What exactly has been achieved here?
As described in a new paper published in Nature, what the Japanese and French research team have discovered is a large secret space hidden within the Great Pyramid of Giza. This space is located above a large 100-foot long room called the Grand Gallery, and is comparable in size. Up until now, no-one was aware of the existence of this space. It is the first major internal structural discovery in the Great Pyramid since the 19th century.
Using a technique called “muon tomography,” the scientists were able to map it out without causing any damage. This is a substantially different approach to the British Egyptologists of the early 1800s, who frequently “investigated” pyramids by using gunpowder to gain access to different sections that had been sealed off.
Next, the researchers want to explore the space in more detail by using tiny flying drones, although this will take time to achieve.
What are muons?
Earth is constantly bombarded with particles, which pass harmlessly through our bodies. A large number of these particles are called muons, which hit Earth’s surface at a rate of approximately 1 per square centimeter each minute of the day. Muons are elementary particles similar to electrons, but don’t lose as much energy when they travel, making them able to penetrate more deeply than other forms of radiation.
They were discovered by American physicists Carl D. Anderson and Seth Neddermeyer in 1936, as part of the pair’s studies into cosmic radiation. Muons can be detected based on the fact that their movement through gas ionizes the gas molecules. This was successfully demonstrated in 1937 through an experiment known as the “cloud chamber,” in which supersaturated vapor in a sealed environment is used to visualize ionizing radiation.
So how do you use them to scan for objects?
Muons are able to penetrate dense materials, such as meters of rock or even steel, more deeply than other types of radiation. Muon Scattering Tomography (MST) is one way of harnessing this ability by using it to peer through much thicker materials than would be possible using x-ray based tomography techniques such as computed tomography (CT) scanning. MST works by scattering the negatively-charged muon particles, and then observing the way they interact with and deflect off other materials.
While they are able to pass through many, they can also be deflected by heavy elements such as uranium, or metals like lead. By using electrodes to collect the signal made by the scattered muons, and then applying some clever geometry and statistical models to measure how they are deflected, it’s possible to work out their trajectory with a high level of accuracy. This allows researchers to build up three-dimensional models of hidden objects, both in terms of shape and material.
Is this the first time that Muon Scattering Tomography has been used?
It’s not. The use of something called muon transmission radiography was actually used back in the late 1960s in a not dissimilar way to look for hidden chambers in the Pyramid of Chephren in Giza. (Check out this 1970 paper, “Search for Hidden Chambers in the Pyramids.”)
The development of Muon Scattering Tomography as an imaging tool, however, is far more recent — and dates back to Los Alamos National Laboratory research in 2003. Since then, it has been used for multiple applications. In notable recent use-cases, it was employed by Toshiba for analyzing the reactor cores at the Fukushima nuclear complex. A company called Decision Sciences International Corporation has also used muon tomography in a scanner for searching for explosives, contraband material, and more, and then producing a 3D image of what has been scanned.
A similar form of muon tomography has additionally been used as a way of imaging magma chambers in volcanos to predict eruptions, and for discovering hidden tunnels inside the Bent Pyramid, named as a result of its unusual shape.