Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session B3: SO-1: Spectroscopy 1 |
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Chair: David Moore, Los Alamos National Laboratory Room: Hermitage C |
Monday, June 29, 2009 9:00AM - 9:15AM |
B3.00001: A Fast NIR emission spectrometer for examining explosive events: emission spectra of PETN explosions containing silver and aluminum Scott Piecuch, Jon Koch, Jim Lightstone, Joel Carney A fast NIR spectrometer was constructed to make temporally and spectrally resolved emission measurements during post-detonation combustion of pure pentaerythritol tetranitrate (PETN) charges and PETN charges doped with 10{\%} (by mass) Ag and Al microparticles. The post-detonation spectra are observed between 750 nm and 1500 nm at rates up to 46k-spectra/sec, and key features are identified. Immediately following break-out of the detonation, all measured spectra are highly structured due to atomic and molecular emission. This emission decays within the first 40 $\mu $s following break-out and is found to have lifetimes similar to that of emission from various species collected in the visible (390-600 nm) by a time-resolved streak spectrometer. For the particle-doped charges, broadband NIR emission signals can be used to determine time-resolved gray-body temperatures of the particles. At early time (0-40 $\mu $s after breakout) gray-body temperatures ranging from 3000 to 4500 K are measured, between 60 $\mu $s and 300 $\mu $s after breakout the particle temperature is found to cool significantly ranging from 1000 K to 1500 K. Complementary two-color pyrometry (800 and 1150 nm) temperature measurements are found to be in good agreement with early time data (0-25 $\mu $s). [Preview Abstract] |
Monday, June 29, 2009 9:15AM - 9:30AM |
B3.00002: Molecular scale shock response: electronic absorption spectroscopy of laser shocked explosives Shawn McGrane, Von Whitley, David Moore, Cindy Bolme, Daniel Eakins Single shot spectroscopies are being employed to answer questions fundamental to shock initiation of explosives. The goals are to: 1) determine the extent to which electronic excitations are, or are not, involved in shock induced reactions, 2) test the multiphonon up-pumping hypothesis in explosives, and 3) provide data on the initial evolution of temperature and chemistry following the shock loading of explosives on scales amenable to comparison to molecular dynamics simulations. The data presented in this talk are focused on answering the first question. Recent experimental results measuring the time history of ultraviolet/visible absorption spectroscopy of laser shocked explosive thin films and single crystals will be discussed. [Preview Abstract] |
Monday, June 29, 2009 9:30AM - 10:00AM |
B3.00003: Optical Spectroscopy of Fireballs from Aluminized High Explosives Invited Speaker: Fireballs produced by explosive detonations in air generate a challenging environment in which to make measurements. Fireballs are typically optically thick, have high inherent luminosity, and exhibit high temperatures and pressures, making many combustion probes impractical for fireball applications. Nevertheless, characterizing the thermochemical environment within the fireball is of critical importance to the development of novel energetic systems, especially those for bioagent defeat or those designed for sustained overpressure (e.g. thermobarics). We have recently been able to quantify optical depth in aluminized fireballs during the time period of reaction of the added aluminum. We have found that attenuation lengths during this early period are of the order of a few centimeters. These measurements suggest that for similar explosives, optical probes (e.g. emission spectroscopy measurements, optical pyrometry) will sample only the outer few cm of the fireball. Thus, conditions near the air/detonation products interface will be over-represented in the measurement, and therefore oxidation reactions and temperatures may be over-estimated. Our second experiments involve multicolor pyrometry as a fireball diagnostic. Despite it apparent simplicity, accurate pyrometry measurements require information on emissivity variation with wavelength. We apply the UIUC heterogeneous shock tube to measure $\epsilon$($\lambda$) for alumina at elevated temperature. We find that $\epsilon$($\lambda$) changes significantly with temperature, starting at approximately $\epsilon$ $\sim$ 1/$\lambda$ at 2000 K and moving towards grey behavior at 3000 K. Based on these results, we present an optimized strategy for pyrometry of aluminized fireballs that works in the limit of optically thin or optically thick fireballs. Finally, we have developed a new broadband dye laser absorption technique that generates generates light pulses of very high spectral irradiance such that, even when the pulses are attenuated by 99\%, the transmitted light is still enough to disperse into a high resolution absorption spectrum. We demonstrate this technique on a very optically dense Al/Bi$_2$O$_3$ explosive mixture, showing clear evidence of the ability to monitor key intermediates such as gas phase Al with detection limits at the ppb level and time resolution on the scale of nanoseconds. [Preview Abstract] |
Monday, June 29, 2009 10:00AM - 10:15AM |
B3.00004: Theoretical Studies on the Reaction Pathways of Electronically Excited DAAF Jason Quenneville, David S. Moore The use of temporally and spectrally shaped ultrafast laser pulses to initiate, as well as detect, high explosives is being explored at Los Alamos. High level ab initio calculations, presented here, are a vital support for this effort. The ground and excited electronic state potential energy surfaces of 3,3'-diamino-4,4'-azoxyfurazan (DAAF) have been investigated using multi-configurational SCF and electron correlation methods. We will describe the geometrical and energetic character of the excited state minima, reaction coordinates and conical intersections of DAAF. The mechanisms for both radiative and non-radiative quenching of excited state population as well as possible pathways for photochemical and spectroscopic control will be outlined. [Preview Abstract] |
Monday, June 29, 2009 10:15AM - 10:30AM |
B3.00005: Decomposition Products of RDX and TNT after Resonant Laser Excitation Jeremy Monat, Jared Gump This presentation describes research on the gas-phase products of decomposition of explosives after resonant laser excitation. We studied RDX, TNT, and formulations containing them after excitation by lasers in the infrared (10.6 4$\mu$m continuous-wave [CW]; resonant with ring vibrational modes) and ultraviolet (266 nm CW and pulsed [ca. 5 ns pulsewidth]; resonant with delocalized ring electronic absorptions). The decomposition products in air were identified by infrared spectroscopy and will be described as a function of laser wavelength and energy deposition timescale. Our results will be compared to decomposition pathways in the literature derived from resistive heating techniques. [Preview Abstract] |
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