Spring 2007 Nuclear Physics Seminar Schedule |
Unless otherwise noted, the nuclear physics seminars are held on Mondays, at 2:20 p.m. in Room 201 of UTK's Nielsen Physics Building. Abstracts are included below the schedule. The UTK Physics Colloquium Schedule and ORNL Physics Division Seminar Schedule might also be of interest. Professor Witek Nazarewicz is chair of the seminar program. He may be contacted via e-mail at: witek @ utk.edu. |
Soren Sorensen
University of Tennessee
Heavy Flavor Physics at RHIC and LHC
The current status of physics related to the production and propagation of heavy quarks (charm and bottom) in ultra relativistic heavy ion collisions will be reviewed. I will also briefly review the prospects for this field over the next 5 years both at RHIC and the new LHC in Geneva.
Iain Darby,
University of Tennessee/ORNL
In-beam and decay spectroscopy using JUROGAM + RITU + GREAT
I will present recent results from experiments performed at the accelerator laboratory of the University of Jyväskylä. I will include highlights demonstrating the ability of this setup to study heavy neutron-deficient nuclei and conclude with the first observation of the new proton emitting nuclide, 159Re. I will conclude with considering the implications of these results for future experimental investigations into even more proton unbound nuclei using in-flight separation methods.
Ted Barnes,
University of Tennessee/ORNL
The NN Force and Meson Exchange Models
The microscopic QCD mechanisms underlying much of the NN force remain poorly understood, despite over 50 years of work on this subject. There is general agreement that the long ranged part of the NN force is due to meson exchange and that the short ranged core is likely due to quark-gluon forces, but the origin of the crucial intermediate ranged attraction remains obscure. In this talk I will summarize the status of our work on the NN force. We revisit the "traditional" meson exchange models, and have augmented them with quark model calculations of the nucleon-meson coupling constants, which are normally taken to be free parameters fitted to data. This is a progress report rather than a definitive answer.
Krzysztof Miernik,
Institute of Experimental Physics,
Warsaw University, Poland
Digital photography of nuclear decays
I will present the capabilities of taking digital photography of nuclear
decays with Optical Time Projection Chamber (OTPC). OTPC is a gaseous
detector designed for three-dimensional measurements of the topology of
45Fe two-proton radioactive decay. The experiment on 45Fe decay is
scheduled for early February 2007 at the National Superconducting
Cyclotron Laboratory (MSU).
The measurements performed last year at Dubna (Russia) at Acculinna
separator will be presented. The results include images of beta-delayed
proton emission from 13O as well as beta-delayed double-alpha decay of
8Be and triple alpha decay of 12C.
Andy Chae,
University of Tennessee
Interference effects among J,pi=3/2+ resonances in 19Ne system
The 18F(p,alpha)15O reaction plays a crucial role in understanding both gamma-ray emission from novae during the first several hours after the expansion and heavy element production in the higher temperature environments of x-ray bursts. The interference effects among J,pi=3/2+ resonances in the 18F+p system, however, have never been measured. The interference has a significant effect on the reaction rate at nova temperatures. An excitation function for the 1H(18F,alpha)15O reaction has been measured using radioactive 18F beams at the Holifield Radioactive Ion Beam Facility in order to study the interference effect. By comparing the measured cross section with theoretical calculations, we could provide the first experimental constraints on the relative signs of reduced widths for all three of the interfering resonances.
Krzysztof Rykaczewski, ORNL
Studies beyond the limits of bound nuclei: proton radioactivity
One of the main nuclear science question is related
to the limits of nuclear existence. What combinations
of protons and neutrons are forming bound nuclei?
Studies of proton radioactivity are going even further,
addressing the physics of nuclei beyond the proton drip line.
In this context, I'll review the investigations
of proton emission performed at the Recoil Mass Separator
at the Holifield Radioactive Ion Beam Facility at Oak Ridge.
It will include recent results on the fine
structure in proton emission of deformed states in 141Ho,
I'll share my view on the near future of proton radioactivity
studies at the HRIBF.
Nicolas Schunck, University of Tennessee/ORNL
Exotic Nuclear Shapes
The nuclear shape is a powerful tool to investigate very fundamental mechanisms that govern the nuclear stability. Many aspects of deformation in atomic nuclei were studied in the past, both on a theoretical and experimental level but, to a large extent, only nuclei with small to moderate quadrupole deformation have been considered. The situation is thus markedly different from other many-body fermionic systems such as clusters or molecules where all sorts of complex geometries are possible. This difference is usually put down to the nuclear surface tension effects that strongly deter such fancy shapes. Only recently was it suggested that nuclei could have low-lying excited states with the tetrahedral symmetry, and several independent calculations pointed out to significant tetrahedral minima in a few regions of the nuclear chart. I will discuss various aspects of such exotic symmetries in the specific context of nuclear physics: realization, influence on the shell structure, potential candidates. The most general framework to think of exotic shapes is the mean-field theory. I will also say a few words about the experimental signatures one may expect.
Jimmy Rotureau, University of Tennessee
Density Matrix Renormalization Group Approach for many-body open quantum
systems
We have applied the Density Matrix Renormalization Group (DMRG) method
in the context of the Gamow Shell Model (GSM)[1]. In this model, which
describes the configuration mixing in open quantum many-body system, the
completeness relation is resolved in the Berggren ensemble consisting
of bound states, resonant states (Gamow states) and complex energy continuum
states.
The eigenvalue problem is inherently non-hermitian and given
by complex-symmetric matrix with complex eigenvalues. Inclusion of resonances
and associated continuum states leads to an explosive growth
of the size of the multiconfigurational space and standard diagonalization
methods cannot be applied. To deal with this difficulty, we have
solved the GSM problem using the DMRG technique in the J-scheme.
This choice ensures the total angular momentum conservation at
each step in the iterative procedure.
I shall present during my talk results we obtained for the description
of weakly bound or unbound states (multi-nucleon resonance) in He and Li
isotopes.
[1] J. Rotureau, N. Michel, W. Nazarewicz, M. Ploszajczak and J. Dukelsky,
Phys. Rev. Lett. 97 (2006) 110603.
Dan Shapira, ORNL
Nucleus Nucleus Capture and Fusion in Reactions Between
Neutron Rich Nuclei
TBA
Brian Moazen , University of Tennessee
The 17O(p,alpha)14N reaction measured using a novel technique
The 17O(p,alpha)14N reaction is important for understanding nucleosynthesis in giant stars and nova. The 183 keV resonance in this reaction is particularly important for the 17O(p,alpha)14N reaction rate at nova temperatures. A recent measurement at Orsay of the 183 keV resonance using a low energy proton beam reported a resonance strength that was over 50 times greater than that inferred from a 17O(p,alpha)18F measurement at TUNL (<0.03 meV). We developed a new approach for measuring (p,alpha) reactions and applied it to measure the strength and energy of this resonance. A beam of 17O from the Holifield Radioactive Ion Beam Facility tandem accelerator bombarded hydrogen gas, which filled a large scattering chamber at pressures up to 4 Torr. The chamber was connected to the beamline via 4 differential pumping stages. Reaction products were detected in coincidence by a large array of silicone strip detectors. We found that 18F production is significantly decreased in low mass ONeMg novae, but less affected in more energetic novae. Results and astrophysical implications will be presented as well as future plans to measure 18F(p,alpha)15O using this technique.
Mike Guidry, University of Tennessee
A New Approach to Solving Large Thermonuclear Reaction Networks
Thermonuclear burning networks as large as thousands of isotopes are necessary to describe nucleosynthesis and energy production in novae, X-ray bursts, thermonuclear supernovae, core-collapse supernovae, neutron star mergers, and gamma-ray bursts (with these categories perhaps not all orthogonal). These burning networks power the explosion for the first three cases, and in all cases the spatial and temporal signature of element and energy production may be a critical diagnostic for the explosion mechanism. Standard networks have stability issues associated with the extremely stiff nature of the coupled system of differential equations, leading to the use of implicit numerical methods with substantial computational overhead. They do not scale well, with computational time typically increasing as the square or cube of network size. As a result, typical simulations of large-scale problems employ only a highly schematic or severely truncated network. I will describe a new approach to solving large sets of coupled differential equations that permits a stable explicit integration with large timesteps, even of very stiff systems. This new approach scales linearly with network size, with far less computational overhead than for standard implicit solvers. It may permit solution of many physically important problems that are beyond the reach of present methods. I will describe applications of this new technique in various fields of science, but will emphasize those in nuclear astrophysics, particularly our current efforts to couple more realistic networks to multidimensional hydrodynamics for Type Ia supernova simulations.
Nick Stone, Oxford University/ORNL
Pathological Science is alive and well - just don't
believe all you read in the Journals!
Pathological science was a term coined by Irving Langmuir to identify
'the science of things that aren't so'. He described several examples of
ideas which had, for a time, a certain measure of acceptance, but were
later shown to be basically wrong, and even suggested some basic
symptoms of 'pathological science'.
In this talk I will review some of Langmuir's classic cases and give
more recent examples of the phenomenon, including 'the hafnium bomb' and
the case of 'vanishing radioactive waste', exploring the extent to which
Langmuir's basic symptoms can be seen to apply. Some serious thoughts on
scientific integrity may emerge.
Previous Nuclear Physics Seminars