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Nuclear Science, IEEE Transactions on

Issue 2  Part 2 • Date Apr 2000

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Displaying Results 1 - 8 of 8
  • Techniques to improve the spatial sampling of MicroPET-a high resolution animal PET tomograph

    Publication Year: 2000 , Page(s): 422 - 427
    Cited by:  Papers (9)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (100 KB)  

    A method is described to improve the spatial sampling of microPET, a high resolution PET scanner designed for imaging small laboratory animals. The high intrinsic resolution of the microPET detector (1.58 mm FWHM), in combination with the stationary ring geometry of the tomograph, generate an imaging system which is inherently spatially undersampled. As a result the imaging resolution measured with a three-dimensional (3-D) filtered backprojection (FBP) algorithm for a point source at the center of the field of view (CFOV) is only 1.8 mm FWHM and has large fluctuations at positions near the CFOV. A small wobble motion was introduced via a circular motion of the scanner bed in the transverse plane, with a wobble radius of 300 μm. The data was acquired with a step-and-shoot method by dividing the wobble circle into a number of equidistantly sampled intervals. The separate sinograms were interpolated to a finely resampled sinogram, which was reconstructed with the 3-D filtered backprojection algorithm. The resulting images demonstrated full recovery of the intrinsic detector resolution and elimination of the local nonuniformities of the point spread function (PSF) at the CFOV, with three wobble samples. The resulting average resolution improvement fur the central 5 cm of the FOV was approximately 13% in the radial and 19% in the tangential direction, with an associated 50% penalty in the reconstructed image noise View full abstract»

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  • Afterglow in LSO and its possible effect on energy resolution

    Publication Year: 2000 , Page(s): 438 - 445
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB)  

    LSO is known to exhibit afterglow for approximately 24 h following exposure to intense room light. We find that LSO also exhibits afterglow following activation by gamma rays in normal scintillation counting. This scintillation afterglow is characterized by an exponential decay time constant of 50 min and an absolute light yield, relative to the fast scintillation component, of 1.7. Unless special attention is paid to the afterglow signal in designing the data acquisition electronics used with LSO, the gamma ray energy resolution of the spectroscopy system can he ruined by baseline shifts occurring during the acquisition of an energy spectrum. With proper provisions to handle these predictable baseline shifts, LSO is a promising new scintillator for fast counting gamma ray spectroscopy View full abstract»

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  • Low noise cryogenic electronics: preamplifier configurations with feedback on the bolometer

    Publication Year: 2000 , Page(s): 428 - 437
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    We have developed preamplifier configurations used to readout resistive bolometers such as those based on neutron transmuted doped Germanium thermometers (so-called NTD Ge thermometers) or NbSi thin film thermometers. We introduce the impedance regulating preamplifier configuration. This configuration is compared to previously proposed readout configurations with feedback on the bolometer. It is shown that the impedance regulating preamplifier achieves extreme electrothermal feedback without using transition edge thermometer and SQUID readout. Thus the detector and readout electronics are straightforwardly calibrated and can handle much larger event rates. Looped configurations simplify the design and improve performance of detection such as bandwidth. Finally, we analyze the impedance regulating amplifier noise contributions, with JFETs as front-end devices, relative to other configurations View full abstract»

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  • Spatial control of a large PHWR by piecewise constant periodic output feedback

    Publication Year: 2000 , Page(s): 389 - 402
    Cited by:  Papers (16)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    The paper presents the design of piecewise constant periodic output feedback control for a discrete-time singularly perturbed system resulting from the discretization of a continuous-time standard singularly perturbed system. By a suitable linear transformation of state variables, the given continuous-time singularly perturbed model is converted into a block triangular form in which the fast subsystem is decoupled. The discrete-time model corresponding to the transformed model also exhibits a two time scale property if sampling period is larger than the parameter E. Now an output injection matrix is found that stabilizes the slow subsystem. The periodic output feedback gain is then calculated only for the slow subsystem and the same for the fast subsystem is set equal to zero. Finally the periodic output feedback gain for the composite system is obtained using the periodic output feedback gains computed separately for the slow and fast subsystems. An approach has been suggested whereby the determination of periodic output feedback gain for the slow subsystem can be converted into an optimization problem. By minimization of the suggested performance index the closed loop system behavior is improved. The method has been applied to a large pressurized heavy water reactor (PHWR) for control of xenon-induced spatial oscillations. A particular grouping of state variables has been suggested for obtaining the model in standard singularly perturbed form. The periodic output feedback gain is then calculated. The efficacy of control has been demonstrated by simulation of transient behavior of the nonlinear model of the PHWR View full abstract»

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  • Longitudinal feedback system kicker for the PLS storage ring

    Publication Year: 2000 , Page(s): 452 - 467
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    The higher order modes (HOMs) of RF cavities at the Pohang Light Source (PLS) storage ring cause longitudinal coupled bunch mode instabilities. A longitudinal feedback system (LFS) is introduced to cure these instabilities. As a key component of the LFS, there is a single-ridged waveguide-overloaded cavity for a longitudinal bunch-by-bunch LFS kicker. Since the RF frequency is 500 MHz, the bandwidth of this kicker should be wider than 250 MHz to damp any coupled bunch mode. Also, a higher shunt impedance of the kicker is selected to use a lower power amplifier. One aluminum kicker is fabricated, and the bandwidth, HOMs, and the shunt impedance of the kicker are measured with a network analyzer. This kicker has several different features from the LFS kicker for DAΦNE. First of all, there are four input/output ports to obtain a wider bandwidth. Second, there is a nose cone to obtain a higher shunt impedance. Third, the symmetric frequency response of the shunt impedance around the central frequency is provided. Finally, low beam coupling power (4 W per port at 400 mA) is obtained. According to the simulation result by the high frequency structure simulator (HFSS) code, we obtained the high shunt impedance of 621.3 Ω (transit time factor considered value) and the wide bandwidth of 255 MHz. These are compared with the measured result View full abstract»

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  • A detailed microscopic analysis of deep levels in heavily irradiated-medium resistivity silicon detectors

    Publication Year: 2000 , Page(s): 446 - 451
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB)  

    In this work we show a detailed deep levels analysis (an energy resolution of 50 meV was reached) of a set of medium resistivity silicon samples, irradiated up to a fluence of 2.5·1015 n/cm 2. In order to discriminate the large number of deep levels which appear to overlap their contributions in TSC and I-DLTS spectra, we adopted an innovative numerical procedure of data analysis which determines a set of deep levels that can account for both TSC and I-DLTS spectra. We finally obtained a consistent and detailed description of deep level population, clearly showing its evolution with fluence. Some results seem to suggest the possibility of quasi-continuous distributions of localized states inside the gap View full abstract»

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  • A quality control method for nuclear instrumentation and control systems based on software safety prediction

    Publication Year: 2000 , Page(s): 408 - 421
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    In the case of safety-related applications like nuclear instrumentation and control (NI&C), safety-oriented quality control is required. The objective of this paper is to present a software safety classification method as a safety-oriented quality control tool. Based on this method, we predict the risk (and thus safety) of software items that are at the core of NI&C systems. Then we classify the software items according to the degree of the risk. The method can be used earlier than at the detailed design phase. Furthermore, the method can also be used in all the development phases without major changes. The proposed method seeks to utilize the measures that can be obtained from the safety analysis and requirements analysis. Using the measures proved to be desirable in a few aspects. The authors have introduced fuzzy approximate reasoning to the classification method because experts' knowledge covers the vague frontiers between good quality and bad quality with linguistic uncertainty and fuzziness. Fuzzy Colored Petri Net (FCPN) is introduced in order to offer a formal framework for the classification method and facilitate the knowledge representation, modification, or verification. Through the proposed quality control method, high-quality NI&C systems can be developed effectively and used safely View full abstract»

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  • Light-hadron induced SER and scaling relations for 16- and 64-Mb DRAMS

    Publication Year: 2000 , Page(s): 403 - 407
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (100 KB)  

    We report on soft error rates (SER) of 16 and 64 Mb dynamic memory chips induced by three types of elementary particles, neutrons, protons, and pions, with emphasis on results obtained with pion beams. Significant SER differences, up to a factor 1000, are seen between various manufacturers and cell technologies. We discuss reaction mechanisms and by comparing SER rates to nuclear reaction cross sections present guidelines for predicting failure rates 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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