Caroline Nesaraja: Providing nothing but the best nuclear data

Nuclear physicist Caroline Nesaraja of the Department of Energy’s Oak Ridge National Laboratory evaluates nuclear data vital to applied and basic sciences. Her work ensures that the scientific community has the best nuclear data for fundamental research and applications including medical isotopes, nuclear energy and national and international security.

“At the heart of nuclear data evaluation is recommending values for a range of nuclear properties for the community to adopt and use,” said Nesaraja. Her exacting evaluation process starts with gathering extensive nuclear structure and decay data from experimental measurements published in peer-reviewed journals.

Through this evaluation process, Nesaraja discovered in 2018 a long-overlooked mistake from a 1975 reference measurement pertaining to the decay of cerium-137.

She presented her finding the following year at the International Atomic Energy Agency, or IAEA, which motivated three research institutions – ORNL, Forschungszentrum Jülich and DOE’s Lawrence Berkeley National Laboratory, or LBNL – to analyze previously available measurements from LBNL, confirming an inaccuracy.

Their publication of the result corrected a reference that had consequences for calculating decay heat in nuclear reactors, element creation in stars and effectiveness of a promising cancer therapy.

Her work supports the mission of the United States Nuclear Data Program, or USNDP, to provide current, accurate, authoritative data for workers in pure and applied areas of nuclear science and engineering. Through the USNDP, which is sponsored by DOE’s Office of Nuclear Physics, Nesaraja and other nuclear physicists at select national labs and universities recommend values for nuclear properties and interactions.

Nesaraja also serves on the International Network of Nuclear Structure and Decay Data Evaluators, which is under the auspices of the IAEA and fills a role similar to USNDP’s for the global scientific community.

She evaluates vast amounts of nuclear data from copious studies done over decades. The diverse experimental measurements reveal nuclear structure, such as ground and excited states, and decay properties including decay modes, half-lives, branching ratios, emission probabilities and radiation energies.

Critical review of the data ensures all state-of-the-art measurements are included. When measurements assessing the same property are inconsistent, Nesaraja pores over details of the experimental methods and analyses.

To determine a best value, she relies on her broad physics knowledge, experimental experience, theory and systematic studies. Sometimes, it’s even necessary to perform a validation experiment to compare measured against reported values.

After peer review, Nesaraja’s evaluated work enters the Evaluated Nuclear Structure Data File, or ENSDF, the preeminent database of evaluated nuclear structure and decay information for 3,350 nuclides. A nuclide is a distinct species of atom characterized by the number of protons and neutrons in its nucleus.

Nesaraja, who is 100% devoted to evaluation, provides one-seventh of the U.S. output to the nuclides data file that is managed by the National Nuclear Data Center at DOE’s Brookhaven National Laboratory.

The need for evaluated nuclear data is growing because of the creation of the Facility for Rare Isotope Beams, a DOE Office of Science user facility, scheduled to open at Michigan State University in 2022.

“It is the biggest challenge for us,” Nesaraja said. “When the facility is fully functional, its many experiments will be followed by publications providing important nuclear data that needs to be compiled and evaluated.”

ORNL’s world-leading position in producing isotopes and developing next-generation nuclear energy technologies also relies on accurate data.

From MacGyver to mass chains

Born in Malaysia, Nesaraja became interested in physics at an early age, inspired by problem-solving adventures in the TV series MacGyver. She has a brother, who is a lecturer, and a sister, who has a doctorate in chemistry; both live in Malaysia but join Nesaraja for travel to Europe and the United States when they can. Nesaraja enjoys trying international cuisines and reading mysteries and thrillers.

She pursued doctoral research at the Forschungszentrum Jülich, Germany’s premier nuclear physics laboratory, and worked with Professor S.M. Qaim, a world-renowned expert in medical isotopes and nuclear reactions. She received her doctorate in nuclear physics in 1998 from the National University of Malaysia and became a lecturer and medical physicist in the university’s hospital.

In 2000, Nesaraja joined the Triangle Universities Nuclear Laboratory at Duke University as a postdoctoral fellow in nuclear astrophysics, a field in which nuclear processes explain the formation of progressively heavier nuclei. While there, a colleague introduced her to nuclear data evaluation, giving her an appreciation for the detailed work and catalyzing her career path.

She accepted a joint postdoctoral appointment with ORNL and the University of Tennessee, Knoxville, in 2004 working with Michael Smith, ORNL’s principal investigator for the USNDP. Nesaraja was trained in nuclear data evaluation by renowned evaluator Murray Martin, retired chief editor of Nuclear Data Sheets.

Nesaraja spent half her time on nuclear data evaluation and half conducting experiments at ORNL’s Holifield Radioactive Ion Beam Facility. She became a staff member in ORNL’s Physics Division in 2008 and continued the 50/50 split until Holifield closed in 2012.

Today, Nesaraja evaluates all nuclides having the same mass number, or sum of protons and neutrons, through a type of assessment called a mass chain evaluation. For example, mass chain 137 has 16 nuclides, such as cesium-137 and xenon-137. Studying nuclides with the same mass number helps scientists follow the beta decay or electron capture and energy states during a nucleus’s lifetime.

Recently, joint evaluations were recommended for four nuclides so three important nuclear databases would provide the same values: that of the Decay Data Evaluation Project at France’s Laboratoire National Henri Becquerel, IAEA’s library of decay data from radionuclides relevant to the Comprehensive Test-Ban-Treaty Organization and the ENSDF database.

Nesaraja and evaluators from France and Australia will evaluate the best value for the decay properties of cesium-137, which is used in part to calibrate radiation detectors.

Her responsibilities will continue with evaluations of mass chains that have not been evaluated for more than 10 years. In addition, she will review evaluations of mass chains assessed by her international colleagues.

The DOE Office of Science supports Nesaraja’s research.

UT-Battelle manages ORNL for the Department of Energy’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.