The human element
If it’s a been a few years—or decades—since you last opened your high school chemistry textbook, its periodic table, that guiding force for chemists worldwide, is almost certainly out of date. Scientists are constantly pushing the boundaries of chemistry and physics in their search for new elements, a quest that ORNL staff and facilities have supported since the lab’s inception in the 1940s.
The United Nations declared 2019 as the International Year of the Periodic Table, recognizing the scientific significance of the chemical categorization system and celebrating a century and a half of scientific discovery since Dmitri Mendeleev first organized elements into the format we know today. Every atom is a specific element depending on the number of protons in its nucleus.
“When you look at any element on the periodic table, you are looking at a building block of the known universe,” said James Roberto, retired ORNL associate laboratory director. “The beauty of the table is that the position of an atom in the table helps you describe its properties. But looking closer, there’s actually a story behind each one—a story of discovery.”
ORNL’s story in element discovery began in secret during the Manhattan Project, as scientists analyzed fission products from the X-10 Graphite Reactor. At that time, the periodic table had gaps, places where radioactive elements were anticipated to exist but where they hadn’t yet been confirmed because of their relatively short half-lives. ORNL chemists filled one of the gaps in 1945 by separating the missing element 61 from irradiated uranium fuel. They named it promethium, born of fire in the world’s first continuously operated nuclear reactor.
Building on the Graphite Reactor’s success in producing isotopes following the war, the research community began looking at ways to study and produce elements beyond plutonium, or element 94. That led to construction of the High Flux Isotope Reactor at ORNL in 1965.
“The intense thermal neutron flux of HFIR enabled it to produce transplutonium isotopes such as californium and berkelium in quantities that allowed the development of the new field of heavy element chemistry,” Roberto said. “The adjacent Radiochemical Engineering Development Center provided a unique capability to do very high-precision chemical separations and obtain very pure products of these isotopes.”
A half century later, HFIR and REDC continue to be the world’s principal source of transplutonium isotopes.
Isotopes produced at HFIR have been sent to accelerator facilities in California and Russia, where they have been used as target materials enabling discoveries of many new elements. In the 2000s, ORNL researchers also became more involved as scientific collaborators, developing and supplying state-of-the-art digital electronics critical to element discovery.
“This is big science that works best when large groups who represent the best capability in their particular area can work together,” Roberto said.
A U.S.-Russian experiment in 2009 led to the lab’s second official element discovery—element 117, which was announced in 2010 and named tennessine to recognize the contributions of ORNL and its Tennessee university partners, the University of Tennessee and Vanderbilt. ORNL’s third new element, moscovium, was discovered in the same collaboration as a decay product of tennessine.
After seven decades of shaping the periodic table, ORNL researchers aren’t resting on their laurels. They’re already involved in experiments to look for elements 119 and 120, using targets produced at ORNL and irradiated in accelerators in Japan and Russia.
“The idea of playing a small part in discovering a new element is very exciting,” said Shelley VanCleve of ORNL’s Isotope and Fuel Cycle Technology Division. “With each campaign we have learned something new, expanding on our techniques to provide a quality product. The gratitude and excitement of those researchers receiving the material feeds our desire to do more.”
The effort is driven in part by the search for the “island of stability,” where scientists anticipate that superheavy elements will have longer lifetimes, enabling detailed studies of the chemistry and physics of these extreme atoms and nuclei.
“We don’t think the periodic table ends at 120,” Roberto said. “However, discovery times are getting longer, and new approaches will be needed to go further.”
ORNL and its international partners are betting that scientific progress and ingenuity will allow the discovery stories to continue.
“The researchers in superheavy element production make up a very small community worldwide, but the passion and excitement they possess for their work make me think the ‘island of stability’ is within reach,” VanCleve said.