Showing papers on "Scintillation published in 1978"
TL;DR: In this article, the authors present early results of the observations; salient points include the following, most of the data are consistent with phase-screen modeling of the production of ionospheric scintillation, including an ƒ−2 frequency dependence for phase variance.
Abstract: A multifrequency (ten spectral lines between VHF and S band) coherent radio beacon is presently transmitting continuously from a 1000-km, high-inclination orbit for the purpose of characterizing the transionospheric communication channel. Its high phase-reference frequency (2891 MHz) permits direct observation of complex-signal scintillation, and its very stable, sun-synchronous orbit allows repeated pre-midnight observations at low latitudes and near-midnight observations at auroral latitudes. We present here early results of the observations; salient points include the following. First, most of the data are consistent with phase-screen modeling of the production of ionospheric scintillation, including an ƒ−2 frequency dependence for phase variance. Second, propagation theories invoking weak, single scatter seldom are adequate, because even moderate intensity scintillation usually is accompanied by phase fluctuations comparable to or greater than a radian. Third, under conditions producing GHz scintillation (near the geomagnetic equator), lower frequencies show marked diffraction effects, including breakdown of the simple ƒ−2 behavior of phase variance and loss of signal coherenceacross a band as narrow as 11.5 MHz at UHF.
269 citations
TL;DR: In this paper, a new optical technique for measuring the refractive-index structure parameter Cn2 was described, using relatively large incoherent transmitting and receiving optics, the scintillometer maintains its calibration and path-weighting function throughout the range of observed refractive turbulence values, even to the case of saturated scintillation.
Abstract: This paper describes a new optical technique for measuring the refractive-index structure parameter Cn2. By using relatively large incoherent transmitting and receiving optics, the scintillometer maintains its calibration and path-weighting function throughout the range of observed refractive turbulence values, even to the case of saturated scintillation.
237 citations
TL;DR: A uniquely located, statistically prominant radiowave scintillation enhancement has been identified in nighttime auroral-zone data as discussed by the authors, which occurs whenever the propagation path coincides with an L-shell in the region of diffuse auroral particle precipitation.
Abstract: A uniquely located, statistically prominant radiowave scintillation enhancement has been identified in nighttime auroral-zone data. The enhancement occurs whenever the propagation path coincides with an L-shell in the region of diffuse auroral particle precipitation. It is hypothesized that this enhancement is a purely geometric effect due to sheet-like ionospheric irregularity structures aligned along L-shells. This hypothesis is confirmed by spaced-receiver data showing that the diffraction pattern is elongated along the geomagnetic east-west direction when the scintillation enhancement occurs.
87 citations
TL;DR: In this paper, the spatial spectrum of electron density in the solar wind was estimated over the frequency range 2 x 10/sup -/3 to 3 × 10/Sup -/2 km/sup-/1 by using 74 MHz observations of interplanetary scintillation.
Abstract: The spatial spectrum of electron density in the solar wind is estimated over the frequency range 2 x 10/sup -/3 to 3 x 10/sup -/2 km/sup -/1 by using 74 MHz observations of interplanetary scintillation. The inversion technique by which the spatial spectrum is estimated from the observed temporal spectrum requires weak scattering. Hence at 74 MHz it can only be applied for solar elongations greater than 40/sup 0/. The shape of the spectrum is best described by a two-component power law (P(q) proportionalq/sup -alpha/) where ..cap alpha..approx. =2.7 at low wave numbers and ..cap alpha..approx. =3.2 at higher wave numbers. Occasionally, a single ..cap alpha..approx. =3.0 gives a satisfactory description. The shape of the spectrum varies significantly from day to day, but no mean variation with solar distance has been observed.
55 citations
TL;DR: In this paper, the possibility of detection of the light emitted by gas scintillation proportional counters (GSPC) with photoionization detectors (PID) is considered.
52 citations
TL;DR: In this paper, the authors compare velocities measured by earth-orbiting spacecraft and interplanetary scintillation (IPS) observations for 1973, a period when high-velocity streams were prevalent.
Abstract: Solar wind velocities measured by earth-orbiting spacecraft are compared with velocities determined from interplanetary scintillation (IPS) observations for 1973, a period when high-velocity streams were prevalent. The spacecraft and IPS velocities agree well in the mean and are highly correlated. No simple model for the distribution of enhanced turbulence within streams is sufficient to explain the velocity comparison results for the entire year. Although a simple proportionality between density fluctuation level and bulk density is consistent with IPS velocities for some periods, some streams appear to have enhanced turbulence in the high-velocity region, where the density is low.
51 citations
TL;DR: In this paper, gas scintillation proportional counter for soft X-rays in the energy range 0.1-1.5 keV is studied, and a significant improvement of the pulse-height distribution is achieved with a mixture of 80% argon and 20% xenon.
51 citations
TL;DR: An experimental investigation has been carried out on turbulence-induced noise in a long-path laser absorption spectrometer which measures sequentially the atmospheric transmission at two preselected wavelengths over the same path, showing that performance degradation can be significantly reduced by exploiting the coherence between fluctuations in received signal at the two wavelengths.
Abstract: An experimental investigation has been carried out on turbulence-induced noise in a long-path laser absorption spectrometer which measures sequentially the atmospheric transmission at two preselected wavelengths over the same path A simple analysis shows that performance degradation due to scintillation can be significantly reduced by exploiting the coherence between fluctuations in received signal at the two wavelengths Auto-correlation and cross-correlation properties for signals at the two wavelengths, recorded experimentally, are compared with results derived from turbulence theory, and implications for choice of spectrometer wavelengths and sampling speed are discussed
46 citations
TL;DR: In this paper, the backscatter measurements made at Jicamarca at 50 MHz provide an additional measurement of the spectral power at 3m wavelength, and the computed intensity is compared with actual back scatter measurements and correlated scintillation observations.
Abstract: In situ measurements of equatorial electron density irregularities in the F-region by rockets and satellites have yielded a power-law form of one-dimensional wave number spectrum of spectral index 2 in a direction transverse to the magnetic field over a scale size range of several km to several tens of m. Equatorial scintillation measurements in the WHF/UHF band which are most sensitive to irregularities of several km to several hundred m are consistent with the in situ spectral results. The backscatter measurements made at Jicamarca at 50 MHz provide an additional measurement of the spectral power at 3m wavelength. Computations are presented for the backscatter intensity expected from irregularities with power law spectrum in the transverse direction but which are infinitely elongated along the magnetic field. The computed intensity is compared with actual backscatter measurements and correlated scintillation observations. It is found that in order to reconcile the backscatter measurements with the simultaneous VHF/UHF scintillation observations a gaussian type cut-off of the power-law spectrum is necessary at m wavelengths near the O+ ion gyro-radius.
46 citations
TL;DR: In this paper, the authors collected together some of the main ideas and experimental results on the twinkling of stars and used statistical methods to characterize the features of the scintillation and investigate the ways in which these depend on the zenith angle of the star, the bandwidth of the light and various other parameters.
Abstract: This article collects together some of the main ideas and experimental results on the twinkling of stars. Statistical methods are used to characterize the features of the scintillation and to investigate the ways in which these depend on the zenith angle of the star, the bandwidth of the light and various other parameters. Some new results are included which demonstrate the advantages of using photon counting methods in experiments on stellar scintillation. Since the twinkling of stars is a consequence of the turbulence in the Earth's atmosphere then measurements can be used to deduce some features of the structure of the turbulence. We discuss some of the experiments designed to do this and report the results.
34 citations
TL;DR: In this paper, the scintillation decay of liquid argon excited by 207Bi internal conversion electrons and by 210Po α-particles has been studied by a single-photon counting technique.
TL;DR: In this article, the flux density of the 74 MHz compact source in the Crab Nebula is estimated from interplanetary scintillation observations using a new method of analysis, which removes the earlier disagreement with very-long-baseline interferometry determinations.
Abstract: The flux density of the 74 MHz compact source in the Crab Nebula is estimated from interplanetary scintillation observations using a new method of analysis. The result removes the earlier disagreement with very-long-baseline interferometry determinations. It also shows a 45% secular decrease in the flux from 1971.4 to 1975.4, in good agreement with observations of the 74 MHz pulsing flux. The differences between this new analysis and the method which had been used to date are described. A procedure for the reinterpretation of other meter-wavelength scintillation observations is discussed.
TL;DR: In this paper, the amplitude scintillation measurements made on two-millimeter microwave links at 36 GHz and 110 GHz along a common 4.1 km path across central London are deseribed.
Abstract: Amplitude scintillation measurements made on two-millimeter microwave links at 36 GHz and 110 GHz along a common 4.1 km path across central London are deseribed. The variances of the logarithmic amplitude scintilliations at these two frequencies are compared for different ranges of the outer scale of turbulence. A comparison is made between the experimental results and the theoretical predictions of Tatarski. Good agreement has been found for the two cases when the outer scale of turbulence is greater than and smaller than the Fresnel zone size.
TL;DR: In this paper, the design of large, time-compensated scintillation detectors for medium and high energy neutrons is analyzed and tested experimentally, and it is shown that with an appropriate geometrical layout and a corresponding choice of timing, neutron and photon transit time effects cancel, resulting in good resolution for large detectors.
TL;DR: In this paper, a large area gas scintillation proportional counter (GSPC) was developed for use as a spectrometer in X-ray astronomy using a crude laboratory version of the xenon cell coupled to a 9 cm diameter ruggedized photomultiplier, with an energy resolution of 11% FWHM at 6 keV over a total geometric area of ~ 300 cm2.
Abstract: A large area gas scintillation proportional counter (GSPC) developed for use as a spectrometer in X-ray astronomy is presented A crude laboratory version of the xenon cell coupled to a 9 cm diameter ruggedised photomultiplier, has an energy resolution of ~ 11% FWHM at 6 keV over a total geometric area of ~ 300 cm2 The instrument has a high rejection ability for charged particles present in a space environment A rejection efficiency for Co60 induced events of ~ 90% was achieved, over the energy range 1-20 keV, for an X-ray acceptance of ~ 80% These results show that the GSPC is a credible improved alternative instrument to a proportional counter with which to study cosmic X-ray sources
TL;DR: In this article, the results of a twelve-month series of scintillation measurements at a frequency of 137 MHz, using signals from a quasi-geostationary satellite were given.
Journal Article•
TL;DR: These investigations show the influence of pileup rejection on counting rate and it is shown that the energy distribution of the photon fluence striking the crystal determines the counting losses and image distortion, rather than the counting rate in the energy window.
Abstract: A method that simulates a clinically relevant situation is used to measure the amount of pulse pileup in the gamma image by distinguishing between correctly and incorrectly positioned events. Comparison was then made between responses from different cameras. These investigations show the influence of pileup rejection on counting rate. Pileup effects can be determined for some cameras at such low count rates as about 10,000/sec with a 30% energy window. Parameters affecting the total count rate of the scintillation camera--such as scattering media, source geometry, collimator, and energy window--have been investigated. It is shown that the energy distribution of the photon fluence striking the crystal determines the counting losses and image distortion, rather than the counting rate in the energy window. The approach described here might fulfill the requirements for a new method to compare scintillation cameras. It is important to note that measurements without scattering medium yield results irrelevant for clinical situations.
TL;DR: In this paper, preliminary results of 1.7 GHz scintillation measurements made in Japan using a geostationary satellite during May-August in 1977 are presented, where the propagation path below about 100km altitude is nearly parallel to the geomagnetic field, and it was possible to observe irregularities along the field direction.
TL;DR: In this paper, the authors used the University of Iowa Cocoa Cross radiotelescope on a 'grid' of 150 selected radio sources covering solar elongation angles up to 180 degrees.
Abstract: Synoptic interplanetary scintillation (IPS) index measurements at 34.3 MHz were obtained during May-December 1974 by means of the University of Iowa Cocoa Cross radiotelescope on a 'grid' of 150 selected radio sources covering solar elongation angles up to 180 deg. Over 80 of these sources displayed definite IPS, and the solar elongation dependence of the 34.3-MHz IPS index is consistent with the elongation of angle dependence measured at higher frequencies. Large enhancements of the IPS index are found to coincide with solar wind (proton) density increases greater than 10/cu cm. Correlation analysis confirms the IPS response to solar wind density and indicates that the events are due primarily to the corotating solar wind turbulent plasma structures which dominated the interplanetary medium during 1974.
TL;DR: In this article, an improved large area gas scintillation proportional counter has been built, suitable for use in X-ray astronomy, which employs electron focusing in a drift region to achieve uniform response.
Abstract: An improved large-area gas scintillation proportional counter has been built, suitable for use in X-ray astronomy. This counter employs electron focusing in a drift region to achieve uniform response. We show that we can obtain a spectral resolution of 9.1% FWHM at 5.9 keV over a useful area of 100 cm2. We demonstrate that signal rise-time discrimination can be used to reject non-X-ray background as efficiently as in ordinary proportional counters.
TL;DR: In this article, the authors investigated the possibility of replacing the conventional photomultiplier tube with a vacuum photodiode as light sensor for gas scintillation counters, which was successfully done for heavy ions in counters where a high light output was available.
Patent•
24 Jul 1978
TL;DR: A radiation detector suitable for use in tomographic scanners comprising at least one cadmium tungstate scintillation crystal optically coupled with a silicon photodiode or other photoelectric transducers is described in this paper.
Abstract: A radiation detector suitable for use in tomographic scanners comprising at least one cadmium tungstate scintillation crystal optically coupled with a silicon photodiode or other photoelectric transducers A plurality of cadmium tungstate crystals may be coupled to one silicon photodiode with fiber optic light guides In a tomographic scanner, radiation passing through the scan circle impinges on the cadmium tungstate crystals causing them to scintillate The light scintillated strikes the area of the p-n junction of the photodiode causing the photoelectric effect to be manifested The intensity of radiation striking the crystal is determined by measuring the photoconductive conductance, photoemissive current or photovoltaic potential From these intensities an image is computed of the radiation attenuation in the examined scan circle
Patent•
25 Sep 1978
TL;DR: In this article, a scintillator for neutron time-of-flight measurements is positioned at a desired angle with respect to the neutron beam, and as a function of the energy thereof.
Abstract: A scintillator for neutron time-of-flight measurements is positioned at a desired angle with respect to the neutron beam, and as a function of the energy thereof, such that the sum of the transit times of the neutrons and photons in the scintillator are substantially independent of the points of scintillations within the scintillator. Extrapolated zero timing is employed rather than the usual constant fraction timing. As a result, a substantially larger scintillator can be employed that substantially increases the data rate and shortens the experiment time.
TL;DR: In this article, a scintillation drift chamber with a gas mixture of 90% Ar + 10% N2 in the range of pressure between 50 and 150 torr is described, where the position where a heavy ion transverses the chamber is determined in one dimension from the drift time of ionization electrons measured as the time delay between primary and secondary SCINTillation flashes; the other dimensions is derived by charge-division techniques from the charge of the electron swarm arriving at the end of the drift space.
TL;DR: The dependence of the scintillation light yield induced by alpha particles upon the electric field has been studied for argon gas in the pressure range of 5-25 atm.
TL;DR: In this article, the S band scintillations observed during the Pioneer 10 and 11 occultation measurements of Jupiter are analyzed and it is shown that the spectrum depends to a large extent on the direction of anisotropy and is therefore useful for measuring the orientation of the magnetic field in regions that have not yet been probed by direct measurements.
Abstract: In this paper the S band scintillations observed during the Pioneer 10 and 11 occultation measurements of Jupiter are analyzed. It is found that while the electron density irregularities are isotropic in the collision-dominated lower ionosphere, they are anisotropic in the upper ionosphere because of alignment along the magnetic field. By using Rytov's approximation the frequency spectrum of the log-amplitude scintillations is derived for a wave propagating in an anisotropic turbulent medium. It is shown that the spectrum depends to a large extent on the direction of anisotropy and is therefore useful for measuring the orientation of the magnetic field in regions that have not yet been probed by direct measurements. This new technique is applied to the Pioneer 10 and 11 observations, and is used to deduce the first measurements of magnetic field orientation in the ionosphere of Jupiter.
TL;DR: In this article, the average behaviour of scintillation versus zenith and azimuth is compared to a theoretical index deduced using weak scattering theory, which shows that the irregularities are elongated along the field lines with an elongation factor ≥ 2.5.
TL;DR: In this paper, a technique utilizing wave-shifter bars was developed for gathering scintillation light from each of these counters into a small number of photomultiplier tubes.
Abstract: Very large area scintillation counters have been developed for use in a neutrino experiment at Fermilab. These counters are used to measure the energy and position of hadronic cascades. In order to do this economically, we have developed a technique utilizing "wave-shifter" bars for gathering scintillation light from each of these counters into a small number of photomultiplier tubes. A low cost acrylic plastic scintillator (5' × 5' × 1.5") and larger (10' × 10' × 1") acrylic tanks filled with liquid scintillator are being viewed with wavelength-shifting bars.
TL;DR: In this paper, the atmospheric refractive index structure parameter Cn2 was determined from amplitude scintillation measurements made on a 36 GHz radio link and also from the refractive frequency spectrum computed from refractivity measurements using a radio refractometer.
TL;DR: It is suggested that the linear correlations of paired values with the two techniques is evidence that scintillation camera detection of 133Xe can be used to quantitate changes in regional myocardial perfusion in the cardiac catheterization laboratory.
Abstract: Measurement of disappearance rates of diffusible isotopes with a scintillation camera has been used to estimate myocardial blood flow in man, although there has been no data to assess the accuracy of the technique. We compared regional flow measurements using scintillation camera detection of 133 Xe with essentially simultaneous measurements using gamma-emitter labeled microspheres and differential spectrometry of left ventricular tissue. In 16 dogs, flows through 20--50% of the left ventricle were obtained at rest and with intravenous isoproterenol; the coefficient of correlation of paired measurements with the two techniques was 0.74. In eight dogs, a coronary artery was ligated, and regions approximately 2.2 cm2 at nearby locations in normal, infarcted and marginal tissue studied; the coefficient of correlation was 0.73. In five dogs, flow in three to five precisely identical 1.1 cm2 regions were measured at rest and with isoproterenol by both methods; correlations within each dog ranging from 0.81 to 0.93 were obtained. Although flows with the scintillation camera technique tended to be lower than values with the microsphere technique, it is suggested that the linear correlations of paired values with the two techniques is evidence that scintillation camera detection of 133Xe can be used to quantitate changes in regional myocardial perfusion in the cardiac catheterization laboratory.