Bulletin of the American Physical Society
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 |
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Chair: Jeff Blackmon, Louisiana State University Room: 103AB |
Wednesday, October 26, 2011 10:30AM - 11:00AM |
2WA.00001: Exploring the Nuclear Chart with LeRIBSS and IRIS-2 Invited Speaker: Robert Grzywacz Exploration of the unknown regions of the chart of the nuclei is essential to both nuclear structure and nuclear astrophysics. Decay spectroscopy studies often provide the first results in previously unexplored areas. The development of new instrumentation dictates the isotopic reach of experiments. New exploratory decay studies have been performed at the Holifield Radioactive Ion Beam Facility on very neutron-rich, medium-mass nuclei produced in the proton induced fission of $^{238}$U. A wealth of new data were obtained in the $^{78}$Ni region on the r-process path. New nuclear lifetimes, decay schemes and decay branching ratios were measured using the recently developed facilities: Low-energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS) and new Injector for Radioactive Ion Species (IRIS-2). The detailed studies of $^{79}$Cu, $^{83}$Zn and $^{85}$Ga were possible owing to the high production rates, isotopic purity and experimental sensitivities provided by these new devices. [Preview Abstract] |
Wednesday, October 26, 2011 11:00AM - 11:30AM |
2WA.00002: Measurement of the $^{25}$Al(d,n)$^{26}$Si(p) reaction at RESOLUT: Spectroscopy of $l=0$ and $l=1$ resonances Invited Speaker: Ingo Wiedenhoever Studies of rp-process nucleosynthesis in stellar explosions show that establishing the lowest $l=0$ and $l=1$ resonances is the most important step to determine reaction rates in the astrophysical $rp$--process path. In an experiment performed at the {\sc resolut} radioactive beam facility of Florida State University, we have studied the $\mathrm{^{25}Al(d,n)^{26}Si}$ reaction in inverse kinematics to establish the spectrum of the lowest $l=0$ and $l=1$ resonances. The spectrum is consistent with a previous experiment using the same reaction at {\sc resolut} [1] and results obtained from recent stable beam experiments [2].\\[4pt] [1] P.N. Peplowski {\it et al.} Phys.Rev.{\bf C 79}, 032801 (2009) \\[0pt] [2] K.A. Chipps {\it et al.} Phys.Rev. {\bf C 82}, 045803 (2010) [Preview Abstract] |
Wednesday, October 26, 2011 11:30AM - 12:00PM |
2WA.00003: Reaction dynamics near the barrier Invited Speaker: W. Loveland 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. [Preview Abstract] |
Wednesday, October 26, 2011 12:00PM - 12:30PM |
2WA.00004: Studies of heavy residues from peripheral collisions near the Fermi energy Invited Speaker: Sherry Yennello Neutron-rich nuclei have been produced in peripheral collisions near the Fermi energy. The heavy residues and intermediate mass fragments from the reactions of 86Kr, 64Ni and 136Xe beams with 112,124Sn and 58,64Ni targets have been measured with MARS and BigSol. Additionally the reactions of 86Kr and 64Ni on 208Pb have been studied. These experiments have been designed to study the deep inelastic reaction mechanism. The exchange of nucleons between projectile and target is dependent on the neutron-richness of the reaction partners and has been linked to the nuclear symmetry energy. Experimental results will be presented and compared with predictions of theoretical models. [Preview Abstract] |
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