second - Physics Department - Utah State University

11:18AM B3.00005 Phase diagram of Ti metal at high pressure , YAHYA AL KHATATBEH, KANANI LEE, BORIS
KIEFER, New Mexico State University — Using density-functional theory based ab-initio computations, we have investigated the hexagonal close-packed (hcp)
and the hexagonal (ω) structures titanium (Ti), and find good agreement with experiment. The hcp phase yields an equation of state of a zero pressure volume
V 0 = 17.37 ( 0.02) Å 3 , an isothermal bulk modulus K 0 = 111.9 ( 0.2) GPa, and its pressure derivative K 0 ’ = 3.60 ( 0.02). Furthermore, the c/a ratio for both
phases increases with increasing pressure. Additionally, the calculated transition pressure from hcp to ω phase compares well with the experimental results with
the ω phase more stable than the hcp phase at pressures greater than ∼ 5 GPa.
11:30AM B3.00006 Temperature dependence of absorption and emission spectra of Ba in solid
Ar , BRIAN MONG, Colorado State University — Detection of a single Ba daughter from extremely rare Xe-136 ββ decay is an essential part of the EXO
(Enriched Xenon Observatory) project. At CSU we have been working on detection methods in both solid and liquid Xenon. This talk will cover the recent
progress we have made on detection of Ba in solid Argon and Xenon. The absorption and fluorescence verses temperature in solid Ar and has been measured.
Two Ba sites have been observed in solid Ar; site B recovers from annealing above 20K while site A does not, it converts to Site B. Recent progress with the
spectroscopy of Ba and Ba+ in solid Xe will also be discussed.
11:42AM B3.00007 Experimental evidence for the existence of eigenvalues of the time evolution
operator governing the behavior of nuclear spins in solids , STEVEN MORGAN, BRIAN SAAM, University of Utah
Department of Physics — The decay of nuclear magnetic resonance (NMR) signals in solids is an extremely difficult many-body problem with no complete
solution. Utilizing frozen xenon polarized by spin-exchange optical pumping, we have observed the long-time behavior of the NMR signal decay for both freeinduction
decay and spin (solid) echoes. The enhanced signal has allowed us to view the behavior of the decay for up to ∼10 decay constants. This has given
us the opportunity to test a theory about this behavior which says that at after a few time constants, the signal should decay either with a simple exponential
or a simple exponential modulated by a sinusoid. The reasoning for this is that the evolution of the density matrix follows from the action of its complete time
evolution operator, and that its eigenvalues determine the evolution of the spin system. Evidence for this type of behavior has been seen in classical chaotic
systems, but ours is the first experimental evidence for this behavior in a quantum system. This work has the potential to help elucidate the role of chaos in
quantum systems.
11:54AM B3.00008 Propagator Methods in Spintronics applied to the Rashba Hamiltonian ,
BAILEY HSU, JEAN-FRANCOIS VAN HUELE, Brigham Young University — In spintronics, the spin of the electrons is manipulated to create spin currents.
New propagators are introduced in order to determine the evolution of the spin systems. Rashba potentials are considered in connection with the spin-orbit
couplings in condensed matter systems. We calculate the propagator for the Rashba Hamiltonian H = P 2
2m + ᾱ (σxPy − σyPx) and comment on how to deal
h
with noncommuting operators.
12:06PM B3.00009 Obtaining an EELS Fingerprint for the Phases of Aluminum Oxide , MICHAEL
TANNER, Brigham Young University, DAVID CULLEN, Arizona State University, RICHARD VANFLEET, Brigham Young University — The crystal structure
of Al 2 O 3 is found naturally in a number of different atomic arrangements or phases (more than seven have been confirmed). By heating Al(OH) 3 (gibbsite) to
different temperature levels in the lab, we obtained the alpha, gamma, and kappa phases which we confirmed by diffraction analysis. We then investigated these
samples using electron energy-loss spectroscopy (EELS) in order to obtain an EELS fingerprint for each phase. A unique EELS fingerprint would allow phase
identification in nanometer scale regions that cannot be measured by other means. Initial results are promising that the different phases can be differentiated
by EELS. Further work will expand these measurements to include all of the phases of Al 2 O 3 .
12:18PM B3.00010 Microstructural Constitutive Theory: Statistical Particulate Mechanics ,
MICHAEL WEBB, —
Friday, October 6, 2006 10:30AM - 11:54AM —
Session B4 Astrophysics Eccles Conference Center Room 305
10:30AM B4.00001 Laboratory Nuclear Astrophysics or The universe as seen from underground.
, JOHN E. ELLSWORTH, STEVEN E. JONES, SHANNON WALCH, MATTHEW R. NERDIN, Physics and Astronomy, Brigham Young University
— Our sun emits 380 yottawatt, yet the nuclear reactant energies producing that power are very low (1 keV). These energies are so low, that replication of
such reactions in the laboratory produce rates that are nearly impossible to detect. Unlike the historical efforts to understand stellar processes by extrapolating
down from higher energy beam experiments, there are efforts to study reactions using low energy reactants. To do so requires specialized equipment and
environments. The results indicate the need to understand the Coulomb screening effects of condensed matter in these processes. An explanation for heat
production in planetary cores may also follow.
10:42AM B4.00002 Low energy accelerator for studying laboratory nuclear astrophysics. ,
MATTHEW R. NERDIN, JOHN E. ELLSWORTH, STEVEN E. JONES, Physics and Astronomy, Brigham Young University — We present progress on the
development of research equipment to study laboratory nuclear astrophysics reactions by bombarding deuterided metallic targets with accelerated ions. This
effort consists of constructing a low energy accelerator and the initial testing of specialized low-rate, neutron and charged-particle detectors.
10:54AM B4.00003 Photoevaporation of Clustered Minihalos by Primordial Stars , JOSEPH SMIDT,
Brigham Young University, DAN WHALEN, Los Alamos National Laboratory — The first primordial stars to form in the universe were extremely luminous
objects that heavily influenced subsequent star formation in their vicinity. We run 1D and 3D simulations of minihalo evaporation by a Pop III star to ascertain
whether its radiation promotes or quenches star formation in the halo. Preliminary results will be presented.
11:06AM B4.00004 Phase-space distribution of unbound dark matter near the Sun , MOQBIL
ALENAZI, PAOLO GONDOLO, Department of Physics, University of Utah, 115 S 1400 E Rm 201, Salt Lake City, Utah 84112-0830, USA — We resolve
discrepancies in previous analyses of the flow of collisionless dark matter particles in the Sun’s gravitational field. We determine the phase-space distribution
of the flow both numerically, tracing particle trajectories back in time, and analytically, providing a simple correct relation between the velocity of particles at
infinity and at the Earth. We use our results to produce sky maps of the distribution of arrival directions of dark matter particles on Earth at various times
of the year. We assume various Maxwellian velocity distributions at infinity describing the standard dark halo and streams of dark matter. We illustrate the
formation of a ring, analogous to the Einstein ring, when the Earth is directly downstream of the Sun.