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This table of nuclides shows the 896 observed nuclides that either are stable or, if radioactive, have half-lives longer than one hour. (A nuclide is defined conventionally as an experimentally examined bound collection of one or more protons and zero or more neutrons, that either is stable or has an observed decay mode.) At least 3,000 nuclides have been experimentally characterized. Those not shown in this 896-member list all have decay half-lives less than 60 minutes. == Introduction == An additional row contains specific data on the type of decay of the nuclide. If a decay has been predicted theoretically but never observed experimentally, it is given in parentheses. 254 nuclides are considered stable; some of these could in theory decay through spontaneous fission, alpha decay, double beta decay, etc. with a very long half-life, but no radioactive decay has ever been observed. Some of these are indicated with a ">" number to show the lower time limit of the half-life known based on experimental observation. Such nuclides are considered to be "stable" until a decay has been observed in some fashion. The next group is the radioactive primordial nuclides. Presently known are 34 of these, of which 29 have half-lives considerably longer than the age of the universe. Tellurium-123 most recently had been reported to be radioactive, but the same experimental group later retracted this report, and it presently remains observationally stable. The total list of 288 primordial nuclides starts with the stable nuclides and ends with the shortest-half-lived primordial nuclide, 244Pu, at position 288. About 50 nuclides have half-lives too short to be primordial, but are nevertheless found in nature as a result of later production by natural processes. These are daughters of longer-lived nuclides (radiogenic nuclides), cosmic-ray reaction products (cosmogenic nuclides), or products of other natural nuclear reactions (nucleogenic nuclides). The remaining radionuclides listed are artificially produced. Some, such as caesium-137, are found in the environment only as a result of contamination from man-made nuclear fission product releases (nuclear weapons, nuclear reactors, and other processes). All the radionuclides, starting with the longest-lived primordial radionuclides, are sorted by decreasing half-life, given in seconds. For more convenient units, half-lives must be divided by the corresponding number of seconds in the time unit (for example, half-life in seconds must be divided by 31,556,926 to obtain half-life in years). 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「List of nuclides」の詳細全文を読む スポンサード リンク
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