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Gold is currently considered the heaviest monoisotopic element. Bismuth formerly held that distinction until alpha-decay of the 209 Bi isotope was observed. All isotopes of gold are either radioactive or, in the case of 197 Au, observationally stable, meaning that 197 Au is predicted to be radioactive but no actual decay has been observed. [4]
A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state levels (higher energy levels). ). "Metastable" describes nuclei whose excited states have half-lives 100 to 1000 times longer than the half-lives of the excited nuclear states that decay with a "prompt" half life (ordinarily on the order of 10
The isotope tantalum-180m, although being a metastable excited state, is long-lived enough that it has never been observed to decay, with a half-life calculated to be least 4.5 × 10 16 years, [9] [10] over 3 million times the current age of the universe.
This is a list of radioactive nuclides (sometimes also called isotopes), ordered by half-life from shortest to longest, in seconds, minutes, hours, days and years. Current methods make it difficult to measure half-lives between approximately 10 −19 and 10 −10 seconds.
The decay scheme of a radioactive substance is a graphical presentation of all the transitions occurring in a decay, and of their relationships. Examples are shown below. It is useful to think of the decay scheme as placed in a coordinate system, where the vertical axis is energy, increasing from bottom to top, and the horizontal axis is the proton number, increasing from left to right.
Pages in category "Metastable isotopes" The following 96 pages are in this category, out of 96 total. This list may not reflect recent changes. A. Aluminium-23m;
Main isotopes of gold; Main ... 4 refer to the decay mode dm#= {{Isotopes/main/isotope | mn ... A nucleus in a metastable state drops to a lower energy state by ...
The single monoisotopic exception to the odd Z rule is beryllium; its single stable, primordial isotope, beryllium-9, has 4 protons and 5 neutrons. This element is prevented from having a stable isotope with equal numbers of neutrons and protons ( beryllium-8 , with 4 of each) by its instability toward alpha decay , which is favored due to the ...