Muon tomography

Cosmic ray muons have been used for decades to radiograph objects such as pyramids and geological structures. The technique of muon transmission imaging was first used in the 1950s by Eric George to measure the depth of the overburden of a tunnel in Australia.In a famous experiment in the 1960s, Luis Alvarez used muon transmission imaging to search for hidden chambers in the Pyramid of Chephren in Giza, although none were found at the time; a later effort discovered a previously unknown void in the Great Pyramid.In all cases the information about the absorption of the muons was used as a measure of the thickness of the material crossed by the cosmic ray particles. More recently, muons have been used to image magma chambers to predict volcanic eruptions. Nagamine et al. continue active research into the prediction of volcanic eruptions through cosmic ray attenuation radiography. Minato used cosmic ray counts to radiograph a large temple gate. Frlez et al. recently reported using tomographic methods to track the passage of cosmic rays muons through cesium iodide crystals for quality control purposes. All of these studies have been based on finding some part of the imaged material that has a lower density than the rest, indicating a cavity. Muon transmission imaging is the most suitable method for acquiring this type of information. The Mu-Ray project is funded by the Istituto Nazionale di Fisica Nucleare (INFN, Italian National Institute for Nuclear Physics) and the Istituto Nazionale di Geofisica e Vulcanologia (Italian National Institute for Geophysics and Volcanology). The Mu-Ray project is committed to map the inside of Mount Vesuvius, located in Naples, Italy. The last time this volcano erupted was in 1944. The goal of this project is to 'see' inside the volcano which is being developed by scientists in Italy, France, the USA and Japan.This technology can be applied to volcanoes all around the world, to have a better understanding of when volcanoes will erupt. In 2003, the scientists at Los Alamos National Laboratory developed a new imaging technique: muon scattering tomography (MT). With muon scattering tomography, both incoming and outgoing trajectories for each particle are reconstructed. This technique has been shown to be useful to find materials with high atomic number in a background of high-z material such as uranium or material with a low atomic number. Since the development of this technique at Los Alamos, a few different companies have started to use it for several purposes, most notably for detecting nuclear cargo entering ports and crossing over borders. The Los Alamos National Laboratory team has built a portable Mini Muon Tracker (MMT). This muon tracker is constructed from sealed aluminum drift tubes, which are grouped into twenty-four 1.2-meter-square (4 ft) planes. The drift tubes measure particle coordinates in X and Y with a typical accuracy of several hundred micrometers. The MMT can be moved via a pallet jack or a fork lift. If a nuclear material has been detected it is important to be able to measure details of its construction in order to correctly evaluate the threat. MT uses multiple scattering radiography. In addition to energy loss and stopping cosmic rays undergo Coulomb scattering. The angular distribution is the result of many single scatters. This results in an angular distribution that is Gaussian in shape with tails from large angle single and plural scattering. The scattering provides a novel method for obtaining radiographic information with charged particle beams. More recently, scattering information from cosmic ray muons has been shown to be a useful method of radiography for homeland security applications.