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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 other words, to the regular succession of eve ...

physics
that studies
atomic nuclei The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford based on the 1909 Geiger-Marsden experiments, Geiger–Marsden gold foil experiment. After the d ...
and their constituents and interactions, in addition to the study of other forms of
nuclear matter Nuclear matter is an idealized system of interacting nucleons (protons and neutrons) that exists in several phase (matter), phases of exotic matter that as yet are not fully established. It is ''not'' matter in a atomic nucleus, but a hypothet ...
. Nuclear physics should not be confused with atomic physics, which studies 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 atom ...

atom
as a whole, including its
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
s. Discoveries in nuclear physics have led to
applications Application may refer to: Mathematics and computing * Application software, computer software designed to help the user to perform specific tasks ** Application layer, an abstraction layer that specifies protocols and interface methods used in a co ...
in many fields. This includes
nuclear power Nuclear power is the use of nuclear reaction 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), ...

nuclear power
,
nuclear weapons 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 and nucl ...

nuclear weapons
,
nuclear medicine Nuclear medicine is a medical specialty A medical specialty is a branch of medical practice that is focused on a defined group of patients, diseases, skills, or philosophy. Examples include children (paediatrics Pediatrics (American and Briti ...
and
magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging Medical imaging is the technique and process of imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of a ...
, industrial and agricultural isotopes,
ion implantation technological facility in Toulouse, France. Ion implantation is a low-temperature process by which ion (physics), ions of one element are accelerated into a solid target, thereby changing the physical, chemical, or electrical properties of the t ...
in
materials engineering The interdisciplinary Interdisciplinarity or interdisciplinary studies involves the combination of two or more academic disciplines into one activity (e.g., a research project). It draws knowledge from several other fields like sociology, ant ...

materials engineering
, and
radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material Organic matter, organic material, or natural organic matter refers to the large source of ...
in
geology Geology (from the γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is a branch of concerned with both the liquid and , the of which it is composed, and the processes by which they change over time. Geology can ...

geology
and
archaeology Archaeology or archeology is the study of human activity through the recovery and analysis Analysis is the process of breaking a complexity, complex topic or Substance theory, substance into smaller parts in order to gain a better underst ...
. Such applications are studied in the field of
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, vehicles, and buildings. The ...
.
Particle physics Particle physics (also known as high energy physics) is a branch of that studies the nature of the particles that constitute and . Although the word ' can refer to various types of very small objects (e.g. , gas particles, or even household d ...
evolved out of nuclear physics and the two fields are typically taught in close association.
Nuclear astrophysics Nuclear astrophysics is an interdisciplinary part of both nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions. Other forms of nuclear matter are also studied. Nuclear physics ...
, the application of nuclear physics to
astrophysics Astrophysics is a science that employs the methods and principles of physics in the study of astronomical objects and phenomena. Among the subjects studied are the Sun, other stars, galaxy, galaxies, extrasolar planets, the interstellar medium and ...
, is crucial in explaining the inner workings of
stars A star is an astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The nearest star to Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. ...

stars
and the origin of the chemical elements.


History

The history of nuclear physics as a discipline distinct from atomic physics starts with the discovery of
radioactivity
radioactivity
by
Henri Becquerel Antoine Henri Becquerel (; 15 December 1852 – 25 August 1908) was a French engineer, physicist, Nobel laureate, and the first person to discover evidence of radioactivity. For work in this field he, along with Marie Skłodowska-Curie (Mar ...

Henri Becquerel
in 1896, made while investigating
phosphorescence Phosphorescence is a type of photoluminescence related to fluorescence. When exposed to light (radiation) of a shorter wavelength, a phosphorescent substance will glow, absorbing the light and reemitting it at a longer wavelength. Unlike flu ...

phosphorescence
in
uranium Uranium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

uranium
salts. The discovery of the
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
by J. J. Thomson a year later was an indication that the atom had internal structure. At the beginning of the 20th century the accepted model of the atom was J. J. Thomson's
"plum pudding" model
in which the atom was a positively charged ball with smaller negatively charged electrons embedded inside it. In the years that followed, radioactivity was extensively investigated, notably by
Marie Curie Marie Salomea Skłodowska Curie ( ; ; , born Maria Salomea Skłodowska ; 7 November 1867 – 4 July 1934) was a Polish and naturalized-French physicist A physicist is a scientist A scientist is a person who conducts Scientific meth ...

Marie Curie
,
Pierre Curie Pierre Curie ( , ; 15 May 1859 – 19 April 1906) was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity, and radioactivity. In 1903, he received the Nobel Prize in Physics with his wife, Marie Curie (née Skłodow ...
,
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 method, scientific resea ...
and others. By the turn of the century, physicists had also discovered three types of
radiation upThe international symbol for types and levels of ionizing radiation (radioactivity) that are unsafe for unshielded humans. Radiation, in general, exists throughout nature, such as in light and sound. In physics Physics (from grc ...

radiation
emanating from atoms, which they named
alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', modern pronunciation ''álfa'') is the first letter Letter, letters, or literature may refer to: Characters typeface * Letter (alphabet) A letter is a segmental symbol A s ...

alpha
,
beta Beta (, ; uppercase , lowercase , or ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the . In the system of Greek numerals it has a value of 2. In , beta represented the . In , it represents the (while in foreig ...

beta
, and
gamma Gamma (uppercase , lowercase ; ''gámma'') is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter rep ...
radiation. Experiments by
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
in 1911 and by
James Chadwick Sir James Chadwick, (20 October 1891 – 24 July 1974) was a British physicist A physicist is a scientist A scientist is a person who conducts scientific research The scientific method is an Empirical evidence, empirical m ...

James Chadwick
in 1914 discovered that the beta decay
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum Continuum may refer to: * Continuum (measurement) Continuum theories or models expla ...

spectrum
was continuous rather than discrete. That is,
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
s were ejected from the atom with a continuous range of energies, rather than the discrete amounts of energy that were observed in gamma and alpha decays. This was a problem for nuclear physics at the time, because it seemed to indicate that energy was not conserved in these decays. The 1903
Nobel Prize The Nobel Prizes ( ; sv, Nobelpriset ; no, Nobelprisen ) are five separate prizes that, according to Alfred Nobel Alfred Bernhard Nobel ( , ; 21 October 1833 – 10 December 1896) was a Swedish chemist, engineer, inventor, busines ...
in Physics was awarded jointly to Becquerel, for his discovery and to Marie and Pierre Curie for their subsequent research into radioactivity. Rutherford was awarded the Nobel Prize in Chemistry in 1908 for his "investigations into the disintegration of the elements and the chemistry of radioactive substances". In 1905,
Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest physicists of all time. Einstein is known for developing the theory of relativity The theo ...

Albert Einstein
formulated the idea of
mass–energy equivalence 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 ...
. While the work on radioactivity by
Becquerel The becquerel (; symbol: Bq) is the SI derived unit SI derived units are units of measurement derived from the seven SI base unit, base units specified by the International System of Units (SI). They are either dimensionless quantity, dimensio ...

Becquerel
and
Marie Curie Marie Salomea Skłodowska Curie ( ; ; , born Maria Salomea Skłodowska ; 7 November 1867 – 4 July 1934) was a Polish and naturalized-French physicist A physicist is a scientist A scientist is a person who conducts Scientific meth ...

Marie Curie
predates this, an explanation of the source of the energy of radioactivity would have to wait for the discovery that the nucleus itself was composed of smaller constituents, the
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 ...
s.


Rutherford discovers the nucleus

In 1906,
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 method, scientific resea ...
published "Retardation of the α Particle from Radium in passing through matter."
Hans Geiger Johannes Wilhelm "Hans" Geiger (; ; 30 September 1882 – 24 September 1945) was a German physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Bra ...

Hans Geiger
expanded on this work in a communication to the
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society A learned society (; also known as a learned academy, scholarly society, or academic association) is an organization that exis ...
with experiments he and Rutherford had done, passing alpha particles through air, aluminum foil and gold leaf. More work was published in 1909 by Geiger and
Ernest Marsden Sir Ernest Marsden (19 February 1889 – 15 December 1970) was an English-New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the ...
, and further greatly expanded work was published in 1910 by Geiger. In 1911–1912 Rutherford went before the Royal Society to explain the experiments and propound the new theory of the atomic nucleus as we now understand it. Published in 1909, with the eventual classical analysis by Rutherford published May 1911, the key preemptive experiment was performed during 1909,Rutherford model
https://www.lumitos.com/en/media-and-portals/chemeurope-com/, LUMITOS AG, "..Rutherford directed the famous Geiger-Marsden experiment in (1909), which suggested to Rutherford's analysis (1911).." Retrieved 13 June 2021
at the
University of Manchester , mottoeng = Knowledge, Wisdom, Humanity , established = 2004 – University of Manchester Predecessor institutions: 1956 – UMIST , mottoeng = By Knowledge and Work , established = 1824 , closed = 2004 (merge ...

University of Manchester
. Ernest Rutherford's assistant, Professor Johannes "Hans" Geiger, and an undergraduate, Marsden, performed an experiment in which Geiger and Marsden under Rutherford's supervision fired alpha particles ( helium 4 nuclei) at a thin film of
gold Gold 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 elemen ...

gold
foil. The
plum pudding model The plum pudding model is one of several historical scientific models Scientific modelling is a scientific activity, the aim of which is to make a particular part or feature of the world easier to Understanding, understand, Definition, define ...

plum pudding model
had predicted that the alpha particles should come out of the foil with their trajectories being at most slightly bent. But Rutherford instructed his team to look for something that shocked him to observe: a few particles were scattered through large angles, even completely backwards in some cases. He likened it to firing a
bullet A bullet is a kinetic projectile A projectile is any object thrown by the exertion of a force. It can also be defined as an object launched into the space and allowed to move free under the influence of gravity and air resistance. Although an ...

bullet
at tissue paper and having it bounce off. The discovery, with Rutherford's analysis of the data in 1911, led to the Rutherford model of the atom, in which the atom had a very small, very dense
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 cell, containing most of the cell's DNA ...
containing most of its mass, and consisting of heavy positively charged particles with embedded electrons in order to balance out the charge (since the neutron was unknown). As an example, in this model (which is not the modern one) nitrogen-14 consisted of a nucleus with 14 protons and 7 electrons (21 total particles) and the nucleus was surrounded by 7 more orbiting electrons.


Eddington and stellar nuclear fusion

Around 1920,
Arthur Eddington Sir Arthur Stanley Eddington (28 December 1882 – 22 November 1944) was an English astronomer, physicist, and mathematician. He was also a philosopher of science and a populariser of science. The Eddington limit, the natural limit to the lumi ...

Arthur Eddington
anticipated the discovery and mechanism of
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
processes in
star A star is an astronomical object consisting of a luminous spheroid of plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral) or heliotrope, a mineral aggregate * Quark ...

star
s, in his paper ''The Internal Constitution of the Stars''. At that time, the source of stellar energy was a complete mystery; Eddington correctly speculated that the source was of hydrogen into helium, liberating enormous energy according to Einstein's equation '' E = mc2''. This was a particularly remarkable development since at that time fusion and thermonuclear energy, and even that stars are largely composed of
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
(see
metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astron ...
), had not yet been discovered.


Studies of nuclear spin

The Rutherford model worked quite well until studies of
nuclear spin 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 exclusion principle to describe the structure of the nucleus in terms of energy levels. The f ...
were carried out by
Franco Rasetti Franco Dino Rasetti (August 10, 1901 – December 5, 2001) was an Italian-born American physicist, paleontologist and botanist. Together with Enrico Fermi Enrico Fermi (; 29 September 1901 - 28 November 1954) was an Italian (later natura ...
at the
California Institute of Technology The California Institute of Technology (Caltech)The university itself only spells its short form as "Caltech"; other spellings such a"Cal Tech" and "CalTech" are incorrect. The Institute is also occasionally referred to as "CIT", most notably ...
in 1929. By 1925 it was known that protons and electrons each had a spin of . In the Rutherford model of nitrogen-14, 20 of the total 21 nuclear particles should have paired up to cancel each other's spin, and the final odd particle should have left the nucleus with a net spin of . Rasetti discovered, however, that nitrogen-14 had a spin of 1.


James Chadwick discovers the neutron

In 1932 Chadwick realized that radiation that had been observed by
Walther Bothe Walther Wilhelm Georg Bothe (8 January 1891 – 8 February 1957) was a German nuclear physicist, who shared the Nobel Prize in Physics in 1954 with Max Born Max Born (; 11 December 1882 – 5 January 1970) was a German physicist A ph ...
, Herbert Becker, Irène and
Frédéric Joliot-Curie Jean Frédéric Joliot-Curie (; né Joliot; 19 March 1900 – 14 August 1958) was a French physicist A physicist is a scientist A scientist is a person who conducts scientific research The scientific method is an Empirical evidenc ...

Frédéric Joliot-Curie
was actually due to a neutral particle of about the same mass as the proton, that he called the
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
(following a suggestion from Rutherford about the need for such a particle). In the same year
Dmitri Ivanenko Dmitri Dmitrievich Ivanenko (russian: Дми́трий Дми́триевич Иване́нко; July 29, 1904 – December 30, 1994) was a Soviet Union, Soviet-Ukrainians, Ukrainian theoretical physicist who made great contributions to the physi ...
suggested that there were no electrons in the nucleus — only protons and neutrons — and that neutrons were spin particles, which explained the mass not due to protons. The neutron spin immediately solved the problem of the spin of nitrogen-14, as the one unpaired proton and one unpaired neutron in this model each contributed a spin of in the same direction, giving a final total spin of 1. With the discovery of the neutron, scientists could at last calculate what fraction of
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
each nucleus had, by comparing the nuclear mass with that of the protons and neutrons which composed it. Differences between nuclear masses were calculated in this way. When nuclear reactions were measured, these were found to agree with Einstein's calculation of the equivalence of mass and energy to within 1% as of 1934.


Proca's equations of the massive vector boson field

Alexandru Proca Alexandru Proca (October 16, 1897 – December 13, 1955) was a Romanian physicist who studied and worked in France. He developed the vector meson theory of nuclear forces and the Relativistic wave equations, relativistic quantum field equations tha ...
was the first to develop and report the massive vector
boson In quantum mechanics 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 thinkin ...

boson
field equations and a theory of the
meson In particle physics Particle physics (also known as high energy physics) is a branch of that studies the nature of the particles that constitute and . Although the word ' can refer to various types of very small objects (e.g. , gas partic ...

meson
ic field of
nuclear force The nuclear force (or nucleon–nucleon interaction, residual strong force, or, historically, strong nuclear force) is a force that acts between the proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1 ...

nuclear force
s. Proca's equations were known to
Wolfgang Pauli Wolfgang Ernst Pauli (; ; 25 April 1900 – 15 December 1958) was an Austrian theoretical physicist and one of the pioneers of quantum physics Quantum mechanics is a fundamental theory in physics that provides a description of the physica ...

Wolfgang Pauli
who mentioned the equations in his Nobel address, and they were also known to Yukawa, Wentzel, Taketani, Sakata, Kemmer, Heitler, and Fröhlich who appreciated the content of Proca's equations for developing a theory of the atomic nuclei in Nuclear Physics.


Yukawa's meson postulated to bind nuclei

In 1935
Hideki Yukawa was a Japanese theoretical physicist and the first Japanese Nobel laureate Nobel laureates of 2012 Alvin E. Roth, Brian Kobilka, Robert J. Lefkowitz">Brian_Kobilka.html" ;"title="Alvin E. Roth, Brian Kobilka">Alvin E. Roth, Brian Kobilka, R ...
proposed the first significant theory of the
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 ...
to explain how the nucleus holds together. In the
Yukawa interactionIn particle physics Particle physics (also known as high energy physics) is a branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the na ...
a
virtual particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior throug ...
, later called a
meson In particle physics Particle physics (also known as high energy physics) is a branch of that studies the nature of the particles that constitute and . Although the word ' can refer to various types of very small objects (e.g. , gas partic ...

meson
, mediated a force between all nucleons, including protons and neutrons. This force explained why nuclei did not disintegrate under the influence of proton repulsion, and it also gave an explanation of why the attractive
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 ...
had a more limited range than the electromagnetic repulsion between protons. Later, the discovery of the
pi meson In particle physics Particle physics (also known as high energy physics) is a branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is th ...
showed it to have the properties of Yukawa's particle. With Yukawa's papers, the modern model of the atom was complete. The center of the atom contains a tight ball of neutrons and protons, which is held together by the strong nuclear force, unless it is too large. Unstable nuclei may undergo alpha decay, in which they emit an energetic helium nucleus, or beta decay, in which they eject an electron (or
positron The positron or antielectron is the antiparticle s (left) and antiparticles (right). From top to bottom; electron The electron is a subatomic particle In physical sciences, subatomic particles are smaller than atom An atom is ...

positron
). After one of these decays the resultant nucleus may be left in an excited state, and in this case it decays to its ground state by emitting high-energy photons (gamma decay). The study of the strong and weak nuclear forces (the latter explained by
Enrico Fermi Enrico Fermi (; 29 September 1901 - 28 November 1954) was an Italian (later naturalized American) physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1. He has been called the "architect of the nuclear age" and ...

Enrico Fermi
via Fermi's interaction in 1934) led physicists to collide nuclei and electrons at ever higher energies. This research became the science of
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 of knowledge which rel ...
, the crown jewel of which is the
standard model of particle physics The Standard Model of particle physics Particle physics (also known as high energy physics) is a branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis ...

standard model of particle physics
, which describes the strong, weak, and .


Modern nuclear physics

A heavy nucleus can contain hundreds of
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 ...
s. This means that with some approximation it can be treated as a classical system, rather than a quantum-mechanical one. In the resulting liquid-drop model, the nucleus has an energy that arises partly from
surface tension Surface tension is the tendency of liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physi ...

surface tension
and partly from electrical repulsion of the protons. The liquid-drop model is able to reproduce many features of nuclei, including the general trend of
binding energy 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
with respect to mass number, as well as the phenomenon of
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
. Superimposed on this classical picture, however, are quantum-mechanical effects, which can be described using the
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 exclusion principle to describe th ...
, developed in large part by
Maria Goeppert Mayer Maria Goeppert Mayer (June 28, 1906 – February 20, 1972) was a German-born American theoretical physicist, and Nobel laureate in Physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of natu ...
and J. Hans D. Jensen. Nuclei with certain "
magic Magic or Magick may refer to: * Ceremonial magic, encompasses a wide variety of rituals of magic * Chaos magic#REDIRECT Chaos magic {{Redirect category shell, 1= {{R from miscapitalization {{R unprintworthy ..., a contemporary magical practic ...
" numbers of neutrons and protons are particularly stable, because their
shells 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, **Oil company Science Biology * Seashell ...
are filled. Other more complicated models for the nucleus have also been proposed, such as the
interacting boson model The interacting boson model (IBM) is a model in nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions. Other forms of nuclear matter are also studied. Nuclear physics should n ...
, in which pairs of neutrons and protons interact as
boson In quantum mechanics 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 thinkin ...

boson
s. Ab initio methods try to solve the nuclear many-body problem from the ground up, starting from the nucleons and their interactions. Much of current research in nuclear physics relates to the study of nuclei under extreme conditions such as high
spin Spin or spinning may refer to: Businesses * or South Pacific Island Network * , an American scooter-sharing system * , a chain of table tennis lounges Computing * , 's tool for formal verification of distributed software systems * , a Mach-like ...
and excitation energy. Nuclei may also have extreme shapes (similar to that of
Rugby ball#REDIRECT Rugby ball A rugby ball is an elongated ellipsoid An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellip ...

Rugby ball
s or even
pear Pears are fruits produced and consumed around the world, growing on a tree and harvested in the Northern Hemisphere in late summer into October. The pear tree and shrub are a species In biology, a species is the basic unit of biological ...

pear
s) or extreme neutron-to-proton ratios. Experimenters can create such nuclei using artificially induced fusion or nucleon transfer reactions, employing ion beams from an accelerator. Beams with even higher energies can be used to create nuclei at very high temperatures, and there are signs that these experiments have produced a
phase transition 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 ...
from normal nuclear matter to a new state, the
quark–gluon plasma Quark–gluon plasma or QGP is an interacting localized assembly of quark A quark () is a type of elementary particle In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of othe ...
, in which the
quark A quark () is a type of elementary particle In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles. Particles currently thought to be elementary include the fundam ...

quark
s mingle with one another, rather than being segregated in triplets as they are in neutrons and protons.


Nuclear decay

Eighty elements have at least one
stable isotope The term stable isotope has a meaning similar to stable nuclide Stable nuclides are nuclide A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by their number of proton A proton is a subat ...
which is never observed to decay, amounting to a total of about 252 stable nuclides. However, thousands of
isotope Isotopes are two or more types of atoms that have the same atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of ...
s have been characterized as unstable. These "radioisotopes" decay over time scales ranging from fractions of a second to trillions of years. Plotted on a chart as a function of atomic and neutron numbers, the binding energy of the nuclides forms what is known as the
valley of stability In nuclear physics, the valley of stability (also called the belt of stability, nuclear valley, energy valley, or beta stability valley) is a characterization of the stability of nuclides to radioactivity based on their binding energy. Nuclides ...
. Stable nuclides lie along the bottom of this energy valley, while increasingly unstable nuclides lie up the valley walls, that is, have weaker binding energy. The most stable nuclei fall within certain ranges or balances of composition of neutrons and protons: too few or too many neutrons (in relation to the number of protons) will cause it to decay. For example, in
beta decay In , beta decay (''β''-decay) is a type of in which a (fast energetic or ) is emitted from an , transforming the original to an of that nuclide. For example, beta decay of a transforms it into a by the emission of an electron accompanie ...

beta decay
, a
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
-16 atom (7 protons, 9 neutrons) is converted to an
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
-16 atom (8 protons, 8 neutrons) within a few seconds of being created. In this decay a neutron in the nitrogen nucleus is converted by the
weak interaction 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 ...
into a proton, an electron and an
antineutrino A neutrino ( or ) (denoted by the Greek letter Nu (letter), ) is a fermion (an elementary particle with spin-1/2, spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electric charge, electri ...
. The element is transmuted to another element, with a different number of protons. In , which typically occurs in the heaviest nuclei, the radioactive element decays by emitting a helium nucleus (2 protons and 2 neutrons), giving another element, plus
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
. In many cases this process continues through several steps of this kind, including other types of decays (usually beta decay) until a stable element is formed. In
gamma decay 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, i ...
, a nucleus decays from an excited state into a lower energy state, by emitting a
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 ...
. The element is not changed to another element in the process (no
nuclear transmutation Nuclear transmutation is the conversion of one chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of a ...
is involved). Other more exotic decays are possible (see the first main article). For example, in
internal conversion Internal conversion is a non-radioactive decay process wherein an excited atomic nucleus, nucleus interacts electromagnetism, electromagnetically with one of the Atomic orbital, orbital electrons of the atom. This causes the electron to be emitted ...
decay, the energy from an excited nucleus may eject one of the inner orbital electrons from the atom, in a process which produces high speed electrons but is not beta decay and (unlike beta decay) does not transmute one element to another.


Nuclear fusion

In
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
, two low-mass nuclei come into very close contact with each other so that the strong force fuses them. It requires a large amount of energy for the strong or
nuclear force The nuclear force (or nucleon–nucleon interaction, residual strong force, or, historically, strong nuclear force) is a force that acts between the proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1 ...

nuclear force
s to overcome the electrical repulsion between the nuclei in order to fuse them; therefore nuclear fusion can only take place at very high temperatures or high pressures. When nuclei fuse, a very large amount of energy is released and the combined nucleus assumes a lower energy level. The binding energy per nucleon increases with mass number up to
nickel Nickel 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 elem ...

nickel
-62.
Star A star is an astronomical object consisting of a luminous spheroid of plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral) or heliotrope, a mineral aggregate * Quark ...

Star
s like the Sun are powered by the fusion of four protons into a helium nucleus, two
positron The positron or antielectron is the antiparticle s (left) and antiparticles (right). From top to bottom; electron The electron is a subatomic particle In physical sciences, subatomic particles are smaller than atom An atom is ...

positron
s, and two
neutrinos A neutrino ( or ) (denoted by the Greek letter ) is a fermion In particle physics, a fermion is a particle that follows Fermi–Dirac statistics and generally has half odd integer spin: spin 1/2, Spin (physics)#Higher spins, spin 3/2, etc. T ...
. The uncontrolled fusion of hydrogen into helium is known as thermonuclear runaway. A frontier in current research at various institutions, for example the
Joint European Torus The Joint European Torus, or JET, is an operational magnetically confined plasma physics experiment, located at Culham Centre for Fusion Energy in Oxfordshire, United Kingdom, UK. Based on a tokamak design, the fusion research facility is a join ...
(JET) and
ITER ITER (initially the International Thermonuclear Experimental Reactor, "iter" meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at replicating the fusion processes of the Su ...
, is the development of an economically viable method of using energy from a controlled fusion reaction. Nuclear fusion is the origin of the energy (including in the form of light and other electromagnetic radiation) produced by the core of all stars including our own Sun.


Nuclear fission

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
is the reverse process to fusion. For nuclei heavier than nickel-62 the binding energy per nucleon decreases with the mass number. It is therefore possible for energy to be released if a heavy nucleus breaks apart into two lighter ones. The process of is in essence a special type of spontaneous
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
. It is a highly asymmetrical fission because the four particles which make up the alpha particle are especially tightly bound to each other, making production of this nucleus in fission particularly likely. From several of the heaviest nuclei whose fission produces free neutrons, and which also easily absorb neutrons to initiate fission, a self-igniting type of neutron-initiated fission can be obtained, in a
chain reaction A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback Positive feedback (exacerbating feedback, self-reinforcing feedback) is a pro ...
. Chain reactions were known in chemistry before physics, and in fact many familiar processes like fires and chemical explosions are chemical chain reactions. The fission or "nuclear" chain-reaction, using fission-produced neutrons, is the source of energy for
nuclear power Nuclear power is the use of nuclear reaction 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), ...

nuclear power
plants and fission-type nuclear bombs, such as those detonated in
Hiroshima is the capital of Hiroshima Prefecture is a prefecture of Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep red circle on a white rectangle , image_coat = Imperi ...
and
Nagasaki is the capital and the largest city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. ...
, Japan, at the end of
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a global war A world war is "a war War is an intense armed conflict between states State may refer to: Arts, entertainment, and media Literatur ...
. Heavy nuclei such as
uranium Uranium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

uranium
and
thorium Thorium is a weakly radioactive 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 sma ...

thorium
may also undergo
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 ...
, but they are much more likely to undergo decay by alpha decay. For a neutron-initiated chain reaction to occur, there must be a
critical mass 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, v ...

critical mass
of the relevant isotope present in a certain space under certain conditions. The conditions for the smallest critical mass require the conservation of the emitted neutrons and also their slowing or
moderation Moderation is the process of eliminating or lessening extremes. It is used to ensure normality throughout the medium on which it is being conducted. Common uses of moderation include: *Ensuring consistency and accuracy in the marking of stud ...
so that there is a greater cross-section or probability of them initiating another fission. In two regions of
Oklo Oklo is a region near the town of Franceville Franceville is one of the four largest cities in Gabon Gabon (; ), officially the Gabonese Republic (french: République gabonaise), is a country on the west coast of Central Africa. Located ...
, Gabon, Africa,
natural nuclear fission reactor A fossil natural nuclear fission reactor is a uranium mineral deposit, deposit where self-sustaining nuclear chain reactions have occurred. This can be examined by analysis of isotope ratios. The conditions under which a natural nuclear reactor cou ...
s were active over 1.5 billion years ago. Measurements of natural neutrino emission have demonstrated that around half of the heat emanating from the Earth's core results from radioactive decay. However, it is not known if any of this results from fission chain reactions.


Production of "heavy" elements

According to the theory, as the Universe cooled after the
Big Bang The Big Bang 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 of consciously making sense of things, applying logic ...

Big Bang
it eventually became possible for common subatomic particles as we know them (neutrons, protons and electrons) to exist. The most common particles created in the Big Bang which are still easily observable to us today were protons and electrons (in equal numbers). The protons would eventually form hydrogen atoms. Almost all the neutrons created in the Big Bang were absorbed into
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
in the first three minutes after the Big Bang, and this helium accounts for most of the helium in the universe today (see
Big Bang nucleosynthesis In physical cosmology Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the univer ...
). Some relatively small quantities of elements beyond helium (lithium, beryllium, and perhaps some boron) were created in the Big Bang, as the protons and neutrons collided with each other, but all of the "heavier elements" (carbon, element number 6, and elements of greater atomic number) that we see today, were created inside stars during a series of fusion stages, such as the proton–proton chain, the CNO cycle and the triple-alpha process. Progressively heavier elements are created during the stellar evolution, evolution of a star. Energy is only released in fusion processes involving smaller atoms than iron 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 ...
peaks around iron (56 nucleons). Since the creation of heavier nuclei by fusion requires energy, nature resorts to the process of neutron capture. Neutrons (due to their lack of charge) are readily absorbed by a nucleus. The heavy elements are created by either a ''slow'' neutron capture process (the so-called s-process, ''s''-process) or the ''rapid'', or r-process, ''r''-process. The ''s'' process occurs in thermally pulsing stars (called AGB, or asymptotic giant branch stars) and takes hundreds to thousands of years to reach the heaviest elements of lead and bismuth. The ''r''-process is thought to occur in supernova explosions, which provide the necessary conditions of high temperature, high neutron flux and ejected matter. These stellar conditions make the successive neutron captures very fast, involving very neutron-rich species which then beta-decay to heavier elements, especially at the so-called waiting points that correspond to more stable nuclides with closed neutron shells (magic numbers).


See also

*Isomeric shift *Neutron-degenerate matter *Nuclear chemistry *Nuclear matter *Nuclear model *Nuclear spectroscopy *Nucleonica, web driven nuclear science portal *QCD matter


References


Bibliography

* ''General Chemistry'' by Linus Pauling (Dover 1970) * ''Introductory Nuclear Physics'' by Kenneth S. Krane (3rd edition, 1987) [Undergraduate textbook] * ''Theoretical Nuclear And Subnuclear Physics'' by John D. Walecka (2nd edition, 2004) [Graduate textbook] * ''Nuclear Physics in a Nutshell'' by Carlos A. Bertulani (Princeton Press 2007)


External links


Ernest Rutherford's biography at the American Institute of PhysicsAmerican Physical Society Division of Nuclear PhysicsAmerican Nuclear SocietyAnnotated bibliography on nuclear physics from the Alsos Digital Library for Nuclear IssuesNuclear science wikiNuclear Data Services – IAEA

Nuclear Physics
BBC Radio 4 discussion with Jim Al-Khalili, John Gribbin and Catherine Sutton (''In Our Time'', Jan. 10, 2002) {{DEFAULTSORT:Nuclear Physics Nuclear physics,