Exploring the Extremes of the Atomic Nucleus
At the center of every atom is a nucleus made from just two basic building blocks—protons and neutrons. Yet from those simple ingredients emerges a remarkably complex system that scientists are still working to understand. To do that, the researchers are developing a new detector concept called TRIDENT.
For Dr. Ben Crider, professor and associate department head in Mississippi State University’s Department of Physics and Astronomy, that complexity is what makes nuclear physics so compelling.
Crider studies atomic nuclei with far more neutrons than the stable nuclei found in everyday matter. These unusual nuclei can exist for only fractions of a second and sometimes are produced in quantities of only a few dozen.
“The fact that we can still learn something meaningful about systems that are so short-lived has always fascinated me,” Crider said.
Studying these nuclei allows scientists to test theories of nuclear structure and explore larger questions about matter and how many of the heavy elements found in nature were formed.
Studying Nuclei at the Limits of Stability
Crider and his research group use particle accelerators to produce short-lived nuclei and observe how they decay. By measuring the beta particles, gamma rays and neutrons emitted, researchers can work backward to learn about the structure of the original nucleus and how the protons and neutrons interact.
Much of this research takes place at the Facility for Rare Isotope Beams, or FRIB, at Michigan State University. Crider also conducts experiments at national laboratories and university accelerator facilities that provide specialized capabilities for studying nuclear structure and neutron interactions.
One area of particular interest is how dramatically nuclear behavior can change when only a few protons or neutrons are added or removed. Crider’s recent work at FRIB has extended measurements into extremely neutron-rich nuclei where little experimental information previously existed.
“As we reach farther from the nuclei we already know well, the experiments become harder, but they also become much more sensitive tests of whether we really understand the underlying physics,” Crider said.
From Fundamental Science to Real-World Applications
While much of Crider’s research addresses fundamental questions, it also has practical applications. Accurate measurements of how neutrons interact with nuclei are important for nuclear energy, radiation transport, detector development and other technologies that rely on dependable nuclear data.
The research also contributes to understanding astrophysical environments and processes responsible for creating heavy elements. Crider hopes his group’s measurements will provide experimental benchmarks that help scientists determine where increasingly sophisticated nuclear models work and where additional understanding is needed.
Collaboration and Training the Next Generation
Experimental nuclear physics is inherently collaborative, bringing together researchers from universities and national laboratories across the country and internationally. Different facilities provide access to rare isotopes, specialized beams and instrumentation needed to investigate different aspects of nuclear physics.
Crider’s students are integral to these collaborations, helping build and test detectors, conduct experiments, analyze data and interpret results.
“One of the most rewarding parts of the work is watching students go from learning how an experiment works to becoming the person in a collaboration who understands a particular measurement or analysis better than anyone else,” Crider said.
Current projects also combine radiation detection, fast electronics, computer simulations and machine learning to pursue measurements that would be difficult for a single research group to accomplish independently.
Developing the Tools for the Next Discovery
One of Crider’s next goals is to obtain a more detailed picture of what happens when neutron-rich nuclei decay. Rather than simply counting the neutrons emitted, his group wants to reconstruct the process neutron by neutron.
The researchers are developing a compact detector using extremely fast light sensors to determine where and when individual neutron interactions occur. A key challenge is that a single neutron can scatter multiple times inside a detector, making one neutron appear to be several. Distinguishing those interactions could provide a clearer picture of how neutron-rich nuclei decay and enable measurements current detectors cannot easily perform.
Crider and his group will continue studying nuclear structure and neutron interactions while developing the experimental tools needed to answer questions that current technology cannot.
For Crider, each discovery provides a starting point for the next question.
“A good measurement usually tells us something we wanted to know, but it also points toward something else that we do not understand yet,” he said.
