Two new superheavy elements have been fleetingly created in a Russian lab. Each has many more protons and neutrons in their nuclei than any naturally occurring elements found on Earth.
The discovery will encourage researchers hoping to fill apparent gaps in the periodic table with “islands” of stable, massive atoms that may exhibit new chemical properties and atomic shapes.
The nuclei of the two new elements are crammed with 113 and 115 protons and reported in a paper in Physical Review C. The heaviest natural element, uranium, contains 92 protons, while the heaviest synthetic element officially confirmed by the International Union of Pure and Applied Chemistry is Darmstadtium, with 110 protons. Claims for elements with 111, 112, 114 and 116 protons are also being investigated.
The new elements were created at a particle accelerator in Dubna, Russia, by a team of researchers from the Joint Institute for Nuclear Research in Dubna and the Lawrence Livermore National Laboratory in California, US.
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Other laboratories will have to vet the findings before the elements can be officially added to the periodic table. Until then, they will go by names indicating their atomic numbers: Ununtrium (113) and Ununpentium (115).
Magic number
Such heavy nuclei, crowded with positively charged protons and uncharged neutrons, tend to very unstable. This is because the protons repel one other with a force proportional to the square of their number. It took just a fraction of a second for Ununpentium to decay to Ununtrium, which itself survived for only a second.
But physicists believe even these “superheavies” could be stable if they contain a “magic” number of protons and neutrons. Such numbers occur when each of the shell-like structures surrounding an atomic nucleus is full to capacity. The next stable superheavy is likely to slot into the periodic table at atomic number 114, 120, or 126, according to scientists.
The new, unstable superheavies were forged by smashing calcium atoms (atomic number 20) into americium (atomic number 95). In a month of experiments in summer 2003, there were just four occasions on which a calcium atom fused to an americium atom.
Each fusion produced an atom of Ununpentium, which decayed to an atom of Ununtrium. Measurements of the magnetic field in the circular accelerator in Dubna allowed scientists to verify the decay products.
Scientists familiar with the new results have called them convincing and solid. But in 2001, the claimed discovery of element 118 was retracted after a scientist was found to have fabricated data, meaning thorough independent confirmation may take months or even years.
Journal reference: Physical Review C (vol 69, article no. 021601 R)
