Physics
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Item Experimental Atomic Spectroscopy of Iron Group Elements for Astrophysics(2021) Ward, Jacob Wolfgang; Nave, Gillian; Rolston, Steve; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The quality of modern astrophysical spectra has made it clear that there is a lack of sufficiently accurate and robust laboratory atomic reference data sets. Particularly for spectra of the iron-group elements, the growing demand for critically evaluated sets of comprehensive atomic data is a direct result of advancing stellar astrophysics models and fundamental physics problems probing beyond the standard model. My thesis reports on my critical evaluation of the Ni V spectrum and the recent laboratory measurements I have conducted to improve the state of available reference data for astrophysical applications that rely on observations of Ni V. Additionally, I report my laboratory measurements of Fe II branching fraction values in the UV/VUV. Using high-resolution grating spectroscopy at the National Institute of Standards and Technology, I have carried out an analysis of quadruply ionized iron and nickel (Fe V & Ni V) in the vacuum ultraviolet (VUV) region by both recording new spectra and critically evaluating previously published data sets. My analysis has resulted in highly accurate wavelengths, presented with calculated oscillator strengths, for roughly 1500 Ni V lines, 200 of which have uncertainties that are almost an order of magnitude lower than in previous publications. Additionally, I present over 300 Ni V energy levels derived from my evaluated wavelengths. This section of my thesis focuses on the large improvements made in the analysis of Ni V, but my work also strongly supports the previous evaluations of Fe V by another author. With the extreme accuracy requirements of modern astrophysics problems, confirming the wavelength scale and uncertainty evaluation of previous Fe V data sets is still significant. In addition to the above work, my thesis also presents measurements of singly ionized iron (Fe II) branching fractions (BFs) in the VUV using high-resolution Fourier-transform spectroscopy. BFs are essential values for interpreting complex astrophysical spectra, but are notoriously difficult to measure in the VUV; for this reason, VUV BFs of Fe II have only been reported by one other research group for just seven levels. My thesis reports accurate BFs for 11 Fe II levels, involving approximately 100 spectral lines (16 in the VUV), which roughly doubles the amount of reported Fe II BFs in VUV.Item Diamagnetism of a Supersonic Rotating Magnetized Plasma(2012) Young, William; Hassam, Adil B; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Maryland Centrifugal Experiment (MCX) combines supersonic rotation with a magnetic mirror geometry to centrifugally confine a hydrogen plasma with the goal of investigating a magnetic confinement scheme applicable as a fusion reactor. To demonstrate this axial confinement of plasma by centrifugal forces, an axial array of magnetic loops was installed, external to the vacuum vessel, to measure the axial and radial components of the magnetic field expelled by the plasma. The diamagnetic measurements show concentration of plasma pressure at locations of magnetic minima, as expected for centrifugal confinement. Additionally, a visible light, multichord spectrometer was upgraded to ten chords allowing for the measurement of plasma rotation and temperature profiles with increased precision. Improved deconvolution techniques are investigated to further increase the precision of radial profiles calculated from multichord measurements. A perturbative, ideal MHD equilibrium solution is then developed to relate the diamagnetic measurements to density, rotation, and temperature profiles of the plasma. This solution, along with density measurements by interferometery, is used to estimate rotation velocity and temperature of the plasma from magnetic data, and then is compared to spectroscopic measurements of rotation velocity and temperature radial profiles. Agreement between spectroscopic measurements and magnetic measurements via the MHD solution further demonstrate the presence of centrifugal confinement and its efficacy.Item Excited Nucleon and Delta Spectra From Lattice QCD(2009) Engelson, Eric; Wallace, Stephen J; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We calculate the nucleon and delta excited state spectra from lattice QCD. Operators which transform as irreducible representations of the lattice symmetry group are used as bases for variational calculations. We compute matrices of corre- lation functions between all the operators in the variational bases. From the time dependence of the eigenvalues of these matrices, we extract energy eigenvalues. By subducing the continuum SU(3) rotation group to the octahedral group, we can identify the spins of the continuum states which correspond to the lattice states. In the nucleon spectrum calculation, we use 24^3 × 64 anisotropic lattices with pion masses of 416 MeV and 576 MeV. The lattices have a spacing of about 0.1 fm and an anisotropy of 3. We use the Wilson gauge and the Wilson fermion actions with two flavors of dynamical light quarks. The low-lying spectrum has many of the qualitative features of the physical spectrum and we are able to identify the continuum states which correspond to several of the lattice states. This includes one of the first observations of a spin- 5 state on the lattice. For the delta spectrum calculation, we use 16^3 × 128 anisotropic lattices. The gauge action is the tree-level tadpole improved Wilson gauge action, while in the fermion sector we use the clover action. The pion mass is about 390 MeV and the anisotropy is 3.5. We have two flavors of dynamical light quarks as well as dynamical strange quarks. To compute the correlation functions, we use the distillation method in which operators are projected on the the low lying eigenmodes of the Laplacian operator, allowing for an exact computation of all-to-all propagators between the distilled source and sink operators. We are able to identify four low-lying states with continuum delta states.Item Studies of atomic properties of francium and rubidium.(2009) Perez Galvan, Adrian; Orozco, Luis A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High precision measurements of atomic properties are excellent probes for elec- troweak interaction studies at the lowest possible energy range. The extraction of standard model coupling constants relies on a unique combination of experimen- tal measurements and theoretical atomic structure calculations. It is only through stringent comparison between experimental and theoretical values of atomic prop- erties that a successful experiment can take place. Francium, with its heavy nucleus and alkali structure that makes it amenable to laser cooling and trapping, stands as an ideal test bed for such studies. Our group has successfully created, trapped and cooled several isotopes of francium, the heaviest of the alkalies, and demonstrated that precision studies of atomic properties, such as the measurement of the 8S1/2 excited state lifetime of 210Fr presented here, are feasible. Further work in our program of electroweak studies requires a better control of the electromagnetic environment observed by the sample of cold atoms as well as a lower background pressure (10-10 torr or better). We have designed and adapted to our previous setup a new &ldquo science &rdquo vacuum chamber that fulfills these requirements and the transport system that will transfer the francium atoms to the new chamber. We use this new experimental setup as well as a rubidium glass cell to perform precision studies of atomic and nuclear properties of rubidium. Spectroscopic studies of the most abundant isotopes of rubidium, 87Rb and 85Rb, are a vital component in our program. Performing measurements in rubidium allows us to do extensive and rigorous searches of systematics that can be later extrapolated to francium. We present a precision lifetime measurement of the 5D3/2 state of 87Rb and a measurement of hyperfine splittings of the 6S1/2 level of 87Rb and 85Rb. The quality of the data of the latter allows us to observe a hyperfine anomaly attributed to an isotopic difference of the magnetization distribution in the nucleus i.e. the Bohr-Weisskopf effect. The measurements we present in this work complement each other in exploring the behavior of the valence electron at different distances from the nucleus. In addition, they constitute excellent tests for the predictions of ab initio calculations using many body perturbation theory and bolster our confidence on the reliability of the experimental and theoretical tools needed for our work.