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Topic: Superheavy elements in the Universe  (Read 6214 times)

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Offline shelanachium

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Superheavy elements in the Universe
« on: August 10, 2007, 08:51:33 AM »
I gather some researchers, believing that Hassium (element 108) may have long-lived isotopes, have been searching for it in Osmium, which it should resemble chemically.

In the likely event that Hassium has a half-life of less than 70 million years, the minimum for survival since the formation of the Solar System, it might be better to look for decay products in very old material, e.g. meteoritic iron which is rich in platinum metals like Osmium and Hassium (if it existed). Long-lived superheavy elements would not decay to lead as do Thorium and Uranium but after a series of alpha-decays reach an isotope, perhaps of element 106, that spontaneously fissions. These fissions should produce a different pattern of nuclides to those of the much lighter U and Pu, and the fission products will include many elements such as lanthanides and iodine that would not otherwise be present in meteoritic iron. This should in any case be little contaminated with fission products of Th, U and Pu as these are lithophile elements not abundant in meteoritic iron.

Even if there are superheavies with half-lives of billions of years these may be rare or nonexistent. The process that forms heavy elements in supernovae involves the rapid addition of neutrons follwed by beta-decay - the process gets stuck at fermium-258 because this spontaneously fissions before more neutrons can be added. So supernovae cannot make post-fermium nuclei.

How about making superheavies top-down, from already neutron-rich material? Perhaps neutron-star coalescence would do the trick. This is however extremely energetic and may disrupt any nuclei - but if it does not, has anyone looked at the spectra of the afterglow of gamma-ray bursters, some of which seem to be the result of neutron-star coalescence?

These events are rare indeed, so even if they make superheavies, these also will be rare indeed.

Offline gippgig

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Re: Superheavy elements in the Universe
« Reply #1 on: August 11, 2007, 02:02:09 AM »
Back in 1975 an article was published (Dec. 26 Science page 1262) that reported excess xenon in a meteorite that was proposed to be due to an extinct superheavy element in the 113-115 range. However, this was apparently disproved by a normal isotopic composition of barium (try Science Dec. 2, 1983 page 1013).
The r process that makes heavy elements in supernovas would bypass Fm-258. However, there is probably a large region of instability around fermium that most likely would block superheavy production but this is far from certain.
Note that a neutron star is a superheavy element. (Has anyone figured out what the atomic number of a typical neutron star would be?)

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