Extinct isotopes of superheavy elements are isotopes of

superheavy element Superheavy elements, also known as transactinide elements, transactinides, or super-heavy elements, are the chemical elements with atomic number greater than 103. The superheavy elements are those beyond the actinides in the periodic table; the l ...

s whose

half-lives Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

were too short to have lasted through the

formation of the Solar System The formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a ...

, and because they are not replenished by natural processes, can nowadays only be found as their

daughters A daughter is a female offspring; a girl or a woman in relation to her parents. Daughterhood is the state of being someone's daughter. The male counterpart is a son. Analogously the name is used in several areas to show relations between group ...

trapped within sediment and meteorite samples dating billions of years ago.

Carbonaceous chondrite fission xenon

Carbonaceous chondrite fission

xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...

, often abbreviated as CCF Xe, are a collection of different

isotopes of xenon Naturally occurring xenon (54Xe) consists of seven stable isotopes and two very long-lived isotopes. Double electron capture has been observed in 124Xe (half-life ) and double beta decay in 136Xe (half-life ), which are among the longest measured ...

that were thought to have arisen from the decay of a superheavy element within the island of stability. Early studies proposed that the half life of the theoretical progenitor of CCF Xe to be on the order of 10⁸ years. A later attempt at characterization of the progenitor in 1975 by Edward Anders, a professor of chemistry at the University of Chicago, and colleague John Larimer suggested a heat of vaporization of 54 kJ/mol and a boiling point of 2500K for the element and, based on estimated accretion temperatures, they also proposed elements 111 and 115 (today named

roentgenium Roentgenium is a chemical element with the symbol Rg and atomic number 111. It is an extremely radioactive synthetic element that can be created in a laboratory but is not found in nature. The most stable known isotope, roentgenium-282, has a h ...

and

moscovium Moscovium is a synthetic element with the symbol Mc and atomic number 115. It was first synthesized in 2003 by a joint team of Russian and American scientists at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. In December 2015, ...

) as the most likely candidates assuming the element condensed in pure form.

Allende meteorite

Anders went on to study samples of the

Allende meteorite The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01:05 on February 8, 1969, falling over the Mexican state of Chihuahua. After it broke up in the atmosphere, an extensive search for p ...

, the largest

carbonaceous chondrite Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 8 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites. The C chondrites represent only a small prop ...

ever found on Earth. Results of these studies suggested elements 111–115 (today

copernicium Copernicium is a synthetic chemical element with the symbol Cn and atomic number 112. Its known isotopes are extremely radioactive, and have only been created in a laboratory. The most stable known isotope, copernicium-285, has a half-life of ap ...

nihonium Nihonium is a synthetic chemical element with the symbol Nh and atomic number 113. It is extremely radioactive; its most stable known isotope, nihonium-286, has a half-life of about 10 seconds. In the periodic table, nihonium is a transact ...

flerovium Flerovium is a superheavy chemical element with symbol Fl and atomic number 114. It is an extremely radioactive synthetic element. It is named after the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in ...

, and

) as the most likely candidates for the progenitor of CCF Xe. These studies also proposed that the progenitor condensed as an iron chromium sulfide. This was later called into question as iron chromium sulfide is very rare with a relative abundance of 0.4%.

Evidence against carbonaceous fission xenon

By the 1980s, CCF Xe actually being the product of fission was doubtful, and the alternate theory that it had arisen from ''r''-process (neutron capture)

nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...

gained more ground. Researchers looked at the isotopic anomalies in neighboring elements

samarium Samarium is a chemical element with symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of samar ...

neodymium Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes ...

, and

barium Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. ...

, and compared to the amount of xenon. Whether CCF Xe was produced by nucleosynthesis or fission, comparable amounts of barium-135 should be produced. When researchers compared the experimental data to predicted amounts of Barium following each model, neither model came close to predicting the anomalies correctly, leading to Lewis et al. calling the experiment an "embarrassment" for both models. However, in the case of nucleosynthesis, it is possible that

, and

were separated from Xe by prior condensation in the supernova shell or plasma processes. Based on this data it was deemed unlikely that CCF Xe had actually arose from fission.

References

{{Reflist Environmental isotopes