Bulletin of the American Physical Society
2007 APS Four Corners Section/SPS Zone 16 Joint Fall Meeting
Volume 52, Number 14
Friday–Saturday, October 19–20, 2007; Flagstaff, Arizona
Session B3: Nuclear and Plasma Physics |
Hide Abstracts |
Chair: Ross Spencer, Brigham Young University Room: Chemistry (Bldg. 20) Room 233 |
Friday, October 19, 2007 2:10PM - 2:22PM |
B3.00001: Fragment Angular Anisotropies for Magic and Non-Magic Nuclei A.N. Behkami, S. Maroofi, A. Esmailipour, S. Rasooli Fission fragment angular distributions have been studied for $^{239} {Pu} (n, f)$ reaction at several neutron energies. Theoretical calculations have been utilized to determine the variance $K_{0}^{2}$ at each bombarding energy from the observed angular anisotropies. The values of $K_{0}^{2}$ show sharp rise from a value of 5-6 to about 13 for higher neutron energies. From the position of one of the breaks in the $K_{0}^{2}$ value, the magnitude of the pairing gap $2\Delta$ in the highly deformed transition nucleus $^{240} Pu$ is estimated to be 2.4 MeV. Fission fragment angular anisotropies from changed particle fission of $^{208} Pb$, $^{209} Bi$, $ ^{235}U$ and $^{238}U$ at laboratory energy of 43.0 MeV have also been analyzed using the traditional transition state model. In all these calculations, optical model transmission coefficients with spin-orbit interaction have been used. In the case of magic nuclei, $^{208}Pb$ and $^{209} Bi$ it is found that the deduced values of $K_{0}^{2}$ are very small as compared to their corresponding values for $^{235}U$ and $^{238}U$ nuclei. This interpreted as due to shell structure, since significant shell and pairing effects appear for the magic nuclei $^{208} Pb$ and $^{209} Bi$. [Preview Abstract] |
Friday, October 19, 2007 2:22PM - 2:34PM |
B3.00002: Effective Shell-Model interactions from the No-Core Shell-Model Michael Kruse, Alexander Lisetskiy, Bruce Barrett, Petr Navr\'atil, James Vary No-Core shell model calculations (NCSM) for heavier nuclei, partially filling the sd-shell is a challenging problem. This is due to the exponential growth in the dimension of the Hilbert space. It is desirable to find an effective interaction, which utilizes a much smaller model space, that accurately reproduces NCSM results. Core shell-model calculations employ either empirical or theoretical effective 2-body matrix elements (TBME) that neglect the many body-correlations present. We show how a NCSM investigation in a 4$\hbar$$\Omega$ model space can yield effective TBME specific for the sd-shell, which accurately reproduce the many-body correlations present in the original calculation. TBME for $^{18}$F are obtained by direct projection, and their capability to reproduce large scale NCSM calculations is demonstrated for F, Ne and Na isotopes. [Preview Abstract] |
Friday, October 19, 2007 2:34PM - 2:46PM |
B3.00003: Electron Screening and Early Dynamics of Ultracold Neutral Plasmas Adam Denning, Scott Bergeson We study how the early electron screening dynamics of ultracold neutral plasmas varies with density and temperature. Calcium atoms are cooled and captured in a magneto optical trap where they are ionized to form a plasma. We measure laser-induced fluorescence from the calcium ions as the plasma evolves. At high densities we see evidence of strong screening for all temperatures. At lower densities, the ions appear to interact on time scales that are shorter than the ion plasma frequency. The mechanism for such an interaction time scale is not known. However, it appears to depend on the initial electron temperature in the ultracold neutral plasma. [Preview Abstract] |
Friday, October 19, 2007 2:46PM - 2:58PM |
B3.00004: Modeling the FTICR-MS signal of a $^{7}$Be Ion Plasma using a 2D PIC code M. Takeshi Nakata, Grant W. Hart, Bryan G. Peterson, Ross L. Spencer Beryllium-7 ($^{7}$Be) decays only by electron capture into Lithium-7 ($^{7}$Li) with a half life of 53 days. As a result, changing its electronic structure will affect its decay rate. We desire to study the effect of ionization on its decay rate. We will do this by trapping a $^{7}$Be ion plasma in a Malmberg-Penning Trap and measuring its and $^{7}$Li's concentration as a function of time by using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). We use this ratio as a function of time to directly measure the decay rate of the confined ion plasma rather than using gamma detection. We have modeled these signals in a 2-dimensional electrostatic particle-in-cell (PIC) code. The two spectrum peaks merges at high densities and at low densities they can be resolved. We also plan to model $^{7}$BeH$^{+}$ and $^{7}$Li at high densities to see if we can differentiate between them. The preliminary results of these investigations will be presented. [Preview Abstract] |
Friday, October 19, 2007 2:58PM - 3:10PM |
B3.00005: Parallelizing and Optimizing Simulations of Nonneutral Plasma Instabilities in a Malmberg-Penning Trap Melissa Powell, Grant Mason, Ross Spencer A Malmberg-Penning trap is a cylindrical apparatus which confines non-neutral plasma (electrons only) with an axial magnetic field and negative electric potentials on both ends. It is a simple system for studying basic plasma behavior, so simple that theory and experiment ought to agree. Theory predicts that a hollow plasma density profile is unstable, and experiments agree. However, the experimental growth rate of the m =1 diocotron mode of the instability is much larger than the theoretical growth rate, by a factor of around 2-4. We are collaborating with Travis Mitchell's experimental research group at the University of Delaware to find the cause for this discrepancy by recreating experimental conditions in our simulation. The growth rates of our simulation test cases have remained less than half the growth rates of Mitchell's experiments. I will report the results of parallelizing the simulation to increase the number of particles to 2 billion. We also optimize the code by converting the field solver from a two grid to a three grid multigrid solver in order to increase the number of grid points. [Preview Abstract] |
Friday, October 19, 2007 3:10PM - 3:22PM |
B3.00006: Auxiliary field GFMC calculation on the possibility of a pion condensate state of neutron matter at high densities Mohamed Bouadani For a long time, theory has speculated on the possibility of a pion condensate phase for highly dense nuclear matter, in particular for neutron matter. Almost all calculations have been based on a mean field approach. The first known calculation using a realistic hamiltonian is the FHNC/SOC of Akmal-Pandharipande. There, the computation was only indirect in showing that at enough density and wavelength there seem to be a favorable high dense phase of matter inferred by the linear response study showing a pion excess which was ``reasonably'' attributed to the pion condensate state. The aim of the present work is to calculate the energy expectation for a liquid phase boxed-plane-wave function and a varied field-modulated wave function in the longitudinal direction of the box with plane wave orbitals in the transverse plane as suggested by the tensor interaction. The calculation is based on the fixed phase constrained auxiliary field GFMC method with potential the Argonne $v^{8}$$'$ and the urbana UIX three body interaction. The energy calculations and distribution statistics show that the potential gain overwhelms reasonably the kinetic increase for the one dimensional laminated structured wave-function reaching a maximum at 3.5 fm for $\rho/\rho_o \approx 5$. More importantly, our results show continuous variations with the defining parameters. The phase transition seems of the second order kind. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700