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Nuclear Science, IEEE Transactions on

Issue 1 • Date Feb 1998

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Displaying Results 1 - 13 of 13
  • The influence of spatial variations of diffusion length on charge collected by diffusion from ion tracks

    Publication Year: 1998 , Page(s): 30 - 40
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (285 KB)  

    Charge collected by diffusion from ion tracks in a semiconductor substrate may be influenced by the substrate diffusion length, which is related to recombination losses. A nonuniform spatial distribution of recombination centers results in a nonuniform diffusion length function. A theoretical analysis shows that, excluding some extreme cases, charge collection is insensitive to spatial variations in the diffusion length function, so it is possible to define an effective diffusion length having the property that collected charge can be approximated by assuming a uniform diffusion length equal to this effective value. Extreme cases that must be excluded are those in which a large number of recombination centers are confined to a narrow region near the substrate boundary. View full abstract»

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  • A neuro-fuzzy controller for axial power distribution an nuclear reactors

    Publication Year: 1998 , Page(s): 59 - 67
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (319 KB)  

    A neuro-fuzzy control algorithm is applied for the core power distribution in a pressurized water reactor. The inputs of the neural fuzzy system are composed of data from each region of the reactor core. Rule outputs consist of linear combinations of their inputs (first-order Sugeno-Takagi type). The consequent and antecedent parameters of the fuzzy rules are updated by the backpropagation method. The reactor model used for computer simulations is a two-point xenon oscillation model based on the nonlinear xenon and iodine balance equations and the one group, one-dimensional neutron diffusion equation having nonlinear power reactivity feedback. The reactor core is axially divided into two regions, and each region has one input and one output and is coupled with the other region. The interaction between the regions of the reactor core is treated by a decoupling scheme. This proposed control method exhibits very fast response to a step or a ramp change of target axial offset without any residual flux oscillations between the upper and lower halves of the reactor core. View full abstract»

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  • Design study on a superconducting multicell RF accelerating cavity for use in a linear collider

    Publication Year: 1998 , Page(s): 114 - 118
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (459 KB)  

    A nine-cell superconducting RF accelerating cavity is designed for the TeV electron linear accelerator collider in the next century. The ratio of the maximum surface electric field to the accelerating gradient, Epk/Eac, is reduced to 2.024 and the cell-to-cell coupling remains as high as 1.95%. The distribution of the higher-order mode passbands is reasonable. There is no overlap between these bands, therefore no trapped modes. The circle-straight/line-ellipse-type structure provides good mechanical strength in the accelerating cavity. According to the present state of the art of surface processing techniques of niobium cavities, it is possible to reach an accelerating gradient of 25-30 MV/m with beam load. View full abstract»

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  • Consequences of radiation effects on pure-silica-core optical fibers used for Raman-scattering-based temperature measurements

    Publication Year: 1998 , Page(s): 50 - 58
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (291 KB)  

    Two types of pure-silica-core fibers (one low-OH, Al-jacketed, one medium-OH, polyimide jacketed) suitable for use as sensing fibers for Raman-scattering-based temperature measurements in nuclear environments have been subjected to gamma and fission reactor irradiation tests. Spectral attenuation measurements were performed between 500 and 1500 nm with samples kept at room temperature, 80 and 300°C. The Al-jacketed fiber was developed for use under ionizing radiation and showed lower loss compared with the polyimide-jacketed fiber at room temperature under gamma irradiation. Both fiber types showed similar spectra at room temperature with the main part of the loss originating from a band tail extending from the ultraviolet. Thermal bleaching of the radiation-induced defects was found to be effective in both fiber types. At 80°C the loss in both fibers was compounded of a band at 625 nm together with the band tail from the ultraviolet, which now had a strength several times lower compared with room-temperature irradiations. At 300°C, both fibers exhibited similar low-loss spectra, except for the band at 625 nm which reached levels of approximately ∼2000 dB/km at an accumulated dose of 2.8×104 Gy(SiO2). In light of the experimental spectral findings, selection of suitable Raman-distributed temperature sensors for nuclear plants can be made. View full abstract»

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  • X-ray fluorescent computer tomography with synchrotron radiation

    Publication Year: 1998 , Page(s): 75 - 88
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (305 KB)  

    This paper describes the possibility of a quantitative calculation of the distribution of a nonradioactive element within a selected cross section with nondestructive methods with the help of X-ray fluorescent tomography (XFCT). In order to increase measurement sensitivity, the use of a lamellar collimator was avoided. One of the main problems for the quantitative determination of concentration was absorption of the stimulating synchrotron ray as well as re-absorption of the emitted fluorescent light. The absorption coefficients required for a consideration of the absorption processes have been determined with two absorption tomograms. The algebraic reconstruction technique (ART) and the maximum likelihood method with expectation maximization (MLEM) were used for the reconstruction of the chemical element to be classified, with close consideration of the absorption phenomenon. The experiments were undertaken at the bending-magnet beamline, CEMO, at the laboratory for synchrotron radiation in Hamburg, HASYLAB (4.5 GeV) (100 mA). The photon intensity flux was approximately 109 photons/mm2/s. The concentration of iodine was calculated with phantoms and an untreated, dissected human thyroid gland with the help of a calibration curve. The total error related to the reconstructed mean value amounts to 20%. One can find at least an iodide concentration of 0.6 mmol/l in this experimental setup. View full abstract»

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  • Automating strategies of emergency operation for optimal shutdown in pressurized water reactors

    Publication Year: 1998 , Page(s): 17 - 29
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (393 KB)  

    In this paper, the automating strategies of emergency operation are proposed for achieving optimal shutdown in pressurized water reactors. These strategies can make emergency operation optimal, and as well they considerably lengthen the operator response time. Decision making and control are investigated in order to develop the automating strategies. In decision-making, diagnostic trees are established to automate the diagnostic tasks for selecting appropriate emergency operations, and the decision-making procedure is developed to automate some decisions which must be made on a plant- and event-specific basis. In control, cooldown is planned by establishing operational goals, forming strategies, and specifying operational means and constraints. The reference set points of the controlled parameters are adaptively adjusted through fuzzy reasoning for optimal cooldown and depressurization. The validation of the proposed strategies was carried out using the micro-simulator for the Kori Unit 2 with steam generator tube rupture events. The results indicated that the automated emergency operation successfully drove the plant at full power to a cold shutdown state with all the operational constraints satisfied. View full abstract»

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  • Modeling and simulation of uniformity effects in Cd1-xZnxTe gamma-ray spectrometers

    Publication Year: 1998 , Page(s): 105 - 113
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (337 KB)  

    Monte Carlo simulations of pulse height spectra for Cd1-xZnxTe detectors are used to investigate the effect of variations in alloy composition and carrier drift lengths on energy resolution. The results, which are based on a simple phenomenological model, show that these nonuniformities can have significant detrimental effects on spectrometer performance. For the case of Bridgman-grown material, the orientation of the growth axis relative to the detector axis is shown to be an important consideration, especially for crystals which come from the heel end of a boule, where the composition gradient due to zinc segregation is large. Other effects which we have simulated include growth striations, zinc segregation at grain boundaries, and trapping by inclusions and grain boundaries; each of these effects is detrimental to energy resolution. We conclude that material nonuniformity is a major obstacle to achieving statistically limited energy resolution in cadmium zinc telluride detectors. View full abstract»

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  • Factors determining the damage coefficients and the low-frequency noise in MeV proton-irradiated silicon diodes

    Publication Year: 1998 , Page(s): 89 - 97
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (325 KB)  

    In this paper, the factors determining the reverse current and the recombination lifetime damage coefficients in high-energy proton-irradiated Si junction diodes are studied. These factors are: the particle energy, the crystal growth technique and corresponding starting material quality, and the substrate doping density and type. The observed macroscopic device degradation is discussed in view of the microscopic damage factor, the nonionizing energy loss (NIEL). Finally, the impact of proton irradiation on the low-frequency noise in forward operation is reported. Several experimental factors lead to the conclusion that the change in the flicker noise is related to the created ionization damage in the lateral oxide isolation at the periphery of the diode rather than to the bulk displacement damage. View full abstract»

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  • Calibration of a neutron polarimeter to measure the electric form factor of the neutron

    Publication Year: 1998 , Page(s): 68 - 74
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (273 KB)  

    We measured the analyzing power and the efficiency of a new neutron polarimeter that was designed to measure GEn, the neutron electric form factor. The polarimeter calibration was performed as experiment E377 at the Indiana University Cyclotron Facility (IUCF) with the 14C(p&oarr;,n&oarr;)14N reaction at proton beam energies of 124.0, 164.6, and 199.7 MeV without any shielding material ahead of the polarimeter; in addition, at 164.6 MeV we measured the analyzing power y> with 10 cm of lead, sandwiched between 3.5-cm iron plates, ahead of the polarimeter. View full abstract»

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  • Design and test of elementary digital circuits based on monolithic SOI JFETs

    Publication Year: 1998 , Page(s): 41 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    Silicon on insulator (SOI) junction field effect transistor (JFETs) are used to develop digital gates for cryogenic applications. Only one type of JFET is necessary to design an NOR gate using a basic inverter circuit and a level shifter. The JFET's involved in these designs are available in a process radiation hard at room temperature and operate with improved characteristics at cryogenic temperatures (90 K, temperature of liquid argon calorimeters for high-energy physics). Test circuits have been designed to evaluate their performance. The measured characteristics prove to be satisfactory compared to the simulated ones, although some improvements are still necessary. A propagation delay of 4.4 ns per gate for a power dissipation of ≈3 mW per gate is obtained. With the present development of cryogenic front end preamplifiers for the readout of calorimeter signals, this study opens some prospects for integrating more mixed digital analog electronics such as pipelines within the detectors. View full abstract»

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  • Automatic fitting of Gaussian peaks using abductive machine learning

    Publication Year: 1998 , Page(s): 1 - 16
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (413 KB)  

    Analytical techniques have been used for many years for fitting Gaussian peaks in nuclear spectroscopy. However, the complexity of the approach warrants looking for machine-learning alternatives where intensive computations are required only once (during training), while actual analysis on individual spectra is greatly simplified and quickened. This should allow the use of simple portable systems for fast and automated analysis of large numbers of spectra, particularly in situations where accuracy may be traded for speed and simplicity. This paper proposes the use of abductive networks machine learning for this purpose. The Abductory Induction Mechanism (AIM) tool was used to build models for analyzing both single and double Gaussian peaks in the presence of noise depicting statistical uncertainties in collected spectra. AIM networks were synthesized by training on 1000 representative simulated spectra and evaluated on 500 new spectra. A classifier network determines the multiplicity of single/double peaks with an accuracy of 5.8%. With statistical uncertainties corresponding to a peak count of 100, average percentage absolute errors for the height, position, and width of single peaks are 4.9, 2.9, and 4.2%, respectively. For double peaks, these average errors are within 7.0, 3.1, and 5.9%, respectively. Models have been developed which account for the effect of a linear background on a single peak. Performance is compared with a neural network application and with an analytical curve-fitting routine, and the new technique is applied to actual data of an alpha spectrum. View full abstract»

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  • Design and performance of a low-noise, low-power consumption CMOS charge amplifier for capacitive detectors

    Publication Year: 1998 , Page(s): 119 - 123
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    In this paper, a new design of low noise, low-power consumption charge amplifier is described. Theoretical results show that a total output noise voltage reduction of 0.261 mV has been obtained. This value corresponds to a 46% reduction compared to the noise performance of a conventional charge amplifier. A complete readout system including the proposed charge amplifier has been realized in a 0.8-μm semiconductor on insulator (SOI) bipolar complementary metal-oxide-semiconductor (BiCMOS) process. A measured noise performance of 450 electrons at 0 pF with a slope of 44 electrons/pF for a shaping time of 45 ns, a conversion gain of 20 mV/fC and 1-mW power consumption have been obtained. View full abstract»

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  • Discriminator design considerations for time-interval measurement circuits in collider detector systems

    Publication Year: 1998 , Page(s): 98 - 104
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (262 KB)  

    An analysis of timing jitter from leading-edge discriminators (LED's) and constant-fraction discriminators (CFD's) is presented. The jitter is calculated for the cases of random white noise, coherent noise (e.g., digital switching noise or ac power-line hum), and mixed (random and coherent) noise for both discriminator architectures. A general jitter equation valid for all of these conditions is derived. It is shown that the discriminator bandwidth for minimum jitter is strongly dependent on the amount of coherent noise. This effect is shown to be more pronounced for the LED. Even though off-line walk adjustments are possible for many timing measurements, the CFD is shown to provide a major advantage by acting as a correlated double sampler that removes much of the coherent noise expected in large, multichannel collider detector systems. 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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