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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Development of Metallic Magnetic Calorimeters for High Precision Measurements of Calorimetric Re-187 and Ho-163 Spectra

The measurement of calorimetric spectra following atomic weak decays, beta (b) and electron capture (EC), of nuclides having a very low Q-value, can provide an impressively high sensitivity to a non-vanishing neutrino mass. The achievable sensitivity in this kind of experiments is directly connected to the performance of the used detectors. In particular an energy resolution of a few eV and a pulse formation time well below 1 microsecond are required. Low temperature Metallic Magnetic Calorimeters (MMCs) for soft X-rays have already shown an energy resolution of 2.0 eV FWHM and a pulse rise-time of about 90 ns for fully micro-fabricated detectors. We present the use of MMCs for high precision measurements of calorimetric spectra following the beta-decay of Re-187 and the EC of Ho-163. We show results obtained with detectors optimized for Re-187 and for Ho-163 experiments respectively. While the detectors equipped with superconducting Re absorbers have not yet reached the aimed performance, a first detector prototype with a Au absorber having implanted Ho-163 ions already shows excellent results. An energy resolution of 12 eV FWHM and a rise time of 90 ns were measured.

Ranitzsch, P. C.-O.↗
NASA NTRS1975

Behavior of some singly ionized, heavy-ion impurities during compression in a theta-pinch plasma

The introduction of a small percentage of an impurity gas containing a desired element into a theta-pinch plasma is a standard procedure used to investigate the spectra and atomic processes of the element. This procedure assumes that the mixing ratio of impurity-to-fill gases remains constant during the collapse and heating phase. Spectroscopic investigations of the constant-mixing-ratio assumption for a 2% neon and argon impurity verifies the assumption only for the neon impurity. However, for the 2% argon impurity, only 20 to 25% of the argon is in the high-temperature compressed plasma. It is concluded that the constant-mixing-ratio assumption is not applicable to the argon impurity.

Jalufka, N. W.↗
NASA NTRS1977

Facular line profiles and facular models

Profiles for lines near 5250 A have been calculated from facular models and compared with observed profiles. The observations are from photographic and photoelectric spectra. The atomic parameters are determined by comparison of calculated profiles with those observed for the quiet sun. The effects of finite spatial resolution and a magnetic field are required to obtain agreement with observed facular line profiles. The empirical magnetic field deduced by matching observed and calculated profiles is reasonably consistent with that in the facular models. The main purpose of this paper is to show that by including the effects of scattered photospheric light and a strong magnetic field, reasonable agreement can be achieved between observed and calculated facular line profiles. Results are also presented for the wing of the Ca II K line, showing line profiles and effective filtergram contrasts for several facular models. It is concluded that observations made with weak Fraunhofer lines are not very useful for discrimination among facular models, particularly without simultaneous magnetic-field measurements. The K line may offer a better discriminator. The facular model presently favored has a magnetic field strength of about 1500 gauss at the surface of the photosphere.

Chapman, G. A.↗
NASA NTRS1977

Apollo-Soyuz pamphlet no. 5: The earth from orbit

Astronaut training in the recognition of various geological features from space is described as well as the cameras, lenses and film used in experiment MA-136 to measure their effectiveness in photographing earth structural features from orbit. Aerosols that affect climate and weather are discussed in relation to experiment Ma-007 which relied on infrared observations of the setting or rising sun, as seen from Apollo, to measure the amount of dust and droplets in the lower 150 km of earth's atmosphere. The line spectra of atomic oxygen and nitrogen and their densities at 22 km above the earth's surface are examined along with experiment MA-059 which measured ultraviolet absorption at that altitude.

Page, L. W.↗
NASA NTRS1977

The pristine nature of comets

Abundance considerations suggest that comets are likely to be the most pristine minor bodies in the solar system. In proportion to solar abundances, the present scanty data suggest that cometary oxygen is not depleted, whereas carbon is by a factor of 4 and hydrogen, by a factor of 2000. This implies that comets are less depleted in H, C, N, O than CI chondrites, namely 10:1 in hydrogen, 4:1 in carbon and 3:1 in oxygen. These results have been obtained by using dust-to-gas ratios in comets to measure the relative abundance of silicon and metals to volatile material, and the spectra of atomic lines, mainly from the vacuum ultraviolet, to determine the H/O and C/O ratios of the mixture of volatile molecules.

Delsemme, A. H.↗
NASA NTRS1979

Some implications of revised OI /7990 A/ and OI /11287 A/ branching ratios

Recent laboratory, geophysical, and theoretical determinations of the O I (7990 A) and O I (11,287 A) branching ratios indicate that the generally used values based on the NBS transition parameters need revision. The O I (7990 A) branching ratio is about 300 times smaller than the NBS value, and the O I (11,287 A) is about one-quarter as large. The transitions are important in the generation of permitted atomic oxygen spectra in several types of astronomical source, including the Orion Nebula (M42), the Seyfert galaxy NGC 4151, Arcturus, and comets. The absence of the O I (7990 A) emission in M42 and NGC 4151 is consistent with its very small branching ratio, and previous conclusions based on its absence, such as the rejection of starlight excitation in the Seyfert galaxy, require reinvestigation. The reduction of the O I (11,287 A) branching ratio is pertinent to hydrogen L-beta fluorescence excitation of O I (1304 A) and O I (8446 A) emission and requires an upward revision of oxygen production rates in comets.

Christensen, A. B.↗
NASA NTRS1987

Hydrogen emission from Jupiter: Hydrogen emission from sunlit atmosphere of Saturn

Successful IUE observations of the equatorial sunlit atmosphere of Jupiter and Saturn have been obtained. Spectra containing atomic and molecular hydrogen and solar reflection continuum emissions have been analyzed, with the purpose of determining the long term temporal behavior of the electroglow process. Quantitative estimates have been established for the first time using a model analysis of the short wavelength region of the spectrum. Both systems show varying degrees of long term variability in hydrogen emission rate, but the time scale is too short to determine whether there is a dependence on solar cycle activity. As part of the emission modeling program, a preliminary point source spreading function for the IUE SWP instrument has been established, suggesting a wavelength dependence in spectral line width different from previous analyses. Further IUE observations are planned for both Jupiter and Saturn.

Shemansky, D. E.↗
NASA NTRS1991

Ground-based observations of comets, the Jupiter plasma Torus, and Io

Aspects of cometary and magnetospheric physics were investigated by means of ground-based astronomical spectroscopy. High-throughput, dual-etalon Fabry-Perot spectrometers were used to obtain very high resolution spectra of atomic, molecular, and ionic emission lines from the diffuse gases and plasmas associated with comets and the Jupiter plasma torus. The Fabry-Perot spectrometers were also used with a charge coupled device (CCD) camera to obtain images of these extended emission sources in individual spectral lines at high spectral resolution. A new program using the McMath solar-stellar spectrograph to observe emission lines from Io was recently initiated. The McMath spectrograph has a high resolution mode which allows the detection of narrow, relatively faint emission lines superimposed on Io's reflected solar spectrum.

Scherb, Frank↗
NASA NTRS1996

NEQAIR96,Nonequilibrium and Equilibrium Radiative Transport and Spectra Program: User's Manual

This document is the User's Manual for a new version of the NEQAIR computer program, NEQAIR96. The program is a line-by-line and a line-of-sight code. It calculates the emission and absorption spectra for atomic and diatomic molecules and the transport of radiation through a nonuniform gas mixture to a surface. The program has been rewritten to make it easy to use, run faster, and include many run-time options that tailor a calculation to the user's requirements. The accuracy and capability have also been improved by including the rotational Hamiltonian matrix formalism for calculating rotational energy levels and Hoenl-London factors for dipole and spin-allowed singlet, doublet, triplet, and quartet transitions. Three sample cases are also included to help the user become familiar with the steps taken to produce a spectrum. A new user interface is included that uses check location, to select run-time options and to enter selected run data, making NEQAIR96 easier to use than the older versions of the code. The ease of its use and the speed of its algorithms make NEQAIR96 a valuable educational code as well as a practical spectroscopic prediction and diagnostic code.

Whiting, Ellis E.↗
NASA NTRS1999

Recent Advances in Laser Remote Sensing

Current terrestrial and hydrographic laser remote sensing research and applications are briefly reviewed. New progress in airborne oceanic lidar instrumentation and applications is then highlighted. Topics include a discussion of the unique role of airborne active-passive (laser-solar) correlation spectroscopy methods in oceanic radiative transfer studies and satellite ocean color algorithm development. Based on a perceived need for high resolution laser-induced resonance Raman and atomic emission spectra of oceanic constituents, future airborne lidar transmitter and receiver configurations are suggested.

Hoge, Frank E.↗
NASA NTRS2010

Partial Least Squares and Neural Networks for Quantitative Calibration of Laser-induced Breakdown Spectroscopy (LIBs) of Geologic Samples

The ChemCam instrument [1] on the Mars Science Laboratory (MSL) rover will be used to obtain the chemical composition of surface targets within 7 m of the rover using Laser Induced Breakdown Spectroscopy (LIBS). ChemCam analyzes atomic emission spectra (240-800 nm) from a plasma created by a pulsed Nd:KGW 1067 nm laser. The LIBS spectra can be used in a semiquantitative way to rapidly classify targets (e.g., basalt, andesite, carbonate, sulfate, etc.) and in a quantitative way to estimate their major and minor element chemical compositions. Quantitative chemical analysis from LIBS spectra is complicated by a number of factors, including chemical matrix effects [2]. Recent work has shown promising results using multivariate techniques such as partial least squares (PLS) regression and artificial neural networks (ANN) to predict elemental abundances in samples [e.g. 2-6]. To develop, refine, and evaluate analysis schemes for LIBS spectra of geologic materials, we collected spectra of a diverse set of well-characterized natural geologic samples and are comparing the predictive abilities of PLS, cascade correlation ANN (CC-ANN) and multilayer perceptron ANN (MLP-ANN) analysis procedures.

Anderson, R. B.↗
NASA NTRS2018

Calculation of Thermochemical Properties of Carbon-cluster Ablation Species

Carbon clusters and hydrocarbons are constituents of the pyrolysis gases injected into the boundary layer of a space vehicle with a carbonaceous heat shield. These molecules have absorption spectra in the VUV and UV region that match the emission spectra of atomic nitrogen and oxygen. Hence, they can potentially absorb the radiation impinging on the heat shield of the space vehicle. This paper studies the ground state thermochemical properties and low-lying excited electronic states of potential radiation absorbing molecules present in the boundary layer using ab initio quantum chemistry methods. These results provide a more accurate prediction of the radiative heat flux on the surface which can lead to improvement in the design of the thermal protection system.

enthalpy↗
NASA NTRS2019

Thermodynamic Analysis of Boundary Layer Species During Ablation

The focus of this work is on carbon clusters, hydrocarbons and other carbonaceous species which are constituents of pyrolysis gases injected into the boundary layer. Some of these molecules are observed to have absorption spectra in the VUV and UV region that match the emission spectra of atomic nitrogen and oxygen. Hence, they can potentially absorb the radiation impinging on the heat shield. Accurate thermodynamic data is not available for many of these species over the relevant temperature range for reentry. The objective of this work is to determine the thermochemical properties of potential radiation absorbing molecules using accurate ab initio quantum chemistry calculations. We have compiled a database of formation enthalpies, anharmonic vibrational frequencies and rotational constants for the ground and low-lying excited electronic states of these carbonaceous species. Using these thermochemical properties, we compute equilibrium mole fractions and observe that the mole fractions of some species of interest are significant, thus they could affect the radiative heat flux. Furthermore, comparisons of the formation enthalpies and mole fractions are made with data from literature.

heatshields↗