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Showing papers on "Scintillation published in 1982"


Journal ArticleDOI
01 Apr 1982
TL;DR: In this article, a review of scintillation of radio waves propagating through the ionosphere is presented, focusing on propagational aspects, including both theoretical and experimental results, with a discussion of the motivation for stochastic formulation of the problem.
Abstract: The phenomenon of scintillation of radio waves propagating through the ionosphere is reviewed in this paper. The emphasis is on propagational aspects, including both theoretical and experimental results. The review opens with a discussion of the motivation for stochastic formulation of the problem. Based on measurements from in-situ, radar, and propagation experiments, ionospheric irregularities ate found to be characterized, in general, by a power-law spectrum. While earlier measurements indicated a spectral index of about 4, there is recent evidence showing that the index may vary with the strength of the irregularity and possibly a two-component spectrum may exist with different spectral indices for large and small structures. Several scintillation theories including the Phase Screen, Rytov, and Parabolic Equation Method (PEM) are discussed next. Statistical parameters of the signal such as the average signal, scintillation index, rms phase fluctuations, correlation functions, power spectra, distributions, etc., are investigated. Effects of multiple scattering are discussed. Experimental results concerning irregularity structures and signal statics are presented. These results are compared with theoretical predictions. The agreements are shown to be satisfactory in a large measure. Next, the temporal behavior of a transionospheric radio signal is studied in terms of a two-frequency mutual coherence function and the temporal moments. Results including numerical simulations are discussed. Finally, some future efforts in ionospheric scintillation studies in the areas of transionospheric communication and space- and geophysics are recommended.

726 citations


Journal ArticleDOI
TL;DR: In this article, a method for calibrating the light output of NE 213 scintillation detectors by means of "monoenergetic" photon sources is described, where the position of the Compton edge can be precisely determined by comparing the measured pulse-height spectrum with a Monte Carlo simulated distribution properly folded with the pulse height dependent resolution.

215 citations


Journal ArticleDOI
01 Apr 1982-Nature
TL;DR: In this paper, the scintillation of celestial radio sources due to small-scale turbulence along lines of sight through the interplanetary medium provides a convenient, ground-based method of monitoring disturbances in inter-planetary space.
Abstract: The scintillation of celestial radio sources due to small-scale turbulence along lines of sight through the interplanetary medium provides a convenient, ground-based method of monitoring disturbances in interplanetary space. With the sensitive 3.6-hectare Array at Cambridge we have carried out a new programme in which ∼900 sources were observed each day for more than 1 yr. When the long-term average scintillation behaviour of each source had been accurately determined we found that transient disturbances could be clearly distinguished. We detected large clouds of enhanced turbulence moving out from the Sun and were able to track them to distances beyond the Earth's orbit. Our observations differ from recent work elsewhere1 in that we used a larger grid of sources and observed them more continuously over a wider range of solar elongations. To illustrate the information that is now being obtained we present observations for 10–21 December 1978, a period of considerable solar activity for which spacecraft and other data are also available.

129 citations


Journal ArticleDOI
TL;DR: In this paper, the statistics of scintillation intensity on an X-band satellite downlink obtained using the orbital test satellite beacon transmissions were analyzed and the experimentally found distribution is shown to depart significantly from the expected log-normal distribution, and this is explained in terms of a Gaussian process with a time variable standard deviation from which a universal model is derived.
Abstract: Extensive experimental results are presented on the statistics of tropospheric amplitude scintillations on an X -band satellite down-link obtained using the orbital test satellite beacon transmissions. The experimentally found distribution is shown to depart significantly from the expected log-normal distribution, and this is explained in terms of a Gaussian process with a time variable standard deviation from which a universal model is derived. It has been found that on average no less than about 100 h of data are required before the probability density and cumulative probability distribution functions approach stationarity. The statistics of the scintillation intensity are also presented, and a log-normal distribution of intensity is shown to be in good agreement with observations from other experimental sites. Link budget implications are outlined together with a simple strategy for the investigation of the scintillation process at any ground station.

105 citations


Journal ArticleDOI
TL;DR: In this article, a review of the application of the phase screen model to the interpretation of data from the Defense Nuclear Agency's Wideband satellite (international designation P76-5), which was operational from May 1976 until August 1979, is presented.
Abstract: Phase screen models have been used for nearly three decades to facilitate the application of the scintillation theory to data interpretation. Only recently, however, as large amounts of multifrequency phase-coherent beacon data have been analyzed, has the full potential of the model been realized. This paper presents a review of the application of the phase screen model to the interpretation of data from the Defense Nuclear Agency's Wideband satellite (international designation P76-5), which was operational from May 1976 until August 1979. The signal structure and experiment configuration allowed measurements of temporal, spatial, and frequency coherence for a wide variety of scintillation conditions. The derived scintillation parameters are in excellent agreement with the phase screen theory. Moreover, the inferred irregularity structure has been confirmed by recent in situ measurements. The principal results can be summarized with simple algebraic formulas for the scintillation level, spatial/temporal coherence, and frequency coherence or coherence bandwidth. With appropriate manipulations, the formulas fully accommodate the propagation angle dependence in highly anisotropic media.

81 citations


Journal ArticleDOI
TL;DR: In this paper, the amplitude and phase scintillation measurements at 30 GHz on an 8.2 km line-of-sight path in the Netherlands were presented, and compared favourably with those obtained from weak-scattering theory.
Abstract: The letter summarises results of amplitude and phase scintillation measurements at 30 GHz on an 8.2 km line-of-sight path in the Netherlands. The measured results compare favourably with those obtained from weak-scattering theory.

69 citations


Journal ArticleDOI
TL;DR: In this article, simultaneous measurements of the spatial covariance of intensity and the angular spectrum of plane waves have been made for a diverging He-Ne laser beam propagating over a 1-km horizontal path.
Abstract: Simultaneous measurements of the spatial covariance of intensity and the angular spectrum of plane waves have been made for a diverging He–Ne laser beam propagating over a 1-km horizontal path. Most of the data are taken during strong scintillation. The measured angular spectrum is used to estimate the wave-structure function D(s). The propagation equation for the intensity covariance depends on the medium only through the longitudinal derivative of D(s). Thus, for a homogeneous medium, D(s) is sufficient to calculate the intensity covariance, although such a calculation has not been done in general. The estimated D(s) is used to calculate the intensity covariance by using weak scintillation theory and also by using an asymptotic theory for strong scintillation. The measured intensity covariances are then compared with these calculations. In both cases there is qualitative agreement, but the quantitative comparison is poor. It is shown that the inner scale of the turbulence is an important factor in weak scintillation, and it is argued that this inner scale is a dominant factor in strong scintillation.

60 citations



Journal ArticleDOI
TL;DR: In this paper, the effect of crystal shape, reflector type, and the refractive index of the PMT window on coupling efficiency was investigated, and it was shown that when internal trapping in clear, polished bismuth germanate (Bi4Ge3O12 or BGO) crystals is reduced by suitable crystal shaping, a PMTwindow with a high refractive ratio, or non-absorbing vacuum bubbles, it is possible to transfer more than 60% of the scintillation light to the POMT.
Abstract: The high density and atomic number of bismuth germanate (Bi4Ge3O12 or BGO) make it a very useful detector for positron emission tomography. Modern tomograph designs use large numbers of small, closely-packed crystals for high spatial resolution and high sensitivity. However, the low light output, the high refractive index (n=2.15), and the need for accurate timing make it important to optimize the transfer of light to the photomultiplier tube (PMT). We describe the results of a Monte Carlo computer program developed to study the effect of crystal shape, reflector type, and the refractive index of the PMT window on coupling efficiency. The program simulates total internal, external, and Fresnel reflection as well as internal absorption and scattering by bubbles. We show that when internal trapping in clear, polished BGO crystals is reduced by (a) suitable crystal shaping, (b) a PMT window with a high refractive index, or (c) non-absorbing vacuum bubbles, it is possible to transfer more than 60% of the scintillation light to the PMT. This transfer is greatly reduced by internal absorption.

53 citations



Journal ArticleDOI
26 Aug 1982-Nature
TL;DR: In this paper, it was shown that the scintillation characteristics of pulsars are closely related to their velocities, as measured by their proper motions, and that the observed fading pattern is due to the combined motion of the pulsar and the observer relative to an effectively stationary and quasi-static interstellar medium.
Abstract: Interstellar scintillation of the intensity of pulsar radio signals is known to be the effect of diffraction in random irregularities in electron density, with typical scales of 1013 cm and density fluctuations of typically 3×10−4 cm−3. The observed fading pattern is believed to be due to the combined motion of the pulsar and the observer relative to an effectively stationary and quasi-static interstellar medium; this has, however, not been clearly demonstrated so far, and the possibility has remained open that the fluctuations are due at least partly to streaming or wave motions in the medium. Recent measurements of the proper motion of pulsars by radio interferometry1 now allow a direct test. We present here new observations which show that the scintillation characteristics of pulsars are closely related to their velocities, as measured by their proper motions.

Journal ArticleDOI
D.F. Anderson1
TL;DR: In this paper, the lowered photoionization threshold of TMAE in the liquid state is utilized to produce a liquid photocathode, with a detector threshold at about 290 nm (4.3 eV), coupled to a low-pressure wire chamber.

Journal ArticleDOI
TL;DR: In this paper, a correlation analysis method developed by Armstrong and Coles has been applied to spaced-receiver data from the Wideband satellite to verify the L-shell aligned, cross-field anisotropy of F region auroral zone irregularities.
Abstract: A correlation analysis method developed by Armstrong and Coles has been applied to spaced- receiver data from the Wideband satellite. The method permits simultaneous estimation of the anisotropy and true drift of the diffraction pattern. The scintillation theory is applied to interpret the measured variations in anisotropy and pattern drift. The results show that in anisotropic media, there is a complicated interplay between apparent drifts and the anisotropy of the diffraction pattern that must be accommodated in spaced-receiver data analyses. The method has been applied to verify the L-shell aligned, cross-field anisotropy of F region auroral zone irregularities.

Journal ArticleDOI
TL;DR: In this article, a review of the general properties of flare-generated collisionless interplanetary shock wave propagation, determined from multiple spacecraft plasma and magnetic field observations and by means of inter-planetary scintillation of radio sources, is presented.
Abstract: This paper presents a review of the general properties of flare-generated collisionless interplanetary shock wave propagation, determined from multiple spacecraft plasma and magnetic field observations and by means of interplanetary scintillation of radio sources.


Journal ArticleDOI
TL;DR: In this paper, the coupling of primary scintillation devices to photoionization detectors (PIPS chamber) is considered, both in the gas and liquid phases, and using the data available some information is given concerning its expected characteristics of energy, position and time resolution.

Journal ArticleDOI
01 Nov 1982-Icarus
TL;DR: In this paper, a poleward decrease in the 65 km scintillations was detected, together with a peak at 60-70 deg latitude, with greater turbulence near the pole, while the same fluctuations were an order of magnitude lower at 45 km altitude, with turbulence considerably lower than at 60 km.

Patent
28 Jan 1982
TL;DR: In this paper, a positron source, position sensing device, particularly with medical applications, is detected using a ring of stacked, individual scintillation crystals, a plurality of photodetectors, separated from the scINTillation crystals by a light guide, and high resolution position interpolation electronics.
Abstract: A positron source, position sensing device, particularly with medical applications, in which positron induced gamma radiation is detected using a ring of stacked, individual scintillation crystals, a plurality of photodetectors, separated from the scintillation crystals by a light guide, and high resolution position interpolation electronics. Preferably the scintillation crystals are several times more numerous than the photodetectors with each crystal being responsible for a single scintillation event from a received gamma ray. The light guide will disperse the light emitted from gamma ray absorption over several photodetectors. Processing electronics for the output of the photodetectors resolves the location of the scintillation event to a fraction of the dimension of each photodetector. Because each positron absorption results in two 180° oppositely traveling gamma rays, the detection of scintillation in pairs permits location of the positron source in a manner useful for diagnostic purposes. The processing electronics simultaneously responds to the outputs of the photodetectors to locate the scintillations to the source crystal. While it is preferable that the scintillation crystal include a plurality of stacked crystal elements, the resolving power of the processing electronics is also applicable to continuous crystal scintillators.

Journal ArticleDOI
TL;DR: The theory of using an array of receivers as a spatial filter shows that a scintillation variance is sensitive to refractive-index fluctuations the size of the inner scale of turbulence, which yields a sensitive method for determining the path-averaged inner scale by measuring scintilation variance.
Abstract: The theory of using an array of receivers as a spatial filter shows that a scintillation variance is sensitive to refractive-index fluctuations the size of the inner scale of turbulence. The competitive scintillation caused by Fresnel zone-sized fluctuations is greatly eliminated even for long propagation paths. This yields a sensitive method for determining the path-averaged inner scale by measuring scintillation variance. The path weighting of the inner-scale determination for plane wave propagation has excellent uniformity along the path. The proposed design resists the impairing effects of saturation of scintillation. The optical measurement of path-averaged inner scale and refractive-index structure parameter can yield estimates of path-averaged turbulence fluxes of momentum and heat in the atmospheric surface layer. The accuracy of such flux estimates is discussed.

Journal ArticleDOI
TL;DR: In this article, a position sensitive gamma-ray detector from which the focal plane of the telescope may be constructed is described, and the results of laboratory tests on the positional and energy resolution of incident gamma-rays are compared to the relevant theory and the expected performance evaluated via Monte Carlo simulation.

Journal ArticleDOI
Georges Charpak1
TL;DR: In this paper, a survey of various methods of correction for parallax errors connected with the finite width of gaseous detectors is made, and two new types of approach to photon detection are discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors consider the phase difference measured at two different wavelengths after propagating through the same turbulence, and describe these differences in terms of amplitude scintillation and amplitude modulation, and show that the geometrical-optics-predicted wavefront distortions may differ from the real diffracted beam.
Abstract: Adaptive-optics systems that use a return-wave concept for compensating for atmospheric turbulence distortions on a transmitted laser beam usually assume that the phase profile of the sensed radiation equals the appropriate phase profile for the laser wavelength. Certainly geometrical optics would predict this to within a scale factor directly related to the index of refraction of the air at the different wavelengths. Diffraction manifests itself in an interference phenomenon and amplitude modulation. Shorter wavelengths are more quickly affected than the longer wavelengths. When amplitude scintillation becomes important, the geometrical-optics-predicted wave-front distortions may differ from the real diffracted beam. The problem reduces to considering the phase difference measured at two different wavelengths after propagating through the same turbulence, and this paper describes these differences.

Journal ArticleDOI
TL;DR: Gaseous scintillators based on the luminescence of low-pressure (⩽ 1 bar) Ar, Xe and ArN 2 gases can be applied advantageously to the detection of heavy charged particles.

Journal ArticleDOI
TL;DR: In this paper, the optical and position sensing properties of the array are unique and all the light from a scintillation is projected from the narrow elements through a light guide and into a ring of PM tubes yielding a narrow light spread function that is independent of the depth of an interaction.
Abstract: The optical and position sensing properties of the array are unique. All the light from a scintillation is projected from the narrow elements through a light guide and into a ring of PM tubes yielding a narrow light spread function that is independent of the depth of an interaction. Position sensing logic based on a maximum likelihood estimator has been employed to ensure high spatial resolution. The spatial sampling has been chosen so not to impose the primary resolution limit.

Patent
04 Aug 1982
TL;DR: In this paper, a light guide is selected to have an index of refraction at least 1.60, higher than in the conventional gamma camera, whereupon it has been found that the detection efficiency and the positional accuracy of each scintillation event can be increased, to thereby increase the sensitivity and the spatial resolution of the gamma camera.
Abstract: A gamma camera comprises a scintillation crystal having an index of refraction of 1.80-190, a collimator for imaging the object on one face of the scintillation crystal, an array of photodetectors arranged around the opposite face of the scintillation crystal, and a light guide interposed between the opposite face of the scintillation crystal and the plurality of photodetectors. The light guide is selected to have an index of refraction of at least 1.60, higher than in the conventional gamma camera, whereupon it has been found that the detection efficiency and the positional accuracy of each scintillation event can be increased, to thereby increase the sensitivity and the spatial resolution of the gamma camera.

Journal ArticleDOI
TL;DR: Silicon avalanche photodiodes have been shown to be a potential replacement for vacuum tube photomultipliers in many nuclear scintillation detector applications as discussed by the authors, which makes them ideally suited to scintillator detector applications where overall size and ruggedness are a major concern.
Abstract: Silicon avalanche photodiodes have recently been shown to be a potential replacement for vacuum tube photomultipliers in many nuclear scintillation detector applications. The large active area, low noise, and ease of use of these solid-state photomultipliers makes them ideally suited to scintillation detector applications where overall size and ruggedness are a major concern. Historically, avalanche photodiodes have been limited for use in this capacity by small active areas, low internal gains, and poor optical sensitivity at the wavelengths at which most solid scintillator materials emit. Recent advances as the result of research aimed directly at the solution to these problems however, have successfully demonstrated one inch active area silicon avalanche photodiodes which produce a FWHM resolution of 9.5% for Cs137 at room temperature when coupled to a 1″ × 1″ NaI(Tl) scintillation crystal. Improvements to both material quality and device structure have advanced the state-of-the-art to make silicon avalanche photodiodes a viable alternative in scintillation gamma spectroscopy as well as for large area optical, beta, and low energy x-ray detectors.

Journal ArticleDOI
TL;DR: In this article, a lead-scintillator shower counter using fluorescent radiation converters to collect scintillation light was tested with electrons and photons in the energy range 70 MeV to 6 GeV.

Journal ArticleDOI
TL;DR: In this article, the response to relativistic (0.600 MeV/amu) Ne, Ar, and Fe ions and to cosmic ray muons of four widely used commercial plastic scintillators, NE110, Pilot Y, Pilot F, and Pilot B, is discussed.

Journal ArticleDOI
TL;DR: In this article, it is shown that when the outer scale is large compared to the Fresnel radius, the scintillation index measured under weak scatter conditions can be used to derive a universal index curve.
Abstract: The structure of intensity scintillation is characterized by the fourth-order complex signal moment Γ4. The differential equation that governs the behavior of Γ4 is written in terms of dimensionless variables to isolate parameters that can be inferred from intensity scintillation data without a priori knowledge of scale sizes, layer thickness, propagation angles, etc. It is shown, for example, that when the outer scale is large compared to the Fresnel radius, the scintillation index measured under weak scatter conditions can be used to derive a universal scintillation index curve. Multifrequency scintillation data are presented to demonstrate the concept.

Journal ArticleDOI
TL;DR: In this article, a position sensitive photomultiplier of new concept is described, which is based on the scaling property of the equation of motion describing electrons moving inside electric and magnetic fields.