In classical novae, the endpoint of nucleosynthesis occurs near A ~ 40. Currently, observations of classical novae predict an order of magnitude enhancement of endpoint elements, such as Ar, K, and Ca, relative to solar abundances; however, simulations predict abundances closer to that of solar abundances. A sensitivity study examining the effect of reaction rates on the abundances of these elements has shown that the reaction 38-K(p,g)39-Ca can change the abundances of endpoint nuclides by an order of magnitude or more. In temperatures characteristic of this environment, this reaction rate is dominated by l =0 resonance reactions within the Gamow window. These correspond to states in 39-Ca with spin-parity of 5/2+ and 7/2+ between Ex = 6.0−6.5 MeV . While a direct measurement was carried out for these states, more precise values for the excitation energies were recommended. In this work high resolution spectroscopic studies of 39-Ca were carried out to provide more information on the various resonances that lie in the Gamow window, and illuminate additional undiscovered states. The first study was conducted at the Maier- Leibnitz-Laboratory (MLL), employing the 40-Ca(d,t)39-Ca reaction, and the follow up study was conducted at the Triangle Universities Nuclear Laboratory (TUNL) using the 39-K(3-He,t)39-Ca reaction. The method and apparatus are discussed in this work. Energy levels in 39-Ca with 10 keV uncertainties had uncertainties reduced to 3-4 keV. In addition, several new states were found in 39-Ca from the TUNL experiment. Finally, there is an ~ 10 keV systematic difference between previously evaluated states and the states measured in this work - a factor that affects the direct measurement carried out previously. This factor in combination with the results of this work show that the reaction rate of this may be higher than previously thought, and have a higher impact on the final abundances of elements synthesized in classical novae. / Thesis / Doctor of Science (PhD) / The goal of this work is to investigate processes that create the chemical elements of the universe. This occurs through nuclear reactions of elements produced after Big Bang nucleosynthesis. These nuclear reactions are only possible in the hot, dense environments found in stars and explosive stellar events. One such stellar event is the classical nova, which can produce elements as heavy as Calcium. Although a multitude of nuclear reactions occur during a classical nova, only a handful have a large effect on the abundance of elements produced. This work studies the properties of a specific nuclear reaction that can strongly affect the abundances of elements synthesized in classical novae.

No description available.

The properties of hadronic and quark matter are studied as a function of density using a chiral model based on quark degrees of freedom. Nucleons are described as quark - diquark states in the Faddeev approach and this description is extended to infinite nuclear matter in the mean field approximation. We calculate the properties of two flavour quark matter, allowing for the possibility of colour superconductivity in the form of a spin zero condensate ( i.e. the 2SC phase ). These calculations are performed using the proper - time regularisation method. We find that the phase diagrams for asymmetric matter in this description can have charge neutral phase transitions from the hadronic phase to the decon - fined phase, depending on the pairing strength for quarks in the 2SC phase. We study the evolution of the phase diagrams as a function of the pairing strength. The properties of nuclear matter are significantly improved once we take into account the self - energy of the nucleon. We also find that the structure of the nucleon has important consequences for the phase diagram. The charge neutral equations of state are used to produce compact star configurations by solving the Tolman - Oppenheimer - Volkoff ( TOV ) equations. We use these solutions to investigate the possibility of hybrid stars. / Thesis (Ph.D.)--School of Chemistry and Physics, 2006.

Thesis (Ph. D.)--University of Idaho, 2006. / Abstract. "August, 2006." Includes bibliographical references (leaves 113-122). Also available online in PDF format.

Classical novae are explained as thermonuclear explosions on the surface of white dwarf stars accreting hydrogen-rich material from less evolved companions in binary star systems. These events occur frequently within our galaxy and have been proposed as significant contributors to the galactic abundance of 13C, 15N, 17/18O and 18/19F. The short-lived isotope 18F (t1/2 = 110 min) is of particular importance since it may provide a signature of novae events through the detection of 511 keVγ-ray emission following the β+ decay of a 18F nucleus. During classical novae the 17O(p,γ)18F reaction governs the production of 18F and affects the synthesis of the rare isotopes mentioned above. Prior to the present study, the 17O(p,γ)18F reaction rate was poorly determined owing to a lack of low-energy experimental data. The present work reports on the first accurate measurements of the resonant and non-resonant contributions to the 17O(p,γ)18F reaction cross section in the energy region relevant for classical novae. Measurements were performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) accelerator facility of the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. Here the γ-ray background is suppressed by up to 3 orders of magnitude, thus providing a unique environment for low-energy measurements of reaction cross sections. Prompt γ rays associated with the formation and decay of states in 18F were analysed to determine the resonant and non-resonant contributions to the reaction cross section. The total non-resonant S-factor was determined at energies between Ecm ≈ 200 - 370 keV and the strength of a key resonance at Ecm = 183 keV was obtained with the best precision to date. The uncertainty in the reaction rate is now sufficiently low to place firmer constraints on nucleosynthesis predictions from accurate models of novae.

This dissertation investigates several problems inspired by the interplay of cosmology and theories beyond the Standard Model of particle physics. The first part of this work is a study of time evolution of unstable dS[subscript p] x S[superscript q] configurations with flux in theories of gravity with a cosmological constant. We find that, depending on the flux, these configurations either evolve towards newly identified stable solutions with a smaller final effective cosmological constant, or tend toward decompactication of the internal sphere. In the second part, we investigate the problem of evolution of vacuum bubbles in inhomogeneous backgrounds. It is expected that the process of inflation will signifcantly smooth out spatial inhomogeneities. However, the initial conditions for inflation are often taken in the already homogeneous and isotropic FRW form, even though it is assumed that initial homogeneity is not necessary for the onset of inflation. We determine the effects of certain inhomogeneities, introduced in the curvature of the outside spacetime, on the propagation of bubbles, and how these effects differ depending on whether the perspective taken is that of the outside observer or an observer on the bubble. The last part of the dissertation presents a model for a novel component of the energy density of the universe. The observational limits on the present energy density allow for a component that redshifts like 1/a² and can contribute significantly to the total. We show that one possible origin for such a contribution is that the universe has a toroidal topology with "wound" scalar fields around its cycles.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics and Mathematical Physics, 2001. / Bibliography: leaves 100-106.

Thesis (Ph.D.)--Montana State University--Bozeman, 2007. / Typescript. Chairperson, Graduate Committee: Richard Canfield. Includes bibliographical references (leaves 83-88).

Includes bibliographical references. / Various calculations· of the evolution of the hadron gas in the early universe are carried out. To determine the starting point for the evolution equations a phase transition between the quark-gluon plasma phase and the hadron gas phase is constructed. A simple calculation leads to an estimate of the chemical potential of baryons at the quark-hadron phase transition in the early universe. We investigate how the transition temperature depends on the equations of state for the bagged quark and the hadron phase. A particle density evolution model is introduced which predicts the temperature at which particle species drop out of equilibrium (freeze-out) in an expanding universe. We then construct dynamical evolution equations to describe the reactions of interacting pions and photons. In order to model a more realistic hadron gas, we include kaons and finally nucleons and hyperons into the model universe. The results indicate that this type of model should be extended to include more interacting particle species and that a more realistic evolution model is dependent on obtaining accurate reaction cross-sections.