Showing papers on "Scintillation published in 1975"

Bismuth Germanate: A High-Z Gamma-Ray and Charged Particle Detector

Abstract: The room-temperature scintillation characteristics of single crystals of Bi4Ge3O2 under gamma-ray and alpha-particle excitation have been determined. The wavelength of maximum intensity in the scintillation spectrum is 480 nm. A decay constant of 0.30 microseconds was measured. Scintillation efficiency (pulse height) varied linearly with gamma-ray energy, E, and the resolution varied as E-1/2. 8% pulse height relative to NaI(Tl) with 15% resolution was measured for a 2.2 cm × 1.7 cm crystal under excitation by Cs137 0.662 Mev gamma-rays.

Ionospheric scintillation by a random phase screen: Spectral approach

Abstract: The theory developed by Briggs and Parkin, given in terms of an anisotropic gaussian correlation function, is extended to a spectral description specified as a continuous function of spatial wavenumber with an intrinsic outer scale as would be expected from a turbulent medium. Two spectral forms were selected for comparison: (1) a power-law variation in wavenumber with a constant three-dimensional index equal to 4, and (2) Gaussian spectral variation. The results are applied to the F-region ionosphere with an outer-scale wavenumber of 2 per km (approximately equal to the Fresnel wavenumber) for the power-law variation, and 0.2 per km for the Gaussian spectral variation. The power-law form with a small outer-scale wavenumber is consistent with recent F-region in-situ measurements, whereas the gaussian form is mathematically convenient and, hence, mostly used in the previous developments before the recent in-situ measurements. Some comparison with microwave scintillation in equatorial areas is made.

Computed scintillation spectra for strong turbulence

Abstract: Spectra of intensity fluctuations resulting from the propagation of a plane wave through a thin but arbitrarily strong layer of refractive index variations are computed using the theory in a companion paper [Rumsey, 1975]. A power law spectrum with index α = 3 was assumed for the turbulence or refractive index spectrum. The intensity spectra were found to duplicate the Born approximation for weak scattering and the high frequency approximation for strong scattering. The scintillation index, or the rms intensity fluctuation, saturates at unity for a plane wave. The scintillation index has been computed for sources of various sizes. The results of the computation are in remarkable agreement with the results of radio star scintillation measurements.

Deconvolution analysis of the scintillation camera renogram

Abstract: A scintillation camera with digital data store has been used to assess renal function. Analysis of the renogram by deconvolution, using an on-line digital computer, shows promise as a means of expressing renal function in terms of tubular transit times for 123I-Hippuran.

A theoretical study of the ionospheric scintillation behavior caused by multiple scattering

Abstract: We investigate in this paper the behavior of transionospheric radio signals in the presence of irregularities with a power-law spectrum. The roles played by multiple scattering and irregularity selection through the Fresnel filtering effect are delineated. The effect of competition between these two processes on the scintillation index and on the transverse correlation is discussed.

Three-dimensional time-of-flight gamma camera system

Abstract: A pair of fast acting elongated plastic scintillation bars are arranged in a skewed spatial relationship to thereby define a unique tetrahedron in space which constitutes the positron sensitive volume of the camera. Each scintillation bar is serviced by a pair of fast acting photomultiplier tubes disposed immediately adjacent the ends of the bars, so that four substantially coincident relative times of activation of the photomultipliers occur when the two opposed 511 keV gamma rays, arising from a positron annihilation within the tetrahedron, happen to hit and be stopped by the two scintillation bars, causing scintillations therein. From measurements and analysis of the various time differences of photomultiplier activations, the location of the respective scintillations along the two bars is defined, thereby defining the gamma ray flight line joining the two scintillations. Measurement and analysis of various time differences of photomultiplier activations then serves to define the point along the gamma ray flight line at which the positron annihilation occurred. In an enhanced sensitivity version, a plurality (p) of pairs of skewed detectors are arranged so that a plurality of detectors are parallel and closely spaced, and the plurality of detectors with which they are paired are also parallel and closely spaced, effectively forming (p 2 ) cameras covering (p 2 ) tetrahedrons, which tetrahedrons may be so closely overlapping as to cover almost identical volumes.

Strong scintillations in astrophysics. III - The fluctuations in intensity

Abstract: Fluctuations in intensity due to wave propagation in a wide range of turbulent media, are discussed on the basis of a previously developed theory of strong scintillations. An asymptotic analytic solution to the fourth-moment equation is presented, and its range of validity is discussed. Various parameters characterizing the intensity fluctuations, such as scintillation index and correlation scale, are expressed in terms of turbulence parameters for both Gaussian and power-law irregularity spectra as well as for thick and thin turbulent media.

Detector for deep well logging

Abstract: A substantial improvement in the useful life and efficiency of a deep-well scintillation detector is achieved by a unique construction wherein the steel cylinder enclosing the sodium iodide scintillation crystal is provided with a tapered recess to receive a glass window which has a high transmittance at the critical wavelength and, for glass, a high coefficient of thermal expansion. A special high-temperature epoxy adhesive composition is employed to form a relatively thick sealing annulus, which keeps the glass window in the tapered recess and compensates for the differences in coefficients of expansion between the container and glass so as to maintain a hermetic seal as the unit is subjected to a wide range of temperatures.

Exciton dynamics in $alpha$-particle tracks in organic crystals: magnetic field study of the scintillation in tetracene crystals

Abstract: The mechanisms of scintillation of organic crystals bombarded by $alpha$ particles are discussed in terms of the current knowledge of exciton dynamics, which has been derived from a study of the photofluorescence of crystals such as anthracene and tetracene. The scintillation of tetracene excited by 4.4-MeV $alpha$ particles incident in a direction perpendicular to the ab plane has been studied in the presence of external magnetic fields (0 to 4000 G) and compared with the scintillation of crystalline anthracene. At 298$sup 0$K, the magnetic field effect on the total scintillation yield is (+2.5 +- 0.5) percent in tetracene and displays a typical fissionlike (fission of one singlet exciton into two triplets) dependence. At low temperatures when fission is suppressed, a fusionlike dependence (reverse of fission) appears with a (-4 to -5) percent effect at 4000 G at 148$sup 0$K. In anthracene, the fusionlike dependence is observed with a (-4 to -5) percent effect at 4000 G at 148$sup 0$K. In anthracene, the fusionlike dependence is observed at all temperatures in the range studied (148 to 298$sup 0$K). Using appropriate kinetic equations, expressions are derived for the prompt (L/sub P) and delayed (L/sub D/) components of the total scintillation yield Lmore » = L/sub P/ + L/sub D/. These expressions describe the temperature and magnetic field dependence of L, which arises because of the temperature and magnetic field dependence of the exciton fission and fusion rate constants in tetracene. In tetracene, L/sub D/ appears to be strongly temperature dependent, while L/sub P/ is not. This is explained in terms of the high density of transient singlet exciton quenchers in the $alpha$-particle track. The density of these transient quenchers is estimated to be in the range of 3 x 10$sup 17$--5 x 10$sup 18$ cm$sup -3$, and they are identified, in accord with a previous suggestion by Schott, as triplet excitons which are created by random recombination of electrons and holes in the $alpha$- particle track. (auth)« less

Frequency and spatial correlation functions in a fading communication channel through the ionosphere

Abstract: Equations for the two-frequency two-position mutual coherence functions are derived under the usual parabolic and Markov approximations. These equations are then solved numerically. It is shown that the mutual coherence functions occur naturally in the study of pulse distortion through a random communication channel and in the investigation of signal correlations. Contour plots of correlation functions show the possibility of having equal values at two frequency separations for a given spatial separation. This behavior is explainable in terms of overlapping Fresnel zones. Recently it has been observed that radio signals from communication satellites at a frequency as high as several GHz may experience the scintillation phenomenon when received on the ground [Pope and Fritz, 1971; Skinner et al., 1971; Sessions, 1972; _ Craft and Westerlund, 1972; Taur, 1973]. This came as a surprise since scintillation was not anticipated to occur at such a high frequency. After some experimentation it is now believed that the scintillation is caused by the electron density irregularities in the ionosphere. As is well known, for a given electron density fluctuation, th e rms fluctuation in the refractive index of the ionospheric medium is inversely proportional to the square of the signal frequency. Therefore, under conditions when GHz scintillation occurs, signals with a lower frequency will experience even more severe fading. This implies that the effects of multiple scattering on signal statistics are very important under such conditions. To obtain their statistics correctly, it is desirable to develop a scintillation theory that takes into account the multiple scattering effects. Thanks to the recent advances in the theory of wave propagation in random media, it is now possible to develop such a theory [Liu et al., 1974a; Yeh et al., 1975]. In this paper, we shall apply a similar technique to investigate the frequency and spatial correlations of signals passing through the irregularity slab. In satellite communications the ability to transmit wideband data is limited primarily by the inter-symbol interference which is closely

Latitude-dependent nonlinear high-speed solar wind streams

Abstract: The theory of the nonlinear interaction between high- and low-speed solar wind streams has been limited either to small amplitudes or to the equatorial plane. It is shown how both of these restrictions can be removed for flow more than a few solar radii away from the sun by employing a quasi-radial approximation to develop a perturbation expansion of the equations of motion. The lowest-order equations describe the radial flow in large-amplitude latitude-dependent streams. Higher-order equations describe the nonradial flow associated with the streams and can be used to test the validity of the quasi-radial approximation for any given set of boundary conditions. As an example, the theory is used to model a set of interplanetary scintillation observations indicating the disappearance, above 40°N latitude, of the scintillation associated with a specific set of streams. The analysis illustrates the relative nonlinear steepening and displacement in phase of the density and velocity peaks as a function of latitude and time. Results are given in terms of the range of possible latitudinal variations at the sun and 1 AU allowed by the observations. It is concluded that a disappearance of the streams above 40°N is not necessary to explain a weakening of stream interactions and thus the disappearance of scintillations at high solar latitudes.

Detector construction for a scintillation camera

Abstract: An improved transducer construction for a scintillation camera in which a light conducting element is equipped with a layer of moisture impervious material. A scintillation crystal is thereafter positioned in optical communication with the moisture impervious layer and the remaining surfaces of the scintillation crystal are encompassed by a moisture shield. Affixing the moisture impervious layer to the light conducting element prior to attachment of the scintillation crystal reduces the requirement for mechanical strength in the moisture impervious layer and thereby allows a layer of reduced thickness to be utilized. Preferably, photodetectors are also positioned in optical communication with the light conducting element prior to positioning the scintillation crystal in contact with the impervious layer.

Introduction to Nuclear Radiation Detectors

Abstract: 1 Introduction.- 2 Nuclear Radiations and Their Interaction with Matter.- 2.1. Radioactivity.- 2.2. Radioactivity Calculations.- 2.3. Calculation of Activities Produced by Nuclear Reactions.- 2.4. Interaction of Heavy Charged Particles with Matter.- 2.5. Electron Interaction.- 2.6. Backscattering of Electrons.- 2.7. Interaction of Gamma and X Rays with Matter.- 2.8. Interaction of Neutrons.- 2.9. Cosmic Rays.- References.- 3 Gas Counters.- 3.1. General Properties of Gas Counters.- 3.2. Ionization Counters.- 3.3. Air-Wall Ionization Chamber.- 3.4. Pocket Dosimeter.- 3.5. Pulse-Type Ionization Counter.- 3.6. Proportional Counter.- 3.7. Position-Sensitive Proportional Counters.- 3.8. Neutron Counters.- 3.9. Geiger-Muller Counters.- 3.10. Counter Gas.- 3.11. Detection of Alpha and Beta Radiations by Geiger Counters.- 3.12. Detection of X Rays and Gamma Rays by Gas Counters.- 3.13. Application of Internal Counting Methods.- References.- 4 Scintillation Counters.- 4.1. General Characteristics of Scintillation Counting Systems.- 4.2. Scintillant Materials and Mechanism of Scintillation.- 4.3. Photomultipliers.- 4.4. The Shape of the Pulse.- 4.5. Scintillation Counter Assembly.- 4.6. Relationship between Pulse Height and Energy.- 4.7. Detection of Gamma Rays by Scintillation Counters.- 4.8. Integral Counting.- 4.9. Differential Counting and Determination of Energy of Gamma Rays.- 4.10. Efficiency of Scintillation Counters for Gamma Detection.- 4.11. Energy Resolution in Scintillant Detectors.- 4.12. Detection of Charged Particles with Scintillation Counters.- 4.13. Detection of Neutrons.- 4.14. Particle Identification by Pulse Shape Discrimination.- 4.15. Other Methods for Particle Identification and Discrimination.- References.- 5 Semiconductor Detectors.- 5.1. Operation of a Semiconductor Counter.- 5.2. Impurity Semiconductors.- 5.3. Detector Types.- 5.4. Pulse Shape and Rise Time.- 5.5. Factors Affecting Energy Resolution.- 5.6. Radiation Damage.- 5.7. Detection of Charged Particles.- 5.8. X-Ray and Gamma-Ray Detection.- 5.9. Neutron Detectors.- 5.10. Other Applications.- 5.11. Special Techniques.- 5.12. Concluding Remarks.- References.- Bibliography,.- 6 Corrections in Radiation Counting.- 6.1. Introduction.- 6.2. Absolute Activity Determination.- 6.3. Random Nature of Decay Process.- 6.4. Frequency Distributions.- 6.5. Statistical Errors in Nuclear Particle Counting.- References.- Appendix: Selected Constants and Conversion Factors.

Method and apparatus for multiplexing of physiological sensor signals with gamma ray camera data signals

Abstract: A method and device for multiplexing time varying amplitude physiological data signals with the signals provided by the photomultiplier tubes of a gamma ray scintillation camera The time varying amplitude signals from physiological sensors are converted to a series of uniformly shaped pulses having a pulse frequency which is directly proportional to the amplitude of the physiological signal The pulses are shaped to correspond to the shape and size of significant pulses provided at the output circuitry of the photomultiplier tubes of the camera The shaped pulses are combined with the pulses provided by a photomultiplier tube, and are processed by the internal circuitry of the gamma ray camera in the same manner as gamma ray scintillation data A computer can be utilized to process the data thus provided, and to display the gamma ray scintillation data in time synchrony with the physiological signal source data

Mass counting of radioactivity samples

Abstract: A method and apparatus for concurrently counting a plurality of radioactive samples. The position sensitive circuitry of a scintillation camera is employed to sort electrical pulses resulting from scintillations according to the geometrical locations of scintillations causing those pulses. A scintillation means, in the form of a scintillating crystal material or a liquid scintillator, is positioned proximate to an array of radioactive samples. Improvement in the accuracy of pulse classification may be obtained by employing collimating means. If a plurality of scintillation crystals are employed to measure the iodine-125 content of samples, a method and means are provided for correcting for variations in crystal light transmission properties, sample volume, and sample container radiation absorption.

Saturation of laser irradiance fluctuations beyond a turbulent layer

Abstract: An asymptotic theory of saturated fluctuations of laser irradiance diffracted by a thin layer of turbulent medium is built. The treatment is carried out in the phase screen approximation for the case of a power law spectrum of inhomogeneities in the layer. Asymptotic forms of the covariance of irradiance fluctuations are obtained and the character of the scintillation index approach to the asymptotic value is investigated. Calculations are made for collimated and focused laser beams.

The Energy Resolution and Window Area Capabilities of the Gas Proportional Scintillation Counter

Abstract: The behaviour of xenon and argon-xenon gas proportional scintillation counters is con sidered. For X-rays, ranges of window area are defined showing competition with semiconductor detectors. Data for primary scintillation of X-rays and alpha particles are included. Relative efficiencies of tetraphenylbutadiene, p-terphenyl, diphenyl-stilbene, sodium salicylate and p-quaterphenyl were measured.

Recent Advances in Gas Scintillation Proportional Counters

Abstract: Various geometrical configurations for gas scintillation proportional counters have been investigated in order to determine which is best for use in a large volume, high efficiency counter for measuring low energy gamma and x-rays. A xenon filled counter having a rod anode inside a cylindrical cathode appears to provide the best configuration for providing a uniform field and the best resolution over the total volume of the counter. The details of construction and operating characteristics of various shaped counters are described.

Precision automatic tracking system

Abstract: An optical tracking system for aircraft and the like which measures positional variations of a portion of a laser transmitter pulse train or beam returned from a tracked object to derive error signals for energizing the tracking servo mechanism. In particular, the system detects such beam position change by measuring variations in energy received by a quadrant-segmented photo sensor relative to the sensor axis of symmetry. Compensation for scintillation (variation with time of the spatial intensity distribution) of the return beam due to change in the index of refraction of the atmosphere is achieved, in accordance with the invention, by focusing the return beam to a small diameter and passing it through a diffusing medium such as opal glass or a fiber optic bundle. The energy in the output beam from this medium is homogeneous and substantially invariant with time so that tracking error due to scintillation is eliminated.

The role of the magnetosphere in satellite and radio-star scintillation

Abstract: A theory is developed to account for the scintillation phenomenon observed in equatorial regions when using communications satellites in the SHF band. The same theory is also used qualitatively to explain strong scintillations in the VHF band. Instead of confining irregularities to a narrow interval of height in the F-region and assuming that they are strong, the alternative hypothesis is used that the irregularities are weak but extend from the F-region upwards into the magnetosphere. It is suggested that the irregularities are field-aligned and extend at least up to an L-shell of 1.3 and possibly up to 2 or more.

Collimator trans-axial tomographic scintillation camera

Abstract: A collimator is provided for a scintillation camera system in which a detector precesses in an orbit about a patient. The collimator is designed to have high resolution and lower sensitivity with respect to radiation traveling in paths laying wholly within planes perpendicular to the cranial-caudal axis of the patient. The collimator has high sensitivity and lower resolution to radiation traveling in otherplanes. Variances in resolution and sensitivity are achieved by altering the length, spacing or thickness of the septa of the collimator.