Showing papers on "Scintillation published in 1985"
Abstract: Dual-frequency observations of flat and steep-spectrum extragalactic radio sources made at Arecibo Observatory over a 20-day period are analyzed. As first reported by Heeschen (1982, 1984), flat-spectrum sources generally have larger intensity variations than steep-spectrum ones. A structure function analysis demonstrates a qualitative difference in the time series of the sources. The case against interstellar scintillation is examined, including a review of applicable scintillation theory. Relativistic source motion is treated as a solution to the brightness-temperature problems which arise if the variations are assumed intrinsic to the sources. 16 references.
330 citations
TL;DR: In this paper, a two-component irregularity spectrum with a shallow slope (p 1 ~ 1.5) at long scalelengths (> 1km) and steep slope ( p 2 ~−3) at shorter scalelsengths has been found in both vertical and horizontal spectra and the temporal structure of scintillations in relation to the in situ measurements of irregularity spatial structure within equatorial bubbles was critically examined.
142 citations
01 Jan 1985-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, the properties of CII(TI) have been investigated and properties of this material are reported, which is an interesting material for calorimeters in high energy physics.
Abstract: CsI(TI) is an interesting material for calorimeters in high energy physics. Properties of this material are reported.
118 citations
TL;DR: In this article, the authors compared the power spectra, estimated by the maximum entropy method and by a fast Fourier transform-based periodogram method, using simulated time series.
Abstract: Power spectra, estimated by the maximum entropy method and by a fast Fourier transform based periodogram method, are compared using simulated time series. The times series are computer generated by passing Gaussian white noise through low-pass filters with precisely defined magnitude response curves such that the output time series have power law spectra in a limited frequency range: P(f) = Af −p, f1 ≤ f ≤ f2. Ten different values of p between 0.5 and 5.0 are used. Using 4000 independent realizations of these simulated time series, it is shown that maximum entropy results are superior (usually greatly superior) to the periodogram results even when end-matching or windowing or both are used before the power spectra are estimated. Without the use of end-matching or windowing or both, the periodogram results are useless at best and very misleading at worst. For an application to geophysical data, a 5-min section of ionospheric scintillation data from the MARISAT satellite was chosen because it illustrates a transition from low-level background noise to moderate scintillation and another transition to fully saturated scintillation. This section was broken into 60 sections, each 10 s long and overlapped by 5 s. Order 5 Burg-MEM spectra from the raw data are compared with periodograms computed from end-matched and windowed data. The superiority of Burg-MEM rests largely in the smoothness of the spectrum: real changes in spectral shape are not obscured by meaningless detail.
115 citations
TL;DR: In this article, the properties of ZnWO4, bismuth doped ZnO4 and antimon doped WO4 were studied. Decay time, light yield and their temperature dependence were reported.
105 citations
TL;DR: In this article, the authors demonstrated the use of radio scattering and scintillation observations, using spacecraft signals, for measuring interplanetary shock waves near the sun, and showed that Doppler noise, a parameter which is routinely observed and recorded by the NASA Deep Space Network, is essentially a measure of doppler scintillations, and provided the first near-sun profiles of solar wind speed and electron density fluctuation for a shock wave produced by a solar flare.
Abstract: It is pointed out that more definitive shock velocity observations near the sun are needed for an improved determination of the extent of shock deceleration from the sun to earth. Woo and Armstrong (1981) have demonstrated the use of radio scattering and scintillation observations, using spacecraft signals, for measuring interplanetary shock waves near the sun. Woo and Armstrong provided the first near-sun profiles of solar wind speed and electron density fluctuation for a shock wave produced by a solar flare. The present investigation has the objective to demonstrate the use of Doppler or phase scintillations for monitoring and observing interplanetary shocks. It is also shown that Doppler noise, a parameter which is routinely observed and recorded by the NASA Deep Space Network, is essentially a measure of Doppler scintillations.
92 citations
TL;DR: A technique is proposed for imaging 2D sections based on measurement of elastic scatter radiation using seven scintillation detectors (BGO) operated in current integration mode to measure radiation falling on the object to be investigated.
Abstract: A technique is proposed for imaging 2D sections based on measurement of elastic scatter radiation. In this new imaging method the radiation from a conventional X-ray source (Philips MCN 165 160 kVp tube operated at 140 kVp and 4.6 mA with 0.6 mm focus) is collimated by a lead diaphragm (1.0 mm) and falls on the object to be investigated. The transmitted radiation and the scatter falling within a range of half-angle 6 degrees (with reference to the object centre) are recorded by seven scintillation detectors (BGO) operated in current integration mode. Each scintillation crystal subtends an angular range of 1 degrees . The detector array comprises three scatter detectors arranged symmetrically on either side of the central transmission detector in such a way that six (partially overlapping) scatter measurements result.
87 citations
01 Dec 1985-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, the authors report on the development of a compact, inexpensive and fast light pulser system designed to set up the timing of scintillators in a medium energy physics spectrometer.
Abstract: We report on the development of a compact, inexpensive and fast light pulser system designed to set up the timing of scintillators in a medium energy physics spectrometer.
81 citations
TL;DR: Spectre des fluctuations d'intensite en presence d'une forte scintillation produite par des inhomogeneites de densite electronique dans le milieu interstellaire as discussed by the authors.
Abstract: Spectre des fluctuations d'intensite en presence d'une forte scintillation produite par des inhomogeneites de densite electronique dans le milieu interstellaire
78 citations
TL;DR: An optical technique is described that uses coherent and incoherent optical scintillation to measure the path-averaged value of the turbulence inner scale, and inner scale values obtained 1.5 m above the ground over a 24-h period are shown.
Abstract: An optical technique is described that uses coherent and incoherent optical scintillation to measure the path-averaged value of the turbulence inner scale. The technique is verified by comparison with an in situ measurement, and inner scale values obtained 1.5 m above the ground over a 24-h period are shown.
77 citations
TL;DR: In this article, a detailed comparison is made between leading-edge timing and constant-fraction timing with scintillation detectors, and typical timing resolution results are given for 60Co.
Abstract: Time spectroscopy involves the measurement of the time relationship between two events. This paper reviews time pick-off techniques, practival time-pickoff circuits, and timing with scintillation detectors. A detailed comparison is made between leading-edge timing and constant-fraction timing. Typical timing resolution results are given for 60Co.
Patent•
07 Nov 1985
TL;DR: In this paper, a two-dimensional photon position encoder system was proposed, which included a detector for enhancing the spatial resolution of the situs of the origin of incident photons of gamma rays, and the statistical distribution of these photoelectrons was processed by an improved pattern recognition technique such that the positioning information can be determined.
Abstract: A two-dimensional photon position encoder system (10) and process which includes a detector (20) for enhancing the spatial resolution of the situs of the origin of incident photons of gamma rays. A plurality of scintillator material members (22) interact with the incident photons and produce a quantifiable number of photons which exit the scintillation material members. A tuned light guide (68) having a plurality of radiation barriers (92) of predetermined lengths define slots which are operatively associated with one of the scintillator material members. These slots (90) serve to enhance the predictability of the statistical distribution of photons along the length of the slotted light guide (68). A detector (20) detects the distribution of the photons at preselected locations along the length of the slotted light guide. In one embodiment, this detector (20) comprises a photomultiplier (70) which gathers information concerning the photoelectrons which are then counted. The statistical distribution of these photoelectrons is processed by an improved pattern recognition technique such that the positioning information can be determined.
01 Aug 1985-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the temperature dependence of scintillation intensity of BaF 2 was measured and it was shown that the intensity of the 315 nm component increases with decreasing temperature, while the 220 nm component is not affected.
Abstract: Measurements of the temperature dependence of the scintillation intensity of BaF 2 indicate that the intensity of the 315 nm component increases with decreasing temperature, while the 220 nm component is not affected.
TL;DR: In this article, a modified Kolmogorov spectrum was used for the index-of-refraction fluctuations and the results in two dimensions were compared with numerical solutions in three dimensions.
Abstract: We demonstrate that a recently derived approximate solution to the fourth-moment equation that was thought to be Valid only for strong scattering is in fact valid for all values of the scattering parameter. We use a modified Kolmogorov spectrum for the index-of-refraction fluctuations and present results in two dimensions for comparison with numerical solutions. We also present results in three dimensions that should represent a quantitatively accurate, theoretical description of the atmospheric-scintillation problem.
TL;DR: The first long-term measurements of phase scintillations at high latitudes from a quasi-stationary Air Force satellite at 250 MHz were reported in this paper, where the measurements were made from Goose Bay, Labrador covering the corrected geomagnetic latitude range of 64°-72°N and Thule, Greenland covering the correction geOMagnetic latitude ranges of 85°-89°N.
Abstract: The first long-term measurements of phase scintillations at high latitudes from a quasi-stationary Air Force satellite at 250 MHz are reported. The measurements were made from Goose Bay, Labrador covering the corrected geomagnetic latitude range of 64°–72°N and Thule, Greenland covering the corrected geomagnetic latitude range of 85°–89°N. Data from December 1979, March–April 1980 and March–April 1982 are presented from both stations. The sunspot numbers during these specific time periods were approximately the same. The scintillation magnitudes were higher during the vernal equinox at both stations than during the winter solstice. The Goose Bay data showed a well ordered diurnal variation with a nighttime maximum and daytime minimum, whereas the Thule data showed no such ordering. The limited phase scintillation data set from Thule is augmented by intensity scintillation measurements made during 1979–1982 using the same quasi-stationary satellites. The long-term Thule data shows that the major variation in scintillation activity is annual with minimum scintillations observed in the local summer, as was determined earlier by Aarons et al. (1981). In contrast to the pronounced annual variation, the dependence of overall scintillation activity on sunspot cycle is not greatly evident during 1979–1982 when the sunspot number varied approximately between 100 and 200. It was found that both Goose Bay and Thule could show phase scintillations of the order of 10 rad (with 82-s detrend period) even during magnetically quiet times. One such case study, conducted during March 1982, is presented and second-order parameters such as phase aad intensity spectral strengths and slopes and intensity decorrelation times are discussed for this event at both stations. The use of geostationary satellite data shows the importance of enhanced magnetospheric convection velocities on the observation of large phase scintillation values at both sites. This underscores the need for incorporating irregularity dynamics in the currently developed static models of ionospheric scintillation.
TL;DR: In this article, the average probability of bit error for a binary CPSK signal on an Earth-space link in the presence of scintillation fading and additive white Gaussian noise is derived.
Abstract: Theoretical estimates are derived of the average probability 〈Pb〉 of bit error rate that would occur for a binary CPSK signal on an Earth-space link in the presence of scintillation fading and additive white Gaussian noise. Strong scintillations are shown to produce a significant degradation in 〈Pb〉. Experimental results of the signal amplitude distribution obtained on a 7.1° elevation satellite downlink lead to values of 〈Pb〉 against 〈Eb/No〉 which agree well with the results obtained using the theoretical Moulsley-Vilar distribution (1982).
TL;DR: In this article, a typical spectrum of differential phase scintillations measured between two frequencies near 54.5 GHz on a 4.1 km line-of-sight path is presented and the measurement system described.
Abstract: A typical spectrum of differential phase scintillations measured between two frequencies near 54.5 GHz on a 4.1 km line-of-sight path is presented and the measurement system described. Results confirm the expected -8/3 dependence of the spectrum. A marked loss of spectral density at very low scintillation frequencies is observed.
TL;DR: In this article, two Bayesian estimators, namely maximum-likelihood (ML) and minimum-meansquare-error (MS), were used to estimate the position of the PMT signal.
Abstract: Digital implementation of position estimation for the modular scintillation camera is presented. The modular camera system, introduced at the 1983 IEEE Nuclear Science Symposium, comprises an array of small, mechanically and electronically independent, all-digital scintillation cameras. This paper addresses how to best determine the event position given the PMT signals. Two Bayesian estimators are investigated, namely maximum-likelihood (ML) and minimum-meansquare-error (MS) estimators. Both estimators performed similarly. The more important aspect of the estimation problem was found to be the shape of the detector responses as a function of position.
TL;DR: In this paper, amplitude scintillations in an 11.5 GHz SIRIO-Earth link have been evaluated by means of scintillation index, and hourly values of this index have been compared to the ground temperature measured in a site close to the vertical projection of the path.
Abstract: Analysis of amplitude scintillations in an 11.5 GHz SIRIO-Earth link has been performed. The intensity of scintillations has been evaluated for July 1984 by means of scintillation index. The hourly values of this index have been compared to the ground temperature measured in a site close to the vertical projection of the path. Both scintillation index and temperature seem to follow a similar cyclical behaviour. The relationship between the number of occurrences and the value of the index is also represented, together with a two-segment linear-wise approximation.
Journal Article•
TL;DR: In this article, the authors used VHF amplitude scintillation measurements made during the period April 1978 through December 1982 at Calcutta (23°N, 88.5°E; 32°N dip) to study the association of post-midnight scintillations with the occurrences of the maximum negative excursion in the variation of the Earth's horizontal magnetic intensity.
TL;DR: In this paper, Bismuth germanate has been shown to be strongly temperature dependent in its scintillation efficiency and fluorescence decay time, and it is shown that luminescence quenching in BGO cannot be characterized by a single thermal activation to a radiationless transition but a more complex model is required to characterize the light output from BGO crystals.
Abstract: Bismuth germanate has become an increasingly popular replacement for NaI(Tl) scintillators in recent years, mainly due to its higher detection efficiency. However, its scintillation efficiency and fluorescence decay time are strongly temperature dependent. Optimum performance of detector systems which employ BGO crystals depends on knowledge of the BGO pulse shape and intensity and its emission spectrum at the operating temperature of the detector. Measurements of these quantities are presented over the temperature range -47°C to ± 111°C. Although the emission spectrum shifts only slightly over this temperature range, the scintillation efficiency and fluorescence decay time are strongly temperature dependent. In addition to the usefulness of these data for optimizing detector design, the results imply that luminescence quenching in BGO cannot be characterized by a single thermal activation to a radiationless transition but that a more complex model is required to characterize the light output from BGO crystals.
TL;DR: In this article, the fourth moment equation is used to compare the effect of diffractive and weak diffractive scattering on the spectral index of a phase spectrum. But the results are not very dependent on how these refractive scatterings are distributed along the path.
TL;DR: In this paper, a nouvelle serie de mesures de scintillation interstellaire of ces deux pulsars a 408 and 1426 MHz faites in 1982 et 1983 is presented.
Abstract: On presente une nouvelle serie de mesures de scintillation interstellaire de ces deux pulsars a 408 et 1426 MHz faites en 1982 et 1983
15 Jan 1985-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, measurements of photon energy resolution in the region around 1 MeV with a small CsI(Tl) photodiode detector were presented, where the authors used a small Tl detector to detect the photon energy.
Abstract: Measurements of photon energy resolution in the region around 1 MeV with a small CsI(Tl) photodiode detector will be presented.
Patent•
21 Aug 1985
TL;DR: In this paper, a radioisotope camera with an array of scintillation crystals arranged in N rows and M columns and adapted to be struck by gamma-rays from a subject, a separate solid state photodetector (15 ) optically coupled to each crystal, and N+M amplifiers (24) connected to the photodeteectors (15) to distinguish the particular row and column of an activated photodeterector.
Abstract: A radioisotope camera (10) having an array (12) of scintillation crystals (13) arranged in N rows and M columns and adapted to be struck by gamma-rays from a subject, a separate solid state photodetector (15 ) optically coupled to each crystal (13), and N+M amplifiers (24) connected to the photodetectors (15) to distinguish the particular row and column of an activated photodetector. One of the anode or cathode leads (33 or 34) of each photodetector (15) is coupled to the row amplifier (24) associated with the row containing that photodetector while the other of the two leads (34 or 33) is coupled to the column amplifier (24) associated with the column containing that photodetector.
TL;DR: In this paper, the effect of the velocity profile on the drift pattern on the ground is investigated using the multiple phase-screen simulation method, which is applicable even in the strong scattering case.
Abstract: HF wave propagation in the turbulent stratified ionosphere is investigated using the multiple phase-screen simulation method. For waves incident along the axis of the background stratification, generalized parabolic equations for the modified complex amplitude u are derived which are applicable even in the strong scattering case. Based on these parabolic equations, several one-dimensional random phase screens are numerically generated to represent the effect of the random irregularities on the wave. For plane wave incidence, various statistical properties of the field, such as correlation, power spectrum, scintillation index, etc., can be directly computed using spatial averaging under the ergodicity assumption. The simulation method is also used to examine the effect of the velocity profile on the drift pattern on the ground.
TL;DR: In this paper, the results of 1.5 GHz scintillation measurements at Yamaguchi, Japan were described. But with regard to the characteristics of ionospheric scintillations at gigahertz frequencies, few data are available in the middle latitude region.
Abstract: Anomalous signal fluctuations due to ionospheric scintillation at 1.5 GHz appear occasionally on earth-space paths in maritime satellite communication. With regard to the characteristics of ionospheric scintillations at gigahertz frequencies, few data are available in the middle latitude region. This paper describes the results of 1.5-GHz scintillation measurements at Yamaguchi, Japan. Measurements were carried out by receiving a 1.5-GHz beacon signal from the MARISAT satellite over the Indian Ocean with an elevation angle of 17.3°. In 13 months of measurements, very severe scintillation with peak-to-peak fluctuations exceeding 30 dB was observed in the equinoctial month, and a number of spike-type scintillations were also observed, particularly at night. Scintillation characteristics, such as diurnal and seasonal variations, amplitude distribution, spectrum, and depolarization are discussed.
Journal Article•
01 Mar 1985-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, it was shown that the scintillation intensity for relativistic heavy ions in liquid argon is proportional to the deposited energy, that is, to Z12, where Z1 is the nuclear charge of heavy ions.
Abstract: Scintillation yields per unit energy deposited by relativistic heavy ions in liquid argon have been measured. They are (1.41 ± 0.07) for 613 MeV/n Ne ions and (1.39 ± 0.07) for 705 MeV/n Fe ions, if the value is normalized to unity for 5.3 MeV alpha particles. These results show that the scintillation intensity for relativistic heavy ions in liquid argon is proportional to the deposited energy, that is, to Z12, where Z1 is the nuclear charge of heavy ions. Furthermore, the variation of ionization and scintillation in liquid argon has been investigated as a function of electric field using relativistic Ne and Fe ions. It is shown that a linear combination of ionization signal I and scintillation signal S, I + aS, is proportional to the deposited energy, independently of electric field strength and types of incident particles. This suggests that if we use both signals, we may construct a massive calorimeter that can be used for nuclear reactions induced by relativistic heavy ions.