In physics, antineutrinos are the antiparticles of neutrinos, which are neutral particles produced in nuclear beta decay. These are emitted in beta particle emissions, where a neutron turns into a proton. They have a spin of 1/2, and they are part of the lepton family of particles. The antineutrinos observed so far all have right-handed helicity (i.e. only one of the two possible spin states has ever been seen), while the neutrinos are left-handed.
In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles. For example, an antielectron (a positron, an electron with a positive charge) and an antiproton (a proton with a negative charge) could form an antihydrogen atom in the same way that an electron and a proton form a normal matter hydrogen atom.
Corresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay. The laws of nature are very nearly symmetrical with respect to particles and antiparticles.
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1, a spin of ⁄2, and the same mass as an electron. When a low-energy positron collides with a low-energy electron, annihilation occurs, resulting in the production of two or more gamma ray photons. Positrons may be generated by positron emission radioactive decay, or by pair production from a sufficiently energetic photon.
An antimatter rocket is a proposed class of rockets that use antimatter as their power source. There are several types of design that attempt to accomplish this goal. The advantage to this class of rocket is that a large fraction of the rest mass of a matter/antimatter mixture may be converted to energy, allowing antimatter rockets to have a far higher energy density and specific impulse than any other proposed class of rocket.
Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton. Its (proposed) chemical symbol is H, that is, H with an overbar.
The antiproton (p, pronounced p-bar) is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy. It was discovered in 1955 by University of California, Berkeley physicists Emilio Segrè and Owen Chamberlain, for which they were awarded the 1959 Nobel Prize in Physics. An antiproton consists of two up antiquark and one down antiquark.
Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil (nothing). A literal translation is "to make into nothing". In physics, the word is used to denote the process that occurs when a subatomic particle collides with its respective antiparticle. Since energy and momentum must be conserved, the particles are not actually made into nothing, but rather into new particles.
The antineutron is the antiparticle of the neutron. It differs from the neutron only in that some of its properties have equal magnitude but opposite sign. It has the same mass as the neutron, and no net electric charge, but has opposite baryon number (+1 for neutron, −1 for the antineutron). This is because the antineutron is composed of antiquarks, while neutrons are composed of quarks. In particular, the antineutron consists of one up antiquark and two down antiquarks.
An antimatter weapon is a hypothetical device using antimatter as a power source, a propellant, or an explosive for a weapon. Antimatter weapons do not currently exist due to the cost of production and the limited technology available to produce enough antimatter in sufficient quantities for it to be an acceptable weapon.
An antiprotonic helium atom is a three-body object composed of an antiproton and an electron orbiting around a helium nucleus. It is thus made partly of matter, and partly of antimatter. The atom is electrically neutral, since both electrons and antiprotons have a charge of -1, whereas helium nuclei have a charge of +2.
The Most Serene Republic of San Marino is a country situated in the Apennine Mountains. It is a landlocked enclave, completely surrounded by Italy. Its size is just over 61 km (24 sq mi) with an estimated population of almost 30,000. Its capital is the City of San Marino. One of the European microstates along with Liechtenstein, the Vatican, Monaco, Andorra, and Malta, San Marino has the smallest population of all the members of the Council of Europe.
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean. The territory of the South Island covers 151,215 square kilometres (58,384 sq mi) and is influenced by a temperate climate. The South Island is sometimes called the "mainland".
The Majiayao culture (馬家窰文化) is a name given by archaeologists to a group of Neolithic communities who lived primarily in the upper Yellow River region in Gansu and Qinghai, China. The culture existed from 3100 BC to 2700 BC. The earliest discoveries of copper and bronze objects in China occur at Majiayao sites. The transition from Yangshao to Majiayao coincides, climatically, with the Piora Oscillation.