High-speed, high-voltage pulsed dc discharge at a constant power dissociated methane by direct electron impact. Experiments were conducted with PD= 30 up to 60 Torr-cm in a flowing gas. H and CH radicals of CH4 were monitored from plasma-induced emissions. Two gated, high-speed photomultipliers with interference filters simultaneously detected H\alpha (656nm) and A-X (431nm) of CH molecule transition emission. H\alpha emission is heavily quenched by CH_4. The drive voltage was varied between 3000 and 7000 Volts for dwell times of 200 or 450ns. The current and voltage rise times were about 20 to 50ns. Steady-state power was held constant, for a voltage series, at either 5 or 10kW (about 2mJ energy/pulse). The efficacy of CH_4 dissociation as functions of power and also plasma reduced-electric field (E/N) was tested. H atom corresponds to the first electron impact dissociation product, and CH is the last fragment. Monitoring these species were expected to provide insight to dependencies and trends.
[D2.002] Space-Borne Optical Tweezer Apparatus
Andrew Resnick (Northrop Grumman)
An optical tweezer apparatus is being developed as part of
an automated microscope to fly on the International Space
Station beginning in 2005. The experiments to use the
tweezers are concerned with the nucleation and growth of
hard-sphere colloidal crystals. This talk will present a
description of the system and results of work done to
characterize the applied trapping force as a function of
index mismatch and particle size.
[D2.003] Low Cost Demonstration and Data Acquisition G-Meters
W. N. Hubin (Kent State University)
(a) A lecture demonstration g-meter, consisting of an
"accelerometer" sensor, an inexpensive microcontroller, and
a large LCD, is described and demonstrated. It displays the
force on a unit mass in real time, as well as storing
maximum and minimum values for later retrieval. (b) With the
substitution of a small (alphanumeric) LCD, the unit becomes
a small, very portable data acquisition system, capable of
recording up to 8K force data points, along two
perpendicular axes.
[D2.004] Using a Fast, LDA-based Method to Model Group III Nitride Crystals
Garett Yoder (Eastern Kentucky University)
A fast Local Density Approximation computational method has
recently been developed for possible use in a wide range of
different types of materials. In this work, the calculation
is used as a durable, but flexible, ab initio base of a
semi-empirical model that is applied to Group III Nitride
semiconducting crystals, including BN, AlN, GaN and InN.
This model has the capability to calculate equilibrium bond
lengths and mechanical properties as well as the band
structure of the materials. Preliminary results for native
defects in modest supercells of 72 atoms indicate the method
is consistent with experimental results and results from
other calculations. These results include calculations of
relaxed bond lengths around the defect, defect energies and
the modified band structure, which allows the identification
of the donor or acceptor states. These and other results
will be presented as well as a discussion of the many
potential applications of this method.
[D2.005] Effect of Particulate Filler on Ultrasound Devulcanization of Poly(dimethyl siloxane) Rubber
E. von Meerwall, S. E. Shim, A. Isayev (Univ. Akron)
We have used proton NMR relaxation and pulsed-gradient
diffusion measurements at 70 deg. C in silica-filled PDMS
rubber after crosslinking, after subsequent devulcanization
by intense ultrasound, and after later revulcanization. As
in unfilled PDMS, transverse relaxation displays three
distint rate components, attributed to entangled and
crosslinked network (similar in T2); light sol plus dangling
network fragments; and unreactive trace oligomers.
Ultrasound produces copious amounts of extractable sol
dependent on reactor settings. We find that all three T2
relaxation times decrease modestly with increasing filler
content, but the components' proportions correlate mainly
with sol fraction, i. e., network degradation. In rupturing
the network, devulcanization produces large diffusing
fragments and dangling ends; revulcanization largely
reverses these effects. The rates and amplitudes of the
bimodal diffusivity distribution confirm this conclusion.
The weakness of the effects of filler shows that ultrasound
devulcanization is easily adaptable to the recycling of the
preponderantly particulate-filled industrial rubbers.
[D2.006] X-ray driven gamma emission
James Carroll (Youngstown State University)
X-ray driven gamma emission describes processes that may
release nuclear energy in a 'clean' way, as bursts of
incoherent or coherent gamma rays without the production of
radioactive by-products. Over the past decade, studies in
this area have gained tremendous momentum. X-ray triggered
gamma emission from long-lived metastable nuclear excited
states has been established since 1987 for one nuclide and
it appears likely that triggering in other isotopes will be
demonstrated conclusively in the near future. With these
experimental results have come new proposals for the
creation of collective and avalanche-like incoherent
gamma-ray bursts and even for the ultimate light source, a
gamma-ray laser. Obviously, many applications would benefit
from controlled bursts of gamma radiation, whether coherent
or not. This talk reviews the experimental results and
concepts for the production of gamma rays, driven by
externally produced x rays.
[D2.007] Search for x-ray driven gamma emission from ^178Hf^m2 at the National Synchrotron Light Source
Tom Drummond, Jason Burnett, Joel Lepak, Ron Propri, David Smith, James Carroll (Youngstown State University), Mike Helba, Hill Roberts (SRS Technologies, Inc.), Sarkis Karamian, Jindrich Adam (Joint Institute for Nuclear Research, Dubna), Frank Stedile (University of Stuttgart), Zhong Zhong (Brookhaven National Laboratory), F.J. Agee (Air Force Office of Scientific Research)
First experiments have been conducted to search for evidence
of x-ray driven, or triggered, gamma emission from the
31-year isomer of ^178Hf using white and monochromatic
beams at the National Synchrotron Light Source. The
techniques used were based on standard nuclear spectroscopy
using a high-purity Ge detector. The approach and
experimental results will be discussed.
[D2.008] Development of the YSU miniball detector array
Ron Propri, Jason Burnett, Tom Drummond, Joel Lepak, David Smith, James Carroll (Youngstown State University), Sarkis Karamian, Jindrich Adam (Joint Institute for Nuclear Research, Dubna), Frank Stedile (University of Stuttgart), F.J. Agee (Air Force Office of Scientific Research)
At present, studies of x-ray driven gamma emission are
constrained by the extremely small size of available
targets. Typical targets of ^178Hf^m2 contain only
10^13 - 10^15 isomers with various amounts of
contaminant radioisotopes. In order to apply a more
sensitive experimental approach to the search for driven
gamma emission from such targets, the YSU miniball detector
array has been constructed. This array utilizes similar
principles to those employed at large many-detector arrays
to capture multiple gamma-ray cascades emitted in
spontaneous and driven events. The experimental approach,
design and testing of the miniball array will be discussed.
[D2.009] Search for x-ray driven gamma emission from ^178Hf^m2 using the YSU miniball array
Jason Burnett, Tom Drummond, Joel Lepak, Ron Propri, David Smith, James Carroll (Youngstown State University), Mike Helba, Hill Roberts (SRS Technologies, Inc.), Sarkis Karamian, Jindrich Adam (Joint Institute for Nuclear Research, Dubna), Frank Stedile (University of Stuttgart), Zhong Zhong (Brookhaven National Laboratory), F.J. Agee (Air Force Office of Scientific Research)
A monochromatic beam from the National Synchrotron Light
Source has been employed in conjunction with the YSU
miniball detector array to search for evidence for x-ray
driven gamma emission from the 31-year isomer of ^178Hf.
This talk will discuss the experimental setup and results.
[D2.010] Tuning Bound Atomic States to Multiphoton Absorption and Susequent Ionization
Glen D. Gillen, Linn D. VanWoerkom (Ohio State University)
Photoelectron spectra have been taken for magnesium atoms exposed to 120-fs, 800-nm, laser pulses with intensities up to 100 TW/cm^2. Photoelectron spectra for all intensities contain structural components separated by the energy of a single photon. The details of the structure reveal the population of excited states whose energy levels are shifted into resonance with an integer number of photons. Higher intensities allow probing of more and more deeply bound atomic states.