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Showing papers on "Scintillation published in 1986"


Journal ArticleDOI
TL;DR: In this paper, the authors used scintillation observations to determine the space velocities of 71 radio pulsars, including most of the 26 objects with proper motions derived from interferometry.
Abstract: Scintillation observations are used to determine the space velocities of 71 radio pulsars, including most of the 26 objects with proper motions derived from interferometry. The scintillation velocity is dominated by the peculiar transverse velocity of the neutron star and is insensitive to differential galactic rotation. Velocities have a broad distribution function ranging up to about 150 km/s with a tail extending to about 300 km/s. There is no definitive appearance of a bimodal distribution, however. A correlation of velocity with PP(dot) is confirmed to be a general property of the radio pulsar population. It cannot be explained by any observational selection effect and most plausibly is due to a relationship between a neutron star's magnetic moment and the momentum impulse given to it at or near the time of its formation. A small fraction of the objects are discrepant with respect to the velocity-PP(dot) relation. For some objects, this discrepancy may be evidence for a peculiar evolutionary history. 41 references.

182 citations


Journal ArticleDOI
TL;DR: In this article, coordinated measurements of F region plasma patches were conducted on February 3/4, 1984, from Thule and Sondrestrom, Greenland, for the first time these patches were directly tracked flowing in the antisunward direction over distances of 3000 km from the center of the polar cap to the poleward edge of the auroral oval.
Abstract: Coordinated measurements of F region plasma patches were conducted on February 3/4, 1984, from Thule and Sondrestrom, Greenland. Optical, ionosonde, amplitude scintillation, total electron content (TEC), and incoherent scatter radar measurements were combined to reveal several new aspects of the structure and transport of these localized regions of enhanced F region ionization. For the first time these patches were directly tracked flowing in the antisunward direction over distances of 3000 km from the center of the polar cap to the poleward edge of the auroral oval. Quantitative measurements of TEC show increases of 10--15 TEC units within the patches, above a background polar cap value of 5 TEC units. Amplitude scintillation measurements show the presence of ionospheric irregularities through the entire patch, with a weak indication of stronger scintillation on the trailing (or E x B unstable) edge.

174 citations



Journal ArticleDOI
TL;DR: Measurements of amplitude scintillations on low-elevation (7.1° and 8.9°) satellite downlinks at X -band and the statistical distributions of scintillation amplitude and rms intensity are approximated using the Moulsley-Vilar model, and an analytical approximation is presented.
Abstract: Amplitude scintillations occurring on low-elevation earthspace paths can be large enough to significantly degrade the quality of satellite communications links at X -band and higher frequencies. This paper presents measurements of amplitude scintillations on low-elevation (7.1° and 8.9°) satellite downlinks at X -band. The statistical distributions of scintillation amplitude and rms intensity are approximated using the Moulsley-Vilar model [1]. An analytical approximation of this model is presented and is shown to be an easy means of predicting system outage time due to scintillations. Theoretical estimates of the average bit error rate for a digital satellite link subject to scintillation fading are presented for NCFSK and CPSK modulations. Other ways in which scintillations can affect a satellite communication link are discussed, and results are also presented showing the seasonal and diurnal variability of the scintillation intensity and long-term correlation with ground temperature.

107 citations


Journal ArticleDOI
TL;DR: In this article, radio wave propagation through electron-density fluctuations in the ISM is studied using a one-dimensional thin-screen model for the turbulent medium, and the importance of various effects for timing and scintillation observations of pulsars, VLBI observations of galactic and extragalactic radio sources, and for variability measurements of extragaleactic sources is assessed.
Abstract: Radio wave propagation through electron-density fluctuations in the ISM is studied. Observable propagation effects are explored using a one-dimensional thin-screen model for the turbulent medium. Diffraction caused by stochastic small-scale irregularities is combined with refraction from deterministic large-scale irregularities. Some of the effects are illustrated with numerical simulations of the wave propagation. Multiple imaging is considered, delineating the possible effects and discussing their extensions to two-dimensional screens and extended three-dimensional media. The case where refraction as well as diffraction is caused by a stochastic medium with a spectrum of a given form is considered. The magnitudes of observable effects is estimated for representative spectra that may be relevant to the ISM. The importance of the various effects for timing and scintillation observations of pulsars, VLBI observations of galactic and extragalactic radio sources, and for variability measurements of extragalactic sources is assessed. 47 references.

105 citations


Journal ArticleDOI
TL;DR: In this article, a theory simplifiee for le phenomene de scintillation interstellaire refractive is proposed, and l'examine en tant qu'interpretation possible des variations observees for de nombreuses radiosources.
Abstract: On propose une theorie simplifiee pour le phenomene de scintillation interstellaire refractive et on l'examine en tant qu'interpretation possible des variations observees pour de nombreuses radiosources

94 citations


Journal ArticleDOI
TL;DR: This Position Sensitive Photomultiplier Tube features an amplification gain of 10/sup 6/ and a quantum efficiency of 20% allowing for low energy radiation measurements and providing an energy resolution that is nearly the same as that of the conventional PMT.
Abstract: The Position Sensitive Photomultiplier Tube (PMT) was developed mainly for scintillation imaging in the field of high energy physics and medical applications. This PMT consists of a proximity-type photocathode and 11 staged mesh dynodes. For performing two-dimensional detection, two sets of wire anodes arranged in perpendicular with each other performs a read-out of the secondary electrons emitted from the last dynode. The intrinsic spatial spread of 4.3 mm FWHM and resolution of 0.3 mm FWHM were obtained for 4000 photons/pulse with LED by centroid calculation. Also, this PMT features an amplification gain of 10/sup 6/ and a quantum efficiency of 20% allowing for low energy radiation measurements and providing an energy resolution that is nearly the same as that of the conventional PMT. Finally, the authors show the reconstruction of two dimensional/scintillation image with 3'' diameter NaI(T1) crystal.

92 citations


28 Mar 1986
TL;DR: In this article, the amplitude and phase structures of VHF/L-band scintillations are characterized by uniform power spectral density from the lowest frequency (10 MHz) to 4 Hz at VHF and to 1 Hz at L-band with power law indices of -5 to 07.
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 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 VHF/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 VHF and L-band are characterized by uniform power spectral density from the lowest frequency (10 MHz) to 4 Hz at VHF and to 1 Hz at L-band and steep rolloff at higher fluctuation frequencies with power law indices of -5 to 07. Such structures are compatible with intensity decorrelation times of 0.1 and 0.3 sec at VHF and L-band frequencies, respectively. The phase spectra are described by power-law variation of psd with frequency with typical spectral indices of -2. 4. The strong scattering at VHF induces extreme phase rates of 200 deg. in 0.1 sec. The 90th percentile values of rms phase deviation at 250 MHz with 100-sec detrend are found to be 16 rads in the early evening hours whereas amplitude scintillation can covermore » the entire dynamic range of 30 dB not only at 250 MHz but at L-band as well.« less

70 citations


Journal ArticleDOI
TL;DR: In this article, the relation between interplanetary scintillation and mean plasma-densily along the line of sight was investigated. But the results were limited to a grid of 900-2500 radio sources.

61 citations


Patent
22 Aug 1986
TL;DR: A positron emission tomography (PET) camera has a patient area with a plurality of fixed detector rings positioned side-by-side around the patient area to detect radiation as discussed by the authors.
Abstract: A positron emission tomography camera having a patient area with a plurality of fixed detector rings positioned side-by-side around the patient area to detect radiation. Each ring includes multiple layers of scintillation detectors in which the detectors in one of the layers is offset relative to the detectors in the other layers. The thickness of each layer increases exponentially from the inside of the ring to the outside of the ring. Identification of the scintillation detector may be performed by using layers with different timing constants, using silicon avalanche photodiodes or using a light guide transferring the light received from the staggered detectors to a non-staggered rectangular matrix.

56 citations


Journal ArticleDOI
D. E. Groom1
TL;DR: In this article, the authors review experimental constraints for magnetic monopoles and provide a 1.5 × 10−2 cm−2 sr−1 s−1 at the 90% confidence level, independently of velocity.

Journal ArticleDOI
TL;DR: In this paper, the origin of the crystal color is discussed and a correlation between the crystal colour and the scintillation output is shown, and methods are suggested to eliminate crystal defects and coloration.

Journal ArticleDOI
TL;DR: In this article, it was shown that the variability of flat-spectrum extragalactic radio sources at lambdaroughly-equal10 cm with rms amplitude of approx.2%--3% and time scale of days is consistent with intensity fluctuations caused by refractive scintillation in an extended interstellar medium in our Galaxy.
Abstract: Recent work has identified variability of flat-spectrum extragalactic radio sources at lambdaroughly-equal10 cm with rms amplitude of approx.2%--3% and time scale of days. We show that this ''flicker'' is consistent with intensity fluctuations caused by refractive scintillation in an extended interstellar medium in our Galaxy. Further observation of flicker may allow the structure of suitable sources to be partially resolved on angular scales smaller than those probed by VLBI.

Journal ArticleDOI
TL;DR: In this article, phase scintillation, phase contrast, wavefront shearing, and interferometry are compared on the basis of their transfer properties, and the criteria relative to the depth of field of imaging instruments in this context are considered.
Abstract: Imaging techniques offer attractive alternatives to small-angle Thomson scattering for scale lengths of density fluctuations causing diffraction in the Raman-Nath regime. This is the case for fluctuations with wavelengths above about 3 mm for Tokamak sized plasmas, when a CO2 laser probe beam is used. Four methods ('phase scintillation', phase contrast, wavefront shearing and interferometry) are compared, on the basis of their transfer properties. They offer new means of studying density fluctuations of magnitude up to the dimensions of the plasma, such as those associated with turbulence, magnetic islands, convective cells or driven waves. The long wavelength limitations are discussed in detail and are related to those encountered for far-field techniques. An experimental comparison of 'phase scintillation' and phase contrast is given, and the criteria relative to the depth of field of imaging instruments in this context are considered.

Patent
21 Nov 1986
TL;DR: In this article, a scintillation detector is provided which has an ionizing particle, such as a thallium-activated alkali halide crystal, which is sealed in a housing containing an atmosphere which is substantially non-reactive to the particle at temperatures ranging from about 100°C to about 250°C.
Abstract: A scintillation detector is provided which has a scintillation member comprised of a substance which converts energy received in the form of an ionizing particle to light. The scintillation member, such as a thallium-activated alkali halide crystal, is sealed in a housing containing an atmosphere which is substantially non-reactive to the scintillation member at temperatures ranging from about 100° C. to about 250° C. Examples of suitable atmospheres include the noble gases including helium, neon argon, krypton, xenon and radon; nitrogen; carbon dioxide, a vacuum, and other atmospheres, such as mixtures of these or air which has been substantially depleted of oxygen. Processes for the manufacture of the detector are taught where the scintillation member is encapsulated in a non-reactive atmosphere such as ones listed above. Alternatively, the reactive atmosphere can be washed from the housing or the sealed housing can be evacuated and refilled with a non-reactive atmosphere.

Patent
24 Oct 1986
TL;DR: A radiation detection/scintillation composite in which a multiplicity of particulate glass carriers embodying radiation target nuclei are embedded within a matrix of solid scintillation plastic composition is described in this paper.
Abstract: A radiation-detection/scintillation composite in which a multiplicity of particulate glass carriers embodying radiation target nuclei are embedded within a matrix of solid scintillation plastic composition. The glass target-containing carriers have an index of refraction which closely matches that of the scintillation plastic. In one embodiment of the invention, the carriers comprise hollow spherical micro-size shells containing He-3 gas detection nuclei under pressure. In another embodiment, Li, B or Pb or other heavy element detection nuclei are contained within the composition of the glass carriers.

Journal ArticleDOI
TL;DR: In this paper, the coherence of the fine structure in the ocean under the influence of advection is exploited for the measurement of ocean flows by modulating sound passing through this fine structure, so that the evolution and motion of the resulting pattern at a distant receiving plane contains information about the intervening flow field.
Abstract: We present a new approach to the measurement of ocean flows. The technique exploits the coherence of the fine structure in the ocean under the influence of advection. Sound passing through this fine structure is modulated in space and time, so that the evolution and motion of the resulting pattern at a distant receiving plane contains information about the intervening flow field. The details of the fine-scale structure itself may also be recovered, to an extent determined by the complexity of the transmitter and receiver array. Two special cases of oceanographic interest are considered. First, a fully developed turbulent flow, such as that encountered in tidal channels, for which the scale of fine structure contributing to the scintillation field lies within the inertial subrange, and second, the internal wave field more generally applicable to the open ocean. We describe an experimental test of the concept. Sound traveling across a 0.66-km path in Cordova Channel, British Columbia, Canada, is detected by two closely spaced receivers. The flow speed is derived using three separate estimators and the results compared with current measurements obtained from a moored current meter. Agreement between the two types of measurement is excellent.

Journal ArticleDOI
TL;DR: The phase screen-diffraction layer method is a powerful tool to study the signal scintillation of a wave propagating in a turbulent, stratified medium as discussed by the authors, which is equivalent to the split-step algorithm known in ocean acoustics but generalized to the case of oblique incidence.
Abstract: The phase screen-diffraction layer method is a powerful tool to study the signal scintillation of a wave propagating in a turbulent, stratified medium. Under the forward scattering approximation, the complex amplitude is shown to satisfy a parabolic equation which describes effects arising from phase changes due to irregularities and diffraction due to phase mixing. Below the turning point, these two effects can be computed sequentially. Stepping in altitude, phase changes are imbeded into each phase screen; diffraction between phase screens is accomplished using FFT techniques. This method is equivalent to the split-step algorithm known in ocean acoustics but generalized to the case of oblique incidence. Near the turning point, the diffraction effects are assumed negligible due to the small vertical thickness of the considered region. The deterministic part of the wave fields is taken to be proportional to the Airy functions. This allows a more accurate evaluation of the phase change near the turning point than the WKB solutions. The coupling between the ascending and descending wave is discussed. The simulation model is described and, as an example, results for a linearly stratified turbulent ionosphere are given, including statistics of the reflected wave such as power spectrum, scintillation index and spatial correlation.

Journal ArticleDOI
Yongtai Zhu1, Junguang Lu1, Y.Y. Shao1, H.S. Sun1, Jun Li1, S.Y. Wang1, B.Z. Dong1, Z. P. Zheng1, Y.D. Zhou 
TL;DR: In this article, the energy resolution, photoelectron yield, decay time distribution and radiation hardness of scintillating zinc tungstate crystals were measured using a laser scanner.
Abstract: We report measurements of the energy resolution, photoelectron yield, decay time distribution and radiation hardness of scintillating zinc tungstate crystals.

Journal ArticleDOI
TL;DR: In this article, a year of VLA observations of the radio source 1741-038 show that it exhibits pronounced variability at 149, 15, and 22 GHz, and somewhat reduced activity at 49 GHz.
Abstract: A year of VLA observations of the radio source 1741-038 show that it exhibits pronounced variability at 149, 15, and 22 GHz, and somewhat reduced activity at 49 GHz We interpret the unusually strong 149 GHz variability as due to refractive interstellar scintillation, and the high-frequency variability as being intrinsic to the source Most of the scintillation is caused by a single thin screen within a few hundred parsecs of the sun, probably located in the North Polar Spur 1741-038 offers a unique opportunity to test the refractive scintillation hypothesis through VLBI observations 35 references

Journal ArticleDOI
01 Jan 1986-Scanning
TL;DR: In this article, a novel detection means for the environmental SEM (ESEM) is described, where the gas can act as a generalized detector device for all signal-gas reactions provided some suitable parameter can be monitored.
Abstract: A novel detection means for the environmental SEM (ESEM) is described. Certain gases, apart from being the environmental conditioning medium, can also act as a scintillator detector. All signals, such as secondary and backscattered electrons which can cause a particular gas to luminesce, can be detected. It is further concluded that the gas can act as a generalized detector device for all signal-gas reactions provided some suitable parameter can be monitored. New possibilities in the detection of specimen cathodoluminesce created by the ESEM are demonstrated.

Journal ArticleDOI
TL;DR: In this paper, the light output and optical properties of new scintillation glasses were analyzed and the performance of scintillating glass fibers fabricated using a new light glass was discussed.
Abstract: We present data on the light output and optical properties of new scintillation glasses. Data on light (ϱ ⋍ 2.6 g/cm 3 ) and heavy (ϱ > 3.4 g/cm3) glasses are presented. In addition, the performance of scintillating glass fibers fabricated using a new light glass is discussed.

Journal ArticleDOI
TL;DR: In this article, the effect of saturation on high-order moments of intensity was investigated in the case of Furutsu's distribution, which is a two-parameter distribution and seems suitable for describing intensity fluctuations that are due to atmospheric turbulence in intermediate and strong scintillation.
Abstract: The deterioration that is due to saturation of a revealing apparatus on high-order moments of intensity is investigated in the case of Furutsu’s distribution. This is a two-parameter distribution and seems suitable for describing intensity fluctuations that are due to atmospheric turbulence in the case of intermediate and strong scintillation. The effect of saturation was shown to depend on only one parameter, αDS, defined as the ratio between the saturation intensity of the system and the mean intensity to be measured, a result already found in the case of a log-normal distribution. An expression of the deteriorated moments is given in terms of αDS and of the two parameters of the distribution. The theoretical results are used to give a qualitative interpretation of measured moments after laser propagation along a 1800-m path above the city of Florence.

Patent
21 Jul 1986
TL;DR: In this article, a new scintillation camera head is designed, which features a new crystal-light guide-collimator unit for a single crystal camera, which is made effective only for photons coming from the "proper" collimator channel, while the absorption of photons from surrounding channels is basically prevented.
Abstract: In order to match the trends and demands of modern nuclear medicine, a new scintillation camera head is designed, which features a new crystal-light guide-collimator unit for a single crystal scintillation camera. The effective crystal thickness is increased by crystal teeth designed as quadrilateral truncated crystal pyramids. The basis of each of these teeth is settled on top of a crystal plate of conventional thickness. The vertical axis of each of the teeth is aligned with the vertical axis of a particular collimator channel. Thus, the total number of crystal pyramids equals the number of (preferably squared) collimator holes. The space between the crystal pyramids is "filled" with an appropriate light guide material such as window glass. The crystal pyramid side is shaped, i.e. angled, according to the direction of the highest (gamma) photon energy the camera is designed for, after penetrating through the upper (close to crystal) portion of the collimator septum for a length equaling 2μ -1 ; where μ is the linear absorption coefficient for the (gamma) photon energy in the particular collimator material, such as tantalum (Ta). Thus, the increased crystal thickness is made effective only for photons coming from the "proper" collimator channel, while the absorption of photons from surrounding channels is basically prevented. Theoretical predictions indicate that about 90% of them will take their primary (and secondary) interactions with the light guide and not with the crystal material.

Journal Article
TL;DR: In this paper, the improvement in spatial resolution and loss of field uniformity for 99mTc, 201Tl, and 131I were measured as a function of window asymmetry.
Abstract: Pulse height analyzer windows that are set on the high side of the photopeak are known to improve spatial resolution and contrast when used for scintillation camera imaging. Asymmetric windows can be used with some scintillation cameras that have energy correction circuitry. In this study the improvement in spatial resolution and loss of field uniformity for 99mTc, 201Tl, and 131I were measured as a function of window asymmetry (up to 30%, defined relative to the loss of counts as compared to a symmetric window under intrinsic conditions). Flood field uniformity was inversely related to the degree of window asymmetry. With 10 cm of scatter the 99mTc integral uniformity deteriorated from 7.9% with a symmetric window to 11.5% for a 30% asymmetric window. The corresponding values for 201Tl were 9.9 and 10.9%. Even without additional scatter, the values for 131I were 23.0 and 26.5%. Spatial resolution, as measured by the full width at half maximum in 10 cm of scatter improved by only 5% for 99mTc and 7% for 201Tl. However, the full width at tenth maximum increased by as much as 20% for 99mTc and 201Tl. A large percentage of this improvement was attained with small degrees of asymmetry. This study demonstrates that 10% or less asymmetry can provide most of the benefit in spatial resolution and contrast that is to be gained without significant losses in field uniformity and count rate.


Journal ArticleDOI
TL;DR: In this paper, the influence of surface roughness and crystal shape on the scintillation output of bismuth germanate scintillators has been experimentally studied.
Abstract: To improve the scintillation output of bismuth germanate scintillators, the influence of surface roughness and crystal shape has been experimentally studied. We found that an optimum scintillation output is obtained for an appropriate aspect ratio of the scintillator, i.e., its length "h" to width "a" (h/a), depending on their surface roughness. A high scintillation light output can be obtained for polished scintillator surfaces when h/a>6, but for rough surfaces when h/a<6. In addition, when scintillator surfaces are provided with a reflective coating, the light output is markedly improved. The dependence of the light output on the surface roughness and crystal shape is discussed in terms of the transmission loss inside the scintillator and the reflection loss at the surface.


Journal ArticleDOI
Yucan Zhu1, Junguang Lu1, Jun Li1, Y.Y. Shao1, H.S. Sun1, B.Z. Dong1, G.P. Zhou1, Z. P. Zheng1, F.Z. Cui1, C.J. Yu1 
TL;DR: In this paper, energy resolutions and photoelectron yields were reported for scintillating BaF 2 crystals, which is a type of BaF2 crystals with high energy resolution.
Abstract: Energy resolutions and photoelectron yields are reported for scintillating BaF 2 crystals.

Patent
Takashi Ichihara1
20 Aug 1986
TL;DR: In this paper, a data memory is provided for storing an energy spectrum of gamma rays in a real-time manner, and the peak valve position of the energy spectrum is calculated based on the data stored in the data memory.
Abstract: A scintillation camera apparatus includes a scintillation camera which generates X and Y position signals representing a detection position of gamma rays radiated from an object to be examined and a Z signal representing the energy level of the gamma rays, and an image memory for storing data indicating the detection frequency of the Z signal having an energy exceeding a predetermined level at a location accessed by the X and Y position signals. A first compensation table for compensating for the nonlinearity of the X and Y position signals and a second compensation table for the Z signal are provided for compensating for the X, Y, and Z signals to be supplied to the image memory. For compensating a change with time in gains of the photomultipliers, a data memory is provided for storing an energy spectrum of gamma rays in a real time manner. The peak valve position of the energy spectrum is calculated based on the data stored in the data memory. If the peak valve position changes, the content of the second compensation table is rewritten in accordance with the shifting of the peak valve position of the energy spectrum.