Twenty-two milligrams of a very pure synthetic material produced at Oak Ridge National Laboratory were used in the discovery of two new chemical elements that will help fill out the seventh row of the periodic table.
The synthetic element, berkelium-249, was produced in a project that started with a six-month irradiation of a target material at the High Flux Isotope Reactor at ORNL. The resulting product was separated and processed during a three-month period at the lab’s Radiochemical Engineering Development Center.
The berkelium-249 was then shipped to the Joint Institute for Nuclear Research, or JINR, in Dubna, Russia, where it was intensely bombarded, or irradiated, with calcium-48 ions, creating six atoms of element 117, said Jim Roberto, ORNL associate lab director for science and technology partnerships. Berkelium-249, which does not exist in nature, has a 300-day lifetime, so researchers had a short time to do their experiments.
Element 117 is one of four new elements that have been officially verified by the International Union for Pure and Applied Chemistry. The IUPAC announced the discoveries on December 30. The other three are elements 113, 115, and 118. Element 115 is produced when element 117 decays.
The IUPAC recognized ORNL and its collaborators, the JINR and Lawrence Livermore National Laboratory in California, for the discovery of elements 115 and 117. The RIKEN collaboration team in Japan discovered element 113, and the Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory discovered element 118.
Roberto said the researchers have extended the periodic table to new nuclei with more neutrons and more protons. They have been invited to submit names and symbols for the new elements.
“These new elements expand our understanding of the nucleus, extend the periodic table, and provide evidence for the possibility of discovery of even heavier nuclei,” ORNL Director Thom Mason said. “The results demonstrate the power of international collaboration for addressing complex challenges in science.”
In addition to providing the unique target material for the discovery of element 117, ORNL said it also took part in all aspects of the experiments and contributed advanced detector technology. The High Flux Isotope Reactor, where some of the work occurred, is described as the world’s most intense thermal neutron flux.
“Six atoms of element 117 were originally observed in 2010 during six months of intense bombardment of a berkelium target from ORNL with calcium ions at one of the world’s most powerful heavy ion accelerators at JINR,” the lab said. “Atoms of element 115, originally seen in earlier experiments at JINR, were also produced in the 2010 experiment from the decay of element 117. These results for elements 115 and 117 were confirmed in 2012 and 2013 by additional experiments at JINR and at GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. Vanderbilt University and the University of Tennessee, Knoxville, also participated in the experiments.”
The four new elements fill out the seventh row, or period, of the periodic table. The last time new elements were added to the periodic table was in 2011, when elements 114 (flerovium, or Fl) and element 116 (livermorium or Lv) were added.
“The discovery of new elements is actually very exciting on a number of different levels, and what we have done with our partners is change the periodic table, and we have changed every high school chemistry book,” Roberto said in an ORNL video.
Including elements 115 and 117, ORNL and its collaborators have now discovered three chemical elements. Element 61, promethium, was originally observed in 1945 from the chemical analysis of fission products at ORNL’s Graphite Reactor.
“Overall, isotopes from ORNL have helped enable the discovery of nine chemical elements,” the lab said.
Roberto said the IUPAC reviewed the published results of experiments and follow-up experiments.
“These extreme nuclei are very sensitive tests of our understanding of nuclear physics,” he said.
ORNL said official recognition of these new elements “provides evidence for the long-sought island of stability for superheavy elements.” The island of stability was originally proposed by Glenn Seaborg in the 1960s, and it refers to a region beyond the current periodic table where superheavy nuclei with enhanced lifetimes may exist. Such an “island” would extend the periodic table to even heavier elements, and the increased lifetimes would enable chemistry experiments on these elements.
“The element 117 results include the observation of 11 new heavy isotopes that represent our closest approach to date to the proposed island of stability,” said Roberto, who played a major role in forming the collaboration with JINR, LLNL, UT, and Vanderbilt. “These new isotopes continue a trend toward increasing stability with increasing neutron number for superheavy elements, providing evidence for the existence of the island.”
The lab said the Russia-U.S. collaboration is currently searching for even heavier nuclei at JINR using a unique target of a mixture of californium isotopes, a byproduct of decades of californium-252 production at ORNL. A new detection system for radioactive nuclei developed at ORNL and UT is enhancing the discovery capability of this experiment.
More information will be added as it becomes available.
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