Fortress wall of Xi’an

Why in News?

• Recently, researchers are examining the fortress wall of Xi’an, an ancient city in China, by using tiny outer space particles Muons that can penetrate hundreds of metres of stone surfaces.

Highlights

• Muons are subatomic particles raining from space. They are created when the particles in Earth’s atmosphere collide with cosmic rays.
• Cosmic rays are the clusters of high-energy particles that move through space at almost the speed of light.
• According to Scientific American magazine, “about 10,000 muons reach every square metre of the Earth’s surface a minute”.
• These particles resemble electrons but are 207 times as massive. Therefore, they are sometimes called “fat electrons”.
• Because muons are so heavy, they can travel through hundreds of metres of rock or other matter before getting absorbed or decayed.
• In comparison, electrons can penetrate through only a few centimetres.
• Also, muons are highly unstable and exist for just 2.2 microseconds.
• With unique advantages, muography has gained increasing attention from archaeologists as a novel and innovative tool to investigate large-scale archaeological sites.
• Example: The first use of muography was in the late 1960s when a Nobel Prize-winning physicist named Luis Alvarez teamed up with Egyptologists to look for hidden rooms in the Pyramid of Khafre in Giza.