Subatomic particles antiparticles

If subatomic particles moving at speeds close to the speed of light collide with nuclei and electrons, new phenomena take place that do not occur in collisions of these particles at slow speeds. For example, in a collision some of the kinetic energy of the moving particles can create new particles that are not contained in ordinaiy matter. Some of these created particles, such as antiparticles of the proton and elec-... 

Since Rutherford s work, scientists have identified other types of nuclear radiation. Some consist of rapidly moving particles, such as neutrons or protons. Others consist of rapidly moving antiparticles, particles with a mass equal to that of one of the subatomic particles but with an opposite charge. For example, the positron has the same mass as an electron but a positive charge it is denoted 3 or f e. When an antiparticle encounters its corresponding particle, both particles are annihilated and completely converted into energy. Table 17.1 summarizes the properties of particles commonly found in nuclear radiation. 

To further complicate the subject of subatomic particles, each kind of particle has an antiparticle. For example, for each kind of qnark there is an antiquark of the same mass and spin, but of opposite charge. The first antiparticle to be observed was the positron, an electron with a positive charge. An antiproton is like a proton, but it has a negative charge. Antiparticles can be observed, and molecules of antimatter can even be generated. A positron orbiting an antiproton, for example, is an antihydrogen atom. 

Every known subatomic particle has a counterpart called the antiparticle. A charged particle and an antiparticle have the same mass, and opposite charge. If a particle is neutral—for example, the neutron—its antiparticle is still neutral. Then their difference is due to some other property, such as magnetic moment. Some particles, like the photon, are identical with their own antiparticles. An antiparticle cannot exist together with the corresponding particle when an antiparticle meets a particle, the two react and new particles appear. 

The investigation of cosmic radiation has had a profound influence on nuclear science. When Chadwick in 1932 discovered the neutron, the picture of matter seemed complete all matter appeared to be composed of four fundamental particles protons, neutrons, electrons, and photons. However, through studies of the cosmic radiation Anderson discovered the positron (the first antiparticle) in the same year. Five years later Anderson and Neddermeyer discovered another new particle with a mass about one-tenth of a proton or about 200 times heavier than the electron. This particle is the muon, designated by p. Since that time a large number of subatomic particles have been discovered. 

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