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What are Muons?


According to a recent study, scientists are investigating the fortress wall of the ancient city Xi’an in China using muons, tiny particles from outer space, which can pass through hundreds of meters of stone.

  • To analyse 14 kilometres long rampart, researchers deployed a technique called muon tomography or muography, which uses muons to generate three-dimensional images of such large structures.


GS III: Science and Technology

Dimensions of the Article:

  1. What are muons?
  2. What is muon tomography or muography?
  3. Muons in Archaeology and Beyond

What are muons?

  • Muons are subatomic particles raining from space.
  • They are created when the particles in Earth’s atmosphere collide with cosmic rays — clusters of high-energy particles that move through space at just below 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 decaying into electrons and neutrinos, said the journal Science.
  • In comparison, electrons can penetrate through only a few centimetres.
  • Muons are highly unstable and exist for just 2.2 microseconds.

What is muon tomography or muography?

  • Muography is conceptually similar to X-ray but capable of scanning much larger and wider structures, owing to the penetration power of muons.
  • As these high-energy particles are naturally produced and ubiquitous, all one needs to do is place a muon detector underneath, within or near the object of interest.
  • The detector then tracks the number of muons going through the object from different directions, to form a three-dimensional image.
  • According to the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), the image is then “then compared with a muon image of the “free sky.”
  • This indicates how many muons have been blocked.
  • The final picture is essentially a shadow of the object, in the light of cosmic muons.

Muons in Archaeology and Beyond

Introduction to Muons and Archaeology
  • Muons are tiny outer space particles that can penetrate hundreds of meters of stone surfaces
  • First use of muons in archaeology was in the late 1960s when Nobel laureate Luis Alvarez and Egyptologists searched for hidden chambers in the Pyramid of Khafre, Giza
  • A repeat of the experiment in 2017 with more advanced muon detectors resulted in the discovery of a previously unknown chamber
Latest Study using Muons in Xi’an
  • Used the Cosmic Ray Muon Imaging System (CORMIS)
  • Deployed six detectors for a week to collect enough data for scanning the whole structure
  • Results indicated density anomalies inside the rampart with unprecedented levels of precision
Applications of Muography Beyond Archaeology
  • Muography has been used in customs security and internal imaging of volcanoes
  • Used to examine the Fukushima nuclear reactors after the 2011 earthquake and tsunami in Japan
  • Detectors were placed in 10 cm thick boxes for protection from high levels of radiation.

-Source: Indian Express

March 2024