In Search of the Beautiful and Unexpected

December 4, 2023

Abhyuday Sharda Wins JLab Fellowship

Abhyuday Sharda likes an open question. For him, that’s where the real beauty of science lies. His search for answers will be supported this academic year with a new graduate fellowship from the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility, commonly known as JLab.

Sharda is a graduate student who’s been working with Professor Nadia Fomin since 2022.

“What I am working on in JLab is studying the structure of the atomic nucleus,” he explained. “The nucleus is more than 99 percent of the visible universe by mass but it is not completely understood. My research is an attempt to understand how protons and neutrons (and their underlying quark distributions) change when inside the nucleus as compared to a free proton or a neutron. We do this by scattering energetic electrons off of nuclei. The way they scatter allows us to infer information about the nucleus.”

With his experimental component complete, Sharda said he’s now analyzing data, the results of which he said are anticipated by the hadronic physics community in general. The JLab graduate fellowship (one of nine granted this year) will support this work, which Fomin pointed out has been rated as high-priority and high-impact by JLab’s Program Advisory Committee.

Going Beyond the Familiar

Sharda’s hometown is Delhi, India, and he traveled across the globe to UT to earn a master’s degree in physics. He said he had such a positive grad school experience he decided to stay on for a PhD. Nuclear physics in particular speaks to his wide-open view of science, and the world in general.

“What I find interesting about it is that the atomic nucleus can be called the building block of the matter in the universe, yet we don’t completely understand it,” he said. “Any open question in physics often leads to beautiful and unexpected discoveries.”

This willingness to embrace the unknown underlies Sharda’s personal philosophy about what science can achieve, summed up nicely by one of his favorite quotes (from Physicist Lisa Randall):

“In the history of physics, every time we’ve looked beyond the scales and energies we were familiar with, we’ve found things that we wouldn’t have thought were there. You look inside the atom and eventually you discover quarks. Who would have thought that? It’s hubris to think that the way we see things is everything there is.”

Raph Hix Elected APS Fellow

October 19, 2023

Star-Stuff, Indeed

We are made of star-stuff, Carl Sagan said in the Cosmos TV series.

William Raphael (Raph) Hix knew that quote. As a high school kid in Maryland he’d taken advanced physics and chemistry. He’d watched Cosmos and heard Sagan talk about stars and elements. But something changed when he encountered this concept in one of his college astronomy textbooks. It took on a gravitas that has captivated him ever since, leading him to climb inside stars (theoretically) to see how the stuff that makes us—carbon, iron, etc.—came to be.

For his “contributions to understanding explosive thermonuclear burning and nucleosynthesis, particularly in contexts like supernovae,” Hix, a UT-Oak Ridge National Laboratory joint faculty professor, has been elected a Fellow of the American Physical Society. This honor is bestowed on only one half of one percent of the Society’s membership each year. Hix is one of 153 Fellows in the 2023 cohort and the second UT physicist elected in the past two years.

Adrian Del Maestro, UT Physics Professor and Department Head, had high praise for the department’s newest APS Fellow.

“Dr. Hix is exemplary of the unique and visionary researchers that bridge the University of Tennessee and Oak Ridge National Lab as joint faculty,” he said. “He is a driving force behind our astrophysics program and is a sought-after mentor and teacher, involving both graduate and undergraduate students in his cutting-edge research on stellar evolution.”

Late Bloomers

Hix is interested in how the chemical elements are made, or nucleosynthesis. The Big Bang gave us hydrogen, helium, and lithium. Since then, nuclear reactions accompanying the life and death of stars have created most of the other elements. As it turns out, stars are late bloomers.

“Most of the elements get made at the end of a star’s life,” he said.

Stars run on the fusion of hydrogen into helium for most of their lives. Hix explained that as a star begins to run out of fuel, temperatures go up and conditions become more extreme. That’s when the heavier elements, like carbon and iron, are made. Once the fuel is exhausted, an ordinary star (like our Sun) violently expels its outer layers, including elements made late in its life, and becomes a white dwarf. For more massive stars, like Betelgeuse, Rigel and Antares, the exhaustion of fuel leads to a supernova—sending those recently made elements into the cosmos—while the stellar core collapses, leaving a neutron star or a black hole.

With colleagues at ORNL and UT, Hix develops sophisticated models to understand how all this works. He leads ORNL’s Theoretical and Computational Physics group, utilizing some of the national lab’s powerful tools, like Summit and Frontier.

“We use the biggest supercomputer we can to model as much physics as possible within the intricate workings inside a star that we (then) blow up,” he said.

The results become part of a chain of handing off data—ultimately going to scientists who use telescopes to see if the model holds up to observation. Hix explained this is how they prove their models are accurate.

“It’s a way to climb inside a star and see the parts that are ordinarily hidden from view,” he said.

When Everything Was Cool and New

Hix finished undergraduate studies at the University of Maryland at College Park, where he re-discovered Sagan’s quote and graduated with bachelor’s degrees in physics and astronomy as well as math. He earned AM and PhD degrees in astronomy at Harvard University. Following a postdoctoral appointment at the University of Texas, he came to UT in Knoxville. He began as a postdoc, became a research professor, and then in 2004 moved (without moving) to ORNL. In 2010, he rejoined the UT faculty with a joint faculty appointment.

In his case, he explained, being joint faculty means that he’s an ORNL astrophysicist and the university subcontracts half of his time to teach courses (like Honors Introductory Astronomy) and supervise students. Hix said he really enjoys working with undergraduates. He loves seeing how excited they are when they come to the national lab and have an office for the summer. He likes being reminded, he said, “of that time in my career when everything was cool and new and interesting.”

About APS Fellows

The APS Fellowship Program was created to recognize members who may have made advances in physics through original research and publication, or made significant innovative contributions in the application of physics to science and technology. They may also have made significant contributions to the teaching of physics or service and participation in the activities of the Society.

Raph Hix is the 10th APS Fellow on UT’s current faculty.

Shape-Shifting Nuclei

August 22, 2023

What determines the shape of a nucleus? UT’s physicists played a key role in recently-reported findings that shed new light on that mystery. Their dedicated work to develop and deploy a sophisticated yet nimble detection system was central to an Oak Ridge National Laboratory-led study of how nuclear shapes evolve. The unexpected results could point to a deeper understanding of how nuclei stay together and how elements form.

Shape Shifters

Nuclei typically appear as spherical or deformed (football-like). Some can shift their shape depending on their energy level— deformed at higher energy (excited state) and spherical at low energy (ground state). The reverse (deformed at low energy; spherical at high energy) has been harder to pin down, especially in regions of the nuclear landscape where little experimental data is available.

In this work, scientists found that a sodium-32 nucleus has an exceptionally long-lived excited state, also known as an isomer. This nucleus sits at the heart of the “island of inversion,” where previous experiments have documented spherical-to-deformed shape reversal. Isomers can help probe nuclear structure, and the one observed in sodium-32 is a rare microsecond isomer in this particular area of the nuclide chart. It can provide a window into the underlying conditions where the spherical-to-deformed transition begins.

The analysis is based on data collected from the very first experiment at the Facility for Rare Isotope Beams (FRIB)—specifically the FRIB Decay Station Initiator (FDSi). This is Professor Robert Grzywacz’s home office, so to speak, as he and his group have invested years in this sensitive, modular detector system, starting with the plans on paper and now actually “catching” the fragments of a rare isotopes created by FRIB’s powerful linear accelerator and measuring their decay.

“We poured an enormous amount of work into this experiment,” he said. “It had to succeed.”

Getting an Early Start

While the observation of the sodium-32 isomer is new, the premise is not. As a graduate student Grzywacz was a lead author on papers outlining a novel method suited to scanning large swaths of the nuclear chart in search of new isomers. His work eventually led him to Tennessee, where in 1998 he became a postdoctoral fellow at UT and in 2003 joined the faculty.

Since then he’s built a talented nuclear physics team of fellow faculty, students, and staff. These latest findings are outlined in Physical Review Letters and UT Physics co-authors include Grzywacz as well as Miguel Madurga (assistant professor); Zhengyu Xu and Kevin Siegl (postdoctoral research associates), Noritaka Kitamura (postdoctoral research associate, now assistant professor at University of Tokyo); Joseph Heideman, Shree Neupane, and Maninder Singh (PhD alumni); Ian Cox and James Christie (graduate students); Harrison Huegen and Amanda Nowicki (undergraduates); and Jason Chan (Electronics Shop Supervisor).

Learn more about the results at Oak Ridge National Laboratory’s website.

With thanks to Dawn Levy of Oak Ridge National Laboratory.