Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session BH: Applications in Nuclear Physics |
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Sponsoring Units: DNP Chair: A. Ramayya, Vanderbilt University Room: Gaylord Opryland Cheekwood F |
Thursday, October 26, 2006 2:00PM - 2:12PM |
BH.00001: Plant Physiology Studies Using Positron-Emitting Isotopes M.R. Kiser, C.R. Howell, A.S. Crowell, C.D. Reid, R.P. Phillips Over the past century the atmospheric carbon dioxide CO$_2$ concentration has increased by more than 25\%, and climate experts predict that CO$_2$ levels will double by the end of this century. Understanding the mechanisms of resource management in plants is important for predicting how plants will respond to the increase in atmospheric CO$_2$ concentration. We use short-lived radioisotope labeling techniques to measure carbon and nitrogen translocation in plants under different global change conditions to gain insight on how plants respond to elevated CO$_2$ levels. Carbon-11 dioxide is produced at TUNL using the $^{14}$N(p,$\alpha$)$^{11}$C reaction. The plants are labeled under environmentally controlled conditions in a specially equipped growing chamber at the Duke University Phytotron facility. The close proximity of TUNL and the Duke University Phytotron creates a unique opportunity for these global change studies. These experiments use single detectors collimated to restrict the field of each detector to one of three regions of the plant (uptake leaf, shoot, and root). Recent results will be presented. [Preview Abstract] |
Thursday, October 26, 2006 2:12PM - 2:24PM |
BH.00002: Background Reduction by Gamma-ray Tracking Detectors Mario Cromaz Low-energy cross-section measurements of capture reactions for astrophysics applications are often limited by gamma-ray background. This background may be reduced with the recent advent of high resolution HPGe tracking detectors which are capable of rejecting background gamma-rays which do not originate from the target position. This is accomplished by segmenting the outer contact of the HPGe crystal and analyzing the transient currents generated at the segments to locate the individual scattering points of the gamma ray and the energy deposited within the crystal. Using the Compton-scattering relation, one can define a cone which specifies the direction of the incident gamma-ray. Furthermore, one can discern from the positions and energies of the scattering points if the gamma-ray scattered out of the crystal. Simulations will be presented that outline detector performance as well as achievable background reduction factors based on the performance characteristics of the prototype detectors for the GRETINA spectrometer. [Preview Abstract] |
Thursday, October 26, 2006 2:24PM - 2:36PM |
BH.00003: Tests of a Cryogenic Gas Cell for Radioactive Ion Beam Experiments K. Chipps, D. Bardayan, J. Blackmon, K. Chae, J. Eastburg, U. Greife, K.L. Jones, R. Kozub, R. Livesay, B. Moazen, C.D. Nesaraja, S. Pain, M. Porter-Peden, F. Sarazin, M.S. Smith The properties of resonances that dominate thermonuclear reaction rates on proton-rich, unstable nuclei can be probed using transfer reactions like ($^{3}$He,p). In inverse kinematics, this is achieved with a radioactive ion beam and a $^{3}$He gas target. A cryogenic gas cell target for such experiments has been constructed at the Colorado School of Mines and tested at Oak Ridge National Laboratory with a stable $^{17}$O beam. The gas cell design has been modified several times, and a number of techniques are being explored to reduce the significant yield from background reactions with the window material. Alternatively, a gas jet target with recycling capability could be a better solution to the long-term problem of using rare gases as targets. Results from our beam tests and future plans will be presented. [Preview Abstract] |
Thursday, October 26, 2006 2:36PM - 2:48PM |
BH.00004: Determination of precipitation ``age'' via gamma rays from accreted radon progeny M.B. Greenfield, N. Ito, A. Iwata, K. Kubo, M. Ishigaki, K. Komura Measurements of $\gamma $ ray activities from $^{214}$Pb and $^{214}$Bi condensed from precipitation can determine the average time activity has been removed from secular equilibrium. Atmospheric $\gamma $ rates arising from adsorbed/absorbed radon progeny on/in the surface/volume of droplets are proportional to the 0.4 to 0.6 power of rain rates, respectively, assuming that on average most progeny are accreted early in the formation of droplets rather than scavenged$^{1}$. Thus, the average elapsed time between accretions of radon progeny onto droplets until the droplets reach ground may be estimated. After removal from secular equilibrium the initial ratio of $^{214}$Bi to$^{ 214}$Pb activity evolves towards a limiting ratio which is independent of absolute activity. Measurement of relative activities may thus determine the ``age'' of precipitation, limited only by the statistical uncertainty. Activity in condensates from 5-30 L of rain viewed with 2$\pi $ solid angle by a 50{\%} efficient, high-resolution Ge detector is typically 10s up to 100s of cts/sec (during thunderstorms)$^{2}$. The half-lives of $\gamma $ activities from $^{214}$Bi and$^{ 214}$Pb, 19.7 and 26.9 minutes, respectively, are on the same scale as rain ``ages'' and close enough to each other to enable estimates of rain ``ages'' to within a few minutes. $^{1}$Greenfield et al., J. of Appl. Phys. \textbf{93,} 5733 (2003); $^{2}$preceding abst. [Preview Abstract] |
Thursday, October 26, 2006 2:48PM - 3:00PM |
BH.00005: Intense $\gamma $ radiation from radon progeny accreted in/on rain during and following thunderstorms M.B. Greenfield, A. Iwata, N. Ito, M. Ishigaki, K. Kubo, K. Komura Delayed atmospheric $\gamma $'s decaying with a half-life of 10s of minutes$^{1}$, has been observed in Japan and in Florida associated with natural and triggered lightning, respectively. This activity may be from 1) excess precipitation of positively charged radon progeny or 2) decay of ejectiles from nuclear reactions initiated by protons or photons. Activity condensed from 5-20 liters of rain, via ion exchange resins, was measured with 2$\pi $ solid angle, by a 50{\%}, high resolution Ge detector. Activities from $^{214}$Bi and$^{ 214}$Pb, initially exceeding up to 100's of cts/sec, decayed with their characteristic half-lives of 19.7 and 26.9 minutes, respectively$^{2}$. Atmospheric radiation was also observed in close proximity to triggered lightning at the Lightning Research Lab in Florida. In both cases excess delayed activity with thunderstorms observed at ground level is almost entirely due to increased precipitation of radon progeny. An enhancement of the 511 keV annihilation peak may be from positron decay of $^{11}$C, $^{18}$F, $^{13}$N following lightning induced nuclear reactions. Identification of corresponding 20, 10 and 100 minute half-lives, respectively, requiring closer lightning, greater volumes of collected rain water, and/or reduction in sample preparation times is in progress. $^{1}$Greenfield et al., J. of Appl. Phys. \textbf{93,} 1839 (2003); $^{2}$ see next abst. [Preview Abstract] |
Thursday, October 26, 2006 3:00PM - 3:12PM |
BH.00006: Experimental Study of LaBr3(Ce) Gamma-Ray Detector Performance in Mixed Radiation Field Alexander Barzilov, Phillip Womble, Jon Paschal, Lindsay Hopper, Ryan Moore, Eric Houchins, Jeremy Board High energy gamma-ray spectrometry has a number of practical applications. Neutron-based explosives detection systems are the important part of active interrogation technology. Pulse neutron technique is excellent choice to rapidly determine bulk elemental content of the cargo in non-destructive and non-intrusive manner. Pulse mode of operation provides simultaneous detection of gamma-rays from neutron inelastic scattering and thermal capture reactions. The physical parameters of chosen detectors govern parameters of system. A gamma-ray detector must be suitable for operation in mixed radiation fields consisting of neutrons and photons. It must have high Z-value to detect photons with energies in 4.4 MeV -10.8 MeV range emitted from neutron scattering reactions on carbon and nitrogen nuclei. In this paper, we discuss results of experimental study of LaBr$_{3}$(Ce) detector operation with the d-T neutron generator. This lanthanum halide scintillator is activated by neutrons in mixed field under 14.1-MeV neutron irradiation showing the beta spectrum with endpoint energy $\sim $2 MeV. [Preview Abstract] |
Thursday, October 26, 2006 3:12PM - 3:24PM |
BH.00007: Future Directions of Space Radiation Protection Ram Tripathi For the success of NASA’s vision for space exploration to Moon, Mars and beyond, exposures from the hazards of severe space radiation in deep space long duration missions is a ‘show stopper’ problem. The payload penalty demands a very stringent requirement on the design of the spacecrafts for human deep space missions. Langley has developed state-of-the-art radiation protection and shielding technology for space missions. The exploration beyond low Earth orbit (LEO) to enable routine access to more interesting regions of space will require protection from the hazards of the accumulated exposures of space radiation; trapped radiation, galactic cosmic Rays (GCR) and solar particle events (SPE), and minimizing the production of secondary radiation is a great advantage. It is desirable to divert them form the spacecraft without paying the payload penalty while taking advantage of the state-of-the-art material shielding. The goal is to repel enough positive charge ions so that they miss the spacecraft without attracting thermal electrons at the same time taking advantage of revolutionary next generation of shielding materials for Mars missions. Aspects of future directions of space radiation protection technology involving a combination of active-electrostatic and passive-material shielding will be presented. [Preview Abstract] |
Thursday, October 26, 2006 3:24PM - 3:36PM |
BH.00008: ABSTRACT WITHDRAWN |
Thursday, October 26, 2006 3:36PM - 3:48PM |
BH.00009: Big Numbers Hypothesis Shantilal Goradia The dark matter predicted by the quantum field theory has a value of force 10$^{120}$ greater than indicated by observations. The product of 10$^{80}$ nucleons and the surface area 10$^{40}$ of each nucleon is 10$^{120}$. The surface area of the universe taken as a single particle is 10$^{120}$. The coupling constant between inter universes calculable, as square of $D$ (Hubble time) as done in [1] is 10$^{120}$. The ratio of Hubble time to nucleon diameter is the same as the ratio of nucleon surface area to Planck length, both equal to 10$^{40}$, raising a question: Are they both inflating at the same time or is it the Planck length that is shrinking since the big bang, and impacting evolution? The universe looks inflationary looking inside out. We are taking Doppler effect as scale invariant, while the fundamental constants of nature are changing. The 2002 publication of the English translation of Einstein's 1919 paper by Hawking reveals clearly that he retracted the 1917 introduction of the cosmological constant. He might have informally uttered to Gamow about his blunder made in 1917 without clarifying his correction in 1919. His 1919 paper and his 1935 paper, both connect particles to normal spacetime implying he held the same view the rest of his life. I connect them too in physics/0210040 and will present more details. [1] S. G. Goradia gr-qc/0507130 (\textit{Indian Journal of Theoretical Physics} \textbf{52} 143 2004) [Preview Abstract] |
Thursday, October 26, 2006 3:48PM - 4:00PM |
BH.00010: A Postulation of a Concept in Fundamental Physics Shantilal Goradia I am postulating that all fermions have a quantum mouth (Planck size) that radiates a flux density of gravitons as a function of the mass of the particle. Nucleons are not hard balls like light bulbs radiating photons challenging Newtonian concepts of centers and surfaces. The hardball analogy is implicit in coupling constants that compare strong force relative to gravity. The radiating mouth is not localized at the center like a hypothetical point size filament of a light bulb with a hard surface. A point invokes mass of zero volume. It is too precise, inconsistent and illogical. Nothing can be localized with more accuracy that Planck length. Substituting the hard glass bulb surface with flexible plastic surface would clearly make the interacting mouths of particles approach each other as close as possible, but no less than the quantum limit of Planck length. Therefore, surface distance in Newtonian gravity would be a close approximation at particle scale and fits Feynman's road map [1]. My postulation reflected by Fig. 2 of gr-qc/0507130 explains observations of increasing values of coupling constants resulting from decreasing values of Planck length (See physics/0210040 v1). Since Planck length is the fundamental unit of length of nature, its variation can impact our observation of the universe and the evolutionary process. [Preview Abstract] |
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