Nuclear physics 21285 225901240 2008-07-15T22:52:20Z 74.74.236.28 /* Protons and neutrons */ {{Nuclear physics}} ==Forces== Nuclei are bound together by the [[strong force]]. The strong force acts over a very short range and causes an attraction between nucleons ([[protons]] and [[neutrons]]). The strong nuclear force is so named because it is significantly larger in magnitude than the other fundamental forces ([[electroweak]], [[Electromagnetic force|electromagnetic]] and [[gravitational]]). The strong force is highly attractive at only very small distances which, combined with repulsion between protons due to the electromagnetic force, allows the nucleus to be stable. The strong force felt between [[Nucleon|nucleons]] arises due to the exchange of [[gluons]]. The study of the strong force is dealt with by [[quantum chromodynamics]] (QCD). {{cleanup|section|date=March 2008}} ==Nuclear models== Nucleons in the nucleus move about in a potential energy well which they themselves create arising from their interaction, and movement, with respect to each other. Nucleons can interact with each other via 2-body, 3-body or multiple-body forces. The fact that many nucleons interact with each other in a complicated way makes the nuclear [[many-body problem]] difficult to solve. There broadly exist two types of nuclear models which attempt to predict and understand characteristics of nuclei. These are microscopic and macroscopic nuclear models. Microscopic nuclear models approximate the potential which the nucleons create in the nucleus. Individual interactions are combined as linear sums of potentials. Almost all models use a central potential plus a [[Spin (physics)|spin]] orbit potential. The difference between models is then defined by the 3-body potential used, and/or the shape of the central potential. The form of this potential is then inserted into the Schrödinger equation. Solution of the [[Schrödinger equation]] then yields the nuclear [[Wave function|wavefunction]], spin, [[Parity (physics)|parity]] and [[Excited state|excitation energy]] of individual levels. The form of the potential used to determine these nuclear properties indicates the type of microscopic model. The [[shell model]] and deformed shell model ([[Nilsson model]]) are two examples of microscopic nuclear models. Macroscopic nuclear models attempt to describe such attributes as the nuclear size, shape and surface diffuseness. Rather than calculating individual levels, macroscopic models predict nuclear radii, degree of deformation and diffuseness parameter. A simple approximation for the nuclear radius is that it is proportional to the cube root of the nuclear mass. <math>R \propto A^{1/3}</math> This implies that all nuclei are spherical and their radius is directly proportional to the cube root of their volume (volume of a sphere = <math>4/3 \pi R^3</math>). Nuclei can also exist in a deformed shape and thus a degree of deformation ,<math> \beta_{2}</math>, can be included to take this into account. The fact that the nucleus may not be entirely [[incompressible]] is also considered by the diffuseness parameter <math>\delta</math>. An example of a macroscopic model is the droplet model of [[Myers and Schmidt]]. Some quite successful attempts have been made to combine the microscopic and macroscopic models together. These so called [[mic-mac]] models begin with a nuclear potential, solve the Schrödinger equation and proceed to predict macroscopic nuclear parameters. ==Protons and neutrons== Protons and neutrons are [[fermions]], with different values of the [[isospin]] [[quantum number]], so two protons and two neutrons can share the same space [[wave function]]. In the rare case of a [[hypernucleus]], a third [[baryon]] called a [[hyperon]], with a different value of the [[Strangeness_(particle_physics)|strangeness]] quantum number can also share the wave function. ==Nuclear activity== ===Alpha decay=== {{main|Alpha decay}} ===Beta decay=== {{main|Beta decay}} ===Gamma decay=== {{main|Gamma decay}} Here, a nucleus decays from an excited state into a lower state by emitting a [[gamma ray]]. ===Fission=== {{main|Nuclear fission}} ===Fusion=== {{main|Nuclear fusion}} ==History== The history of nuclear physics began with the discovery of the nucleus by [[Ernest Rutherford|Rutherford]] in 1911. While the work on radioactivity by Becquerel, Pierre and Marie Curie predates this, an explanation of radioactivity would have to wait for the discovery that the nucleus itself was composed of smaller constituents, the [[nucleon]]s. Attempts to split the atom led to the discovery of nuclear fission. ==See also== {{portal|Physics}} *[[Nuclear fission]] *[[Nuclear fusion]] *[[Nuclear model]] *[[Nuclear reactor physics]] ==References== {{reflist}} {{Unreferenced|date=March 2008}} Nuclear Physics by Irving Kaplan 2Nd edition, 1962 Addison-Wesley General Chemistry by Linus Pauling 1970 Dover Pub. ISBM 0-486-65622-5 ==External links== {{Sisterlinks|Nuclear power}} <!--Please add new links sparingly and remove any links to websites that are dead, unreliable or not very useful for readers. You should usually link to the home page or an index page rather than having multiple links to the same site. 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