Muons are formed when cosmic rays from deep space interact with the atmosphere. The particles, which strike earth's surface at the rate of about 10,000 per square meter per minute, pass through large amounts of rock or metal with ease, yet their charge makes them easy to track.
Researchers described several promising uses for muon radiography, as it is called, at the annual meeting of the American Association for the Advancement of Science (AAAS).
Arturo Menchaca-Rocha, director of the physics institute at the National Autonomous University of Mexico leads a team that is deploying muon detectors in a tunnel 26 feet below the base of the Pyramid of the Sun in Teotihuacan, about 30 miles northeast of Mexico City. The researchers hope to find any hidden burial chambers or other interior features of the massive pyramid, which is about 740 feet on each side and 215 feet tall. Linda Manzanilla, an archaeologist, is collaborating in the research effort.
Menchaca-Rocha's team has been doing calibration of its instruments in preparation for taking a year's data on muon flux through the pyramid. The team will be looking for any surplus of muons striking a portion of its detector array compared to the background flux. That would be an indication that voids in the pyramid have allowed more particles to pass through to the detectors than expected. The denser an object, the less likely the muons are to pass through. The detector consists of an array of thin wires immersed in a gas. A muon passing through the detector will create an electric charge in the gas that ca