(ORDO NEWS) — The city wall in Xi’an is one of the oldest, largest and best preserved Chinese city walls.
The fortress, recognized as a UNESCO World Heritage Site, was built in the 14th century by Zhu Yuanzhang, the first emperor of the Ming Dynasty. Now researchers have used cosmic rays to look inside the wall.
The method revealed some anomalies inside the wall that need to be corrected.
Scientists used what is known as muon tomography to look inside the city wall in Xi’an. Muons are naturally occurring subatomic particles formed when cosmic rays hit the Earth‘s upper atmosphere.
These particles are similar to electrons, but 207 times more massive. They can travel hundreds of meters of rock or other matter before being absorbed or decaying into electrons and neutrinos.
By comparison, electrons can only travel a few centimeters. Muons are extremely unstable and exist for only 2.2 microseconds.
Application of muon tomography
Muon tomography has been around since the 1960s, but has been used infrequently until now.
The method was applied to volcanoes (including Mount Etna and Vesuvius) and glaciers, and also looked into the Cheops Pyramid at Giza with its help.
What did muons show inside Chinese walls?
Looking inside the city wall in Xi’an, the researchers found small density anomalies. They believe that this is a threat to the safety of the structure and that they should be eliminated to prevent the wall from collapsing.
In conclusion, the scientists add that muon tomography can be an invaluable tool not only for studying archaeological sites, but also for their preservation.
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