IceTop ist ein Detektorfeld fuer kosmische Strahlung, das momentan am Suedpol errichtet wird. Es ist Teil des IceCube-Observatoriums und wird nach Fertigstellung eine Flaeche von 1km^2 ueberspannen. Es zielt auf den Nachweis von Teilchenkaskaden ab, die von kosmischer Strahlung mit Energien im PeV-Bereich induziert werden. Die Dissertation beinhaltet die erste Analyse hochenergetischer kosmischer Strahlung mit IceTop. Zunaechst wird hierfuer die Lichtausbeute der Detektortanks untersucht. Dies ermoeglicht die Erstellung einer Erwartungswertverteilung der Schauersignale, und eines entsprechenden Likelihood-Rekonstruktionsalgorithmus. Die damit erreichten Aufloesungen werden untersucht und Effizienzen berechnet. Anschliessend wird das Ansprechverhaltenn von IceTop im Bezug auf die Energie genauer evaluiert. Aus den Ergebnissen werden Faltungsmatrizen fuer unterschiedliche Primaerteilchensorten extrahiert. Darauf basierend werden zwei Entfaltungsalgorithmen vorgestellt, und vier Faltungsmatrizen fuer verschiedene Kompositionsannahmen berechnet. Im August 2007 genommene Daten werden in drei Zenithwinkel-Abschnitte eingeteilt und separat mit den Kompositionsmodellen entfaltet. Die resultierenden Spektren decken einen Energiebereich von 1-80PeV ab. Mit der Forderung isotropen Flusses lassen sich Wahrscheinlichkeiten definieren, die sensitiv sind auf die Konsistenz der Kompositionsannahmen. Diese neue Methode ermoeglicht eine Untersuchung der Komposition ohne Zuhilfenahme weiterer Detektorkomponenten. Die Analyse zeigt eine klare Praeferenz der Modelle gemischter Komposition. Schliesslich wird das Spektrum mit der hoechsten relativen Wahrscheinlichkeit untersucht. Die gemessenen Parameter stimmen innerhalb der systematischen Fehler gut mit denen anderer Experimente ueberein. Die ermittelte Position des sogenannten Knies des Spektrums ist 3,1+-0,3(stat.)+-0,3(sys.)PeV, die Exponenten davor und danach sind -2,71+-0,07(stat.) und -3,110+-0,014(stat.)+-0,08(sys.). / IceTop is a square-kilometer scale detector array for highly energetic cosmic radiation. It is a part of the IceCube Observatory that is presently being built at the geographic South Pole. It aims for the detection of huge particle cascades induced by PeV cosmic rays in the atmosphere. This thesis presents the first analysis of highly energetic cosmic ray data taken with IceTop. First, the light response of the IceTop tanks is parametrised as a function of energy and particle type. An expectation function for the distribution of shower signals in the detector plane is developed. Based on that, a likelihood reconstruction algorithm is developed and its resolution and performance is studied. The resulting energy response of the array is investigated to set up response matrices for different primary nuclei and inclinations. Two unfolding algorithms are implemented, and response matrices are modeled for four different composition assumptions. With each assumption, energy spectra are unfolded for three different bins in inclination, using a data sample taken in August 2007. The range of the spectrum is 1-80PeV. Finally, a new analysis method is developed that uses the fact that cosmic rays in the PeV range are expected to be isotropic. It is shown that this requirement can be used for a likelihood estimation that is sensitive to composition without using additional information from other detector components. The analysis shows a clear preference of the mixed composition models over pure proton or iron assumption. The spectrum with the highest likelihood shows good agreement with results from other experiments within the systematic uncertainties. The found position of the so-called knee feature is 3.1+-0.3(stat.)+-0.3(sys.)PeV, the power indices before and after that are -2.71+-0.07(stat.) and -3.110+-0.014(stat.)+-0.08 (sys.).

Este trabalho visa determinar as razões espectrais e o espectro de energia de nêutrons no interior do combustível do Reator Nuclear IPEN/MB-01. Estes parâmetros são de grande importância para determinar com precisão parâmetros físicos de reatores nucleares, como taxas de reação, tempo de vida do combustível e também parâmetros de segurança, tais como reatividade. Para o experimento, utilizou-se detectores de ativação na forma de finas folhas metálicas, introduzidas em uma vareta combustível experimental desmontável. Em seguida, a vareta foi colocada na posição central do núcleo, que tem uma configuração retangular padrão de 26x28 varetas combustível. Foram utilizados detectores de ativação de diferentes elementos como 197Au, 238U, 45SC, 58Ni, 24Mg, 47Ti e 115In para cobrir grande parte do espectro de energia dos nêutrons. Após a irradiação, os detectores de ativação foram submetidos a espectrometria gama utilizando um sistema de contagem com Germânio hiper-puro, afim de se obter a taxa de reação (atividade de saturação) por núcleo alvo. As razões espectrais foram comparadas com valores obtidos através do método de Monte Carlo utilizando o código MCNP-4C. O espectro de energia de nêutrons foi obtido no interior da vareta combustível utilizando o código SANDBP com um espectro de entrada obtido pelo código MCNP-4C, a partir dos valores de atividade de saturação por núcleo alvo dos detectores de ativação irradiados. / This study aims to determine the spectral ratios and the neutron energy spectrum inside the fuel of IPEN/MB-01 Nuclear Reactor. These parameters are of great importance to accurately determine spectral physical parameters of nuclear reactors like reaction rates, fuel lifetime and also security parameters such as reactivity. For the experiment, activation detectors in the form of thin metal foils were introduced in a collapsible fuel rod. Then the rod was placed in the central position of the core which has a standart rectangular configuration of 26x28 fuel rods. There were used activation detectors from different elements such Au-197, U-238, Sc-45, Ni-58, Mg-24, Ti-47 and In-115 to cover a large range of the neutrons energy spectrum. After the irradiation, the activation detectors were submitted to gamma spectrometry using a counting system with high purity Germanium, to obtain the reaction rates (saturation activity) per target nucleus. The spectral ratios were compared with calculated values obtained by the Monte Carlo method using the MCNP-4C code. The neutron energy spectrum was obtained inside the fuel rod using the SANDBP code with an input spectrum obtained by the MCNP-4C code, based on the saturation activity per target nucleus values of the activation detectors irradiated.

Este trabalho visa determinar as razões espectrais e o espectro de energia de nêutrons no interior do combustível do Reator Nuclear IPEN/MB-01. Estes parâmetros são de grande importância para determinar com precisão parâmetros físicos de reatores nucleares, como taxas de reação, tempo de vida do combustível e também parâmetros de segurança, tais como reatividade. Para o experimento, utilizou-se detectores de ativação na forma de finas folhas metálicas, introduzidas em uma vareta combustível experimental desmontável. Em seguida, a vareta foi colocada na posição central do núcleo, que tem uma configuração retangular padrão de 26x28 varetas combustível. Foram utilizados detectores de ativação de diferentes elementos como 197Au, 238U, 45SC, 58Ni, 24Mg, 47Ti e 115In para cobrir grande parte do espectro de energia dos nêutrons. Após a irradiação, os detectores de ativação foram submetidos a espectrometria gama utilizando um sistema de contagem com Germânio hiper-puro, afim de se obter a taxa de reação (atividade de saturação) por núcleo alvo. As razões espectrais foram comparadas com valores obtidos através do método de Monte Carlo utilizando o código MCNP-4C. O espectro de energia de nêutrons foi obtido no interior da vareta combustível utilizando o código SANDBP com um espectro de entrada obtido pelo código MCNP-4C, a partir dos valores de atividade de saturação por núcleo alvo dos detectores de ativação irradiados. / This study aims to determine the spectral ratios and the neutron energy spectrum inside the fuel of IPEN/MB-01 Nuclear Reactor. These parameters are of great importance to accurately determine spectral physical parameters of nuclear reactors like reaction rates, fuel lifetime and also security parameters such as reactivity. For the experiment, activation detectors in the form of thin metal foils were introduced in a collapsible fuel rod. Then the rod was placed in the central position of the core which has a standart rectangular configuration of 26x28 fuel rods. There were used activation detectors from different elements such Au-197, U-238, Sc-45, Ni-58, Mg-24, Ti-47 and In-115 to cover a large range of the neutrons energy spectrum. After the irradiation, the activation detectors were submitted to gamma spectrometry using a counting system with high purity Germanium, to obtain the reaction rates (saturation activity) per target nucleus. The spectral ratios were compared with calculated values obtained by the Monte Carlo method using the MCNP-4C code. The neutron energy spectrum was obtained inside the fuel rod using the SANDBP code with an input spectrum obtained by the MCNP-4C code, based on the saturation activity per target nucleus values of the activation detectors irradiated.

Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-19T14:26:49Z No. of bitstreams: 1 arquivototal.pdf: 24337857 bytes, checksum: 4dcf09dcc5c804cc2b7b0de0feb30331 (MD5) / Made available in DSpace on 2017-09-19T14:26:49Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 24337857 bytes, checksum: 4dcf09dcc5c804cc2b7b0de0feb30331 (MD5) Previous issue date: 2013-03-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The Graphene is a two-dimensional(2-D) semiconductor crystal with null gap, where charge carriers behave as massless particles. In this speci c dynamics in the limit of low energies, the energy dispersion relation is linear, and this material can be described by massless Dirac equation contrasts with the semiconductors, for which the charge carriers are massive. In this framework, there is the problem of the electronic con nement in graphene because of tunneling. For overcome this di culty, is proposed a new model of quantum ring, based on Dirac oscillator and models of rings Tan-Inkson and Bakke- Furtado. From this new coupling, are obtainable the energy spectrum, persistent currents and positive spinors to a graphene sheet with / without topological defect type disclination by massless Dirac equation (2+1). / O grafeno e um cristal bidimensional(2-D) semicondutor com gap nulo, onde os portadores de cargas se comportam como part culas sem massa. Nesta din^amica espec ca, no limite de baixas energias, a rela c~ao de dispers~ao de energia e linear, sendo que este material pode ser descrito pela equa c~ao de Dirac sem massa contrastando com os semicondutores, cujos portadores de cargas t^em massa. Neste quadro, h a o problema do con namento eletr^onico no grafeno devido ao tunelamento. Para contornar esta di culdade, e proposto um novo modelo de anel qu^antico, baseado no oscilador de Dirac e nos modelos de an eis de Tan-Inkson e Bakke-Furtado. A partir desse novo acoplamento, s~ao obtidos o espectro de energia, as correntes persistentes e os espinores positivos para uma folha de grafeno com/sem defeito topol ogico do tipo desclina c~ao, via equa c~ao de Dirac (2+1) sem massa

No description available.

This thesis presents the energy spectrum of cosmic rays deduced from Cherenkov-dominated data measured by the fluorescence detector of the Pierre Auger Observatory. Cherenkov-dominated events, used in the energy spectrum analysis at the Observatory for the first time, enable to decrease the energy threshold for the spectrum measurement down to 1015.5 eV. This energy is more than one order of magnitude lower than in preceding studies. The fluorescence detector was originally designed to detect the fluorescence light generated by extensive air showers in a hybrid mode with the surface detector of the Pierre Auger Observatory. The reconstruction of events dom- inated by Cherenkov light is available due to a newly developed reconstruc- tion technique, the profile constrained geometry fit. Its implementation in the Pierre Auger Observatory software is documented. Aspects of the energy spectrum analysis are described. They consist of exposure calculations done with the use of extensive Monte Carlo simulations, unfolding of the detec- tor effects, and inferring the invisible energy correction in the energy region below 1017 eV. Systematic uncertainties of the measurement are estimated. 1

IceTop ist ein Luftschauerdetektor am geographischen Südpol und die Oberflächenkomponente des Neutrinoteleskops IceCube. Seit der Fertigstellung im Dezember 2010 besteht IceTop aus 81 Detektorstationen auf einer Fläche von einem Quadratkilometer. Die vorliegende Dissertation umfasst eine Analyse von Daten, die im Jahr 2007 mit den 26 damals installierten Stationen genommen wurden. Dazu wurden zunächst Schauerposition und -richtung und ein Maß für die Größe des Schauers aus den Signalen rekonstruiert. Der Zusammenhang zwischen Primärenergie und Schauergröße wurde aus Monte-Carlo-Simulationen bestimmt. Dabei wurde eine Annahme über die chemische Zusammensetzung der kosmischen Strahlen gemacht. Damit wurde das Spektrum der Schauergrößen entfaltet um das Energiespektrum zu bestimmen. Dies wurde getrennt für verschiedene Zenitwinkelbereiche durchgeführt. Das Resultat der Entfaltung hängt von der angenommenen Massenkomposition ab. Die Ergebnisse, der Entfaltung in verschiedenen Zenitwinkelintervallen, müssen übereinstimmen, wenn man Isotropie der komischen Strahlung voraussetzt. Es wurde bereits gezeigt, dass dies ausgenutzt werden kann, um die möglichen Annahmen über die Zusammensetzung einzugrenzen. Eine gute Übereinstimmung von Spektren aus verschiedenen Zenitwinkelbereichen wird unter der Annahme von reinen Protonen als Primärteilchen gefunden, sowie für eine Mischung aus Protonen und Eisen mit einem hohen Protonanteil bei niedrigen Energien und einer Mehrheit von Eisen bei hohen Energien. Unter diesen Annahmen ergibt sich die Position des Knies im Spektrum zu 3,97 bis 4,20PeV. Der spektrale Index unterhalb des Knies ist etwa -2,7 und oberhalb des Knies variiert er zwischen -3,08 und -3,15. Reines Eisen auf der anderen Seite kann mit sehr großer Wahrscheinlichkeit ausgeschlossen werden. Unabhängig von der Annahme über die Zusammensetzung wird oberhalb von etwa 30PeV ein Abflachen des Spektrums mit einem Index von etwa -3,0 beobachtet. / IceTop is an air shower array at the geographic South Pole. It is the surface component of the IceCube neutrino telescope. Since its completion in December 2010, IceTop consists of 81 detector stations covering an area of 1km². In this dissertation, an analysis of data taken in 2007 with 26 IceTop stations operational at that time is presented. Air showers were reconstructed in order to determine the location of the shower core, their direction and the shower size. The relation between primary energy and shower size was determined from Monte Carlo simulations. An assumption was made about the chemical composition of cosmic rays. The information obtained in these simulations were then used to unfold the spectrum of measured shower sizes in order to obtain the all-particle cosmic ray energy spectrum. This was done independently for particles from three different zenith angle intervals. The result of the unfolding depends on the assumed primary composition. Due to the isotropy of cosmic rays, results obtained in different zenith angle intervals must agree. It has already been shown that this requirement can be used to constrain the range of possible assumptions on the chemical composition of primary particles. Good agreement of spectra from different zenith angle ranges has been found under the assumption of pure proton primaries, as well as for a mixture of protons and iron with a relatively large proton contribution at low energies and proton dominance at high energies. Under these assumptions the knee of the cosmic ray energy spectrum has been observed at energies between 3.97 and 4.20PeV. The spectral index below the knee is about -2.7 and varies between -3.08 and -3.15 above the knee. Pure iron as primary particles can be excluded at a high confidence level below 25PeV. Independent of the primary composition assumption a flattening of the energy spectrum with an index of about -3.0 has been observed above 30PeV.

This report describes the development and testing of the upgraded Control and Monitoring (C&Mu) system for the TOFOR neutron spectrometer. TOFOR is currently performing plasma diagnostics for the JET experimental fusion reactor. The purpose of the C&Mu system is to enable monitoring of the amplitude dependent time delays of TOFOR. In order to perform this monitoring function the C&Mu system must comprise a pulsed light source with variable intensity and a reference time signal. In this work a reference time signal has been retrieved from a laser comprising a motorized polarizer. This has been accomplished by installing a photomultiplier tube and a beamsplitter cube. The beamsplitter cube splits the laser light into two parts and directs one part into the photomultiplier tube. The photomultiplier tube converts the light into an electrical reference time signal. A control program has been developed for the motorized polarizer, enabling the user to vary the intensity of the light over the interval from 0% to 100%. The C&Mu system has been performance tested and it was found that the time resolution of the system is about 0.1ns and the time stability of the system is about 0.12ns over 27 hours. The system is more than adequate to monitor variations in time delays at TOFOR of several nanoseconds, over a full JET day. The C&Mu system is ready to be installed on TOFOR.

Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the dots into complex assemblies creates many opportunities for scientific discovery. This motivated our present research work on QDIPs, DWELLs, and graphene like QDs. The intention of this research was to study the size dependent achievements of QDIPs, DWELLs, and graphene like QDs with those of competitive technologies, with the emphasis on the material properties, device structure, and their impact on the device performance. In this dissertation four research studies pertaining to optical properties of quantum dot and dot-in-a-well infrared photodetectors, I-V characteristics of graphene quantum dots, and energy and spin texture of germanene quantum dots are presented. Improving self-assembled QD is a key issue in the increasing the absorption and improving the performance. In the present research work, an ideal self-assembled QD structure is analyzed theoretically with twenty-hole levels (Intraband optical transitions within the valence band) and twenty-electron energy levels (DWELL). Continuing the efforts to study self-assembled QDs we extended our work to graphene like quantum dots (graphene and germanene) to study the electronic transport properties. We study numerically the intraband optical transitions within the valence band of InxGa1-xAs/GaAs pyramidal quantum dots. We analyze the possibility of tuning of corresponding absorption spectra by varying the size and composition of the dots. Both ‘x ’ and the size of the quantum dot base are varied. We have found that the absorption spectra of such quantum dots are more sensitive to the in-plane incident light. We present numerically obtained absorption optical spectra of n-doped InAs/In0.15Ga0.85As/GaAs quantum dot-in-a-well systems. The absorption spectra are mainly determined by the size of the quantum dot and have weak dependence on the thickness of the quantum well and position of the dot in a well. The dot-in-a-well system is sensitive to both in-plane and out-of-plane polarizations of the incident light with much stronger absorption intensities for the in-plane-polarized light. We also present theoretically obtained I-V characteristics of graphene quantum dots, which are realized as a small piece of monolayer graphene. We describe graphene within the nearest-neighbor tight-binding model. The current versus the bias voltage has typical step-like shape, which is due to discrete energy spectrum of the quantum dot. The current through the dot system also depends on the position of the electrodes relative to the quantum dot. In relation to graphene quantum dots, we present our study of buckled graphene-like materials, like germanene and silicene. We consider theoretically germanene quantum dot, consisting of 13, 27, and 35 germanium atoms. Due to strong spin-orbit interaction and buckled structure of the germanene layer, the direction of the spin of an electron in the quantum dot depends on both the electron energy and external perpendicular electric field. With variation of energy, the direction of spin changes by approximately 4.50. Application of external electric field results in rotation of electron spin by approximately 0.50, where the direction of rotation depends on the electron energy.

In this work a numerical approach for the determination of the energy spectra and the calculation of thermodynamic properties of magnetic molecules is presented. The work is focused on the treatment of spin systems which exhibit point-group symmetries. Ring-like and archimedean-type structures are discussed as prominent examples. In each case the underlying spin quantum system is modeled by an isotropic Heisenberg Hamiltonian. Its energy spectrum is calculated either by numerical exact diagonalization or by an approximate diagonalization method introduced here. In order to implement full spin-rotational symmetry the numerical approach at hand is based on the use of irreducible tensor operators. Furthermore, it is shown how an unrestricted use of point-group symmetries in combination with the use of irreducible tensor operators leads to a reduction of the dimensionalities as well as to additional information about the physics of the systems. By exemplarily demonstrating how the theoretical foundations of the irreducible tensor operator technique can be realized within small spin systems the technical aspect of this work is covered. These considerations form the basis of the computational realization that was implemented and used in order to get insight into the investigated systems.