A $100 DIY muon tomographer

In the mid-1960s, the Nobel Prize–winning physicist Luis Alvarez had a wild idea. He proposed using muons, highly penetrating subatomic particles created when cosmic rays strike Earth’s atmosphere, to search for hidden chambers within one of the pyramids of Giza. These muon particles are heavyweight cousins of electrons that travel close to the speed of light. They can penetrate through many meters of solid rock, including the limestone and granite blocks used to build the pyramids. But some of the muons will be absorbed by this dense material, meaning that they can be used to essentially “X-ray” a pyramid, revealing its inner structure. So in 1968, Alvarez and his colleagues began making muon measurements from a chamber located at the base of the Pyramid of Khafre. They didn’t find a hidden chamber, but they did confirm the feasibility of what has come to be called muon tomography. Physicists have since used the technique to discover hidden access shafts above tunnels, study magma c ... Read full article.