A new chemical element has been added to the Periodic Table: A paper on the
discovery of element 117 has been accepted for publication in Physical Review
Letters.
Oak Ridge National Laboratory is part of a team that includes the Joint
Institute of Nuclear Research (Dubna, Russia), the Research Institute for
Advanced Reactors (Dimitrovgrad), Lawrence Livermore National Laboratory,
Vanderbilt University and the University of Nevada Las Vegas.
Berkelium-249, contained in the greenish fluid in the tip of the vial, was crucial to the experiment that discovered element 117. It was made in the research reactor at DOE's Oak Ridge National Laboratory.
ORNL's role included production of the berkelium-249 isotope necessary for
the target, which was subjected to an extended, months-long run at the heavy ion
accelerator facility at Dubna, Russia.
"Without the berkelium target, there could have been no experiment," says
ORNL Director of Strategic Capabilities Jim Roberto, who is a principal author
on the PRL paper and who helped initiate the experiment.
The berkelium was produced at the High Flux Isotope Reactor and processed at
the adjoining Radiochemical Engineering & Development Laboratory as part of
the most recent campaign to produce californium-252, a radioisotope widely used
in industry and medicine.
"Russia had proposed this experiment in 2004, but since we had no californium
production at the time, we couldn't supply the berkelium. With the initiation of
californium production in 2008, we were able to implement a collaboration,"
Roberto says.
Professor Joe Hamilton of Vanderbilt University (who helped establish the
Joint Institute for Heavy Ion Research at ORNL) introduced Roberto to Yuri
Oganessian of Russia's JINR. Five months of the Dubna JINR U400 accelerator's
calcium-48 beam--one of the world's most powerful--was dedicated to the
project.
The massive effort identified a total of six atoms of element 117 and the
critical reams of data that substantiate their existence.
The two-year experimental campaign began with a 250-day irradiation in HFIR,
producing 22 milligrams of berkelium-249, which has a 320-day half-life. The
irradiation was followed by 90 days of processing at REDC to separate and purify
the berkelium. The Bk-249 target was prepared at Dimitrovgrad and then bombarded
for 150 days at the Dubna facility.
Lawrence Livermore, which now has been involved in the discovery of six
elements with Dubna (113, 114, 115, 116, 117, and 118), contributed data
analysis, and the entire team was involved in the assessment of the results.
This is the second element that ORNL has had a role in discovering, joining
element 61, promethium, which was discovered at the Graphite Reactor during the
Manhattan project and reported in 1946. ORNL, by way of its production of
radioisotopes for research, has contributed to the discovery of a total of seven
new elements.
Members of the ORNL team include the Physics Division's Krzysztof Rykaczewsi,
Porter Bailey of the Nonreactor Nuclear Facilities Division, and Dennis Benker,
Julie Ezold, Curtis Porter and Frank Riley of the Nuclear S&T Division.
Roberto says the success of the element-117 campaign underscores the value of
international collaborations in science.
"This use of ORNL isotopes and Russian accelerators is a tremendous example
of the value of working together," he says.
"The 117 experiment paired one of the world's leading research
reactors--capable of producing the berkelium target material--with the
exceptional heavy ion accelerator and detection capabilities at Dubna."
Islands of Stability
Roberto also says the experiment, in addition to discovering a new chemical
element, has pushed the Periodic Table further into the neutron-rich regime for
heaviest elements.
"New isotopes observed in these experiments continue a trend toward higher
lifetimes for increased neutron numbers, providing evidence for the proposed
"island of stability" for super-heavy nuclei," he says.
"Because the half-lives are getting longer, there is potential to study the
chemistry of these nuclei," Roberto says. "These experiments and discoveries
essentially open new frontiers of chemistry."
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