Muon tomography

The apparatuses record the trajectory of each event to produce a muogram that displays the matrix of the resulting numbers of transmitted muons after they have passed through objects up to multiple kilometers in thickness.

[8] Twenty years after Carl David Anderson and Seth Neddermeyer discovered that muons were generated from cosmic rays in 1936,[9] Australian physicist E.P.

George made the first known attempt to measure the areal density of the rock overburden of the Guthega-Munyang tunnel (part of the Snowy Mountains Hydro-Electric Scheme) with cosmic ray muons.

Although he succeeded in measuring the areal density of rock overburden placed above the detector, and even successfully matched the result from core samples, due to the lack of directional sensitivity in the Geiger counter, imaging was impossible.

The first muogram was produced in 1970 by a team led by American physicist Luis Walter Alvarez,[13] who installed detection apparatus in the Belzoni Chamber of the Pyramid of Khafre to search for hidden rooms within the structure.

Exposures of nuclear emulsions were taken in the direction of the volcano and then analyzed with a newly invented scanning microscope, custom built for the purpose of identifying particle tracks more efficiently.

Emil Frlež et al.[21] reported using tomographic methods to track the passage of cosmic rays muons through cesium iodide crystals for quality control purposes.

[22] The Mu-Ray project [23] has been using muography to image Vesuvius, famous for its eruption of 79 AD, which destroyed local settlements including Pompeii and Herculaneum.

From August 2017 to October 2019, time sequential muography imaging of the Etna edifice was conducted to study differences in density levels which would indicate interior volcanic activities.

The images revealed a low-density zone at the summit of the volcano which is thought to influence the stability of the “Sciara del Fuoco” slope (the source of many landslides).

[31] It has been using the existing closed building structures located directly underneath the southern and eastern sides of the volcano for equipment testing and experiments.

Preliminary muographs have revealed previously unknown density features at the top of Puy de Dôme that have been confirmed with gravimetric imaging.

[32] A joint measurement was conducted by French and Italian research groups in 2013-2014 during which different strategies for improved detector designs were tested, particularly their capacities to reduce background noise.

5-6 double side coated emulsion films were set in frames with stainless steel plates for shielding to be installed in 3 regions of a railway tunnel which was located underneath the targeted glacier.

[35][36] TRIUMF and its spin-off company Ideon Technologies developed a muograph designed specifically for surveys of possible uranium deposit sites with industry-standard boreholes [37] Muography has been used to map the inside of big civil engineering structures, such as dams, and their surroundings for safety and risk prevention purposes.

The analysis was based on point of closest approach, where the track pairs were projected to the mid-plane of the target, and the scattered angle was plotted at the intersection.

The safe but effective use of cosmic rays can be implemented in ports to help non-proliferation efforts, or even in cities, under overpasses, or entrances to government buildings.

In 2015, 45 years after Alvarez’s experiment, the ScanPyramids Project, which is composed of an international team of scientists from Egypt, France, Canada, and Japan, started using muography and thermography imaging techniques to survey the Giza pyramid complex.

[53] In 2017, scientists involved in the project discovered a large cavity, named "ScanPyramids Big Void", above the Grand Gallery of the Great Pyramid of Giza.

A low density region approximately 60 meters wide was reported as a preliminary result, which has led some researchers to suggest that the structure of the pyramid might have been weakened and it is in danger of collapse.

[8] In 2020, the US National Science Foundation awarded a US-Mexico international group a grant for muography to investigate El Castillo, the largest pyramid in Chichen Itza.

[58] Yuanyuan Liu of the Beijing Normal University and her group showed the feasibility of muography to image the underground chamber of the first emperor of China.

The “NASA Innovative Advanced Concepts (NIAC) program” is now in the process of assessing whether muography may be used for imaging the density structures of small Solar System bodies (SSBs).

[62] While the SSBs tend to generate lower muon flux than the Earth's atmosphere, some are sufficient to allow for muography of objects ranging from 1 km or less in diameter.

The program includes calculating the muon flux for each potential target, creating imaging simulations and considering the engineering challenges of building a more lightweight, compact apparatus appropriate for such a mission.

Time-dependent fluctuations of the muon flux due to atmospheric pressure variations are suppressed when muography is conducted under the seafloor by the “inverse barometric effect (IBE)” of seawater.

[citation needed] LANL and its spinoff company Decision Sciences applied the MST technique to image the interiors of large trucks and other storage containers in order to detect nuclear materials.

[66] A similar system that used MST was developed at the University of Glasgow and its spin-off company Lynkeos Technology to apply towards monitoring the robustness of nuclear waste containers at the Sellafield storage site.

[77] Mu-CAT revealed the three-dimensional position of a fractured zone below the crater floor of an active volcano related to a past eruption that had caused a large pyroclastic and lava flow on its northern slope.

There are several different kinds of muon sensors used in muography apparatuses: plastic scintillators,[82] nuclear emulsions,[29] or gaseous ionization detectors.

Left – Lead reactor core with conic void. Right – Observed core where average scattering angles of muons are plotted. The void in the core is clearly imaged through two 2.74 metres (9 ft 0 in) concrete walls. The lead core of 0.7 metres (2 ft 4 in) thickness gives an equivalent radiation length to the uranium fuel in Unit 1, and gives a similar scattering angle. Hot spots at the corners are artifacts caused by edge effect of MMT. [ 43 ]
Detectors installed in the descending corridor (DC) and in the al-Ma’mun corridor (MC). a The Chevron, which consists of huge gabled limestone beams, covering the original entrance to the DC on the North side of Khufu’s Pyramid. b 3D model and positions of the detectors from Nagoya University, indicated by red dots and of the detectors from CEA, indicated by orange dots, in the DC and in the MC. c–h The detectors. c shows EM3, d shows EM2, e shows EM5, f shows Charpak, g shows Joliot and h shows Degennes. [ 52 ]
East-West cut view of the Great Pyramid and front view of the North face Chevron area. a Subterranean chamber, b queen’s chamber, c grand gallery, d king’s chamber, e descending corridor, f ascending corridor, g al-Ma’mun corridor, h north face Chevron area, i ScanPyramids Big Void with horizontal hypothesis (red hatching) and inclined hypothesis (green hatching) as published in November 2017. [ 52 ]