Physicists at GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany, have used calcium-ion beams and radioactive berkelium-249 to produce two atoms of the element with atomic number 117, which bears the temporary name Ununseptium (one-one-seven in Latin).
Decay chains assigned to the element 117: experimental energies of all events together with their digitized traces are shown; boxes with triangles are corresponding to events observed during beam-off periods. Image credit: J. Khuyagbaatar et al / Phys. Rev. Lett.
Elements beyond atomic number 104 are referred to as superheavy elements. The most long-lived ones are expected to be situated on a so-called ‘island of stability.’
Although these elements have not been found in nature, they can be produced by accelerating beams of nuclei and shooting them at the heaviest possible target nuclei. Fusion of two nuclei occasionally produces a superheavy element. They generally only exist for a short time.
The element 117 was first detected in 2010 by a Russia-U.S. team at the Joint Institute for Nuclear Research in Dubna, Russia.
In the same year, physicists from GSI Helmholtz Center for Heavy Ion Research in Darmstadt teamed up with scientists from Japan, the United States, UK, Australia, Sweden, India, Norway, Finland, Switzerland and Poland, to confirm its existence.
A special berkelium target, essential for the synthesis of element 117, was produced at the Oak Ridge National Laboratory in Oak Ridge, Tennessee. About 13 milligrams of the highly-purified isotope berkelium-249, which has a half-life of only 330 days, were then transported to Germany.
In their experiments in Germany, the physicists bombarded a berkelium target with calcium ions until they collided and formed element 117. The element 117 then decayed into elements 115 and 113.
“The successful experiments on element 117 are an important step on the path to the production and detection of elements situated on the ‘island of stability’ of superheavy elements,” said Prof Horst Stöcker from GSI Helmholtz Center for Heavy Ion Research.
The scientists also identified both a previously unknown alpha-decay pathway in dubnium-270 and a new isotope of lawrencium, Lr-266. With half-lives of about one hour and about 11 hours respectively, they are among the longest-lived superheavy isotopes known to date.
“This is of paramount importance as even longer-lived isotopes are predicted to exist in a region of enhanced nuclear stability,” said Dr Christoph Düllmann, also from GSI Helmholtz Center for Heavy Ion Research, who is a co-author of the paper published in the Physical Review Letters.
The next step is for the International Union of Pure and Applied Chemistry (IUPAC) to accept the confirmation.
The IUPAC will review the new findings and the original research and decide whether further experiments are needed before acknowledging the element’s discovery.
After acceptance, IUPAC would determine which institution may propose official names.
______
J. Khuyagbaatar et al. 2014. Ca48+Bk249 Fusion Reaction Leading to Element Z=117: Long-Lived α-Decaying Db270 and Discovery of Lr266. Phys. Rev. Lett. 112, 172501; doi: 10.1103/PhysRevLett.112.172501
