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Nuclide
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A nuclide (from nucleus, originally from Latin, meaning kernel of a nut) is a species of atom characterized by the constitution of its nucleus and hence by the number of protons, the number of neutrons, and the energy content of the nucleus.
The various nuclides of a particular chemical element with equal proton number (atomic number), but different neutron numbers are called isotopes of this element. Before the term "nuclide" was internationally accepted (ca.
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A nuclide (from nucleus, originally from Latin, meaning kernel of a nut) is a species of atom characterized by the constitution of its nucleus and hence by the number of protons, the number of neutrons, and the energy content of the nucleus.
The various nuclides of a particular chemical element with equal proton number (atomic number), but different neutron numbers are called isotopes of this element. Before the term "nuclide" was internationally accepted (ca. 1950), the term "isotope" was also loosely used to describe a nuclear species, i.e., a nuclide. Nuclides with equal mass number but different atomic number are called isobars (isobar = equal in weight). Isotones are nuclides of equal neutron number but different proton numbers.
There are about 256 nuclides in nature which are so stable that they have never been observed to decay. They occur among the 80 different elements which have one or more stable nuclides. See Stable isotopes.
Nuclear isomers are atomic nuclei of a particular nuclide that have equal proton number and equal mass number, differ in energy content, and are long-lived. An example is the two states of shown among the decay schemes. The most long-lived theoretically unstable nuclear isomer is tantalum-180m, which has a halflife in excess of 1000 trillion years, and has never been observed to decay to tantalum-180.
Unstable nuclides are radioactive and are called radionuclides. Their decay products ('daughter' products) are called radiogenic nuclides.
About 256 stable and about 83 unstable (radioactive) nuclides exist naturally on Earth.
Natural radionuclides may be conveniently subdivided into three types. Firstly, those whose half-lives T1/2 are at least 10% as long as the age of the earth (4.6×109 years). These are remnants of nucleosynthesis that occurred in stars before the formation of the solar system. For example, the isotope (T1/2 = 4.5×109 a) of uranium occurs in nature, but the shorter-lived isotope, (T1/2 = 0.7 ×109 a), is 138 times rarer. The second group consists of isotopes such as (T1/2 = 1602 a), an isotope of radium, which are formed in the radioactive decay chains of uranium or thorium. Some of these isotopes are very short lived, such as Francium. The third group consists of nuclides which are continually being made in another fashion, such as (radiocarbon) that are made by cosmic-ray bombardment of other elements, and Promethium which is still being created by neutron bombardment in other stars, and has been detected there by its spectrum.
More than 3000 nuclides have been artificially produced.
The known nuclides are shown in charts of the nuclides (see Weblinks)
See also
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