Standing beneath the Maya temple of El Castillo in Chichén Itzá, Mexico, University of Virginia third-year physics student Sydney Roberts could feel the gulf of time that stretched before her, back to the ancient civilization whose monuments still stand.

Roberts could also envision a futuristic scene playing out in front of her. Dense particles called “muons” – created when cosmic rays crash into atoms in the atmosphere – were coursing through the seemingly impenetrable pyramid in search of hidden chambers.

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Sydney Roberts in a hard hat and orange vest poses for photo in front of El Castillo

That’s the science behind the Non-invasive Archaeometry Using Muons project. It’s an international partnership between a half-dozen universities, including UVA, and the Exploring the Great Pyramids project.

The UVA portion of the project, led by physics professor Craig Dukes, is particularly focused on designing a detector to record cosmic-ray muons passing through the pyramid to scan the interior for hidden voids.

Researchers have been working on the detector’s design since 2016 and are now in the process of raising funds for the Exploring the Great Pyramids project and building a prototype for El Castillo. The prototype will first be tested at Fermilab, a particle physics and accelerator laboratory in Batavia, Illinois.

Dukes invited Roberts to work on the pyramid project after he heard about her work as an undergraduate researcher on other Fermilab projects.

“I had prior experience fabricating, testing and analyzing data for cosmic-ray detectors through UVA’s High Energy Physics Laboratory, so I was excited to accept Professor Dukes’ offer to join this interesting project,” Roberts said.

Portrait of Craig Dukes

Together, the two applied for a grant from the Jefferson Trust – a donor-led initiative of the UVA Alumni Association – to work on the project in Chichén Itzá, once one of the largest Maya cities. That funding was approved in early 2022 and Roberts and Dukes traveled to Mexico over spring break. Their goal was to complete a series of preliminary measurements needed to construct the detector.

From Space to Ancient History

The detector will harness the power of cosmic-ray muons, which Dukes said are particularly suitable because they are very energetic. That means they can easily pass through large masses and penetrate roughly 100 feet of limestone.

“It is effectively like taking a very detailed X-ray of the pyramid,” Dukes said. “And, importantly, it is noninvasive. It does not damage the structure in any way.”

A similar project called Scan Pyramids discovered a previously unknown chamber in the Great Pyramid of Giza in Egypt. Now, Dukes and his team hope to build on that work by creating an even more powerful detector with greater resolution to place inside El Castillo. Eventually, the team hopes to place detectors at the base of the Great Pyramid and others in Egypt. It will scan both external and internal structures and create a tomographic, or three-dimensional, image.

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The team published the detector design earlier this year, garnering some media attention. It is essentially a modular telescope system that can be placed in shipping containers. As designed, the detector can then scan a structure from numerous different angles with up to 100 times the sensitivity of previous designs used, creating a tomographic image with unprecedented detail.

Dukes’ UVA physics colleague, research scientist Ralf Ehrlich, has validated the technique on the Open Science Grid, a worldwide collection of technological resources for research.

Four people in orange vests and hard hats relax near an entrance at the base of the pyramid.

On the spring break trip, Dukes, Roberts and their colleagues took preliminary cosmic-ray muon flux data with a simplified detector at seven locations, on- and off-site. They scanned the exterior and interior of the pyramid with a laser to create a detailed CAD model of the structure, and they also took drone photos and videos of El Castillo and other structures. This data will help the team simulate how the detector will work, determine what resolution is needed to see inside the pyramid effectively, and identify the variables needed for the detector’s algorithms.

Next year, the team hopes to put the full-size, complete detector into the tunnels at the base of El Castillo and begin scanning the interior.

From Maya Cities to Egyptian Pyramids

Dukes is also part of a group working to scan the Great Pyramid of Giza, the burial place of the ancient Egyptian monarch Khufu. This team hopes to confirm the void discovered by the Scan Pyramids project and develop more detailed images of the pyramid’s interior. Because the Great Pyramid is five times taller and four times wider than El Castillo in Chichén Itzá, the project will require multiple large detectors to be placed in refrigerated shipping containers on the four sides of the pyramid.

“We plan to have eight in place at one time and move them around as needed,” creating a fairly flexible system for its size, Dukes said.

Dukes believes the resulting images will offer never-before-seen clues into the pyramid’s interior and its construction. They could also reveal previously unknown artifacts that might help us better understand the civilization that Khufu presided over.

Three views of the pyramid of Khufu in Egypt
This diagram, showing the Egyptian Pyramid of Khufu, illustrates how particles called “muons” pass through the structure. Modern instruments allow scientists to more clearly track the presence of those cosmic-ray muons (simulated in middle image), and in the process, reveal hidden spaces or voids in the pyramid that remain unexplored (diagrammed in right image).

For Roberts, that sense of the unknown is part of what made the El Castillo project so compelling.

“Walking up to the site and seeing the brilliant capability of the Maya people to build these immense cultural and historic landmarks over a thousand years ago is fascinating, and I’m honored to now be part of that history,” she said. “As a physicist, my job is to use our scientific field of study to give back to society. With muon tomography, we can explore inside cultural structures previously uninvestigated while preserving the history, delving into the substructures with particles and uncovering the mysteries there.

“One of the archeologists on site captured the feeling perfectly by calling the temple an enigma, a mystery, and that he, along with us all, looks forward to the day El Castillo’s secrets are revealed.”

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McGregor McCance

Associate Vice President for Communications and Executive Editor, UVA Today Office of University Communications