Search NASA⌕ Search

SEARCH · Search NASA

Results for “low background”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

The X-ray Timing Explorer

The capabilities of the X-ray Timing Explorer (XTE) are described with particular attention paid to current scientific problems it will address from galactic neutron star systems to active galactic nuclei. It features a low-background continuous 2-200 keV response with large apertures (a 0.63 sq m proportional counter array and a 0.16 sq m dual rocking NaI/CsI scintillation array). Rapid response (in hours) to temporal phenomena, e.g. transients, is obtained by virtue of a scanning all-sky monitor and rapid maneuverability. XTE will carry out detailed energy-resolved studies of phenomena close to neutron stars (e.g. QPO's) because of its submillisecond timing, its high telemetry rates, and the high throughput of its data system.

Bradt, H. V.↗
NASA NTRS1991

High resolution, two-dimensional imaging, microchannel plate detector for use on a sounding rocket experiment

We discuss a high resolution microchannel plate (MCP) imaging detector to be used in measurements of Doppler-shifted hydrogen Lyman-alpha line emission from Jupiter and the interplanetary medium. The detector is housed in a vacuum-tight stainless steel cylinder (to provide shielding from magnetic fields) with a MgF2 window. Operating at nominal voltage, the four plate configuration provides a gain of 1.2 x 10 exp 7 electrons per incident photon. The wedge-and-strip anode has two-dimensional imaging capabilities, with a resolution of 40 microns FWHM over a one centimeter diameter area. The detector has a high quantum efficiency while retaining a low background rate. A KBr photocathode is used to enhance the quantum efficiency of the bare MCPs to a value of 35 percent at Lyman-alpha.

Bush, Brett C.↗
NASA NTRS1992

Observation of the Coma cluster of galaxies with ROSAT during the all-sky survey

The Coma cluster of galaxies was observed with the position sensitive proportional counter (PSPC) during the ROSAT all sky survey. We find evidence for substructure in this cluster. Diffuse X-ray emission is detected from the regions of the NGC 4839 and 4911 subgroups at 6 percent and 1 percent of the total cluster emission respectively. There may be emission associated with the NGC 4874 and 4889 subgroups as well. The NGC 4839 group appears to be in the process of merging with the cluster. These X-ray data show that at least some of the groups previously found in projection are in fact physical objects possessing potential wells deep enough to trap their own X-ray gas. Because of the unlimited field of view of the all sky survey and the low background of the PSPC, we were able to measure the azimuthally averaged surface brightness of Coma out to approximately 100 arcmin, twice as far as was previously possible. Given the validity of our mass models, these new X-ray data imply that within 5/h(50) Mpc the binding mass of the Coma cluster is 1.8 +/- 0.6 x 10 exp 15/h(50) solar mass, and the fraction of cluster mass contained in hot gas is 0.30 +/- 0.14h(50) exp -3/2. Furthermore, the binding mass is more centrally concentrated than is the X-ray gas.

Briel, U. G.↗
NASA NTRS1983

UCSD IR detector development programs

A diagram is presented for the UCSD low background infrared spot scanner. The spot scanner parameters are outlined. The testing that is planned for the charge injection device is outlined. The Aerojet linear 128 element array is also outlined.

Jones, B.↗
NASA NTRS1983

Si:Bi array detectors and astronomical applications of the Goddard 10 micron camera

An improved 4 to 18 micron array camera system was developed at NASA Goddard SFC for astronomical photometry, using an Aerojet Electro Systems Corp. 16 x 16 Si:Bi accumulation mode charge injection device (AMCID) which could be suitable for eventual low-background spaceflight applications. An astronomical observing program using this device was carried out as a collaboration between NASA Goddard (Infrared and Radio Astronomy Branch and Micro Electronics Branch), the Harvard/Smithsonian Center for Astrophysics, and Steward Observatory of the University of Arizona. In 1983 the camera system was revised, and a new Aeroject Si:Bi array with 16 x 16 active pixels was obtained from NASA/Ames Research Center as part of a new scientific collaboration between the Ames and Goddard infrared array research groups. The 16 x 16 device had sufficiently good sensitivity, uniformity and noise characteristics to be used for successful observations at the Mt. Lemmon 60 and 61 inch telescopes in May 1983. Complete laboratory characterization of the 16 x 16 array was carried out in summer of 1983. Initial results indicate that this detector has sensitivity and noise characteristics comparable to other devices from the same generation of Aerojet arrays.

Lamb, Gerald↗
NASA NTRS1993

Germanium blocked-impurity-band detector arrays - Unpassivated devices with bulk substrates

We have fabricated and characterized six-element monolithic arrays of Ge:Ga blocked-impurity-band detectors, with threshold wavelength 220 microns, peak quantum efficiency 14 percent, detective quantum efficiency 9 percent, dark current 300 e(-)/s, and response uniformity better than 4 percent. The devices are described very well by the standard model of blocked-impurity-band detectors and appear to satisfy many of the requirements of low-background astronomical instruments.

Watson, Dan M.↗
NASA NTRS1994

Coronal observations from the soft x-ray telescope on Yohkoh

The Yohkoh payload includes a Soft X-ray Telescope (SXT) which is capable of taking high-resolution (2.5 arcsec) images of the Sun through several X-ray and optical filters. A Charge Coupled Devices (CCD) camera provides images with a low background, and large dynamic range and at a rapid cadence (greater than 2 s), which enables the SXT to observe the effects of flares while continuing to observe the fainter quiet-Sun features. We present the observations from the SXT that illustrate how the faint coronal loops that make up the complex structure of the quiet Sun evolve on a variety of timescales from seconds to months. We describe a variety of coronal structures, such as coronal holes, bright points, the large-scale quiet coronal loops, and active regions, to show the wide range of opportunities that Yohkoh presents to further our understanding of the solar corona.

Strong, K. T.↗
NASA NTRS1994

The first large format SI:SB BIB arrays

The first 128x128 Si:Sb blocked impurity band (BIB) detectors, manufactured by Rockwell International, are sensitive detectors from 10 to at least 40 micrometers. While further work is required to make these arrays suitable for the low backgrounds of space infrared telescopes, they can be used now for observations from the ground and aircraft.

Van Cleve, J. E.↗
NASA NTRS1994

Anisotropy in the microwave sky at intermediate angular scales

Observations of a low-background region of sky at high Galactic latitude in a frequency band centered at nu = 90 GHz reveal highly significant detections of anisotropy on intermediate (aprroximately 1 deg) angular scales. The instrument is a 2 x 2 array of bolometric detectors operating at 50 mK, coupled to a 0.75 m off-axis parabolic telescope by single-mode corrugated feedhorns. The FWHM beamwidth of the instrument is 0.75 deg, with a beamswitch of +/- 2.75 deg on the sky. Interpreting the detected fluctuations as due to anisotropy in the cosmic microwave background, a likelihood analysis assuming a Gaussian correlation function in the temperature fluctuations yields most likely values of (delta T)/T of 3.1(sub -0.9)(sup +2.5) x 10(exp -5) and 3.8(sub -1.2)(sup +2.9) x 10(exp -5) at a coherence angle of 1.0 deg, for the left- and right-hand detectors, respectively. The stated errors are 95% confidence limits. Confirmation at other frequencies is required to rule out the possibility of foreground contamination.

Dragovan, M.↗
NASA NTRS1998

NO(x) Concentrations in the Upper Troposphere as a Result of Lightning

Upper tropospheric NO(x) controls, in part, the distribution of ozone in this greenhouse-sensitive region of the atmosphere. Many factors control NO(x) in this region. As a result it is difficult to assess uncertainties in anthropogenic perturbations to NO from aircraft, for example, without understanding the role of the other major NO(x) sources in the upper troposphere. These include in situ sources (lightning, aircraft), convection from the surface (biomass burning, fossil fuels, soils), stratospheric intrusions, and photochemical recycling from HNO3. This work examines the separate contribution to upper tropospheric "primary" NO(x) from each source category and uses two different chemical transport models (CTMS) to represent a range of possible atmospheric transport. Because aircraft emissions are tied to particular pressure altitudes, it is important to understand whether those emissions are placed in the model stratosphere or troposphere and to assess whether the models can adequately differentiate stratospheric air from tropospheric air. We examine these issues by defining a point-by-point "tracer tropopause" in order to differentiate stratosphere from troposphere in terms of NO(x) perturbations. Both models predict similar zonal average peak enhancements of primary NO(x) due to aircraft (approx. = 10-20 parts per trillion by volume (pptv) in both January and July); however, the placement of this peak is primarily in a region of large stratospheric influence in one model and centered near the level evaluated as the tracer tropopause in the second. Below the tracer tropopause, both models show negligible NO(x) derived directly from the stratospheric source. Also, they predict a typically low background of 1 - 20 pptv NO(x) when tropospheric HNO3 is constrained to be 100 pptv of HNO3. The two models calculate large differences in the total background NO(x) (defined as the source of NO(x) from lightning + stratosphere + surface + HNO3) when using identical loss frequencies for NO(x). This difference is primarily due to differing treatments of vertical transport. An improved diagnosis of this transport that is relevant to NO(x) requires either measurements of a surface-based tracer with a substantially shorter lifetime than Rn-222 or diagnosis and mapping of tracer correlations with different source signatures. Because of differences in transport by the two models we cannot constrain the source of NO(x) from lightning through comparison of average model concentrations with observations of NO(x).

Penner, Joyce E.↗
NASA NTRS2000

The Chandra Multi-Wavelength Project (ChaMP): A Serendipitous X-Ray Survey Using Chandra Archival Data

The launch of the Chandra X-ray Observatory in July 2000 opened a new era in X-ray astronomy. Its unprecedented, < 1" spatial resolution and low background is providing views of the X-ray sky 10-100 times fainter than previously possible. We have begun to carry out a serendipitous survey of the X-ray sky using Chandra archival data to flux limits covering the range between those reached by current satellites and those of the small area Chandra deep surveys. We estimate the survey will cover about 8 sq.deg. per year to X-ray fluxes (2-10 keV) in the range 10(exp -13) - 6(exp -16) erg cm2/s and include about 3000 sources per year, roughly two thirds of which are expected to be active galactic nuclei (AGN). Optical imaging of the ChaMP fields is underway at NOAO and SAO telescopes using g',r',z' colors with which we will be able to classify the X-ray sources into object types and, in some cases, estimate their redshifts. We are also planning to obtain optical spectroscopy of a well-defined subset to allow confirmation of classification and redshift determination. All X-ray and optical results and supporting optical data will be place in the ChaMP archive within a year of the completion of our data analysis. Over the five years of Chandra operations, ChaMP will provide both a major resource for Chandra observers and a key research tool for the study of the cosmic X-ray background and the individual source populations which comprise it. ChaMP promises profoundly new science return on a number of key questions at the current frontier of many areas of astronomy including solving the spectral paradox by resolving the CXRB, locating and studying high redshift clusters and so constraining cosmological parameters, defining the true, possibly absorbed, population of quasars and studying coronal emission from late-type stars as their cores become fully convective. The current status and initial results from the ChaMP will be presented.

Wilkes, Belinda↗
NASA NTRS2000

Performance of The Far Ultraviolet Spectroscopic Explorer Mirror Assemblies

The Far Ultraviolet Spectroscopic Explorer is a NASA astrophysics satellite which produces high-resolution spectra in the far-ultraviolet (90.5-118.7 nm bandpass) using a high effective area and low background detectors. The observatory was launched on its three-year mission from Cape Canaveral Air Station on 24 June 1999. The instrument contains four coaligned, normal incidence, off-axis parabolic mirrors which illuminate separate Rowland circle spectrograph channels equipped with holographically ruled diffraction gratings and delay line microchannel plate detectors. The telescope mirrors have a 352 x 387 mm aperture and 2245 mm focal length and are attached to actuator assemblies, which provide on-orbit, tip, tilt, and focus control. Two mirrors are coated with silicon carbide (SiC) and two are coated with lithium fluoride over aluminum (Al:LiF). We describe mirror assembly in-flight optical and mechanical performance. On-orbit measurements of the far-ultraviolet point spread function associated with each mirror are compared to expectations based on pre-flight laboratory measurements and modeling using the Optical Surface Analysis Code and surface metrology data. On-orbit imaging data indicate that the mirrors meet their instrument-level requirement of 50 percent and 95 percent slit transmission for the high- and mid-resolution spectrograph entrance slits, respectively. The degradation of mirror reflectivity during satellite integration and test is also discussed. The far-ultraviolet reflectivity of the SiC- and AlLiF-coated mirrors decreased about six percent and three percent, respectively, between coating and launch. Each mirror is equipped with three actuators, which consist of a stepper motor driving a ball screw via a two-stage planetary gear train. We also discuss the mechanical performance of the mirror assemblies, including actuator performance and thermal effects.

Ohi, Raymond G.↗
NASA NTRS2000

Micromechanical and Electrical Properties of Monolithic Aluminum Nitride at High Temperatures

Micromechanical spectroscopy of aluminum nitride reveals it to possess extremely low background internal friction at less than 1x10(exp-4) logarithmic decrement (log dec) from 20 to 1200 T. Two mechanical loss peaks were observed, the first at 350 C approximating a single Debye peak with a peak height of 60x10(exp-4) log dec. The second peak was seen at 950 'C with a peak height of 20x 10' log dec and extended from 200 to over 1200 C. These micromechanical observations manifested themselves in the electrical behavior of these materials. Electrical conduction processes were predominately intrinsic. Both mechanical and electrical relaxations appear to be thermally activated processes, with activation energies of 0.78 and 1.32 eV respectively.

Goldsby, Jon C.↗
NASA NTRS2001

Micromechanical and Electrical Properties of Monolithic Aluminum Nitride at High Temperatures

Micromechanical spectroscopy of aluminum nitride reveals it to possess extremely low background internal friction at less than 1 x 10 (exp -4) logarithmic decrement (log dec.) from 20 to 1200 C. Two mechanical loss peaks were observed, the first at 350 C approximating a single Debye peak with a peak height of 60 x 10 (exp -4) log dec. The second peak was seen at 950 C with a peak height of 20 x 10 (exp -4) log dec. and extended from 200 to over 1200 C. These micromechanical observations manifested themselves in the electrical behavior of these materials. Electrical conduction processes were predominately intrinsic. Both mechanical and electrical relaxations appear to be thermally activated processes, with activation energies of 0.78 and 1.32 eV respectively.

Goldsby, Jon C.↗
NASA NTRS2001

SAFIRE: A Far-Infrared Imaging Spectrometer for SOFIA

The SOFIA airborne observatory will provide a high spatial resolution, low background telescope for far-infrared astrophysical investigations. Selected as a PI instrument for SOFIA, SAFIRE is an imaging Fabry-Perot spectrograph covering 145 micrometers-655 micrometers with spectral resolving power of approx. 1500 (200km/s). This resolution is well matched to extragalactic emission lines and yields the greatest sensitivity for line detection. SAFIRE will make important scientific contributions to the study of the powering of ULIRGs and AGN, the role of CII cooling in extragalactic star formation, the evolution of matter in the early Universe, and the energetics of the Galactic center. SAFIRE will employ a two-dimensional pop-up bolometer array to provide background-limited imaging spectrometry. Superconducting transition edge bolometers and SQUID amplifiers have been developed for these detectors. An engineering prototype of SAFIRE with a small but cutting edge detector array will be available for use during the initial SOFIA operations; further expansion to larger format arrays will be incorporated during SAFIRE's lifetime.

Shafer, Richard A.↗
NASA NTRS2000

An Explorer-Class Astrobiology Mission

In this paper we describe a potential new Explorer-class space mission, the AstroBiology Explorer (ABE), consisting of a relatively modest dedicated space observatory having a 50 cm aperture primary mirror which is passively cooled to T less than 65 K, resides in a low-background orbit (heliocentric orbit at 1 AU, Earth drift-away), and is equipped with a suite of three moderate order (m approx. 10) dispersive spectrographs equipped with first-order cross-dispersers in an "echellette" configuration and large format (1024xl024 pixel) near- and mid-IR detector arrays cooled by a modest amount of cryogen. Such a system would be capable of addressing outstanding problems in Astrochemistry and Astrophysics that are particularly relevant to Astrobiology and addressable via astronomical observation. The observational program of this mission would make fundamental scientific progress in each of the key areas of the cosmic history of molecular carbon, the distribution and chemistry of organic compounds in the diffuse and dense interstellar media, and the evolution of ices and organic matter in young planetary systems. ABE could make fundamental progress in all of these areas by conducting an approximately one year mission to obtain a coordinated set of infrared spectroscopic observations over the 2.5-20 micrometers spectral range at spectral resolutions of R greater than or equal to 1000 of approximately 1000 galaxies, stars, planetary nebulae, and young star planetary systems.

Sandford, Scott↗
NASA NTRS2001

Far-Infrared Imaging Spectroscopy with SAFIRE on SOFIA

The SOFIA airborne observatory will provide a high spatial resolution, low background telescope for far-infrared astrophysical investigations. Selected as a PI instrument for SOFIA, SAFIRE is an imaging Fabry-Perot spectrograph covering 100 micrometers - 655 micrometers, with spectral resolving power of approx. 1500 (200 kilometers per second). This resolution is well matched to extragalactic emission lines and yields the greatest sensitivity for line detection. SAFIRE will make important scientific contributions to the study of the powering of ULIRGs and AGN, the role of CII cooling in extragalactic star formation, the evolution of matter in the early Universe, and the energetics of the Galactic center. SAFIRE will employ a two-dimensional pop-up barometer array in a 16 x 32 format to provide background-limited imaging spectrometry. Superconducting transition edge barometers and SQUID amplifiers have been developed for these detectors.

Shafer, Richard A.↗
NASA NTRS2002

SAFIRE: Far-Infrared Imaging Spectroscopy with SOFIA

The SOFIA airborne observatory will provide a high spatial resolution, low background telescope for far-infrared astrophysical investigations. Selected as a PI instrument for SOFIA, SAFIRE is an imaging Fabry-Perot spectrograph covering 145 microns-655microns, with spectral resolving power of approx. 1500 (200 kilometers per second). This resolution is well matched to extragalactic emission lines and yields the greatest sensitivity for line detection. SAFIRE will make important scientific contributions to the study of the powering of ULIRGs and AGN, the role of CII cooling in extragalactic star formation, the evolution of matter in the early Universe, and the energetics of the Galactic center. SAFIRE will employ a two-dimensional pop-up bolometer array to provide background limited imaging spectrometry. Superconducting transition edge bolometers and SQUID amplifiers have been developed for these detectors.

Benford, Dominic↗