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A nuclide (from nucleus) 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 nuclear energy state. The word ''nuclide'' was proposed〔(original proposal for the word nuclide )〕 by Truman P. Kohman〔(Biographical material about Dr. Kohman )〕 in 1947. Kohman originally suggested ''nuclide'' as referring to a "species of nucleus" defined by containing a certain number of neutrons and protons. The word thus was originally intended to focus on the nucleus. ==Nuclides and isotopes== 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). In similar manner, 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 emphasize 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).〔 〕 See Isotope#Notation for an explanation of the notation used for different nuclide or isotope types. Nuclear isomers are members of a set of nuclides with equal proton number and equal mass number (thus making them by definition the same isotope), but different states of excitation. An example is the two states of the single isotope shown among the decay schemes. Each of these two states (technetium-99m and technetium-99) qualifies as a different nuclide, illustrating one way that nuclides may differ from isotopes (an isotope may consist of several different nuclides of different excitation states). The most long-lived non-ground state nuclear isomer is the nuclide tantalum-180m(), which has a half-life in excess of 1,000 trillion years. This nuclide occurs primordially, and has never been observed to decay to the ground state. (In contrast, the ground state nuclide tantalum-180 does not occur primordially, since it decays with a half life of only 8 hours to 180Hf (86%) or 180W (14%)). There are about 254 nuclides in nature that have never been observed to decay. They occur among the 80 different elements that have one or more stable isotopes. See stable isotope and primordial nuclide. Unstable nuclides are radioactive and are called radionuclides. Their decay products ('daughter' products) are called radiogenic nuclides. About 254 stable and about 85 unstable (radioactive) nuclides exist naturally on Earth, for a total of about 339 naturally occurring nuclides on Earth.〔() (This source gives 339 naturally occurring nuclides, but names 269 of them as stable, rather than 254 listed in stable nuclide See also list of nuclides for nearly stable nuclides. Disagreements in these numbers are in part due to certain very long-lived radioisotopes such as bismuth-209 that, when found, move known primordial nuclides from the category of stable nuclide to radioactive primordial nuclide categories, but do not change the total sum of naturally occurring nuclides. An expanded list of 339 nuclides found naturally on Earth would includes nuclides like radium and carbon-14 which are found on Earth as products of radioactive decay chains and natural process like cosmic radiation, but which are not primordial radionuclides. The latter are more easily counted, and number about 34 over the number of stable primordial nuclides, for a total of 288 primordially occurring nuclides.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「nuclide」の詳細全文を読む スポンサード リンク
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