FY2010 - Oak Ridge National Laboratory

Director’s R&D Fund—
General
supported by the DOE Office of Science for the studies of new super heavy nuclei, also helps the nuclear
security and nuclear forensic fields, where the efficient detection of different kinds of radiation is
important. These electronics may be operated in various modes adapting to changing experimental
conditions thanks to their digital and programmable circuitry.
While at present there are two laboratories capable and authorized to run intense 48 Ca and 50 Ti beams
(above 1 particle-microampere) on radioactive trans-actinides targets (JINR Dubna, Russia, and GSI
Darmstadt, Germany), two other laboratories are coming on-line and intending to pursue the super heavy
elements studies, Spiral 2 part of GANIL at Caen, France, and RIKEN near Tokyo, Japan. Success of the
current experiment on element Z=117 (with ORNL-produced target material) created a high demand for
the continuation of trans-plutonium elements production and chemistry at HFIR/REDC. We expect it will
lead to the creation of a new program at DOE targeting super-heavy element research. Already now, in
addition to the ongoing joint project at Dubna, GSI Darmstadt and GANIL Caen are proposing
collaboration with ORNL, to jointly continue research on super heavy elements.
Within this project, 30 mg of 243 Am oxide were provided in September 2010 for a new joint experiment
on Z=115 isotopes aiming for a direct Z-identification of SHE decay products, to be performed at the
TASISpec facility (GSI, Darmstadt, Germany) in 2011. A new digital data acquisition system (concept
developed through this project) is foreseen to be used in 2012 in the experiment searching a new element
Z=120 at the SHIP facility (GSI Darmstadt).
Results and Accomplishments
Over 22 mg of 249 Bk activity (having a half-life of 320 days) were separated at the ORNL REDC, from
over 50 g of curium and americium seed material irradiated with neutrons at the ORNL HFIR for about
two years. The project co-author, J. Ezold (ORNL NSTD), was the trans-plutonium “campaign 74”
manager at REDC. Following the Material Transfer and Scientific Collaboration Agreement, established
in 2009 between ORNL and JINR Dubna, this material was transferred to Russia within three weeks after
final purification. Six 249 Bk arc-shaped targets, suitable for irradiation with intense heavy-ions beams,
were made at IAR Dimitrovgrad. The irradiations at the DGFRS started in July at the FLNR Dubna and
lasted till the end of February 2010, with a total of about 150 days with beam on target and a total beam
dose of 4.4 10 19 projectiles. K. Rykaczewski and J. Roberto participated in the experiment in August
2009 and September 2009. Two isotopes of new chemical element Z=117 were identified among fusionevaporation
reaction products. Five decay chains of 293(117) isotope and one long decay chain starting at
294(117) isotope were observed, leading to the identification of 11 new super heavy nuclei. These results
were published in Physical Review Letters 104, 142502 in April 2010. Measured alpha-decay properties
for newly identified super heavy nuclei indicated an increased stability with larger neutron number. It
represents an experimental verification for the existence of the predicted Island of (Enhanced) Stability
for Super Heavy Elements.
This publication triggered a lot of popular and scientific media attention—the news on the discovery of
element 117 appeared in New York Times, Science, and Physics Today, and garnered over two hundred
other articles.
The new digital data acquisition system foreseen to be used during the search for Z>117 chemical
elements has been designed by two project participants, R. Grzywacz and K. Rykaczewski. The first
items related to this novel digital data acquisition system, the equipment and software, were delivered in
September 2009. Further hardware purchases will follow the funding ($435,000) recently received from
DOE for continuation of the studies on super heavy nuclei.
168