At its most glamorous, the life of an experimental high-energy physicist consists of smashing obscure subatomic particles with futuristic-sounding names into each other to uncover truths about the universe—using science's biggest, most expensive toys in exciting locations such as Switzerland or Illinois. 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. Besides probing pyramids in Belize and Mexico, physicists are applying the muon method to studying active volcanoes and detecting nuclear materials.
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.
