Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session Y16: Nuclear Fragmentation and Structure Studies |
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Sponsoring Units: DNP Chair: Paul Mantica, Michigan State University Room: Hyatt Regency Jacksonville Riverfront City Terrace 12 |
Tuesday, April 17, 2007 1:30PM - 1:42PM |
Y16.00001: Anomalous behaviour of the 2$^+$ mixed-symmetry state in $^{94}$Zr Nico Orce, Esmat Elhami, Sharmistha Mukhopadhyay, Sadia Choudry, Marcus Scheck, Marcus McEllistrem, Steve Yates The low-spin structure of $^{94}$Zr has been studied with the (n,n$'$$\gamma$) reaction, and branching ratios, lifetimes, multipolarities and spin assignments were determined. The 2$^+_2 $ state at 1671.4 keV has been identified as the lowest mixed-symmetry state in $^{94}$Zr. The 752.5 keV transition from this state to the 2$^+_1$ level has a large B(M1) value of 0.33 (5) $\mu_N^2$, and the B(E2) of the transition to the ground state has an unusually large value of 8(1) W.u. The $M1$ transition strength is in agreement with IBM-2 predictions in the U(5) vibrational limit, whereas the large B(E2;2$^+_{1,MS} $$\rightarrow$0$^+_1$) value significantly exceeds the $E2$ strength predicted by the IBM-2. For the first time, the 2$^+_ {1,MS}$$\rightarrow$0$^+_1$ E2 transition is observed to have a larger E2 transition strength than the 2$^+_{1}$$\rightarrow$0 $^+_1$ decay. [Preview Abstract] |
Tuesday, April 17, 2007 1:42PM - 1:54PM |
Y16.00002: ABSTRACT WITHDRAWN |
Tuesday, April 17, 2007 1:54PM - 2:06PM |
Y16.00003: Application of Symmetry Theories to the Design of Fragment Separators for Exotic Isotope Accelerators James Maloney Exotic isotope accelerators are posed to provide us with unique abilities to investigate and test current theories regarding nuclei structure, weak-force interaction symmetry, and cosmologic evolution. Crucial to this powerful experimental tool is the design of its fragment separator. Designs for such a fragment separator can be developed through use of symmetry theories and simulation software. The goals and requirements of such designs include mechanical specifications; minimizing the effects of beam aberrations, fringe fields, and stochastic effects of the systems elements; allowing large acceptance; and providing a high-intensity beam of pure ions to be transported to experiments through the accelerator. Beam aberrations create substantial problems in any design, particularly beyond the first- and second-order terms. Symmetry theories help understanding the cause of these aberrations and provide clues to correct the design. This thesis explores a variety of designs that have been tested and compared to develop a proposed system layout that will best meet the needs and goals of the next-generation exotic isotope accelerator. [Preview Abstract] |
Tuesday, April 17, 2007 2:06PM - 2:18PM |
Y16.00004: Evaluation of a Semiemperical Nuclear Fragmentation Database Ryan Norman, Steve Blattnig, John Norbury The semiemperical nuclear abrasion-ablation model NUCFRG2 has been updated with more precise absorption cross sections, the addition of alpha cluster knockout for oxygen, and corrected neutron and proton production from electromagnetic disassociation. In this talk, we present a comparison of the model cross sections to newly available experimental fragmentation and charge-changing cross sections and give a discussion of the results. [Preview Abstract] |
Tuesday, April 17, 2007 2:18PM - 2:30PM |
Y16.00005: Properties of the largest fragment in multifragmentation; a canonical thermodynamic calculation Gargi Chaudhuri, Subal Dasgupta Many calculations for the production of light and intermediate mass particles resulting from heavy ion collisions at intermediate energies exist. Calculations of properties of the largest fragment resulting from multifragmentation are rare. In this presentation we compute these properties and compare them with the data for the case of gold on carbon. We use the canonical thermodynamic model. The model also gives a bimodal distribution for the largest fragment in a narrow energy range. [Preview Abstract] |
Tuesday, April 17, 2007 2:30PM - 2:42PM |
Y16.00006: Excited states of neutron rich Pd from fragmentation A.A. Hecht, W.B. Walters, N. Hoteling, P.F. Mantica, A. Becerril, T. Fleckenstein, G. Lorusso, J. Pereira, J. Pinter, J. Stoker, M. Quinn The neutron rich region approaching N=82 and Z=50 is interesting for nuclear structure and nuclear astrophysics, both as a test of the shell closures far from stability and as the path for r-process nucleosynthesis. This region is difficult to access with fusion-evaporation reactions and novel techniques must be used. At the National Superconducting Cyclotron Laboratory (NSCL) an experiment was recently performed by fragmentation of a Xe beam using a Be target to examine isomers and beta decay from these neutron rich nuclei. The radioisotope fragments passed through several Si planar detectors and were implanted in a double-sided Si strip detector (DSSD) in the Beta Counting System (BCS). Fragments were identified via $\Delta $E and TOF. Particle emitting decays were tracked in several layers of single sided strip detectors following the DSSD, while the SEGA array surrounding the DSSD was used to collect gamma emission following beta and isomer decay. Several neutron rich nuclei were observed in this experiment, including Ru, Rh, Pd, Ag, Cd, and In. Results on Pd will be discussed. [Preview Abstract] |
Tuesday, April 17, 2007 2:42PM - 2:54PM |
Y16.00007: Radioactive Ion Beam Production from the Fission of Thorium Oxide Targets Hakan Armagan, H.K. Carter, D.W. Stracener, E.H. Spejewski, A. Kronenberg Hollifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory is one of the few facilities in the world that provides radioactive ion beams (RIB), crucial for nuclear astrophysics, nuclear structure, and stewardship science. Neutron-rich beams are produced by proton-induced nuclear fission of actinide compounds such as uranium carbide or thorium oxide. The goal of this project has two folds. First, compare the beam yield produced from both a low density and a high-density ThO$_2$ target. Second, find the relation the 40 MeV proton beam that drives the RIB production is fully stopped in the high density, $\sim$8 g/cm$^3$ ThO$_2$, but not in the low-density 0.8 g/cm$^3$ ThO$^2$. The low-density target does not use all of the beam intensity. In this particular experiment, the production yields from 40MeV and 30MeV protons have been measured on the low-density target. The comparison of the calculated production yields of 40 MeV and 30 MeV protons shows a factor of two between these different energies. The experiment was conducted using an on-line mass separator, and specific masses of the RIB were collected onto a tape. This allows a direct comparison of the low and high density ThO$_2$ target. Release data from the high and low-density targets will be shown and discussed. [Preview Abstract] |
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