Bulletin of the American Physical Society
2016 Annual Meeting of the APS Mid-Atlantic Section
Volume 61, Number 16
Saturday–Sunday, October 15–16, 2016; Newark, Delaware
Session G2: Spectroscopy in Condensed Matter II |
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Chair: Harsha Kannan, University of Delaware Room: Sharp Laboratory 130 |
Sunday, October 16, 2016 1:30PM - 2:06PM |
G2.00001: Neutron Studies of Excitations in Relaxor Ferroelectrics Invited Speaker: Peter Gehring Neutron scattering has played a seminal role in elucidating fundamental concepts in ferroelectrics, such as the existence of soft modes and how they relate to the dielectric permittivity. Similarly, our current understanding of the complex physics of relaxors has benefited significantly from studies based on a wide variety of neutron scattering methods. This is primarily due to the neutron’s ability to probe spatial and temporal correlations simultaneously in condensed matter spanning many orders of magnitude in distance and time, which is arguably the most powerful aspect of the neutron scattering technique. For this reason, neutron scattering is ideally suited to studies of relaxors, which not only exhibit relaxational effects over an enormous frequency range, but which also display competing short and long-range spatial correlations. Nevertheless, after more than a half century of research, no unified picture of the relaxor lattice dynamics has emerged. Disagreement about the nature of the mode coupling in relaxors has spawned divergent models of the soft mode, while the strong diffuse scattering has been attributed either to a relaxational mode or to a local, harmonic mode. Here I will briefly review the excitations in relaxors studied using various neutron methods. [Preview Abstract] |
Sunday, October 16, 2016 2:06PM - 2:18PM |
G2.00002: Detection of far ultraviolet radiation by wavelength-shifting tetraphenyl butadiene Chandra B. Shahi, Joshua R. Graybill, Robert E. Vest, Michael A. Coplan, Alan K. Thompson, Charles W. Clark Far ultraviolet radiation (FUV) is used by a number of detectors employed in low-energy particle physics,\footnote{V. Chepel and H. Ara\'{u}jo, J. Inst. {\bf 8}, R04001 (2013).} dark matter searches\footnote{E. Aprile, {\em et al.}, Astroparticle Phys. {\bf 35}, 573 (2012).} and neutron dosimetry.\footnote{J. C. McComb, {\em et al.}, J. Appl. Phys. {\bf 115}, 144504 (2014).} Particularly difficult to detect due to its strong absorption by most materials, FUV can be converted to visible light by use of wavelength-shifting scintillators. Tetraphenyl butadiene (TPB) is a widely-used wavelength shifting compound that fluoresces at wavelengths $\lambda \approx 420 \, $ nm when excited by FUV. We have used two methods to coat glass disks with thin films of TPB: direct vapor-phase deposition; and spin-coating of TPB suspended in polystyrene/toluene solutions. Using the NIST SURF III Synchrotron Ultraviolet Radiation Facility,\footnote{see {\tt http://j.mp/surf111} and {\tt http://j.mp/N3utr0n}} we have measured the absolute fluorescence efficiency of TPB in the range $120 \, \mathrm{nm} < \lambda < 400 \, \mathrm{nm}$. Our results are compared with previous studies using FUV discharge sources .\footnote{V. M. Gehman, {\em et al.}, Nuc. Instr. Meth. Phys. Res. A {\bf 654}, 116 (2011).} [Preview Abstract] |
Sunday, October 16, 2016 2:18PM - 2:54PM |
G2.00003: New detectors for new light source: Progress in semiconducting detectors for spectroscopy and imaging applications at next generation synchrotron sources Invited Speaker: Abdul Rumaiz The development of new synchrotron sources has led to a remarkable increase in brightness and coherence. This development, combined with improved energy and spatial resolution has led to new measurements techniques. However, it is well known that most of the synchrotron and x-ray free electron laser (XFEL) experiments are detector limited. Complete realization of the scientific capabilities of new synchrotrons and XFEL will require novel detection schemes. As with everything else, there is no one size fits all. The requirement of detectors is different depending on the experiment. This presentation will discuss some of the detector developments efforts for the next generation sources. In particular the presentation will highlight the detector R{\&}D effort at National Synchrotron Light Source II at Brookhaven National laboratory. The talk will describe some of these projects and the scientific techniques for which they are intended. . [Preview Abstract] |
Sunday, October 16, 2016 2:54PM - 3:06PM |
G2.00004: The Development of a n-type GaN Fast Neutron Spectrometer that is also “Gamma-Blind” Noel A. Guardala, Johnathan D. Wensman, V. K. Mathur GaN has attracted a good deal of interest in recent years as an attractive scintillation material based on both its intrinsic electronic and light-emitting properties and its response to a variety of differing types of energetic ionizing radiation and have led to a number of studies devoted to the understanding and practical use of GaN devices for radiation detectors. Some of these studies have focused on the potential use of GaN for thermal neutron detection via the incorporation of nuclides that have large thermal-neutron capture cross sections like: 6Li, 10B or 155,157 Gd. We have demonstrated for the first time that fast recoil Ga and N ions produced via neutron elastic scattering a fast neutron spectrum related to the energy and intensity of various neutron beams can be obtained for energy and flux determination and in characterizing the fast neutron source. Such a device can have an impact in the areas of: nuclear physics studies, monitoring of nuclear reactor and nuclear materials (in a covert and overt manner), radiation health physics for both area and personnel monitoring and medical applications under therapy conditions where fast neutrons can be emitted as by-products of the incident beam with the patient and surroundings. [Preview Abstract] |
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