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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Directional Degradation of Spectralon Diffuser Under Ionizing Radiation for Calibration of Space-Based Sensors

Assessment of the effect of Vacuum Ultra Violet (VUV) irradiation on the Bidirectional Reflectance Distribution Function (BRDF) of Spectralon is presented in this paper. The sample was a 99% white Spectralon calibration standard irradiated with VUV source positioned at 60o off the irradiation direction for a total of 20 hours. The BRDF before and after VUV irradiation was measured and compared at number of wavelengths in the UV, VIS and IR. Non-isotropic directional degradation of Spectralon diffuser under ionizing radiation was detected at different BRDF measurement geometries primarily at UV spectral range. The 8o directional/hemispherical reflectance of the same sample was also measured and compared from 200nm to 2500nm. Index Terms BRDF, Reflectance, Multiangular, Spectralon, Remote Sensing

Georgiev, G. T.↗
NASA NTRS2010

Characterization and Absolute QE Measurements of Delta-Doped N-Channel and P-Channel CCDs

In this paper we present the methodology for making absolute quantum efficiency (QE) measurements from the vacuum ultraviolet (VUV) through the near infrared (NIR) on delta-doped silicon CCDs. Delta-doped detectors provide an excellent platform to validate measurements through the VUV due to their enhanced UV response. The requirements for measuring QE through the VUV are more strenuous than measurements in the near UV and necessitate, among other things, the use of a vacuum monochromator, and good camera vacuum to prevent chip condensation, and more stringent handling requirements. The system used for these measurements was originally designed for deep UV characterization of CCDs for the WF/PC instrument on Hubble and later for Cassini CCDs.

Jacquot, Blake C.↗
DOE OSTI2025

Probing the pH Effect on Boehmite Particles in Water Using Vacuum Ultraviolet Single-Photon Ionization Mass Spectrometry

Boehmite has been widely used in theoretical research and industry, especially for hazardous material processing. For the liquid-phase treating process, the interfacial properties of boehmite are believed to be affected by pH conditions, which change its physicochemical behavior. However, molecular-level detection on cluster ions is challenging when using bulk approaches. Herein we employ in situ vacuum ultraviolet single-photon ionization mass spectrometry (VUV SPI-MS) coupled with a vacuum-compatible microreactor system for analysis at the liquid–vacuum interface (SALVI) to investigate the solute molecular composition of boehmite under different pH conditions for the first time. The mass spectral results show that more complex clustering of solute molecules exists at the solid–liquid (s–l) interface than conventionally perceived in a “simple” aqueous solution. Besides solute ions, such as boehmite molecules and fragments, the composition and appearance energies of these newly discovered solvated cluster ions are determined by VUV SPI-MS in different pH solutions. We offer new results for the pH-dependent effect of boehmite and provide insights into a more detailed solvation mechanism at the s–l interface. By comparing the key products under different pH conditions, fundamental understanding of boehmite dissolution is revealed to assist the engineering design of waste processing and storage solutions.

SALVI↗
DOE OSTI2025

A Synchrotron-Based Vacuum Ultraviolet Photoionization Mass Spectrometer-Coupled Microreactor To Probe Thermocatalysis

Vacuum ultraviolet photoionization (VUV-PI) mass spectrometry offers an isomer-selective and universal ionization with minimal fragmentation detection of organics in complex chemical systems such as pyrolysis and combustion. Here, in this study, we report a state-of-the-art experimental setup of a universal catalytic microreactor combined with a molecular beam to investigate the thermocatalytic oxidation of a heterogeneous system relevant for probing reactions at gas–solid interfaces. In strong contrast to traditional off-line analytical methods, this technique is capable of identifying and quantifying short-lived species (radicals) as well as stable products to decipher initial reaction steps via the detection of nascent products. The thermocatalytic oxidative degradation of exo-tetrahydrodicyclopentadiene (JP-10), a high energy-density hydrocarbon fuel, over solid titanium–aluminum–boron reactive mixed metal nanopowder (Ti-Al-B RMNP) is exploited to showcase potential applications. Overall, some 59 nascent gas-phase products are identified via photoionization efficiency (PIE) curves, including oxygenated species and hydrocarbons comprising closed-shell molecules and radicals. The critical temperature for complete oxidative decomposition of JP-10 was lowered by 450 K from 1400 K to 950 K, indicating an efficient thermocatalytic action of Ti-Al-B nanoparticles on JP-10. The enabling of a universal chemical microreactor along with VUV-PI mass spectrometry broadens the applicability of this technique to hydrocarbon fuel oxidation and pyrolysis characterization. This isomer-selective sensitive probing along with the detection of radical transients makes the aforementioned technique superior to other conventional analytical techniques such as microflow tube and pyrolysis-gas chromatography coupled with mass spectrometry for investigating similar pyrolysis reactions and comprehensive quantification.

Paul, Dababrata [Univ. of Hawaii at Manoa, Honolul↗
DOE OSTI2025

Time-resolved vacuum-ultraviolet photoelectron spectroscopy of the à 1 A u state of acetylene

Ultrafast time-resolved photoelectron spectra are reported for the vacuum-ultraviolet (VUV) photoionization of acetylene following excitation to the à 1 A u state via UV absorption at 200 nm. The excitation energy lies above the lowest dissociation threshold to C 2 H X̃ 2 Σ + + H, as well as above the threshold for adiabatic dissociation of the à 1 A u state to form C 2 H (à 2 Π) + H. The time-dependent mass spectra and photoelectron spectra provide insight into the intramolecular decay processes of the à 1 A u state. In addition, photoelectron spectra of the à 1 A u state with VUV light access both the X̃ 2 Π u and à 2 Σ g + states of the ion, as well as the predicted, but previously unobserved, 1 2 Π g state, which corresponds to a two-hole, one-particle configuration that lies in close proximity to the à 2 Σ g + state. The 1 2 Π g state is split into 2 A 2 + 2 B 2 and 2 A g + 2 B g states in the cis and trans configurations, respectively. In conclusion, electronic structure calculations, along with trajectory calculations, reproduce the principal features of the experimental data and confirm the assignment of the 1 2 Π g state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1976

The spectral properties of uranium hexafluoride and its thermal decomposition products

This investigation was initiated to provide basic spectral data for gases of interest to the plasma core reactor concept. The attenuation of vacuum ultraviolet (VUV) radiation by helium at pressures up to 20 atm over path lengths of about 61 cm and in the approximate wavelength range between 80 and 300 nm was studied. Measurements were also conducted to provide basic VUV data with respect to UF6 and UF6/argon mixtures in the wavelength range between 80 and 120 nm. Finally, an investigation was initiated to provide basic spectral emission and absorption data for UF6 and possible thermal decomposition products of UF6 at elevated temperatures.

Krascella, N. L.↗
NASA NTRS1979

Experimental setup for decomposition of UF6

The rate at which UF6 decomposes into UF5 and UF4 was determined as a function of neutron fluence. To study UF6 decomposition rate, an absorption cell for VUV and the associated VUV spectroscopy system was used to measure UF6 while under irradiation. The cell contains 50 torr of UF6 at room temperature to insure that the UF6 is in a gaseous state. It is shown that by determining the absorption coefficient below 2100A for UF6, above 2100A for F2, and at 4100A for cell degradation, UF6 decomposition can be measured at a neutron flux of 10 to the 12th power/sq cm for 72 continuous hours.

Rowe, M.↗
NASA NTRS1980

Pristine nature of comets as revealed by their UV spectrum

Satellite and rocket VUV observations of comets are discussed with reference to observations of OH and NH; the Lyman-alpha halo of hydrogen; and C, O, S atoms, ions, and molecules. Attention is also given to the study of production rates, and elemental and molecular abundances. It is shown that the observation of the VUV spectrum of comets has revealed new clues about comets, which could serve as a link between interstellar molecules and planetary atmospheres as well as between stellar and planetary astrophysics.

Delsemme, A. H.↗
NASA NTRS1981

Vacuum ultraviolet Mach-Zehnder interferometer with CaF2 optics

CaF2 beam splitters and compensation and test cell windows have been installed in a VUV Mach-Zehnder interferometer. Results of an evaluation of their performance in the VUV, namely, a measurement of the oscillator strength (f value) of the resonance transition at atomic xenon at 146.9610 nm are reported.

Smith, P. L.↗
NASA NTRS1982

General contamination criteria for optical surfaces

Physical models are developed for establishing criteria to decide on the acceptable contamination level of optical devices in space-borne conditions. Optical systems can be degraded in terms of decreased throughput, i.e., transmissivity or reflectivity, or increases in the total integrated scatter (TIS). Performance losses can be caused by particulate accretion, molecular film accretion, and impact cratering. A quantitative relationship is defined for film thickness and loss of throughput. Formulas are also developed for cases where induced surface defects are larger than the desired viewing wavelengths, or smaller or of the same order of the observed wavelengths. The techniques are used to quantify the degradation of a VUV solar coronagraph, a VUV stellar telescope, and a solar cell due to TIS. Applications are projected for estimating the contamination sensitivity of specific instruments, assessing the contamination hazard from known particulates, or to define clean room standards.

Bremer, J. C.↗
NASA NTRS1981

Photon-counting array detectors for space and ground-based studies at ultraviolet and vacuum ultraviolet /VUV/ wavelengths

The Multi-Anode Microchannel Arrays (MAMAs) are a family of photoelectric photon-counting array detectors, with formats as large as (256 x 1024)-pixels that can be operated in a windowless configuration at vacuum ultraviolet (VUV) and soft X-ray wavelengths or in a sealed configuration at ultraviolet and visible wavelengths. This paper describes the construction and modes of operation of (1 x 1024)-pixel and (24 x 1024)-pixel MAMA detector systems that are being built and qualified for use in sounding-rocket spectrometers for solar and stellar observations at wavelengths below 1300 A. The performance characteristics of the MAMA detectors at ultraviolet and VUV wavelengths are also described.

Timothy, J. G.↗
NASA NTRS1984

Quantum efficiency measurements for several waveshifter coatings in the extreme vacuum ultraviolet

Quantum efficiency measurements are given for coronene and liumogen coatings designed to enhance UV sensitivity for silicon charge coupled device imaging detectors. Coatings on quartz and on UDT PIN 10DP photodiodes were tested. The wavelength range extended from 153.7 to 50.0 nm in the vacuum ultraviolet. Similar measurements were made for coronene, liumogen, and stilbene-3 laser dye films on quartz disks relative to sodium salicylate. Sodium salicylate and coronene are the most efficient waveshifters down to 50 nm so far observed. Coronene's fairly constant quantum efficiency over such a wide wavelength range into the far VUV makes it a useful waveshifter for UV and VUV applications.

Butner, C. L.↗
NASA NTRS1984

Surface sensitive photoemission EXAFS: A new structural tool

A new technique for surface EXAFS has been developed. In this technique the absorption fine structure is observed by monitoring the photoelectrons emitted from core levels as a function of photon energy. The surface sensitivity is achieved by detecting elastic photoelectrons that escape to the vacuum from a few atomic layers near the surface. EXAFS from Mn 3p and F2s outer core levels in MnF2 were measured, the results were compared with transmission EXAFS from Mn ls core level and good agreement was found. This development is significant because: (1) almost all elements have suitable core levels of low binding energy; (2) since photopeaks from adjacent core levels do not cross as the photon energy is varied, the limitations imposed on other surface EXAFS techniques by this interference is removed. Auger electrons, which have fixed kinetic energies and so can cross photopeaks, will generally have low energies if they originate from outer core levels and be unlikely to appear in the EXAFS region of kinetic energies, i.e., in excess of about 50 eV; (3) VUV light is used, which greatly extends the usable range of photon energies; (4) more than one element in a solid may be studied with the same monochromator. The experiments were carried out on the VUV beam line U14A at NSLS.

Choudhary, K. M.↗
NASA NTRS1987

Vacuum ultraviolet images of the Large Magellanic Cloud

Linearized, absolutely calibrated VUV images of the LMC with a resolution of about 50 arcsec are presented. The images were made by a sounding rocket payload in two bandpasses with effective wavelengths for hot stars near 1500 A and 1930 A. The flux in each bandpass is measured for the associations in the list of Lucke and Hodge (1970). The results are discussed and their relationship to the overall characteristics of star formation in the LMC are discussed. A simple model for propagating star formation in the LMC is presented whose results closely resemble the distribution of associations revealed by the VUV images.

Smith, Andrew M.↗
NASA NTRS1988

Simple ultraviolet calibration source with reference spectra and its use with the Galileo orbiter ultraviolet spectrometer

A simple compact electron impact laboratory source of UV radiation has been developed and is used to obtain calibrated optically thin VUV spectra and synthetic spectral models for important molecular band systems of H2, N2, and the n 1P0 Rydberg series of He. The relative spectral intensity of the electron impact source can be used as the primary calibration standard for VUV instrumentation in the 80-230 nm range and with FWHM of not less than 0.4 nm. The accuracy of the present method is 10 percent in the FUV and 20 percent in the EUV. Results for calibration of the Galileo orbiter ultraviolet spectrometer have been compared with those obtained using other methods.

Shemansky, D. E.↗
NASA NTRS1987

Self-contained space qualifiable optical contamination monitor

Experiments operating in the VUV as well as those employing cryocooled optical surfaces are the most seriously affected by spacecraft contamination due to outgassing of foreign materials, reaction byproducts of thruster firings, system venting emissions, etc. Attention is presently given to a self-contained optical contamination monitor, furnishing in-flight and/or real-time monitoring of VUV reflectivity and transmittance. The time-lining of measurement results with other spacecraft events will allow the direct evaluation of spacecraft operation effects on critical optical surfaces.

Jarratt, R. V., Jr.↗
NASA NTRS1988

Contamination effects study

The in-situ optical surface measurement system is a facility designed to study the deleterious effects of particulate materials on the surface reflectivities of optical materials in the vacuum ultraviolet (VUV). This arrangement is designed to simulate the on-orbit effects of contamination and degradation of optical surfaces. This simulation is accomplished through the use of non-coherent VUV sources illuminating optical surfaces located in a high vacuum chamber. Several sources of contamination are employed. The reflectivity is measured both at the specular reflection as well as at two scattered positions, forward and reverse. The system components are described and an operating procedure is given.

Source record↗
NASA NTRS1989

A comparison of ionospheric conductances and auroral luminosities observed simultaneously with the Chatanika radar and the DE 1 auroral imagers

Auroral luminosities at vacuum ultraviolet (VUV) wavelengths are combined with simultaneous and coincident ionospheric electron density measurements made by the Chatanika radar to relate ionospheric conductances to optical emissions. The auroral luminosities are obtained along the magnetic meridian through Chatanika with the auroral imaging photometers on the Dynamics Explorer 1 satellite as the radar scans in the magnetic meridian to measure electron density and conductivity as a function of altitude and latitude. The observations are used to determine an empirical relationship between the luminosities measured at VUV wavelengths and the Hall and Pedersen conductances.

Robinson, R. M.↗