For the drawing style of anime and manga, see Super deformed

Super deformed

Super deformed or SD is a specific style of Japanese caricature where characters are drawn in an exaggerated way, typically small and chubby, with stubby limbs and oversized heads, to make them resemble small children...

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In nuclear physics

Nuclear physics

Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...

 a superdeformed nucleus

Atomic nucleus

The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...

 is a nucleus that is very far from spherical

Sphere

A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...

, forming an ellipsoid with axes in ratios of approximately 2:1:1. Normal deformation is approximately 1.3:1:1. Only some nuclei can exist in superdeformed states.

The first superdeformed states to be observed were the fission isomer

Nuclear isomer

A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...

s, low-spin states of elements in the Actinide and Lanthanide series. The strong force decays much faster than the Coulomb force, which becomes stronger when nucleons are greater than 2.5 femtometers apart. For this reason, these elements undergo spontaneous fission

Spontaneous fission

Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...

. Spontaneous fission of superdeformed nuclei is unique in that no radiation is emitted, and specific atoms will always decay into specific parts. In the late 1980s, high-spin superdeformed rotational bands were observed in other regions of the periodic table. Specific elements include ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, gold, and mercury.

The existence of superdeformed states occurs because of a combination of macroscopic and microscopic factors, which together lower their energies, and make them stable minima of energy as a function of deformation. Macroscopically, the nucleus can be described by the liquid drop model. The liquid drop's energy as a function of deformation is at a minimum for zero deformation, due to the surface tension term. However, the curve may become soft with respect to high deformations because of the Coulomb repulsion (especially for the fission isomers, which have high Z) and also, in the case of high-spin states, because of the increased moment of inertia. Modulating this macroscopic behavior, the microscopic shell correction creates certain superdeformed magic number

Magic number (physics)

In nuclear physics, a magic number is a number of nucleons such that they are arranged into complete shells within the atomic nucleus...

s that are analogous to the spherical magic numbers. For nuclei near these magic numbers, the shell correction creates a second minimum in the energy as a function of deformation.

Even more deformed states (3:1) are called hyperdeformed

Hyperdeformation

In nuclear physics, hyperdeformation is theoretically predicted states of an atomic nucleus with extremely elongated shape and very high angular momentum. Less elongated states, superdeformation, has been well observed, but the experimental evidence for hyperdeformation is more limited....

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External links

• "New Outlook on the Possible Existence of Superheavy Elements in Nature", by Marinov, Gelberg, Kolb, Brandt, and Pape, Physics of Atomic Nuclei, Vol. 66, No. 6, 2003, pp. 1137–1145.