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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Measurements on the development of cascades in a tungsten-scintillator ionization spectrometer

The response of a tungsten-scintillator ionization spectrometer to accelerated particle beams has been investigated. Results obtained from exposure of the approx. 1000 g/sq cm apparatus to 5, 10, and 15 GeV/c electrons and pions as well as to 2.1 GeV/nucleon C-12 and O-16 ions are presented. These results include cascade-development curves, fractions of the primary energy measured by the spectrometer, and resolutions of the apparatus for measuring the primary energies. For 15 GeV/c electrons, an average of about 82% of the incident energy is measured by the apparatus with resolution (normal standard deviation) of about 6%. For 15 GeV/c pions, an average of about 65% of the incident energy is measured with resolution of about 18%. The energy resolution improves with increasing energy and with increasing depth of the spectrometer.

Cheshire, D. L.↗
NASA NTRS1975

Remote sensing of atmospheric temperature profiles with the Nimbus 5 microwave spectrometer

The paper discusses the accuracy of atmospheric vertical temperature profile measurements performed by the Nimbus 5 microwave spectrometer and compares results obtained during the first 6 months of its operation with independent ground-truth measurements (coincident radiosonde measurements). The microwave spectrometer can measure temperature profiles averaged over the instrument weighting function (about 10 km) layers with a root-mean-square accuracy of a few tenths of a degree K for measurement integration times of 16 s. Lower tropospheric temperature data from the spectrometer measurements is used in the numerical weather prediction model of the National Meteorological Center.

Waters, J. W.↗
NASA NTRS1976

Comparison of layer thickness as observed by Nimbus E microwave spectrometer and by radiosonde

Atmospheric layer thicknesses observed by the microwave spectrometer of the Nimbus E satellite are compared with radiosonde-derived thicknesses for selected short periods. An average 45 m rms discrepancy is found for the 100-50 kPa layer, and several sources of this discrepancy are quantified in the following way. Correlation coefficients between pairs of spectrometer observations and between pairs of radiosonde observations are each extrapolated to zero separation distance to provide measures of instrument noise. Microwave spectrometer noise is found to be 16 m rms and radiosonde noise 23 m rms. Estimates are also made of those portions of the total discrepancy which are due to different resolution of the sensors (about 15 m rms) and real spatial and temporal variation of the atmosphere between observations (about 17 m rms).

Wilcox, R. W.↗
NASA NTRS1977

A global thermospheric model based on mass spectrometer and incoherent scatter data MSIS. II - Composition

Measurements of O, He, and Ar from neutral gas mass spectrometers on four satellites (Ogo 6, San Marco 3, Aeros A, and AEC-C) and inferred oxygen and hydrogen densities from an ion mass spectrometer on AE-C have been combined with a neutral temperature and nitrogen density model to produce a global model of thermospheric composition in terms of inferred variations at 120 km. The data set covers the time period from mid-1969 to mid-1975. The MSIS (mass spectrometer and incoherent scatter data) model is compared with the Ogo 6 model (Hedin et al., 1974). Ar variations at 120 km tend to be in phase with temperature variations and inverse to the He, O, and H variations.

Hedin, A. E.↗
NASA NTRS1977

Mariner 10 ultraviolet spectrometer - Airglow experiment

An extreme ultraviolet airglow spectrometer was flown on Mariner 10 to examine the atmosphere of Venus and Mercury. An objective grating spectrometer was used with channel electron multipliers at fixed positions in the image plane to continuously monitor the resonance-scattered emission rate of expected atomic atmospheric constituents He, H, A, Ne, O and C. A mechanical collimator placed in the entrance aperture of the spectrometer provided spectral separation of 19 A over the wavelength range from He/+/ at 304 A to C at 1657 A and provided spatial separation of 0.125 deg consistent with the spacecraft and trajectory capabilities. The calibration techniques are discussed.

Broadfoot, A. L.↗
NASA NTRS1977

A focussing iron line crystal spectrometer for Spacelab

A crystal spectrometer system is described which employs conical focusing of 12 curved LiF crystal panels to minimize the detector size and reduce the background counting rate. The wavelength range from 1.70 to 1.98 A is covered, including the resonance lines of Fe XXV and Fe XXVI as well as the Fe I K-alpha line and absorption edge. Operation of the spectrometer is discussed, noting that diffracted X-rays are registered in one-dimensional position-sensitive detectors and that the arrival position of a photon in a detector is related to its wavelength due to the fixed curvature of the crystal panels in the dispersion plane. Some characteristics of the multianode position-sensitive detectors are reviewed along with the crystal arrangement and mounting. The instrument sensitivity is evaluated in relation to the strengths of 6.7-keV emission features detected by the Ariel 5 and OSO 8 proportional-counter spectrometers.

Catura, R. C.↗
NASA NTRS1977

Bent crystal spectrometer for solar X-ray spectroscopy

A bent crystal spectrometer employs a collimated beam of X-rays incident on the crystal over a range of Bragg angles determined by the orientation and curvature of the crystal surface. It provides continuous and simultaneous coverage of all X-ray wavelengths within its spectral range. In-flight testing for solar X-ray spectroscopy was performed using a small instrument to supplement the wavelength coverage of several scanning spectrometers used to study solar active regions in the 9-24 A range. Later testing included modifications to alleviate problems caused by ultraviolet radiation. Future usage of the device will include studies of time variable emission from solar flares or discrete galactic X-ray sources, and the first major experiment to utilize bent crystal spectrometers will be the Solar Maximum Mission satellite in 1979.

Rapley, C. G.↗
NASA NTRS1977

Mass spectrometer beam system for applications in the stratosphere

A special gas inlet system is required for reduction of high ambient pressures to ion source operating pressures for mass spectrometer investigations in the stratosphere for the determination of the abundance of minor constituents. A system has been designed which combines a mass spectrometer and a gas inlet system reducing pressure by differential pumping using high-speed liquid helium pumps and small orifices. The gas particles are formed into a neutral beam with a flag mechanism proceeding into the mass spectrometer ion source where they are ionized for subsequent mass separation. A laboratory model has been tested under conditions simulating stratospheric pressures. It was shown that the process is able to identify gases with abundances below 10 to the -8th. Some of the problems associated with gas analysis of trace constituents have been alleviated, and other applications of the system have been identified, such as pollution control and medicine.

Mauersberger, K.↗
NASA NTRS1977

Photoelectron spectrometer with means for stabilizing sample surface potential

An improved X-ray photoelectron spectrometer is disclosed, which includes circuit means to determine the surface potential of a sample, e.g., an insulator. The circuit means comprise an electron gun, whose potential is modulated at a preselected frequency above and below a selected potential with respect to the spectrometer common potential, e.g., ground. The beam of electrons is directed to the sample surface. The sample's surface potential is offset by an offset power supply with respect to the spectrometer common potential until the ac current which flows through the sample reaches a peak amplitude. A lock-in amplifier is included to measure the ac current in phase with the modulating frequency.

Grunthaner, F. J.↗
NASA NTRS1978

A small gas inlet system for orbital mass-spectrometer calibrations

A gas inlet system is described for generating precise gas pressures that are to be used as calibration references for the mass spectrometers aboard the dual air density Explorer satellites. This gas inlet system was developed as an inflight calibration technique in which a known amount of onboard gas is released in the satellite cavity and is detected by the mass spectrometer. Although several flight mass spectrometer experiments have been proposed, none make use of the inflight calibration technique described in this report. Laboratory measurements and calibration of the metering leak technique for the gas inlet systems are discussed. The systems tested have metering leak rates between 2 and 4 microliters/sec at 298 K for argon-40, and they produce molecular flow up to 100 torr, which is the highest test pressure in this experiment. Test data show that metering leak rates are reproducible within 1 percent of established means for helium-3, helium-4, and argon-40.

Smith, A.↗
NASA NTRS1977

Fourier and Hadamard transform spectrometers - A limited comparison. II

A mathematical approach was used to compare interferometric spectrometers and Hadamard transform spectrometers. The principle results are reported, noting that the simple Hadamard spectrometer encodes more efficiently than a Michelson interferometer which, in turn, encodes less efficiently than is usually acknowledged. Hirschfeld's (1977) major objections to these findings are discussed, although it is noted that none of his objections is supported by evidence.

Harwit, M.↗
NASA NTRS1977

The University of Colorado OSO-8 spectrometer experiment. I - Introduction and optical design considerations

The optical design of the high-resolution ultraviolet spectrometer prepared for the OSO-8 spacecraft is discussed. The instrument is a conventional 1 m Ebert-Fastie spectrometer fed by a Cassegrainian telescope. The instrument operates in the spectral range 1200-2000 A with spectral resolution of order 0.02 A. Spatial resolution is about 2.5 arcsec normal to the direction of the slit and is selectable from about 3 arcsec to 15 arcmin along the direction of the slit. Time resolution for the single spectrometer channel is selectable according to the needs of an individual observation and is limited to a maximum sampling rate of 40 ms per data point. The instrument is controlled by an internal general purpose computer.

Bruner, E. C., Jr.↗
NASA NTRS1977

A mass spectrometer-beam experiment for investigations of planetary atmospheres

An experimental concept for investigation of planetary atmospheres using a mass spectrometer is discussed. High atmospheric pressures are reduced to mass spectrometer operating pressures by means of differential pumping. Sampling is accomplished through the formation of a molecular beam. A flag in front of the mass spectrometer can be used to separate ambient gases from system background. Laboratory tests have confirmed the feasibility of the experiment, particularly in CO2 dominated atmospheres.

Mauersberger, K.↗
NASA NTRS1979

Global model of longitude/UT variations in thermospheric composition and temperature based on mass spectrometer data

Measurements of N2, O, He, and Ar densities from neutral gas mass spectrometers on four satellites and inferred O2 and H densities from an ion mass spectrometer have been combined to produce a model of longitude/UT variations in thermospheric neutral composition and temperature. The longitude/UT model is an extension of the mass spectrometer-incoherent scatter thermospheric model (Hedin et al., 1977) and uses spherical harmonic terms dependent on geographic latitude, longitude, and UT. The combined longitude and UT variations reflect the influence of the geomagnetic field but indicate that the variations may not simply be represented in magnetic coordinates.

Hedin, A. E.↗
NASA NTRS1979

A liquid-helium-cooled grating spectrometer for far infrared astronomical observations

A liquid-helium-cooled grating spectrometer has been developed for low-resolution far-infrared spectrometric measurements of astronomical sources conducted by the 30-cm NASA Lear Jet telescope. Simple MOSFET coupled transimpedance preamplifiers were adopted for the spectrometer design. The infrared spectrometer has resolving powers from 10 to 150 over the wavelength range from 45 to 115 microns.

Houck, J. R.↗
NASA NTRS1979

Comparison of atmospheric density data from mass spectrometers and atmospheric drag on the Aeros satellites

The comparison of perigee density data near 230 km for satellite Aeros-A has been extended to the complete mission time. The average ratio between orbital drag derived density and mass spectrometer measurements is very near to 1 with a large scatter reflected by a standard deviation of the order of 20%. A method of comparison was developed and tested which uses the observed rate of change of orbital period in comparison with the orbital decay computed from the actual mass spectrometer data measured at discrete positions along the orbit. This method proves that deviations from the average ratio of 1 between perigee densities from drag and mass spectrometers are due to the smoothing and poor resolution of the orbital drag technique.

Roemer, M.↗
NASA NTRS1980

Cosmic ray studies with a gas Cherenkov counter in association with an ionization spectrometer

The results from a balloon-borne gas Cherenkov counter (threshold 16.5 GeV/nucleon) and an ionization spectrometer are presented. The gas Cherenkov counter provides an absolute energy distribution for the response of the calorimeter for 5 or = Z 26 nuclei of cosmic rays. The contribution of scintillation to the gas Cherenkov pulse height was obtained by independently selecting particles below the gas Cherenkov threshold using the ionization spectrometer. Energy spectra were derived by minimizing the chi squared between Monte Carlo simulted data and flight data. Best fit power laws, dN/dE = AE-gamma, were determined for C, N, O, Ne, Mg, and Si. The power laws, all consistent with E (-2.7) are not good fits to the data. A better fit is obtained using the spectrum derived from the spectrometer. The data from the ionization calorimeter and the gas Cherenkov are thus completely self-consistent.

Balasubrahmanyan, V. K.↗
NASA NTRS1980

Cooled echelle grating spectrometer

A cooled echelle grating spectrometer for detecting wavelengths between one micron and fifteen microns is disclosed. More specifically, the spectrometer has a cross-dispersing grating for ordering infrared energy and an echelle grating for further ordering of the infrared energy. Ordered radiation from the echelle grating is sensed by a detecting means. Also disclosed is use of a Schmidt camera for focusing the further ordered radiation from the echelle grating onto a detector array having individual detectors dispersed on a plane which substantially corresponds to a curved focal plane of the Schmidt camera. A spectrometer constructed according to the teachings of the present invention will continuously cover the spectrum between one micron and fifteen microns and have a resolution of 0.1/cm.

Beer, R.↗