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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.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1963

NASA Facility for the Study of Space Radiation Effects

Space particulate radiation from the Van Allen belts, solar flares, galactic cosmic, and manmade sources have energies and fluxes which are capable of producing damage in space mission payloads. NASA - Langley Research Center, Hampton, Virginia, has initiated the construction of a ground-based Space Radiation Effects Laboratory which simulates most of the space particulate energy spectrum and which can be used in a radiation research program for minimizing or eliminating deleterious radiation effects. A 600-megaelectronvolt synchrocyclotron of variable energy and electron accelerators from 1 to 10 megaelectronvolts will be included in the laboratory for accelerated testing. The plan of the proposed test areas reflects the latest advances in the state of the art as it pertains to the engineering and basic experimental requirements in flexibility, radiation background levels, shielding, and isolation. The laboratory operational plan permits three Virginia institutions of higher learning to cooperate with the Langley Research Center in carrying out radiation programs.

RADIATION EFFECT↗
NASA NTRS1995

A new Fabry-Perot spectrometer for observations of diffuse near-infrared line emission

We describe a new Fabry-Perot spectrometer that is optimized for the detection of extended, low-surface-brightness line emission from 1.4 to 2.4 microns. The instrument combines high throughput and high sensitivity, yet limits the background radiation falling on the detector. The instrument has a single 20 sec - 200 sec beam and a resolving power lambda/delta(lambda) approximately 2500. The system is background shot-noise limited in the K window and limited by a combination of read noise, dark-current shot noise, and fluctuations in the OH airglow lines in the H window. We present sample data of some of the lowest-surface-brightness H2 line emission in the near infrared obtained to date.

Luhman, M. L.↗
NASA NTRS1998

Issues in the reconstruction of environmental doses on the basis of thermoluminescence measurements in the Techa riverside

The potential of thermoluminescence measurements of bricks from the contaminated area of the Techa river valley, Southern Urals, Russia, for reconstructing external exposures of affected population groups has been studied. Thermoluminescence dating of background samples was used to evaluate the age of old buildings available on the river banks. The anthropogenic gamma dose accrued in exposed samples is determined by subtracting the natural radiation background dose for the corresponding age from the accumulated dose measured by thermoluminescence. For a site in the upper Techa river region, where the levels of external exposures were extremely high, the depth-dose distribution in bricks and the dependence of accidental dose on the height of the sampling position were determined. For the same site, Monte Carlo simulations of radiation transport were performed for different source configurations corresponding to the situation before and after the construction of a reservoir on the river and evacuation of the population in 1956. A comparison of the results provides an understanding of the features of the measured depth-dose distributions and height dependencies in terms of the source configurations and shows that bricks from the higher sampling positions are likely to have accrued a larger fraction of anthropogenic dose from the time before the construction of the reservoir. The applicability of the thermoluminescent dosimetry method to environmental dose reconstruction in the middle Techa region, where the external exposure was relatively low, was also investigated.

NASA Discipline Radiation Health↗
NASA NTRS1981

Intergalactic shells at large redshift

The intergalactic shells produced by galactic explosions at large redshift, whose interiors cool by inverse Compton scattering off the cosmic background radiation, have a characteristic angular size of about 1 arcmin at peak brightness. At z values lower than 2, the shells typically have a radius of 0.5 Mpc, a velocity of about 50 km/sec, a metal abundance of about 0.0001 of cosmic values, and strong radiation in H I(Lyman-alpha), He II 304 A, and the IR fine-structure lines of C II and Si II. The predicted extragalactic background emission from many shells, strongly peaked toward the UV, sets an upper limit to the number of exploding sources at z values of about 10. Shell absorption lines of H I, C II, Si II, and Fe II, which may be seen at more recent epochs in quasar spectra, may probe otherwise invisible explosions in the early universe.

Shull, J. M.↗
NASA NTRS1990

Performance of bismuth germanate active shielding on a balloon flight over Antarctica

The GRAD (Gamma-Ray Advanced Detector) gamma-ray spectrometer was flown on a balloon at an altitude of 36.6 km over Antarctica on January 8-10, 1988, where it was used to make observations of SN 1987A. The performance of the bismuth germanate (BGO) active shielding in the near-space environment over Antarctica is examined. The promised effectiveness of this shielding in the suppression of unwanted background has been demonstrated. The BGO-shielded GRAD spectrometer detected gamma-ray lines with fluxes of 0.002/sq cm sec from SN 1987A in a radiation background approximately a factor of 4 more intense than that over Alice Springs, Australia. This level of sensitivity indicates that BGO is at least as effective as CsI when used as active shielding. Isomerism is common, both in the bismuth and germanium regions of the nuclear chart, but is found to be less of a problem for background suppression in the latter region than in the former.

Rester, A. C.↗
NASA NTRS1991

The diffuse infrared background - COBE and other observations

The Diffuse Infrared Background Experiment (DIRBE) on the Cosmic Background Explorer (COBE) satellite is designed to conduct a sensitive search for an isotropic cosmic infrared background radiation over the spectral range from 1 to 300 micrometers. The cumulative emissions of pregalactic, protogalactic, and evolving galactic systems are expected to be recorded in this background. The DIRBE instrument, a 10 spectral band absolute photometer with an 0.7 deg field of view, maps the full sky with high redundancy at solar elongation angles ranging from 64 to 124 degrees to facilitate separation of interplanetary, Galactic, and extragalactic sources of emission. Initial sky maps show the expected character of the foreground emissions, with relative minima at wavelengths of 3.4 micrometers and longward of 100 micrometers. Extensive modelling of the foregrounds, just beginning, will be required to isolate the extragalactic component. In this paper, we summarize the status of diffuse infrared background observations from the DIRBE, and compare preliminary results with those of recent rocket and satellite instruments.

Hauser, M. G.↗
NASA NTRS2001

Neutron environments on the Martian surface

Radiation is a primary concern in the planning of a manned mission to Mars. Recent studies using NASA Langley Research Center's HZETRN space radiation transport code show that the low energy neutron fluence on the Martian surface is larger than previously expected. The upper atmosphere of Mars is exposed to a background radiation field made up of a large number of protons during a solar particle event and mixture of light and heavy ions caused by galactic cosmic rays at other times. In either case, these charged ions interact with the carbon and oxygen atoms of the Martian atmosphere through ionization and nuclear collisions producing secondary ions and neutrons which then interact with the atmospheric atoms in a similar manner. In the past, only these downward moving particles have been counted in evaluating the neutron energy spectrum on the surface. Recent enhancements in the HZETRN code allow for the additional evaluation of those neutrons created within the Martian regolith through the same types of nuclear reactions, which rise to the surface. New calculations using this improved HZETRN code show that these upward moving neutrons contribute significantly to the overall neutron spectrum for energies less than 10 MeV.

NASA Center LaRC↗
NASA NTRS1980

Baffle design for earth radiation rejection in the Cryogenic Limb-Scanning Interferometer/Radiometer

The Cryogenic Limb-Scanning Interferometer/Radiometer (CLIR) is being developed to observe infrared emissions of the earth's upper atmosphere from space. The earth's surface is an extended source of intense background radiation with a small angular separation from the desired scene. The CLIR employs an off-axis Gregorian Telescope whose primary mirror and baffles are cooled by an open-cycle cryogen system. A system of specular annular baffles has been developed to minimize both stray light problems and cryogen consumption by retro-mapping the aperture into itself. Each off-axis ray which enters the aperture and strikes the specular baffle surface is reflected so that it passes out of the aperture and is not absorbed on a cryogenic surface. The specular baffle which lies closest to the aperture is an ellipsoid whose foci trace out the circular aperture on revolution about the axis. Its theoretical 'ray trace' efficiency is 100 percent. A subsequent baffle has an elliptical cross section whose near focus traces out the central hole in the ellipsoidal baffle and whose far focus traces out the aperture. Its theoretical efficiency is about 90 percent. These baffles reduce the earth radiation heat load on the cryogenic cooler by an order of magnitude, changing it from the dominant cause of cryogen consumption to a relatively small effect. An aperture shield is also desirable to reduce cryogen consumption, stray light, and contamination.

Bremer, J. C.↗
NASA NTRS1982

Application of upconversion detection to pulsed CO2 lidar

In this paper the application of an upconversion detector to pulsed CO2 lidar is investigated. In this device a nonlinear IR crystal would be used to convert 10-micron lidar radiation into the visible region for conventional detection with a photomultiplier tube. A pulsed CO2 lidar can be substantially improved with an upconversion detector configured for rejection of thermal background radiation using a narrowband filter for the upconverted signal or a cold filter front end. The sensitivity of the upconversion detector with the narrowband visible wavelength filter is estimated to be 2 orders of magnitude better than that of the usual direct detection diode. The cold filter can improve upconversion detection to nearly the signal-shot limit. These upconversion detectors are not limited by speckle noise as is a pulsed heterodyne detector.

Itabe, T.↗
NASA NTRS1989

Optical alignment and testing of the Diffuse IR Background Experiment IR cryogenic telescope

Diffuse Infrared Background Experiment (DIRBE) optical alignment and testing methods are discussed. Using strobe videography, vibration and performance testing of a 32 hz tuning-fork chopper was carried out. The Cosmic Background explorer satellite provides improved microwave and IR all-sky maps of the cosmic background radiation from a polar orbit. A liquid helium cryostat houses the DIRBE and the Far IR Absolute Spectrophotometer (FIRAS) instruments at a temperature of 2 K. Differential MicRowave Radiometers (DMRs) provide large scale maps of anisotropy of the 3 K background at wavelengths of 3.3, 5.7, and 9.6 mm. The DIRBE telescope is an IR photometric instrument with 10 wavelength bands between 1 and 300 microns, designed to measure radiation from the epoch of galaxy formation. Stringent stray light requirements mean that the DIRBE flight instrument has to be built and tested in a class 100 environment.

Wood, H. John↗
NASA NTRS2009

Using Prominence Mass Inferences in Different Coronal Lines to Obtain the He/H Abundance

In a previous study we developed a new technique for deriving prominence mass by observing how much coronal radiation in the Fe XII (lambda195) spectral Line is absorbed by prominence material. In the present work we apply this method. which allows us to consider the effects of both foreground and background radiation in our calculations, to a sample of prominences absorbing in a coronal line that ionizes both H and He (lambda < 504 Angstroms), and a line that ionizes only H (504 Angstroms < lambda < 911 Angstroms). This approach, first suggested by Mucera et al. (1998). permits the determination of the abundance ratio [He I]/[H I] of neutral helium and hydrogen in the prominence. This ratio should depend on how the prominence is formed, on its current thermodynamic state, and on its dynamical evolution. Thus, it may provide useful insights into the formation and evolution of prominences.

Gilbert, Holly↗
NASA NTRS2008

Using Prominence Mass Inferences in Different Coronal Lines to Obtain the He/H Abundance

In a previous study we developed a new technique for deriving prominence mass by observing how much coronal radiation in the Fe XI1 (lambda 195) spectral line is absorbed by prominence material. In the present work we apply this method, which allows us to consider the effects of both foreground and background radiation in our calculations, to a sample of prominences absorbing in a coronal line that ionizes both H and He (h < 504 Angstroms), and a line that ionizes only H (504 Angstroms < lambda < 911 Angstroms). This approach, first suggested by Kucera et al. (1998), permits the determination of the abundance ratio [He I]/[H I] of neutral helium and hydrogen in the prominence. This ratio should depend on how the prominence is formed, on its current thermodynamic state, and on its dynamical evolution. Thus, it may provide useful insights into the formation and evolution of prominences.

Gilbert, Holly↗
NASA NTRS1988

Cosmological cosmic strings

The effect of an infinite cosmic string on a cosmological background is investigated. It is found that the metric is approximately a scaled version of the empty space string metric, i.e., conical in nature. Results are used to place bounds on the amount of cylindrical gravitational radiation currently emitted by such a string. The gravitational radiation equations are then analyzed explicitly and it is shown that even initially large disturbances are rapidly damped as the expansion proceeds. The implications of the gravitational radiation background and the limitations of the quadrupole formula are discussed.

Gregory, Ruth↗
NASA NTRS2000

Background Simulation of the MSFC GSPC Balloon Payload

Numerical simulations are used to predict the cosmic-ray induced background in a passively shielded gas scintillation proportional counter to be used as the focal plane instrument of a balloon-borne hard x-ray telescope system. The predicted background in the 20-75 keV operating range of the detector shows a spectral shape characteristic of a power law photoelectrically absorbed by the stainless steel pressure vessel walls. It is found that the dominant background radiation component is simply cosmic diffuse and atmospheric gamma-ray leakage though there is a contribution from nuclear interactions of energetic particles in the walls and nearby payload structures. The correlation between shielding properties and background flux is examined parametrically using one-dimensional slab models, within material and weight constraints, in order to optimize predicted sensitivity. The addition of a few mm thick Sn passive shielding reduces the primary photon contribution by up to 50% at the spectral peak, E 150 keV, and adds only negligibly to the flux due to photon production within the high-Z shields at lower energies.

Swartz, D. A.↗
NASA NTRS1973

Gamma-ray Background Spectrum and Annihilation Rate in the Baryon-symmetric Big-bang Cosmology

An attempt was made to acquire experimental information on the problem of baryon symmetry on a large cosmological scale by observing the annihilation products. Data cover absorption cross sections and background radiation due to other sources for the two main products of annihilation, gamma rays and neutrinos. Test results show that the best direct experimental test for the presence of large scale antimatter lies in the gamma ray background spectrum between 1 and 70 MeV.

Puget, J. L.↗
NASA NTRS1977

Ultrasoft X-rays from the southern galactic hemisphere

Results are reported for sounding-rocket measurements of the X-ray background at ultrasoft energies (90 to 280 eV) in selected regions of the southern galactic hemisphere. The spectrum of the background is found to be extremely soft, being characterized by a kinetic temperature of less than 100 eV in thermal models. A lower limit of about 0.2 per cu pc is set on the space density of stellar sources in a discrete-source model for the background. The results show that the observed background radiation in the southern galactic hemisphere is about 50% less intense than that sampled at corresponding northern latitudes, the intensity at energies less than 150 eV varies along the scan path and is strongest south of -60 deg, there is no evidence for the existence of any ultrasoft pointlike sources, and the background is probably diffuse in origin. A temperature of about 600,000 K and an electron density of the order of 0.007 per cu cm are derived from a simple model where the radiation originates in a hot interstellar plasma interspersed with cold gas along the line of sight.

Levine, A.↗
NASA NTRS1993

Testing for the Gaussian nature of cosmological density perturbations through the three-point temperature correlation function

One of the crucial aspects of density perturbations that are produced by the standard inflation scenario is that they are Gaussian where seeds produced by topological defects tend to be non-Gaussian. The three-point correlation function of the temperature anisotropy of the cosmic microwave background radiation (CBR) provides a sensitive test of this aspect of the primordial density field. In this paper, this function is calculated in the general context of various allowed non-Gaussian models. It is shown that the Cosmic Background Explorer and the forthcoming South Pole and balloon CBR anisotropy data may be able to provide a crucial test of the Gaussian nature of the perturbations.

Luo, Xiaochun↗