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In
nuclear physics Nuclear physics is the field of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in ot ...
and
nuclear chemistry Nuclear chemistry is the sub-field of chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compo ...
, a nuclear reaction is a process in which two
nuclei ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...
, or a nucleus and an external
subatomic particle In physical sciences, subatomic particles are smaller than atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All ...
, collide to produce one or more new
nuclide A nuclide (or nucleide, from nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic c ...

nuclide
s. Thus, a nuclear reaction must cause a transformation of at least one nuclide to another. If a nucleus interacts with another nucleus or particle and they then separate without changing the nature of any nuclide, the process is simply referred to as a type of nuclear
scattering Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light Light or visible light is electromagnetic radiation within the portion of the electromagnetic ...

scattering
, rather than a nuclear reaction. In principle, a reaction can involve more than two
particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascribed several physical property, physical or chemical property, chemical p ...

particle
s
colliding In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great fo ...

colliding
, but because the probability of three or more nuclei to meet at the same time at the same place is much less than for two nuclei, such an event is exceptionally rare (see
triple alpha process Triple is used in several contexts to mean "threefold" or a " treble": Sports * Triple (baseball), a three-base hit * A basketball three-point field goal * A figure skating jump with three rotations * In bowling terms, three strikes in a row * In ...
for an example very close to a three-body nuclear reaction). The term "nuclear reaction" may refer either to a change in a nuclide induced by collision with another particle or to a spontaneous change of a nuclide without collision. Natural nuclear reactions occur in the interaction between
cosmic ray Cosmic rays are high-energy proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approx ...
s and matter, and nuclear reactions can be employed artificially to obtain nuclear energy, at an adjustable rate, on-demand.
Nuclear chain reaction In nuclear physics Nuclear physics is the field of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the ord ...
s in
fissionable In nuclear engineering Nuclear engineering is the branch of engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, ve ...
materials produce induced
nuclear fission Nuclear fission is a reaction Reaction may refer to a process or to a response to an action, event, or exposure: Physics and chemistry *Chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic tr ...

nuclear fission
. Various
nuclear fusion Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products ...

nuclear fusion
reactions of light elements power the energy production of the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
and stars.


History

In 1919,
Ernest Rutherford Ernest Rutherford, 1st Baron Rutherford of Nelson, (30 August 1871 – 19 October 1937) was a New Zealand-born British physicist A physicist is a scientist A scientist is a person who conducts scientific research The sci ...
was able to accomplish transmutation of nitrogen into oxygen at the University of Manchester, using alpha particles directed at nitrogen 14N + α → 17O + p.  This was the first observation of an induced nuclear reaction, that is, a reaction in which particles from one decay are used to transform another atomic nucleus. Eventually, in 1932 at Cambridge University, a fully artificial nuclear reaction and nuclear transmutation was achieved by Rutherford's colleagues
John Cockcroft Sir John Douglas Cockcroft, (27 May 1897 – 18 September 1967) was a British physicist who shared with Ernest Walton the Nobel Prize in Physics in 1951 for splitting the atomic nucleus The atomic nucleus is the small, dense region ...
and
Ernest Walton Ernest Thomas Sinton Walton (6 October 1903 – 25 June 1995) was an Irish Irish most commonly refers to: * Someone or something of, from, or related to: ** Ireland, an island situated off the north-western coast of continental Europe ** Northe ...

Ernest Walton
, who used artificially accelerated protons against lithium-7, to split the nucleus into two alpha particles. The feat was popularly known as "splitting the
atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of ato ...

atom
", although it was not the modern
nuclear fission Nuclear fission is a reaction Reaction may refer to a process or to a response to an action, event, or exposure: Physics and chemistry *Chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic tr ...

nuclear fission
reaction later (in 1938) discovered in heavy elements by the German scientists
Otto Hahn Otto Hahn (; 8 March 1879 – 28 July 1968) was a German chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin Medieval Latin was the form of Latin Latin (, or , ) is a classical language ...

Otto Hahn
,
Lise Meitner Elise Meitner ( , ; 7 November 1878 – 27 October 1968) was a leading Austrian-Swedish physicist A physicist is a scientist A scientist is a person who conducts scientific research The scientific method is an Empirical evidence, ...

Lise Meitner
, and
Fritz Strassmann Friedrich Wilhelm "Fritz" Strassmann (''german: Fritz Straßmann'', ; 22 February 1902 – 22 April 1980) was a German chemist who, with Otto Hahn in early 1939, identified the element barium Barium is a chemical element with the Symbol (chemis ...
.


Nomenclature

Nuclear reactions may be shown in a form similar to chemical equations, for which
invariant mass The invariant mass, rest mass, intrinsic mass, proper mass, or in the case of bound systems simply mass, is the portion of the total mass of an object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** ...
must balance for each side of the equation, and in which transformations of particles must follow certain conservation laws, such as conservation of charge and baryon number (total atomic
mass number The mass number (symbol ''A'', from the German word ''Atomgewicht'' tomic weight, also called atomic mass number or nucleon number, is the total number of s and s (together known as s) in an . It is approximately equal to the of the expre ...
). An example of this notation follows: : To balance the equation above for mass, charge and mass number, the second nucleus to the right must have atomic number 2 and mass number 4; it is therefore also helium-4. The complete equation therefore reads: : or more simply: : Instead of using the full equations in the style above, in many situations a compact notation is used to describe nuclear reactions. This style of the form A(b,c)D is equivalent to A + b producing c + D. Common light particles are often abbreviated in this shorthand, typically p for proton, n for neutron, d for
deuteron Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element ...

deuteron
, α representing an
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Proto ...

alpha particle
or
helium-4 Helium-4 () is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consists ...

helium-4
, β for
beta particle A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β ...
or electron, γ for
gamma photon A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nucleus, atomic nuclei. It consists of the shortest wavelength electromagnetic wav ...
, etc. The reaction above would be written as 6Li(d,α)α.


Energy conservation

Kinetic energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...
may be released during the course of a reaction (
exothermic reaction In thermochemistry, an exothermic reaction is a "reaction for which the overall Standard enthalpy of reaction, standard enthalpy change Δ''H''⚬ is negative." Exothermic reactions usually release heat and entail the replacement of weak bonds wi ...
) or kinetic energy may have to be supplied for the reaction to take place (
endothermic reaction In thermochemistry Thermochemistry is the study of the heat energy which is associated with chemical reactions and/or physical transformations. A reaction may release or absorb energy, and a phase change may do the same, such as in melting and bo ...
). This can be calculated by reference to a table of very accurate particle rest masses, as follows: according to the reference tables, the nucleus has a
standard atomic weight The standard atomic weight (''A''r, standard(E)) of a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their c ...
of 6.015
atomic mass unit The dalton or unified atomic mass unit (symbols: Da or u) is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece o ...
s (abbreviated
u
u
), the deuterium has 2.014 u, and the helium-4 nucleus has 4.0026 u. Thus: * the sum of the rest mass of the individual nuclei = 6.015 + 2.014 = 8.029 u; * the total rest mass on the two helium-nuclei = 2 × 4.0026 = 8.0052 u; * missing rest mass = 8.029 – 8.0052 = 0.0238 atomic mass units. In a nuclear reaction, the total (relativistic) energy is conserved. The "missing" rest mass must therefore reappear as kinetic energy released in the reaction; its source is the nuclear
binding energy In physics and chemistry, binding energy is the smallest amount of energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of know ...

binding energy
. Using Einstein's mass-energy equivalence formula ''E'' = ''mc''2, the amount of energy released can be determined. We first need the energy equivalent of one
atomic mass unit The dalton or unified atomic mass unit (symbols: Da or u) is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece o ...
: : 1 u ''c''2 = (1.66054 × 10−27 kg) × (2.99792 × 108 m/s)2  : = 1.49242 × 10−10 kg (m/s)2 = 1.49242 × 10−10 J (
joule The joule ( ; symbol: J) is a derived unit of energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates ...

joule
) × (1 
MeV In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...
 / 1.60218 × 10−13 J) : = 931.49 MeV, : so 1 u ''c''2 = 931.49 MeV. Hence, the energy released is 0.0238 × 931 MeV = 22.2
MeV In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...
. Expressed differently: the mass is reduced by 0.3%, corresponding to 0.3% of 90 PJ/kg is 270 TJ/kg. This is a large amount of energy for a nuclear reaction; the amount is so high because the binding energy per
nucleon In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
of the helium-4 nucleus is unusually high because the He-4 nucleus is " doubly magic". (The He-4 nucleus is unusually stable and tightly bound for the same reason that the helium atom is inert: each pair of protons and neutrons in He-4 occupies a filled 1s
nuclear orbital #REDIRECT Nuclear shell model #REDIRECT Nuclear shell model#REDIRECT Nuclear shell model In nuclear physics, atomic physics, and nuclear chemistry, the nuclear shell model is a nuclear model, model of the atomic nucleus which uses the Pauli excl ...
in the same way that the pair of electrons in the helium atom occupy a filled 1s electron orbital). Consequently, alpha particles appear frequently on the right-hand side of nuclear reactions. The energy released in a nuclear reaction can appear mainly in one of three ways: *kinetic energy of the product particles (fraction of the kinetic energy of the charged nuclear reaction products can be directly converted into electrostatic energy); *emission of very high energy
photon The photon ( el, φῶς, phōs, light) is a type of elementary particle In , an elementary particle or fundamental particle is a that is not composed of other particles. Particles currently thought to be elementary include the fundamental s ...

photon
s, called
gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, it ...
s; *some energy may remain in the nucleus, as a
metastable In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's ground state, state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. I ...

metastable
energy level A quantum mechanical Quantum mechanics is a fundamental theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking ...
. When the product nucleus is metastable, this is indicated by placing an
asterisk The asterisk , from Late Latin , from Ancient Greek , ''asteriskos'', "little star", is a Typography, typographical symbol. It is so called because it resembles a conventional image of a star (heraldry), star. Computer scientists and mathem ...

asterisk
("*") next to its atomic number. This energy is eventually released through
nuclear decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the small, dense region consisting of proton A ...
. A small amount of energy may also emerge in the form of
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Moti ...

X-ray
s. Generally, the product nucleus has a different atomic number, and thus the configuration of its
electron shell In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo durin ...
s is wrong. As the electrons rearrange themselves and drop to lower energy levels, internal transition X-rays (X-rays with precisely defined
emission line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission (electromagnetic radiation), emission or absorption (electromagnetic radiation), absorption of light in a narrow frequency range, c ...
s) may be emitted.


Q-value and energy balance

In writing down the reaction equation, in a way analogous to a
chemical equation A chemical equation is the symbolic representation of a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical ...
, one may, in addition, give the reaction energy on the right side: :Target nucleus + projectile → Final nucleus + ejectile + ''Q''. For the particular case discussed above, the reaction energy has already been calculated as Q = 22.2 MeV. Hence: : The reaction energy (the "Q-value") is positive for exothermal reactions and negative for endothermal reactions, opposite to the similar expression in
chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. T ...

chemistry
. On the one hand, it is the difference between the sums of kinetic energies on the final side and on the initial side. But on the other hand, it is also the difference between the nuclear rest masses on the initial side and on the final side (in this way, we have calculated the Q-value above).


Reaction rates

If the reaction equation is balanced, that does not mean that the reaction really occurs. The rate at which reactions occur depends on the energy and the
flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...

flux
of the incident particles, and the reaction
cross section Cross section may refer to: * Cross section (geometry), the intersection of a 3-dimensional body with a plane * Cross section (electronics), a common sample preparation technique in electronics * Cross section (geology), the intersection of a 3-dim ...
. An example of a large repository of reaction rates is the REACLIB database, as maintained by the Joint Institute for Nuclear Astrophysics.


Charged vs. uncharged particles

In the initial collision which begins the reaction, the particles must approach closely enough so that the short-range
strong force In nuclear physics Nuclear physics is the field of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and ...
can affect them. As most common nuclear particles are positively charged, this means they must overcome considerable
electrostatic repulsion Electrostatics is a branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), m ...
before the reaction can begin. Even if the target nucleus is part of a neutral
atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of ato ...

atom
, the other particle must penetrate well beyond the
electron cloud In atomic theory Atomic theory is the scientific theory A scientific theory is an explanation of an aspect of the that has been and verified in accordance with the , using accepted of , measurement, and evaluation of results. Where p ...
and closely approach the nucleus, which is positively charged. Thus, such particles must be first accelerated to high energy, for example by: *
particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high speeds and energies, and to contain them in well-defined particle beam, beams. Large accelerators are used for funda ...
s; *
nuclear decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the small, dense region consisting of proton A ...
(alpha particles are the main type of interest here since beta and gamma rays are rarely involved in nuclear reactions); *very high temperatures, on the order of millions of degrees, producing
thermonuclear Thermonuclear fusion is a way to achieve nuclear fusion by using extremely high temperatures. There are two forms of thermonuclear fusion: ''uncontrolled'', in which the resulting energy is released in an uncontrolled manner, as it is in thermonucl ...
reactions; *
cosmic ray Cosmic rays are high-energy proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approx ...
s. Also, since the force of repulsion is proportional to the product of the two charges, reactions between heavy nuclei are rarer, and require higher initiating energy, than those between a heavy and light nucleus; while reactions between two light nuclei are the most common ones.
Neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behav ...

Neutron
s, on the other hand, have no electric charge to cause repulsion, and are able to initiate a nuclear reaction at very low energies. In fact, at extremely low particle energies (corresponding, say, to thermal equilibrium at room temperature), the neutron's
de Broglie wavelength Matter waves are a central part of the theory of quantum mechanics Quantum mechanics is a fundamental Scientific theory, theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic ...
is greatly increased, possibly greatly increasing its capture cross-section, at energies close to
resonance Resonance describes the phenomenon of increased amplitude The amplitude of a ic is a measure of its change in a single (such as or ). There are various definitions of amplitude (see below), which are all s of the magnitude of the differ ...

resonance
s of the nuclei involved. Thus low-energy neutrons ''may'' be even more reactive than high-energy neutrons.


Notable types

While the number of possible nuclear reactions is immense, there are several types that are more common, or otherwise notable. Some examples include: *
Fusion
Fusion
reactions — two light nuclei join to form a heavier one, with additional particles (usually protons or neutrons) emitted subsequently. *
Spallation Spallation is a process in which fragments of material (spall Spall are fragments of a material that are broken off a larger solid physical object, body. It can be produced by a variety of mechanisms, including as a result of projectile im ...

Spallation
— a nucleus is hit by a particle with sufficient energy and momentum to knock out several small fragments or smash it into many fragments. *
Induced gamma emissionIn physics, induced gamma emission (IGE) refers to the process of fluorescent emission of gamma rays from excited nuclei, usually involving a specific nuclear isomer. It is analogous to conventional fluorescence, which is defined as the emission of a ...
belongs to a class in which only photons were involved in creating and destroying states of nuclear excitation. *
Alpha decay
Alpha decay
— Though driven by the same underlying forces as spontaneous fission, α decay is usually considered to be separate from the latter. The often-quoted idea that "nuclear reactions" are confined to induced processes is incorrect. "Radioactive decays" are a subgroup of "nuclear reactions" that are spontaneous rather than induced. For example, so-called "hot alpha particles" with unusually high energies may actually be produced in induced
ternary fissionImage:ThermalFissionYield.svg, 350px, Fission product yields by mass for thermal neutron fission of Uranium-235, U-235, Pu-239, a combination of the two typical of current nuclear power reactors, and Uranium-233, U-233 used in the thorium cycle. Tern ...
, which is an induced nuclear reaction (contrasting with spontaneous fission). Such alphas occur from spontaneous ternary fission as well. *
Fission Fission, a splitting of something into two or more parts, may refer to: Biology * Fission (biology), division of a single entity into two or more parts and the regeneration of those parts into separate entities resembling the original * Mitochondri ...

Fission
reactions — a very heavy nucleus, after absorbing additional light particles (usually neutrons), splits into two or sometimes three pieces. This is an induced nuclear reaction.
Spontaneous fission Spontaneous fission (SF) is a form of radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy b ...
, which occurs without assistance of a neutron, is usually not considered a nuclear reaction. At most, it is not an ''induced'' nuclear reaction.


Direct reactions

An intermediate energy projectile transfers energy or picks up or loses nucleons to the nucleus in a single quick (10−21 second) event. Energy and momentum transfer are relatively small. These are particularly useful in experimental nuclear physics, because the reaction mechanisms are often simple enough to calculate with sufficient accuracy to probe the structure of the target nucleus.


Inelastic scattering

Only energy and momentum are transferred. *(p,p') tests differences between nuclear states. *(α,α') measures nuclear surface shapes and sizes. Since α particles that hit the nucleus react more violently, elastic and shallow inelastic α scattering are sensitive to the shapes and sizes of the targets, like light scattered from a small black object. *(e,e') is useful for probing the interior structure. Since electrons interact less strongly than do protons and neutrons, they reach to the centers of the targets and their
wave function A wave function in quantum physics Quantum mechanics is a fundamental theory A theory is a rational Rationality is the quality or state of being rational – that is, being based on or agreeable to reason Reason is the capacity ...

wave function
s are less distorted by passing through the nucleus.


Charge-exchange reactions

Energy and charge are transferred between projectile and target. Some examples of this kind of reactions are: * (p,n) * (3He,t)


Nucleon transfer reactions

Usually at moderately low energy, one or more nucleons are transferred between the projectile and target. These are useful in studying outer
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard out ...
structure of nuclei. Transfer reactions can occur, from the projectile to the target; stripping reactions, or from the target to the projectile; pick-up reactions. *(α,n) and (α,p) reactions. Some of the earliest nuclear reactions studied involved an alpha particle produced by
alpha decay
alpha decay
, knocking a nucleon from a target nucleus. *(d,n) and (d,p) reactions. A
deuteron Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element ...

deuteron
beam Beam may refer to: Streams of particles or energy *Light beam, or beam of light, a directional projection of light energy **Laser beam *Particle beam, a stream of charged or neutral particles **Charged particle beam, a spatially localized group ...
impinges on a target; the target nuclei absorb either the neutron or proton from the deuteron. The deuteron is so loosely bound that this is almost the same as proton or neutron capture. A compound nucleus may be formed, leading to additional neutrons being emitted more slowly. (d,n) reactions are used to generate energetic neutrons. *The
strangeness In particle physics Particle physics (also known as high energy physics) is a branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department ...
exchange reaction (
K
K
,
π
π
) has been used to study hypernuclei. *The reaction 14N(α,p)17O performed by Rutherford in 1917 (reported 1919), is generally regarded as the first
nuclear transmutation Nuclear transmutation is the conversion of one chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike che ...
experiment.


Reactions with neutrons

Reactions with
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behav ...

neutron
s are important in
nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction 300px, A possible nuclear fission chain reaction: 1) A uranium-235 atom absorbs a neutron">uranium-235.html" ;"ti ...

nuclear reactor
s and
nuclear weapon A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics Nucl ...
s. While the best-known neutron reactions are
neutron scattering Neutron scattering, the irregular dispersal of free neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons ...
,
neutron capture Neutron capture is a nuclear reaction In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two atomic nucleus, nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclide ...
, and
nuclear fission Nuclear fission is a reaction Reaction may refer to a process or to a response to an action, event, or exposure: Physics and chemistry *Chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic tr ...

nuclear fission
, for some light nuclei (especially odd-odd nuclei) the most probable reaction with a
thermal neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a ...
is a transfer reaction: Some reactions are only possible with
fast neutrons The neutron detection temperature, also called the neutron energy, indicates a free neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a ...
: *(n,2n) reactions produce small amounts of protactinium-231 and
uranium-232 Uranium-232 () is an isotope of uranium. It has a half-life of around 68.9 years and is a side product in the thorium cycle. It has been cited as an obstacle to nuclear proliferation Nuclear proliferation is the spread of nuclear weapons ...

uranium-232
in the thorium cycle which is otherwise relatively free of highly radioactive
actinide The actinoid (IUPAC nomenclature The International Union of Pure and Applied Chemistry The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemis ...
products. *9Be + n → 2''α'' + 2n can contribute some additional neutrons in the
beryllium Beryllium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical el ...

beryllium
neutron reflector A neutron reflector is any material Material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical compositi ...
of a
nuclear weapon A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics Nucl ...
. *7Li + n →
T
T
+ ''α'' + n unexpectedly contributed additional yield in the
Bravo Bravo is an interjection used to signify strong approval, particularly for a performance. It may also refer to: Places *Bravo, Cuba, a community in the municipality of Santiago de Cuba *Rio Grande, a river that flows through Mexico and the United ...
,
Romeo Romeo Montague () is the male protagonist 200px, Shakespeare's ''Hamlet, Prince of Denmark.'' William Morris Hunt, oil on canvas, c. 1864 A protagonist (from grc, πρωταγωνιστής, translit=prōtagōnistḗs, lit=one who plays the fi ...

Romeo
and
Yankee The term ''Yankee'' and its contracted form ''Yank'' have several interrelated meanings, all referring to people from the United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or Amer ...
shots of
Operation Castle Operation Castle was a United States series of nuclear weapon yield, high-yield (high-energy) nuclear tests by Joint Task Force 7 (JTF-7) at Bikini Atoll beginning in March 1954. It followed ''Operation Upshot–Knothole'' and preceded ''Opera ...
, the three highest-yield
nuclear test Nuclear weapons tests are experiments carried out to determine nuclear weapons' effectiveness, yield Yield may refer to: Measures of output/function Computer science * Yield (multithreading) is an action that occurs in a computer program duri ...
s conducted by the U.S.


Compound nuclear reactions

Either a low-energy projectile is absorbed or a higher energy particle transfers energy to the nucleus, leaving it with too much energy to be fully bound together. On a time scale of about 10−19 seconds, particles, usually neutrons, are "boiled" off. That is, it remains together until enough energy happens to be concentrated in one neutron to escape the mutual attraction. The excited quasi-bound nucleus is called a compound nucleus. *Low energy (e, e' xn), (γ, xn) (the xn indicating one or more neutrons), where the gamma or virtual gamma energy is near the giant dipole resonance. These increase the need for radiation shielding around electron accelerators.


See also

*Acoplanarity *Atomic mass *Atomic nucleus *Atomic number *CNO cycle *
Nuclear chain reaction In nuclear physics Nuclear physics is the field of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the ord ...
*Oppenheimer–Phillips process *Nuclear Power


References


Sources

* * {{DEFAULTSORT:Nuclear reaction Physical phenomena Nuclear chemistry Nuclear physics Nuclear fission Nuclear fusion Radioactivity