The e + e − bound system is called positronium. The Dirac theory predicts that an electron and a positron, because of Coulomb attraction of their opposite charges, will combine to form an intermediate bound state, just as an electron and a proton combine to form a hydrogen atom. The inverse reaction γ → e + + e − can also proceed under appropriate conditions, and the process is called electron-positron creation, or pair production. This process is called annihilation, and the resultant energy is emitted in the form of gamma rays (γ), high-energy quanta of electromagnetic radiation. A collision between the positron and the electron results in their simultaneous disappearance, their masses ( m) being converted into energy ( E) in accordance with the Einstein mass-energy relation E = m c 2, where c is the velocity of light. Unless the positron is moving extremely fast, it will be drawn close to an ordinary electron by the attraction between opposite charges. The life expectancy or duration of the positron in ordinary matter is very short.
However, it was discovered in 1932 among particles produced in the interactions of cosmic rays in matter and thus provided experimental confirmation of Dirac’s theory.ġ,000,000,001 − 1,000,000,000 = 1 See all videos for this article Such a particle, called the positron, is not to be found in ordinary stable matter. Dirac on the energy states of the electron implied the existence of a particle identical in every respect but one-that is, with positive instead of negative charge. The concept of antimatter first arose in theoretical analysis of the duality between positive and negative charge. Matter and antimatter cannot coexist at close range for more than a small fraction of a second because they collide with and annihilate each other, releasing large quantities of energy in the form of gamma rays or elementary particles. The electrical properties of antimatter being opposite to those of ordinary matter, the positron has a positive charge and the antiproton a negative charge the antineutron, though electrically neutral, has a magnetic moment opposite in sign to that of the neutron. The antimatter particles corresponding to electrons, protons, and neutrons are called positrons ( e +), antiprotons ( p), and antineutrons ( n) collectively they are referred to as antiparticles. Learn about antimatter and its properties, and understand the annihilation of matter and antimatter See all videos for this articleĪntimatter, substance composed of subatomic particles that have the mass, electric charge, and magnetic moment of the electrons, protons, and neutrons of ordinary matter but for which the electric charge and magnetic moment are opposite in sign.
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