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Muons arriving on the Earth's surface are created indirectly as decay products of collisions of cosmic rays with particles of the Earth's atmosphere. [12] About 10,000 muons reach every square meter of the earth's surface a minute; these charged particles form as by-products of cosmic rays colliding with molecules in the upper atmosphere.
The emergence of the muons is caused by the collision of cosmic rays with the upper atmosphere, after which the muons reach Earth. The probability that muons can reach the Earth depends on their half-life, which itself is modified by the relativistic corrections of two quantities: a) the mean lifetime of muons and b) the length between the upper and lower atmosphere (at Earth's surface).
Cosmic rays collide in the atmosphere, generating particle showers. [19] The muons in these showers travel close to the speed of light and spread out as they travel through the atmosphere. They reach the ground at almost the same time, so by sharing the information provided by these muons, clocks can be synchronized. [20]
In the laboratory, slow muons are produced; and in the atmosphere, very fast-moving muons are introduced by cosmic rays. Taking the muon lifetime at rest as the laboratory value of 2.197 μs, the lifetime of a cosmic-ray-produced muon traveling at 98% of the speed of light is about five times longer, in agreement with observations.
In 2022, he expanded muography to image targets in the atmosphere and the ocean. First, Tanaka set his sights on tropical cyclones and measured the muon flux before the storm arrived. [ 5 ] [ 20 ] He showed the cyclone's cross sections and revealed variations in density [ 21 ] to provide information on wind speed and storm strength. [ 4 ]
Unlike pions, these muons do not interact strongly with matter, and can travel through the atmosphere to penetrate even below ground level. The rate of muons arriving at the surface of the Earth is such that about one per second passes through a volume the size of a person's head. [15]
Air showers are extensive cascades of subatomic particles and ionized nuclei, produced in the atmosphere when a primary cosmic ray enters the atmosphere. Particles of cosmic radiation can be protons, nuclei, electrons, photons, or (rarely) positrons. Upon entering the atmosphere, they interact with molecules and initiate a particle cascade that ...
First, muons are naturally abundant and travel from the atmosphere towards the Earth’s surface. [83] This abundant muon flux is nearly constant, therefore muography can be used worldwide. Second, because of the high-contrast resolution of muography, a small void of less than 0.001% of the entire volume can be distinguished. [ 13 ]