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Nuclide - Wikipedia

2010-09-03 2页 pdf 31KB 32阅读

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Nuclide - Wikipedia Nuclide From Wikipedia, the free encyclopedia A nuclide (from nucleus, originally from Latin, meaning kernel of a nut) is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and i...
Nuclide - Wikipedia
Nuclide From Wikipedia, the free encyclopedia A nuclide (from nucleus, originally from Latin, meaning kernel of a nut) is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its energy state.[1] Thus, all nuclides are atoms which have at least one electron (though certain ions may be included), but naked nuclei (such as those occurring in cosmic rays and sufficiently hot plasmas) do not technically qualify for the term (these are instead naked nuclei of various nuclear species(elements)). In short, a nuclide is an umbrella term for all nuclei with one or more electrons orbiting. A set of nuclides with equal proton number (atomic number), i.e. of the same chemical element, but different neutron numbers, are called isotopes of the element. Particular nuclides are still often loosely called "isotopes", but the term "nuclide" is the correct one in general (i.e. when Z is not fixed). A set of nuclides with equal mass number A but different atomic number are called isobars (isobar = equal in weight), and isotones are nuclides of equal neutron number but different proton numbers. The name isotone has been derived from the name isotope to remind that in the first group of nuclides it is the number of neutrons (n) that is constant, whereas in the second the number of protons (p).[2] No matter how the IUPAC definition of the atom will develop (at present it is still considered as a neutral entity formed by a nucleus containing Z>0 protons surrounded by Z electrons), the neutral atoms will always be the “default” for any nuclide. This is so because the atomic weight, or more precisely: the average relative atomic mass Ar(E) of an element E, is calculated from the relative atomic masses of its isotopes weighted with their atomic abundances. The relative atomic masses of nuclides in general are also called (relative) “nuclidic masses” in short. These are the mass data that you find in data bases. Note that such masses always refer to neutral atoms in their lowest energy state. 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 isotopes. See stable isotope and primordial nuclide. Nuclear isomers are members of a set of nuclides with equal proton number and equal mass number, but different states of excitation. An example is the two states of 9943Tc shown among the decay schemes. The most long-lived non-ground-state nuclear isomer is tantalum-180m, which has a halflife in excess of 1000 trillion years, and has not been observed to decay to tantalum-180. Unstable nuclides are radioactive and are called radionuclides. Their decay products ('daughter' products) are called radiogenic nuclides. Designation Characteristics Example Remarks Isotopes equal proton number 126C, 13 6C Isotones equal neutron number 136C, 14 7N Isobars equal mass number 177N, 17 8O, 17 9F see beta decay Mirror nuclei neutron and proton number exchanged 31H, 3 2He Nuclear isomers different energy states 9943Tc, 99m 43Tc long-lived or stable 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 T½ 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 238U (T½ = 4.5×109 a) of uranium is still fairly abundant in nature, but the shorter-lived isotope, 235U (T½ = 0.7 ×109 a), is 138 times rarer. The second group consists of nuclides such as 226Ra (T½ = 1602 a), an isotope of radium, which are formed in the radioactive decay chains of uranium or thorium. Some of these nuclides are very short lived, such as isotopes of francium. The third group consists of nuclides which are continually being made in another fashion, such as 14C (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 external links) See also List of Nuclides Primordial element Primordial nuclide Table of nuclides sorted by half-life Table of nuclides Isotope geochemistry Radionuclide Monoisotopic element Mononuclidic element Stable isotope Nuclide - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Nuclide 第1页 共2页 2010-9-3 12:36 List of elements by stability of isotopes List of elements by nuclear stability References ^ nuclide entry (http://goldbook.iupac.org/N04257.html) in the IUPAC Compendium of Chemical Terminology - the Gold Book1. ^ Cohen E.R., Giacomo P. (1987). Symbols, units, nomenclature and fundamental constants in physics. Physica A, 146A, 1-682. External links Karlsruhe Nuclide Chart (http://www.karlsruhenuclidechart.net/) Chart of the nuclides (http://www.nndc.bnl.gov/nudat2/) NUCLEONICA nuclear science portal (http://www.nucleonica.net) Details about the nuclides (http://atom.kaeri.re.kr/ton/) Periodic system with details of the nuclides (http://www.webelements.com/) Universal Nuclide Chart from Nucleonica (http://www.nucleonica.net/unc.aspx) Interacive Chart of the nuclides, isotopes and Periodic Table (http://www.yoix.org/elements.html) The LIVEChart of Nuclides - IAEA (http://www-nds.iaea.org/livechart) in Java (http://www-nds.iaea.org/livechart) or HTML (http://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html) Retrieved from "http://en.wikipedia.org/wiki/Nuclide" Categories: Isotopes | Nuclear physics This page was last modified on 28 June 2010 at 01:18. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. See Terms of Use for details. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. Nuclide - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Nuclide 第2页 共2页 2010-9-3 12:36
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