The nucleus of an atom is the very small dense region of an atom, in its center consisting of nucleons (protons and neutrons). History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny In Physics a nucleon is a collective name for two Baryons the Neutron and the Proton. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. 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). The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International 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 electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J 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”. Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English The modern atomic meaning was proposed by Ernest Rutherford in 1912. Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist [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”. Gilbert Newton Lewis ( October 23, 1875 - March 23, 1946) was a famous American physical chemist known for the discovery
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Introduction
Nuclear makeup
The nucleus of an atom consists of protons and neutrons (two types of baryons) bound by the nuclear force. Baryons are the family of Subatomic particles with a Baryon number of 1 The nuclear force (or nucleon-nucleon interaction or residual strong force) is the force between two or more Nucleons It is responsible for These baryons are further composed of sub-atomic fundamental particles known as quarks bound by the strong interaction. In Physics, a quark (kwɔrk kwɑːk or kwɑːrk is a type of Subatomic particle. In particle physics the strong interaction, or strong force, or color force, holds Quarks and Gluons together to form Protons and
Isotopes and nuclides
The isotope of an atom is determined by the number of neutrons in the nucleus. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Different isotopes of the same element have very similar chemical properties. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Different isotopes in a sample of a particular chemical can be separated by using a centrifuge or by using a mass spectrometer. A centrifuge is a piece of equipment generally driven by a motor that puts an object in Rotation around a fixed axis, applying a force perpendicular to the axis Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles The first method is used in producing enriched uranium from a sample of regular uranium, and the second is used in carbon dating. Enriched uranium is a kind of Uranium in which the percent composition of Uranium-235 has been increased through the process of Isotope separation. Radiocarbon dating is a Radiometric dating method that uses the naturally occurring Radioisotope Carbon-14 (14C to determine the age of
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 mass number ( A) also called atomic mass number or nucleon number, is the total number of Protons and Neutrons (together known as The atomic mass (ma is the Mass of an atom most often expressed in unified atomic mass units The atomic mass may be considered to be the total mass 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.
History
The discovery of the electron by J. J. Thomson was the first indication that the atom had internal structure. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Sir Joseph John “JJ” Thomson, OM, FRS (18 December 1856 &ndash 30 August 1940 was a British Physicist and Nobel laureate 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. The plum pudding model of the Atom by JJ Thomson, who discovered the Electron in 1897 was proposed in 1904 before the discovery of the atomic nucleus 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. Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy Alpha decay is a type of radioactive decay in which an Atomic nucleus emits an Alpha particle (two protons and two neutrons bound together into a particle In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions 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. Year 1911 ( MCMXI) was a Common year starting on Sunday (link will display the full calendar of the Gregorian calendar (or a Common year Lise Meitner (7 or 17 November 1878 &ndash 27 October 1968 was an Austrian born later Swedish physicist who studied Radioactivity and Otto Hahn (8 March 1879 &ndash 28 July 1968 was a German Chemist who received the 1944 Nobel Prize in Chemistry for discovering Nuclear fission Sir James Chadwick, CH (20 October 1891 &ndash 24 July 1974 was an English Physicist and Nobel laureate in physics awarded for his discovery of the A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. 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. Alpha decay is a type of radioactive decay in which an Atomic nucleus emits an Alpha particle (two protons and two neutrons bound together into a particle This was a problem for nuclear physics at the time, because it indicated that energy was not conserved in these decays. In Physics, the law of conservation of energy states that the total amount of Energy in an isolated system remains constant and cannot be created although it may The problem would later lead to the discovery of the neutrino (see below).
In 1906 Ernest Rutherford published "Radiation of the α Particle from Radium in passing through Matter"[2]. Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist Geiger expanded on this work in a communication to the Royal Society[3] with experiments he and Rutherford had done passing α particles through air, aluminum foil and gold foil. Johannes (Hans Wilhelm Geiger ( September 30, 1882 &ndash September 24, 1945) was a German Physicist. More work was published in 1909 by Geiger and Marsden[4] and further greatly expanded work was published in 1910 by Geiger, [5] 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. Johannes (Hans Wilhelm Geiger ( September 30, 1882 &ndash September 24, 1945) was a German Physicist. Sir Ernest Marsden ( 19 February 1889 - 15 December 1970) was a English - New Zealand Physicist. Johannes (Hans Wilhelm Geiger ( September 30, 1882 &ndash September 24, 1945) was a German Physicist.
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. Year 1909 ( MCMIX) was a Common year starting on Friday (link will display full calendar of the Gregorian calendar (or a Common year starting Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist The Geiger-Marsden experiment (also called the Gold foil experiment or the Rutherford experiment) was an experiment done by Hans Geiger and Ernest Johannes (Hans Wilhelm Geiger ( September 30, 1882 &ndash September 24, 1945) was a German Physicist. Sir Ernest Marsden ( 19 February 1889 - 15 December 1970) was a English - New Zealand Physicist. Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 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.
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. In Quantum mechanics, spin is a fundamental property of atomic nuclei, Hadrons and Elementary particles For particles with non-zero spin Franco Dino Rasetti ( August 10, 1901 &ndash December 5, 2001) was an Italian scientist The California Institute of Technology (commonly referred to as Caltech) is a private, Coeducational research university located in Pasadena Year 1929 ( MCMXXIX) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar. 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. Year 1925 ( MCMXXV) was a Common year starting on Thursday (link will display the full calendar of the Gregorian calendar. Rasetti discovered, however, that nitrogen-14 has a spin of one.
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". Year 1930 ( MCMXXX) was a Common year starting on Wednesday (link will display 1930 calendar of the Gregorian calendar. Tübingen, a traditional University town in Baden-Württemberg, Germany, is situated 30 km (19 miles southwest of Stuttgart, on a ridge between 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. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost 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 L. Becker, Irène and Frédéric Joliot-Curie was actually due to a massive particle that he called the neutron. Year 1932 ( MCMXXXII) was a Leap year starting on Friday of the Gregorian calendar. Walther Wilhelm Georg Bothe (8 January 1891 in Oranienburg &ndash 8 February 1957 in Heidelberg) was a German nuclear physicst Dr Herbert L Becker (Born August 12 19-- in Hollywood FL is the inventor and patent/copyright holder for BOIP (broadcasting over internet protocol and the founder of IPTV (internet Irène Joliot-Curie ( 12 September 1897 &ndash 17 March 1956) was a French scientist the Daughter of Marie Skłodowska-Curie Jean Frédéric Joliot-Curie born Joliot ( March 19, 1900 &ndash August 14, 1958) was a French Physicist and 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. Dmitri Ivanenko (Дмитрий Дмитриевич Иваненко ( July 29, 1904, Poltava, Ukraine — December 30, 1994 Francis Perrin ( Paris, 1901 - id 1992 was a French Physicist, the son of Jean Perrin. To cap the year off, Fermi submitted a theory of the neutrino to Nature (which the editors rejected for being "too remote from reality"). Nature is a prominent Scientific journal, first published on 4 November 1869 Fermi continued working on his theory and published a paper in 1934 which placed the neutrino on solid theoretical footing. Year 1934 ( MCMXXXIV) was a Common year starting on Monday (link will display full 1934 calendar of the Gregorian calendar. In the same year Hideki Yukawa proposed the first significant theory of the strong force to explain how the nucleus holds together. né, was a Japanese Theoretical physicist and the first Japanese Nobel laureate.
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). The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron. 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 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. Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them The Standard Model of Particle physics is a theory that describes three of the four known Fundamental interactions together with the Elementary particles
Modern nuclear physics
A light nucleus can contain hundreds of nucleons which means that with some approximation it can be treated as a classical system, rather than a quantum-mechanical one. In Physics a nucleon is a collective name for two Baryons the Neutron and the Proton. Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons 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. In Nuclear physics, the semi-empirical mass formula ( SEMF) sometimes also called Weizsäcker's formula is a formula used to approximate the Mass For the work of fiction see Surface Tension (short story. Surface tension is a property of the surface of a Liquid that causes it to 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. Binding energy is the Mechanical energy required to disassemble a whole into separate parts The mass number ( A) also called atomic mass number or nucleon number, is the total number of Protons and Neutrons (together known as Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing Free neutrons and other smaller nuclei which may
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. In Nuclear physics, the nuclear shell model is a model of the Atomic nucleus which uses the Pauli principle to describe the structure Maria Goeppert-Mayer ( June 28, 1906 &ndash February 20, 1972) was a German -born American Nuclei with certain numbers of neutrons and protons (the magic numbers 2, 8, 20, 50, 82, 126, . In Nuclear physics, a magic number is a number of Nucleons (either Protons or Neutrons such that they are arranged into complete shells . . ) are particularly stable, because their shells are filled.
Much of current research in nuclear physics relates to the study of nuclei under extreme conditions such as high spin and excitation energy. Nuclear physics is the field of Physics that studies the building blocks and interactions of Atomic nuclei. In Quantum mechanics, spin is a fundamental property of atomic nuclei, Hadrons and Elementary particles For particles with non-zero spin Nuclei may also have extreme shapes (similar to that of American footballs) or extreme neutron-to-proton ratios. American football, known in the United States and Canada simply as football, is a competitive Team sport known for mixing strategy with 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. In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another A quark-gluon plasma (QGP is a phase of Quantum chromodynamics (QCD which exists at extremely high Temperature and/or Density. In Physics, a quark (kwɔrk kwɑːk or kwɑːrk is a type of Subatomic particle.
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. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the In this decay a neutron in the nitrogen nucleus is turned into a proton and an electron by the weak nuclear force. The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four Fundamental interactions of nature 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.
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. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus 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. Binding energy is the Mechanical energy required to disassemble a whole into separate parts The mass number ( A) also called atomic mass number or nucleon number, is the total number of Protons and Neutrons (together known as Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Stars like our sun are powered by the fusion of four protons into a helium nucleus, two positrons, and two neutrinos. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost The uncontrolled fusion of hydrogen into helium is known as thermonuclear runaway. 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). JET, the Joint European Torus, is the largest Nuclear fusion experimental reactor yet built ITER is an international Tokamak ( Magnetic confinement fusion) research/engineering proposal for an experimental project that will help to make the transition from
Nuclear fission
For nuclei heavier than nickel-62 the binding energy per nucleon decreases with the mass number. Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing Free neutrons and other smaller nuclei which may Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Binding energy is the Mechanical energy required to disassemble a whole into separate parts The mass number ( A) also called atomic mass number or nucleon number, is the total number of Protons and Neutrons (together known as 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.
The process of alpha decay may be thought of as a special type of spontaneous nuclear fission. Alpha decay is a type of radioactive decay in which an Atomic nucleus emits an Alpha particle (two protons and two neutrons bound together into a particle Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing Free neutrons and other smaller nuclei which may 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.
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. A chain reaction is a sequence of Reactions where a reactive product or by-product causes additional reactions to take place [Chain reactions were known in chemistry before physics, and in fact many familiar processes like fires and chemical explosions are chemical chain reactions]. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. 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. Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions The United States of America —commonly referred to as the The Japanese city of ( is the capital of Hiroshima Prefecture, and the largest city in the Chūgoku region of western Honshū, the largest of Japan 's ( is the Capital and the largest city of Nagasaki Prefecture in Japan. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including Heavy nuclei such as uranium and thorium may undergo spontaneous fission, but they are much more likely to undergo decay by alpha decay. Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the Thorium (ˈθɔːriəm is a Chemical element with the symbol Th and Atomic number 90 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
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). A critical mass is the smallest amount of Fissile material needed for a sustained Nuclear chain reaction. There is one known example of a natural nuclear fission reactor, which was active in two regions of Oklo, Gabon, Africa, over 1. A natural nuclear fission reactor is a Uranium deposit where analysis of Isotope Ratios has shown that self-sustaining Nuclear chain reactions Oklo is a region near the town of Franceville, in the Haut-Ogooué province of the Central African state of Gabon. 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.
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 Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. 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). Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 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. The proton-proton chain reaction is one of several fusion reactions by which Stars convert Hydrogen to Helium, the primary alternative being the The CNO cycle (for Carbon - Nitrogen - Oxygen) or sometimes Bethe-Weizsäcker-cycle, is one of two sets of fusion reactions The triple alpha process is a set of Nuclear fusion reactions by which three Helium nuclei ( Alpha particles are transformed into Carbon. Progressively heavier elements are created during the evolution of a star. Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime 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 because 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). In Nuclear physics, a magic number is a number of Nucleons (either Protons or Neutrons such that they are arranged into complete shells The r process duration is typically in the range of a few seconds.
See also
References
- ^ Nucleus – Online Etymology Dictionary
- ^ Philosophical Magazine (12, p 134-46)
- ^ Proc. This is a list of the different types of particles known and hypothesized Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing Free neutrons and other smaller nuclei which may Nuclear medicine is a branch of Medicine and Medical imaging that uses the nuclear properties of matter in diagnosis and therapy Nuclear physics is the field of Physics that studies the building blocks and interactions of Atomic nuclei. See also List of elements by atomic number In Chemistry and Physics, the atomic number (also known as the proton The atomic mass (ma is the Mass of an atom most often expressed in unified atomic mass units The atomic mass may be considered to be the total mass Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides In Nuclear physics, the semi-empirical mass formula ( SEMF) sometimes also called Weizsäcker's formula is a formula used to approximate the Mass In Nuclear physics, the semi-empirical mass formula ( SEMF) sometimes also called Weizsäcker's formula is a formula used to approximate the Mass Roy. Soc. July 17, 1908
- ^ Proc. Roy. Soc. A82 p 495-500
- ^ Proc. Roy. Soc. Feb. 1, 1910
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