speckle-tracking: a software suite for ptychographic X-ray speckle tracking
Explore the source record for details and available documents.
99 GENERAL AND MISCELLANEOUS↗
Engineering topics
Bajt, S.
Publications and source records attributed to Bajt, S..
Ultrafast nonthermal heating of water initiated by an X-ray Free-Electron Laser
Explore the source record for details and available documents.
99 GENERAL AND MISCELLANEOUS↗
Time-Resolved XUV Opacity Measurements of Warm Dense Aluminum
The free-free opacity in plasmas is fundamental to our understanding of energy transport in stellar interiors and for inertial confinement fusion research. However, theoretical predictions in the challenging dense plasma regime are conflicting and there is a dearth of accurate experimental data to allow for direct model validation. Here we present time-resolved transmission measurements in solid-density Al heated by an XUV free-electron laser. We use a novel functional optimization approach to extract the temperaturedependent absorption coefficient directly from an oversampled pool of single-shot measurements, and find a pronounced enhancement of the opacity as the plasma is heated to temperatures of order of the Fermi energy. Plasma heating and opacity enhancement are observed on ultrafast timescales, within the duration of the femtosecond XUV pulse. We attribute further rises in the opacity on ps timescales to melt and the formation of warm dense matter
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Status of the Stardust ISPE and the Origin of Four Interstellar Dust Candidates
Some bulk properties of interstellar dust are known through infrared and X-ray observations of the interstellar medium. However, the properties of individual interstellar dust particles are largely unconstrained, so it is not known whether individual interstellar dust particles can be definitively distinguished from interplanetary dust particles in the Stardust Interstellar Dust Collector (SIDC) based only on chemical, mineralogical or isotopic analyses. It was therefore understood from the beginning of the Stardust Interstellar Preliminary Examination (ISPE) that identification of interstellar dust candidates would rest on three criteria - broad consistency with known extraterrestrial materials, inconsistency with an origin as secondary ejecta from impacts on the spacecraft, and consistency, in a statistical sense, of observed dynamical properties - that is, trajectory and capture speed - with an origin in the interstellar dust stream. Here we quantitatively test four interstellar dust candidates, reported previously [1], against these criteria.
Westphal, A. J.↗
Constraints on the Interstellar Dust Flux Based on Stardust at Home Search Results
Recent advances in active particle selection in the Heidelberg Van de r Graaf (VdG) dust accelerator have led to high-fidelity, low-backgro und calibrations of track sizes in aerogel as a function of particle size and velocity in the difficult regime above 10 km sec..1 and sub micron sizes. To the extent that the VdG shots are analogs for inters tellar dust (ISD) impacts, these new measurements enable us to place preliminary constraints on the ISD flux based on Stardust@home data.
Zolensky, Michael E.↗
Identification of Impact Craters in Foils from the Stardust Interstellar Dust Collector
The Stardust Interstellar Dust Collection tray provides the first opportunity for the direct laboratory-based measurement of contemporary interstellar dust. The total exposed surface of the tray was approximately 0.1 square meters, including 153 square centimeters of Al foil in addition to the silica aerogel tiles that are the primary collection medium. Preliminary examination of aerogel tiles has already revealed 16 tracks from particle impacts with an orientation consistent with an interstellar origin, and to date four of the particles associated with these tracks have a composition consistent with an extraterrestrial origin. Tentative identification of impact craters on three foil samples was also reported previously. Here we present the definitive identification of 20 impact craters on five foils.
Stroud, R. M.↗
A New View on Interstellar Dust - High Fidelity Studies of Interstellar Dust Analogue Tracks in Stardust Flight Spare Aerogel
In 2000 and 2002 the Stardust Mission exposed aerogel collector panels for a total of about 200 days to the stream of interstellar grains sweeping through the solar system. The material was brought back to Earth in 2006. The goal of this work is the laboratory calibration of the collection process by shooting high speed [5 - 30km/s] interstellar dust (ISD) analogues onto Stardust aerogel flight spares. This enables an investigation into both the morphology of impact tracks as well as any structural and chemical modification of projectile and collector material. First results indicate a different ISD flux than previously assumed for the Stardust collection period.
Zolensky, Michael E.↗
FTIR Analysis of Aerogel Keystones from the Stardust Interstellar Dust Collector: Assessment of Terrestrial Organic Contamination and X-Ray Microprobe Beam Damage
The Stardust Interstellar Dust Collector (SIDC) was intended to capture and return contemporary interstellar dust. The approx.0.1 sq m collector was composed of aerogel tiles (85% of the collecting area) and aluminum foils and was exposed to the interstellar dust stream for a total exposure factor of 20 sq m day. The Stardust Interstellar Preliminary Examination (ISPE) is a consortium-based project to characterize the collection using nondestructive techniques. Sandford et al. recently assessed numerous potential sources of organic contaminants in the Stardust cometary collector. These contaminants could greatly complicate the analysis and interperetation of any organics associated with interstellar dust, particularly because signals from these particles are expected to be exceedingly small. Here, we present a summary of FTIR analyses of over 20 aerogel keystones, many of which contained candidates for interstellar dust.
Zolensky, M. E.↗
Four Interstellar Dust Candidates from the Stardust Interstellar Dust Collector
In January 2006, the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, Comet 81P/Wild2, and a collector dedicated to the capture and return of contemporary interstellar dust. Both collectors were approx. 0.1 sq m in area and were composed of aerogel tiles (85% of the collecting area) and aluminum foils. The Stardust Interstellar Dust Collector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 sq m/day. The Stardust Interstellar Preliminary Examination (ISPE) is a consortium-based project to characterize the collection using nondestructive techniques. The goals and restrictions of the ISPE are described . A summary of analytical techniques is described.
Westphal, A. J.↗
Stardust Interstellar Preliminary Examination (ISPE)
In January 2006 the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, C omet 81P/Wild2, and a collector dedicated to the capture and return o f contemporary interstellar dust. Both collectors were approximately 0.1m(exp 2) in area and were composed of aerogel tiles (85% of the co llecting area) and aluminum foils. The Stardust Interstellar Dust Col lector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 m(exp 2-) day during two periods before the co metary encounter. The Stardust Interstellar Preliminary Examination ( ISPE) is a three-year effort to characterize the collection using no ndestructive techniques. The ISPE consists of six interdependent proj ects: (1) Candidate identification through automated digital microsco py and a massively distributed, calibrated search (2) Candidate extr action and photodocumentation (3) Characterization of candidates thro ugh synchrotronbased FourierTranform Infrared Spectroscopy (FTIR), S canning XRay Fluoresence Microscopy (SXRF), and Scanning Transmission Xray Microscopy (STXM) (4) Search for and analysis of craters in f oils through FESEM scanning, Auger Spectroscopy and synchrotronbased Photoemission Electron Microscopy (PEEM) (5) Modeling of interstell ar dust transport in the solar system (6) Laboratory simulations of h ypervelocity dust impacts into the collecting media
Westphal, A. J.↗
Overview of the Results of the Organics PET Study of the Cometary Samples from Comet Wild 2 by the Stardust Mission
STARDUST is the first mission designed to bring samples back to Earth from a known comet. The captured samples were successfully returned to Earth on 15 Jan 2006, after which they were subjected to a preliminary examination by a number of teams of scientists from around the world. This abstract describes the efforts of the Organics Preliminary Examination Team (PET). More detailed discussions of specific analyses of the samples can be found in other papers presented at this meeting by individual members of the Organics PET (see the author list above for team members). The studied Wild 2 gas and dust samples were collected by impact onto aerogel tiles and Al foils when the spacecraft flew through the coma of 81P/Wild 2 on 2 Jan 2004 at a relative velocity of approx.6.1 kilometers per second. After recovery of the Sample Return Capsule (SRC) on 15 Jan 2006, the aerogel collector trays were removed in a clean room at JSC. After documentation of the collection, selected aerogel tiles and aluminum foils were removed and aerogel and cometary samples extracted for study.
Sandford, S. A.↗
Nitrogen Isotopic Anomalies in a Hydrous Interplanetary Dust Particle
Interplanetary dust particles (IDPs) collected in the stratosphere are the fine-grained end member (5 - 50 microns in size) of the meteoritic material available for investigation in the laboratory. IDPs are derived from either cometary or asteroidal sources. Some IDPs contain cosmically primitive materials with isotopic signatures reflecting presolar origins. Recent detailed studies using the NanoSIMS have shown there is a wide variation of isotopic signatures within individual IDPs; grains with a presolar signature have been observed surrounded by material with a solar isotopic composition. The majority of IDPs studied have been anhydrous. We report here results from integrated NanoSIMS/FIB/TEM/Synchrotron IR studies of a hydrous IDP, focused on understanding the correlations between the isotopic, mineralogical and chemical compositions of IDPs.
Smith, J. B.↗
Chemical compositions of primitive solar system particles
Chemical studies of micrometeorites are of fundamental importance primarily because atmospheric entry selection effects (such as destruction of friable objects) are less significant than those for conventional meteorites. As a result, particles that have experienced very little postaccretional processing have a significant chance of surviving the Earth encounter and subsequent collection. Thus, chemical analyses of these relatively unaltered micrometeorites may lead to a better understanding of the compositions of the most primitive materials in the solar system and thereby constrain the conditions (physical and chemical) that existed in the early solar nebula. Micrometeorites have been collected from the stratosphere, polar ices, and ocean sediments, but the stratospheric collection is the best source for the most unaltered material because they are small and are not heated to their melting points. Despite the fact that the stratospheric micrometeorites have masses in the nanogram range, a variety of microanalytical techniques have been applied to bulk chemical analyses with part-per-million sensitivity. In some cases, multi-disciplinary studies (e.g., chemistry and mineralogy) have been performed on individual particles. The first-order conclusion is that the chondrite-like particles are chemically similar to carbonaceous chondrites but in detail are distinct from members of the conventional meteorite collection. The purpose of this paper is to provide an overview of the results to date and identify important areas for further study.
Sutton, Steve R.↗
Reduced chromium in olivine grains from lunar basalt 15555 - X-ray Absorption Near Edge Structure (XANES)
The oxidation state of Cr in 200-micron regions within individual lunar olivine and pyroxene grains from lunar basalt 15555 was inferred using X-ray Absorption Near Edge Structure (XANES). Reference materials had previously been studied by optical absorption spectroscopy and included Cr-bearing borosilicate glasses synthesized under controlled oxygen fugacity and Cr-doped olivines. The energy dependence of XANES spectral features defined by these reference materials indicated that Cr is predominantly divalent in the lunar olivine and trivalent in the pyroxene. These results, coupled with the apparent f(02)-independence of partitioning coefficients for Cr into olivine, imply that the source magma was dominated by divalent Cr at the time of olivine crystallization.
Sutton, S. R.↗
Trace element content of chondritic cosmic dust: Volatile enrichments, thermal alterations, and the possibility of contamination
Trace element abundances in 51 chondritic Interplanetary Dust Particles (IDP's) were measured by Synchrotron X-Ray Fluorescence (SXRF). The data allow us to determine an average composition of chondritic IDP's and to examine the questions of volatile loss during the heating pulse experienced on atmospheric entry and possible element addition due to contamination during atmospheric entry, stratospheric residence, and curation.
Flynn, G. J.↗
Depletions of sulfur and/or zinc in IDPs: Are they reliable indicators of atmospheric entry heating?
The degree of heating of interplanetary dust particles (IDP's) on Earth atmospheric entry is important in distinguishing cometary particles from main-belt asteroidal particles. Depletions in the volatile elements S and Zn were proposed as chemical indicators of significant entry heating. The S and Zn contents of cosmic dust particles were correlated with physical indicators of atmospheric entry heating, such as the production of magnetite and the loss of solar wind implanted He. The results indicate that the Zn content of IDP's is a useful indicator of entry heating, but the S content seems to be less useful.
Flynn, G. J.↗
New low-Ni (igneous?) particles among the C and C? types of cosmic dust
Low-Ni particles with major element abundances, optical properties, and morphologies sufficiently similar to chondritic interplanetery dust particles (IDP's) to receive JSC Cosmic Dust Catalog classifications of C or C?-types were shown to have trace element contents and mineralogies similar to igneous material. Examination of the JSC Catalog EDX spectra by Cooke et al. has shown that 13 percent of the C-type and 38 percent of the C?-type particles are potentially low-Ni particles. Two new low-Ni particles were identified, and it was shown that an additional fragment from the L2002*C cluster has an igneous composition. A newly analyzed fragment of the W7066*A cluster has a chondritic composition. The W7066*A cluster is important because it has yielded a fragment of igneous composition and another fragment having high concentrations of He and Ne suggesting an extraterrestrial origin.
Flynn, G. J.↗
Wavelength dispersive analysis with the synchrotron x ray fluorescence microprobe
A wavelength dispersive spectrometer (WDS) was tested on the synchrotron x ray fluorescence microprobe at Brookhaven National Laboratory. Compared to WDS spectra using an electron microprobe, the synchrotron WDS spectra have much better sensitivity and, due to the absence of bremsstrahlung radiation, lower backgrounds. The WDS spectrometer was successfully used to resolve REE L fluorescence spectra from standard glasses and transition metal K fluorescence spectra from kamacite.
Rivers, M. L.↗