Muons to study the fortress wall of Xi’an

Muons to study the fortress wall of Xi’an

Recently, researchers have been examining the fortification wall at Xi’an, an ancient city in China, using muons, extraterrestrial particles that can penetrate stone surfaces to within hundreds of meters.

Scientists used a muon detector called CORMIS (Cosmic Ray Muon Imaging System) to examine the Xi’an city wall.

What are Muons?

  • Muons are subatomic particles raining down from space. They are formed when these particles collide with cosmic rays in the Earth’s atmosphere.
  • Cosmic rays are groups of high-energy particles that move through space at nearly the speed of light.
  • According to Scientific American magazine, “about 10,000 muons reach every square meter of Earth’s surface in one minute”.


  • These particles are similar to electrons but are 207 times more massive. As a result they are sometimes referred to as “fat electrons”.
  • Muons are so massive that they can travel hundreds of meters through rock or other matter before being absorbed or decaying.
  • In comparison, electrons can penetrate only a few centimeters.
  • Furthermore muons are highly unstable and only exist for 2.2 microseconds.


Because of the penetrating power of muons, the method of scanning large structures is called muography.

Source – Indian Express

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