An induced nuclear fission event where a slow-moving neutron is absorbed by the nucleus of a uranium-235 atom, which in turn releases two fast-moving lighter elements (fission products), free neutrons and energy. Also shown is the capture of a neutron by uranium-238 to become uranium-239.

Nuclear physics Radioactive decay Nuclear fission Nuclear fusion This box: view • talk • edit

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 eventually produce photons (in the form of gamma rays). Nuclear physics is the field of Physics that studies the building blocks and interactions of Atomic nuclei. 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 The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom A free neutron is a Neutron that exists outside of an Atomic nucleus. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). An exothermic reaction is a Chemical reaction that releases Heat. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. The kinetic energy of an object is the extra Energy which it possesses due to its motion In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Fission is a form of elemental transmutation because the resulting fragments are not the same element as the original atom. Nuclear transmutation is the conversion of one Chemical element or Isotope into another which occurs through Nuclear reactions Natural transmutation occurs A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus.

Nuclear fission produces energy for nuclear power and to drive the explosion of nuclear weapons. Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. Both uses are made possible because certain substances called nuclear fuels undergo fission when struck by free neutrons and in turn generate neutrons when they break apart. Nuclear fuel is any material that can be consumed to derive Nuclear energy, by analogy to chemical Fuel that is burned to derive energy This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon. A chain reaction is a sequence of Reactions where a reactive product or by-product causes additional reactions to take place This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion.

The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very tempting source of energy; however, the products of nuclear fission are radioactive and remain so for significant amounts of time, giving rise to a nuclear waste problem. In Thermodynamics, the term thermodynamic free energy refers to the amount of work that can be extracted from a System, and is helpful in Engineering Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. Radioactive wastes are Waste types containing radioactive Chemical elements that do not have a practical purpose Concerns over nuclear waste accumulation and over the destructive potential of nuclear weapons may counterbalance the desirable qualities of fission as an energy source, and give rise to ongoing political debate over nuclear power. Politics Politics is the process by which groups of people make decisions

Physical overview

Nuclear fission differs from other forms of radioactive decay in that it can be harnessed and controlled via a chain reaction: free neutrons released by each fission event can trigger yet more events, which in turn release more neutrons and cause more fissions. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. A chain reaction is a sequence of Reactions where a reactive product or by-product causes additional reactions to take place This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. Chemical isotopes that can sustain a fission chain reaction are called nuclear fuels, and are said to be fissile. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Nuclear fuel is any material that can be consumed to derive Nuclear energy, by analogy to chemical Fuel that is burned to derive energy In Nuclear engineering, a fissile material is one that is capable of sustaining a Chain reaction of Nuclear fission. The most common nuclear fuels are ²³⁵U (the isotope of uranium with an atomic mass of 235 and of use in nuclear reactors) and ²³⁹Pu (the isotope of plutonium with an atomic mass of 239). Uranium-235 is an isotope of uranium that differs from the element's other common isotope Uranium-238, by its ability to cause a rapidly expanding fission Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the 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 Plutonium-239 is an Isotope of Plutonium. Plutonium-239 is the primary Fissile isotope used for the production of Nuclear weapons although These fuels break apart into a bimodal range of chemical elements with atomic masses centering near 95 and 135 u (fission products). Fission products are the atomic fragments left after a large nucleus fissions. Most nuclear fuels undergo spontaneous fission only very slowly, decaying mainly via an alpha/beta decay chain over periods of millennia to eons. 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 Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a Beta particles are high-energy high-speed Electrons or Positrons emitted by certain types of Radioactive nuclei such as Potassium -40 In Nuclear science, the decay chain refers to the Radioactive decay of different discrete radioactive decay products as a chained series of transformations A millennium (pl millennia) is a period of Time equal to one thousand Years (from Latin la mille, thousand and la annum In a nuclear reactor or nuclear weapon, most fission events are induced by bombardment with another particle such as a neutron. This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled

Typical fission events release about two hundred million eV of energy for each fission event. By contrast, most chemical oxidation reactions (such as burning coal or TNT) release at most a few eV per event, so nuclear fuel contains at least ten million times more usable energy than does chemical fuel. A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Trinitrotoluene ( TNT) is a Chemical compound with the formula C6H2(NO23CH3 The energy of nuclear fission is released as kinetic energy of the fission products and fragments, and as electromagnetic radiation in the form of gamma rays; in a nuclear reactor, the energy is converted to heat as the particles and gamma rays collide with the atoms that make up the reactor and its working fluid, usually water or occasionally heavy water. The kinetic energy of an object is the extra Energy which it possesses due to its motion Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature The working fluid in a machine is the pressurized gas or liquid which actuates the machine Water is a common Chemical substance that is essential for the survival of all known forms of Life. Heavy water is water which contains a higher proportion than normal of the Isotope Deuterium, as deuterium oxide, D2O or ²H2O

Nuclear fission of heavy elements produces energy because the specific binding energy (binding energy per mass) of intermediate-mass nuclei with atomic numbers and atomic masses close to ⁶¹Ni and ⁵⁶Fe is greater than the specific binding energy of very heavy nuclei, so that energy is released when heavy nuclei are broken apart. Binding energy is the Mechanical energy required to disassemble a whole into separate parts 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

The total rest masses of the fission products (Mp) from a single reaction is less than the mass of the original fuel nucleus (M). The excess mass Δm = M - Mp is the invariant mass of the energy that is released as photons (gamma rays) and kinetic energy of the fission fragments, according to the mass-energy equivalence formula E = mc². In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions In Physics, mass–energy equivalence is the concept that for particles slower than light any Mass has an associated Energy and vice versa.

In nuclear fission events the nuclei may break into any combination of lighter nuclei, but the most common event is not fission to equal mass nuclei of about mass 120; the most common event (depending on isotope and process) is a slightly unequal fission in which one daughter nucleus has a mass of about 90 to 100 u and the other the remaining 130 to 140 u [1]. Unequal fissions are energetically more favorable because this allows one product to be closer to the energetic minimum near mass 60 u (only a quarter of the average fissionable mass), while the other nucleus with mass 135 u is still not far out of the range of the most tightly bound nuclei (another statement of this, is that the atomic binding energy curve is slightly steeper to the left of mass 120 u than to the right of it). Binding energy is the Mechanical energy required to disassemble a whole into separate parts

The variation in specific binding energy with atomic number is due to the interplay of the two fundamental forces acting on the component nucleons (protons and neutrons) that make up the nucleus. In Physics, a force is whatever can cause an object with Mass to Accelerate. 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. Nuclei are bound by an attractive strong nuclear force between nucleons, which overcomes the electrostatic repulsion between protons. In particle physics the strong interaction, or strong force, or color force, holds Quarks and Gluons together to form Protons and Valence shell electron pair repulsion (VSEPR theory (1957 is a model in Chemistry, which is used for predicting the shapes of individual Molecules based However, the strong nuclear force acts only over extremely short ranges, since it follows a Yukawa potential. A Yukawa potential (also called a screened Coulomb potential is a Potential of the form V(r= -g^2 \\frac{e^{-mr}}{r} Hideki Yukawa For this reason large nuclei are less tightly bound per unit mass than small nuclei, and breaking a very large nucleus into two or more intermediate-sized nuclei releases energy.

Because of the short range of the strong binding force, large nuclei must contain proportionally more neutrons than do light elements, which are most stable with a 1-1 ratio of protons and neutrons. Extra neutrons stabilize heavy elements because they add to strong-force binding without adding to proton-proton repulsion. Fission products have, on average, about the same ratio of neutrons and protons as their parent nucleus, and are therefore usually unstable because they have proportionally too many neutrons compared to stable isotopes of similar mass. This is the fundamental cause of the problem of radioactive high level waste from nuclear reactors. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. High level waste (HLW is a type of Nuclear waste that arises from the use of uranium fuel in a Nuclear reactor and Nuclear weapons processing Fission products tend to be beta emitters, emitting fast-moving electrons to conserve electric charge as excess neutrons convert to protons inside the nucleus of the fission product atoms. Beta particles are high-energy high-speed Electrons or Positrons emitted by certain types of Radioactive nuclei such as Potassium -40 In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction.

The most common nuclear fuels, ²³⁵U and ²³⁹Pu, are not major radiologic hazards by themselves: ²³⁵U has a half-life of approximately 700 million years, and although ²³⁹Pu has a half-life of only about 24,000 years, it is a pure alpha particle emitter and hence not particularly dangerous unless ingested. Half-Life (computer-game page here It's already listed in the disambiguation page Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a Once a fuel element has been used, the remaining fuel material is intimately mixed with highly radioactive fission products that emit energetic beta particles and gamma rays. This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled Beta particles are high-energy high-speed Electrons or Positrons emitted by certain types of Radioactive nuclei such as Potassium -40 Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Some fission products have half-lives as short as seconds; others have half-lives of tens of thousands of years, requiring long-term storage in facilities such as Yucca Mountain until the fission products decay into non-radioactive stable isotopes.

Chain reactions

A schematic nuclear fission chain reaction. 1. A uranium-235 atom absorbs a neutron and fissions into two new atoms (fission fragments), releasing three new neutrons and some binding energy. Uranium-235 is an isotope of uranium that differs from the element's other common isotope Uranium-238, by its ability to cause a rapidly expanding fission This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. 2. One of those neutrons is absorbed by an atom of uranium-238 and does not continue the reaction. Uranium-238 (U-238 is the most common isotope of Uranium found in nature Another neutron is simply lost and does not collide with anything, also not continuing the reaction. However one neutron does collide with an atom of uranium-235, which then fissions and releases two neutrons and some binding energy. 3. Both of those neutrons collide with uranium-235 atoms, each of which fissions and releases between one and three neutrons, which can then continue the reaction.

Main article: Nuclear chain reaction

Many heavy elements, such as uranium, thorium, and plutonium, undergo both spontaneous fission, a form of radioactive decay and induced fission, a form of nuclear reaction. A nuclear chain reaction occurs when one Nuclear reaction causes an average of one or more nuclear reactions thus leading to a self-propagating number of these reactions 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 Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. In Nuclear physics, a nuclear reaction is the process in which two nuclei or nuclear particles collide to produce products different from the initial particles Elemental isotopes that undergo induced fission when struck by a free neutron are called fissionable; isotopes that undergo fission when struck by a thermal, slow moving neutron are also called fissile. This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. In Nuclear engineering, a fissile material is one that is capable of sustaining a Chain reaction of Nuclear fission. The neutron temperature, also called the neutron energy, indicates a free neutron's Kinetic energy, usually given in Electron volts The term In Nuclear engineering, a fissile material is one that is capable of sustaining a Chain reaction of Nuclear fission. A few particularly fissile and readily obtainable isotopes (notably ²³⁵U and ²³⁹Pu) are called nuclear fuels because they can sustain a chain reaction and can be obtained in large enough quantities to be useful. Nuclear fuel is any material that can be consumed to derive Nuclear energy, by analogy to chemical Fuel that is burned to derive energy

All fissionable and fissile isotopes undergo a small amount of spontaneous fission which releases a few free neutrons into any sample of nuclear fuel. Such neutrons would escape rapidly from the fuel and become a free neutron, with a half-life of about 15 minutes before they decayed to protons and beta particles. A free neutron is a Neutron that exists outside of an Atomic nucleus. Half-Life (computer-game page here It's already listed in the disambiguation page The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive Beta particles are high-energy high-speed Electrons or Positrons emitted by certain types of Radioactive nuclei such as Potassium -40 However, neutrons almost invariably impact and are absorbed by other nuclei in the vicinity long before this happens (newly-created fission neutrons are moving at about 7% of the speed of light, and even moderated neutrons are moving at about 8 times the speed of sound). Some neutrons will impact fuel nuclei and induce further fissions, releasing yet more neutrons. If enough nuclear fuel is assembled into one place, or if the escaping neutrons are sufficiently contained, then these freshly generated neutrons outnumber the neutrons that escape from the assembly, and a sustained nuclear chain reaction will take place.

An assembly that supports a sustained nuclear chain reaction is called a critical assembly or, if the assembly is almost entirely made of a nuclear fuel, a critical mass. A critical mass is the smallest amount of Fissile material needed for a sustained Nuclear chain reaction. A critical mass is the smallest amount of Fissile material needed for a sustained Nuclear chain reaction. The word "critical" refers to a cusp in the behavior of the differential equation that governs the number of free neutrons present in the fuel: if less than a critical mass is present, then the amount of neutrons is determined by radioactive decay, but if a critical mass or more is present, then the amount of neutrons is controlled instead by the physics of the chain reaction. A differential equation is a mathematical Equation for an unknown function of one or several variables that relates the values of the Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. The actual mass of a critical mass of nuclear fuel depends strongly on the geometry and surrounding materials. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object

Not all fissionable isotopes can sustain a chain reaction. For example, ²³⁸U, the most abundant form of uranium, is fissionable but not fissile: it undergoes induced fission when impacted by an energetic neutron with over 1 MeV of kinetic energy. But too few of the neutrons produced by ²³⁸U fission are energetic enough to induce further fissions in ²³⁸U, so no chain reaction is possible with this isotope. Instead, bombarding ²³⁸U with slow neutrons causes it to absorb them (becoming ²³⁹U) and decay by beta emission to ²³⁹Np which then decays again by the same process to ²³⁹Pu; that process is used to manufacture ²³⁹Pu in breeder reactors, but does not contribute to a neutron chain reaction. In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted A breeder reactor is a Nuclear reactor that generates new Fissile or fissionable material at a greater rate than it consumes such material

Fissionable, non-fissile isotopes can be used as fission energy source even without a chain reaction. Bombarding ²³⁸U with fast neutrons induces fissions, releasing energy as long as the external neutron source is present. That effect is used to augment the energy released by modern thermonuclear weapons, by jacketing the weapon with ²³⁸U to react with neutrons released by nuclear fusion at the center of the device. Nuclear weapon designs are physical chemical and engineering arrangements that cause the physics package of a nuclear weapon to detonate In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus

Fission reactors

Critical fission reactors are the most common type of nuclear reactor. This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled In a critical fission reactor, neutrons produced by fission of fuel atoms are used to induce yet more fissions, to sustain a controllable amount of energy release. Devices that produce engineered but non-self-sustaining fission reactions are subcritical fission reactors. Such devices use radioactive decay or particle accelerators to trigger fissions. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation.

Critical fission reactors are built for three primary purposes, which typically involve different engineering trade-offs to take advantage of either the heat or the neutrons produced by the fission chain reaction:

• power reactors are intended to produce heat for nuclear power, either as part of a generating station or a local power system such as a nuclear submarine. Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions Electricity generation is the process of converting non-electrical Energy to Electricity. A nuclear submarine is a Submarine powered by Atomic energy. Previously conventional submarines used diesel engines that required air for moving on the
• research reactors are intended to produce neutrons and/or activate radioactive sources for scientific, medical, engineering, or other research purposes. Research reactors are Nuclear reactors that serve primarily as a Neutron source.
• breeder reactors are intended to produce nuclear fuels in bulk from more abundant isotopes. A breeder reactor is a Nuclear reactor that generates new Fissile or fissionable material at a greater rate than it consumes such material Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides The better known fast breeder reactor makes ²³⁹Pu (a nuclear fuel) from the naturally very abundant ²³⁸U (not a nuclear fuel). The fast breeder or fast breeder reactor ( FBR) is a Fast neutron reactor designed to breed fuel by producing more Fissile material Thermal breeder reactors previously tested using ²³²Th continue to be studied and developed.

While, in principle, all fission reactors can act in all three capacities, in practice the tasks lead to conflicting engineering goals and most reactors have been built with only one of the above tasks in mind. (There are several early counter-examples, such as the Hanford N reactor, now decommissioned). The Hanford Site is a decommissioned nuclear production complex on the Columbia River in south-central Washington operated by the United States government The N-Reactor was a graphite- moderated Nuclear reactor constructed during the Cold War and operated by the U Power reactors generally convert the kinetic energy of fission products into heat, which is used to heat a working fluid and drive a heat engine that generates mechanical or electrical power. The working fluid in a machine is the pressurized gas or liquid which actuates the machine A heat engine is a physical or theoretical device that converts Thermal energy to mechanical output The working fluid is usually water with a steam turbine, but some designs use other materials such as gaseous helium. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Research reactors produce neutrons that are used in various ways, with the heat of fission being treated as an unavoidable waste product. Breeder reactors are a specialized form of research reactor, with the caveat that the sample being irradiated is usually the fuel itself, a mixture of ²³⁸U and ²³⁵U.

For a more detailed description of the physics and operating principles of critical fission reactors, see nuclear reactor physics. See also Critical mass Most Nuclear reactors use a Chain reaction to induce a controlled rate of Nuclear fission in fissile material releasing For a description of their social, political, and environmental aspects, see nuclear reactor. This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled

Fission bombs

One class of nuclear weapon, a fission bomb (not to be confused with the fusion bomb), otherwise known as an atomic bomb or atom bomb, is a fission reactor designed to liberate as much energy as possible as rapidly as possible, before the released energy causes the reactor to explode (and the chain reaction to stop). A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. Nuclear weapon designs are physical chemical and engineering arrangements that cause the physics package of a nuclear weapon to detonate Development of nuclear weapons was the motivation behind early research into nuclear fission: the Manhattan Project of the U.S. military during World War II carried out most of the early scientific work on fission chain reactions, culminating in the Little Boy and Fat Man and Trinity bombs that were exploded over test sites, the cities Hiroshima, and Nagasaki, Japan in August of 1945. The World War II Manhattan Project developed the first Nuclear weapon (atomic bomb The United States Armed Forces are the overall unified military forces of the United States 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 Little Boy was the Codename of the Atomic bomb, developed via the "Manhattan Project" which was dropped on Hiroshima, on August 6 1945 by the "Fat Man" is the codename for the Atomic bomb that was detonated over Nagasaki, Japan, by the United States on August 9 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. For a topic outline on this subject see List of basic Japan topics.

Even the first fission bombs were thousands of times more explosive than a comparable mass of chemical explosive. An explosive material is a material that either is chemically or otherwise Energetically unstable or produces a sudden expansion of the material usually accompanied An explosive material is a material that either is chemically or otherwise Energetically unstable or produces a sudden expansion of the material usually accompanied For example, Little Boy weighed a total of about four tons (of which 60 kg was nuclear fuel) and was 11 feet (3. 4 m) long; it also yielded an explosion equivalent to about 15 kilotons of TNT, destroying a large part of the city of Hiroshima. Trinitrotoluene ( TNT) is a Chemical compound with the formula C6H2(NO23CH3 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 Modern nuclear weapons (which include a thermonuclear fusion as well as one or more fission stages) are literally hundreds of times more energetic for their weight than the first pure fission atomic bombs, so that a modern single missile warhead bomb weighing less than 1/8th as much as Little Boy (see for example W88) has a yield of 475,000 tons of TNT, and could bring destruction to 10 times the city area. The W88 is a United States thermonuclear warhead, with an estimated yield of 475 Kiloton (kt and is small enough to fit on MIRVed missiles

While the fundamental physics of the fission chain reaction in a nuclear weapon is similar to the physics of a controlled nuclear reactor, the two types of device must be engineered quite differently (see nuclear reactor physics). A nuclear chain reaction occurs when one Nuclear reaction causes an average of one or more nuclear reactions thus leading to a self-propagating number of these reactions See also Critical mass Most Nuclear reactors use a Chain reaction to induce a controlled rate of Nuclear fission in fissile material releasing It is impossible to convert a nuclear reactor to cause a true nuclear explosion, or for a nuclear reactor to explode the way a nuclear explosive does, (though partial fuel meltdowns and steam explosions have occurred), and similarly difficult to extract useful power from a nuclear explosive (though at least one rocket propulsion system, Project Orion, was intended to work by exploding fission bombs behind a massively padded vehicle!). This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled A steam Explosion (also called a Littoral explosion, or fuel-coolant interaction, FCI) is a violent A rocket or rocket vehicle is a Missile, Aircraft or other Vehicle which obtains Thrust by the reaction of the Project Orion was the first engineering design study of a Spacecraft powered by Nuclear pulse propulsion, an idea first proposed by Stanisław Ulam

The strategic importance of nuclear weapons is a major reason why the technology of nuclear fission is politically sensitive. A Strategy is a long term plan of action designed to achieve a particular goal, most often "winning Technology is a broad concept that deals with a Species ' usage and knowledge of Tools and Crafts and how it affects a species' ability to control and adapt Viable fission bomb designs are, arguably, within the capabilities of bright undergraduates (see John Aristotle Phillips) being incredibly simple, but nuclear fuel to realize the designs is thought to be difficult to obtain being rare (see uranium enrichment and nuclear fuel cycle). John Aristotle Phillips is a US entrepreneur "A-Bomb Kid" Philips was born in 1954 or 1955 to Greek immigrants. Enriched uranium is a kind of Uranium in which the percent composition of Uranium-235 has been increased through the process of Isotope separation. The nuclear fuel cycle, also called nuclear fuel chain, is the progression of Nuclear fuel through a series of differing stages

History

Unlike nuclear fusion which occurs in stars, natural nuclear fission is less common. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus A natural nuclear fission reactor is a Uranium deposit where analysis of Isotope Ratios has shown that self-sustaining Nuclear chain reactions At three ore deposits at Oklo in Gabon, sixteen sites have been discovered at which self-sustaining nuclear fission took place approximately 1. Oklo is a region near the town of Franceville, in the Haut-Ogooué province of the Central African state of Gabon. Gabon (gəˈbɒn or /gaˈbõ/ in French) is a country in west central Africa sharing borders with Equatorial Guinea, Cameroon, Republic 5 billion years ago.

While many believe that Ernest Rutherford became the first person to deliberately split the atom by bombarding nitrogen with naturally occurring alpha particles from radioactive material and observing a proton emitted with energy higher than the alpha particle. Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist ^[1] In 1932 his students John Cockcroft and Ernest Walton, working under Rutherford's direction, attempted to split the nucleus by entirely artificial means, using a particle accelerator to bombard lithium with protons thereby producing two alpha particles. Sir John Douglas Cockcroft OM KCB CBE ( May 27, 1897 &ndash September 18, 1967) was a British physicist. Ernest Thomas Sinton Walton (6 October 1903 &ndash 25 June 1995 was an Irish physicist and Nobel laureate for his work with John Cockcroft with Lithium (ˈlɪθiəm is a Chemical element with the symbol Li and Atomic number 3 This did split the nucleus, but nevertheless was not quite the classical nuclear fission which is induced in heavy nuclei, because the daughter fragments are alpha particles-- already well-known fragments of excited nuclei, and not considered to be a truly new phenomenon, even if two of them had been produced, and nothing else.

The first clear induced (manmade) nuclear fission as we know it occurred in results of the bombardment of uranium by neutrons, which proved interesting and puzzling. First studied by Enrico Fermi and his colleagues in 1934, these results were not properly interpreted and understood until several years later.

After the Fermi publication, Lise Meitner, Otto Hahn and Fritz Strassmann began performing similar experiments in Germany. 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 Friedrich Wilhelm "Fritz" Strassman ( February 22, 1902 - April 22, 1980) was a German chemist who with Meitner, an Austrian Jew, lost her citizenship with the Anschluss in 1938. The ( German: "link-up" also known as the, was the 1938 Annexation of Austria into Greater Germany by the Nazi She fled and wound up in Sweden, but continued to collaborate by mail and through meetings with Hahn in Sweden. By coincidence her nephew Otto Robert Frisch, also a refugee, was also in Sweden when Meitner received a letter from Hahn describing his chemical proof that some of the product of the bombardment of uranium with neutrons, was barium and not barium's much heavier chemical sister element radium (barium's atomic weight is half that of uranium). Otto Robert Frisch ( 1 October 1904 &ndash 22 September 1979) Austrian British Physicist. Frisch was skeptical, but Meitner believed Hahn was too good a chemist to have made a mistake. Marie Curie had been separating barium from radium for many years, and the techniques were well-known. According to Frisch:

Was it a mistake? No, said Lise Meitner; Hahn was too good a chemist for that. But how could barium be formed from uranium? No larger fragments than protons or helium nuclei (alpha particles) had ever been chipped away from nuclei, and to chip off a large number not nearly enough energy was available. Nor was it possible that the uranium nucleus could have been cleaved right across. A nucleus was not like a brittle solid that can be cleaved or broken; George Gamow had suggested early on, and Bohr had given good arguments that a nucleus was much more like a liquid drop. George Gamow (pronounced as ˈgamof ( March 4, 1904 &ndash August 19, 1968), born Georgiy Antonovich Gamov (Георгий Антонович Perhaps a drop could divide itself into two smaller drops in a more gradual manner, by first becoming elongated, then constricted, and finally being torn rather than broken in two? We knew that there were strong forces that would resist such a process, just as the surface tension of an ordinary liquid drop tends to resist its division into two smaller ones. But nuclei differed from ordinary drops in one important way: they were electrically charged, and that was known to counteract the surface tension.

The charge of a uranium nucleus, we found, was indeed large enough to overcome the effect of the surface tension almost completely; so the uranium nucleus might indeed resemble a very wobble unstable drop, ready to divide itself at the slightest provocation, such as the impact of a single neutron. But there was another problem. After separation, the two drops would be driven apart by their mutual electric repulsion and would acquire high speed and hence a very large energy, about 200 MeV in all; where could that energy come from? . . . Lise Meitner. . . worked out that the two nuclei formed by the division of a uranium nucleus together would be lighter than the original uranium nucleus by about one-fifth the mass of a proton. Now whenever mass disappears energy is created, according to Einstein's formula E=mc2, and one-fifth of a proton mass was just equivalent to 200MeV. So here was the source for that energy; it all fitted!

In December 1938, the German chemists Otto Hahn and Fritz Strassmann sent a manuscript to Naturwissenschaften reporting they had detected the element barium after bombarding uranium with neutrons;^[2] simultaneously, they communicated these results to Lise Meitner. 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 Friedrich Wilhelm "Fritz" Strassman ( February 22, 1902 - April 22, 1980) was a German chemist who with Die Naturwissenschaften ( The Natural Sciences) is a weekly publication of the Max-Planck-Gesellschaft. Barium (ˈbɛəriəm is a Chemical element. It has the symbol Ba, and Atomic number 56 Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. Lise Meitner (7 or 17 November 1878 &ndash 27 October 1968 was an Austrian born later Swedish physicist who studied Radioactivity and Meitner, and her nephew Otto Robert Frisch, correctly interpreted these results as being nuclear fission. Otto Robert Frisch ( 1 October 1904 &ndash 22 September 1979) Austrian British Physicist. ^[3] Frisch confirmed this experimentally on 13 January 1939. ^[4] In 1944, Hahn received the Nobel Prize for Chemistry for the discovery of nuclear fission. The Nobel Prize in Chemistry (Nobelpriset i kemi is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of Chemistry. Some historians have documented the history of the discovery of nuclear fission and believe Meitner should have been awarded the Nobel Prize with Hahn. ^{[5] [6] [7]}

Meitner’s and Frisch’s interpretation of the work of Hahn and Strassmann crossed the Atlantic Ocean with Niels Bohr, who was to lecture at Princeton University. Niels Henrik David Bohr (nels ˈb̥oɐ̯ˀ in Danish 7 October 1885 – 18 November 1962 was a Danish Physicist who made fundamental contributions to understanding Princeton University is a private Coeducational research university located in Princeton, New Jersey. Isidor Isaac Rabi and Willis Lamb, two Columbia University physicists working at Princeton, heard the news and carried it back to Columbia. Isidor Isaac Rabi ( July 29, 1898 &ndash January 11, 1988) Galician born Physicist, and Nobel laureate. Willis Eugene Lamb Jr ( July 12, 1913 &ndash May 15, 2008) was a Physicist who won the Nobel Prize in Physics in Columbia University is a private University in the United States and a member of the Ivy League. Rabi said he told Enrico Fermi; Fermi gave credit to Lamb. Bohr soon thereafter went from Princeton to Columbia to see Fermi. Not finding Fermi in his office, Bohr went down to the cyclotron area and found Herbert L. Anderson. Herbert L Anderson ( 24 May 1914 in New York City, New York &ndash 16 July, 1988 in Los Alamos, New Mexico Bohr grabbed him by the shoulder and said: “Young man, let me explain to you about something new and exciting in physics. ”^[8] It was clear to a number of scientists at Columbia that they should try to detect the energy released in the nuclear fission of uranium from neutron bombardment. On 25 January 1939, a Columbia University team conducted the first nuclear fission experiment in the United States,^[9] which was done in the basement of Pupin Hall; the members of the team were Herbert L. Anderson, Eugene T. Booth, John R. Dunning, Enrico Fermi, G. Norris Glasoe, and Francis G. Slack. Pupin Hall is the home of the physics and astronomy departments at Columbia University in New York City. Herbert L Anderson ( 24 May 1914 in New York City, New York &ndash 16 July, 1988 in Los Alamos, New Mexico Eugene Theodore Booth (1912 in Rome, Georgia &ndash 6 March 2004) was an American Nuclear physicist. John Ray Dunning ( September 24, 1907 in Shelby Nebraska - August 25, 1975 in Key Biscayne Florida) was an American G Norris Glasoe (1902 &ndash?) was an American Nuclear physicist. Francis Goddard Slack ( November 1, 1897 in Superior, Wisconsin &ndash 1985 was an American Physicist. The next day, the Fifth Washington Conference on Theoretical Physics began in Washington, D.C. under the joint auspices of The George Washington University and the Carnegie Institution of Washington. Washington DC ( formally the District of Columbia and commonly referred to as Washington, the District, or simply D The George Washington University ( GW or GWU) is a private coeducational university located in Washington D The Carnegie Institution for Science (also called the Carnegie Institution of Washington (CIW) is a organization in the United States established to support Scientific There, the news on nuclear fusion was spread even further, which fostered many more experimental demonstrations. ^[10]

Frédéric Joliot-Curie's team in Paris discovered that secondary neutrons are released during uranium fission, thus making a nuclear chain-reaction feasible. Jean Frédéric Joliot-Curie born Joliot ( March 19, 1900 &ndash August 14, 1958) was a French Physicist and The figure of about two neutrons being emitted with nuclear fission of uranium was verified independently by Leo Szilard and Walter Henry Zinn. Leó Szilárd (Szilárd Leó February 11, 1898 – May 30, 1964) was an Hungarian - American Physicist who Walter Henry Zinn ( December 14, 1906, Kitchener Ontario - February 14, 2000, Clearwater Florida) was a Nuclear physicist The number of neutrons emitted with nuclear fission of uranium-235 was then reported at 3. 5/fission, and later corrected to 2. 6/fission by Frédéric Joliot-Curie, Hans von Halban and Lew Kowarski. Jean Frédéric Joliot-Curie born Joliot ( March 19, 1900 &ndash August 14, 1958) was a French Physicist and Hans von Halban ( Leipzig, 24 January 1908 - Paris, 28 November 1964) was a French Physicist, of Lew Kowarski ( 10 February, 1907 - 30 July, 1979) was a Naturalized French Physicist, of Russian-Polish descent

"Chain reactions" at that time were a known phenomenon in chemistry, but the analogous process in nuclear physics, using neutrons, had been foreseen as early as 1933 by Leo Szilard, although Szilard at that time had no idea with what materials the process might be initiated (Szilard thought it might be done with light neutron-rich elements elements). A chain reaction is a sequence of Reactions where a reactive product or by-product causes additional reactions to take place Leó Szilárd (Szilárd Leó February 11, 1898 – May 30, 1964) was an Hungarian - American Physicist who Szilard, a Hungarian born Jew, also fled mainland Europe after Hitler's rise, eventually landing in the US.

With the news of fission neutrons from uranium fission, Szilard immediately understood the possibility of a nuclear chain reaction using uranium. In the summer, Fermi and Szilard proposed the idea of a nuclear reactor (pile) to mediate this process. This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled The pile would use natural uranium as fuel, and graphite as the moderator of neutron energy (it had previously been shown by Fermi that neutrons were far more effectively captured by atoms if they were moving slowly, a process called moderation when the neutrons were slowed after being released from a fission event in a nuclear reactor).

In August Hungarian-Jewish refugees Szilard, Teller and Wigner thought that the Germans might make use of the fission chain reaction, and persuaded Austrian-Jewish refugee Einstein to warn President Roosevelt of the this possible German menace. The letter suggested the possibility of a uranium bomb deliverable by ship, which would destroy "an entire harbor and much of the surrounding countryside. " The President received the letter on 1939. 10. 11 shortly after WWII began in Europe, but two years before U. S. entry into it.

In England, James Chadwick proposed an atomic bomb utilizing natural uranium, based on a paper by Rudolf Peierls with the mass needed for critical state being 30-40 tons. 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 Sir Rudolf Ernst Peierls, ( June 5 1907, Berlin &ndash September 19 1995, Oxford) was a German -born British In America, J. Robert Oppenheimer thought that a cube of uranium deuteride 10 cm on a side (about 11 kg of uranium) might "blow itself to hell. " In this design it was still thought that a moderator would need to be used for nuclear bomb fission (this turned out not to be the case if the fissile isotope was separated).

In December, Heisenberg delivered a report to the Germany Department of War on the possibility of a uranium bomb.

In Birmingham, England Otto Robert Frisch teamed up with Rudolf Peierls who had also fled German anti-Jewish laws. Otto Robert Frisch ( 1 October 1904 &ndash 22 September 1979) Austrian British Physicist. Sir Rudolf Ernst Peierls, ( June 5 1907, Berlin &ndash September 19 1995, Oxford) was a German -born British They conceived the idea of utilizing a purified isotope of uranium, uranium-235, and worked out that an enriched uranium bomb could have a critical mass of only 600 grams, instead of tons, and that the resulting explosion would be tremendous. (The amount actually turned out to be 15 kg, although several times this amount was used in the actual uranium (Little Boy) bomb). Little Boy was the Codename of the Atomic bomb, developed via the "Manhattan Project" which was dropped on Hiroshima, on August 6 1945 by the In February 1940 they delivered the Frisch-Peierls memorandum. The Frisch-Peierls memorandum was written by Otto Frisch and Rudolf Peierls while they were both working at Birmingham University, England and given Ironically, they were still officially considered "enemy aliens" at the time.

Glenn Seaborg, Joe Kennedy, Art Wahl and Italian-Jewish refugee Emilio Segrè shortly discovered plutonium-239 in the decay products of uranium-239 produced by bombarding uranium-238 with neutrons, and determined it to be fissionable like U-235. Glenn Theodore Seaborg ( Glenn Teodor Sjöberg) ( April 19, 1912 &ndash February 25, 1999) won the 1951 Nobel Prize in Chemistry Emilio Gino Segrè ( February 1, 1905 – April 22, 1989) was an Italian Physicist and Nobel laureate in (Lawrence controversially dropped Segrè's pay by half when he learned he was trapped in the U. S. by Mussolini's race laws. )

On June 28, 1941, the Office of Scientific Research and Development was formed in the U. S. to mobilize scientific resources and apply the results of research to national defense. In September, Fermi assembled his first nuclear "pile" or reactor, in an attempt to create a slow neutron induced chain reaction in uranium, but the experiment failed for lack of proper materials, or not enough of the materials which were available.

Producing a fission chain reaction in natural uranium fuel was found to be far from trivial. Early nuclear reactors did not use isotopically enriched uranium, and in consequence they were required to use large quantities of highly purified graphite as neutron moderation materials. Use of ordinary water (as opposed to heavy water) in nuclear reactors requires enriched fuel--- the partial separation and relative enrichment of the rare ²³⁵U isotope from the far more common ²³⁸U isotope. Heavy water is water which contains a higher proportion than normal of the Isotope Deuterium, as deuterium oxide, D2O or ²H2O Typically, reactors also require inclusion of extremely chemically pure neutron moderator materials such as deuterium (in heavy water), helium, beryllium, or carbon, the latter usually as graphite. In Nuclear engineering, a neutron moderator is a medium which reduces the velocity of Fast neutrons thereby turning them into Thermal neutrons capable Deuterium, also called heavy hydrogen, is a Stable isotope of Hydrogen with a Natural abundance in the Oceans of Earth Heavy water is water which contains a higher proportion than normal of the Isotope Deuterium, as deuterium oxide, D2O or ²H2O Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 The Mineral graphite, as with Diamond and Fullerene, is one of the Allotropes of carbon. (The high purity for carbon is required because many chemical impurities such as the boron-10 component of natural boron, are very strong neutron absorbers and thus poison the chain reaction. Boron (ˈbɔərɒn is a Chemical element with Atomic number 5 and the chemical symbol B. A nuclear poison, also called a neutron poison is a substance with a large neutron absorption cross-section in applications such as Nuclear reactors )

Production of such materials at industrial scale had to be solved for nuclear power generation and weapons production to be accomplished. Up to 1940, the total amount of uranium metal produced in the USA was not more than a few grams, and even this was of doubtful purity; of metallic beryllium not more than a few kilograms; concentrated deuterium oxide (heavy water) not more than a few kilograms. Heavy water is water which contains a higher proportion than normal of the Isotope Deuterium, as deuterium oxide, D2O or ²H2O Finally, carbon had never been produced in quantity with anything like the purity required of a moderator.

The problem of producing large amounts of high purity uranium was solved by Frank Spedding using the thermite process. Frank H Spedding (1902 &ndash 1984 was an American Chemist who led a group of chemists at Ames Laboratory which developed an efficient process for obtaining high Thermite is a Pyrotechnic composition of Aluminium powder and a metal oxide which produces an Aluminothermic reaction known as a Ames Laboratory was established in 1942 to produce the large amounts of natural (unenriched) uranium metal that would be necessary for the research to come. Ames Laboratory is a United States Department of Energy National laboratory located in Ames Iowa. The success of the Chicago Pile-1 which used unenriched (natural) uranium, like all of the atomic "piles" which produced the plutonium for the atomic bomb, was also due specifically to Szilard's realization that very pure graphite could be used for the moderator of even natural uranium "piles". Chicago Pile-1 ( CP-1) was the world's first artificial Nuclear reactor. In wartime Germany, failure to appreciate the qualities of very pure graphite led to reactor designs dependent on heavy water, which in turn was denied the Germans by Allied attacks in Norway, where heavy water was produced. Heavy water is water which contains a higher proportion than normal of the Isotope Deuterium, as deuterium oxide, D2O or ²H2O These difficulties prevented the Nazis from building a nuclear reactor capable of criticality during the war.

Unknown until 1972 (but postulated by Paul Kuroda in 1956), when French physicist Francis Perrin discovered the Oklo Fossil Reactors, it was realized that nature had beaten humans to the punch. Francis Perrin ( Paris, 1901 - id 1992 was a French Physicist, the son of Jean Perrin. A natural nuclear fission reactor is a Uranium deposit where analysis of Isotope Ratios has shown that self-sustaining Nuclear chain reactions Large-scale natural uranium fission chain reactions, moderated by normal water, had occurred some 2,000 million years in the past. This ancient process was able to use normal water as a moderator only because 2,000 million years in the past, natural uranium was highly "enriched" with the shorter-lived fissile isotope ²³⁵U, as compared with natural uranium available today.

For more detail on the early development of the first nuclear reactors and nuclear weapons, see Manhattan Project. This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. The World War II Manhattan Project developed the first Nuclear weapon (atomic bomb

External links

• The Effects of Nuclear Weapons
• Annotated bibliography for nuclear fission from the Alsos Digital Library
• The Discovery of Nuclear Fission Historical account complete with audio and teacher's guides from the American Institute of Physics History Center
• atomicarchive.com Nuclear Fission Explained
• Nuclear Files.org What is Nuclear Fission?
• Nuclear Fission Animation
• The nuclear fission process A simple explanation of the process of nuclear fission

References

See also