Extreme elements: Superheavy exotic atomic nuclei form naturally
Man-made heavy elements may not be the heaviest in the universe after all. Even the heaviest known atomic nuclei appear to form in space.
© NASA Goddard Space Flight Center/CI Laboratory/(svs.gsfc.nasa.gov/12740) (detail)
When neutron stars merge, the heaviest elements in the universe are created.
The heaviest elements ever created, such as Tenness or Oganesson, contain up to 294 protons and neutrons. But even in complex collision experiments, only a few of these exotic atomic nuclei are formed, and they decay within milliseconds. They do not occur in nature. Or is it? A team led by Ian Yu found… Roeder of the University of Michigan has found evidence in stellar spectra that atomic nuclei containing more than 260 nuclear building blocks form in the universe. As reported by the team in “Al-Ilm” magazine.Some very old stars contain increased proportions of elements that arise from the decay of these very heavy elements. This suggests that extremely heavy elements are formed from the edge of the periodic table during neutron star mergers or in supernovae.
The heaviest elements in the universe are not created by ordinary nuclear fusion, but by a mechanism called the r process. During a supernova explosion or neutron star collision, elements such as iron capture many neutrons in a very short time. Some of these elements are converted into protons through beta decay and the nuclei capture more neutrons. This is how nuclei with high atomic numbers are formed under extremely harsh conditions. But how the nuclei of the heaviest transuranic elements form is still not well understood.
In their study, the team examined stars known to contain elements formed during the r process. You can calculate which elements are formed and in what proportions during the process. But as the team wrote, there are also two sets of elements that are more common than one might expect. On the one hand, ruthenium, rhenium, silver and palladium with mass numbers up to 110, and on the other a series of elements from gadolinium to platinum with mass numbers up to 195. Experts around Roeder suspect that the additional proportions of these elements come from nuclear fission.
Interactive periodic table of elements on Spektrum.de
But from which original nuclei did they once arise? Experts use models to say that the neutron-rich heavy elements created in the r process split asymmetrically. This means that they are divided into heavier and lighter cores. These fission products will then convert the neutrons into protons through further beta decay thus reducing the high neutron excess without losing any further mass. Accordingly, the group of elements surrounding silver corresponds to the lighter parts, and those above gadolinium correspond to the heavier parts. The mass of the heavy nuclei originally generated in the r process must be compatible with the sum of the fragments – in extreme cases more than 300, which exceeds even the heaviest artificially generated nuclei.
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