What lies beneath: Muon detectors are unleashing the secrets of what lies beneath Egyption and Mayan pyramids, as well as other ancient archaeological ruins.
Credit: Photolibrary
Without a muon detector, Manzanilla can't test her predictions. "The Pyramid of the Sun is so wide and high," she says. "Ground-penetrating radar can see only a small depth and width. We can expand that view using the muon detector." And, she hopes, put to rest speculation about what is inside.
Scwitters is eager to answer similar questions at La Milpa in Belize, but the design of his detector is slightly different.
It's a gas-filled cylinder wrapped with strips of material that detect muons as they enter and leave. Another detector, at the bottom of the cylinder, picks up fl ashes of light from muons zipping through the gas.
Rather than putting his detector directly below the pyramid, which would require digging a tunnel, Schwitters plans to place two detectors in shallow shafts on either side and 50 to 60 metres apart. This will eliminate blind spots and make it easier to construct a 3-D image.
Only the most energetic muons will be used for the reconstruction; since they are not as easily deflected, their paths through the site are truer and more direct. Schwitters says it should take about 10 days to record and trace 1,000 muon arrivals.
While waiting for the funding they need to set up a laboratory in Belize, Schwitters and his team have been testing the five-metre-long prototype detector they have built at the University of Texas in Austin.
Big stacks of bricks stand in for the stony bulk of the pyramid; the team moves the bricks up onto the roof and into other difficult positions to see how the detector handles the challenge. From the data, Schwitters and his group can see not only the piles of bricks, but also the shadows of the nearby engineering and physics buildings, massive structures that impede the flow of muons. If the detector can distinguish these dense objects, Schwitters says, it can find cavities as well.
"The technology has really improved since the time of Alvarez," says Schwitters. "The detectors are simpler and more robust. We're looking to make the detector more portable and improve our software, and then we can get serious."
Designing the detector is the first of many challenges for the Schwitters team. Once they get funding and permission, they will have to transport the detectors to Belize and dig holes in which to put them. They'll also need to find a way to power the lab at the remote site. "It's a slow process and we've got a lot to do here," Schwitters says, adding that he hopes to move to Belize by the first half of 2009.
La Milpa remains shrouded in mystery. Hammond says, "Some questions we cannot yet answer are: why was the city founded? What was its strategic or economic importance? Why did it collapse? And why was it abandoned in a time of great construction?" Muon detection may answer at least some of these questions and give archaeologists an edge to unearth the next exciting discovery.
Haley Bridger is a science writer at the Broad Institute in Boston. This article originally appeared in Symmetry magazine, Mar/Apr 2008.
