Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “SCINTILLATIONS”

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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Entopistic scintillators

Trajectories of cosmic rays through a balloon-borne experiment will be determined by pulse height analyzing the signals from each of the two or more phototubes coupled to each scintillator. Thin or tapered scintillators produce sufficiently strong gradients of phototube signal with respect to scintillation position that position uncertainties of about 1 cm can be achieved over 1-sq-m areas. Calculations and some test results for entopistic, or position determining, scintillators are presented.

Arens, J. F.↗
NASA NTRS1976

Angular sensitivities of scintillator slab configurations for location of gamma ray bursts

Thin flat scintillator slabs are a useful means of measuring the angular location of gamma ray fluxes of astronomical interest. A statistical estimate of position error was made of two scintillator systems suitable for gamma ray burst location from a balloon or satellite platform. A single rotating scintillator with associated flux monitor is compared with a pair of stationary orthogonal scintillators. Position error for a strong burst is of the order of a few arcmin if systematic errors are ignored.

Gregory, J. C.↗
NASA NTRS1977

Measuring solar wind velocity with spacecraft phase scintillations

The measurement of spacecraft phase scintillations with a coherent dual-frequency radio system permits solar-wind velocity measurements based on multiple-station phase scintillations. Advantages of measuring solar-wind velocity on the basis of multiple-station phase scintillations are discussed with respect to amplitude scintillations. These advantages include the ability to carry out observations closer to the sun, a much wider range of possible baselines, a lower S/N ratio for long-baseline phase measurements, and a wider range of antenna sizes and receiver noise temperatures. NASA antennas particularly suitable for these measurements are identified, and observations with the coherent S/X radio system aboard various NASA spacecraft intended for deep-space missions are proposed.

Woo, R.↗
NASA NTRS1977

Scintillation statistics measured in an earth-space-earth retroreflector link

Scintillation was measured in a vertical path from a ground-based laser transmitter to the Geos 3 satellite and back to a ground-based receiver telescope and, the experimental results were compared with analytical results presented in a companion paper (Bufton, 1977). The normalized variance, the probability density function and the power spectral density of scintillation were all measured. Moments of the satellite scintillation data in terms of normalized variance were lower than expected. The power spectrum analysis suggests that there were scintillation components at frequencies higher than the 250 Hz bandwidth available in the experiment.

Bufton, J. L.↗
NASA NTRS1977

Preliminary comparisons of VHF radar maps of F-region irregularities with scintillations in the equatorial region

Multiantenna 50 MHz radar backscatter maps of echo power from night-time F-region equatiorial irregularities obtained at Jicamarca, Peru were compared with simultaneous VHF scintillation observations from Huancayo at 137 and 254 MHz during the period 20 November to 12 December 1975. Saturation of VHF scintillations in excess of 20 dB was observed at both these frequencies during times when radar maps showed large intense plume structures rising into the topside ionosphere. On nights when only thin layers of bottomside irregularities were observed, moderate to weak scintillations were recorded at VHF. Preliminary values of east-west horizontal irregularity drift velocities were obtained and compared with scintillation rate observations. Using the 1.5-deg and 4.5-deg longitudinal separation between the Jicamarca radar and ionospheric observation points of the two satellites from Huancayo, information was derived regarding large-scale east-west structure during the development phase of the irregularities.

Basu, S.↗
NASA NTRS1978

Simultaneous observations of equatorial ionospheric scintillation on four frequencies

The variation with frequency of ionospheric scintillations, simultaneously observed at 40, 140, 360, and 860 MHz at equatorial latitudes, was studied. The ATS 6 geostationary satellite was equipped with radio beacons at 40, 140, and 360 MHz, and also with a television downlink at 860 MHz. The signals were recorded at Ootacamund, India (dip 4 deg N) and were most common between 2000 and 2300 LT. It was found that the spectral index of an expression used by Aarons et al (1967) was not constant but decreased with increasing magnitude of scintillations. For weak scintillations the spectral index (referred to as the exponent) was found to be close to 1.0. The analysis of the records involved scaling at 15-sec intervals and the calculation of the average scintillation index.

Rastogi, R. G.↗
NASA NTRS1980

Multifrequency equatorial ionospheric scintillations in American and Indian zones

Amplitude scintillations of 40/41, 140 and 360 MHz transmissions recorded at Huancayo (phase I) and at Ootacamund (phase II) of the ATS-6 program are compared. The scintillations were found to be strongest between 20 and 24 hr LT with another peak around midday. The daytime scintillations do not show a significant seasonal variation at either of these stations. The nighttime scintillations were maximum during December solstices at Huancayo and during equinoxes at Ootacamund and suggested to be due to non-q type of sporadic E following the occurrence of counter-electrojet.

Rastogi, R. G.↗
NASA NTRS1988

A synoptic study of Doppler scintillation transients in the solar wind

This paper conducts the first synoptic study of Doppler scintillation transients caused by interplanetary disturbances. The Doppler scintillation data used are part of the 2.3-GHz navigation data collected by the NASA Deep Space Network when tracking planetary spacecraft during 1979-1983, a period that includes solar maximum. A total of 148 separate transients covering a heliocentric distance range of 5-179 solar radii were detected, including 26 transients detected by more than one spacecraft. The frequency of occurrence was highest near the sun and decreased with radial distance, a reflection of the radial evolution of the transients and the sensitivity of the Doppler scintillation measurements to transients. Since transients can be disruptive, as was demonstrated during the encounter of Saturn by Pioneer 11 in 1979, information on Doppler scintillation transients is essential.

Woo, Richard↗
NASA NTRS1988

The Scintillating Optical Fiber Isotope Experiment

This paper describes the Scintillating Optical Fiber Isotope Experiment (SOFIE) which is being developed by Washington University and the University of New Hampshire to study the abundances of cosmic ray isotopes in the iron charge region. This detector system is a Cerenkov-Range-dE/dx experiment and utilizes range and trajectory detectors made of scintillating optical fibers, a fused silica Cerenkov counter, and plastic scintillator dE/dx counters to determine the charge and mass of cosmic ray nuclei. A brief description of the balloon flight instrument presently being developed will be given followed by initial results of an engineering model calibration at the LBL Bevalac heavy ion accelerator. In addition a brief discussion of the potential of scintillating fiber trajectory detectors for use in experiments requiring precise trajectory determination such as those being planned for the NASA Particle Astrophysics Magnet Facility (Astromag) program is presented.

Binns, W. Robert↗
NASA NTRS2005

Mitigation of Laser Beam Scintillation in Free-Space Optical Communication Systems Through Coherence-Reducing Optical Materials

Free-space optical communication systems (also known as lasercom systems) offer several performance advantages over traditional radio frequency communication systems. These advantages include increased data rates and reduced operating power and system weight. One serious limiting factor in a lasercom system is Optical turbulence in Earth's atmosphere. This turbulence breaks up the laser beam used to transmit the information into multiple segments that interfere with each other when the beam is focused onto the receiver. This interference pattern at the receiver changes with time causing fluctuations in the received optical intensity (scintillation). Scintillation leads to intermittent losses of the signal and an overall reduction in the lasercom system's performance. Since scintillation is a coherent effect, reducing the spatial and temporal coherence of the laser beam will reduce the scintillation. Transmitting a laser beam through certain materials is thought to reduce its coherence. Materials that were tested included: sapphire, BK7 glass, fused silica and others. The spatial and temporal coherence of the laser beam was determined by examining the interference patterns (fringes) it formed when interacting with various interferometers and etalons.

Renner, Christoffer J.↗
NASA NTRS2012

Dual-Frequency Observations of 140 Compact, Flat-Spectrum Active Galactic Nuclei for Scintillation-Induced Variability

The 4.9 GHz Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey detected a drop in Interstellar Scintillation (ISS) for sources at red shifts z > or approx. 2, indicating an apparent increase in angular diameter or a decrease in flux density of the most compact components of these sources, relative to their extended emission. This can result from intrinsic source size effects or scatter broadening in the Intergalactic Medium (IGM) , in excess of the expected (1+z)1/2 angular diameter scaling of brightness temperature limited sources resulting from cosmological expansion. We report here 4.9 GHz and 8.4 GHz observations and data analysis for a sample of 140 compact, fiat-spectrum sources which may allow us to determine the origin of this angular diameter-redshift relation by exploiting their different wavelength dependences. In addition to using ISS as a cosmological probe, the observations provide additional insight into source morphologies and the characteristics of ISS. As in the MASIV Survey, the variability of the sources is found to be significantly correlated with line-of-sight H(alpha) intensities, confirming its link with ISS. For 25 sources, time delays of about 0.15 to 3 days are observed between the scintillation patterns at both frequencies, interpreted as being caused by a shift in core positions when probed at different optical depths. Significant correlation is found between ISS amplitudes and source spectral index; in particular, a large drop in ISS amplitudes is observed at alpha < -0.4 confirming that steep spectrum sources scintillate less. We detect a weakened redshift dependence of ISS at 8.4 GHz over that at 4.9 GHz, with the mean variance at 4-day timescales reduced by a factor of 1.8 in the z > 2 sources relative to the z < 2 sources, as opposed to the factor of 3 decrease observed at 4.9 GHz. This suggests scatter broadening in the IGM, but the interpretation is complicated by subtle selection effects that will be explored further in a follow-up paper.

Koay, J. Y.↗
NASA NTRS2015

Scintillating Quantum Dots for Imaging X-Rays (SQDIX) for Aircraft Inspection

Scintillation is the process currently employed by conventional X-ray detectors to create X-ray images. Scintillating quantum dots (StQDs) or nano-crystals are novel, nanometer-scale materials that upon excitation by X-rays, re-emit the absorbed energy as visible light. StQDs theoretically have higher output efficiency than conventional scintillating materials and are more environmentally friendly. This paper will present the characterization of several critical elements in the use of StQDs that have been performed along a path to the use of this technology in wide spread X-ray imaging. Initial work on the scintillating quantum dots for imaging X-rays (SQDIX) system has shown great promise to create state-of-the-art sensors using StQDs as a sensor material. In addition, this work also demonstrates a high degree of promise using StQDs in microstructured fiber optics. Using the microstructured fiber as a light guide could greatly increase the capture efficiency of a StQDs based imaging sensor.

Burke, E. R.↗
DOE OSTI2010

Cerium doped elpasolite halide scintillators.

Low-cost, high-performance gamma-ray spectrometers are urgently needed for proliferation detection and homeland security. The cost and availability of large scintillators used in the spectrometer generally hinge on their mechanical property and crystal symmetry. Low symmetry, intrinsically brittle crystals, such as these emerging lanthanide halide scintillators, are particularly difficult to grow in large sizes due to the development of large anisotropic thermomechanical stresses during solidification process. Isotropic cubic scintillators, such as alkali halides, while affordable and can be produced in large sizes, are poor spectrometers due to severe nonproportional response and modest light yield. This work investigates and compares four new elpasolite based lanthanide halides, including Cs2LiLaBr6, Cs2NaLaBr6, Cs2LiLaI6, and Cs2NaLaI6, in terms of their crystal symmetry, characteristics of photoluminescence and optical quantum efficiency. The mechanical property and thermal expansion behavior of the cubic Cs2LiLaBr6 will be reported. The isotropic nature of this material has potential for scaled-up crystal growth, as well as the possibility of low-cost polycrystalline ceramic processing. In addition, the proportional response with gamma-ray energy of directionally solidified Cs2LiLaBr6 will be compared with workhorse alkali halide scintillators. The processing challenges associated with hot forged polycrystalline elpasolite based lanthanide halides will also be discussed.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2012

Silicon photomultiplier choice for the scintillating fibre tracker in second generation proton computed tomography scanner

Scintillating fibers are capable of charged particle tracking with high position resolution, as demonstrated by the central fiber tracker of the D0 experiment. The charged particles will deposit less energy in the polystyrene scintillating fibers as opposed to a typical silicon tracker of the same thickness, while SiPM's are highly efficient at detecting photons created by the passage of the charged particle through the fibers. The current prototype of the Proton Computed Tomography (pCT) tracker uses groups of three 0.5 mm green polystyrene based scintillating fibers connected to a single SiPM, while first generation prototype tracker used Silicon strip detectors. The results of R&D for the Scintillating Fiber Tracker (SFT) as part of the pCT detector are outlined, and the premise for the selection of SiPM is discussed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Segmented scintillation antineutrino detector

The various technologies presented herein relate to incorporating a wavelength-shifting material in a scintillator to facilitate absorption of a first electromagnetic particle (e.g., a first photon) having a first wavelength and subsequent generation and emission of a second electromagnetic particle (e.g., a second photon) having a second wavelength. The second electromagnetic particle can be emitted isotropically, with a high probability that the direction of emission of the second electromagnetic particle is disparate to the direction of travel of the first electromagnetic particle (and according angle of incidence). Isotropic emission of the second electromagnetic particle enables the second electromagnetic particle to be retained in the scintillator owing to internal reflection. Accordingly, longer length scintillators can be constructed, and accordingly, the scintillator array has a greater area (and volume) over which to detect electromagnetic particles (e.g., antineutrinos) being emitted from a nuclear reaction.

36 MATERIALS SCIENCE↗
DOE OSTI2017

High-symmetry organic scintillator systems

An ionizing radiation detector or scintillator system includes a scintillating material comprising an organic crystalline compound selected to generate photons in response to the passage of ionizing radiation. The organic compound has a crystalline symmetry of higher order than monoclinic, for example an orthorhombic, trigonal, tetragonal, hexagonal, or cubic symmetry. A photodetector is optically coupled to the scintillating material, and configured to generate electronic signals having pulse shapes based on the photons generated in the scintillating material. A discriminator is coupled to the photon detector, and configured to discriminate between neutrons and gamma rays in the ionizing radiation based on the pulse shapes of the output signals.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

High-symmetry organic scintillator systems

An ionizing radiation detector or scintillator system includes a scintillating material comprising an organic crystalline compound selected to generate photons in response to the passage of ionizing radiation. The organic compound has a crystalline symmetry of higher order than monoclinic, for example an orthorhombic, trigonal, tetragonal, hexagonal, or cubic symmetry. A photodetector is optically coupled to the scintillating material, and configured to generate electronic signals having pulse shapes based on the photons generated in the scintillating material. A discriminator is coupled to the photon detector, and configured to discriminate between neutrons and gamma rays in the ionizing radiation based on the pulse shapes of the output signals.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

High-symmetry organic scintillator systems

An ionizing radiation detector or scintillator system includes a scintillating material comprising an organic crystalline compound selected to generate photons in response to the passage of ionizing radiation. The organic compound has a crystalline symmetry of higher order than monoclinic, for example an orthorhombic, trigonal, tetragonal, hexagonal, or cubic symmetry. A photodetector is optically coupled to the scintillating material, and configured to generate electronic signals having pulse shapes based on the photons generated in the scintillating material. A discriminator is coupled to the photon detector, and configured to discriminate between neutrons and gamma rays in the ionizing radiation based on the pulse shapes of the output signals.

36 MATERIALS SCIENCE↗