Robinet, G 1988 1988 Schotanus, P bibliography 1988 1988 Küchler, G 1-10MeV 1:2+ Be9 J(pi) bibliography 1986 1986 Dupieux, P bibliography proton proton 1988 1988 Muñoz, R C bibliography 1983 1983 Wolschke, U 1986 1986 Tidén, E 1986 1986 Jones, K S 1985 1985 Thiel, W 1985 1985 Heiniger, F 1983 1983 Al-Ani, T H 1984 1984 Kerboul, C 1984 1984 Stoquert, J P 1984 1984 Tayeb-Cherif, R 1983 1983 Jääskeläinen, M 4pi Yb157 Yb158 Yb159 Yb160 Yb161 1983 1983 Lorthiois, I 1983 1983 Hajjar, V 1983 1983 Humbert, B 1981 1981 Martin, P 1982 1982 Cambou, B 1981 1981 Maloeuvre, M 1982 1982 Chalot, J F 1981 1981 Foessel, P 1981 1981 Cordova-Costa, F 1982 1982 Koskelo, M J 1981 1981? Fernández, F L 1981 1981 Greenberg, W L 1980 1980 Barrier, E 1980 1980 Thirion, B 1980 1980 Tendeku, F K 1980 1980 Galli, A 1980 1980 Albrecht, M 1980 1980 Moltz, D M 1979 1979 Ramanantsizehena, P 1979 1979 Pastor, C 1979 1979 Buschbeck, F 1972 1972 Habiballah, B 1979 1979 Werner, G 1978 1978? Ben-Braham, A 1978 1978 Henein, K L 1978 1978 Cabrera, B 1975 1975 Lakhroufi, D 1977 1977 Tassan-Got, L 1977 1977 Jalabert-Scoupe, C 1977 1977 Kostarakis, P 1976 1976 Malriq, J 1976 1976 Weisz, S 1977 1977 Trussell, H J 1976 1976 Heland, M F 1976 1976 Äystö, J 1977 1977 Valette, S 1977 1977 Sauer, Maria 1976 1976 Perrine, J P 1976 1976 Chantepie, Benoit 2008 2008 Vaguine, V 1970 1970 Rahkonen, O K 1977 1977 Schäfer, R 1976 1976 Derbyshire, J A 1995 1995 Echo-planar imaging (EPI) techniques are useful for obtaining magnetic resonance images of dynamic processes because of their minimal acquisition times (typically 16-100ms), and natural T sub 2 or T sub 2 * contrast. This thesis describes the implementation of EPI methods with standard MRI hardware, without the use of actively shielded gradient coils driven by high-performance amplifiers or high bandwidth data acquisition sub-systems. Image reconstruction techniques are discussed and a reconstruction algorithm capable of compensating for some of the time-varying field inhomogeneities induced by gradient switching is described. These methods have been implemented on a variety of MRI systems, demonstrating the robustness of this low-cost approach whereby EPI can be performed routinely using conventional MRI hardware Benítez, R 2000 2000 This work consists in the development of a data acquisition system related to the radiation levels of each one of the laboratories or installations of the ININ, setting up an interconnection of the existing radiological monitoring system (RMS-II), with a personal computer through the use and programming of a data acquisition card (PC-LPM-16). This system works in real time, presenting on the PC screen the measurement of each one of the connected detectors, the alarm signals that are being had been when the allowed levels have been exceeded and the registry of these alarm levels; for their later processing in rapidity graphs of exposure against time. Also aspects such as : brief history of the ionizing radiations and their nature, their interaction with matter and the method which were discovered are treated as well as how it is possible to detect and to measure them. The radiological protection and the standards on which that is based. The RMSII radiation monitoring system and its calibration as well as the obtention of performance curves are treated too. Finally, it is described the performance of the Data acquisition circuit, the based programming in virtual instrumentation and its importance. (Author) Feiel, R 1999 1999 Causes and magnitude of error in measurement and resolution are investigated for electronic speckle photography (ESP), which is used like a strain gauge in material testing. For this purpose a model of the rough surface which allows the description of cross correlation of speckle images under the influence of material strain is developed. The process through which material strain leads to decorrelation of speckle images is shown. The error in measurement which is caused by defocused imaging and statistical errors in the displacement estimation of speckle images is investigated theoretically. The results are supported by simulations and experiments. Moreover the resolution of ESP can be improved through increased optical magnification as well as adjusted aperture. Resolutions which are usually considered to be accessible only to interferometric techniques are achieved. Spring, J A 2000 2000 Helium, with its two electrons and one nucleus, is a three-body system. One of the models for investigating correlated electron motion in this system is autoionization, produced via double excitation of the electrons. Predictions about the autoionization spectrum of helium have differed from each other and from preliminary experimental data. However, previous experiments have not been able to distinguish among the theoretical predictions because their energy resolution is not high enough to resolve the narrow linewidths of quasi-forbidden peaks and the resonances that appear in the highest excited states. Consequently, a team of researchers at Lawrence Berkeley National Laboratory have embarked on a project for building a high-resolution Fourier-Transform Soft X-ray (or VUV) interferometer (FTSX) to provide definitive data to answer remaining questions about the autoionization spectrum of helium. The design and construction of this interferometer is described in detail below, including the use of a flexure stage to provide the large path length difference necessary for high resolution measurements, the manufacture of x-ray beamsplitters, a description of the software, and the solution to the problems of stick-slip, vibration, and alignment. Current progress of its development is also described, as well as future goals. Schulz, C 2000 2000 The pulsed high-flux neutron source ESS, in synergy with advanced neutron optics and spectrometers, will require imaging detectors with better resolution and faster response than presently available. Thus in this work, which is part of a project of the Hahn-Meitner-Institut (HMI), a novel neutron detector has been developed. In the central detector plane a composite foil converter ( sup 1 sup 5 sup 7 Gd/CsI) is located, emitting, after neutron capture and subsequent emission of conversion electrons, a detectable cluster of low-energy electrons. In two adjacent low-pressure gas gaps, sandwiched between fourfold segmented micro-strip gas chamber (MSGC) plates on each side, the clusters are pre-amplified in parallel-plate mode and further in the strong alternating fields between the micro-strips. The advanced micro-strip design is made in multilayer technology on a robust glass substrate. Two closely spaced electrode planes are used for two-dimensional position readout. The expected position resolution is 0.1 - 0.3 mm and the time-of-flight resolution for thermal neutrons is less than 4 ns. Within the scope of this work all electrodes have been optimised for low-pressure, two-stage amplification by a comprehensive modelling. For the second coordinate plane a new electrode structure was found, which gives fast and high signals. Stockinger, M 2000 2000 chosen suitable for ultra-low-power purposes. In a first optimization study the drive current of NMOS transistors is maximized while keeping the leakage current below a limit of 1 pA/mu m. This results in peaking channel doping devices (PCD) with narrow doping peaks placed asymmetrically in the channel. Drive current improvements of 45 % and 71 % for the 0.25 mu m and 0.1 mu m devices, respectively, are achieved compared to uniformly doped devices. The PCD device is studied in detail and explanations for its superior drive performance are given. It is compared to already known device structures and practical alternatives are suggested with respect to its manufacturability. In a second optimization study the gate delay times of complete CMOS inverters are minimized. Both the doping profiles of the NMOS and PMOS transistors are optimized at the same time which results again in PCD devices. The inverter speeds are improved by 54 % and 97 % for the 0.25 mu m and 0.1 mu m devices, respectively. Ultra-low-power CMOS integrated circuits have constantly gained importance due to the fast growing portable electronics market. High-performance applications like mobile telephones ask for high-speed computations and low stand-by power consumption to increase the actual operating time. This means that transistors with low leakage currents and high drive currents have to be provided. Common fabrication methods will soon reach their limits if the on-chip feature size of CMOS technology continues to shrink at this very fast rate. New device architectures will help to keep track with the roadmap of the semiconductor industry. Especially doping profiles offer much freedom for performance improvements as they determine the 'inner functioning' of a transistor. In this work automated doping profile optimization is performed on MOS transistors within the TCAD framework SIESTA. The doping between and under the source/drain wells is discretized on an orthogonal optimization grid facilitating almost arbitrary two-dimensional shapes. A linear optimizer issued to find the optimum doping profile by variation of the doping parameters utilizing numerical device simulations with MINIMOS-NT. Gaussian functions are used in further optimization runs to make the doping profiles smooth. Two device generations are considered, one with 0.25 mu m, the other with 0.1 mu m gate length. The device geometries and source/drain doping profiles are kept fixed during optimization and supply voltages are Pyka, W 2000 2000 mesh of the gas domain above the feature. For each time-step of the deposition simulation the mesh is automatically generated as counterpart to the surface of the three-dimensional structure evolving with time. The CVD model has also been coupled with equipment simulations. recipe, and hence is extremely helpful for the automatic generation of three-dimensional structures. Its usefulness has been proven with several interconnect examples. Regarding topography models, resist development not only turned out to be very helpful for predicting exposed and etched resist profiles within a rigorous lithography simulation, but, by means of benchmark examples, also demonstrated the extraordinary stability of the proposed cellular surface movement algorithm. With respect to modeling of ballistic transport determined low-pressure processes, the equations for the calculation of local etching and deposition rates have been revised. New extensions like the full relation between angular and radial target emission characteristics and particle distributions resulting at different positions on the wafer have been added, and results from reactor scale simulations have been linked to the feature scale profile evolution. Moreover, a fitting model has been implemented, which reduces the number of parameters for particle distributions, scattering mechanisms, and angular dependent surface interactions. Concerning diffusion determined high-pressure CVD processes, a continuum transport and reaction model for the first time has been implemented in three dimensions. It comprises a flexible interface for the formulation of the involved process chemistry and derives the local deposition rate from a finite element diffusion calculation carried out on the three-dimensional Simulation of etching and deposition processes as well as three-dimensional geometry generation are important issues in state of the art TCAD applications. Three-dimensional effects are gaining importance for semiconductor devices and for their interconnects. Therefore a strictly physically based simulation of their topography is required. Accurate investigation of single etching and deposition processes has become equally important as process integration. Within this context several aspects of three-dimensional topography simulation have been covered by this thesis and new and interesting results have been achieved in various areas. The algorithmic core of the cell-based structuring element surface propagation method has been optimized and has been eliminated from its position as factor which predominantly determines the required CPU time. In parallel with investigated optimization techniques and required by various process models, the implementation of the surface normal calculation and the special handling of voids and unconnected parts of the geometry has been completed in three dimensions. A process-step-based solid modeling tool which incorporates layout data as well as aerial image simulation has been supplied. It can be coupled with the topography simulation and includes simple geometrically based models for CMP and oxidation. In the presented combination, the tool makes use of the design information stored in the layout file, combines it with the manufacturing Blaum, K 2000 2000 In the framework of the present thesis the diode-laser quadrupole mass spectrometer system existing in the working group LARISSA was developed for the trace and ultratrace analysis of elements in the range of the rare earths and especially brought to application on the element gadolinium. Akram, N 1999 1999 In this report we describe the concept of adaptive noise canceling, an alternative method of estimating signals corrupted by additive noise of interference. The method uses 'primary' input containing the corrupted signal and a 'reference' input containing noise correlated in some unknown way with the primary noise, the reference input is adaptively filtered and subtracted from the primary input to obtain the signal estimate. Adaptive filtering before subtraction allows the treatment of inputs that are deterministic or stochastic, stationary or time variable. When the reference input is free of signal and certain other conditions are met then noise in the primary input can be essentially eliminated without signal distortion. It is further shown that the adaptive filter also acts as notch filter. Simulated results illustrate the usefulness of the adaptive noise canceling technique. Nawaz, R 1999 1999 The objective of this project is to design and develop a gamma ray survey meter, capable of measuring exposure and providing an alarm when exposure exceeds a pre-set value. This survey meter consists of an ionization chamber, a power supply, a current amplifier and an alarm system. The survey meter was developed using locally available materials. The effective volume of the ion chamber is 486 cm/sup 3/, the useful cm, the outer diameter is 8.62 cm and total length is 30 cm. Argon gas is used as fill gas at a pressure of 160 psi. Power supply was SG3524 as regulating pulse width modulator which provides square waves. Power amplifier using MOSFET transistors is used in push pull configuration to amplify these pulses. Ferrite core transformer is used to step up the voltage with two secondary winding. After rectification, three outputs, i.e. 500-1000 volts, +12 volts and -12 volts are available. This power supply is operated from 12 volt dc source. A current amplifier is designed and developed to amplify current as low as 50 pA. This current amplifier uses Op-Amp LH0042 as an active device. Gain of this current amplifier is 1.5 x 10/sup 7/. An alarm circuit is also designed and developed. Combining all these parts gamma ray survey meter is developed and tested. It can response to an exposure rate of 50 mR/h or less. Along with alarm it had an option for visual indication of dose rate. Mirza, A H 1999 1999 The objective of this project is to carry audio signal from transmitting station to a short distance receiving station along line of sight and also communication through fiber optics is performed, using diode laser light as carrier. In this project optical communication system, modulation techniques, basics of laser and causes of using diode laser are discussed briefly. Transmitter circuit and receiver circuit are fully described. Communication was performed using pulse width modulation technique. Optical fiber communication have many advantages over other type of conventional communication techniques. This report contains the description of optical fiber communication and compared with other communication systems. Iqbal, T 1999 1999 The objective of this project is to re-evaluate the airborne gamma ray spectrometric data of Dadu-Hyderabad-Karachi area obtained during the airborne gamma ray spectrometric survey conducted in early 1984. The data was re-evaluated to discover any new Uranium anomalies which could not be discovered during the early evaluation of data. During this evaluation 116 new anomalies were discovered and these anomalies were transferred to the overlay maps (map 2-map 9). After transferring these anomalies to the overlay maps their location with respect to the fight lines and their occurrences with respect to the geological formations hosting them have been discussed and recommendations for the further detailed exploratory work have been given. Knoke, S 1998 1998 transverse and longitudinal mode is reduced by aberrations of the thermal lens, investigations in the compensation of the thermooptical effects by the laser crystal geometry and the resonator configuration were performed. In addition to the conventional cylindrical rod geometry slab laser crystals with a square cross-section and an internal zig-zag-pass were investigated. Based on the results, the output power of Nd:YAG lasers both in rod and slab geometry could be scaled to more than 20W in single-frequency operation for the first time. A maximum output power of up to 45W was demonstrated with a Nd:YAG rod laser system. Finally principal power limitations of these laser systems could be determined. Laser radiation of high coherence and with diffraction limited beam quality opens up many opportunities for applications in optic metrology, fundamental physics and nonlinear frequency conversion. Light sources with high single-frequency output powers are employed in large Michelson-type interferometers with armlengths of 300meters to 4 kilometers for the detection of gravitational waves. For spectroscopic applications broadband tunable continuous-wave light sources based on optical parametric processes are of interest. An efficient, narrow-band excitation of suitable solid-state materials is realized by single-frequency pump radiation, which allow for the generation of high spectral and spatial power densities in nonlinear crystals. Laser light sources with output powers of more than 10 watts, oscillating in only one transversal and longitudinal mode are a great challenge in laser development. The scope of this work was therefore to develop new concepts for Nd:YAG-lasers, that can deliver high output powers in single-frequency operation and to show principal limits of these systems. The technique of injection locking was applied to realize single-frequency operation of Nd:YAG high-power lasers. In this way the spectral properties of a stable master laser of a lower output power could be transferred to high power lasers. Fiber-coupled diode lasers were chosen to achieve a homogeneous excitation of the Nd:YAG crystals. Due to the fact, that the output power in a single Sumetsberger, B 1998 1998 filling - using a Ba getter in the sealed cell - enables cleaner conditions and, consequently, leads to a correction of the Tl*/Tl self-quenching cross section sigma sub s sub e sub l sub f from 5x10 sup - sup 1 sup 6 cm sup 2 to 2x10 sup - sup 1 sup 7 cm sup 2. We achieved an overall quantum efficiency of 1.5 %, which is an extremely high value for ALFs; the OBW ranged from approx 4.5 to 9 GHz, the signal bandwidth of the filter is 15 MHz. The Thallium Atomic Line Filter (Tl-ALF) is an ultra-narrowband, wide- field-of-view optical, filter for the detection of a weak narrowband laser signal (frequency-doubled Nd:BEL, lambda=535 nm) against a bright broadband background. In an optically pre-excited Tl-vapor incoming 535 nm signal photons are absorbed (from the metastable 6p* sub 3 sub / sub 2 to 7 s) and subsequently re-emitted at 378 nm (7 s to ground-state 6p sub 1 sub / sub 2), up- shifted in energy. All other arriving photons are blocked by the combination of a long-wave-pass, UV-blocking input and a UV-transmitting output filter. The metastable 6p* sub 3 sub / sub 2 level is pumped by 378 nm radiation from a Tl spectral lamp (6p sub 1 sub / sub 2-> 7 s -> 6p* sub 3 sub / sub 2); pump and sensing phases alternate. The optical bandwidth (OBW) of the filter is defined solely by the extremely narrow absorption profile of the atomic transition. Part I deals with the development of the pump lamp. It is an rf-driven, capacitively coupled Tl/rare-gas discharge lamp. Different gas fillings and pressures are investigated with respect to intensity and line-width of the desired 378 nm pump output. An up to fourfold increase in 378 nm output was achieved by modulating the 144 MHz rf driving power with a 1 kHz square wave. This new effect was explained by different diffusion processes in the plasma. Part II describes the measurements performed to optimize the filling of the Tl vapor cell. A new approach in cell Körner, S 2000 2000 automated neutron tomography facility has been built at the Atominstitut with this detector. Digital Image Processing: Due to special detector properties of the CCD-camera NR detector, a standard image processing procedure has been developed that always has to be applied, when the CCD-detector is used. It consists of the following steps: white spot correction - dark frame correction and flat field correction. Radiation, which hits the CCD-chip causes an overflow of one or several pixels, which appears in the image as white spots. These disturbing spots have to be removed by means of digital image processing. Several filters have been tested, but the results were insufficient. Therefore, a new threshold-median-mean value filter was designed and a proper code was written in IDL (interactive data language). The new filter removes white spots very well by hardly blurring the images. A dark frame is an image made with closed camera shutter. It contains undesired detector signal caused by read out noise and dark current produced by the CCD-camera. The dark frame correction is the subtraction of a dark frame from the image of the object. The open beam image is an image taken without sample between collimator exit and detector. It contains spatial fluctuations of the camera sensitivity as well as inhomogeneities of the scintillator and the neutron beam profile. The images of the samples are corrected for these spatial impurities by a division by the open beam signal, which is called flat field correction. Beside this standard image processing method, several other useful image processing tools, as i. e. contrast enhancement, the application of pseudo colors, the use of line profiles and histograms, etc. have been identified and implemented for the enhancement, visualization and data extraction from neutron radiographic images of different samples. These new methods were also successfully applied on the investigation of fusion relevant structure materials and their bonding. Furthermore, another IDL code has been written, which enables convenient data preparation for the 3D reconstruction of samples from 2D neutron transmission images taken from different view angles at the new neutron tomography facility at the Atominstitut. high efficiency and a good linearity. The detector output should be inherently digitized. The key components of the detector system selected on the basis of these requirements consist of a neutron sensitive scintillator screen, a CCD-camera and a mirror to reflect the light emitted by the scintillator to the CCD-camera. This detector design enables to place the camera out of the direct neutron beam. The whole assembly is placed in a light shielded aluminum box. The camera is controlled by a computer. After extensive test measurements performed at Paul Scherrer Institute in Switzerland, the following detector components have been selected: a nitrogen cooled slow scan CCD-camera with 16 bit digitization (65536 gray levels). The chip array consists of (512x512) pixels with a pixel size of (24x24) m2. Depending on the required spatial resolution, it can be chosen between two different lenses, a 58 mm F1,2 and a 180 mm F2,8 lens. The detective area is then (22x22) cm2 or (5x5) cm2, respectively. After extensive test measurements with different neutron sensitive scintillator screens, a Levy Hill ZnS(Ag)-6Li scintillator has been selected. Reasonable exposure times at the thermal column of the TRIGA reactor at the Atominstitut (flux: 1,3x105 neutrons/(cm2s)) can get as low as 20 s per image. This means, that it is possible to perform a set of measurements necessary for neutron tomography (about 200 images) within several hours. Therefore, in a second working step, an entirely Neutron radiography is a method for the visualization of the macroscopic inner-structure and material distributions of various samples. The basic experimental arrangement consists of a neutron source, a collimator functioning as beam formatting assembly and of a plane position sensitive integrating detector. The object is placed between the collimator exit and the detector, which records a two dimensional image. This image contains information about the composition and structure of the sample-interior, as a result of the interaction of neutrons by penetrating matter. Due to rapid developments of detector and computer technology as well as deployments in the field of digital image processing, new technologies are nowadays available which have the potential to improve the performance of neutron radiographic investigations enormously. Therefore, the aim of this work was to develop a state-of-the art digital imaging device, suitable for the two neutron radiography stations located at the 250 kW TRIGA Mark II reactor at the Atominstitut der Oesterreichischen Universitaeten and furthermore, to identify and develop two and three dimensional digital image processing methods suitable for neutron radiographic and tomographic applications, and to implement and optimize them within data processing strategies. The first step was the development of a new imaging device fulfilling the requirements of a high reproducibility, easy handling, high spatial resolution, a large dynamic range, Cortes, C A P 1999 1999 presented in the fifth chapter and they are applied to establish the optimum conditions for the measurement of the activity of a gamma transmitter isolated radioactive source with a spectrometer with germanium detector. (Author) The objective of this work is to analyse the influence magnitudes which affect the activity measurement of gamma transmitter isolated radioactive sources. They prepared by means of the gravimetric method, as well as, determining the uncertainty of such measurement when this is carried out with a gamma spectrometer system with a germanium detector. This work is developed in five chapters: In the first one, named Basic principles it is made a brief description about the meaning of the word Measurement and its implications and the necessaries concepts are presented which are used in this work. In the second chapter it is exposed the gravimetric method used for the manufacture of the gamma transmitter isolated radioactive sources, it is tackled the problem to determine the main influence magnitudes which affect in the measurement of their activity and the respective correction factors and their uncertainties are deduced. The third chapter describes the gamma spectrometry system which is used in this work for the measurement of the activity of isolated sources and also its performance and experimental arrangement that it is used. In the fourth chapter are applied the three previous items with the object of determining the uncertainty which would be obtained in the measurement of an isolated radioactive source elaborated with the gravimetric method in the experimental conditions less favourable predicted above the obtained results from the chapter two. The conclusions are Altintas, E 1998 1998 Pyroelectric coefficient measurements were made in various temperature for poled and unpoled form of PVDF which is pyroelectric material. For these experiments the quasi-static techniques was used. PVDF samples were poled in various electric strengths and relation between poling field strength and pyroelectric coefficient was investigated. It was observed that as poling field strength was increased, the pyroelectric coefficient increased as well. The other study was the effect of poling temperature on pyroelectricity. The best result was obtained when PVDF sample was poled at 340 K. This temperature value is about the Curie temperature of PVDF is and given in the literature. For poled and unpoled samples, there was an increase in pyroelectric coefficient with the increase of measurement temperature up to T sub c. The dielectric permittivity and dielectric loss measurement of PVDF which is a semi-crystalline polymer was taken in the 125-375 K temperature and 100-20 khz frequency interval. The measurements showed that its dielectric loss is low up to 10 khz frequency and the dielectric loss of PVDF increases with temperature. All pyroelectric and dielectric properties were measured in a measurement system which provides a working room for the temperature interval 90-375 K within high vacuum (10 sup - sup 6 torr). Hann, S 2001 2001 This work demonstrates the development of highly sensitive and selective analytical methods, which make use of the hyphenation of high performance ion chromatography (HPIC) to inductively coupled plasma sector field mass spectrometry (ICP-SFMS). On-line coupling a chromatographic separation method with an elemental detection method provides two advantages: (1) the components of a possibly interfering matrix can be separated allowing accurate and precise ultra trace analysis of the element of interest and (2) elemental species of an element can be separated and quantified. In this work, matrix separation methods for interference free determination of 232Th, 234U, 235U and 238U in geological matrices were developed and employed. Furthermore HPIC-ICP-SFMS was applied for ultra trace analysis of Pd in environmental and geological matrices. The usefulness of HPIC-ICP-SFMS for speciation studies was demonstrated by investigating the interaction of an anti-cancer drug (cisplatin) with guanosine monophosphates. Boardman, D 2002 2002 A new monolithic semi-insulating (SI) GaAs sensor design for X-ray imaging applications between 10-100keV has been proposed. Monolithic pixel detectors offer a number of advantages over hybrid bump-bonded detectors, such as high device yield, low costs and are easier to produce large scale arrays. In this thesis, an investigation is made of the use of a SI GaAs wafer as both a detector element and substrate for the epitaxially grown High Electron Mobility Transistors (HEMTs). The design of the HEMT transistors, optimised for this application, were produced with the aid of the Silvaco 'Virtual Wafer Fab' simulation package. It was determined that the device characteristics would consist of a small positive threshold voltage, a low off-state drain current and high transconductance. The final HEMT transistor design, that would be integrated to a pixel detector, had a threshold voltage of 0.17V, an off-state leakage current of approx 1nA and a transconductance of 7.4mS. A number of test detectors were characterised using an ion beam induced charge technique. Charge collection efficiency maps of the test detectors were produced to determine their quality as a X-ray detection material. From the results, the inhomogeneity of SI GaAs, homogeneity of epitaxial GaAs and granular nature of polycrystalline GaAs, were observed. The best of these detectors was used in conjunction with a commercial field effect transistor to produce a hybrid device. The charge switching nature of the hybrid device was shown and a sensitivity of 0.44pC/mu Gy mm sup 2 , for a detector bias of 60V, was found. The functionality of the hybrid sensor was the same to that proposed for the monolithic sensor. The fabrication of the monolithic sensor, with an integrated HEMT transistor and external capacitor, was achieved. To reach the next stage of producing a monolithic sensor that integrates charge, requires further work in the design and the fabrication process. Herbert, D J 2002 2002 Dallimore, M 2001 2001 Ravello-R, Y R 2001 2001 The main aim of this work was to characterize and adjust the neutron radiography facility of the RP-10 nuclear reactor, and therefore be able to offer with this technique services to the industry and research centers in general. This technique will be complemented with others such as x-rays and gamma radiography. First, the shielding capacity of the facility was analyzed, proving that it complies with the radiological safety requirements established by the radiological safety code. Then gamma filtration tests were conducted in order to implement the direct method for image formation, optical density curves were built according to the thickness of the gamma filter, the type of film and the type of irradiation. Also, the indirect method for image formation was implemented for two types of converters: indium and dysprosium. Growth curves for optical density were also made according to contact time between converter-film, for different types of films. The resolution of the facility was also analyzed using two methods: Klasens (1946) and Harms (1986). Harms method came closer to the resolution of the human eye when compared to the Klasens method. Finally, the application fields of neutron radiography are presented, including those conducted at the neutron radiography facility of the RP-10 nuclear reactor. With this work, the RP-10 neutron radiography facility is ready to offer inspection and research services. Chilumbu, C 2002 2002 Bruckner, G 1998 1998 Recent advances in the technology of position sensitive silicon detectors and the corresponding electronics allow the construction of fast time response thermal neutron detectors. These detectors also exhibit excellent position resolution and good efficiency by combination of Silicon sensors with Gadolinium converter foils. The neutron detection is based on the (n,y) reaction in Gd which produces a quite complex conversion electron spectra with significant energy lines between 29 keV and about 200 keV, which can be detected in the Si sensors. Due to the high absorption cross section of Gd the converter can be made very thin. Hence the range of the conversion electrons is sufficient to reach the Si-sensor. This thin converter together with the short charge collection time in Si ensures the good time resolution of the device. We constructed several one- and two-dimensional prototype detectors, using DC and AC coupled silicon strip detectors, pad detectors and different VLSI readout electronics. The position resolution and the detector efficiency were determined for converters made of natural Gadolinium and 90.5 % enriched sup 1 sup 5 sup 7 Gd at wavelengths from 1.1 A to 3.3 A at the TRIGA reactor in Vienna and at the ILL in Grenoble. Spatial resolutions of less than 100 pm and efficiencies up to 40 % have been achieved. The results of these measurements are compared with a simple calculation of the detector operation. Lichtenstein, N 2002 2002 The following work deals with the realization, characterization and modeling of GaInP / AlGaInP high power semiconductor laser diodes in the visible wavelength range. In addition to the exploration and optimization of efficiency, temperature stability and maximum output power of multi-mode lasers especially methods for longitudinal and lateral mode stabilization of high power laser diodes have been investigated. Although often the focus of optimization is on the threshold current density, in this work the performance of the laser diode for an operation point around 1 Watt under continous wave operation is regarded as the figure of merit. It turns out that low carrier densities are key for an efficient reduction of the heterobarrier leakage currents. In addition, large optical cavity structures with low internal losses enable high external quantum efficiencies even for long cavities. Finally high laser effiency as well as an efficient cooling leads to a reduced temperature load for the devices. Based on these results, lateral as well as high-power lateral and longitudinal singlemode operation has been achieved with unstable tapered resonator devices and with monolithically integrated DFB-master-oscillator power-amplifiers realized for the first time ever. Wang, T W 2002 2002 The ability of a human observer to identify an explosive device concealed in complex arrangements of objects routinely encountered in the 2D x-ray screening of passenger baggage at airports is often problematic. Standard dual-energy x-ray techniques enable colour encoding of the resultant images in terms of organic, inorganic and metal substances. This transmission imaging technique produces colour information computed from a high-energy x-ray signal and a low energy x-ray signal (80keV<E<140keV). The broad nature of this materials discrimination places plastic explosive in the same organic window as other innocuous organic items. Also, images of a threat substance which has been masked by other materials will result in colour encoding which is proportional to the effective atomic number of the threat material and the masking material. The work presented in this thesis enables the effective atomic number of the target material within a specified window (6.6 <= Z sub e sub f sub f <= 13) to be automatically discriminated from many layers of overlapping substances. This is achieved by applying a basis materials subtraction technique to the data provided by a wavelet image segmentation algorithm. This imaging technique is reliant upon the image data for the masking substances to be discriminated independently of the target material. Further work investigated the extraction of depth data from stereoscopic images to estimate the mass density of the target material. A binocular stereoscopic dual-energy x-ray machine previously developed by the Vision Systems Group at The Nottingham Trent University in collaboration with The Home Office Science and Technology Group provided the image data for the empirical investigation. This machine utilises a novel linear castellated dual-energy x-ray detector recently developed by the Vision Systems Group. This detector array employs half the number of scintillator-photodiode sensors in comparison to a conventional linear dual-energ Scannavini, M G 2001 2001 The work presented in this thesis is aimed at the study of Compton scatter as an alternative method of collimating gamma-rays in nuclear medicine applications. Conventional approaches to radioisotope medical imaging and their current limitations are examined. The theory of electronic collimation based on Compton scatter is introduced and it is shown that in principle its application could provide an advantageous imaging method, with both high spatial resolution and high sensitivity. The current status of research in the field, of Compton cameras is assessed and potential niches for applications of clinical interest are suggested. The criteria for the design of a Compton scatter camera are examined. A variety of semiconductors are considered for the construction of an electronic collimator and results from Monte Carlo computer simulations are presented for photon energies of clinical interest. It is concluded that the most viable approach is to design a silicon collimator for the imaging of high-energy (511 ke V) photons. A computer model of a Compton camera is developed in order to study the phenomena that affect the angular resolution and the sensitivity of the system. This simulation tool is applied to select the optimum characteristics of the silicon scatter detector. Such results are employed to design and initiate the construction of an experimental prototype of Compton camera, based on the use of double-sided silicon microstrip detectors. The development of special readout electronics required for the camera operation is described. Experimental tests are performed for the characterisation of the silicon strip detectors and the results are presented. Predictions are made on the performance of the designed system. Finally, the current stage of system development is assessed and the main areas for future work are identified. Reis, L C A 2000 2000 This work objectives the design of a hot-cell that will be used for dismantling of nuclear gauges. In the hot-cell, nuclear gauges received as radioactive waste at the Centro de Desenvolvimento da Tecnologia Nuclear - CDTN will be dismantled, in order to decrease the volume of radioactive waste to be stored at the Center. Sources originally conditioned as special form radioactive material will be tested and in case do not present leakage, the respective gauges will be disposable for reusing by radioisotope users. The remaining sources will be taken off the original shielding and conditioned in special packages adequate for storage and disposal. All steps of work, the hot-cell design and methodology for conditioning are also described. Medeiros, I M M A 2001 2001 The gamma-rays in sup 1 sup 4 sup 9 Pm following the beta decay of sup 1 sup 4 sup 9 Nd (1.7 h) have been studied using both single and coincidence gamma spectroscopy techniques. The gamma-rays spectra were obtained with high-resolution HPGe detector. The energies and relative intensities of 198 gamma-rays have been determined, 45 of them were observed for the first time. The coincidence apparatus uses the Camac multidetector module and a HPGe (89cm sup 3) - Ge(Li) (45 cm sup 3). The total number of gamma transitions observed, 181 have been placed in a proposed level scheme with 51 levels. This includes 6 new levels at: 1406.88(6)keV; 1363.85(4)keV; 1328.79(9)keV; 1293.4(4)keV and 1181.18(6)keV. The present results together with the results of earlier studies permitted assignments of spin and parity for many of the levels studied. Fitas, I R 1998 1998 This work presents the results of an experiment series, which was developed intending to determine some parameters' influence in the sensibility of an Ionization Chamber applied to gamma radiation detection. The theoretical results of the mathematical model use to calculate de collected current were compared with experimental ones. Saturation curves were showing the results of the experimental exposures of the detector to a sup 6 sup 0 Co gamma radiation source. During these experiments, some parameters were changed and controlled, like: electrical potential, gas filling type and pressure; for what the Argon, Nitrogen, 'Argometa' and some partial mixtures of A - N sub 2 are used like gas filling. Windischberger, C 2001 2001 Functional magnetic resonance imaging represents a non-invasive technique to examine neuronal activity in the brain. It applies radio waves to excite nuclear spins, using the emitted signal during relaxation for image generation. Signal modulations from local blood flow and oxygenation level changes caused by neuronal activity are the basis for calculating functional brain maps with high spatial resolution. The present work discusses concepts for improving the spatial and temporal resolution, as well as sophisticated analysis approaches. Besides an exhaustive description of image reconstruction algorithms, computational simulations on echo-shifting in echo-planar imaging are presented and effects on spatial resolution are quantified. The results demonstrate that echo-shifting causes only minimal resolution losses for high signal-to-noise data, but leads to severe resolution degradation (up to 30 %) in images with low signal-to-noise ratios. After an overview of the mechanisms that cause fMRI signal changes subsequent to neuronal activity, explorative analysis algorithms like Fuzzy Cluster Analysis, as well as parametric approaches are described and discussed. In the context of fMRI artifacts, effects of respiratory motion are examined. For the first time, well-defined breathing patterns are used to quantify the influences on fMRI signal intensity. Also, the variability of fMRI activation in a mental rotation paradigm are investigated, using single-trial analysis. Such, intra-subject activation consistency was determined successfully. Finally, in a second study on mental rotation explorative data analysis was applied to retrieve neuro-functional hypotheses. Daie-Moreno, J A 1994 1994 This thesis aims to develop a monitor for fast neutron dose, made of graphite, and based on measuring the change in the electric resistivity of the monitor with the irradiation of neutrons. Traditional methods of measuring doses are based on measuring the neutronic activation of pure materials and are, therefore, more complex. The work was carried out in the nuclear research reactor at the La Reina Nuclear Studies Center, belonging to the Chilean Nuclear Energy Commission. Graphite discs of nuclear purity were built for this study and were submitted to successives neutronic irradiations in the nuclear reactor. After each irradiation, the dose of absorbed neutrons and the resistivity of the monitor were measured. The correlation of the data obtained was studied, based on a physical mathematical model that was developed for this purpose. The experimental data that were obtained confirm a sensitive variation in the resistivity of the monitors with the irradiation in the reactor. The model that was developed properly correlated the resistivity with the doses of irradiation. The model's range of validity is for neutronic dose that meet: PHI <=1.3x10 sup 1 sup 8 (cm sup - sup 2) and for neutronic flow densities that meet: 1.40x10 sup 1 sup 3 (cm sup - sup 2 s sup - sup 1)<= THETA <=9.00x10 sup 1 sup 3 (cm sup - sup 2 s sup - sup 1). There are now calibrated graphite monitors to measure the doses of neutrons absorbed by materials irradiated by neutrons in the nuclear reactor Azcurra, M 2002 2002 Monte Carlo simulations of simple neutron oil well logging tools into typical geological formations are presented.The simulated tools consist of both 14 MeV pulsed and continuous Am-Be neutron sources with time gated and continuous gamma ray detectors respectively.The geological formation consists of pure limestone with 15% absolute porosity in a wide range of oil saturation.The particle transport was performed with the Monte Carlo N-Particle Transport Code System, MCNP-4B.Several gamma ray spectra were obtained at the detector position that allow to perform composition analysis of the formation.In particular, the ratio C/O was analyzed as an indicator of oil saturation.Further calculations are proposed to simulate actual detector responses in order to contribute to understand the relation between the detector response with the formation composition Scarioni, L Keyser, U 2003 2003 Behrens, R 2003 2003 Khin, V 1976 1976 Spiwack, A 1976 1976 Cornet, A 1976 1976 Stuck, R 1976 1976 Conrad, R 1975 1975 Casparis, R Egert, G Dachs, H J. Appl. Crystallogr. 1976 1976 Duchateau, J L 1975 1975 Peyer, U 1974 1974 Chatain, D 1975 1975 Kirsch, R 1975 1975? Bonnes, G 1975 1975 Majewski, P 2002 2002 Legou, T Péter, J 2002 2002 Boujrad, A Bloyet, D 2001 2001 Reifarth, R Gils, H J 2002 2002 Schwan, T 1997 1997 Kugelmeier, T 1996 1996 Oliveira-Santos, F D 1995 1995 Saktoun, A 1991 1991 Stassi, P 1989 1989 Saint-Martin, J 1988 1988 Rousset, P 1986 1986 Prunier, J 1974 1974 Schär, F 1973 1973 Besson, R 1974 1974 Persson, B 1974 1974 Knoll, P M 1973 1973 Martin, T 1998 1998 Vallet, C 1994 1994 Bauer, F 1997 1997 Chbihi El Wahoudi, A 1996 1996 Guirande, P 1997 1997 Novotny, T 1997 1997 Guoping, C 1996 1996 Wang, J G 1997 1997 Zhang, S 1996 1996 Chazal, V 1996 1996 Cao, F 1996 1996 Egger, M 1996 1996 Laguna, M 1995 1995 Messous, M Y 1995 1995 Michel, L 1995 1995 Han, L 1995 1995 Bobin, C 1995 1995 Görtz, S 1995 1995 Saoudi, A 1994 1994 Leconte, A 1994 1994 Diarra, C 1994 1994 Bouvier, S 1993 1993 Sun, W Y 1993 1993 Radke, R E C 1993 1993 Sabry, I 1994 1994 Goret, P 1993 1993 Vacanti, G 1993 1993 Von Kienlin, A 1994 1994 Laniece, P 1992 1992 Verghese, S 1993 1993 Glasser, F 1988 1988 Noguès, C 1992 1992 Nahum, M 1992 1992 Kadionik, P 1992 1992 Daba, A G 1992 1992 Ninov, V 1991 1991 Tezkratt, R 1992 1992 Mergui, S 1991 1991 Mahrt-Olt, K 1992 1992 Hofmann, T 1992 1992 Hanelt, E 1991 1991 Delorme, Sophie 1992 1992 Mears, C A bibliography 1991 1991 Zude, E 1991 1991 Lutz, M P bibliography 1991 1991 Bossu, Y 1990 1990 Schöpf, H 1991 1991 Kraus, B bibliography 1991 1991 Aoun, W 1990 1990 Simond, I 1990 1990 El-Manouni, A 1990 1990 Copinet, N 4pi 1990 1990 Meier, H J 1990 1990 Carli, Christian 1989 1989 Sahuc, P 1989 1989 Bakir, B 1989 1989 Strüder, L bibliography 1989 1989 Schröter, A e+ e- 1989 1989 Besson, P 1989 1989 Krichi, M 68000 1988 1988 Heimrich, B bibliography 1989 1989 Pastor, C 4pi 1987 1987 Sterzik, M F 1988 1988