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Nuclear Science, IEEE Transactions on

Issue 3 • Date June 1968

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Displaying Results 1 - 25 of 84
  • [Front cover]

    Page(s): c1
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    Freely Available from IEEE
  • IEEE Nuclear Science Group

    Page(s): c2
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    Freely Available from IEEE
  • The Nucleus

    Page(s): 1
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    Freely Available from IEEE
  • Table of contents

    Page(s): 2 - 6
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  • Recent Advances in X-Ray Detection Technology

    Page(s): 10 - 46
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    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. View full abstract»

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  • The Use of Semiconductors Doped with Isoelectronic Traps in Scintillation Counting

    Page(s): 47 - 57
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    The use of semiconductors as scintillation phosphors is discussed. Donoracceptor pair recombination is efficient but it is often slow. The presence of free carriers from high concentrations of electrically active defects causes concentration quenching probably by means of an Auger effect. One is led therefore to consider the use of semiconductors doped with "isoelectronic traps". Experiments are reported for CdS doped with tellurium and ZnTe doped with oxygen. Promising preliminary results have been obtained. For CdS:Te at room temperature using 5 MeV ¿ particles pulse heights have been recorded 7 times greater than those provided by the scintillator Pilot B, and with a rise time of 300 ns. At 100°K the results are even better. An excellent linearity of response at 100°K was found for particles with energies between 7 keV and 5.2 MeV. In addition to detecting ¿, ß and ¿ particles, CdS:Te is also a good potential detector of thermal neutrons. View full abstract»

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  • Quantitative Studies of Weak Light Sources in Biological Systems by Means of an Image Intensifier

    Page(s): 58 - 66
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    Several image intensifier systems have been calibrated for gain and single electron detection efficiency. When these intensifiers are coupled to conventional microscopes the combined system provides sufficient light to allow photographic recording in short exposure times of certain biological systems that would ordinarily not be photographable or would require undesirably long exposure times. The photographs also provide quantitative information on the amount of light entering the microscope objective. Experiments are described in which an image intensifier microscope system has been used to study bioluminescence, providing data on the temporal and spatial distribution of light output in several organisms. Other experiments are described in which the location of weak radioactive tracers has been possible in short exposure times, using thin overlying scintillators to provide the necessary light. System requirements are discussed for the extension of this technique to X-ray studies and fluorescence microscopy. View full abstract»

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  • New Developments in Gas-Filled Image Intensifier Detectors for X and Gamma Rays

    Page(s): 67 - 75
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    In spark operation, with short-circuit electronics having a triggering delay of ¿ 40 ns and yielding a peak current of 15 amperes, the detector, which is filled with xenon (720Torr) and diethylamine (40 Torr) has a counting plateau equal to 4% of the mean operating voltage. The electronic short-circuit is more effective when diethylamine replaces methylal. It is shown that this vapour produces a delay in the triggering of the spark. The life is improved. Study of electron avalanches has shown that, in the case of detection of X-rays of a mean energy of 27 keV, the number of carriers which they contain may reach 108 and that the probability is then less than 10-4 for triggering sparks. These avalanches also make it possible to obtain completely proportional amplitude spectra of excellent resolution (9% for 27 keV). When the detector is used in avalanche operation, the light emitted by the latter enables an image of the X-ray emitting source to be recorded. The quantity of light emitted can be increased by increasing the number of carriers in the avalanche but at the risk of creating a spark. This risk is eliminated by a short-circuit system similar to that operating for spark conditions but with a triggering threshold corresponding to about 105 electrons. The possibility of using this detector for recording X-ray diffraction patterns on biological molecules is discussed. View full abstract»

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  • A NaI(T1) spectrometer for γ-rays in the GeV range

    Page(s): 82 - 83
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    As part of a program to develop methods for detecting and measuring high energy gamma rays, produced for example by the bombardment of targets with particles in the GeV range, the behavior of a large NaI(Tl) crystal spectrometer is being explored using the facilities of the Stanford Linear Accelerator Center (SLAC). In the following paragraphs we indicate the results of our initial sutdies. View full abstract»

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  • Gas Proportional Scintillation Counter with Xenon and Xenon Mixtures

    Page(s): 84 - 91
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    The light output of the recently developed gas proportional scintillation counter - a gas scintillation counter with light multiplication produced by a cylindrical geometry electric field - is investigated for heavy gaseous media under alpha particle excitation with a 56 UVP phototube. The gases used are Xe, and Xe-Ar and Xe-N2 mixtures for a wide range of concentrations, at a total pressure of about 965 Torr. The light output of the Xe-Ar mixtures shifts towards the ultraviolet (¿ ¿ 3250 Å) region as the electric field intensity increases. Xe-Ar mixtures with Xe concentrations ranging from about 1 to 10% give - with a p-quaterphenyl wavelength shifter - a light output more than two orders of magnitude larger than that of a CsI(T1) scintillator. In Xe-N2 mixtures - with wavelength shifter - nitrogen has a quenching effect. For the mixtures of noble gases the rise time of the secondary component of the light pulse is slow, typically 15 ¿s. Methane and nitrogen while having a quenching effect, reduce this rise time. View full abstract»

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  • An Image Intensifier - Television System for the Direct Recording of X-Ray Diffraction Patterns

    Page(s): 92 - 94
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    A system has been designed which will permit the scanning of X-ray diffraction patterns and the direct reading in of the digitized intensities of X-ray diffraction spots into a computer. The system makes use of two image intensifiers and a slow-scan television camera in tandem. View full abstract»

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  • Rare Earth Phosphors and Scintillators

    Page(s): 95 - 101
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    Luminescent rare earth compounds are receiving renewed attention as a result of their successful application as phosphors for color television and lighting and as crystals for solid state lasers. The compounds of practical interest are hardy materials, frequently simple or complex oxides in which the rare earth activator occurs in the trivalent state. We report here the results of a partially completed survey of electron- and x-ray-stimulated luminescence of the rare earths in selected oxide hosts, on the basis of which it is possible to draw preliminary conclusions regarding the suitability of such materials for scintillation and other radiation detection and measurement applications. The luminescent compounds fall into two categories. Materials of the first category exhibit the sharp line spectra characteristic of transitions within the 4f electron shell. Efficiencies of materials in this category are high but decay times range from microseconds to milliseconds. As a result, their greatest utility would seem to lie in imaging and energy conversion applications. Materials of the second category exhibit broad-band spectra. These spectra arise from either 5d to 4f transitions of the activator ions or from emission of the host itself. Decay times fall in the range from tens of nanoseconds to microseconds. Consequently, these materials have the greatest potential for scintillation counting application. The best materials from each of the classes are discussed. View full abstract»

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  • New Liquid Scintillators with Higher Speed and Efficiency

    Page(s): 102 - 106
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    The variation of light intensity with time following excitation by gamma rays has been measured for toluene solutions of quaterphenyl, quinquiphenyl, and sexiphenyl compounds whose solubilities were enhanced by substitution of alkyl groups. The decay curves, measured by use of a light-intensity-sampling technique, were analyzed to yield the mean lives ¿1 for energy transfer from solvent to solute, ¿2 for decay of the fast component (from the singlet state), and ¿3 for decay of the slower component (probably from excimers). Preliminary estimates of ¿2 for quaterphenyl, quinquiphenyl, and sexiphenyl are 1.27, 1.22, and 1.02 nsec, respectively. As expected, ¿1 appears to vary inversely with solute concentration, and at the highest concentration of quaterphenyl in toluene (~ 65 g/liter, y = 1.12 × 10-2) was < 0.1 nsec. At this concentration, the amount of light in the slower component was only about 1/6 of the total light. This indicates that formation of excimers is inhibited. In addition, the photoelectrons produced in an RCA-8575 photomultiplier per keV of energy lost in the scintillator was measured to be 2.1 for quaterphenyl, 2.2 for quinquiphenyl, and 1.9 for sexiphenyl solutions. The improvement in efficiency and speed is reflected in a corresponding improvement in the time resolution achievable with these scintillators. For a 300-keV energy loss in the quaterphenyl solution, the FWHM was 0.20 nsec and the effective T1 /2 was 0.035 nsec. View full abstract»

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

    Page(s): 107 - 113
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    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. View full abstract»

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  • Temperature Dependence of Energy Degradation in Organic Liquid Scintillators

    Page(s): 114 - 116
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    Under high energy excitation, organic molecules are generally excited to electronic states above the first excited state. Since, at not too high solute concentrations, energy transfer in organic liquid scintillators occurs via the first excited electronic state, the efficiency of degradation to this state affects the overall light output. Experimental results for a number of systems, at temperatures from 20°C to 24°C are reported. It was found that the efficiency of degradation to the first excited state generally decreases with increasing temperature, with some variation among the solvents tested. It was found that; the greater the efficiency of degradation to the first excited state at 20°C, the less this efficiency varies with temperature. View full abstract»

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  • Emission and Decay of Excited Organic Molecules under Electron Impact

    Page(s): 117 - 121
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    The emission and decay of a number of benzene derivatives in the liquid phase, excited by electron impact, are characteristic of singlet state excimers. View full abstract»

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  • Anisotropy of Scintillation Response of Anthracene to Neutron Generated Recoil Protons and Carbon Ions

    Page(s): 122 - 126
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    The directional anisotropy in the scintillation response of an anthracene crystal to heavy charged particles was investigated. Energetic carbon and hydrogen ions were produced internally by scattering fast neutrons from the constituent nuclei. By use of a two detector coincidence system, the scintillations due to monoenergetic ions recoiling in a particular direction were selected and analyzed. The energies of the ions ranged from 2 to 3.5 MeV for the carbon recoils and from .9 to 7.3 MeV for the hydrogen recoils. Even though there was a wide variation in the average specific energy loss of the heavy charged particles considered, the magnitude of the anisotropy only varied between 39% for the carbon recoils and 20% for the 7.3 MeV hydrogen recoils. The measured hydrogen ion response in a particular direction as a function of energy was found to be approximately described by the formula suggested by Birks, dL/dE = (1 + kBdE/dx)-1, with kB being directionally dependent. The directional carbon ion response appeared to be a linear function of energy over the energy range investigated. View full abstract»

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  • The Response of Stilbene to Internally Generated Protons

    Page(s): 127 - 135
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    A thick radiator neutron spectrometer has been constructed in which protons recoiling forward in the stilbene escape from the crystal and are detected in a silicon surface barrier counter. The coincident pulses from the two counters are recorded using a two-parameter analyzer. The instrument has been used to investigate (1) the response of stilbene to protons originating within the scintillator and (2) the behavior of the pulse shape discrimination as a function of the energy deposited in the stilbene crystal. The response function, which is required for the analysis of the neutron spectra, is compared with one obtained for protons incident externally on the same crystal. Small differences between the two response functions are observed and analyzed. Concerning the behavior of the pulse shape discrimination between protons and electrons it is found that, for internally generated protons, the ability to separate protons from electrons worsens as the energy deposited in the scintillator decreases. This contrasts with the behavior for protons which stop in the scintillator. The results support the hypothesis that the fast component of the pulse decreases with increasing stopping power whereas the slow component depends primarily on the energy lost. The results are analyzed and may be interpreted with certain assumptions to give the ratio of the fast and slow scintillation components. View full abstract»

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  • Transient Nonlinear Response of Plastic Scintillators

    Page(s): 136 - 143
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    The peak dose rate for which light output is linearly proportional to incident radiation intensity was measured by bombarding 80-mil-thick samples of NE 102 and MEL 150C scintillators with 12-MeV electrons from the EG&G/AEC linear accelerator. To obtain the equivalent gamma dose rate, the sensitivity of the scintillator-photodiode detector used in this work was measured with a calibrated Co60 source. Nonlinear behavior was observed for excitation pulse widths between six nanoseconds and 0.5 microseconds. Analysis of the detector signals indicates that nonlinearity is a function of total dose as well as dose rate. Thus for an excitation pulse width of 0.5 microseconds, scintillator output was found to be linear at the start of the burst, but showed marked nonlinearity by the end of the pulse. The data also indicate that if the dose rate drops below the threshold value after a scintillator is driven into nonlinear operation, the scintillator will continue to behave nonlinearily for some time. The decay time associated with recovery from nonlinearity is greater than 0.5 microsecond. Data are presented, showing the average dose rate required to produce 5% and 10% nonlinear behavior as a function of exposure time. As a typical case, 10% nonlinear behavior for NE 102 results from an average dose rate of 6.5 × 1011 R/sec for an exposure time of 10 nanoseconds. View full abstract»

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  • Development of a Double Layered Scintillator for Separating and Detecting Low Energy Protons and Electrons

    Page(s): 144 - 146
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    A scintillator system consisting of a thin (5,000 Å - 15,000 Å) CsI(Tl) layer evaporated onto a plastic scintillator (NE-102) has been developed for the purpose of distinguishing low energy protons from electrons and measuring the energy of each species. Evaporations in a high vacuum (10-8 Torr) produced layers of CsI(Tl) that scintillate with an efficiency comparable to optimally doped bulk material, If the CsI(Tl) layer thickness is 15,000 Å, it stops protons with energies below 170 keV and electrons with energies below 18 keV. Thus, protons with energies between about 25 and 250 keV can be distinguished from electrons with energies above 18 keV by examining the shape of the light pulse generated in the dual scintillator. Results obtained with protons and electron beams will be presented. View full abstract»

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  • Scintillation Characteristics of Thin NaI(Tl) and CsI (Tl) Layers Fabricated by Vacuum Deposition

    Page(s): 147 - 152
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    The scintillation characteristics of thin vacuum-deposited layers of NaI (Tl) and CsI (Tl) were investigated. Scintillation layers with thicknesses ranging from 0.2 to 20 mg/cm2 were evaluated as detectors with 6- and 22-keV x rays. In this energy region they were found to be comparable in performance to the thicker, commercially available NaI (Tl) and CsI (Tl) scintillation crystals. Fabrication methods, scintillator evaluation techniques, and applications in selective low-energy x-ray detection will be reported. View full abstract»

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  • Dependence of the NaI(Tl) Pulse Shape on Thallium Concentration and Temperature

    Page(s): 153 - 157
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    The pulse shape of ¿-induced photopeak scintillations in NaI(Tl) has been measured as a function of temperature for several standard commercial crystals and for crystals containing known thallium concentrations. A detailed analysis of the data indicates that the first two microseconds of the pulse is characterized by at least nine separate decay processes. Four of these are attributed to one radiative and three metastable states associated with a thallous ion. Two fast processes are attributed to emission characteristic of pure NaI while two others are associated with high thallium concentration. Energy transport is suggested as the ninth process. View full abstract»

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  • Luminescence from NaI(Tl) between 5°K and 30°K

    Page(s): 158 - 161
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    The several emission bands of scintillator crystal NaI(TlI) excited by X-irradiation have been studied between 5° and 80°K. It was possible to trap electrons as Tl° and holes as I2- and Tl++ during irradiation and cause recombination thermally or by optical stimulation after irradiation to give the same emissions. The processes responsible for recombination after irradiation are discussed and assignments based on these results made for processes during irradiation. View full abstract»

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IEEE Transactions on Nuclear Science focuses on all aspects of the theory and applications of nuclear science and engineering, including instrumentation for the detection and measurement of ionizing radiation; particle accelerators and their controls; nuclear medicine and its application; effects of radiation on materials, components, and systems; reactor instrumentation and controls; and measurement of radiation in space.

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