering at the Spallation Neutron Source."

Agnew teaches one class a semester, among which are "Introduction to Materials Science," "Physical Metallurgy," and "Mechanical Behavior of Materials." Three of his five graduate students have already obtained M.S. degrees and three are currently pursuing Ph.D. degrees.

Dividing His Time

Thomas Papenbrock, a native of Germany, has a joint faculty appointment with the University of Tennessee and the Laboratory. He spends two to three days a week at UT and the remainder at ORNL.

He received a doctoral degree in physics from the University of Heidelberg in Germany. He completed a three-year postdoctoral assignment at the Institute for Nuclear Theory at the University of Washington in Seattle. In late 2000, he became a Wigner fellow in ORNL's Physics Division, where he investigated nuclei and other quantum many-body systems.

In August 2004 he was appointed a joint faculty mem- ber for UT and ORNL. "Now I am based at UT where I co-taught the nuclear physics course last fall," he says. "I apply quantum many-body theory to nuclei, to systems of ultra-cold, trapped atoms, and to spin chains."

Using the SGI Altix supercomputer and data acquired from experiments at the Holifield Radioactive Ion Beam Facility (HRIBF) at ORNL, Papenbrock aims to achieve a better understanding of the "strong force" between protons and neutrons that make up short-lived, unstable, neutron-rich nuclei.

"The strong force between any pair of nucleons in these nuclei is not simple to measure or predict," Papenbrock says. "By doing calculations and comparing the answers with the results of nuclear physics experiments at HRIBF, we can determine new aspects of the strong force that holds the nucleus together.

"When physicists 'ping' a nucleus with a probe, the nucleus becomes excited and might, for instance, vibrate or rotate. We can infer whether the nucleus is spherical or deformed by measuring its mass and analyzing its excitations. We can, for instance, determine whether neutron-rich nuclei have a neutron skin or a neutron halo."

The understanding of the strong force, and how it determines the structure of nuclei, is far from complete. The importance of three-body forces for the structure of light nuclei has only recently been established. Papenbrock is now extending this theoretical treatment toward heavier nuclei. He is also developing new approximation methods that make theoretical calculations addressing the nuclear many-body problem more feasible and less expensive.

East European in East Tennessee

Robert Grzywacz works in ORNL's Physics Division and teaches astronomy as a faculty member at UT.

Roberyt Grzywacz is a star physicist at ORNL who teaches astromony at UT.
Roberyt Grzywacz is a star physicist at ORNL who teaches astromony at UT.

He emerged as a scientific superstar in nuclear physics 10 years ago while working on his thesis at Warsaw University in Poland. In 1995 he was awarded a prestigious scholarship for young researchers by the Foundation for Polish Science. The award recognized his development of a method for discovering metastable states in exotic nuclei that decay in one-millionth of a second after being produced in heavy-ion fragmentation reactions.

"I discovered a neat method of plotting the data to identify and quantify the excited isomers that decay to the ground state by emitting gamma rays," he says. "This highly sensitive method finds short-lived isotopes in metastable states that are produced at very low rates after a beam of accelerated ions collides with a target."

The Warsaw group was the second to produce and identify the doubly magic tin-100 isotope. "We produced 22 atoms of this isotope while doing research in France." Grzywacz was recruited from Poland to continue his nuclear physics studies in the United States, first as a postdoctoral researcher at the University of Tennessee and later as a Wigner Fellow at HRIBF. "I was recruited by Krzysztof Rykaczewski, my first thesis advisor at Warsaw University, who later joined the ORNL staff," Grzywacz says. "He helped me get a postdoctoral assignment at UT from 1998 through 2000 and a Wigner Fellowship later, allowing me to do nuclear physics research at ORNL.

"We developed new methods of detecting short-lived proton emitters at HRIBF using next-generation, digital-signal processing electronics to acquire data in real time," he says. "The electronics, which can be easily modified by only changing the codes, enable detection of tiny signals—such as the emission of protons or electrons—almost instantly after the radioactive ion arrives at the detector."

After Grzywacz became assistant professor of physics at Warsaw University, he conducted research at Germany's GSI laboratory. "We discovered a new type of radioactivity," he says. "We found a nucleus that simultaneously emits two protons from the ground state. We used the electronics and experience gained at ORNL during our proton radioactivity experiments."

This advanced electronics will likely be used to help determine the fundamental properties of the neutron at the Spallation Neutron Source at ORNL.

* UT-Battelle's core university partners are Duke, Florida State, Georgia Tech, North Carolina State, Virginia, Virginia Tech, and Vanderbilt.


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