An international team of scientists from Russia and the United States, including
two Department of Energy national laboratories and two universities, has discovered
the newest superheavy element, element 117.
Illustration of the newly created element 117. Animation by Kwei-Yu Chu/LLNL
The team included scientists from the Joint Institute of Nuclear Research (Dubna,
Russia), the Research Institute for Advanced Reactors (Dimitrovgrad), Lawrence
Livermore National Laboratory, Oak Ridge National Laboratory, Vanderbilt
University, and the University of Nevada, Las Vegas.
“The discovery of element 117 is the culmination of a decade-long journey
to expand the periodic table and write the next chapter in heavy element research,”
said Academician Yuri Oganessian, scientific leader of the Flerov Laboratory
of Nuclear Reactions at JINR and spokesperson for the collaboration.
The team established the existence of element 117 from decay patterns observed
following the bombardment of a radioactive berkelium target with calcium ions
at the JINR U400 cyclotron in Dubna. The experiment depended on the availability
of special detection facilities and dedicated accelerator time at Dubna, unique
isotope production and separation facilities at Oak Ridge, and distinctive nuclear
data analysis capabilities at Livermore.
“This is a significant breakthrough for science,” LLNL director
George Miller said. “The discovery of a new element provides new insight
into the makeup of the universe and is a testimony to the strength of science
and technology at the partner institutions.”
“This collaboration and the discovery of element 117 demonstrates the
fundamental importance of scientists from different nations and institutions
working together to address complex scientific challenges,” ORNL Director
Thom Mason added.
The two-year experimental campaign began at the High Flux Isotope Reactor in
Oak Ridge with a 250-day irradiation to produce 22 mg of berkelium. This was
followed by 90 days of processing at Oak Ridge to separate and purify the berkelium,
target preparation at Dimitrovgrad, 150 days of bombardment at one of the world’s
most powerful heavy ion accelerators at Dubna, data analysis at Livermore and
Dubna, and assessment and review of the results by the team. The entire process
was driven by the 320-day half-life of the berkelium target material.
The experiment produced six atoms of element 117. For each atom, the team
observed the alpha decay from element 117 to 115 to 113 and so on until the
nucleus fissioned, splitting into two lighter elements. In total, 11 new “neutron-rich”
isotopes were produced, bringing researchers closer to the presumed “island
of stability” of superheavy elements.
The island of stability is 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.
Element 117 was the only missing element in row seven of the periodic table.
On course to the island of stability, researchers initially skipped element
117 due to the difficulty in obtaining the berkelium target material. The observed
decay patterns in the new isotopes from this experiment, as close as researchers
have ever approached the island of stability, continue a general trend of increasing
stability for superheavy elements with increasing numbers of neutrons in the
nucleus. This provides strong evidence for the existence of the island of stability.
“It fills in the gap and gets us incrementally closer than element 116
— on the edge of the island of stability,” said Ken Moody, one of
the LLNL collaborators and a long term veteran of superheavy element research.
“The experiments are getting harder, but then I thought we were done 20
years ago.”
This discovery brings the total to six new elements discovered by the Dubna-Livermore
team (113, 114, 115, 116, 117, and 118, the heaviest element to date). This
is the second new element discovery for Oak Ridge (61 and 117). In addition,
Oak Ridge isotopes have contributed to the discovery of a total of seven new
elements.
Since 1940, 26 new elements beyond uranium have been added to the periodic
table.
“These new elements expand our understanding of the universe and provide
important tests of nuclear theories,” said Vanderbilt University Professor
of physics Joe Hamilton. “The existence of the island of stability, a
pure theoretical notion in the 1960s, offers the possibility of further expansion
of the periodic table with accompanying scientific breakthroughs in the physics
and chemistry of the heaviest elements.”