The claims for four new elements have been validated in two new reports from the IUPAC/IUPAP Joint Working Party (JWP) and accepted for publication in Pure and Applied Chemistry. The addition of the four, namely elements 113, 115,117, and 118, represents a significant milestone because it completes the seventh row of the Periodic Table. The new elements add to the remarkable progress in extending the periodic table following 114 and 116 validated in 2011, and element 112 validated in 2009. How much further the periodic table will extend is an open and interesting question.
The recent confirmation is the result of years of work to produce a few atoms of these new elements and validation experiments worldwide to confirm their existence. Discovery of new elements requires the use of particle accelerators to induce nuclear reactions that add protons to the nuclei of more common elements. To produce element 113 the group of Morita et al. at the RIKEN laboratory in Japan used a nuclear fusion reaction of zinc-70 with bismuth-209 in 2004 and were finally able to confirm the results in 2012 .In the course of their studies, they produced three atoms over an 8 year period. The particular nuclear reaction used by the Morita group is an example of what is known as “cold fusion” where the bombarding energy is relatively low and in these studies the radioactive alpha-decays can be traced to known elements. Additional key information came from experiments at the Heavy Ion Research Facility in Lanzhou China (HIRFL) as well as the Morita group themselves to confirm the steps in the decay chain of element 113, most importantly the decay of bohium-266.
The other three new elements were produced at the Joint Institute for Nuclear Research (JINR) in Russia using intense beams of the rare calcium isotope calcium-48 fused with actinide targets. The experiments were carried out at relatively higher bombarding energies than the element 113 experiments in so-called “hot fusion” reactions. The breakthrough of the new “hot fusion” approach produced elements 115, 117, and 118 and elements 114 and 116 in earlier experiments. The new element 115 was produced by calcium-48 fusion reactions on americium-243 and berkelium-249 targets by Yu. Ts. Oganessian and collaborators. The very rare berkelium-249 targets were produced from less than 50 mg of material produced at Oak Ridge National Laboratory at the High Flux Reactor. The targets are sufficiently radioactive that after about a year half of the target is californium. Element 117 was also produced at Dubna with the berkelium-249 target by a Dubna-Oak Ridge National Laboratory-Lawrence Livermore National Laboratory collaboration. Element 118 was produced in a similar way by fusing calcium-48 and a californium target by the Dubna-Oak Ridge National Laboratory-Lawrence Livermore National Laboratory collaboration. Important experiments confirming these results were performed at GSI Helmholtz zentrum für Schwerionen forschung in Darmstadt and Lawrence Berkeley National Laboratory in California. Among these there are the searches for X-rays, which are element specific, and would definitively identify the produced atoms and their decay products. The results were not conclusive but do point to a new generation of experiments that will definitively identify the element and isotope.
Researchers are continuing their searches for even heavier elements. Predictions on where the periodic table ends vary, but elements up to 170 may be possible. The limit chemically due to relativistic effects in the electron shells or the limit physically due to the binding of the nucleus is simply not known or currently predictable with any accuracy. Equally intriguing but also unknown is the possibility of very long-lived super-heavy isotopes. Some theories predict decay half-lives in the range of several years or longer for more neutron-rich isotopes of the known super-heavy elements.
Michigan State University
- Discovery of the elements with atomic numbers Z = 113, 115 and 117 (IUPAC Technical Report) (DOI 10.1515/pac-2015-0502)
- Discovery of the element with atomic number Z = 118 completing the 7th row of the periodic table (IUPAC Technical Report) (DOI 10.1515/pac-2015-0501)