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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]
Of the 26 "monoisotopic" elements that have only a single stable isotope, all but one have an odd atomic number—the single exception being beryllium. In addition, no odd-numbered element has more than two stable isotopes, while every even-numbered element with stable isotopes, except for helium, beryllium, and carbon, has at least three.
Tin-121m (121m Sn) is a radioisotope and nuclear isomer of tin with a half-life of 43.9 years. In a normal thermal reactor, it has a very low fission product yield; thus, this isotope is not a significant contributor to nuclear waste. Fast fission or fission of some heavier actinides will produce tin-121 at higher yields. For example, its yield ...
The other six isotopes forming 82.7% of natural tin have capture cross sections of 0.3 barns or less, making them effectively transparent to neutrons. [30] Tin has 31 unstable isotopes, ranging in mass number from 99 to 139. The unstable tin isotopes have half-lives of less than a year except for tin-126, which has a half-life of
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. [1]
In a normal thermal reactor, tin-121m has a very low fission product yield; thus, this isotope is not a significant contributor to nuclear waste. Fast fission or fission of some heavier actinides will produce 121m Sn at higher yields. For example, its yield from U-235 is 0.0007% per thermal fission and 0.002% per fast fission. [10]
The 80 elements with one or more stable isotopes comprise a total of 251 nuclides that have not been shown to decay using current equipment. Of these 80 elements, 26 have only one stable isotope and are called monoisotopic. The other 56 have more than one stable isotope. Tin has ten stable isotopes, the largest number of any element.
It is prevented from having a stable isotope with 4 protons and 6 neutrons by the very large mismatch in proton/neutron ratio for such a light element. (Nevertheless, beryllium-10 has a half-life of 1.36 million years, which is too short to be primordial, but still indicates unusual stability for a light isotope with such an imbalance.)