muondetector.com

Muon tomography is a new technique that uses cosmic ray muons to generate three-dimensional images of volumes using information contained in the Coulomb scattering of the muons. Since muons are much more deeply penetrating than X-rays, muon tomography can be used to image through much thicker material than x-ray based tomography such as CT scanning. The muon flux at the Earth’s surface is such that a single muon passes through a volume the size of a human hand per second. Since its development in the 1950s, muon tomography has taken many forms, the most important of which are muon transmission radiography and muon scattering tomography. Muon detectors can detect the muons location, and when several are stacked on top of each other, they can track the paths of the fast moving particles. The denser the material a muon passes through, the more its path is deflected. Uranium and plutonium are two of the densest elements in the periodic table, so the detectors are used to look for places where the paths of muons are the most disrupted.

To look for nuclear materials, a shipping container is placed between two sets of large GEM detector plates. Two plates on top of the container track the paths of incoming muons, and two plates underneath track them on their way out. If there’s little or no dense material in the container, than the two parts of the muon’s path should line up. Even iron won’t deflect muons a great deal. However, if there’s a lot of dense material, like plutonium, uranium or lead shielding, the paths should veer sharply. Then, muon detector are more and more used for anti-terrorist purposes.