Showing papers on "Scintillation published in 1968"

Time Dependence of Scintillations and the Effect on Pulse-Shape Discrimination

Abstract: The time dependence of the light following excitation by gamma rays and neutrons was measured for stilbene and for the liquids NE-213, NE-213M, and NE-218.? In addition, the number of photoelectrons produced at the cathode of an RCA-8575 photomultiplier per keV energy loss in the scintillator has been determined for each of these scintillators. A straightforward technique for pulse-shape discrimination is described; it consists in measuring the time difference between the start and the instant at which the integrated photomultiplier pulse reaches a specified fraction of its final amplitude. From the measured scintillation decay, the probability distribution of these rise times has been calculated for different fractions and for different photon and neutron energies on the assumption of Poisson statistics. These calculated distributions are in agreement with the experimental results obtained with the above-mentioned technique. The pulse-shape discriminating system is very stable and will accept 80% of the neutrons at 350 keV and only approximately 1% of the gamma rays producing scintillations with equal integrated light.

Observations of the Interplanetary Plasma

Abstract: Observations bearing on the nature and properties of the interplanetary plasma are reviewed, and consideration is given to possible fruitful directions for further work. The observations are classified according as they involve traditional (comet tail, optical, geomagnetic, cosmic ray), radio (solar noise, radar, radio-source scattering and scintillation, space-probe transmission) or direct (space-probe) measurements. A fairly complete set of references up to September 1967 is given for the cases of comet tail, radar, radio-source scattering and scintillation, and space-probe measurements. An important development concerns observations of the composition of the solar wind. High-resolution measurements of the positive ion energy per charge spectra have been made using the Vela-3 satellites (Bame et al., 1968). Ionic components other than H+ and He++ have been detected, notably the various ions of oxygen, O+5, O+6, O+7, (Hundhausen et al., 1968). A promising technique for unambiguously distinguishing H+ and He++ ions, based on velocity as well as energy per unit charge, has been flown successfully on the satellite IMP-F by Ogilvie and Williamson (1968).

The luminescence decay of organic scintillators

Abstract: Results obtained in the laboratory on the luminescence decay of organic scintillators are reviewed. Theoretical equations, resulting from an analysis of the scintillation process, are shown to be in good agreement with experimental decay curves obtained with crystals and liquid scintillators. The pulse shape discrimination of particles is discussed, and a technique allowing to separate α-particles, protons and β-rays if presented.

RADAR Target Amplitude, Angle, and Doppler Scintillation from Analysis of the Echo Signal Propagating in Space

Abstract: RADAR target scintillation is observed in every type of RADAR system and has generally been analyzed on the basis of the performance of specific types of RADAR systems. However, the target scintillation phenomenon, including Doppler scintillation, may be expressed as distortions of the RADAR echo signal propagating in space, independent of RADAR system parameters. In this form it is convenient for visualizing the overall effects on RADAR systems and how these effects are altered by the RADAR system parameters. Past literature has demonstrated the target angle scintillation as a distortion of the RADAR echo signal phase front. Extension of this approach by a Poynting-vector analysis of the RADAR echo signal from a complex source shows a corresponding deviation of the direction of power flow consistent with the phase-front distortion theory and target scintillation measurements as well as describing all other target scintillation characteristics. The analysis demonstrates that deviations in the direction of the echo signal power flow from a complex target can be so large that the apparent source falls many target spans away from the actual target location. This is demonstrated by both tracking RADAR and single-beam search-t ype RADAR experiments. Although the theoretical angle deviations approach infinite error in target location, RADAR parameters, such as the finite size antenna aperture which perform a space integration of the echo signal, impose practical limitations. Typically, when a complex target such as an aircraft subtends an angle approaching a few tenths of a beamwidth, the antenna aperture integration will significantly limit the rms angle scintillation. Furthermore, the ways in which intentional means, such as diversity techniques, may be employed to reduce the effects of target scintillation on a RADAR are observed in Poynting-vector analysis. The analysis of the echo signal propagating in space provides a readily visualized basis for derivation of the Doppler scintillation caused by the airframe (rigid body portion) of a complex target which spreads the Doppler over a finite bandwidth when it has random yaw, pitch, and roll motion typical of aircraft in flight. The derivation relates the Doppler scintillation to the angle scintillation and the random motions typical of aircraft targets. A typical aircraft target with Gaussian-distributed angle scintillation and Gaussian-distributed rates of random motion will have a spike-shaped Doppler spectrum described by the modified Hankel function K/sub 0/ where the parameters are determined from the values of the rms angle scintillation and the rms angular rates of random motion. These values can be closely approximated without extensive measurements on the target. Experimental results verify the theory. The expressions used to derive the Doppler spectrum may be modified to accommodate non-Gaussian distributed angle scintillation and rates of angle motion.

Energy transfer in organic systems VI. Fluorescence response functions and scintillation pulse shapes

Abstract: Expressions are derived for the fluorescence response functions of organic solution systems in which non-radiative energy transfer occurs and obeys either Stern-Volmer or Forster kinetics. Scintillation pulse shapes are evaluated for typical crystals, binary and ternary liquid solutions, and binary plastic solutions. The scintillation decay time is inadequate to describe the time characteristics of a solution system, and alternative parameters are introduced. Criteria for a fast solution scintillator are established, and binary liquid and plastic scintillators with improved time characteristics are proposed.

Recent Advances in X-Ray Detection Technology

Abstract: A review is presented of recent developments in x-ray photon detectors and in the associated detector electronics. The first portion of the paper is devoted to a survey of the presently available physical inforrnation on the "intrinsic" resolution of silicon and germanium radiation detectors, proportional counters and NaI(Tl) scintillation crystals. Semiconductor detectors suitable for x-ray applications and low noise electronics are then analyzed in some detail. Discussions follow on scintillation detectors, proportional counters, and "external" photoelectric detectors. Recent spectral achievements and interesting applications are illustrated.

The Scintillation Efficiency of Benzene

Abstract: The scintillation efficiency of a benzene + p-terphenyl solution, extrapolated to unit energy transfer efficiency, has been determined to be 0.042 (or equivalently 0.0116 ± .004 photon/ev). This corresponds to a G value for production of 1B2u benzene of 1.55 ± .05. It is suggested that the difference between this value and that for other alkyl benzene liquids (1.9–2.5) and for anthracene crystal (2.20) is related to the efficiency with which upper states of these substances make internal conversion to the emitting or transferring state.

The scintillation method

Abstract: Publisher Summary A scintillation counter is an instrument for detecting and measuring ionizing radiation. The proceedings of the Scintillation Counter Symposia provide an especially valuable compilation of status reports and discussions of current problems and applications. The scintillation counter has always been at a basic disadvantage in comparison with the other methods of primary charged particle spectrometry. Despite its shortcomings, the combination of a scintillating phosphor and photo-multiplier is extremely useful in particular applications. The chapter describes scintillation counter and discusses methods for charged particle spectrometry. The choice of a phosphor for heavy charged particle spectrometry requires a weighing of several characteristics. The scintillation counter is the standard y-spectrometer. Gamma rays interact with a phosphor or other matter by three principal processes: (1) Compton scattering, (2) photoelectric effect, and (3) pair production. The response of the spectrometer depends upon the source distance from the phosphor. The relative contribution of backscattered radiation is a strong function of the crystal and source to wall spacing.

Indicating or detecting apparatus for nuclear radiation such as gamma rays

Abstract: A nuclear radiation detecting or indicating apparatus comprises a mosaic of optically separate scintillator elements which are arranged in a series of first and second elements rows respectively parallel to first and second intersecting axes, each element being in a first and in a second row; a plurality of scintillation detectors arranged to view the scintillation elements, the detectors being more widely spaced from each other than are the elements, and being arranged in first and second detector rows, parallel to the first and second element rows, each detector being in a first and a second detector row, each detecting being adapted to produce a detector pulse in response to a scintillation detected thereby, the amplitude of the pulse being dependent on the position of the scintillation relative to the detector; a respective first output channel for each first element row, and a respective second output channel for each second element row; means for summing simultaneous detector pulses from the detectors in each detector row; an analyzer for each row of detectors for analyzing the simultaneous summed detector pulses thereof into one of a plurality of amplitude ranges, each analyzer having a respective analyzer output for each amplitude range; gating means arranged to receive the outputs of the analysers and to produce simultaneous pulses in a said first and a said second output channel in response to a scintillation of brightness within a predetermined range, thereby in operation defining the element in which said scintillation occurs; the gating means comprising a plurality of logic gates, at least one pair of which is connected in common to at least two analyzer outputs, the logic gates of said at least one pair being adapted to respond differently from each other to a pulse or pulses from the analyzer outputs to which they are connected in common, so that they do not permit simultaneous pulses to occur in their respective output channels.

Using Xenon-133 and a scintillation camera to evaluate pulmonary function.

Abstract: tion has been given to evaluating pulmonary disease using radioisotopic techniques. The majority of the radioactive preparations used for these studies can be divided into two general categories : colloidal aggregates of albumin and radioactive gases. Macro aggregates labeled with 1311or 99@'Tchave been used extensivelyfor determining regional pulmonary per fusion and, as such, are useful for evaluating patients with suspected pulmonary emboli (1—5) . The dis tribution of these macroaggregates in the lung is usually determined by conventional rectilinear scan ning although the scintillation camera has also been used effectively (4,5). To obtain information on ventilation and diffusion one of the radioactive gases—oxygen, carbon dioxide, krypton or xenon—must be used. The half-lives of gamma-emitting oxygen and carbon radioisotopes are extremely short so that the cyclotron used for their production must be very close to the pul monary-function laboratory (6—9). Thus because of their universal availability, the noble gases are being used more extensively, and, of these gases, †̃33Xe has the best physical characteristics (5, 10—13). In this paper we report our preliminary experience using an Anger scintillation camera to record pul monary uptake and clearance of †̃33Xe in patients referred to our service for pulmonary-function evalu ation. The radioactive xenon was administered either by inhalation or intravenous injection.

Optical heterodyne communications experiments at 10.6 µm

Abstract: A 10.6-μ optical heterodyne communication system that is in operation over a 30-km (18-mile) path is described. Television signals have been transmitted over the beam by the use of optical FM achieved with internal electrooptic phase modulation of the transmitter oscillator. A frequency deviation of 3 MHz is thus obtained for a driving voltage of 1 kV compared with the fundamental frequency noise of the system of about 1 kHz. For clear-day operation, average carrier-to-noise ratios at the receiver approach 60 dB, and demodulated video signal-to-noise ratios average 50 dB. Optical propagation experiments reveal amplitude scintillation noise in excess of 20 dB, represented by fluctuations of +10 dB and -10 dB from the average carrier level. Other observations show that the 10.6-μ beam has a remarkable ability to penetrate fog. Data related to scintillation, visibility, temperature, humidity, and optical absorption are presented.

The Solar Wind and Jovian Decametric Radio Emission

Abstract: Spaced-receiver observations of the 19·7 MHz radio emission from Jupiter during 1963 and 1964 demonstrate that many of the so-called bursts with quasiperiods of 1-10 sec are caused by the sweeping of an interplanetary diffraction pattern across the receiver by the motion of scattering irregularities in the solar wind. Measurements made on these scintillations include arrival time differences at spaced receivers, scintillation rate, angular position scintillation, and the width of the scattered angular power spectrum.

Phenomena Resulting from the Heating of Small Wires in He II

Abstract: In a previous experiment the scintillation of He II was found to be enhanced at certain critical values of heat flux introduced into the fluid by a small heated wire. Results are presented here which demonstrate that this phenomenon is related to the formation of some form of visible turbulence or, alternatively, of a vapor bubble around the wire, depending on the depth of the wire in the He II bath. Results are presented also on the dependence of the critical heat current on wire depth and on temperature.

A video system for recording dynamic radioisotope studies with the Anger scintillation camera.

Abstract: Summary A method has been described whereby random light flashes occurring on the oscilloscope cathode-ray tube of the Anger scintillation camera are recorded on video magnetic tape for subsequent replay and nondestructive manipulation of the original data. The system is used primarily for recording rapid dynamic radioisotope studies such as vascular time-flow measurements in which it is essential to minimize the deadtime between individual frames of information.

Detection of gravitational waves by stellar scintillation in space.

Abstract: It is shown that gravitational waves generated by close binaries in our galaxy will lead to stellar scintillation This scintillation seems to be large enough to be detectable with sensitive photocounters in space With two observation stations separated by a sufficiently large distance in space, it should be also possible to measure the space-time correlation of the predicted scintillation effect and, hence, the propagation velocity of gravitational waves It is believed that quasars, depending on their state of gravitational collapse, can emit a large amount of gravitational radiation Under certain assumptions, one can show that the gravitational waves emitted by quasars may result in large brightness scintillation of far distant quasars The observations of quasars seem to support the theoretically-predicted brightness fluctuations and characteristic fluctuation times Finally, the question of gravitational background radiation in the universe is considered in connection with the recently discovered 4°K electromagnetic black-body radiation

A – general procedures

Abstract: Publisher Summary This chapter discusses the general processes and procedures used in determining disintegration schemes through a study of the β- and γ-rays emitted. In the study described in the chapter, the processes involved in working out disintegration schemes have been concerned primarily with the problems arising when magnetic spectrographs with counter recording are used. TA converter of reasonable thickness has been used in the study to measure an appreciable number of photoelectrons. The energies of γ-rays can be determined by various means: scintillation counting, measurement of Compton electrons, photoelectrons, and, in certain cases, internal conversion electrons. This chapter focuses on the difficulties encountered in determining relative intensities of electromagnetic radiation. The scintillation method is now standardized, gives reasonably good results and does not require large sources.