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.[1] Nuclear physics should not be confused with atomic physics, which studies the atom as a whole, including its electrons.

Discoveries in nuclear physics have led to applications in many fields. This includes nuclear power, nuclear weapons, nuclear medicine and magnetic resonance imaging, industrial and agricultural isotopes, ion implantation in materials engineering, and radiocarbon dating in geology and archaeology. Such applications are studied in the field of nuclear engineering.

Particle physics evolved out of nuclear physics and the two fields are typically taught in close association. Nuclear astrophysics, the application of nuclear physics to astrophysics, is crucial in explaining the inner workings of stars and the origin of the chemical elements.

History

Cloud chambers played an important role of particle detectors
Since 1920s cloud chambers played an important role of particle detectors and eventually lead to the discovery of positron, muon and kaon.

The history of nuclear physics as a discipline distinct from atomic physics starts with the discovery of radioactivity by Henri Becquerel in 1896,[2] while investigating phosphorescence in uranium salts.[3] The discovery of the electron by J. J. Thomson[4] 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 and Pierre Curie as well as by Ernest Rutherford and his collaborators. By the turn of the century physicists had also discovered three types of radiation emanating from atoms, which they named alpha, beta, and gamma radiation. Experiments by Otto Hahn in 1911 and by James Chadwick in 1914 discovered that the beta decay spectrum was continuous rather than discrete. That is, electrons were ejected from the atom with a 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 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 formulated the idea of mass–energy equivalence. While the work on radioactivity by Becquerel and 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 nucleons.

Rutherford's team discovers the nucleus

In 1906 Ernest Rutherford published "Retardation of the α Particle from Radium in passing through matter."[5] Hans Geiger expanded on this work in a communication to the Royal Society[6] 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,[7] and further greatly expanded work was published in 1910 by Geiger.[8] 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.

The key experiment behind this announcement was performed in 1910 at the University of Manchester: Ernest Rutherford's team performed a remarkable experiment in which Geiger and Marsden under Rutherford's supervision fired alpha particles (helium nuclei) at a thin film of gold foil. The 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 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 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.

Around 1920, Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars.[9][10] At that time, the source of stellar energy was a complete mystery; Eddington correctly speculated that the source was fusion 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 (see metallicity), had not yet been discovered.

The Rutherford model worked quite well until studies of nuclear spin were carried out by Franco Rasetti at the California Institute of Technology in 1929. By 1925 it was known that protons and electrons each had a spin of ​+/-12. 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 ​12. 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, Herbert Becker, Irène and Frédéric Joliot-Curie was actually due to a neutral particle of about the same mass as the proton, that he called the neutron (following a suggestion from Rutherford about the need for such a particle).[11] In the same year Dmitri Ivanenko suggested that there were no electrons in the nucleus — only protons and neutrons — and that neutrons were spin ​12 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 ​12 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 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 was the first to develop and report the massive vector boson field equations and a theory of the mesonic field of nuclear forces. Proca's equations were known to Wolfgang Pauli[12] 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.[13][14][15][16][17]

Yukawa's meson postulated to bind nuclei

In 1935 Hideki Yukawa[18] proposed the first significant theory of the strong force to explain how the nucleus holds together. In the Yukawa interaction a virtual particle, later called a 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 had a more limited range than the electromagnetic repulsion between protons. Later, the discovery of the pi meson 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). 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 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, the crown jewel of which is the standard model of particle physics which describes the strong, weak, and electromagnetic forces.

Modern nuclear physics

A heavy nucleus can contain hundreds of nucleons. 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,[19] the nucleus has an energy which arises partly from surface tension and partly from electrical repulsion of the protons. The liquid-drop model is able to reproduce many features of nuclei, including the general trend of binding energy with respect to mass number, as well as the phenomenon of nuclear fission.

Superimposed on this classical picture, however, are quantum-mechanical effects, which can be described using the nuclear shell model, developed in large part by Maria Goeppert Mayer[20] and J. Hans D. Jensen.[21] Nuclei with certain numbers of neutrons and protons (the magic numbers 2, 8, 20, 28, 50, 82, 126, ...) are particularly stable, because their shells are filled.

Other more complicated models for the nucleus have also been proposed, such as the interacting boson model, in which pairs of neutrons and protons interact as bosons, analogously to Cooper pairs of electrons.

Ab initio methods try to solve the nuclear many-body problem from the ground up, starting from the nucleons and their interactions.[22]

Much of current research in nuclear physics relates to the study of nuclei under extreme conditions such as high spin and excitation energy. Nuclei may also have extreme shapes (similar to that of Rugby balls or even pears) or extreme neutron-to-proton ratios. Experimenters can create such nuclei using artificially induced fusion or nucleon transfer reactions, employing ion beams from an accelerator. Beams with even higher energies can be used to create nuclei at very high temperatures, and there are signs that these experiments have produced a phase transition from normal nuclear matter to a new state, the quark–gluon plasma, in which the quarks mingle with one another, rather than being segregated in triplets as they are in neutrons and protons.

Nuclear decay

Eighty elements have at least one stable isotope which is never observed to decay, amounting to a total of about 254 stable isotopes. However, thousands of isotopes 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. 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 a nitrogen-16 atom (7 protons, 9 neutrons) is converted to an oxygen-16 atom (8 protons, 8 neutrons)[23] within a few seconds of being created. In this decay a neutron in the nitrogen nucleus is converted by the weak interaction into a proton, an electron and an antineutrino. The element is transmuted to another element, with a different number of protons.

In alpha decay (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. 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 nucleus decays from an excited state into a lower energy state, by emitting a gamma ray. The element is not changed to another element in the process (no nuclear transmutation is involved).

Other more exotic decays are possible (see the first main article). For example, in internal conversion 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, 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 forces 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-62. Stars like the Sun are powered by the fusion of four protons into a helium nucleus, two positrons, and two neutrinos. The uncontrolled fusion of hydrogen into helium is known as thermonuclear runaway. A frontier in current research at various institutions, for example the Joint European Torus (JET) and ITER, 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 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 alpha decay is in essence a special type of spontaneous 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 certain 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. Chain reactions were known in chemistry before physics, and in fact many familiar processes like fires and chemical explosions are chemical chain reactions. The fission or "nuclear" chain-reaction, using fission-produced neutrons, is the source of energy for nuclear power plants and fission type nuclear bombs, such as those detonated in Hiroshima and Nagasaki, Japan, at the end of World War II. Heavy nuclei such as uranium and thorium may also undergo spontaneous fission, 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 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 so that there is a greater cross-section or probability of them initiating another fission. In two regions of Oklo, Gabon, Africa, natural nuclear fission reactors were active over 1.5 billion years ago.[24] 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 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 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).

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 evolution of a star.

Since the binding energy per nucleon peaks around iron (56 nucleons), energy is only released in fusion processes involving smaller atoms than that. 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) or the rapid, or r-process. The s process occurs in thermally pulsing stars (called AGB, or asymptotic giant branch stars) and takes hundreds to thousands of years to reach the heaviest elements of lead and bismuth. The r-process is thought to occur in supernova explosions 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

References

  1. ^ European Science Foundation (2010). NuPECC Long Range Plan 2010: Perspectives of Nuclear Physics in Europe (PDF) (Report). p. 6. Nuclear physics is the science of the atomic nucleus and of nuclear matter.
  2. ^ B. R. Martin (2006). Nuclear and Particle Physics. John Wiley & Sons, Ltd. ISBN 978-0-470-01999-3.
  3. ^ Henri Becquerel (1896). "Sur les radiations émises par phosphorescence". Comptes Rendus. 122: 420–421.
  4. ^ Thomson, Joseph John (1897). "Cathode Rays". Proceedings of the Royal Institution of Great Britain. XV: 419–432.
  5. ^ Rutherford, Ernest (1906). "On the retardation of the α particle from radium in passing through matter". Philosophical Magazine. 12 (68): 134–146. doi:10.1080/14786440609463525.
  6. ^ Geiger, Hans (1908). "On the scattering of α-particles by matter". Proceedings of the Royal Society A. 81 (546): 174–177. Bibcode:1908RSPSA..81..174G. doi:10.1098/rspa.1908.0067.
  7. ^ Geiger, Hans; Marsden, Ernest (1909). "On the diffuse reflection of the α-particles". Proceedings of the Royal Society A. 82 (557): 495. Bibcode:1909RSPSA..82..495G. doi:10.1098/rspa.1909.0054.
  8. ^ Geiger, Hans (1910). "The scattering of the α-particles by matter". Proceedings of the Royal Society A. 83 (565): 492–504. Bibcode:1910RSPSA..83..492G. doi:10.1098/rspa.1910.0038.
  9. ^ Eddington, A. S. (1920). "The Internal Constitution of the Stars". The Scientific Monthly. 11 (4): 297–303. JSTOR 6491.
  10. ^ Eddington, A. S. (1916). "On the radiative equilibrium of the stars". Monthly Notices of the Royal Astronomical Society. 77: 16–35. Bibcode:1916MNRAS..77...16E. doi:10.1093/mnras/77.1.16.
  11. ^ Chadwick, James (1932). "The existence of a neutron". Proceedings of the Royal Society A. 136 (830): 692–708. Bibcode:1932RSPSA.136..692C. doi:10.1098/rspa.1932.0112.
  12. ^ W. Pauli, Nobel lecture, December 13, 1946.
  13. ^ Poenaru, Dorin N.; Calboreanu, Alexandru (2006). "Alexandru Proca (1897–1955) and his equation of the massive vector boson field". Europhysics News. 37 (5): 25–27. Bibcode:2006ENews..37...24P. doi:10.1051/epn:2006504 – via http://www.europhysicsnews.org.
  14. ^ G. A. Proca, Alexandre Proca.Oeuvre Scientifique Publiée, S.I.A.G., Rome, 1988.
  15. ^ Vuille, C.; Ipser, J.; Gallagher, J. (2002). "Einstein-Proca model, micro black holes, and naked singularities". General Relativity and Gravitation. 34 (5): 689. doi:10.1023/a:1015942229041.
  16. ^ Scipioni, R. (1999). "Isomorphism between non-Riemannian gravity and Einstein-Proca-Weyl theories extended to a class of scalar gravity theories". Class. Quantum Gravity. 16 (7): 2471–2478. arXiv:gr-qc/9905022. Bibcode:1999CQGra..16.2471S. doi:10.1088/0264-9381/16/7/320.
  17. ^ Tucker, R. W; Wang, C (1997). "An Einstein-Proca-fluid model for dark matter gravitational interactions". Nuclear Physics B: Proceedings Supplements. 57 (1–3): 259–262. Bibcode:1997NuPhS..57..259T. doi:10.1016/s0920-5632(97)00399-x.
  18. ^ Yukawa, Hideki (1935). "On the Interaction of Elementary Particles. I". Proceedings of the Physico-Mathematical Society of Japan. 3rd Series. 17: 48–57. doi:10.11429/ppmsj1919.17.0_48.
  19. ^ J.M.Blatt and V.F.Weisskopf, Theoretical Nuclear Physics, Springer, 1979, VII.5
  20. ^ Mayer, Maria Goeppert (1949). "On Closed Shells in Nuclei. II". Physical Review. 75 (12): 1969–1970. Bibcode:1949PhRv...75.1969M. doi:10.1103/PhysRev.75.1969.
  21. ^ Haxel, Otto; Jensen, J. Hans D; Suess, Hans E (1949). "On the "Magic Numbers" in Nuclear Structure". Physical Review. 75 (11): 1766. Bibcode:1949PhRv...75R1766H. doi:10.1103/PhysRev.75.1766.2.
  22. ^ Stephenson, C.; et., al. (2017). "Topological properties of a self-assembled electrical network via ab initio calculation". Scientific Reports. 7 (1): 932. Bibcode:2017NatSR...7..932B. doi:10.1038/s41598-017-01007-9. PMC 5430567. PMID 28428625.
  23. ^ Not a typical example as it results in a "doubly magic" nucleus
  24. ^ Meshik, A. P. (November 2005). "The Workings of an Ancient Nuclear Reactor". Scientific American. 293 (5): 82–91. Bibcode:2005SciAm.293e..82M. doi:10.1038/scientificamerican1105-82. Retrieved 2014-01-04.

Bibliography

  • General Chemistry by Linus Pauling (Dover 1970) ISBN 0-486-65622-5
  • Introductory Nuclear Physics by Kenneth S. Krane (3rd edition, 1987) ISBN 978-0471805533 [Undergraduate textbook]
  • Theoretical Nuclear And Subnuclear Physics by John D. Walecka (2nd edition, 2004) ISBN 9812388982 [Graduate textbook]

External links

Atomic nucleus

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 gold foil experiment. After the discovery of the neutron in 1932, models for a nucleus composed of protons and neutrons were quickly developed by Dmitri Ivanenko and Werner Heisenberg. An atom is composed of a positively-charged nucleus, with a cloud of negatively-charged electrons surrounding it, bound together by electrostatic force. Almost all of the mass of an atom is located in the nucleus, with a very small contribution from the electron cloud. Protons and neutrons are bound together to form a nucleus by the nuclear force.

The diameter of the nucleus is in the range of 1.7566 fm (1.7566×10−15 m) for hydrogen (the diameter of a single proton) to about 11.7142 fm for the heaviest atom uranium. These dimensions are much smaller than the diameter of the atom itself (nucleus + electron cloud), by a factor of about 26,634 (uranium atomic radius is about 156 pm (156×10−12 m)) to about 60,250 (hydrogen atomic radius is about 52.92 pm).The branch of physics concerned with the study and understanding of the atomic nucleus, including its composition and the forces which bind it together, is called nuclear physics.

Centre national de la recherche scientifique

The French National Center for Scientific Research (French: Centre national de la recherche scientifique, CNRS) is the largest governmental research organisation in France and the largest fundamental science agency in Europe. In 2016, it employed 31,637 staff, including 11,137 tenured researchers, 13,415 engineers and technical staff, and 7,085 contractual workers. It is headquartered in Paris and has administrative offices in Brussels, Beijing, Tokyo, Singapore, Washington, D.C., Bonn, Moscow, Tunis, Johannesburg, Santiago de Chile, Israel, and New Delhi.

Decay energy

The decay energy is the energy released by a radioactive decay. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide.

Decay product

In nuclear physics, a decay product (also known as a daughter product, daughter isotope, radio-daughter, or daughter nuclide) is the remaining nuclide left over from radioactive decay. Radioactive decay often proceeds via a sequence of steps (decay chain). For example, 238U decays to 234Th which decays to 234mPa which decays, and so on, to 206Pb (which is stable):

In this example:

These might also be referred to as the daughter products of 238U.

Decay products are important in understanding radioactive decay and the management of radioactive waste.

For elements above lead in atomic number, the decay chain typically ends with an isotope of lead or bismuth. Bismuth itself decays to thallium, but the decay is so slow as to be practically negligible.

In many cases, individual members of the decay chain are as radioactive as the parent, but far smaller in volume/mass. Thus, although uranium is not dangerously radioactive when pure, some pieces of naturally occurring pitchblende are quite dangerous owing to their radium-226 content, which is soluble and not a ceramic like the parent. Similarly, thorium gas mantles are very slightly radioactive when new, but become more radioactive after only a few months of storage as the daughters of 232Th build up.

Although it cannot be predicted whether any given atom of a radioactive substance will decay at any given time, the decay products of a radioactive substance are extremely predictable. Because of this, decay products are important to scientists in many fields who need to know the quantity or type of the parent product. Such studies are done to measure pollution levels (in and around nuclear facilities) and for other matters.

Electron capture

Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shell. This process thereby changes a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino.

p + e− → n + νeSince this single emitted neutrino carries the entire decay energy, it has this single characteristic energy. Similarly, the momentum of the neutrino emission causes the daughter atom to recoil with a single characteristic momentum.

The resulting daughter nuclide, if it is in an excited state, then transitions to its ground state. Usually, a gamma ray is emitted during this transition, but nuclear de-excitation may also take place by internal conversion.

Following capture of an inner electron from the atom, an outer electron replaces the electron that was captured and one or more characteristic X-ray photons is emitted in this process. Electron capture sometimes also results in the Auger effect, where an electron is ejected from the atom's electron shell due to interactions between the atom's electrons in the process of seeking a lower energy electron state.

Following electron capture, the atomic number is reduced by one, the neutron number is increased by one, and there is no change in mass number. Simple electron capture by itself results in a neutral atom, since the loss of the electron in the electron shell is balanced by a loss of positive nuclear charge. However, a positive atomic ion may result from further Auger electron emission.

Electron capture is an example of weak interaction, one of the four fundamental forces.

Electron capture is the primary decay mode for isotopes with a relative superabundance of protons in the nucleus, but with insufficient energy difference between the isotope and its prospective daughter (the isobar with one less positive charge) for the nuclide to decay by emitting a positron. Electron capture is always an alternative decay mode for radioactive isotopes that do not have sufficient energy to decay by positron emission.

Electron capture is sometimes included as a type of beta decay, because the basic nuclear process, mediated by the weak force, is the same. In nuclear physics, beta decay is a type of radioactive decay in which a beta ray (fast energetic electron or positron) and a neutrino are emitted from an atomic nucleus.

Electron capture is sometimes called inverse beta decay, though this term usually refers to the interaction of an electron antineutrino with a proton.If the energy difference between the parent atom and the daughter atom is less than 1.022 MeV, positron emission is forbidden as not enough decay energy is available to allow it, and thus electron capture is the sole decay mode. For example, rubidium-83 (37 protons, 46 neutrons) will decay to krypton-83 (36 protons, 47 neutrons) solely by electron capture (the energy difference, or decay energy, is about 0.9 MeV).

Fissile material

In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typified by either slow neutrons (i.e., a thermal system) or fast neutrons. Fissile material can be used to fuel thermal-neutron reactors, fast-neutron reactors and nuclear explosives.

High energy nuclear physics

High-energy nuclear physics studies the behavior of nuclear matter in energy regimes typical of high energy physics. The primary focus of this field is the study of heavy-ion collisions, as compared to lower atomic mass atoms in other particle accelerators. At sufficient collision energies, these types of collisions are theorized to produce the quark–gluon plasma. In peripheral nuclear collisions at high energies one expects to obtain information on the electromagnetic production of leptons and mesons which are not accessible in electron-positron colliders due to their much smaller luminosities.

Previous high-energy nuclear accelerator experiments have studied heavy-ion collisions using projectile energies of 1 GeV/nucleon up to 158 GeV/nucleon. Experiments of this type, called "fixed target" experiments, primarily accelerate a "bunch" of ions (typically around to ions per bunch) to speeds approaching the speed of light (0.999c) and smash them into a target of similar heavy ions. While all collision systems are interesting, great focus was applied in the late 1990s to symmetric collision systems of gold beams on gold targets at Brookhaven National Laboratory's Alternating Gradient Synchrotron (AGS) and uranium beams on uranium targets at CERN's Super Proton Synchrotron.

Currently, high-energy nuclear physics experiments are being conducted at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) and in CERN's new Large Hadron Collider. The four primary experiments at RHIC (PHENIX, STAR, PHOBOS, and BRAHMS) study collisions of highly relativistic nuclei. Unlike fixed target experiments, collider experiments steer two accelerated beams of ions toward each other at (in the case of RHIC) six interaction regions. At RHIC, ions can be accelerated (depending on the ion size) from 100 GeV/nucleon to 250GeV/nucleon. Since each colliding ion possesses this energy moving in opposite directions, the maximum energy of the collisions can achieve a center of mass collision energy of 200GeV/nucleon for gold and 500GeV/nucleon for protons.

The ALICE (A Large Ion Collider Experiment) detector at the LHC at CERN is specialized in studying Pb-Pb nuclei collisions at a centre of mass energy of 2.76 TeV per nucleon pair. Other LHC detectors like CMS, ATLAS, and LHCb also have heavy ion programs.

Isobar (nuclide)

Isobars are atoms (nuclides) of different chemical elements that have the same number of nucleons. Correspondingly, isobars differ in atomic number (or number of protons) but have the same mass number. An example of a series of isobars would be 40S, 40Cl, 40Ar, 40K, and 40Ca. The nuclei of these nuclides all contain 40 nucleons; however, they contain varying numbers of protons and neutrons.The term "isobars" (originally "isobares") for nuclides was suggested by Alfred Walter Stewart in 1918. It is derived from the Greek word isos, meaning "equal" and baros, meaning "weight".

Istituto Nazionale di Fisica Nucleare

The Istituto Nazionale di Fisica Nucleare (INFN; "National Institute for Nuclear Physics") is the coordinating institution for nuclear, particle and astroparticle physics in Italy.

Journal of Physics G

Journal of Physics G: Nuclear and Particle Physics is a peer-reviewed journal that publishes theoretical and experimental research into nuclear physics, particle physics and particle astrophysics, including all interface areas between these fields.

The editor-in-chief is Professor Jacek Dobaczewski, University of York, UK.

Kurchatov Institute

The Kurchatov Institute (Russian: Hациональный исследовательский центр "Курчатовский Институт" (since 2010) i.e. (Russia's) National Research Centre "Kurchatov Institute"; 1991-2010: Роcсийский научный центр "Курчатовский Институт" — Russian Scientific Centre "Kurchatov Institute") is Russia's leading research and development institution in the field of nuclear energy.

In the Soviet Union it was known as I. V. Kurchatov Institute of Atomic Energy (Russian: Институт Атомной Энергии им. И.В. Курчатова), abbreviated KIAE (Russian: КИАЭ). The Kurchatov Institute is located at 1 Kurchatov Square, Moscow. It is named after Igor Kurchatov.

Magic number (physics)

In nuclear physics, a magic number is a number of nucleons (either protons or neutrons, separately) such that they are arranged into complete shells within the atomic nucleus. The seven most widely recognized magic numbers as of 2007 are 2, 8, 20, 28, 50, 82, and 126 (sequence A018226 in the OEIS). For protons, this corresponds to the elements helium, oxygen, calcium, nickel, tin, lead and the hypothetical unbihexium, although 126 is so far only known to be a magic number for neutrons. Atomic nuclei consisting of such a magic number of nucleons have a higher average binding energy per nucleon than one would expect based upon predictions such as the semi-empirical mass formula and are hence more stable against nuclear decay.

The unusual stability of isotopes having magic numbers means that transuranium elements can be created with extremely large nuclei and yet not be subject to the extremely rapid radioactive decay normally associated with high atomic numbers. Large isotopes with magic numbers of nucleons are said to exist in an island of stability. Unlike the magic numbers 2–126, which are realized in spherical nuclei, theoretical calculations predict that nuclei in the island of stability are deformed. Before this was realized, higher magic numbers, such as 184, 258, 350, and 462 (sequence A033547 in the OEIS), were predicted based on simple calculations that assumed spherical shapes: these are generated by the formula (see binomial coefficient). It is now believed that the sequence of spherical magic numbers cannot be extended in this way. Further predicted magic numbers are 114, 122, 124, and 164 for protons as well as 184, 196, 236, and 318 for neutrons.

Max Planck Institute for Nuclear Physics

The Max-Planck-Institut für Kernphysik ("MPI for Nuclear Physics" or MPIK for short) is a

research institute in Heidelberg, Germany.

The institute is one of the 80 institutes of the Max-Planck-Gesellschaft (Max Planck Society), an independent, non-profit research organization. The Max Planck Institute for Nuclear Physics was founded in 1958 under the leadership of Wolfgang Gentner. Its precursor was the Institute for Physics at the MPI for Medical Research.

Today, the institute's research areas are: crossroads of particle physics and astrophysics (astroparticle physics) and

many-body dynamics of atoms and molecules (quantum dynamics). There are five scientific divisions and several further research groups and junior groups. Scientific and technical departments as well as the administration support the researchers. The institute has about 390 employees, as well as many diploma students and scientific guests.

The research field of Astroparticle Physics, represented by the divisions of Werner Hofmann and Manfred Lindner, combines questions related to macrocosm and microcosm. Unconventional methods of observation for gamma rays and neutrinos open new windows to the universe. What lies behind “dark matter” and “dark energy” is theoretically investigated.

The research field of Quantum Dynamics is represented by the divisions of Klaus Blaum, Christoph Keitel and Thomas Pfeifer. Using reaction microscopes, simple chemical reactions can be “filmed”. Storage rings and traps allow precision experiments almost under space conditions. The interaction of intense laser light with matter is investigated using quantum-theoretical methods.

Further research fields are cosmic dust, atmospheric physics as well as fullerenes and other carbon molecules.

Scientists at the MPIK collaborate with other research groups in Europe and all over the world and are involved in numerous international collaborations, partly in a leading role. Particularly close connections to some large-scale facilities like GSI (Darmstadt), DESY (Hamburg), CERN (Geneva), TRIUMF (Canada), and INFN-LNGS (Assergi L‘Aquila) exist.

In the local region, the Institute cooperates closely with the University of Heidelberg, where the directors and further members of the Institute are teaching. Three International Max Planck Research Schools (IMPRS) and a graduate school serve to foster young scientists.

The institute operates accelerators (12 MeV Tandem, 15 MeV high-current injector, 25 MeV linear postaccelerator) injecting highly charged atomic ions or molecular ions into a storage ring (TSR). The electron-beam ion trap (EBIT) is able to produce and store 78-fold charged mercury ions.

Nuclear Physics (journal)

Nuclear Physics A, Nuclear Physics B, Nuclear Physics B: Proceedings Supplements and discontinued Nuclear Physics are peer-reviewed scientific journals published by Elsevier. The scope of Nuclear Physics A is nuclear and hadronic physics, and that of Nuclear Physics B is high energy physics, quantum field theory, statistical systems, and mathematical physics.

Nuclear Physics was established in 1956, and then split into Nuclear Physics A and Nuclear Physics B in 1967. A supplement series to Nuclear Physics B, called Nuclear Physics B: Proceedings Supplements has been published from 1987 onwards.Nuclear Physics B is part of the SCOAP3 initiative.

Nuclear astrophysics

Nuclear astrophysics is an interdisciplinary branch of physics involving close collaboration among researchers in various subfields of nuclear physics and astrophysics: notably stellar modeling; measurement and theoretical estimation of nuclear reaction rates; physical cosmology and cosmochemistry; gamma ray, optical and X-ray astronomy; and extending our knowledge about nuclear lifetimes and masses. In general terms, nuclear astrophysics aims to understand the origin of the chemical elements and the energy generation in stars.

Physics Letters

Physics Letters was a scientific journal published from 1962 to 1966, when it split in two series now published by Elsevier:

Physics Letters A: condensed matter physics, theoretical physics, nonlinear science, statistical physics, mathematical and computational physics, general and cross-disciplinary physics (including foundations), atomic, molecular and cluster physics, plasma and fluid physics, optical physics, biological physics and nanoscience.

Physics Letters B: nuclear physics, theoretical nuclear physics, experimental high-energy physics, theoretical high-energy physics, and astrophysics.Physics Letters B is part of the SCOAP3 initiative.

Positron emission

Positron emission or beta plus decay (β+ decay) is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (νe). Positron emission is mediated by the weak force. The positron is a type of beta particle (β+), the other beta particle being the electron (β−) emitted from the β− decay of a nucleus.

An example of positron emission (β+ decay) is shown with magnesium-23 decaying into sodium-23:

2312Mg → 2311Na + e+ + νeBecause positron emission decreases proton number relative to neutron number, positron decay happens typically in large "proton-rich" radionuclides. Positron decay results in nuclear transmutation, changing an atom of one chemical element into an atom of an element with an atomic number that is less by one unit.

Positron emission should not be confused with electron emission or beta minus decay (β− decay), which occurs when a neutron turns into a proton and the nucleus emits an electron and an antineutrino.

Positron emission is different from proton decay, the hypothetical decay of protons, not necessarily those bound with neutrons, not necessarily through the emission of a positron and not as part of nuclear physics, but rather of particle physics.

Saha Institute of Nuclear Physics

The Saha Institute of Nuclear Physics (SINP) is an institution of basic research and training in physical and biophysical sciences located in Bidhannagar, Kolkata, India. The institute is named after the famous Indian physicist Meghnad Saha.

Spontaneous fission

Spontaneous fission (SF) is a form of radioactive decay that is found only in very heavy chemical elements. The nuclear binding energy of the elements reaches its maximum at an atomic mass number of about 56; spontaneous breakdown into smaller nuclei and a few isolated nuclear particles becomes possible at greater atomic mass numbers.

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