Literatura científica selecionada sobre o tema "Ramo-Shockley Theorem"

Motivated by a recent approach to solve quantum dynamics with full Coulomb correlations [X. Oriols, Phys. Rev. Lett.98 (2007) 066803], we present here an extension of the Ramo–Shockley–Pellegrini theorem for quantum systems to compute the total (conduction plus displacement) current in terms of quantum (Bohmian) trajectories. By way of test, we derive an extension of the Ramo-Shockley-Pellegrini theorem using standard quantum mechanics and we compare it to our former result. As expected, both formulations give identical results, however we emphasize the numerical viability of computing self-consistently the total current by means of quantum trajectories in front of the difficulties to do it in terms of standard quantum mechanics.

Several methods to derive relationships between currents in the external circuit and variations in parameters of samples that induce such currents are considered. The relationships generalize the Shockley–Ramo theorem and may serve as a development of Kirchhoff laws for electrical circuits.

By means of the Ramo–Shockley–Pellegrini theorem, an analytical discussion on how different geometries of gate-all-around 1D ballistic transistors affect their time-dependent current and their (intrinsic) high-frequency noise spectrum is presented. In particular, it is shown that the frequency range where the high-frequency noise spectrum is meaningful increases when the lateral area is decreased.

The damage produced by 2 MeV protons on a 4H-SiC Schottky diode has been investigated by monitoring the charge collection efficiency as the function of the ion fluence. A new algorithm based on the Shockley-Ramo-Gunn theorem has been developed to interpret the experimental results. The fitting procedure provides a parameter which is proportional to the average number of active electrical traps generated by a single ion, which can be profitably used to estimate the radiation hardness of the material.

Le suivi en ligne du flux de neutrons rapides en réacteur à eau est un enjeu pour l’instrumentation in-core des réacteurs et notamment pour les expériences d’irradiation de matériaux. Les collectrons sont des détecteurs utilisés pour la surveillance en ligne des flux de neutrons thermiques et/ou de rayonnements γ. Fonctionnant sans polarisation et pour des débits de fluence importants, ils sont particulièrement adaptés à des mesures en cœur. Les collectrons sont principalement coaxiaux, composés de trois éléments principaux : un émetteur, un isolant et une gaine. En choisissant judicieusement ces trois matériaux, il est possible d’accroître la sélectivité des interactions avec une particule d’intérêt (neutrons ou γ). Cette thèse vise à développer un nouveau collectron sélectif au flux de neutrons rapides dans le but de monitorer les expériences d’irradiation de matériaux. L’une des contraintes majeures de la conception d’un tel détecteur est l’environnement de mesure où les neutrons rapides ne sont pas prédominants. Obtenir une contribution significative des neutrons rapides nécessite de minimiser les contributions des neutrons thermiques et des γ. Le développement et les tests en réacteur d'un prototype de collectrons sensibles aux neutrons rapides sont les principaux objectifs de ces travaux de thèse. Une compréhension complète de la génération du signal collectron est nécessaire pour le développement de nouveaux détecteurs. Or, certains aspects théoriques de la génération de courants dans les collectrons restent encore incomplets. Dans le cadre de ces travaux, et dans le but d’améliorer la modélisation numérique des collectrons, tous les mécanismes affectant la génération de courant sont étudiés. Appuyé par une expérience sur faisceau d’électrons, la résolution des équations de continuité et l'application du théorème de Shockley-Ramo au cas des collectrons ont permis d’améliorer la compréhension du fonctionnement des collectrons. La difficulté principale dans la conception d'un collectron sensible et sélectif aux neutrons rapides réside dans le choix des matériaux. Les sections efficaces des matériaux utilisés usuellement sont beaucoup plus importantes pour neutrons thermiques que pour les neutrons rapides. Dans un environnement réacteur, les rayonnements γ sont également présents dans des proportions significatives. Les interactions des rayonnements γ avec les matériaux composant le collectron peuvent également produire un signal important par rapport aux interactions des neutrons rapides. Par conséquent, le matériau sélectionné pour l’émetteur du collectron développé doit maximiser la contribution des neutrons rapides, tandis que l’isolants et la gaine doivent produire un signal très limité. L'estimation des contributions du courant collectron est possible grâce à la modélisation et aux calculs numériques. Cela a conduit à la définition d'un prototype de collectron sélectif aux neutrons rapides. Des prototypes de ce détecteur innovant ont été construits et testés dans le réacteur de recherche slovène TRIGA Mark II (Jožef Stefan Institute), fournissant une preuve de concept pour le matériau émetteur spécifique proposé
Selective on-line measurement of fast neutron flux in a water-pool type reactor environment remains a challenge for in-core measurements. Self-powered neutron or gamma detectors (SPDs) are detectors used for on-line monitoring of thermal neutron and/or gamma ray fluxes. Operating without high voltage, their use is suitable for high flux levels and thus for in-core measurements. SPDs are mainly coaxial and consist of three main components: an emitter, an insulator and a sheath. Provided a wise choice of these three materials, the SPD could focus on interactions with particles of interest (neutrons or gamma). To meet the need for on-line fast neutron measurements in material testing reactors (MTR), this thesis aims to develop a new Self-Powered Neutron Detector (SPND) selective to fast neutrons flux. The design of such a detector with significant fast neutron contribution to the signal means reducing thermal neutron and gamma contributions to a minimum level in radiation environments where fast neutrons are the least flux. Prototype development and reactor tests of this new selective self-powered neutron detector are the main objectives of this PhD thesis work. Despite several publications in literature, some theoretical aspects of signal generation in SPDs remain incomplete, especially when it comes to small contributions. Also within the framework of this PhD thesis, and with the aim of a better understanding of SPNDs operation, all mechanisms affecting the current generation are studied by means of an electron beam experiment, helping for a better understanding of the behavior for insulation part of the sensor. Solving continuity equation systems and applying the Shockley-Ramo theorem to the SPD case is also part of this study. A complete understanding of the SPD signal generation is required in the development of new detectors.The main effort in designing a SPND sensitive and selective to fast neutrons lies in the choice of materials. In fact, thermal neutron cross-sections for common materials are much larger than fast neutron cross-sections. In reactor environment, gamma rays are also present in significant proportions. Gamma ray interactions with detector materials can also produce a significant signal compared to fast neutron interactions. Consequently, the SPND materials must maximize the fast neutron contribution. Fast neutron interactions have to be predominant in the emitter to induce a sufficiently large signal for measurement, meanwhile insulator and sheath materials shall produce a very limited signal. The estimation of the SPND current contributions is possible by means of numerical modelling and calculations. This led to the definition of a prototype of a fast neutron selective SPND. Prototypes of this innovative detector have been manufactured and tested at the Slovenian TRIGA Mark II research reactor (Jožef Stefan Institute), providing a proof of concept for the proposed specific emitter material

Normally modern detectors are read out electronically. The signals that are induced on the detector electrodes are generated by the movement of charges relative to the electrodes. The general principle for the calculation of the signals is introduced on the basis of the Shockley-Ramo theorem applying the concept of weighting fields to an arbitrary number of electrodes in field volumes with and without space charge. Examples of the time development of signals are calculated for electrode arrangements with plate and cylinder geometry and for electrodes with strip or pixel segmentation.

Abstract The ideas that drive the design of particle detectors are presented in Chapter 3. It starts from the interactions of heavy charged particles with matter deriving the Bohr formula and extending it to the Bethe formula. Electron interactions with matter are discussed in general and illustrated in detail thanks to Anderson’s experiment, which brought the discovery of the first anti-particle. Photon interactions are introduced on the general ground as a function of the photon energy (photoelectric, Compton, and pair production) and described together with photon detectors for energy measurements. The basic principles – from the Bethe formula to the Shockley–Ramo theorem – are applied to gaseous detectors (ionization and proportional chambers, Multi-Wire Proportional Chamber (MWPC), time projection chamber (TPC), and Geiger counters). We then describe the physics of trajectory trackers and multiple Coulomb scattering. Finally, the most important tool for detector simulation is introduced: the Monte Carlo technique.

This paper presents the Finite Element Analysis (FEA) of an ionic polymer-metal composite (IPMC) material. The IPMC materials are known to bend when electric field is applied on the electrodes. The material also produces potential difference on the electrodes when is bent. Several authors have used the FEA to describe that fenomenon and rather precise basic Finite Element (FE) models already exist. Therefore the current study is mainly focused on the modeling of the electrodes of IPMC. The first goal of this research is to model the electric currents in the electrodes. The basis of the electric current calculations is the Ramo-Shockley theorem, which has been used in the other areas of physics to describe the currents in a circuit due to a charge movement in a media. We have used the theorem to calculate the current density in the continuous electrodes of IPMC due to the ion migration in the backbone polymer. Along the current densities we are able to calculate voltage on the electrode at a given time moment. The model is demonstrated to give some physically reasonable results. However, the model is rather complex and as the solution times are quite large, some possible optimizations have been considered as well. The second goal of this study is to include the dynamic resistance and capacitance of the electrodes in our model. Lot of research has been done to develop a physically reasonable capacitor-resistor model of an IPMC and the results have been promising. Furthermore, some authors have managed to develop partial differential equations (PDE) to describe the model. We try to include some simplified versions of those equations into our physical model. As the FE model for IPMC is nonlinear and gets complicated very fast when additional equations are added, the final sections of this paper briefly considers some novel optimization ideas in regard to modeling IPMC with FE method.