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Nuclear Science, IEEE Transactions on

Issue 4 • Date Aug. 1995

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Displaying Results 1 - 25 of 207
  • Pulse-height-spectrum distortion in xenon gaseous detectors for soft X-rays: experimental results

    Page(s): 611 - 614
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (327 KB)  

    The results of an experimental determination of the pulse-height distortion in soft X-ray spectra in gaseous xenon detectors are presented. The study confirms previous Monte Carlo simulation results and emphasizes the importance of the electric field in the drift region in reducing spectral degradation while the effect of a strong magnetic field in the same region is shown to be negligible.<> View full abstract»

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  • Monolithic cryogenic preamplifiers based on large gate-area GaAs MESFETs

    Page(s): 758 - 761
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    Monolithic preamplifiers using large gate-area Gallium-Arsenide Metal-Semiconductor Field-Effect Transistors (GaAs MESFETs) at the input have been designed and fabricated using an ion-implanted GaAs process. Large gate-area is necessary to obtain low series noise. A differential voltage-sensitive preamplifier has at the input two MESFETs with a gate width W=6000 μm, it is fully DC coupled, has a large common-mode rejection ratio (CMRR) and dissipates low power at 4 K. Dual current-sensitive preamplifiers using at the input MESFETs with W=24000 μm, designed for the readout of noble liquid calorimeters, have been integrated in a single chip. Recent tests with a LAr calorimeter prototype demonstrated strong noise reduction compared to previous state-of-the-art hybrid readout circuits. Radiation damage tests have been performed at cold on the current-sensitive preamplifier chips View full abstract»

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  • An integrated CMOS 0.15 ns digital timing generator for TDC's and clock distribution systems

    Page(s): 753 - 757
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    This paper describes the architecture and performance of a new high resolution timing generator used as a building block for Time to Digital Converters (TDC) and clock alignment functions. The timing generator is implemented as an array of delay locked loops. This architecture enables a timing generator with sub-gate delay resolution to be implemented in a standard digital CMOS process. The TDC function is implemented by storing the state of the timing generator signals in an asynchronous pipeline buffer when a hit signal is asserted. The clock alignment function is obtained by selecting one of the timing generator signals as an output clock. The proposed timing generator has been mapped into a 1.0 μm CMOS process and a RMS error of the time taps of 48 ps has been measured with a bin size 0.15 ns. Used as a TDC device a RMS error of 76 ps has been obtained. A short overview of the basic principles of major TDC and timing generator architectures is given to compare the merits of the proposed scheme to other alternatives View full abstract»

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  • LuAlO3:Ce-a high density, high speed scintillator for gamma detection

    Page(s): 275 - 279
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    We present measurements of the scintillation properties of cerium doped lutetium aluminum perovskite, LuAlO3:Ce, a new dense (ρ=8.34 g/cm3) inorganic scintillator. This material has a 511 keV interaction length and photoelectric fraction of 1.1 cm and 32% respectively, which are well suited to gamma ray detection. In powdered form with 0.5% cerium concentration, the scintillation light output is estimated to be 9,600 photons/MeV of deposited energy, the emission spectrum is a single peak centered at 390 nm, and the fluorescence lifetime is described by the sum of 3 exponential terms, with 60% of the light being emitted with a 11 ns decay time, 26% with a 28 ns decay time, and 13% with a 835 ns decay time. Single crystals contaminated with ≈10% lutetium aluminum garnet (Lu3Al5O12) have significantly altered scintillation properties. The light output is 26,000 photons/MeV (3.2 times that of BGO), but the decay time increases significantly (1% of the light is emitted with a 10 ns decay time, 15% with a 245 ns decay time, and 85% with a 2010 ns decay time) and the emission spectrum is dominated by a peak centered at 315 nm with a secondary peak centered at 500 nm. The short decay lifetime, high density, and reasonable light output of LuAlO3:Ce (the perovskite phase) suggest that it is useful for applications where high counting rates, good stopping power, good energy resolution, and fast timing are important. However, it is necessary to grow single crystals that are uncontaminated by the garnet phase to realize these properties View full abstract»

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  • CsI(Tl) with photodiodes for identifying subsurface radionuclide contamination

    Page(s): 288 - 291
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    A cylindrical (15×61 mm) CsI(Tl) scintillation detector with two side-mounted photodiodes has been developed to collect spectral gamma-ray data in subsurface contaminated formations at the US Department of Energy's Hanford Site. It operates inside small-diameter, thick-wall steel pipes pushed into the ground to depths up to 20 m by a cone penetrometer system. The detector provides a rugged, efficient, magnetic-field-insensitive means for identifying gamma-ray-emitting contaminants (mainly 137Cs and 60Co). Mounting two 3×30-mm photodiodes end-to-end on a flat area along the detector's side provides efficient light collection over the length of the detector View full abstract»

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  • Effect of scatter from radioactivity outside of the field of view in 3D PET

    Page(s): 1157 - 1161
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    The contribution of the scattered events originating from radioactivity outside the tomograph field of view (ROFOV) is treated differently by different scatter correction algorithms. Using measured data we have evaluated the amount of scatter originating from ROFOV, its axial and transaxial distribution in two energy windows for direct and a subset of oblique planes in 3D PET. Nonuniform distributions were observed with the total contribution found to be non-negligible when the amount of ROFOV was comparable to the radioactivity in the field of view (FOV) View full abstract»

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  • The effect of bi- and trivalent cation impurities on the luminescence of CsI

    Page(s): 285 - 287
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    The effect of states of bi- (Ca) and trivalent (Sb, Bi) impurities on the optical and scintillation characteristics of CsI crystals is studied. The variation of point defect states (quenching, deformation, impurity concentration, diffusional activation) changes the correlation between different components of luminescence. The analysis of the obtained results leads to a conclusion about the role of cation vacancy type defects for the localization of the exciton in CsI crystals View full abstract»

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  • Comparison of different imaging geometries of brain SPECT systems

    Page(s): 1147 - 1153
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    Since many different configurations of brain SPECT systems are available for clinical imaging, it is informative to investigate whether there are significant differences in their performance potentials. However, the difference in configurations and performance characteristics make direct comparison between systems difficult. To clarify the issue, we have developed a method to analyze the relative merits of different basic system geometries and configurations. This method is based on the calculated system geometric efficiency (SGE) which is obtained when the system spatial resolution is normalized to a reference level under a specified imaging condition. During the normalization process, the design parameters and performance of the collimators are iteratively adjusted to match the system resolution of an appropriately defined reference specification. After the collimator is normalized, the geometric efficiency (GE) of the collimator is calculated by summing the point source geometric efficiency (PSGE) over a brain source model while imposing narrow-beam attenuation effect. The SGE is then derived for each system configuration based on the calculated GE for each collimator. This analysis has been applied to many existing geometries and detector-collimator configurations of current brain SPECT systems View full abstract»

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  • A resonance measuring wire tension monitor for high-energy physics

    Page(s): 1419 - 1424
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    The design, construction, and operation of a wire tension monitor is presented. The technique used is unique in that the electric force is used to excite the wire into harmonic resonance. The amplitude of the wire is in turn monitored using the variation of the oscillating wire's capacitance measured by a resonance circuit. Finally, the resonance is found electronically using phase lock loop techniques. Wire tension is measured to an accuracy of 0.3% with this device View full abstract»

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  • LuAlO3:Ce and other aluminate scintillators

    Page(s): 280 - 284
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    A new scintillator, LuAlO3:Ce, has been found to have properties that put it in the forefront when stopping power and timing is of importance. This material, an extension of other well known cerium-doped scintillators, the yttrium-based orthoaluminate and garnet, can be readily pulled from the melt, and displays particularly promising performance. We summarize the results achieved when Y is replaced by Lu in this class of oxide crystals View full abstract»

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  • Feasibility of using cadmium-zinc-telluride detectors in electronically collimated SPECT

    Page(s): 1139 - 1146
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    Replacing cryogenically cooled germanium (Ge) with room-temperature operable cadmium-zinc-telluride (CZT) semiconducting detectors as the first detector of an electronically collimated SPECT system would have certain practical advantages. To determine the feasibility of this approach, we have performed a theoretical and experimental study comparing the resolution and detection efficiency of a Ge based system to that of a CZT based system. The results indicate that the detection efficiency of a CZT based system would be a factor of 2.5 lower than a comparable Ge based system at 140 keV and the spatial resolution would also be approximately a factor of two worse. However, at higher energies, the difference between CZT and Ge would decrease, and at 662 keV, for example, the CZT and the Ge systems could have nearly equal detection efficiency and resolution View full abstract»

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  • Development of an on-line fuzzy expert system for integrated alarm processing in nuclear power plants

    Page(s): 1406 - 1418
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1240 KB)  

    An on-line fuzzy expert system, called alarm filtering and diagnostic system (AFDS), was developed to provide the operator with clean alarm pictures and system-wide failure information during abnormal states through alarm filtering and diagnosis. In addition, it carries out alarm prognosis to warn the operator of process abnormalities. Clean alarm pictures that have no information overlapping are generated from multiple activated alarms at the alarm filtering stage. The meta rules for dynamic filtering were established on the basis of the alarm relationship network. In the case of alarm diagnosis, the relations between alarms and abnormal states are represented by means of fuzzy relations, and the compositional inference rule of fuzzy logic is utilized to infer abnormal states from the fuzzy relations. The AFDS offers the operator related operating procedures as well as diagnostic results. At the stage of alarm prognosis, the future values of some important critical safety parameters are predicted by means of Levinson algorithm selected from the comparative experiments, and the global trends of these parameters are estimated using data smoothing and fuzzy membership. This information enables early failure detection and is also used to supplement diagnostic symptoms. The AFDS has been validated and demonstrated using the full-scope simulator for Yonggwang Units 1, 2. From the validation results, it can be concluded that the AFDS is able to aid the operator to terminate early and mitigate plant abnormalities View full abstract»

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  • Silicon detector system for high rate EXAFS applications

    Page(s): 585 - 589
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    A multichannel silicon pad detector for EXAFS (Extended X-ray Absorption Fine Structure) applications has been designed and built. The X-ray spectroscopic measurements demonstrate that an adequate energy resolution of 230 eV FWHM (corresponding to 27 rms electrons in silicon) can be achieved reliably at -35°C. A resolution of 190 eV FWHM (corresponding to 22 rms electrons) has been obtained from individual pads at -35°C. At room temperature (25°C) an average energy resolution of 380 eV FWHM is achieved and a resolution of 350 eV FWHM (41 rms electrons) is the best performance. A simple cooling system constituted of Peltier cells is sufficient to reduce the reverse currents of the pads and their related shot noise contribution, in order to achieve resolutions better than 300 eV FWHM which is adequate for the EXAFS applications View full abstract»

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  • Calculations of scintillators for radiation detector systems: dependence of spectrometric characteristics on shape, size and reflector type

    Page(s): 357 - 360
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    Spectrometric characteristics of ionizing radiation detectors based on Bi4Ge3O12 and CdWO4 scintillators were calculated as a function of size, shape (rectangular or cylindrical) and reflector type. Unlike previous work, allowance was made for the dependence of the diffuse reflection indicatrix on the light incidence angle which is of importance for light transfer in a scintillator. The calculation method was verified by the experimental statistics. The regions of parameters are derived where the rough or polished version of the reflecting surface is preferable View full abstract»

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  • Program for life extension and preserving existing resources for motor control center components [nuclear plants]

    Page(s): 1000 - 1004
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    Many nuclear power plants have motor control centers (MCCs) installed in a harsh, radiation only, environment. Procurement of safety-related replacement devices for these MCCs is an economic burden for the stations if these MCCs have become obsolete. Identical replacement components for many MCCs installed in older plants (ITE Gould, Allis-Chalmers, Klockner-Moeller, Cutler-Hammer, etc.) are no longer available. Plants are left with the option of either retrofitting these MCCs or finding ways to extend the qualified lives of the safety-related components to minimize replacement costs. ComEd nuclear station has embarked on a program to minimize the economic burden for the replacement of Klockner-Moeller (K-M) MCC components. This paper discusses the program adopted by this station and its economic benefits to ComEd View full abstract»

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  • Experience with the first level trigger of H1

    Page(s): 900 - 904
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    H1 is a high energy physics experiment at the electron proton collider HERA at DESY, routinely taking data since 1992. Calorimetric and tracking systems record the properties of the particles produced in the collisions in a total of 270000 electronic channels. The collision frequency of 10.4 MHz necessitates pipelining of all data in the centrally clocked trigger and front end readout systems. This report outlines the architecture of the trigger and data acquisition system and describes the experience gained in the first years of running the experiment. A crucial aspect is the clock phase adjustment and stability of all trigger signals View full abstract»

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  • Accuracy of spectral gamma-log interpretation models

    Page(s): 615 - 619
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    Considered are benefits of new interpretation models of the natural spectral gamma-ray log based the application of the analytical algorithms of radial “geometrical factors”. A combined technique of computer simulation and analytical interpretation models is used to study the influence of geological and downhole conditions and statistical errors on the the accuracy of interpretations of spectral gamma logs. A comparison between analytical algorithms and those based on the reduction to standard downhole conditions is presented. The analytical structure of the new interpretation algorithms provides upper estimates of the interpretation accuracy and concurrent computation of radionuclide abundances View full abstract»

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  • Spectroscopy charge amplifier for detectors with integrated front-end FET

    Page(s): 1399 - 1405
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    A charge amplifier, especially designed for FET integrated on silicon radiation detectors, is presented. The circuit is based on the forward biased FET amplifier configuration, which does not require the feedback resistor nor additional devices for resetting. The severe constraints on the preamplifier design, imposed by the low transconductance of small size integrated FET's, are analyzed as far as loop-gain, bandwidth, and noise are concerned. A circuit topology which satisfies all the requirements even at relatively fast shaping time (1 μs) is proposed and experimentally tested View full abstract»

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  • Evaluation of hydrogen content in metallic samples by neutron computed tomography

    Page(s): 580 - 584
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    Neutron radiography is currently a well-known technique, which is employed for non-destructive testing in a number of industrial and environmental applications. Originally developed for reactor fuel examinations, it is now effective in detecting small amounts of corrosion and infiltrations of hydrogen or light materials within thick metallic structures due to the particular behaviour of total neutron cross sections. Nevertheless, improvements related to the development of tomographic systems, which allow far better imaging performances, have been achieved only in the last few years, as a consequence, primarily, of the production of large, charge coupled device (CCD) arrays. Nowadays, neutron computed tomography is the technique most suited for the study of the distribution of hydrogen within metallic matrices. In this field, a series of experimental tests were carried out employing a set of nickel samples containing a H2O-D2O solution in known percentages. It was possible, therefore, to obtain a calibration curve for the total neutron cross section vs. Gray level in the reconstructed image View full abstract»

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  • GAUSS IX: an interactive program for the analysis of gamma-ray spectra from Ge semiconductor detectors

    Page(s): 267 - 271
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    The newest member of a series of computer programs developed at the INEL for analysis of gamma-ray spectra from Ge semiconductor detectors is GAUSS IX. This program makes use of the computational routines of GAUSS VII in an interactive structure. The interactive features are implemented with OSF/Motif and the X Window System. This interactive version can dramatically decrease the turnaround time for spectral analyses, especially when the user needs to refit some of the peaks with specially-chosen fitting parameters. The graphic features increase the opportunity for detecting patterns and anomalies in the spectral analyses. The user of this program can set up the analysis parameters (i.e., peaks, peak regions, etc.) interactively via window dialogs. The user can interactively display and review the results, selectively re-fit peaks, and save or purge the results, as appropriate. The spectral displays can include the spectral data, peak locations, peak fitting regions, fit curves, and background curves; and the display is completely zoomable, scrollable, and resizable View full abstract»

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  • NANA-an integrated signal processor and record builder for the level-2 readout of asynchronous event-filtering digital pipelines

    Page(s): 849 - 853
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    NANA implements some fast and simple processing algorithms, for use in future High Energy Physics (HEP) experiments. After the first level trigger, the data rate is sufficiently small to allow channel merging and some processing with dedicated hardware. For detectors whose signal is companded prior to digitization, the data samples need to be expanded to the original dynamic range, as further physics analysis usually deals with linear values. A 16 bit integer piece-wise polynomial approximation of the expansion function recovers the original dynamic range, without introducing significant degradation on the detector's intrinsic resolution. A 16 bit integer multiplier and adder-accumulator is accurate enough for time information extraction and for determination of the energy deposited in one channel. The time resolution is sufficient to correctly identify the bunch crossing that corresponds to a particular pulse. The energy accuracy is limited only by the detector's resolution. The extracted features carry all the information subsequently needed. The whole set of samples of a pulse can thus be replaced by a few data words. Initially aimed at the calorimetry front-end, the algorithms may be applied to any similar sampled detector signal View full abstract»

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  • Introduction to IEEE Std. 7-4.3.2 Annex D-“Qualification of existing commercial computers”

    Page(s): 997 - 999
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    On September 15th of 1993 the IEEE standards board approved IEEE Std. 7-4.3.2-1993, IEEE Standard for Digital Computers in Safety Systems of Nuclear Power Generating Stations. This paper is an introduction to Annex D of this document which concerns the commercial grade dedication of existing computers or new non-1E computers View full abstract»

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  • New ideas in CsI-based photon detectors: wire photomultipliers and protection of the photocathodes

    Page(s): 298 - 305
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    We discuss the idea of a vacuum or gaseous photomultiplier with a CsI-coated wire photocathode. It benefits from an electric field enhanced quantum efficiency. We present a method for protecting air-sensitive photocathodes with thin dielectric film coating. Results of CsI coated with thin LiF and MgF2 films are shown. The protection of other UV and visible photocathodes is discussed View full abstract»

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  • A new high-precision current supply for magnets

    Page(s): 1460 - 1465
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    A new, high-precision, low-ripple current power supply (CPS) for magnets, based on a combination of an SCR converter and a single transistor switched mode power supply (SMPS) is described. The load power is primarily supplied by the SCR converter. The SMPS handles only a small fraction of the load power, and also, what is more significant, a very small part of the load current. In this paper, the topology and operating principle of the new power supply is discussed. A CPS, rated at 200 A at 45 V, was constructed and tested. The power supply energizes a family of quadrupole magnets at the Brazilian Synchrotron Light Source-LNLS. Making use of the current limit modulation control method, magnetic field variations at full current are 5 ppm, with only 8 A passing through the switching transistor. The design and performance of the power supply under different operating conditions are described. Variations of the proposed topology, suitable for high-current and high-voltage loads, are also discussed 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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