77th Annual Meeting of the Southeastern Section of the APS
Volume 55, Number 10
Wednesday–Saturday, October 20–23, 2010;
Baton Rouge, Louisiana
Session FA: Pygmies, Superheavies, and Magic: The Exotica of Nuclear Structure
8:30 AM–10:30 AM,
Friday, October 22, 2010
Nicholson Hall
Room: 119
Chair: Paul Cottle, Florida State University
Abstract ID: BAPS.2010.SES.FA.2
Abstract: FA.00002 : Synthesis of a new element with Z=117*
9:00 AM–9:30 AM
Preview Abstract
Abstract
Author:
Joseph Hamilton
(Vanderbilt University)
The synthesis of new elements with neutron number (N) approaching
184
provide important tests of nuclear structure models used to
predict closed
spherical shells in the heaviest elements. Earlier, elements with
Z=113-116,
and 118 were synthesized in reactions of $^{48}$Ca with actinide
targets at
JINR. The synthesis of previously unknown Z=117 can provide
additional
crucial tests of the shell structure near the predicted Island of
Stability
with N=184. Here we report the synthesis of $^{293,294}$117
(N=176,177) in
the $^{48}$Ca + $^{249}$Bk 4n and 3n reactions. The $^{249}$Bk
was produced
at ORNL in the High Flux Isotope Reactor and chemically separated
at the
Radiochemical Engineering Development Center at ORNL. Six
arc-shaped targets
of 0.31 mg/cm$^{2}$ of $^{249}$Bk were made at the Research
Institute of
Atomic Reactors (Dimitrovgrad). The experiments were performed
employing the
Dubna Gas-Filled Recoil Separator and the heavy-ion cyclotron
U-400 at JINR,
Russia. Separated evaporation residues were registered by a
time-of-fight
system and implanted in a 4 cm x 12 cm Si-detector array with 12
vertical
position-sensitive strips surrounded by eight 4 cm x 4 cm side
detectors.
Irradiation at 252 MeV for 70 days starting July 27, with a total
beam dose
of 2.4 x 10$^{19}$ yielded five position-correlated ($\le $1.2mm)
decay
chains of 3 $\alpha $'s followed by spontaneous fission. These
were assigned
to $^{293}$117 produced in the 4n reaction. At a $^{48}$Ca energy
of 247 MeV
a new decay chain was detected involving six consecutive $\alpha
$-decays
and ending in SF and assigned to $^{294}$117 (3n channel). The
daughters of
$^{293,294}$117 have one or two more neutrons than previously
observed
isotopes and have much longer half-lives. The decays of the
eleven newly
identified isotopes expand substantially our knowledge of odd-Z
nuclei of
the most neutron-rich isotopes of elements 105 to 117. These
nuclei display
increasing stability with increase in neutron number to strongly
support the
island of stability. Their longer half lives open up further
studies of the
chemistry of super-heavy elements and their place in the Periodic
Table.
*For the Joint Institute for Nuclear Research, Oak Ridge National Lab, Vanderbilt U, Lawrence Livermore National Lab, Research Institute of Atomic Reactors, and U. Nevada LV collaboration.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2010.SES.FA.2