Browsing by Subject "Muons"
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Item Localization and local motion of muons in antiferromagnetic oxides: vanadium oxide and iron oxide(Texas Tech University, 1986-05) Chan, Kwaichow B.The behavior of muons in the antiferromagnetic insulating oxides, a-Fe203 sirid V2O3 has been examined using dipole field calculations. The results verify muon sites suggested by potential calculations for hydrogen in similar systems, and imply the formation of muon-oxygen bonds at low temperatures. In both of these corundum structured oxides two sets of muon sites are located, each approximately lA from an oxygen ion. These are the Rodriguez sites in the vacant octahedral interstices of the oxygen ions and the Bates sites near the oxygen basal plane. Only a subset of sites found in a-Fe203are also found V2O3 because of a slight distortion of V2O3 from rhombohedral to monoclinic symmetry below the metal-insulator temperature at 155K. Above 350K, muons diffuse globally and no MuSR precession signal is observed. At intermediate temperatures, between 120K and 350K, muons diffuse locally as illustrated in the case of a-Fe203. Calculations show that diffusion among a subset of sites is consistent with the data in this temperature range. It is concluded that muon-oxygen bonding and motion among a group of closely spaced sites are the low temperature localized states for muons in the corundum structured oxides.Item A measurement of muon neutrino disappearance with the MINOS detectors and NuMI beam(2008-12) Ospanov, Rustem; Lang, KarolMINOS is a long-baseline two-detector neutrino oscillation experiment that uses a high intensity muon neutrino beam to investigate the phenomena of neutrino oscillations. The neutrino beam is produced by the NuMI facility at Fermilab, Batavia, Illinois, and is observed at near and far detectors placed 734 km apart. The neutrino interactions in the near detector are used to measure the initial muon neutrino flux. The vast majority of neutrinos travel through the near detector and Earth matter without interactions. A fraction of muon neutrinos oscillate into other flavors resulting in the disappearance of muon neutrinos at the far detector. This thesis presents a measurement of the muon neutrino oscillation parameters in the framework of the two-neutrino oscillation hypothesis.Item Item Muon sites in transition-metal oxides(Texas Tech University, 1988-08) Chan, Kwaichow B.Muon behavior in a selected series of transition-metal oxides has been investigated by the Muon Spin Rotation (fiSR) technique. The materials studied are the corundum structured oxides (M2O3: M=Fe, Cr, V, Ti) and the high-Tc superconducting oxides in Y-Ba-Cu-0 system. The muon is first implanted into the oxide crystalline and its subsequent behavior in the presence of magnetic field is monitored through counting the positron emitted by the decayed muon. The muon is found to behave like a free muon and to become localized at low temperatures and diffusional at higher temperatures. The location of the muon is important for interpreting the |J.SR data. To identify muon sites, a combination of electrostatic potential and magnetic dipolar field calculation is used. Dipolefield calculation allows matching the experimental results to the calculated values if the origin of the magnetic field is dominantly dipolar as in the case V2O3 and Cr203. In the potential model, in addition to the coulombic interaction, the muon is assumed to form a muon-oxygen bond in analogy to the hydroxyl bond (0H)~. Morse potential is used to simulate the µ+o= bonding. The potential minima found are then assigned as muon sites. A set of muon sites thus found in these oxides and their implications are presented. The inadequacies of the classical model and a more realistic model for predicting muon sites are also discussed.Item Muonic x-rays and equivalent radius of nuclear charge distribution(Texas Tech University, 1973-08) Khan, Mazahir HasanNot availableItem Muonium defect centers in aluminum nitride and silicon carbide(Texas Tech University, 2007-05) Bani-Salameh, Hisham Nahar; Lichti, Roger L.; Lamp, Carl D.; Myles, Charles W.; Estreicher, Stefan K.We report the results of ƒÝSR measurements on Aluminum Nitride (AlN) and Silicon Carbide (SiC). The importance of studying muonium states comes from its analogy to atomic hydrogen making it an excellent source of information on isolated hydrogen impurities in various materials. Neutral muonium exists in AlN to high temperatures, a large hyperfine constant of ~4450 MHz with a small temperature-dependent dipolar contribution indicating weak anisotropy is obtained from decoupling curves. Tentative site assignments and results on the diffusion of these Mu0 centers along with the associated conversion rates are presented. The low-energy location of neutral muonium in AlN lies off-axis in the unblocked c-axis channels at sites anti-bonding to Aluminum. Motion of Mu0 at low temperatures is due to tunneling and is dominated by thermally activated processes at high temperatures. Diffusion-limited conversion out of the mobile Mu0 state is observed in both low and high temperature regimes. All electrical types, high-resistivity, n-type and p-type, of the hexagonal 4H and 6H polytypes of SiC were studied. Two isotropic Mu0 states were found in 4H-SiC and a total of four Mu0 states were seen in the 6H-SiC samples. Temperature dependence of the hyperfine constant (AHF) for each state is discussed. Data on the hyperfine interactions imply isotropic atomic-like states with no hint of any bond-centered Mu0 species in SiC. Temperature and field dependences of signal amplitudes and relaxation rates were studied. Tentative assignments for locations and some of the dynamical characteristics of the muonium centers have been reached; however, more work is needed to fully understand the nature of these centers in SiC.Item Observation of disappearance of muon neutrinos in the NuMI beam(2008-05) Pavlović, Žarko, 1977-; Kopp, SachaThe Main Injector Neutrino Oscillation Search (MINOS) is a two detector long-baseline neutrino experiment designed to study the disappearance of muon neutrinos. MINOS will test the v[subscript mu] → v[subscript tau] oscillation hypothesis and measure precisely [Delta]m[superscript 2 subscript 23] and sin² 2[theta subscript 23] oscillation parameters. The source of neutrinos for MINOS experiment is Fermilab's Neutrinos at the Main Injector (NuMI) beamline. The energy spectrum and the composition of the beam is measured at two locations, one close to the source and the other 735 km downstream in the Soudan Mine Underground Laboratory in northern Minnesota. The precision measurement of the oscillation parameters requires an accurate prediction of the neutrino flux at the Far Detector. This thesis discusses the calculation of the neutrino flux at the Far Detector and its uncertainties. A technique that uses the Near Detector data to constrain the uncertainties in the calculation of the flux is described. The data corresponding to an exposure of 2.5×1020 protons on the NuMI target is presented and an energy dependent disappearance pattern predicted by neutrino oscillation hypotheses is observed in the Far Detector data. The fit to MINOS data, for given exposure, yields the best fit values for [Delta]m[superscript 2 subscript 23] and sin² 2[theta subscript 23] to be (2.38[superscript +0.20, subscript -0.16] x 10⁻³eV²/c⁴ and 1.00[subscript -0.08], respectively.Item Radial-moment analysis for muonic x-rays(Texas Tech University, 1977-12) Ray, Asok KumarThe crucial question to be answered in studying the radial shapes of spherical nuclei is: éxactly what parameter of the nuclear charge distribution is determined by each transition energy in muonic atoms? The measurement of the 2p , ->-ls. . energy for a particular muonic atom determines, of course, only a single parameter of the nuclear charge distribution. Since the earliest days of analyzing muonic x-ray energies, workers have recognized that different transitions determine different parameters, so that, in principle, energy measurements for a number of different transitions in a given atom might provide information about the radial shape of the nuclear charge density. T ^Y radial shape, we mean simply the form of the charge density p(r) "] . However, it has not been clear exactly what nuclear parameter is determined by a particular transition, except in the low-Z limit, where non-relativistic perturbation theory shows that level shifts are proportional to even moments of the charge density. In this limit, for instance, the 2p->-ls transitions measure the mean square radius . One occasionally hears or reads that the same is true for heavy atoms. This is not then case. Even for Z as low as 6, the 2p-^ls transitions do not determine exactly the mean square radius.Item Search for the muon-stopping sites in rare-earth orthoferites [i.e. orthoferrites] by means of dipolar calculation(Texas Tech University, 1986-08) Lin, Tsai-kuThe uSR data for RFe03 (R=Er, Ho, Y, Dy, Eu and Sm) indicates that three separate localized muon sites may exist. In Ref.(12) one of these sites lying in the R-0 plane of the perovskite structure was identified, hereafter referred to as the Holzschuh-1 site. We have performed dipole sum calculations of the internal fields in the orthoferrites for the magnetic orderings present within the series. Using a weighting scheme requiring a match to the experimental values for the magnitude and directions of internal fields from observed uSR signals, and a muon-oxygen distance consistent with bond formation, we have verified the Holzschuh-1 site and have identified two additional muon-oxygen bonding sites. The three sites thus located provide a satisfactory explanation for all of the uSR signals reported in the orthoferrite series. The two newly identified sites, which we have called "Holzschuh-2 and Hofmann sites" are associated with the corner oxygen of the rare-earth oxygen plane in the pseudolattice picture (Fe=origin). At higher temperatures, increased muon motion results in migration of muons to the more stable Holzschuh-1 site, so that only one signal is seen.Item Search for the muon-stopping sites in rare-earth orthoferites [i.e. orthoferrites] by means of dipolar calculation(Texas Tech University, 1986-08) Lin, Tsai-kuThe uSR data for RFe03 (R=Er, Ho, Y, Dy, Eu and Sm) indicates that three separate localized muon sites may exist. In Ref.(12) one of these sites lying in the R-0 plane of the perovskite structure was identified, hereafter referred to as the Holzschuh-1 site. We have performed dipole sum calculations of the internal fields in the orthoferrites for the magnetic orderings present within the series. Using a weighting scheme requiring a match to the experimental values for the magnitude and directions of internal fields from observed uSR signals, and a muon-oxygen distance consistent with bond formation, we have verified the Holzschuh-1 site and have identified two additional muon-oxygen bonding sites. The three sites thus located provide a satisfactory explanation for all of the uSR signals reported in the orthoferrite series. The two newly identified sites, which we have called ''Holzschuh-2 and Hofmann sites" are associated with the corner oxygen of the rare-earth oxygen plane in the pseudolattice picture (Fe=origin). At higher temperatures, increased muon motion results in migration of muons to the more stable Holzschuh-1 site, so that only one signal is seen.