As physicists continue to push the boundaries of known science, researchers rely on precise atomic and nuclear data to conduct accurate experiments and to reveal unknowns such as dark matter.
Information about the tiny size of the nucleus, the dense and massive core of atoms, is crucial for testing of the most accurate theories of physics. However, scientists did not have definitive size estimates for heavy elements, which limited the impact of otherwise highly precise laser-based experiments.
A research team led by Endre Takacs, a professor in the Clemson University Department of Physics and Astronomy, along with collaborators from several research institutions, developed a novel method to determine the size of the center nucleus of elements. The experiments and part of the theoretical work were conducted at the Atomic Physics Group at the National Institute of Standards and Technology, led by Yuri Ralchenko. Theoretical support was provided by Steven Blundell at the University of Grenoble Alpes, while several other groups contributed to the experimental efforts.
Groundbreaking research, supported by theoretical insights from newly hired Clemson assistant professor Dipti, demonstrates how highly charged ions offer a unique method for determining nuclear charge radii where other techniques face challenges. As a result, Ph.D. student Hunter Staiger and Takacs represented the United States at an International Atomic Energy Agency Conference in Vienna, Austria.
The IAEA in an international organization within the United Nations family that works with member states to promote the safe, secure and peaceful use of nuclear technology.
International invitation
The conference was an invitation-only technical meeting organized by the Nuclear Data Section of the IAEA. It featured leading experts from around the world. The IAEA requested Takacs and Staiger’s participation from the U.S. government, as the only two in-person U.S. representatives at the meeting.
“Both Hunter and I are excited to be involved in this important international program and to contribute meaningfully to the field,” said Takacs, who was elected to chair the meeting.
Other groups at the meeting shared progress in well-established methods of measuring the nuclear size, such as electron scattering or muonic atom spectroscopy. These methods work well for lighter atoms, but conducting these types of experiments with larger, heavier atoms can be expensive and may not work well with radioactive atoms due to their instability. The technique developed at Clemson requires only a few hundred-thousand trapped atoms, making it well suited for studying rare or radioactive elements.
As a graduate student in Takacs’ lab, Roshani Silwal conducted an experiment on two different isotopes of the element xenon to determine the change in the nuclear radius between them. Silwal earned her Ph.D. in physics from Clemson and is currently an associate professor at Appalachian State University.
New method
Adam Hosier, another Clemson physics Ph.D. graduate from Takacs’ lab, took Silwal’s results a step further and developed a method to find the difference in atomic nucleus size between two elements, iridium and osmium, the cornerstone of Hosier’s thesis.
He made both elements sodium-like by removing all but 11 bound electrons, leading to a compressed, negatively charged electron cloud around the nucleus. These exotic ions are created by a dense beam of electrons in an electron beam ion trap (EBIT) and radiate extreme ultraviolet light. Using this method, the team determined the atomic nucleus size of iridium by referencing well-known values of osmium.
The enhanced compression of the electron cloud allows for observations of the nucleus that scientists could not see in a neutral atom, making approximations for theoretical calculations more precise.
Reduced uncertainty
The group’s experiment reduced the uncertainty of iridium’s nuclear radius from previously calculated experiments by a factor of eight. The experiment also requires only a few hundred thousand atoms, much less than most experiments, saving up to millions of dollars, Hosier said.
This developed methodology could help build more accurate theoretical models to describe the world around us. Other physicists can use the novel methodology the group developed to explore unknown atomic nucleus sizes further using an electron beam ion trap, or EBIT.
“We can produce better results for a fraction of the price while using very robust, spectroscopic techniques that have been around for decades,” says Hosier who now works as a quantitative analyst at an energy storage developer in Charlottesville, Virginia.
Staiger continued work on that line of research and proposed at the international meeting a new analysis method for the next generation of recommended values for nuclear charge radii in collaboration with Istvan Angeli, a leading expert from Hungary who is considered a pioneer in the field of nuclear physics. Angeli was Takacs’s advisor and Staiger affectionately calls him his “grand-advisor.”
The new analysis method will be included in an IAEA report.
Staiger received his bachelor’s degree in electrical engineering from Clemson. He decided to stay in Tigertown and began pursuing his Ph.D. Now in his second year, Staiger changed to physics after conducting research with Takacs as an undergraduate student. Takacs is now his advisor.
With the growing popularity of EBITs in research labs worldwide, Staiger has been invited to complete a predoctoral fellowship at Harvard, where he will set up the EBIT at the Center for Astrophysics | Harvard & Smithsonian to conduct these measurements using the Clemson-developed technique. He also plans to measure radioactive isotopes at the TRIUMF TITAN facility in Vancouver, Canada.
Staiger went into physics partially for his love of programming. Physics provided real-world application problems to solve with his programming skills. Staiger, who as an undergraduate tutored other students at the Class of 1956 Academic Success Center, said he hopes to become a professor after he graduates.
“I love building the confidence of people getting into STEM and to show them that they can succeed,” Staiger says. He believes that a career as a professor would provide a rewarding combination of solving complex problems in research and building up the next generation of scientists.
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