Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session D2: Bethe and Bonner Prizes |
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Sponsoring Units: DNP Chair: Lawrence Cardman, Thomas Jefferson National Accelerator Facility Room: Thurgood Marshall East |
Saturday, February 13, 2010 1:30PM - 2:06PM |
D2.00001: Hans A. Bethe Prize Talk: LUNA: a Laboratory Underground for Nuclear Astrophysics Invited Speaker: C. Rolfs It is in the nature of astrophysics that many of the processes and objects one tries to understand are physically inaccessible. Thus, it is important that those aspects that can be studied in the laboratory be rather well understood. One such aspect are the nuclear fusion reactions, which are at the heart of nuclear astrophysics: they influence sensitively the nucleosynthesis of the elements in the earliest stages of the universe and in all the objects formed thereafter, and control the associated energy generation, neutrino luminosity, and evolution of stars. I review a new experimental approach for the study of nuclear fusion reactions based on an underground accelerator laboratory, named LUNA. [Preview Abstract] |
Saturday, February 13, 2010 2:06PM - 2:42PM |
D2.00002: Tom W. Bonner Prize in Nuclear Physics Talk: Nuclear Forces and the Universe Invited Speaker: Robert Wiringa A major goal in nuclear physics is to understand how nuclear binding, structure, and reactions can be obtained from the underlying interactions between individual nucleons. Significant progress in formulating realistic Hamiltonian descriptions of nuclear interactions, and in accurately solving the many-nucleon Schr\"odinger equation, has been made over the past two decades. This includes the development of a number of two-nucleon ($N\!N$) potentials that accurately reproduce elastic $N\!N$ scattering data and deuteron properties, as well as consistent three-nucleon ($3N$) potentials and multi-nucleon charge and current operators. Using sophisticated many-body theory, such as the quantum Monte Carlo (QMC) methods described in the following talk, we find that realistic Hamiltonians can indeed reproduce the structure and reactions of light nuclei extremely well. The interactions that reproduce $N\!N$ scattering are quite complicated, including central, spin, isospin, tensor, and spin-orbit terms. One-pion exchange between nucleons and iterated two-pion exchange with intermediate-$\Delta$ excitations, which contributes to both $N\!N$ and $3N$ potentials, are crucial components. Using fully realistic potentials and progressively simplified versions in our QMC calculations, we have studied what elements of these forces are necessary to get some key features of nuclear structure, like the absence of stable five- and eight-body nuclei. This absence is important for primordial nucleosynthesis and the long-lived stability of stars like our sun. We can also study the sensitivity of nuclear binding to possible variations in hadronic masses. Thus we can address several questions about how ``fine-tuned'' our universe is. [Preview Abstract] |
Saturday, February 13, 2010 2:42PM - 3:18PM |
D2.00003: Tom W. Bonner Prize in Nuclear Physics Talk: Finding Real Nuclei in Imaginary Time Invited Speaker: Steven C. Pieper Ab initio calculations of nuclei treat a nucleus as a system of $A$ nucleons interacting by realistic two- ($N\!N$) and three-nucleon ($N\!N\!N$) forces. Variational Monte Carlo (VMC) followed by Green's function Monte Carlo (GFMC) is a very successful ab initio method for light nuclei. The VMC gives an upper bound to the true energy of a nucleus for a given Hamiltonian; the closeness of the upper bound to the exact solution of the Schr\"odinger equation depends on the physical insight built into the trial wave function, $\Psi_T$, that is used. GFMC starts with a $\Psi_T$ and, by propagation in imaginary time, allows the exact lowest eigenenergy for a given set of quantum numbers to be computed. The first VMC calculations of nuclei were published in 1981 by Lomnitz-Adler, Pandharipande, and Smith. They were for $^3$H and $^4$He using the Reid $N\!N$ potential. Six years later, Carlson published the first GFMC calculations of nuclei, again for $^3$H and $^4$He, but using a slightly-simplified $N\!N$ potential; in the following year he used the full Reid V8 potential. Pudliner, Pandharipande, Carlson, and Wiringa published GFMC calculations of $A$=6 nuclei in 1995, using the Argonne V18 $N\!N$ potential and the Urbana IX $N\!N\!N$ potential. Since then there has been steady progress in applying GFMC to larger nuclei. This has been from both increasing computer power and new or improved algorithms. The largest computers are increasingly difficult to use efficiently, but, as a result of a SciDAC collaboration, we now get excellent scalability up to 131,000 cores on Argonne's IBM Blue Gene/P. In addition we have found that the GFMC can be used for multiple states with the same quantum numbers. With the Argonne V18 and Illinois $N\!N\!N$ potentials, we obtain an excellent description of the properties of nuclei up to $A = 12$. I will describe these methods, present recent advances in using the largest computers, and some recent results. [Preview Abstract] |
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