Post by Andrei Tchentchik on Aug 25, 2020 15:34:51 GMT 2
(.#495).- Where can we find antimatter on Earth ?
Where can we find antimatter on Earth ?
Richard Taillet
Teacher, Physical Researcher.
Published 07/01/2005 - Modified 10/28/2015.
Archives
What surrounds us on Earth is made almost exclusively of matter. In other words, the amount of antimatter found there is extremely small. We know this because the coexistence of the two would lead to violent annihilations that we would detect. You noted the "almost", and indeed, we saw above that the positrons had been discovered in the atmosphere, which means that at least a small amount of antimatter exists in its natural state around us . The processes for creating antimatter that we described on the previous page are at work on Earth. When antimatter is created, it does not disappear instantly, because it takes time to find a particle with which to annihilate. It is therefore possible to detect antiparticles which have not yet been annihilated. This was the case with the positrons discovered by Anderson in 1932.
We can cite two sources of antimatter at Earth level: natural radioactivity and cosmic rays.
Cosmic rays
The space around the Earth contains charged particles of high energy (up to 1020eV, the most important contribution coming from those which have an energy of a few GeV, where 1 GeV is worth a billion electron volts, see page above for definition), which were probably accelerated in the Galaxy (by shock waves created during supernova explosions). These particles are called cosmic rays, and we now know that they are mainly protons. When they reach the level of the Earth's atmosphere, they meet the nuclei that compose it and high energy reactions can take place. Among the products of these reactions are positrons (see previous page). Note that this is the origin of the first positrons discovered by Anderson.
Cosmic rays can create particles (including antimatter) when they enter the atmosphere.
Natural radioactivity
We have previously seen that certain radioactive isotopes can emit positrons, by ß + radioactivity. Do these isotopes exist in their natural state?
Earth's rock naturally contains extremely little. Indeed, the nuclei that compose it are at least 4.5 billion years old, and it turns out that nuclei with such long life times decay in another way (alpha radioactivity).
On the other hand, during reactions induced by the bombardment of the atmosphere by cosmic rays, radioactive nuclei are produced, and among these some are unstable by ß + radioactivity (sodium 22, half-life 2.6 years ), so that our natural environment contains it.
The reactions induced by the collision of the cosmic proton on the nuclei of the atmosphere can produce radioactive species (14C, 22Na), some of which (notably 22Na) can disintegrate by radioactivity ß +
F I N .
Where can we find antimatter on Earth ?
Richard Taillet
Teacher, Physical Researcher.
Published 07/01/2005 - Modified 10/28/2015.
Archives
What surrounds us on Earth is made almost exclusively of matter. In other words, the amount of antimatter found there is extremely small. We know this because the coexistence of the two would lead to violent annihilations that we would detect. You noted the "almost", and indeed, we saw above that the positrons had been discovered in the atmosphere, which means that at least a small amount of antimatter exists in its natural state around us . The processes for creating antimatter that we described on the previous page are at work on Earth. When antimatter is created, it does not disappear instantly, because it takes time to find a particle with which to annihilate. It is therefore possible to detect antiparticles which have not yet been annihilated. This was the case with the positrons discovered by Anderson in 1932.
We can cite two sources of antimatter at Earth level: natural radioactivity and cosmic rays.
Cosmic rays
The space around the Earth contains charged particles of high energy (up to 1020eV, the most important contribution coming from those which have an energy of a few GeV, where 1 GeV is worth a billion electron volts, see page above for definition), which were probably accelerated in the Galaxy (by shock waves created during supernova explosions). These particles are called cosmic rays, and we now know that they are mainly protons. When they reach the level of the Earth's atmosphere, they meet the nuclei that compose it and high energy reactions can take place. Among the products of these reactions are positrons (see previous page). Note that this is the origin of the first positrons discovered by Anderson.
Cosmic rays can create particles (including antimatter) when they enter the atmosphere.
Natural radioactivity
We have previously seen that certain radioactive isotopes can emit positrons, by ß + radioactivity. Do these isotopes exist in their natural state?
Earth's rock naturally contains extremely little. Indeed, the nuclei that compose it are at least 4.5 billion years old, and it turns out that nuclei with such long life times decay in another way (alpha radioactivity).
On the other hand, during reactions induced by the bombardment of the atmosphere by cosmic rays, radioactive nuclei are produced, and among these some are unstable by ß + radioactivity (sodium 22, half-life 2.6 years ), so that our natural environment contains it.
The reactions induced by the collision of the cosmic proton on the nuclei of the atmosphere can produce radioactive species (14C, 22Na), some of which (notably 22Na) can disintegrate by radioactivity ß +
F I N .
