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Coming Home

Two Tennesseans go to graduate school in New England, but Wigner fellowships bring them home.

As a teenager in Nashville, Tennessee, Dan Bardayan watched the clouds and pondered weather data. But during his undergraduate years as a physics major at Tennessee Tech University in Cookeville,

Dan Bardayan
Dan Bardayan performs experiments at the Holifield Radioactive Ion Beam Facility.

he became less interested in becoming a meteorologist and more excited about pursuing graduate degrees in nuclear physics. In his senior year he looked beyond the clouds to the radioisotopes that make up cosmic rays. By the time he graduated, his name had appeared in Physical Review C on his first scientific paper, which he coauthored with his thesis adviser, a Yale University graduate.

"Using gamma-ray detectors, we studied rare beta decays in certain radioisotopes with long half lives that exist in cosmic rays," Bardayan says. "By measuring the rare decay lifetimes of these isotopes and determining the ratios of these isotopes in cosmic rays, we can predict how many millions of years ago these isotopes were generated, in effect making them cosmic ray chronometers."

Thanks partly to this paper, great grades and standardized test scores, and his adviser's influence, Bardayan was able to study nuclear physics at Yale, where he received two master's degrees and a Ph.D. degree by 1999.

To earn his doctoral degree, Bardayan returned to Tennessee and spent three years conducting nuclear astrophysics research at ORNL's Holifield Radioactive Ion Beam Facility (HRIBF). He conducted a successful thesis experiment with radioactive ion beams to get information that scientists had tried unsuccessfully to obtain with stable beams for 30 years. On the basis of that work, Bardayan received the 2001 Dissertation in Nuclear Physics Award from the American Physical Society, "for the best dissertation in nuclear physics over a two-year period by a graduate student at a North American university." Bardayan also received the 2000 UT-Battelle Author of the Year award for his scientific paper on this experiment, published in the July 1999 issue of Physical Review Letters.

Back to Tennessee

Bardayan came to Oak Ridge for his thesis research because his Yale thesis advisor and professor of nuclear astrophysics happened also to be the thesis adviser of ORNL physicist Michael Smith. When Smith started to set up a nuclear astrophysics program at HRIBF, this same Yale professor promised him a graduate student. That graduate student ended up being Bardayan. "As a native Tennessean, I was interested in doing research in Oak Ridge," he says.

The goal of Bardayan and Smith's experiment was to search for the theoretically predicted quantum state of neon-18 nuclei, which could be produced only when radioactive fluorine-17 nuclei fuse with hydrogen. "It was only when ORNL researchers were able to develop a radioactive ion beam of fluorine-17 that we were able to find the reported quantum state," Bardayan says.

"Our team performed experiments to determine nuclear reactions that produce fluorine-18, and then we conducted experiments to identify the nuclear reactions that destroy fluorine-18." Bardayan says. "Our findings indicate that more net fluorine-18 is produced in novas than scientists previously believed. Novas are explosions in stars; our galaxy has about 30 of these a year. Fluorine-18 is abundant and has a long half-life. Gamma rays from fluorine-18 in space can be detected by observatories in satellite telescopes. Because we cannot send a space probe to a nova, we need HRIBF to help us determine the nuclear reactions that produce and destroy fluorine-18. In the next 10 to 15 years, a satellite telescope may be pointed in the right direction during a nova explosion and verify that fluorine-18 is there."

To perform these experiments, Bardayan had to find ways to come back to Oak Ridge. So, for four years he conducted research at ORNL as a postdoctoral scientist with the University of North Carolina and then as a Wigner Fellow. During that time, he developed SIDAR, a silicon detector array that detects alpha particles and other light ions emitted when radioactive ion beams collide with targets at HRIBF.

Bardayan now is helping with the development of the next-generation version of SIDAR, which will detect 10 times more particles for the same number of beam ions. He found another route to ORNL; he was hired in 2003 as a staff member in the Physics Division, whose director is Glenn Young, also a former Wigner fellow and a Tennessee native.

Meeting Wigner

Glenn Young grew up in Kingsport, surrounded by scientists and engineers both at home and in his neighborhood. His father has a Ph.D. degree in physical chemistry and his mother earned an M.S. degree in biology.

Glenn Young
"The key words in his pitch were 'permanent job after two years.'" - Glenn Young

Young obtained a bachelor's degree in physics from the University of Tennessee and a doctoral degree in nuclear physics from the Massachusetts Institute of Technology in 1978.

Young was not sure what he would do after he got his Ph.D. degree. While walking through the MIT biology building on his way to the elevator to go home, he happened to see a poster advertising the Wigner Fellowship program in Oak Ridge.

"I couldn't tell whether a nuclear physicist doing basic research qualified," he says. "I happened to see Lee Riedinger (now an ORNL associate lab director) in Rochester, New York, that fall at a conference. He invited me to come to Oak Ridge over winter break to give a seminar, which I did. Ed Gross sent me a job application, and John Pinajian called and offered me a job at ORNL.

"My MIT professors found out and started to press me about staying there to take an instructorship. However, I'd seen young men take instructorships and not make the next step onto the faculty, so I was skeptical. A week later, John called back and offered me a Wigner Fellowship. The key words in his pitch were 'permanent job after two years.' That was unheard of in 1978, so I said yes."

As one of the Laboratory's early Wigner fellows, Young had the privilege of discussing his research with Eugene Wigner. "I described my research to Professor Wigner concerning a transition from one type of reaction to another, as indicated by neutron and alpha particle emission following inelastic collisions of light nuclei. He poked and prodded. He characterized something I said as 'very interesting.' That comment made me happy, but 20 years later I was told that that was his polite way of saying he didn't believe a word you were saying. He was right, but it took us two years to work this out experimentally."

Young describes the latter part of his research career as a rather long quest for a state of deconfined quarks and gluons, called the quark-gluon plasma, believed by scientists to have been present in the first 10 microseconds after the universe's birth. With imagery unique to Tennessee, he says, "It's like letting the innards of a proton or neutron out to roam freely, quite in contrast to their normal confined state."

This quest has led Young, other ORNL researchers, and researchers throughout the world to collider experiments, wherein atomic nuclei were smashed from 1986 to 1996 at the CERN lab near Geneva, Switzerland, to incredibly high-energy experiments since 1989 at Brookhaven National Laboratory's Relativistic Heavy Ion Collider.

In Oak Ridge, the pathways of the universe are being explored by two Tennesseans whose Wigner fellowships led them home.


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