IUPAC adds four superheavy elements to periodic table

The International Union for Pure and Applied Chemistry (IUPAC) welcomed the new year with a bang, confirming the discovery of four new elements and once again shaking up the periodic table. Elements 113, 115, 117 and 118 complete the seventh row of the table. Each has been assigned a temporary working name while the discoverers—from Japan, Russia and the USA—have been invited to suggest permanent names and symbols.

Elements beyond atomic number 104 are referred to as superheavy elements. Although superheavy 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—a very rare event—occasionally produces a superheavy element and generally only exists for a short time.

The discovery of heavier and heavier elements brings researchers one step closer to the “island of stability,” a term in nuclear physics that refers to the possible existence of a region beyond the current periodic table where new superheavy elements with special numbers of neutrons and protons would exhibit increased stability. Such an island would extend the periodic table to even heavier elements and support longer isotopic lifetimes to enable chemistry experiments.

“The chemistry community is eager to see its most cherished table finally being completed down to the seventh row,” said Professor Jan Reedijk, president of the Inorganic Chemistry Division of IUPAC. The proposed names and symbols will be checked by the Reedijk’s team for consistency, translatability into other languages, possible prior historic use for other cases, etc. New elements can be named after a mythological concept, a mineral, a place or country, a property or a scientist. After divisional acceptance, the names and two-letter symbols will be presented for public review for five months, before the highest body of IUPAC, the Council, will make a final decision on the names of these new chemical elements and the two-letter symbols used for each in the Periodic Table of the Elements.

“We are excited about these new elements, and we thank the dedicated scientists who discovered them for their painstaking work, as well the members of the IUPAC/IUPAP Joint Working Party for completing their essential and critically important task,” said IUPAC President Dr. Mark C. Cesa.

RIKEN in Japan was given priority for element 113, and a Joint Institute for Nuclear Research (JINR)-Lawrence Livermore National Laboratory (LLNL) collaboration was given priority for element 118. The JINR and the Oak Ridge (CSA CSM) and Lawrence Livermore national laboratories meanwhile met the criteria for the discovery of elements 115 and 117.

Element 113 is the first element on the periodic table discovered in Asia. In the late 1980s, a group led by Kosuke Morita began using RIKEN’s Linear Accelerator Facility and the GARIS ion separator to explore new synthetic superheavy elements. The work of discovering new superheavy elements is difficult as the elements tend to decay quickly. Isotopes for 113, for example, lasted for less than a thousandth of a second. The search at RIKEN for element 113 started in September 2003 when Morita’s group began bombarding a thin layer of bismuth with zinc ions traveling at about 10 percent the speed of light. Theoretically, these materials would occasionally fuse, forming an atom of element 113.

Less than a year later the team observed two atomic nuclei fusing, leading to the creation of a nucleus of element 113. It quickly underwent four alpha decays to transform into dubnium-262 (element 105), and then underwent spontaneous fission. A second event on April 2, 2005 resulted in identical decay and fission, but neither event demonstrated firm connections to known nuclides and thus were not considered conclusive evidence for the existence of 113.

“For over seven years,” said Morita, “we continued to search for data conclusively identifying element 113, but we just never saw another event. I was not prepared to give up, however, as I believed that one day, if we persevered, luck would fall upon us again.”

Luck held out until August 12, 2012, when the group observed a crucial third event. This time, following the four initial decays, the dubnium-262 continued to undergo alpha decays rather than spontaneous fission, transforming into lawrencium-258 (element 103) and then finally mendelevium-254 (element 101). As the chain had been clearly characterized, it demonstrated clearly that element 113 was the source of the decay chain.

“Now that we have conclusively demonstrated the existence of element 113,” Morita said, “we plan to look to the uncharted territory of element 119 and beyond, aiming to examine the chemical properties of the elements in the seventh and eighth rows of the periodic table, and someday to discover the island of stability.”

LLNL teamed with JINR in 2006 to discover element 118, and both institutions collaborated with ORNL and others for the discovery of element 115 in 2004 and element 117 in 2010.

“I am so proud of all of the hard work that this group has done over the years performing these experiments,” said Dawn Shaughnessy, Lawrence Livermore’s principal investigator for the Heavy Element Group. “Our colleagues in Russia have worked endless hours at the accelerator working toward these results. It is a wonderful gift to the entire group that we are recognized for our efforts in accomplishing these highly difficult experiments and for the years of work it takes to successfully create a new chemical element.”

This discovery brings the total to six new elements reported by the Dubna-Livermore team (113, 114, 115, 116, 117, and 118, the heaviest element to date). The LLNL/JINR team submitted a paper on the discovery of elements 113 about the same time as RIKEN.

Six atoms of element 117 were originally observed in 2010 during six months of intense bombardment of a berkelium target from Oak Ridge National Laboratory (ORNL) with calcium ions at one of the world’s most powerful heavy ion accelerators at JINR. 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.

“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,” said ORNL director Thom Mason. “The results demonstrate the power of international collaboration for addressing complex challenges in science.”

The berkelium target material was produced during a six-month irradiation in the world’s most intense thermal neutron flux at ORNL’s High Flux Isotope Reactor, a DOE Office of Science User Facility. The resulting product was separated and processed during a three-month campaign at ORNL’s Radiochemical Engineering Development Center, resulting in 22 milligrams of ultrapure berkelium. In addition to providing this unique target material, ORNL participated in all aspects of the experiments and contributed advanced detector technology to the effort.

“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,” says ORNL’s Jim 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 island of stability, originally proposed by Glenn Seaborg in the 1960s, 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 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.

Elements 115 and 117 bring to three the number of new chemical elements discovered by ORNL with its collaborators. 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.