PNNL

Christian Boutan, Tirthankar "TC" Chakraborty, Ben Legg, and Maria Laura di Vacri of Pacific Northwest National Laboratory (PNNL) were selected by the Department of Energy (DOE) to receive 2023 Early Career Research Program (ECRP) awards. The four researchers have wide-ranging expertise, exploring subjects from the minerals that make up the Earth to dark matter.

The four PNNL researchers are among the 93 scientists who received this competitive award. Established in 2010, this program provides five years of funding for researchers across disciplines supported by the DOE Office of Science.

“Christian, TC, Ben, and Maria Laura each exemplify how passion for scientific discovery and dedication to mission lead to exceptional contributions regardless of where we are in our careers,” said Steven Ashby, PNNL director. “They represent some of the brightest minds in the nation, and we are fortunate they have chosen to share their exceptional talents with us at PNNL advancing Office of Science research.”

Searching for dark matter

While on the hunt for dark matter, physicist Boutan nabbed PNNL’s first Early Career Research award in High Energy Physics.

This ECRP highlights PNNL researchers’ ability to leverage existing strengths in detector development, quantum information science, and machine learning to break ground in new research.

The axion is a particularly compelling hypothetical particle that could account for the existence of dark matter in our universe and solve a perplexing mystery in nuclear physics. Boutan saw a lack of cohesion in the community's axion dark matter detection strategy and proposed to combine viable—but otherwise competing—discovery pathways by adopting a systems engineering approach. The project will build on Boutan's existing work—which focused on developing a microwave quantum sensing capability at PNNL—to enhance existing detection techniques. The multi-detector system to be designed through this proposal will implement a superconducting qubit-based readout for improved signal-to-noise and incorporate machine learning-inspired automation into the control system to combat instrumentation complexity.

"Together, the engineered synthesis of several lone wolf detection strategies will pave the road to discovery," Boutan said.

Boutan has been a key member of the Axion Dark Matter eXperiment (ADMX) since 2011, and in 2014, he spearheaded a high-frequency pathfinder search for axions, called the ADMX Sidecar.

Better modeling urban land

Historically, urban areas have grown rapidly and are a diverse mix of surface materials, land cover, and other characteristics, with implications for weather and local climate. However, the current generation of Earth system models either ignore urban areas or do not adequately represent their diversity. “These model simplifications can lead to inaccurate simulation results for urban and near-urban regions, particularly in complicated areas like along coastlines, which house most of the global urban population,” said Chakraborty.

Chakraborty plans to improve the current simplistic treatment of urban areas in Earth system models, with a focus on DOE’s flagship Energy Exascale Earth System Model. The proposed improved urban model will incorporate information about the biological, radiative, and structural variations in urban areas across space and time and better represent critical urban-scale processes. After these improvements, this model is expected to more accurately capture how urbanization interacts with the rest of the Earth system. Chakraborty will use the model to enhance our understanding of future weather extremes in U.S. coastal urban environments.

Building the new urban model will require bringing together multiple tools and techniques. Chakraborty plans to perform a global-scale analysis of urban areas on the Earth’s surface by combining satellite and ground-based observations, several gridded datasets, and machine learning, in addition to standard model development strategies. Part of this work will also generate new datasets and approaches that can be incorporated by scientists to develop and improve other Earth system models. His research is supported by the Biological and Environmental Research program.

Understanding mineral surfaces

Minerals can have complex effects on their surrounding environment: they can create local electric fields and even change the molecular structure of ions and water near their surfaces. The unique environments that are created by mineral surfaces can allow new phases of material to form and alter the distribution of chemical elements—including critical elements such as the rare earth elements (REEs).

REEs are essential to modern electronics and energy technologies but can be challenging to obtain. The United States has a limited domestic supply available with current technologies. Understanding how deposits of REEs form and behave may help researchers develop new routes to isolating these valuable elements.

Legg will study how different surface properties influence the formation of “light” and “heavy” REE materials. They will combine advanced experimental and theoretical tools, ranging from atomic-level imaging to high-powered molecular modeling. “I’m excited to find ways to tackle these complex geochemical problems,” said Legg.

While REEs are the primary case study in Legg’s work, the fundamental insights on geochemistry and materials behavior have wide-reaching applicability. This holistic approach to studying the geochemical behavior of REEs will hopefully lead to an enhanced understanding of how surfaces affect the formation of minerals. During the five-year award period, Legg plans to build a body of knowledge that will be useful for basic science researchers and those interested in recovering critical materials. His research is supported by the Basic Energy Sciences program.

Exploring the nature of neutrinos

Originally hailing from Italy, di Vacri began pursuing radiopure materials for nuclear physics at the Università degli Studi dell'Aquila and Laboratori Nazionali del Gran Sasso. Since joining PNNL in 2017, she has applied that knowledge to identify and mitigate trace-level radioactive backgrounds in the materials used for building ultra-sensitive detectors. Now, through her recently awarded ECRP, she will enhance the science reach of the next Enriched Xenon Observatory (nEXO) detector to understand the nature of neutrinos.

Through nEXO, scientists aim to observe a rare type of nuclear decay called neutrinoless double beta decay to learn more about neutrinos. The observation of this decay is extremely challenging due to the presence of naturally occurring radioactive backgrounds. di Vacri will apply her expertise in low-background detectors to improve the nEXO detector’s sensitivity.

As di Vacri describes the research, “The observation of neutrinoless double beta decay would have revolutionary implications. It would suggest that neutrino particles are equal to their own antiparticles. This could help explain the unsolved matter-antimatter asymmetry in the universe, shed light on the origin of our universe, and possibly open a window into new physics. Radioactive backgrounds make all experimental searches for neutrinoless double beta decay very challenging. This work will leverage PNNL’s unique low-background material and assay capabilities to tackle the most prevalent backgrounds predicted for nEXO, to enhance its science potential and ensure its success.”

Though she will focus on nEXO in this proposal, di Vacri’s work “highlights the importance of mitigating backgrounds in materials and from the environment for achieving high sensitivity in low-background experiments,” said di Vacri. Her research is supported by the Office of Nuclear Physics.

The four researchers will begin their projects later this year. “Supporting America’s scientists and researchers early in their careers will ensure the United States remains at the forefront of scientific discovery,” said U.S. Secretary of Energy Jennifer M. Granholm. “The funding announced today gives the recipients the resources to find the answers to some of the most complex questions as they establish themselves as experts in their fields.”