Theses and Dissertations - Department of Physics & Astronomy

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Interfacial interactions of FeCo/Pd and FeCo/Ru multilayers
(University of Alabama Libraries, 2009) Walock, Michael James; Mankey, Gary J.; University of Alabama Tuscaloosa
The FeCo system of alloys is perched atop the Slater-Pauling curve. As a result of this and its relatively low cost and ease of deposition, it is heavily used within the magnetic recording industry. However, new technology requires an advance past this system with respect to high moment, high magnetization materials. One possible step is the enhancement of the FeCo system. One approach is the lamination of thin, nonmagnetic Pd spacer layers with FeCo. Prior published results have shown an increase in not only the moment, but also the magnetization of the samples. We have developed a FeCo/Pd superlattice samples to test this hypothesis. Our results, using a combination of conventional magnetometry, x-ray magnetic circular dichroism, and polarized neutron reflectivity, show a different result from prior reports. The magnetic dichroism experiments show a definite decrease in the magnetic moments of both the Fe and Co with the introduction of Pd. The preliminary analysis of the neutron reflectivity data shows no increase in the magnetic moment of the alloy, nor an induced moment in the Pd. For comparison with the FeCo/Pd superlattice, we studied an antiferromagnetically coupled FeCo/Ru superlattice.
Magnetic anisotropy graded media and Fe-Pt alloy thin films
(University of Alabama Libraries, 2009) Lu, Zhihong; Butler, W. H.; University of Alabama Tuscaloosa
Anisotropy graded media is promising to overcome the writability problem in achieving ultrahigh areal density for magnetic recording media. To more conveniently study and compare various media with regard to a particular figure of merit, a new energy landscape method of analysis is suggested. Using this method, the theoretical limit of the figure of merit for a graded medium is found to be 4. This limit can be approached by a graded medium with anisotropy quadratically increasing from zero to its maximum value. In order to characterize the anisotropy distribution of a graded medium, hard axis loops of graded media with various anisotropy profiles are simulated and analyzed. It is found that the second derivative of the hard axis loop can give useful information on the anisotropy distribution in a graded medium. Fe₅₀Pt₅₀ with the L1₀ structure, as one of the magnetically hardest materials, has great potential for media application. By using a first-principles calculation method, the magnetic and electronic structures of L1₀ structured Fe₅₀Pt₅₀ have been studied. These calculations show that although the ferromagnetic phase is the most stable phase for Fe₅₀Pt₅₀ with the L1₀ structure, there is a competition between the antiferromagnetic and the ferromagnetic phases when the ratio of lattice constants, c/a, decreases. Experimental investigations of Fe₅₀Pt₅₀ films with graded order parameter fabricated by varying the growth temperature during deposition demonstrate that these films have much smaller switching field than fully ordered Fe₅₀Pt₅₀, which suggests it is possible to make graded media by using this kind of films. Fe₁₀₋ₓPtₓ films with compositional gradient were also studied; however, the large easy axis dispersion in these films makes them unsuitable for the fabrication of graded media. Films with [FePt₃ordered)/FePt₃ (disordered)]n superlattices were deposited on MgO substrates and sapphire substrates. It was found that the exchange bias in superlattices deposited on MgO substrate show higher exchange bias field. Polarized neutron reflectivity results show that ferromagnetic layers on MgO substrates contain more antiferromagnetic component than those on sapphire substrates. The larger exchange bias of the superlattice on MgO substrate is hypothesized to be due to larger exchange bias in its ferromagnetic layers.
First observation of 7Be solar neutrinos with KamLAND
(University of Alabama Libraries, 2009) Keefer, Gregory John; Piepke, Andreas; University of Alabama Tuscaloosa
The international KamLAND collaboration operates a 1 kton liquid scintillation detector in the Kamioka mine in Gifu, Japan. KamLAND's main scientific results are the precision measurement of the solar Δm²₁₂ = 7.58 + +0.14_{-0.13 stat}± 0.15_syst and tan² θ₁₂ = 0.56+0.10_{-0.07 stat}+0.10_{-0.06 syst} utilizing reactor antinuetrinos and first evidence for the observation of geologically produced antineutrinos. In an effort to extend KamLAND's scientific reach, extensive research has been performed on preparing a spectroscopic measurement of ⁷Be solar neutrinos. This work provides the first inclusive analysis of KamLAND's backgrounds below 1 MeV. ⁸⁵Kr and ²¹⁰Pb, dissolved in KamLAND liquid scintillator, were found to be the dominant source of low energy backgrounds. The concentration of these ultra-trace contaminants were determined to be 10⁻²⁰ g/g. This is more then 6 orders of magnitude lower then commercially available ultra-pure liquids. To attain a signal-to-background ratio suitable for the detection of ⁷Be solar neutrinos, the concentration of these contaminants had to be reduced by 5 orders of magnitude. A comprehensive study of ²¹⁰Pb removal was undertaken over the course of this thesis. This work further covers techniques for the removal of ²²⁰Rn, ²²²Rn and their daughter nuclei from liquid scintillator at concentrations of 10⁻¹⁸ g/g . Purification techniques studied in this work include water extraction, isotope exchange, adsorption, and distillation. These laboratory studies guided the design and implementation of a large scale purification system in the Kamioka mine. The purification system's design and operation is discussed in detail as well as specific experiments devised to control scintillator quality and radio-purity. The purification system's effectiveness in removing radioactive trace impurities is analyzed in detail. The total scintillator purified over two years of operation was more then 4.6 ktons. It is shown here that the KamLAND collaboration has successfully reduced the ⁸⁵Kr specific activity of the scintillator by a factor of 2.6 x 10⁴ while ²¹⁰Bi was reduced by a factor 2 x 10³. Due to the success in reducing the intrinsic backgrounds through multiple purifications, this work provides the first evidence for a ⁷Be solar neutrino signal in KamLAND. The presented analysis covers 5.448 kton-days of exposure time. While the current work is not yet providing a robust measurement of the ⁷Be solar neutrino flux, the presence of ⁷Be solar neutrino is shown to be statistically preferred over a null hypothesis.
Bacterium E. coli- and phage P22-templated synthesis of semiconductor nanostructures
(University of Alabama Libraries, 2010) Shen, Liming; Gupta, Arunava; University of Alabama Tuscaloosa
The properties of inorganic materials in the nanoscale are found to be size- and shape-dependent due to quantum confinement effects, and thereby nanomaterials possess properties very different from those of single molecules as well as those of bulk materials. Assembling monodispersed nanoparticles into highly ordered hierarchical architectures is expected to generate novel collective properties for potential applications in catalysis, energy, biomedicine, etc. The major challenge in the assembly of nanoparticles lies in the development of controllable synthetic strategies that enable the growth and assembly of nanoparticles with high selectivity and good controllability. Biological matter possesses robust and precisely ordered structures that exist in a large variety of shapes and sizes, providing an ideal platform for synthesizing high-performance nanostructures. The primary goal of this thesis work has been to develop rational synthetic strategies for high-performance nanostructured materials using biological templates, which are difficult to achieve through traditional chemical synthetic methods. These approaches can serve as general bio-inspired approaches for synthesizing nanoparticle assemblies with desired components and architectures. CdS- and TiO_2 -binding peptides have been identified using phage display biopanning technique and the mechanism behind the specific affinity between the selected peptides and inorganic substrates are analyzed. The ZnS- and CdS-binding peptides, identified by the phage display biopanning, are utilized for the selective nucleation and growth of sulfides over self-assembled genetically engineered P22 coat proteins, resulting in ordered nanostructures of sulfide nanocrystal assemblies. The synthetic strategy can be extended to the fabrication of a variety of other nanostructures. A simple sonochemical route for the synthesis and assembly of CdS nanostructures with high yield under ambient conditions has been developed by exploiting the chemical characteristics and structure of permeabilized E. coli bacteria. The crystal phase, morphology, micro/nanostructure, optical absorption, and photocatalytic properties of the CdS nanostructures are tailored over a wide range by merely changing the synthetic conditions. Photoanodes fabricated using the nanoporous hollow CdS microrods exhibit excellent performance for the photocatalytic hydrogen production. This facile approach has been extended to the synthesis and assembly of other semiconducting sulfides, including PbS, ZnS, and HgS.
Neutrino-nucleus neutral current elastic interactions measurement in MiniBooNE
(University of Alabama Libraries, 2010) Perevalov, Denis; Stancu, Ion; University of Alabama Tuscaloosa
The MiniBooNE experiment at the Fermi National Accelerator Laboratory (Fermilab) was designed to search for electron to muon neutrino oscillations at Delta m^2~1 eV^2 using an intense neutrino flux with an average energy of about 700 MeV. From 2002 to 2009 MiniBooNE has accumulated more than 1.0x10^{21} protons on target (POT) in both neutrino and antineutrino modes. MiniBooNE provides a perfect platform for detailed measurements of exclusive and semiinclusive neutrino cross-sections, for which MiniBooNE has the largest samples of events up to date, such as neutral current elastic (NCE), neutral current pi^0, charged current quasi-elastic (CCQE), charged current pi^+, and other channels. These measured cross-sections, in turn, allow to improve the knowledge of nucleon structure. This thesis is devoted to the study of NCE interactions. Neutrino-nucleus neutral current elastic scattering accounts for about 18% of all neutrino interactions in MiniBooNE. Using a high-statistics, high purity sample of NCE interactions in MiniBooNE, the flux-averaged NCE differential cross-section has been measured and is being reported here. Further study of the NCE cross-section allowed for probing the structure of nuclei. The main interest in the NCE cross-section is that it may be sensitive to the strange quark contribution to the nucleon spin, $Delta s$, this however requires a separation of NCE proton from NCE neutron events, which in general is a challenging task. MiniBooNE uses a Cherenkov detector, which imposes restrictions on the measured nucleon kinematic variables, mainly due to the impossibility to reconstruct the nucleon direction below the Cherenkov threshold. However, at kinetic energies above this threshold MiniBooNE is able to identify NCE proton events that do not experience final state interactions. These events were used for the $Delta s$ measurement. In this thesis MiniBooNE reports the NCE (n+p) cross-section, the measurement of the axial mass, $M_A$, and the $Delta s$ parameter from the NCE data.
Theory and practice of brine processing by industrial-scale magnetic ion polarization and optimization of personal-scale passive solar desalination
(University of Alabama Libraries, 2010) Wofsey, Michael Henry; Tipping, Richard H.; University of Alabama Tuscaloosa
In the first section of this work we hope to add to the science of brine management in desalination. We have undertaken a feasibility analysis of a method of brine processing where the ions in solution are transported by an axial magnetic field in a long pipe, and an off-center cross-section of the flow is extracted with a lower ion concentration than that near the edges of the pipe. We constructed an apparatus that examines this process and allows us to measure the change in voltage in a solution during treatment. The goal of this process is to separate brine effluent from the desalination system into two components; one close to ocean water which can be safely injected back into the ocean or reprocessed into potable water using standard desalination techniques. The second component will have an ion concentration higher than typical waste brine, and can be more economically treated using a conventional process such as an evaporation pond or solar drying. This research addresses an emerging problem, the Achilles' heel of large-scale desalination. Specifically, systems for municipal-sized water demands can produce desalinated water in quantities exceeding a million liters per day. A basic mass balance shows that all the freshwater that is extracted from seawater will leave a nearly equal quantity of high-salt brine. Ejected brine from commercial-scale desalination facilities has been shown to cause distress and damage to marine organisms and possibly even saline gradient inversions, which lead to unpredictable solar heating of littoral ocean waters. In the second section of this work we add to the general knowledge of the science of solar desalination. We have used common and straightforward measurement techniques, physical analyses and quantitative analyses to optimize efficient methods of personal-scale solar desalination. In this research we have used simple modifications to stills of our own design that increase efficiency and output of distilled water. We also examine a theoretical efficiency model that may be useful in determining the efficiency of solar stills and offer potential predictor of solar still output efficiency.
Testing the Sersic bulge: black hole mass relation in Seyfert galaxies
(University of Alabama Libraries, 2010) May, Alana; Keel, W. C.; University of Alabama Tuscaloosa
Using a sample of Active Galactic Nuclei (AGN), we investigated the relationship between host galaxy and black hole mass using the Sérsic index. We performed two-dimensional (2-D) decompositions of high-resolution Hubble Space Telescope images of (AGN) using GALFIT 3 beta. Taking independent mass estimates for a subsample of the selected galaxies, we test both linear and quadratic regressions in order to find an optimal relation for estimating black hole mass in other galaxies. Our results show that there was little difference between the linear and higher order fits. We examine the effects of these analysis techniques on the black hole mass to luminosity relationship. Application of the data was also looked at concerning properties of pseudo- and classical bulges.
Susy transitions in compact objects
(University of Alabama Libraries, 2010) Perevalova, Irina A.; Clavelli, L.; University of Alabama Tuscaloosa
From the very moment of discovery, gamma-ray bursts (GRB) became a very fascinating subject for study. Although this phenomena has been observed for four decades, the origin of such extraordinary events is yet to be discovered. In our research, we propose one possible explanation of the phenomena. We support our proposal with detailed theoretical calculations and computer simulations which give us confidence to consider the proposed model as consistent. The structure of the dissertation is the following: in the first chapter, after a brief introduction to the history of the GRB, we give a description of existing models of GRB origin, pointing out, however, the reasons why we cannot accept the models entirely. Then we give a review of the astronomical objects that will be important for our model. Finally in the end of the chapter we introduce our model. Chapter two is entirely theoretical. After a brief introduction of supersymmetry (SUSY) we provide the apparatus we used in later calculations. In chapter three we present the calculations for the fermion → s-fermion transition cross-sections for the Dirac sea and results of Monte Carlo simulations for these transitions. In chapter four we present different collective nuclear models and the results of numerical evaluations of the energy release during the SUSY transition. Energy balance for possible nuclear reactions is also provided in this chapter. Finally, we present our conclusions in chapter five.
Theoretical investigation of new magnetic recording media using an energy landscape method
(University of Alabama Libraries, 2011) Zhu, Ru; Visscher, Pieter B.; University of Alabama Tuscaloosa
Magnetic material has played an important role in the information storage technology. We have worked out a phase diagram showing spin torque switching for perpendicular anisotropy media at nonzero temperature. A new area is predicted where the system can vibrate between precessional and parallel states quickly and therefore creates "telegraph" noise region. The result was later confirmed by a nanopillar experiment. The density of magnetic recording is restricted by the superparamagnetic limit. To overcome this limit people have used perpendicular recording to replace the traditional longitudinal recording and are working on other approaches to get over the superparamagnetic limit including heat assisted recording, patterned media and exchange coupled media. Anisotropy graded media provides an alternative solution to achieve high areal density while keeping the writing field relatively low and good thermal stability. A two-dimensional energy landscape of the switching of anisotropy graded media is calculated to give an intuitive way of understanding the switching, as well as a way to quantitatively calculate the switching rate by mapping the problem onto a one-dimensional Langevin random walk. Then an iterative algorithm of for finding the saddle point of the energy landscape, which we call barbell algorithm, is used to locate the saddle point and the whole switching trajectory.
Radiative symmetry breaking in the supersymmetric minimal B-L extended standard model
(University of Alabama Libraries, 2011) Burell, Zachary Michael; Okada, Nobuchika; University of Alabama Tuscaloosa
The Standard Model (SM) of particle physics is a precise model of electroweak interactions. However, there is evidence from neutrino physics and astrophysical cosmology which is at odds with the SM framework. It appears likely that the validity of the SM will be compromised at energy scales of a few TeV. A more fundamental theory will certainly be required, and such devlopment is already motivated by the existing dark matter and neutrino data. We confirm the viability of the Supersymmetric B-L extension of the SM as a natural Supersymmetric SM extension which resolves the neutrino mass problem, the dark matter problem, and the hierarchy problem, and which has the ability to explain the observed baryon asymmetry of the Universe. When we include quantum corrections to the Higgs potential of the model, we find that Radiative B-L symmetry breaking occurs through the interplay between large Majorana Yukawa couplings and SUSY breaking masses. This realization shows that B-L symmetry breaking naturally occurs at the TeV scale, in addition to TeV scale SUSY breaking, the Z' boson and right-handed neutrino masses are also near the TeV scale, which we explicitly confirm numerically, making them accessible to the LHC. Moreover we show that the right-handed neutrinos acquire mass through radiative breaking of the B-L symmetry, and thus the seesaw mechanism is naturally implemented. Finally, we show that the the model naturally links Radiative EWSB, Spontaneous SUSY breaking and the Radiative B-L breaking at the TeV scale, which places this model in an ideal regime to be confirmed at the LHC.
Half-metallic CrO_2 thin films for spintronic applications
(University of Alabama Libraries, 2011) Pathak, Manjit; LeClair, Patrick R.; University of Alabama Tuscaloosa
CrO_2 is a well-established half-metallic oxide with near perfect spin polarization - known to have the highest spin polarization among all known materials theoretically as well as experimentally. This means that the conduction electrons in CrO_2 have only one kind of spin i.e. conduction is due only to the majority spin electrons. Because of its high spin polarization, CrO_2 stands as an ideal and one of the most attractive candidates for spin-electronic applications as well as of fundamental interests. The enormous potential of CrO_2 is still untapped since thin film growth modes, interface/surface properties and various factors affecting them are not very well understood or, relatively unknown. Reported works confirm strained growth of (100) CrO_2 films and strain free growth of (110) CrO_2 films on iso-structural TiO_2 substrates investigated using X$ - $ray diffraction. Superconducting quantum interference device (SQUID) and element specific X-ray magnetic circular dichroism (XMCD) techniques were employed to investigate the effect of this substrate-induced strain on the magnetic properties of the films. Magnetic tunnel junctions (MTJ) were fabricated with CrO_2 , Cr_2 O_3 [natural oxide of Cr] as the thin insulating barrier and Co as the other ferromagnetic electrode using photolithography. I-V characteristics of this spin-electronic device are reported. Also, results on the low pressure chemical vapor deposition (CVD) growth of CrO_2 and its comparison with standard growth technique under atmospheric pressure are reported.
Measuring ultraviolet extinction with GALEX in overlapping galaxies
(University of Alabama Libraries, 2011) Manning, Anna; Keel, W. C.; University of Alabama Tuscaloosa
Dust in spiral galaxies is an all encompassing factor in star formation history, measurements of luminosity, and galaxy dynamics. To learn more about galaxy formation and the influence of dust, White & Keel 1992 formulated a direct method to estimate optical depth. In the past few years, with the aid of the Galaxy Zoo forum and its members, known as zooites, a scientifically acceptable number of galaxy pairs have been identified to create a full catalog for this particular research. The White & Keel 1992 method uses differential photometry which eliminates many of the errors that plague statistical techniques that rely on the internal structure of a galaxy to estimate optical depth. The method relies heavily on the symmetry of the galaxies that make up the pair. To fulfill the symmetry requirement of the ideal geometry, the most suitable pair consists of a foreground spiral backlit by an elliptical galaxy. As evidenced here, non-interacting visually symmetric galaxies pairs yield the best results. Observations at the WIYN telescope combined with exposures downloaded from the GALEX archive are used to estimate the optical depth in these pairs as outlined by White & Keel 1992 and additionally, to trace the star formation in UV detections. Two examples of extended dust far beyond the optical radius were observed and analyzed for extinction. In this sample of galaxies, the optical depth of each wavelength scaled to the B filter was generally constant across the wavelengths observed. The effects of clumpy dust structure in the spiral arms dominated the reddening law which likely resulted in an overestimate of the optical depth measurements.
Multiwavelength selection of obscured agn and contributions to the X-ray background
(University of Alabama Libraries, 2011) May, Branyon; Keel, W. C.; University of Alabama Tuscaloosa
Obscuration in AGN is a crucial component to understanding the observed spectrum of the X-ray Background. We tested numerous AGN selection techniques in X-ray, mid-infrared, and optical to test for multiwavelength correlations and to help establish selection criteria for obscured AGN. With AGN sources dominating background X-ray sources, we selected medium-depth archival Chandra observations covering 5.6 deg^2 of sky and generating a large sample of serendipitous X-ray sources (greater than 10,000). The mid-infrared component came from archival Spitzer data, with ~3,500 sources being detected in at least two IRAC bands and 1,485 in all 4 bands. For the optical component, greater than 70% of the Chandra observations also had full coverage within the SDSS Data Release 7, >2,300 optical counterparts and 125 spectra. In analyzing the sample, we have identified the parameter spaces in the X-ray/mid-infrared/optical that are optimized for containing members of the elusive class of obscured AGN, and provide a candidate list. We cross-check our X-ray number counts and source densities with contributions to the X-ray background, and find that we resolve approximately 90% of the X-ray Background in the 0.5-8.0 keV range. Testing populations divided on X-ray hardness and flux-level confirms that the unresolved hard X-ray background will be dominated by large populations of increasingly fainter and harder sources.
Diffuse ionized regions in the vicinity of active galaxies
(University of Alabama Libraries, 2011) Darnell, Erin Kay; Keel, W. C.; University of Alabama Tuscaloosa
Using a sample of 39 Active Galactic Nuclei (AGN), we investigated the incidence of giant ionized clouds in the vicinity of active galaxies. We carried out remote observations of the sample using the Southeastern Association for Research in Astronomy (SARA) North telescope at Kitt Peak and the SARA South telescope on Cerro Tololo. Frames were taken in continuum V and using a narrowband filter that transmits the redshifted [O III] 5007 Å line. We formed an emission line image by subtracting the combined and scaled V frames from the combined [O III] frames. To reduce uncorrelated noise, the emission line images are median filtered with a 1".9 x 1".9 box size. To bring out large diffuse regions, we convolve the emission line image with a circular Gaussian function of 3".42 FWHM. Emergent structures are determined to be starlight or ionized gas. 21 members of our sample were recently shown to be tidally disrupted in an atomic Hydrogen (HI) study. No extended [O III]-line emission clouds were seen in the vicinity of any from this group. We found one new instance of extended ionized emission clouds near the Seyfert 1 galaxy RX J1103.2-0654.
Theory based design and optimization of materials for spintronics applications
(University of Alabama Libraries, 2012) Xu, Tianyi; Butler, W. H.; University of Alabama Tuscaloosa
The Spintronics industry has developed rapidly in the past decade. Finding the right material is very important for Spintronics applications, which requires good understanding of the physics behind specific phenomena. In this dissertation, we will focus on two types of perpendicular transport phenomena, the current-perpendicular-to-plane giant-magneto-resistance (CPP-GMR) phenomenon and the tunneling phenomenon in the magnetic tunnel junctions. The Valet-Fert model is a very useful semi-classical approach for understanding the transport and spin-flip process in CPP-GMR. We will present a finite element based implementation for the Valet-Fert model which enables a practical way to calculate the electron transport in real CPP-GMR spin valves. It is very important to find high spin polarized materials for CPP-GMR spin valves. The half-metal, due to its full spin polarization, is of interest. We will propose a rational way to find half-metals based on the gap theorem. Then we will focus on the high-MR TMR phenomenon. The tunneling theory of electron transport in mesoscopic systems will be covered. Then we will calculate the transport properties of certain junctions with the help of Green's function under the Landauer-Büttiker formalism, also known as the scattering formalism. The damping constant determines the switching rate of a device. We can calculate it using a method based on the Extended Hückel Tight-Binding theory (EHTB). The symmetry filtering effect is very helpful for finding materials for TMR junctions. Based upon which, we find a good candidate material, MnAl, for TMR applications.
Measuring the neutrino mixing angle theta-13 with the double chooz far detector
(University of Alabama Libraries, 2012) Ostrovskiy, Igor; Busenitz, Jerome K.; University of Alabama Tuscaloosa
The neutrino mixing angle theta-13 is the last one which value is still unknown. This dissertation presents an analysis suggesting a non-zero value of the theta-13. The analysis is based on four months of data taken with the far Double Chooz reactor anti-neutrino detector. Using only rate information yields a best fit value of sin2(2theta-13) equal to 0.0934±0.0785 (1 sigma). Incorporating information on the shape of the signal energy spectrum in the analysis results in a best fit value of 0.0849±0.0509 (1 sigma). Based on frequentist studies, sin2(2theta-13)=0 is excluded at the 92.6% confidence level. The frequentist construction using delta chi-square as an ordering rule gives [0.0098, 0.1825] interval for sin2(2theta-13) at 90% C.L.
A Monte Carlo approach to 7Be solar neutrino analysis with KamLAND
(University of Alabama Libraries, 2012) Grant, Christopher; Piepke, Andreas; University of Alabama Tuscaloosa
Terrestrial measurements of neutrinos produced by the Sun have been of great interest for over half a century because of their ability to test the accuracy of solar models. The first solar neutrinos detected with KamLAND provided a measurement of the ^8B solar neutrino interaction rate above an analysis threshold of 5.5 MeV. This work describes efforts to extend KamLAND's detection sensitivity to solar neutrinos below 1 MeV, more specifically, those produced with an energy of 0.862 MeV from the ^7Be electron-capture decay. Many of the difficulties in measuring solar neutrinos below 1 MeV arise from backgrounds caused abundantly by both naturally occuring, and man-made, radioactive nuclides. The primary nuclides of concern were ^210Bi, ^85Kr, and ^39Ar. Since May of 2007, the KamLAND experiment has undergone two separate purification campaigns. During both campaigns a total of 5.4 ktons (about 6440 m^3) of scintillator was circulated through a purification system, which utilized fractional distillation and nitrogen purging. After the purification campaign, reduction factors of 1.5 x 10^3 for ^210Bi and 6.5 x 10^4 for ^85Kr were observed. The reduction of the backgrounds provided a unique opportunity to observe the ^7Be solar neutrino rate in KamLAND. An observation required detailed knowledge of the detector response at low energies, and to accomplish this, a full detector Monte Carlo simulation, called KLG4sim, was utilized. The optical model of the simulation was tuned to match the detector response observed in data after purification, and the software was optimized for the simulation of internal backgrounds used in the ^7Be solar neutrino analysis. The results of this tuning and estimates from simulations of the internal backgrounds and external backgrounds caused by radioactivity on the detector components are presented. The first KamLAND analysis based on Monte Carlo simulations in the energy region below 2 MeV is shown here. The comparison of the Δχ^2 between the null hypothesis and the existence of the ^7Be solar neutrino signal in the data shows a change of 27.9 units, providing evidence that the signal is statistically favored. This analysis reports a measured interaction rate from ^7Be solar neutrinos of R = 343.3 ± 65.0(stat) ± 99.2(syst) events/(kton·day), which corresponds to a total flux of ɸ = (3.41 ±; 1.18) x 10^9 cm^-2 s^-1. The ^7Be solar neutrino flux reported in this work is only the second measurement made of this quantity worldwide. It provides an important cross-check of the Borexino experiment. The flux measurement reported here agrees within 1σ with the standard solar model predictions thus validating our basic understanding of solar fusion reaction processes.
Antineutrino neutral current interactions in MiniBooNE
(University of Alabama Libraries, 2012) Dharmapalan, Ranjan; Stancu, Ion; University of Alabama Tuscaloosa
The antineutrino nucleon neutral current elastic scattering cross section measured at the MiniBooNE experiment is reported. The data set corresponds to 10.1 × 10^20 protons on target which is a world record neutral current elastic antineutrino sample. An antineutrino to neutrino neutral current scattering cross section ratio is measured after accounting for all associated errors. This is the first time such a ratio has been experimentally reported. Previous MiniBooNE neutrino cross section measurements have indicated a higher value for the axial mass, M_A, as compared to the nominal value of M_A=1.0 GeV. A Χ^2 test was performed to find the best value of M_A which matches the antineutrino neutral current elastic data. Finally, an exciting possibility to search for dark matter in the MiniBooNE experiment, using the neutral current interactions is discussed
The magnetic and chemical structural property of the epitaxially-grown multilayered thin film
(University of Alabama Libraries, 2012) Lee, Hwachol; Mankey, Gary J.; University of Alabama Tuscaloosa
L10 FePt- and Fe-related alloys such as FePtRh, FeRh and FeRhPd have been studied for the high magnetocrystalline anisotropy and magnetic phase transition property for the future application. In this work, the thin film structural and magnetic property is investigated for the selected FePtRh and FeRhPd alloys. The compositionally-modulated L10 FePtRh multilayered structure is grown epitaxially on a-plane Al2O3 with Cr and Pt buffer layer at 600degC growth temperature by DC sputtering technique and examined for the structural, interfacial and magnetic property. For the epitaxially grown L10 [Fe50Pt45Rh5 (FM) (10nm) / Fe50Pt25Rh25 (AFM) (20nm)]×8 superlattice, the magnetically and chemically sharp interface formation between layers was observed in X-ray diffraction, transmission electron microscopy and polarized neutron reflectivity measurements with the negligible exchange bias at room and a slight coupling effect at lower temperature regime. For FeRhPd, the magnetic phase transition of epitaxially-grown 111-oriented Fe46Rh48Pd6 thin film is studied. The applied Rhodium buffer layer on a-plane Al2O3 (1120) at 600degC shows the extraordinarily high quality of epitaxial film in (111) orientation, where two broad and coherent peak in rocking curve, and Laue oscillations are observed. The epitaxially-grown Pd-doped FeRh on Pt (111) grown at 600degC, 700degC exhibits the co-existing stable L10 (111) and B2 (110) structures and magnetic phase transition around 300degC. On the other hand, the partially-ordered FeRhPd structure grown at 400degC, 500degC shows background high ferromagnetic state over 5K~350K temperature. For the reduced thickness of Fe46Rh48Pd6, the ferromagnetic state becomes dominant with a reduced portion of the film undergoing a magnetic phase transition. For some epitaxial FeRhPd film, the spin-glass-like disordered state is also observed in field dependent SQUID measurement. For the tri-layered FeRhPd with thin Pt spacer, the background ferromagnetic state is significantly reduced and spin-glass-like state also disappears. In polarized neutron reflectivity, magnetic depth profiles of tri-layered FeRhPd reveals the asymmetric magnetization between two FeRhPd layers. The asymmetric magnetic profile of FeRhPd tri-layered structure is closely related to the thickness dependent epitaxial film growth of B2 structure.
Simulation and identification of non-Poissonian noise triggers in the IceCube neutrino detector
(University of Alabama Libraries, 2013) Larson, Michael James; Williams, Dawn R.; University of Alabama Tuscaloosa
The IceCube neutrino detector, located in the clear glacial ice at the South Pole, completed construction in 2011. The low-energy infill extension, DeepCore, forms a denser sub-detector using higher quantum efficiency photosensors. DeepCore has been taking data since May 2010 and lowers IceCube's energy threshold to about 10 GeV. These low-energy events are dim compared to higher energy events, necessitating the study of low-light backgrounds. While Monte Carlo predictions give an expected rate of approximately 6 Hz due to atmospheric muons, DeepCore records a significantly higher rate of 13.5 Hz with most of the discrepancy due to unsimulated noise events. Much of the rate difference may be resolved by rejecting especially dim events by counting the number of locally coincident hits, retaining 55% of the ν_e and 62% of the ν_μ events sampled with energies of 10-300 GeV while rejecting 96% of noise events. However, differences in the timing distributions of noise hits indicates a need for further study. A new source of correlated noise has been discovered, necessitating an updated noise simulation model. IceCube's new noise generator is able to reproduce the correlated noise in both IceCube and DeepCore sensors. A Metropolis-Hastings algorithm has been used to identify relevant parameters for nearly all of the 5160 sensors that make up the IceCube detector. Initial low quality fits reduce the rate discrepancy between data and simulation from 32% using a Poissonian noise model to 20% using the updated noise model with additional reduction possible. Noise which triggers the DeepCore detector is evaluated and rejected using the NoiseEngine filtering module. Minimal cleaning removes 94% of noise triggers while retaining 85% of ν_e and 87% of ν_μ events with energies of 10-300 GeV. Stringent cleaning removes 99.9% of noise triggers while retaining only 55% of ν_e and 60\% of ν_μ signal events in the same energy range.

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