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Encyclopedia > Atomic nucleus

The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). The size (diameter) of the nucleus is in the range of 1.6 fm (10-15 m) (for a proton in light hydrogen) to about 15 fm (for the heaviest atoms, such as uranium). These dimensions are much smaller than the size of the atom itself by a factor of about 23,000 (uranium) to about 145,000 (hydrogen). Almost all of the mass in an atom is made up from the protons and neutrons in the nucleus with a very small contribution from the orbiting electrons. The etymology of the term nucleus is from 1704 meaning “kernel of a nut”. In 1844, Michael Faraday used the term to refer to the “central point of an atom”. The modern atomic meaning was proposed by Ernest Rutherford in 1912.[1] The adoption of the term “nucleus” to atomic theory, however, was not immediate. In 1916, for example, Gilbert N. Lewis stated, in his famous article The Atom and the Molecule, that “the atom is composed of the kernel and an outer atom or shell”. For other uses, see Atom (disambiguation). ... In physics a nucleon is a collective name for two baryons: the neutron and the proton. ... In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 940 MeV/c² (1. ... ‹ The template below (Unit of length) is being considered for deletion. ... For other uses, see Electron (disambiguation). ... Michael Faraday, FRS (September 22, 1791 – August 25, 1867) was an English chemist and physicist (or natural philosopher, in the terminology of that time) who contributed significantly to the fields of electromagnetism and electrochemistry. ... Ernest Rutherford, 1st Baron Rutherford of Nelson OM PC FRS (30 August 1871 - 19 October 1937), widely referred to as Lord Rutherford, was a nuclear physicist who became known as the father of nuclear physics. ... Lewis in the Berkeley Lab Gilbert Newton Lewis (October 23, 1875-March 23, 1946) was a famous American physical chemist. ...

A semi-accurate depiction of the helium atom. In the nucleus, the protons are in red and neutrons are in blue. In reality, the nucleus is also spherically symmetrical.
A semi-accurate depiction of the helium atom. In the nucleus, the protons are in red and neutrons are in blue. In reality, the nucleus is also spherically symmetrical.

Contents

Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ...

Overview

Nuclear makeup

The nucleus of an atom consists of protons and neutrons (two types of baryons) bound by the nuclear force. These baryons are further composed of sub-atomic fundamental particles known as quarks bound by the strong interaction. In particle physics, the baryons are a family of subatomic particles including the proton and the neutron (collectively called Greek barys, meaning heavy, as they are heavier than the other main groups of particles. ... A Feynman diagram of a strong proton-neutron interaction mediated by a neutral pion. ... For other uses of this term, see: Quark (disambiguation) 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ...


Nucleus size

Main article: Nuclear size

The HEAD of a nucleus is of the order of 10 − 15m compared to the atom, which is of the order 10 − 10m. This is comparable to a fly in a cathedral. Hence, the atom is made up of mostly empty space. The size of a nucleus is of the order of metres. ...


Isotopes and nuclides

The isotope of an atom is determined by the number of neutrons in the nucleus. Different isotopes of the same element have very similar chemical properties. Different isotopes in a sample of a particular chemical can be separated by using a centrifuge or by using a mass spectrometer. The first method is used in producing enriched uranium from a sample of regular uranium, and the second is used in carbon dating. Isotopes are any of the several different forms of an element each having different atomic mass (mass number). ... For other uses, see Chemistry (disambiguation). ... A laboratory tabletop centrifuge A centrifuge is a piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying force perpendicular to the axis. ... Mass spectrometry is a technique for separating ions by their mass-to-charge (m/z) ratios. ... These pie-graphs showing the relative proportions of uranium-238 (blue) and uranium-235 (red) at different levels of enrichment. ... Radiocarbon dating is the use of the naturally occurring isotope of carbon-14 in radiometric dating to determine the age of organic materials, up to ca. ...


The number of protons and neutrons together determine the nuclide (type of nucleus). Protons and neutrons have nearly equal masses, and their combined number, the mass number, is approximately equal to the atomic mass of an atom. The combined mass of the electrons is very small in comparison to the mass of the nucleus, since protons and neutrons weigh roughly 2000 times more than electrons. The mass number (A), also called atomic mass number (not to be confused with atomic number (Z) which denotes the number of protons in a nucleus) or nucleon number, is the number of nucleons (protons and neutrons) in an atomic nucleus. ... The atomic mass (ma) is the mass of an atom at rest, most often expressed in unified atomic mass units. ...


History

The discovery of the electron was the first indication that the atom had internal structure. At the turn of the 20th century the accepted model of the atom was J. J. Thomson's "plum pudding" model in which the atom was a large positively charged ball with small negatively charged electrons embedded inside of it. By the turn of the century physicists had also discovered three types of radiation coming from atoms, which they named alpha, beta, and gamma radiation. Experiments in 1911 by Lise Meitner and Otto Hahn, and by James Chadwick in 1914 discovered that the beta decay spectrum was continuous rather than discrete. That is, electrons were ejected from the atom with a range of energies, rather than the discrete amounts of energies that were observed in gamma and alpha decays. This was a problem for nuclear physics at the time, because it indicated that energy was not conserved in these decays. The problem would later lead to the discovery of the neutrino (see below). For other uses, see Electron (disambiguation). ... Sir Joseph John Thomson, OM, FRS (18 December 1856 – 30 August 1940) usually known as J. J. Thomson, was a British scientist. ... A schematic representation of the plum pudding model of the atom. ... Radiation as used in physics, is energy in the form of waves or moving subatomic particles. ... Alpha decay Alpha decay is a type of radioactive decay in which an atom emits an alpha particle (two protons and two neutrons bound together into a particle identical to a helium nucleus) and transforms (or decays) into an atom with a mass number 4 less and atomic number 2... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ... This article is about electromagnetic radiation. ... Year 1911 (MCMXI) was a common year starting on Sunday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Saturday of the 13-day-slower Julian calendar). ... Lise Meitner ca. ... Otto Hahn and Lise Meitner, 1913, at the KWI for Chemistry in Berlin Otto Hahn (March 8, 1879 – July 28, 1968) was a German chemist and received the 1944 Nobel Prize in Chemistry. ... Sir James Chadwick, CH (20 October 1891 – 24 July 1974) was an English physicist and Nobel laureate who is best known for discovering the neutron. ... In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ... Alpha decay Alpha decay is a type of radioactive decay in which an atom emits an alpha particle (two protons and two neutrons bound together into a particle identical to a helium nucleus) and transforms (or decays) into an atom with a mass number 4 less and atomic number 2... In physics, the conservation of energy states that the total amount of energy in an isolated system remains constant, although it may change forms, e. ...


In 1906 Earnest Rutherford published "Retardation of the α Particle from Radium in passing through Matter" in Philosophical Magazine (12, p 134-46). Geiger expanded on this work in a communication to the Royal Society (Proc. Roy. Soc. July 17, 1908) with experiments he and Rutherford had done passing α particles through air, aluminum foil and gold foil. More work was published in 1909 by Gieger and Marsden (Proc. Roy. Soc. A82 p 495-500) and further greatly expanded work was published in 1910 by Geiger (Proc. Roy. Soc. Feb. 1, 1910). In 1911-2 Rutherford went before the Royal Society to explain the experiments and propound the new theory of the atomic nucleus as we now understand it. Ernest Rutherford, 1st Baron Rutherford of Nelson, OM, FRS (August 30, 1871 - October 19, 1937), called father of nuclear physics, pioneered the orbital theory of the atom notably in his discovery of rutherford scattering off the nucleus with his gold foil experiment. ... The name Geiger (which means violinist) can refer to: Abraham Geiger (1810-1874), German reform Rabbi Arno Geiger (*1968), Austrian writer George Geiger, U.S. Medal of Honor recipient, Jewish (Johannes) Hans (Wilhelm) Geiger (1882-1945), inventor of the Geiger counter (a device for detecting radiation), son of Wilhelm Geiger... Marsden is a surname, and may refer to: Alistair Marsden, fictional character Betty Marsden (24 February 1919 – 18 July 1998), British comedy actress Brian G. Marsden, British astronomer Chris Marsden, former Football player David Marsden, Canadian radio broadcaster Dora Marsden (5 March 1882 – 13 December 1960), author Edward Marsden Elaine...


Around the same time that this was happening (1909) Ernest Rutherford performed a remarkable experiment in which Hans Geiger and Ernest Marsden under his supervision fired alpha particles (helium nuclei) at a thin film of gold foil. The plum pudding model predicted that the alpha particles should come out of the foil with their trajectories being at most slightly bent. He was shocked to discover that a few particles were scattered through large angles, even completely backwards in some cases. The discovery, beginning with Rutherford's analysis of the data in 1911, eventually led to the Rutherford model of the atom, in which the atom has a very small, very dense nucleus consisting of heavy positively charged particles with embedded electrons in order to balance out the charge. As an example, in this model nitrogen-14 consisted of a nucleus with 14 protons and 7 electrons, and the nucleus was surrounded by 7 more orbiting electrons. Year 1909 (MCMIX) was a common year starting on Friday (link will display full calendar) of the Gregorian calendar (or a common year starting on Thursday of the 13-day-slower Julian calendar). ... Ernest Rutherford, 1st Baron Rutherford of Nelson OM PC FRS (30 August 1871 - 19 October 1937), widely referred to as Lord Rutherford, was a nuclear physicist who became known as the father of nuclear physics. ... Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed. ... Johannes (Hans) Wilhelm Geiger (September 30, 1882 – September 24, 1945) was a German physicist. ... Sir Ernest Marsden (1888 - 1970), was a British-New Zealand physicist. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ...


The Rutherford model worked quite well until studies of nuclear spin were carried out by Franco Rasetti at the California Institute of Technology in 1929. By 1925 it was known that protons and electrons had a spin of 1/2, and in the Rutherford model of nitrogen-14 the 14 protons and six of the electrons should have paired up to cancel each others spin, and the final electron should have left the nucleus with a spin of 1/2. Rasetti discovered, however, that nitrogen-14 has a spin of one. In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... Franco Dino Rasetti (August 10, 1901 – December 5, 2001) was an Italian scientist. ... The California Institute of Technology (commonly referred to as Caltech)[1] is a private, coeducational research university located in Pasadena, California, in the United States. ... Year 1929 (MCMXXIX) was a common year starting on Tuesday (link will display the full calendar) of the Gregorian calendar. ... Year 1925 (MCMXXV) was a common year starting on Thursday (link will display the full calendar) of the Gregorian calendar. ...


In 1930 Wolfgang Pauli was unable to attend a meeting in Tübingen, and instead sent a famous letter with the classic introduction "Dear Radioactive Ladies and Gentlemen". In his letter Pauli suggested that perhaps there was a third particle in the nucleus which he named the "neutron". He suggested that it was very light (lighter than an electron), had no charge, and that it did not readily interact with matter (which is why it hadn't yet been detected). This desperate way out solved both the problem of energy conservation and the spin of nitrogen-14, the first because Pauli's "neutron" was carrying away the extra energy and the second because an extra "neutron" paired off with the electron in the nitrogen-14 nucleus giving it spin one. Pauli's "neutron" was renamed the neutrino (Italian for little neutral one) by Enrico Fermi in 1931, and after about thirty years it was finally demonstrated that a neutrino really is emitted during beta decay. Year 1930 (MCMXXX) was a common year starting on Wednesday (link will display 1930 calendar) of the Gregorian calendar. ... This article is about Austrian-Swiss physicist Wolfgang Pauli. ... Tübingen, Neckar front Tübingen, a traditional university town of Baden-Württemberg, Germany, is situated 20 miles southwest of Stuttgart, on a ridge between the River Neckar and the Ammer. ... Neutrinos are elementary particles denoted by the symbol ν. Travelling close to the speed of light, lacking electric charge and able to pass through ordinary matter almost undisturbed, they are extremely difficult to detect. ... Enrico Fermi (September 29, 1901 – November 28, 1954) was an Italian physicist most noted for his work on the development of the first nuclear reactor, and for his contributions to the development of quantum theory, particle physics and statistical mechanics. ... Year 1931 (MCMXXXI) was a common year starting on Thursday (link will display full 1931 calendar) of the Gregorian calendar. ...


In 1932 Chadwick realized that radiation that had been observed by Walther Bothe, Herbert Becker, Irène and Frédéric Joliot-Curie was actually due to a massive particle that he called the neutron. In the same year Dmitri Ivanenko suggested that neutrons were in fact spin 1/2 particles and that the nucleus contained neutrons and that there were no electrons in it, and Francis Perrin suggested that neutrinos were not nuclear particles but were created during beta decay. To cap the year off, Fermi submitted a theory of the neutrino to Nature (which the editors rejected for being "too remote from reality"). Fermi continued working on his theory and published a paper in 1934 which placed the neutrino on solid theoretical footing. In the same year Hideki Yukawa proposed the first significant theory of the strong force to explain how the nucleus holds together. Year 1932 (MCMXXXII) was a leap year starting on Friday (the link will display full 1932 calendar) of the Gregorian calendar. ... Walther Wilhelm Georg Bothe (January 8, 1891 – February 8, 1957) was a German physicist, mathematician, chemist, and Nobel Prize winner. ... Irène Joliot-Curie née Curie, (12 September 1897 – 17 March 1956) was a French scientist, the daughter of Marie SkÅ‚odowska-Curie and Pierre Curie and the wife of Frédéric Joliot-Curie. ... Frédéric Joliot-Curie Jean Frédéric Joliot-Curie né Joliot (March 19, 1900 – August 14, 1958) was a French physicist and Nobel laureate. ... Dmitri Ivanenko (Russian: Дмитрий Дмитриевич Иваненко) (1904 - 1994) was a Professor of Moscow State University (since 1943), made the great contribution to the physical science (especialy, to gravitational physics) of the twentieth century. ... Francis Perrin (Paris, 1901 - id. ... Nature is one of the most prominent scientific journals, first published on 4 November 1869. ... Year 1934 (MCMXXXIV) was a common year starting on Monday (link will display full 1934 calendar) of the Gregorian calendar. ... Hideki Yukawa Hideki Yukawa FRSE (湯川 秀樹, January 23, 1907 - September 8, 1981) was a Japanese theoretical physicist and the first Japanese to win the Nobel prize. ...


With Fermi and Yukawa's papers the modern model of the atom was complete. The center of the atom contains a tight ball of neutrons and protons, which is held together by the strong nuclear force. Unstable nuclei may undergo alpha decay, in which they emit an energetic helium nucleus, or beta decay, in which they eject an electron (or positron). After one of these decays the resultant nucleus may be left in an excited state, and in this case it decays to its ground state by emitting high energy photons (gamma decay). The first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle or the antimatter counterpart of the electron. ...


The study of the strong and weak nuclear forces led physicists to collide nuclei and electrons at ever higher energies. This research became the science of particle physics, the crown jewel of which is the standard model of particle physics which unifies the strong, weak, and electromagnetic forces. Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ...


Modern nuclear physics

A heavy nucleus can contain hundreds of nucleons (neutrons and protons), which means that to some approximation it can be treated as a classical system, rather than a quantum-mechanical one. In the resulting liquid-drop model, the nucleus has an energy which arises partly from surface tension and partly from electrical repulsion of the protons. The liquid-drop model is able to reproduce many features of nuclei, including the general trend of binding energy with respect to mass number, as well as the phenomenon of nuclear fission. In physics a nucleon is a collective name for two baryons: the neutron and the proton. ... It has been suggested that this article or section be merged with Classical mechanics. ... Fig. ... The liquid drop model is a model in nuclear physics which treats the nucleus as a drop of incompressible nuclear fluid. ... In physics, surface tension is an effect within the surface layer of a liquid that causes that layer to behave as an elastic sheet. ... Binding energy is the energy required to disassemble a whole into separate parts. ... The mass number (A), also called atomic mass number (not to be confused with atomic number (Z) which denotes the number of protons in a nucleus) or nucleon number, is the number of nucleons (protons and neutrons) in an atomic nucleus. ... An induced nuclear fission event. ...


Superimposed on this classical picture, however, are quantum-mechanical effects, which can be described using the nuclear shell model, developed in large part by Maria Goeppert-Mayer. Nuclei with certain numbers of neutrons and protons (the magic numbers 2, 8, 20, 50, 82, 126, ...) are particularly stable, because their shells are filled. In nuclear physics, the nuclear shell model is a model of the atomic nucleus. ... Maria Goeppert Mayer: Physicist (Women in Science) ISBN 0791072479 Maria Goeppert-Mayer (June 28, 1906 – February 20, 1972) was born Maria Goeppert in Katowice, Silesia (then in Germany, now part of Poland). ... In nuclear physics, a magic number is a number of nucleons (either protons or neutrons) such that they are arranged into complete shells within the atomic nucleus. ...


Much of current research in nuclear physics relates to the study of nuclei under extreme conditions such as high spin and excitation energy. Nuclei may also have extreme shapes (similar to that of American footballs) or extreme neutron-to-proton ratios. Experimenters can create such nuclei using artificially induced fusion or nucleon transfer reactions, employing ion beams from an accelerator. Beams with even higher energies can be used to create nuclei at very high temperatures, and there are signs that these experiments have produced a phase transition from normal nuclear matter to a new state, the quark-gluon plasma, in which the quarks mingle with one another, rather than being segregated in triplets as they are in neutrons and protons. Nuclear physics is the branch of physics concerned with the nucleus of the atom. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... United States simply as football, is a competitive team sport that is both fast-paced and strategic. ... For the DC Comics Superhero also called Atom Smasher, see Albert Rothstein. ... In physics, a phase transition, (or phase change) is the transformation of a thermodynamic system from one phase to another. ... A QGP is formed at the collision point of two relativistically accelerated gold ions in the center of the STAR detector at the relativistic heavy ion collider at the Brookhaven national laboratory. ... The six flavours of quarks and their most likely decay modes. ...


Modern topics in nuclear physics

Spontaneous changes from one nuclide to another: nuclear decay

If a nucleus has too few or too many neutrons it may be unstable, and will decay after some period of time. For example, nitrogen-16 atoms (7 protons, 9 neutrons) beta decay to oxygen-16 atoms (8 protons, 8 neutrons) within a few seconds of being created. In this decay a neutron in the nitrogen nucleus is turned into a proton and an electron by the weak nuclear force. The element of the atom changes because while it previously had seven protons (which makes it nitrogen) it now has eight (which makes it oxygen). Many elements have multiple isotopes which are stable for weeks, years, or even billions of years. General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ...


Nuclear fusion

Main article: Nuclear fusion

When two light nuclei come into very close contact with each other it is possible for the strong force to fuse the two together. It takes a great deal of energy to push the nuclei close enough together for the strong force to have an effect, so the process of nuclear fusion can only take place at very high temperatures or high densities. Once the nuclei are close enough together the strong force overcomes their electromagnetic repulsion and squishes them into a new nucleus. A very large amount of energy is released when light nuclei fuse together because the binding energy per nucleon increases with mass number up until nickel-62. Stars like our sun are powered by the fusion of four protons into a helium nucleus, two positrons, and two neutrinos. The uncontrolled fusion of hydrogen into helium is known as a thermonuclear weapon. Research to find an economically viable method of using energy from a controlled fusion reaction is currently being undertaken by various research establishments (see JET and ITER). The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... Binding energy is the energy required to disassemble a whole into separate parts. ... The mass number (A), also called atomic mass number (not to be confused with atomic number (Z) which denotes the number of protons in a nucleus) or nucleon number, is the number of nucleons (protons and neutrons) in an atomic nucleus. ... For other uses, see Nickel (disambiguation). ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... A positron is the antiparticle of the electron. ... The neutrino is an elementary particle. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, in 1945 lifted nuclear fallout some 18 km (60,000 feet) above the epicenter. ... Split image of JET with right side showing hot plasma during a shot. ... ITER is an international tokamak (magnetic confinement fusion) research/engineering project designed to prove the scientific and technological feasibility of a full-scale fusion power reactor. ...


Nuclear fission

Main article: Nuclear fission

For nuclei heavier than nickel-62 the binding energy per nucleon decreases with the mass number. It is therefore possible for energy to be released if a heavy nucleus breaks apart into two lighter ones. This splitting of atoms is known as nuclear fission. An induced nuclear fission event. ... For other uses, see Nickel (disambiguation). ... Binding energy is the energy required to disassemble a whole into separate parts. ... The mass number (A), also called atomic mass number (not to be confused with atomic number (Z) which denotes the number of protons in a nucleus) or nucleon number, is the number of nucleons (protons and neutrons) in an atomic nucleus. ...


The process of alpha decay may be thought of as a special type of spontaneous nuclear fission. This process produces a highly asymmetrical fission because the four particles which make up the alpha particle are especially tightly bound to each other, making production of this nucleus in fission particularly likely. Alpha decay Alpha decay is a type of radioactive decay in which an atom emits an alpha particle (two protons and two neutrons bound together into a particle identical to a helium nucleus) and transforms (or decays) into an atom with a mass number 4 less and atomic number 2... An induced nuclear fission event. ...


For certain of the heaviest nuclei which produce neutrons on fission, and which also easily absorb neutrons to initiate fission, a self-igniting type of neutron-initiated fission can be obtained, in a so-called chain reaction. [Chain reactions were known in chemistry before physics, and in fact many familiar processes like fires and chemical explosions are chemical chain reactions]. The fission or "nuclear" chain-reaction, using fission-produced neutrons, is the source of energy for nuclear power plants and fission type nuclear bombs such as the two that the United States used against Hiroshima and Nagasaki at the end of World War II. Heavy nuclei such as uranium and thorium may undergo spontaneous fission, but they are much more likely to undergo decay by alpha decay. A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions. ... For other uses, see Chemistry (disambiguation). ... This is a discussion of a present category of science. ... For fusion power, see Fusion power. ... The Japanese city of Hiroshima ) is the capital of Hiroshima Prefecture, and the largest city in the ChÅ«goku region of western HonshÅ«, the largest of Japans islands. ... Nagasaki ) ( ) is the capital and the largest city of Nagasaki Prefecture in Japan. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... General Name, symbol, number uranium, U, 92 Chemical series actinides Group, period, block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Standard atomic weight 238. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Standard atomic weight 232. ... Spontaneous fission (SF) is a form of radioactive decay characteristic of very heavy isotopes, and is theoretically possible for any atomic nucleus whose mass is greater than or equal to 100 amu (elements near ruthenium). ...


For a neutron-initiated chain-reaction to occur, there must be a critical mass of the element present in a certain space under certain conditions (these conditions slow and conserve neutrons for the reactions). There is one known example of a natural nuclear fission reactor, which was active in two regions of Oklo, Gabon, Africa, over 1.5 billion years ago. Measurements of natural neutrino emission have demonstrated that around half of the heat emanating from the earth's core results from radioactive decay. However, it is not known if any of this results from fission chain-reactions. For other uses of critical mass, see critical mass (disambiguation). ... Natural Reactors refer to a handful of Uranium deposits that have been discovered, mostly in Oklo, Gabon. ... Oklo is a place in the West African state of Gabon. ...


Production of heavy elements

As the Universe cooled after the big bang it eventually became possible for particles as we know them to exist. The most common particles created in the big bang which are still easily observable to us today were protons (hydrogen) and electrons (in equal numbers). Some heavier elements were created as the protons collided with each other, but most of the heavy elements we see today were created inside of stars during a series of fusion stages, such as the proton-proton chain, the CNO cycle and the triple-alpha process. Progressively heavier elements are created during the evolution of a star. Since the binding energy per nucleon peaks around iron, energy is only released in fusion processes occurring below this point. Since the creation of heavier nuclei by fusion costs energy, nature resorts to the process of neutron capture. Neutrons (due to their lack of charge) are readily absorbed by a nucleus. The heavy elements are created by either a slow neutron capture process (the so-called s process) or by the rapid, or r process. The s process occurs in thermally pulsing stars (called AGB, or asymptotic giant branch stars) and takes hundreds to thousands of years to reach the heaviest elements of lead and bismuth. The r process is thought to occur in supernova explosions due to the fact that the conditions of high temperature, high neutron flux and ejected matter are present. These stellar conditions make the successive neutron captures very fast, involving very neutron-rich species which then beta-decay to heavier elements, especially at the so-called waiting points that correspond to more stable nuclides with closed neutron shells (magic numbers). The r process duration is typically in the range of a few seconds. For other uses, see Big Bang (disambiguation). ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... The proton-proton chain reaction is one of two fusion reactions by which stars convert hydrogen to helium, the other being the CNO cycle. ... This article does not cite its references or sources. ... Overview of the Triple-alpha process. ... In astronomy, stellar evolution is the sequence of radical changes that a star undergoes during its lifetime (the time in which it emits light and heat). ... In nuclear physics, a magic number is a number of nucleons (either protons or neutrons) such that they are arranged into complete shells within the atomic nucleus. ...


See also

This is a list of particles in particle physics, including currently known and hypothetical elementary particles, as well as the composite particles that can be built up from them. ... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... An induced nuclear fission event. ... Shown above is the bone scintigraphy of a young woman. ... Nuclear physics is the branch of physics concerned with the nucleus of the atom. ... It has been suggested that List of elements by atomic number be merged into this article or section. ... The atomic mass (ma) is the mass of an atom at rest, most often expressed in unified atomic mass units. ... Isotopes are any of the several different forms of an element each having different atomic mass (mass number). ... The liquid drop model is a model in nuclear physics which treats the nucleus as a drop of incompressible nuclear fluid, first proposed by George Gamow. ... This article or section does not adequately cite its references or sources. ...

External links

  • The Nucleus - a chapter from an online textbook
  • SCK.CEN Belgian Nuclear Research Centre Mol, Belgium

  Results from FactBites:
 
Atomic nucleus - definition of Atomic nucleus in Encyclopedia (809 words)
The nucleus (atomic nucleus) is the center of an atom.
The number of protons in an atom's nucleus is called the atomic number, and determines which element the atom is (for example hydrogen, carbon, oxygen, etc.).
Protons and neutrons have nearly equal masses, and their combined number, the mass number, is approximately equal to the atomic mass of an atom (each isotope of an element has a unique atomic mass).
  More results at FactBites »

 
 

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