Showing papers on "Scintillation published in 1987"

Rapid variability of extragalactic radio sources

Abstract: Thirty-one extragalactic radio sources have been observed at 2-4 hr intervals for 3-4 days at each of three epochs. The 15 compact sources in the sample appear to display two types of variability. One is probably weak flickering caused by refractive interstellar scintillation. The other is a larger amplitude variability, which is characterized by a narrow range of timescales of about 1-2 days. Three possible causes of the second type are discussed: (1) intrinsic variability; (2) scintillation from a very narrow disk component of the ISM; and (3) scintillation from clouds associated with a particular region of the ISM. It is suggested that the latter is the more likely explanation. 24 references.

Refractive Scintillation in the Interstellar Medium

Abstract: It is shown here that the large-scale component of interstellar scintillation which causes the slow variation in the apparent intensity of pulsars on time scales of days to months can be greatly enhanced when the turbulence spectrum has a limiting inner scale of the order 10 to the 9th m. This solution is extended to the spherical diverging geometry appropriate for a pulsar embedded in the ISM, and a similar enhancement is found. A comparison of this solution with pulsar observations is used to place bounds on the inner scale of the ISM. 39 references.

Depth-of-interaction determination in NaI(Tl) and BGO scintillation crystals using a temperature gradient

Abstract: A method for determining the depth of interaction in both NaI(Tl) and BGO crystals is investigated. This technique takes advantage of the relationship between temperature and decay time in a scintillation crystal. The depth of interaction is ascertained by measuring the decay time in a crystal with a uniform temperature gradient applied along its depth. The application of determining the depth of interaction in positron emission tomography scanners is discussed.

250 MHz/GHz Scintillation Parameters in the Equatorial, Polar, and Auroral Environments

Abstract: Ionospheric scintillation effects encountered in the equatorial anomaly crest, polar cap, and auroral regions have been contrasted to provide information for the design and evaluation of the performance of multifrequency satellite communication links in these regions. The equatorial anomaly region is identified as the most disturbed irregularity environment where the amplitude and phase structures of 250 MHz and L -band scintillations are primarily dictated by the strength of scattering rather than ionospheric motion. In the anomaly region, the spectra of intense amplitude scintillations at these frequencies are characterized by uniform power spectral density from the lowest frequency (10 MHz) to 4 Hz at 257 MHz and to 1 Hz at L -band (1541 MHz) and steep rolloff at higher fluctuation frequencies with power law indexes of -5 to -7. Such structures are compatible with intensity decorrelation times of 0.1 and 0.3 s at 257 and 1541 MHz, respectively. The phase spectra at 244 MHz are described by power law variation of psd with frequency with typical spectral indexes of -2.4. The strong scattering at VHF induces extreme phase rates of 200° in 0.1 s. The 90th percentile values of rms phase deviation at 244 MHz with 100 s detrend are found to be 16 rad in the early evening hours, whereas amplitude scintillation can cover the entire dynamic range of 30 dB not only in the 250 MHz band but at L -band as well. In the polar cap, the 50th and 90th percentile values of rms phase deviation at 250 MHz for 82 s detrend are 3 and 12 rad, respectively, with comparable values being obtained in the auroral oval. The corresponding values for the S 4 index of scintillation are 0.5 and 0.8 in the polar cap, which are slightly higher than those recorded in the auroral oval. The power law index of phase scintillation at high latitudes is in the vicinity of -2.3, which is not a result of very strong turbulence as in the equatorial region but is considered to be a consequence of shallow irregularity spectral indexes. The phase rates at auroral locations are an order of magnitude smaller than in the equatorial region and attain values of 100° in 0.5 s. The extreme variability of ionospheric motion in the auroral oval sensitively controls the structure of scintillations. The long-term morphology (period 1979-1984) of intensity scintillations at 250 MHz in the polar cap shows that, in addition to the absence of diurnal variation of scintillations, and the presence of an annual variation with a pronounced minimum during local summer, there exists a marked solar control of scintillation activity such that it abruptly decreases when the solar activity falls below a threshold level.

Millimetre-wave propagation through hydrocarbon flame

Abstract: The propagation of microwave and millimetre-wave signals through flame has been investigated with reference to the reliability of future communications systems on deep-water oil production platforms. The results show that the 0.5 m thick flame investigated produced little attenuation,>0.5 dB at frequencies between 37 and 210 GHz, but that scintillation effects were enhanced by the presence of flame, particularly at the higher frequencies, with ~4 dB peak-to-peak fluctuations at 210 GHz.

Wind and CN2 profiling by single-star scintillation analysis

Abstract: The spatiotemporal cross-correlation function of single-star scintillation is estimated. From this estimation and using a priori knowledge of the theoretical shape of the correlation peaks, a method for simultaneously measuring horizontal velocity, altitude, and integrated C(2)(N) value for each atmospheric turbulent layer between 2 and 20 km is described. Taylor's hypothesis is tested for one particular layer and the lifetime of certain turbulent eddies is estimated. Results are in good agreement with two other methods.

Scintillation detector for three-dimensionally measuring the gamma-ray absorption position and a positron CT apparatus utilizing the scintillation detector

Abstract: A scintillation detector for three-dimensionally measuring the absorption position of the gamma-rays entering the detector and a positron computed tomography apparatus employing as a gamma-rays detector plural scintillation detectors arranged in the form of a ring are provided which can prevent the degradation of the spatial resolution in the peripheral region of the visual field and uniformly detect a positron distribution over the entire visual field with high resolution. The scintillation detector comprises a bundle of pillar-shaped scintillator elements and position detecting photodetectors coupled to the end surfaces of each scintillator element, and the apparatus comprises a plurality of scintillation detectors formed in a ring, each of which includes a bundle of scintillator elements, and plural position detecting photodetectors each of which is connected to both ends of the scintillator bundle.

Highly stable silicon pin photodiode

Abstract: Silicon photodiodies have several interesting advantages as scintillation detectors. Recently the manufacturing techniques for making photodiodes have been greatly improved. Furthermore the selection of optimum operating parameters for the use of photodiodes and their stability are very important. This paper discusses the recently improved characteristics of Hamamatsu Photonics KK photodiodes.

A new analysis technique for estimating zonal irregularity drifts and variability in the equatorial F region using spaced receiver scintillation data

Abstract: A new technique for analyzing spaced receiver measurements of equatorial scintillation is applied to VHF scintillation data. The technique is based on a model that includes both propagation effects and the statistical characteristics of scintillation-producing irregulatities. Nonlinear least squares fitting is used to fit the model to measured auto- and cross-correlation functions of the signal amplitude fading on spaced receivers. The results are compared with mean and “random” drift estimates obtained using the classical type of correlation analysis.

Ionization and Scintillation Signals Produced by Relativistic La Ions in Liquid Argon

Abstract: We have observed simultaneously the ionization and scintillation signals produced by relativistic La ions in liquid argon. The two signals are highly correlated and the sums of these signals are constant with the standard deviation of 1.2% over the range of the electric field from 0 to 7.5 kV/cm. The ratio of the sum signals expressed in unit of the number of species to the value N i + N ex is close to unity, where N i and N ex are the numbers of ion pairs and excitons, respectively, produced by La ions in liquid argon. The pulse height resolution of the sum of the signals is better than that of ionization or scintillation alone. Almost no quenching is found in the scintillation signal from relativistic La ions when compared to signals from lighter ions.

A fast module for pulse shape analysis

Abstract: A pulse shape discrimination module, capable of providing particle identification by analysis of scintillation decay time, is described. It has been designed for use in photo-nuclear reaction experiments where a very high rate electromagnetic background has to be rejected, so that very low rate hadronic reaction products can be efficiently counted. Results of tests performed with a liquid scintillator irradiated by neutron and gamma ray sources are presented. These show that the module is capable of handling counting rates of up to 500 kHz and producing a hardware logic decision on the species of interacting particle in

Liquid xenon scintillation spectrometer

Abstract: A liquid xenon scintillation detector has been worked out. Liquid xenon fills up a volume 27 mm diameter by 12–30 mm long inside a quartz cylinder with a teflon reflector. Both ends of the cylinder are sealed with photomultipliers with quartz windows. The energy resolution of the detector was found to be of the same order of magnitude as NaI(Tl) crystals for the energy 120 KeV. However, the resolution increases for the higher energies and comes up to 15% for 662 KeV. The reasons of such deterioration of resolution with increasing energy are discussed.

Ionization and scintillation produced by relativistic Au, He and H ions in liquid argon

Abstract: We have measured ionization and scintillation produced by relativistic ions of Au, He and H in liquid argon. The sum of ionization signal and scintillation signal per unit energy deposition is the same for He and H ions, which is also the same as that for relativistic Ne, Fe and La ions previously measured. We have found that quenching occurs when liquid argon is irradiated by relativistic Au ions and that the sum per unit energy deposition for the Au ions is 70–76% of that for the other ions mentioned above.

A small spherical NE213 scintillation detector for use in in-assembly fast neutron spectrum measurements

Abstract: A small spherical 14 mm diameter NE213 scintillation spectrometer has been developed. Its linearity, gain stability and pulse shape discrimination were examined through experiments using a 14 MeV neutron field. The pulse responses were analyzed by a Monte Carlo code and compared with the measured ones. The detector proposed by us is superior in in-assembly measurements.

Highly resolvable scintillation fiber plate

Abstract: PURPOSE: To prevent a luminous efficiency from being reduced by the deliquescence of a columnar crystal scintillator, improve its mechanical strength and facilitate handling by covering the scintillator by a film and fixedly supporting the scintillator. CONSTITUTION: A columnar crystal scintillator 1 formed on a fiber plate 3 is covered by an organic film 8 and fixedly supported. As the organic film 8, a xylene resin, for example, polyparaxylene, polymonochloroxylene or the like is used. A water vapor permeability is low due to the film formed by CVD (Chemical Vapor Deposition) method so that the scintillator 1 composed of columnar crystals is not brought into contact with are and an X-ray transmittance is high, being able to be used down to a low energy region. Further, in order to prevent a loss from being generated in the amount of emitted light by the phenomenon that the light emitted from the scintillator 1 returns to an input side and emitted outside therefrom, a reflecting mirror (or light absorbing film) 7 is coated on the outer or inner surface of the organic film 8. COPYRIGHT: (C)1988,JPO&Japio

The Galactic Latitude Dependence of Centimeter-Wavelength Flicker

Abstract: Small-amplitude flickering of the flux density of extragalactic radio sources has been found at 9 cm by Heeschen (1984). It that paper, it was concluded that there was no apparent dependence of the flicker on Galactic latitude. Here, all the pertinent 9 cm data are reanalyzed, and it is found that flicker amplitude does show a latitude dependence consistent with that expected from interstellar scintillation. 7 references.

A model of the solar wind turbulence from radio occulation experiments

Abstract: On developpe un modele de turbulence du vent solaire en utilisant les donnees experimentales d'occultation radio a l'aide de satellites artificiels et de sources radio naturelles

Astronomical Observations: An Optical Perspective

Abstract: Preface 1. Astronomical sources 2. Observational limits 3. Telescopes 4. Seeing, speckles, and scintillation 5. Spectrographs 6. Dilute apertures 7. Single channelled detectors 8. Multi-channelled incoherent detectors References Index.

Process for fabricating tuned light guide for photoelectrons

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. Photons exiting the scintillator material members (22) enter an operatively associated slot in said slotted light guide. 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.

The gas scintillation proportional counter in the spacelab environment: in-flight performance and post-flight calibration

Abstract: We describe the in-orbit performance of the gas scintillation proportional counter which formed part of the Spacelab-1 payload. Discontinuities in the instrument gain are observed (similar to those of the xenon-filled GSPC's on the EXOSAT and TENMA satellites). A post-flight recalibration of the instrument was performed using synchrotron radiation, which found the discontinuities to be coincident with the xenonL edges.

Scintillation detector for tomographs

Abstract: The present invention relates to a scintillation detector for a tomograph comprising at least two scintillators having different scintillation characteristics and being optically coupled to a photodetector.

A Gas Scintillation Proportional Counter for the X-Ray Astronomy Satellite SAX

Abstract: A driftless gas scintillation proportional counter is described. The instrument has several advantages over conventional GSPCs especially for applications at low x-ray energies (~0.l - 30 keV) and small dimensions such as imaging focal plane detectors for x-ray telescopes or concentrators. The x-ray astronomy satellite project SAX has such a requirement and an imaging GSPC of this configuration is presented in this context.