Elemental discoveries: Ununpentium pr-pr-proven

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  • Published: Sep 1, 2013
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Elemental discoveries: Ununpentium pr-pr-proven

Room for 115

An international team of researchers, led by physicists from Lund University, in Sweden, has verified the discovery of element 115, a decade after first reports of its discovery. The team bombarded a thin film of the element americium with calcium ions and measured the pattern of X-ray photons released, to confirm predicted energies expected for the alpha decay of ununpentium. From Wikimedia: http://en.wikipedia.org/wiki/File:Electron_shell_115_Ununpentium_-_no_label.svg

An international team of researchers, led by physicists from Lund University, in Sweden, has verified the existence of element 115, a decade after first reports of its discovery. The team bombarded a complex foil of the element americium with calcium ions measured the alpha-decay pattern and tried to measure X-ray photons from the superheavy atoms at the same time. The energies of the X rays are element specific, so offer a "direct" measurement of the element.

Two superheavy elements were spotted fleetingly a decade ago by scientists from the Joint Institute for Nuclear Research in Russia (JINR) and the Glenn T. Seaborg Institute and the Chemical Biology and Nuclear Science Division at the Lawrence Livermore National Laboratory, they found evidence of element 113 and element 115. In experiments conducted at the JINR U400 cyclotron with the Dubna gas-filled separator between 14th July and 10th August 2003, the research team identified the alpha decay patterns, or chains, that suggested they had made elements 115 and element 113. In these decay chains, element 113 is produced via the alpha decay of element 115. More chains have been observed at Dubna in the meantime, also in connection with element 117 experiments. The (mainly) Dubna-Livermore collaboration associates 37 decay chains with the production of element 115 (throughout the years), Lund's Dirk Rudolph told SpectroscopyNOW. "We have 30 in three weeks, but of course we run a very dedicated experiment close to maximum production cross section/probability," he says.

A decade for reproducability

Details were published in 2004 in the journal Physical Review C, but the four atoms of each element synthesized through the fusion reaction of calcium-48 nuclei impinging on an americium-243 target were short-lived. The team observed three similar decay chains consisting of five consecutive alpha decays that took less than 30 seconds in all to occur and terminated with a spontaneous fission of an element 105 (dubnium) isotope with a relatively long half-life (16 hours). An interesting fourth decay chain also was observed that consisted of decays that were unlike the previous three chains. "The new experiment reports decay chains compatible with both types of previously observed ones, and adds photons to the list, two of which are candidates for X-ray fingerprinting," Rudolph told us.

Of course, in science, results are not "proven" until experiments are independently verified. Now, some ten years since 113 and 115 were first posited, researchers have provided new evidence for their existence. The experiment was conducted at the GSI research facility in Germany. "This was a very successful experiment and is one of the most important in the field in recent years," says Rudolph. 

Back to school

The super-heavy element has had the provisional and unwieldy name of ununpentium for many years, but is yet to receive an official pronouncement on nomenclature from the international unions of pure and applied physics and chemistry. Its approved name will be reviewed by committee but presumably not before final assessment of this new evidence for its existence and even subsequent peer-reviewed data. Although this is a step forward textbook publishers can rest easy that they do not have to rush to update the periodic table in time for the "back-to-school" period this autumn. Of course, we are still waiting for new evidence of the other element discovered a decade ago, 113. Future statistically significant fingerprinting experiments could prove it, or if the evidence for 115 is accepted based on the confirmation by Rudolph et al, then that would imply the discovery of element 113 simultaneously because 113 and 115 are connected by many alpha decays.

The story as a whole is a bit more complex because Japanese research led by Morita generated element 113 in a different way to the Dubna-Livermore work and they both compete heavily on the discovery claims.

Rudolph told us that in general the hunt for elements 119 and 120 are underway with various attempts having made to find these even heavier superheavy elements. "We hope for Mother Nature providing us with a clearer case for X-ray fingerprinting, so we can try to fingerprint with unambigous X-ray energies and statistics. We have proven that setups like ours are able to do so in finite time for the heaviest man-made elements," he says.

Related Links

Phys Rev Lett 2013, in press

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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