Thesis (M.S.)--University of Michigan, 1958.

The development of a high-resolution gamma ray spectrometer incorporating a germanium lithium-drift radiation detector is described. Sources of electrical noise in detectors and low-noise field-effect transistor preamplifiers are discussed. Modifications were made to available preamplifier circuits with a slight improvement in noise characteristics. A very-low-noise preamplifier using a 2N3823 field-effect transistor was tested, and an unconventional design inductive-load field-effect transistor preamplifier was built and tested. Refinements on germanium detector preparation techniques previously in use are described with particular reference to the starting material used. The design of a stainless steel cryostat to house germanium detectors is discussed. Performance characteristics of a 5 cc. detector are given. Preliminary measurements with it of the Doppler broadening of the annihilation peak in Ni and Zn are presented. A spectrum of annihilations of ortho-positronium formed in Freon 12 is given. The detector system is evaluated with reference to suitability in positron physics. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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No description available.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2006. / Ansari, Armin, Committee Member ; Wang, C.-K. Chris, Committee Member ; Hertel, Nolan, Committee Chair.

Two types of experiments involving the Mossbauer atom as a dilute impurity in a host lattice are discussed. For a zero-phonon experiment with Fe⁵⁷ in Pt¹⁹⁵ at room temperature, the expected shift of the central Mossbauer peak is [symbol omitted]/3000. The minimum time required to experimentally determine this shift to within 10% is found to be 16 weeks of counting with a 5 millicurie source. For a one-phonon experiment with Fe⁵⁷ in Pt¹⁹⁵, the count rate due to resonance scattering is found to be 3.14 x 10⁻⁴/sec., and the count rate due to Rayleigh scattering 2.2 x l0⁻²/sec. The case of Fe⁵⁷ in Be⁹ is also discussed. An air trough Mossbauer shift spectrometer constructed to perform the zero-phonon experiment is described. Vibrations present in this apparatus, making it inadequate for experimental work, are discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

One of the main challenges during the ultra-high count rate gamma-ray spectrometry is the large dead time. Using a LaBr3(Ce) detector (TRT 0.3 µs, TFT 0.5 µs), with an input count rate of 4.8×10E5 cps, the dead time could be as high as 87%. Such high dead time could significantly reduce the quality of the data collected as a considerable number of counts would be lost. Thus, this project aimed to reduce the dead time by modifying the detector system. Based on the setup used by previous research, the new system has its preamp, which is normally used for signal processing, removed. Experiments were made with calibration sources to optimize the new system. The calibration sources (Cs-137 and Co-60), Cs-137 resin sources, and Shephard Cs-137 sources were used to create different count rates, with the highest being 1.22×10E6 cps, for measurements. Side-by-side measurements were performed with the setup with preamp and the one without preamp at various count rates. The analysis, which focused on the dead time and resolution, shows the setup without preamp would have much lower dead time, especially during ultra-high count rate measurements. The method was proved to be successful, for, at 4.8×10E5 cps, the dead time decreased from 87% to 54%. / Thesis / Master of Science (MSc)

Digitized by Kansas Correctional Industries

Lithium ion batteries, due to their relatively high energy density, are now widely used as the power source for portable electronics. Commercial lithium ion cells currently employ layered LiCoO₂ as a cathode but only 50% of its theoretical capacity can be utilized. The factors that cause the limitation are not fully established in the literature. With this perspective, prompt gamma-ray activation analysis (PGAA) has been employed to determine the hydrogen content in various oxide cathodes that have undergone chemical extraction of lithium (delithiation). The PGAA data is complemented by data obtained from atomic absorption spectroscopy (AAS), redox titration, thermogravimetric analysis (TGA), and mass spectroscopy to better understand the capacity limitations and failure mechanisms of lithium ion battery cathodes. As part of this work, the PGAA facility has been redesigned and reconstructed. The neutron and gamma-ray backgrounds have been reduced by more than an order of magnitude. Detection limits for elements have also been improved. Special attention was given to the experimental setup including potential sources of error and system calibration for the detection of hydrogen. Spectral interference with hydrogen arising from cobalt was identified and corrected for. Limits of detection as a function of cobalt mass present in a given sample are also discussed. The data indicates that while delithiated layered Li[subscript 1-x]CoO₂, Li[subscript 1-x]Ni[subscript 1/3]Mn[subscript 1/3]Co[subscript 1/3]O₂, and Li[subscript 1-x]Ni[subscript 0.5]Mn[subscript 0.5]O₂ take significant amounts of hydrogen into the lattice during deep extraction, orthorhombic Li[subscript 1-x]MnO₂, spinel Li[subscript 1-x]Mn₂O₄, and olivine Li[subscript 1-x]FePO₄ do not. Layered LiCoO₂, LiNi[subscript 0.5]Mn[subscript 0.5]O₂, and LiNi[subscript 1/3]Mn[subscript 1/3]Co[subscript 1/3]O₂ have been further analyzed to assess their relative chemical instabilities while undergoing stepped chemical delithiation. Each system takes increasing amounts of protons at lower lithium contents. The differences are attributed to the relative chemical instabilities of the various cathodes that could be related to the position of the transition metal band and the top of the O²-:2p band. Chemically delithiated layered Li[Li[subscript 0.17]Mn[subscript 0.33]Co[subscript0.5-y]Ni[subscript y]]O₂ cathodes have also been characterized. The first charge and discharge capacities decrease with increasing nickel content. The decrease in the capacity with increasing nickel content is due to a decrease in the lithium content present in the transition metal layer and a consequent decrease in the amount of oxygen irreversibly lost during the first charge. / text