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Top Comments: Using Muons to See Inside Pyramids and Volcanos. [1]

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Date: 2023-01-29

The paths of muon particles depicted as short white lines, penetrating the Great Pyramid of Giza. Muons were used to discover a previously unknown void in the pyramid in 2017.

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When he learned of the discovery, in 1936, of a new particle called the muon, physicist Isidor I. Rabi famously quipped “Who ordered that?” It was entirely unexpected. It didn’t fit into any existing theory, and it didn’t have any obvious role to play in the structure or dynamics of ordinary matter. The mystery of where they belonged in the zoo of elementary particles had to wait for the discovery of other unexpected, “strange” particles and the development of the quark theory of such particles. The physics of the muon is identical to that of the electron, with two differences. First, it’s about 200 times heavier than the electron, and second, the muon decays with a half-life of about 2.2 microseconds (millionths of seconds). (The electron does not decay.)

From being viewed as something of a nuisance immediately after their discovery, these particles have since found a use in studying the insides of massive objects, such as pyramids and volcanos. Muons are produced high in the atmosphere from collisions of fast-moving cosmic particles with atoms in the upper atmosphere, so they are present all over the surface of the Earth at all times. So, you don’t need to expend energy to produce a beam of muons, as one has to do with x-rays, for example. Muons are everywhere, and they’re free. Second, the fact that they are more massive than electrons means that they penetrate further into the objects being studied. Third, the technology requires to detect them is simple and relatively low-tech, so it can be used anywhere. When muons pass through dense material, they get scattered or absorbed at a greater rate than if they pass through less dense matter, or through voids. So, in an image produced using this technique, light regions are places where many muons managed to travel though the object, indicating low density, while dark regions, where not many muons make it to the detector, are regions of high density. This is how the void in the Great Pyramid was discovered, as an unexpected light region in a muon photograph.

Further, this technique has been used to measure the density of rock and magma in volcanos in order to evaluate the likelihood of an eruption, or to determine which regions around the volcano are most vulnerable to destruction. For example, in the eruption of Mt. St. Helens, one side of the volcano collapsed unexpectedly, killing 57 people who might have survived otherwise including a scientist who thought he was observing the eruption from a safe place. This technique could have predicted this outcome.

So a particle previously thought of as useless has proven its utility after all.

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[1] Url: https://www.dailykos.com/stories/2023/1/29/2150019/-Top-Comments-Using-Muons-to-See-Inside-Pyramids-and-Volcanos

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