2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011;
East Lansing, Michigan
Session 2WA: Workshop on New Insights in Nuclear Physics and Astrophysics from Stopped and Reaccelerated Rare Isotopes II
10:30 AM–12:30 PM,
Wednesday, October 26, 2011
Room: 103AB
Chair: Jeff Blackmon, Louisiana State University
Abstract ID: BAPS.2011.DNP.2WA.3
Abstract: 2WA.00003 : Reaction dynamics near the barrier*
11:30 AM–12:00 PM
Preview Abstract
Abstract
Author:
W. Loveland
(Oregon State University)
The availability of modest intensity (10$^{3}$-10$^{7}$ p/s)
radioactive
nuclear beams has had a significant impact on the study of
nuclear reactions
near the interaction barrier. The role of isospin in capture
reactions is a
case in point. Using heavy elements as a laboratory to explore these
effects, we note that the cross section for producing an
evaporation residue
is
\begin{displaymath}
\sigma_{EVR}(E_{c.m.}) = \sum\limits_{J=0}^{J_{max}}
\sigma_{CN}(E_{c.m.},J)W_{sur}(E_{c.m.},J)
\end{displaymath}
where $\sigma _{CN}$ is the complete fusion cross section and
W$_{sur}$ is
the survival probability of the completely fused system. The
complete fusion
cross section can be written as,
\begin{displaymath}
\sigma_{CN}(E_{c.m.}) = \sum\limits_{J=0}^{J_{max}}
\sigma_{capture}(E_{c.m.})P_{CN}(E_{c.m.},J)
\end{displaymath}
where $\sigma _{capture}$(E$_{c.m.}$,J) is the ``capture'' cross
section
at center-of mass energy E$_{c.m.}$ and spin J and P$_{CN}$ is the
probability that the projectile-target system will evolve inside
the fission
saddle point to form a completely fused system rather than
re-separating
(quasi-fission).
The systematics of the isospin dependence of the capture cross
sections has
been developed and the deduced interaction barriers for all known
studies of
capture cross sections with radioactive beams are in good
agreement with
recent predictions of an improved QMD model and semi-empirical
models. The
deduced barriers for these n-rich systems are lower than one
would expect
from the Bass or proximity potentials. In addition to the barrier
lowering,
there is an enhanced sub-barrier cross section in these n-rich
systems that
is of advantage in the synthesis of new heavy nuclei.
Recent studies of the ``inverse fission'' of uranium
($^{124,132}$Sn +
$^{100}$Mo) have yielded unexpectedly low upper limits for this
process due
apparently to low values of the fusion probability, P$_{CN}$.
The fusion of halo nuclei, like $^{11}$Li with heavy nuclei, like
$^{208}$Pb, promises to give new information about these and
related nuclei
and has led/may lead to unusual reaction mechanisms.
*This work was sponsored, in part, by the USDOE Office of Nuclear Physics
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.DNP.2WA.3