From smuggled cargo to the remnants of nuclear accidents, Matt Durham, a nuclear physicist at Los Alamos National Laboratory, can manipulate cosmic-ray particles called muons to peer inside objects that are otherwise impenetrable. He's reminded of the wonder of it all as doctoral student Jesus Valencia gets acquainted with muon scattering tomography for the first time.
At Los Alamos Neutron Science Center, or LANSCE, Jesus is running tests on a 15-foot-high muon tracker. A towering frame holding layers of aluminum drift tubes that function as detectors, it will soon be folded up and trucked to Idaho National Laboratory for an experiment. There, it will be craned back together around a giant storage container filled with burned-up nuclear reactor fuel.
"He's going to get a Ph.D. out of it," says Matt, who's mentoring Jesus, a nuclear engineering student, as he works on his graduate research project — a collaboration between the University of New Mexico and the Laboratory's Muon Tomography team, which Matt is part of.
Using muons to monitor spent nuclear fuel
All around the country, the nation’s discarded nuclear fuel gets stored in dry casks located at nuclear power plants in 37 states. The casks provide a safe way to store discarded fuel when reactors refresh their supplies because they restrain radiation and prevent nuclear fission, according to the U.S. Nuclear Regulatory Commission. But constant monitoring and surveillance are required.
The new experiment at Idaho National Lab could help develop a tool for international nuclear safeguards inspectors, eliminating the need to move these containers, which can easily weigh over 100 tons, to a spent fuel pool to open and visually inspect the contents.
"In the U.S. and a lot of other countries, there is no good solution for what to do with spent fuel. So international safeguards inspectors have to keep an eye on the fuel because it has plutonium in it and check up on it and make sure it's not diverted to a clandestine nuclear weapons program," Matt says. "One of the problems is when spent fuel that contains plutonium is inside this heavily shielded container, there’s no good way to monitor it. You can't X-ray it. You can’t look at the neutrons or gamma rays that come off it because they’re shielded. But muons will go right through the shielding, they'll go right through the spent fuel, and they'll emerge with radiographic information on the spent fuel content of the cask."
The beauty of this "passive" imaging technology is how natural and harmless it is, Matt notes. Muons are particles that basically originate from Earth's upper atmosphere, a result of interactions with naturally occurring radiation in space.
Attentive mentor
Like a computed tomography scan that allows physicians to see inside a body, a muon tomography scan can create three-dimensional pictures of sealed dry cask storage containers. Matt's teaching Jesus how to make measurements of muon scattering on bundles of spent fuel rods, which contain plutonium. Ultimately, Matt and Jesus' experiment strives to verify that premise in real-world conditions.
"The biggest challenge is the scale of the project. Since it is such a big endeavor, we are doing everything we can to make sure we make the most of the measurements in Idaho," Jesus says.
Luckily, Matt is an expert guide. Not only did he perform proof-of-concept studies on this specific application, but he was mentored by muon tomography's chief inventor in the craft. Ten years ago, Chris Morris, another Los Alamos scientist, gave Matt his first permanent job at the Lab. Chris also signed off on the work orders for the Idaho-bound muon tracker.
"Matt has been enthusiastic in supporting my work and also when describing other projects he is working on," Jesus says.
When Jesus had a question about a technical paper, for instance, Matt talked him through the project. "He could've answered my question in a few sentences. Instead, I was able to learn a lot more than I had initially imagined — all of which are things I will definitely apply in future work," Jesus says.
From Hobbs, New Mexico, Jesus says he chose to study nuclear engineering after learning about jobs at the national labs in Los Alamos and Albuquerque, DOE's Waste Isolation Pilot Plant in Carlsbad and the Urenco plant in Eunice. "I thought the work was interesting and figured there would be plenty of career options to keep me in New Mexico near family," he says.
In grad school, Jesus' research became focused on radiation detection systems for nonproliferation purposes. He has used mostly gamma and neutron detection systems, until now.
"When my adviser talked me through how this muon tomography group at Los Alamos was utilizing cosmic-ray muons to image dry cask spent fuel containers, I was immediately interested and thought it was a good way to broaden my horizons and work more directly with charged particle detection and imaging applications," Jesus says.
Sept. 11 spurs radiation-detecting technology
The need for specialized detection technology arose when Congress, in response to the 9/11 terrorist attacks, led the charge to scan all incoming cargo for signs of nuclear smuggling. A Los Alamos team found an answer in naturally occurring muons, which can make 3D pictures of special nuclear material such as uranium, without emitting harmful radiation in the imaging process and while penetrating materials hidden inside lead containers.
For the U.S. Department of Homeland Security, a commercialized version of the invention first analyzed shipping containers in the Bahamas. Since then, researchers inside and outside the Lab have explored far-flung applications for the technology, from surveying nuclear weapons and nuclear reactors to characterizing structures, pipes, closed vessels and geological formations.
Over the years, Matt's name has been on numerous muon-related papers. A new one out this February, co-authored by Japanese and Los Alamos scientists, describes a muon scattering scanner designed to measure nuclear debris in the reactor of the destroyed Fukushima Daiichi Nuclear Power Plant.
That muon scanner exists right here at Los Alamos, and eventually uranium samples from the Fukushima meltdown might be used as test objects. Matt says the concept is closely related to the Idaho approach: "Fuel in a canister we have to image, and muons are the only way to handle it."
Once the waste is removed and potentially characterized with muon tomography, the fuel will get stored somewhere else, he says.
Heavy ions, heavy metal
For Matt, who received his doctorate in physics from the State University of New York at Stony Brook in 2011, the Lab has been a place where he can solve important problems in the national interest and chip away at fundamental science questions.
While he keeps his hand in muon projects, the bulk of Matt's time is spent on heavy ion physics research. He's going deeper and deeper into the kind of questions that brought him to the Lab as a postdoctoral researcher, such as the evolution of particles that make up visible matter. (Fun fact: His heavy ion crew is known for rocking heavy metal band T-shirts at LANSCE on Fridays.)
Being a mentor is now a way of life for Matt, who leads the High Energy Nuclear Physics team in the Nuclear and Particle Physics and Applications group. He interacts with students daily, both at the Lab and after they return to their universities.
"It's one of the most rewarding parts, getting to work with students from all different walks of life," he says. "I feel like I learn as much from the students — at least — as they learn from me."
Matt says he depends on a steady influx of postbaccalaureate and graduate students to round out his team, and Jesus is one of nine on the roster now. Some are full time; others just come for the summer. His commitment pays off: Many students and postdocs become permanent Lab employees in the Physics division and other Lab organizations.
Expanding our understanding of the universe
Matt originally came to the Lab to work on the Pioneering High Energy Nuclear Interaction Experiment, or PHENIX, at the Relativistic Heavy Ion Collider, where he joined Physics division scientists studying how nuclear matter melts and refreezes. Today, he leads the study of exotic tetra-quark particles in heavy ion collisions at the Large Hadron Collider, the world's largest and highest-energy particle collider at the CERN facility in Geneva, Switzerland. Matt is applying new methods of studying these particles that expands our understanding of what forms of matter are allowed to exist in the universe.
In 2021, a high point for Matt was winning substantial multiyear funding through the Department of Energy’s Early Career Awards Program, which supports research at universities and national laboratories. He continues to draw on that money to advance his team’s study of exotic particles, and recently published the first-ever measurement of nuclear modification of tetraquarks, which was selected as a highlight by the editors of Physical Review Letters.
Being part of international collaborations boosts the Lab’s reputation and opens avenues for Matt to build his team. "We are the public face of Los Alamos National Lab within the international nuclear physics community. So having us out there and working on these big experiments allows us to recruit some of the best people internationally to come to the Lab," Matt says.
Meanwhile, for his U.S. students, these collaborations lead to enriching experiences any "suitcase physicist" would love.
Fort Lewis College undergraduate student Victoria Nofchissey has participated in one of these collaborations through the Lab's Engaging Indigenous Women in Nuclear Physics program, which was started by Matt's colleagues. Read more about this program and a surprising observation published this year.
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