Muons Meet the Maya

Submitted by coldrum on Saturday, 15 December 2007 Page Views: 1416

The life of an experimental high-energy physicist consists of smashing subatomic particles with futuristic-sounding names into each other to uncover truths about the universe—using science's biggest, most expensive toys. But it takes a decade or two to plan and build multibillion-dollar atom smashers. While waiting, what's a thrill-seeking physicist to do?
How about using some of the perfectly good, and completely free, subatomic particles that rain down on Earth from space every day to peek inside something really big and mysterious, like, say, a Mayan pyramid?

That's exactly what physicist Roy Schwitters of the University of Texas at Austin is preparing to do.

High-energy particles known as muons, which are born of cosmic radiation, have ideal features for creating images of very large or dense objects. Muons easily handle situations that hinder other imaging techniques. Ground-penetrating radar, for instance, can reach only 30 meters below the surface under ideal conditions. And seismic reflection, another method, doesn't fare well in a complex medium. With muons, all you need is a way to capture them and analyze their trajectories.

The concept sounds out of this world, but it's really quite simple. When cosmic rays hit the Earth's atmosphere, collisions with the nuclei of air atoms spawn subatomic particles called pions that quickly decay into muons that continue along the same path. Many of the muons survive long enough to penetrate the Earth's surface. Because of their high energy, the particles can easily pass through great volumes of rock or metal or whatever else they encounter. However, they are deflected from their path by atoms in the material, and the denser the material, the greater the deflection.

Schwitters wants to exploit this deflection to see if there are any rooms or chambers inside a Mayan pyramid in Belize, he told science journalists in Spokane, Wash., at a recent meeting sponsored by the Council for the Advancement of Science Writing. His team is building several muon detectors that would be buried in shallow holes around the base of the pyramid to create an image of what's inside by measuring the trajectories of the muons that pass through it.

"What you see is very much like an X ray," he says. "If you see a spot with more muons, it means there's a space there. If you see fewer muons, it means there's something extra-dense there."

Schwitters won't be the first to marry physics and archaeology in this way. In 1967, Nobel prize–winning physicist Luis Alvarez of the University of California, Berkeley placed a muon detector in a chamber beneath the pyramid of Khafra in Egypt to see if it was hiding any burial chambers like those discovered in the larger pyramid of Khufu. He found none, but the experiment showed that the method worked.

From physics to archaeology
As the director of the Superconducting Supercollider laboratory in Texas until 1993, when Congress gave the project the axe, Schwitters is no stranger to waiting for the next big thing. And he has always been intrigued by the possibility of applying the tools of the high-energy physics trade elsewhere, so a chance conversation with one of Alvarez' former colleagues, combined with a little spare time, got Schwitters wondering what other enigmatic ancient structures were waiting to be probed.

Archaeologist Fred Valdez, director of the Mesoamerican Archaeological Research Laboratory at UT Austin, had the answer: an enormous pyramid in the third-largest Mayan city in Belize. The city is in an area in northwestern Belize known as La Milpa, which was home to one of the densest populations of Maya from as early as 1000 B.C. until around A.D. 850. The area was packed with four large cities, each with 20,000 or more residents, that were only around 8 to 12 kilometers apart with 60 or more towns, villages, and hamlets in between. Valdez believes there is much to be learned from the society that existed there.

"The amazing part is how close how many of these large cities are to each other," he said. "The Maya were clearly expert at adapting to their environment and exploiting their environment, clearly making better use of things than we are today, just to support the populations that were there."

Because there isn't a chamber below the La Milpa pyramid, Schwitters plans to harness muons with four or five smaller detectors spaced around the structure to get a three-dimensional view inside. Each detector will be a cylinder wrapped with strips of polystyrene, which emits light when hit by a muon. The bursts of light as each particle passes through both sides of the detector will be recorded by photo detectors at the end of the cylinder and used to reconstruct the muon trajectories.

Dense matter will deflect muons away from their paths, so fewer muons will hit the detectors from that area while more particles will pass through empty spaces to reach the detectors. A computer program will translate the information into an image that can be read like a CT scan or an X ray with bright spots indicating voids and dark areas correlating to more dense matter. Because muons hit the Earth at the rate of about 1 per square centimeter per minute, it will take several months to get a good image of the guts of the pyramid. Schwitters hopes he'll be able to resolve chambers as small as a cubic meter.

20/20 hindsight
Knowing exactly where to dig to find potential tombs or other chambers could save precious time when dealing with very large structures like the pyramid in Belize. It could also save artifacts that need special treatment, sometimes within hours, to keep them from deteriorating from exposure. Dust in a tomb that is normally trampled during excavation could contain valuable information about diseases that affected the Maya, or about the plants and herbs they used.

"Ideally, the results would give us a look into the building without having to do the destructive process of excavation," Valdez said.

He envisions being able to drill a small auger hole into a chamber and send a fiber-optic camera down to take a look. That way he can study the chambers exactly as they were left, and the appropriate experts and equipment can be on hand to deal with the contents as they are exposed by coating them with resin, immersing them in water, or sealing them in an airtight case.

"That's tremendous information," he said. "It's almost like 20/20 hindsight."

For more planned Muon Expeditions, see the article in Science News.

Note: Muons set to also probe unexcavated areas of Ancient Sites in the Americas, physicist says.

Contributor Bio for coldrum: Based in Milkyway, contributing since 2002. Favourite site: Avebury.

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