京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18672号 / 理博第4021号 / 新制||理||1580(附属図書館) / 31605 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 中家 剛, 准教授 市川 温子, 教授 谷森 達 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Doctor of Philosophy / Department of Physics / Glenn A. Horton-Smith / The next generation of nuclear fission reactor based neutrino experiments seeking to measure the Theta-13 mixing angle rely upon measurements made by detectors placed close to the reactor, and therefore less shielded from cosmic ray muons by the earth. 9Li production in liquid scintillator by these cosmic ray muons becomes a serious problem for these experiments that must be dealt with since the 9Li production rate is still a significant fraction of the neutrino interaction rate. This 9Li background reduces the experiment’s sensitivity to measure the Theta-13 mixing angle. This thesis discusses a small detector designed to measure the 9Li production rate in liquid scintillator at the earth’s surface by cosmic ray muons. The detector was designed, built, and finally, calibrated. The ability to find the signals necessary to actually measure the 9Li production rate is shown, establishing that this detector will be able to measure the production rate. A 90% significance level upper limit for the 9Li-like production rate, based on only 3.5 days worth of data, is reported as 213 9Li-like events per day per ton.

The Daya Bay experiment has determined the last unknown mixing angle $theta_{13}$. This thesis describes the layout of the experiment and the detector design. The analysis presented in the thesis covered the water attenuation, spent fuel neutrino and electron anti-neutrino spectrum. Other physics analysis and impact to future experiments are also discussed. / Ph. D.

Orientador: Ernesto Kemp / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-14T15:55:52Z (GMT). No. of bitstreams: 1 GomezGonzalez_LuisFernando_M.pdf: 24049879 bytes, checksum: 5735f73e431cd5cc1a8ba7358ca57950 (MD5) Previous issue date: 2009 / Resumo: Reatores nucleares constituem uma copiosa fonte de anti-neutrinos, cujo espectro é determinado pelo decaimento beta dos isótopos radioativos presentes no combustível nuclear. A medida que o combustível é consumido sua composição isotópica é alterada, com reflexos diretos no espectro de anti-neutrinos. Desse modo, detectores de anti-neutrinos podem ser aplicados no monitoramento da composição isotópica do combustível de reatores nucleares e da taxa de consumo deste combustível de uma forma não intrusiva e independente de informações do operador da usina nuclear. Nesse trabalho, investigamos os requisitos da resolução em energia de um detector de anti-neutrinos, posicionado na proximidades do reator, que possibilitem uma precisa espectroscopia de forma a permitir a reconstrução das contribuições individuais dos isótopos 235U, 2380, 239pu e 241Pu no número total de fissões. Para esse fim, construímos simulações de Moute Carlo de modo a avaliar os desvios em energia intrínsecos de um possível detector do Projeto Neutrinos Angra. Por fim, analisamos os dados de simulação utilizando modelos da literatura e propomos um modelo novo, na tentativa de melhor ajustar nossos dados de simulação / Abstract: Nuclear reactors are an abundant source of anti-neutrinos, whose spectrum is determined by the hera decay of radioactive isotopes in the nuclear fuel. As the fuel is consumed, their isotopic composition is altered, with direct consequences on the spectrum of anti-neutrlnos. Thus, detection of anti-neutrinos can be applied in monitoring the isotopic composition of fuel in nuclear reactors and their rate of consumption, on a non-intrusive and independent way from the nuclear plant operator information. In this study, we investigated the requirements in energy resolution of an anti-neutrino detector, positioned in close proximity to the reactor, enabling a precise spectroscopy to enable reconstruction of the individual contributions ofthe isotopes 235U, 238U, 239Pu and 241Pu to the total flux. To do this, we built a Monte Carlo simulations to evaluate the intrinsic energy resolution of a possible detector of the Neutrinos Angra Project. Final1y, we analyzed the simulated data using models found in article and propose a new model in an attempt to berrer adjust our data / Mestrado / Física das Particulas Elementares e Campos / Mestre em Física

Simulations have demonstrated that high-energy neutrinos (E > 1017 eV) are detected cost-efficiently via the Askaryan effect in ice, where a particle cascade induced by the neutrino interaction produces coherent radio emission that can be picked up by antennas installed below the surface. A good knowledge of the near surface ice (aka firn) properties is required to reconstruct the neutrino properties. In particular, a continuous monitoring of the snow accumulation (which changes the depth of the antennas) and the index-of-refraction profile are crucial for an accurate determination of the neutrino's direction and energy. 14 months of data of the ARIANNA detector on the Ross Ice Shelf, Antarctica, are presented where a prototype calibration system was successfully used to monitor the snow accumulation with unprecedented precision of 1 mm. Several algorithms to extract the time differences of direct and reflected (off the surface) signals (D'n'R time difference) from noisy data (including deep learning) are explored. This constitutes an in-situ test of the neutrino vertex distance reconstruction using the D'n'R technique which is needed to determine the neutrino energy. Additionally, an in-situ calibration system is proposed that extends the radio detector station with a radio emitter to continuously monitor the firn properties by measuring D'n'R time difference. In a simulation study the station layout is optimized and the achievable precision is quantified.

High-energy neutrino physics offers a unique way to investigate the most violent phenomena in our universe. The detection of energies above E > 1017 eV is most efficient using the Askaryan effect, where a neutrino-induced particle shower produces coherent radio emission that is detectable with radio antennas. By using radio techniques large volumes can be covered with few stations at moderate cost exploiting the large attenuation length of radio in cold ice. Key to the reconstruction of the neutrino properties visa precise and continuous monitoring of the firn properties. In particular the snow accumulation (changing the absolute depth of the antennas thus the propagation path of the signal) and the index-of-refraction profile are crucial for the neutrino energy and direction reconstruction. This work presents an in-situ calibration design that acts as an detector extension by adding additional emitter antennas to the station design to continuously monitor the firn properties by measuring the direct and reflected signals (D’n’R). In a simulation study the optimal station layout is determined and the achievable precision is quantified. Furthermore 14 months of data from an ARIANNA station at the Ross Ice Shelf, Antarctica, are presented where a prototype of this calibration system has been successfully installed to monitor the snow accumulation with unprecedented precision of 1 mm. Several algorithms, including deep learning algorithms, to compute the D’n’R time difference from radio traces are considered.