Types of particle

Physics

Neutron

A Neutron is an uncharged particle, one of the fundamental particles of which matter is composed. The mass of a neutron is 1.0086654 atomic mass units (amu). The existence of the neutron was predicted in 1920 by the British physicist Ernest Rutherford and by Australian and American scientists, but experimental verification of its existence was exceedingly difficult because the net charge on the neutron is zero.

Discovery

The neutron was first identified in 1932 by the British physicist Sir James Chadwick. The Joliot-Curies had produced what Chadwick recognized as neutrons by the interaction of alpha particles with beryllium nuclei. When this newly discovered radiation was passed through paraffin wax, collisions between the neutrons and the hydrogen atoms in the wax produced readily detectable protons.

Behavior

The neutron is a constituent particle of all nuclei of mass number greater than 1. Free neutrons—those outside of atomic nuclei—are produced in nuclear reactions. They can be ejected from atomic nuclei at various speeds or energies and are readily slowed down to very low energy by a series of collisions with light nuclei, such as those of hydrogen, deuterium, or carbon. When expelled from the nucleus, the neutron is unstable and decays to form a proton, an electron, and a neutrino. Like the proton and the electron, the neutron possesses angular momentum, or spin. Neutrons act as small, individual magnets; this property enables beams of polarized neutrons to be created. The neutron has a negative magnetic moment of -1.913141 nuclear magnetons. Its half-life was fixed approximately at 10.61 minutes.

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Anti-Neutron

The antiparticle of a neutron, known as an antineutron, has the same mass, spin, and beta-decay constant. These particles are sometimes the result of the collisions of antiprotons with protons, and they possess a magnetic moment equal and opposite to that of the neutron. According to current particle theory, the neutron and the antineutron—and other nuclear particles—are themselves composed of quarks.

Proton

A Proton is a nuclear particle having a positive charge identical in magnitude to the negative charge of an electron and, together with the neutron, a constituent of ...

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Anti-Neutron

Proton

A Proton is a nuclear particle having a positive charge identical in magnitude to the negative charge of an electron and, together with the neutron, a constituent of all atomic nuclei. The proton is also called a nucleon, as is the neutron. The proton forms, by itself, the nucleus of the hydrogen atom. The mass of a proton is approximately 1836 times that of an electron, or 1.6726 × 10-24 g. Consequently, the mass of an atom is contained almost entirely in the nucleus. The proton has an intrinsic angular momentum, or spin, and thus a magnetic moment. In addition, the proton obeys the exclusion principle. The number of protons in the nucleus of an atom determines what element it is; the atomic number of an element denotes the number of protons in the nucleus. In nuclear physics, the proton is used as a projectile in large accelerators to bombard nuclei to produce fundamental particles. As the hydrogen ion, the proton plays an important role in chemistry.

Anti-Proton

The antiproton, the antiparticle of the proton, is also called a negative proton. It differs from the proton in having a negative charge and not being a constituent of atomic nuclei. The antiproton is stable in a vacuum and does not decay spontaneously. When an antiproton collides with a proton or a neutron, however, the two particles are transformed into mesons, which have an extremely short half-life. Although physicists had postulated the existence of this elementary particle since the 1930s, the antiproton was positively identified for the first time in 1955 at the University of California Lawrence Berkeley National Laboratory.

Because protons are essential parts of ordinary matter, they are obviously stable. Particle physicists are nevertheless interested in learning whether protons eventually decay after all, on a time scale of many billions of billions of years. This interest derives from current attempts at grand unification theories that would combine all four fundamental interactions of matter in a single scheme. Many of these attempts call for the ultimate instability of the proton, so research groups at a number of accelerator facilities are conducting tests to detect such decays.

Electron

An Electron is a type of elementary particle that, along with protons and neutrons, make up atoms and molecules. Electrons play a role in a wide variety of phenomena. The flow of an electric current in a conductor is caused by the drifting of free electrons in the conductor. Heat conduction is also primarily a phenomenon of electron activity. In vacuum tubes a heated cathode emits a stream of electrons that can be used to amplify or rectify an electric current. If such a stream is focused into a well-defined beam, it is called a cathode-ray beam. Cathode rays directed against suitable targets produce X rays; directed against the fluorescent screen of a television tube, they produce visible images. Also, the negatively charged beta particles emitted by some radioactive substances are electrons. Electrons have a rest mass of 9.109 x 10-28 grams, and an electrical charge of negative 1.602 x 10-19 coulombs. The charge of the electron is the basic unit of electricity. Electrons are classified as fermions because they have half-integral spin; spin is a quantum mechanical property of subatomic particles that indicates the particle's angular momentum. The antimatter version of the electron is the positron.

Positron

A Positron is an elementary antimatter particle having a mass equal to that of an electron and a positive electrical charge equal in magnitude to the charge of the electron. The positron is sometimes called a positive electron or anti-electron. Electron-positron pairs are formed if cosmic rays or gamma rays of energies of more than 1 million electron volts are made to strike particles of matter. The reverse of the pairing process, called annihilation, is initiated when an electron and a positron interact, destroying each other and producing gamma rays.

The existence of the positron was first suggested in 1928 by the British physicist Paul Adrien Maurice Dirac as a necessary consequence of his quantum-mechanical theory of electron motion. In 1932 the American physicist Carl David Anderson experimentally confirmed the existence of the positron.