+publisher:"University of North Carolina" +contributor:("Clegg, Thomas")

University of North Carolina

1. Couture, Alexander Hoff. Cross-Section Measurement of 2H(n,np)n at 16 MeV in Symmetric Constant Relative Energy Configurations.

Degree: Physics and Astronomy, 2011, University of North Carolina

URL: https://cdr.lib.unc.edu/record/uuid:339b2db0-6ab0-476f-ad57-7acde3e4f2df

► The neutron-deuteron (nd) breakup reaction serves as a fertile testing ground for theories of three nucleon dynamics and meson exchange descriptions of nuclear systems. The… (more)

▼ The neutron-deuteron (nd) breakup reaction serves as a fertile testing ground for theories of three nucleon dynamics and meson exchange descriptions of nuclear systems. The three-body kinematics of the nd breakup reaction allow observables to be studied in a variety of exit-channel configurations to test nucleon-nucleon potential models as well as three-nucleon force models. Over the last two decades there have been significant advances in modeling three-nucleon dynamics using empirical nucleon-nucleon potential models. These calculations have shown excellent agreement with most experimental data. However, there remain some exceptions where serious discrepancies arise. We have undertaken new cross-section measurements to provide further insight into one of these discrepancies, the space-star anomaly. The space-star configuration is a special case of the symmetric constant relative energy (SCRE) configuration in nd breakup. The SCRE configuration occurs when the three outgoing nucleons have the same energy and are separated by 120° in the center-of-mass frame. The space-star configuration occurs when the plane containing the outgoing nucleons is perpendicular to the incident beam. The other SCRE configuration measured in this experiment is the coplanar-star, in which this plane contains the incident beam. The space-star anomaly is a discrepancy between theoretical predictions and experimental measurements for the nd breakup differential cross sections; the data are systematically higher than theory at all energies where measurements have been taken. This anomaly has been established by eight previous measurements taken at neutron beam energies of 10.3, 13.0, 16.0, and 25.0 MeV. Three of these experiments were performed in Germany at Bochum and Erlangen, one at the Chinese Institute of Atomic Energy, and four at Triangle Universities Nuclear Lab at Duke. All previous measurements were taken with essentially the same experimental setup, the common features being: (1) the scatterer was a deuterated scintillator, (2) two neutrons were detected in coincidence, (3) the target-beam integrated luminosity was determined through nd elastic scattering by detection of the scattered neutron. To determine if there could be a common experimental error in previous measurements, our experiment utilizes a technique similar to the one developed by Huhn et al. to measure the neutron-neutron scattering length. The primary distinctions between our technique and those used in previous SST measurements are: (1) the deuterated target was a thin foil, (2) a neutron was detected in coincidence with the scattered proton, and (3) the integrated target-beam luminosity was determined by nd elastic scattering via detection of the scattered deuteron. To compare the results of this experiment with theoretical predictions, a Monte-Carlo simulation of the experiment was developed which averaged point-geometry Faddeev calculations over the finite geometry of the experimental apparatus. Along with this averaging process several other effects were… Advisors/Committee Members: Couture, Alexander Hoff, Clegg, Thomas.

Subjects/Keywords: College of Arts and Sciences; Department of Physics and Astronomy

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APA (6^th Edition):

Couture, A. H. (2011). Cross-Section Measurement of 2H(n,np)n at 16 MeV in Symmetric Constant Relative Energy Configurations. (Thesis). University of North Carolina. Retrieved from https://cdr.lib.unc.edu/record/uuid:339b2db0-6ab0-476f-ad57-7acde3e4f2df

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Couture, Alexander Hoff. “Cross-Section Measurement of 2H(n,np)n at 16 MeV in Symmetric Constant Relative Energy Configurations.” 2011. Thesis, University of North Carolina. Accessed March 03, 2021. https://cdr.lib.unc.edu/record/uuid:339b2db0-6ab0-476f-ad57-7acde3e4f2df.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Couture, Alexander Hoff. “Cross-Section Measurement of 2H(n,np)n at 16 MeV in Symmetric Constant Relative Energy Configurations.” 2011. Web. 03 Mar 2021.

Vancouver:

Couture AH. Cross-Section Measurement of 2H(n,np)n at 16 MeV in Symmetric Constant Relative Energy Configurations. [Internet] [Thesis]. University of North Carolina; 2011. [cited 2021 Mar 03]. Available from: https://cdr.lib.unc.edu/record/uuid:339b2db0-6ab0-476f-ad57-7acde3e4f2df.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Couture AH. Cross-Section Measurement of 2H(n,np)n at 16 MeV in Symmetric Constant Relative Energy Configurations. [Thesis]. University of North Carolina; 2011. Available from: https://cdr.lib.unc.edu/record/uuid:339b2db0-6ab0-476f-ad57-7acde3e4f2df

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of North Carolina

2. Arnold, Charles William. A New Absolute Total Cross-Section for Photodisintegration of Beryllium-9.

Degree: Physics and Astronomy, 2011, University of North Carolina

URL: https://cdr.lib.unc.edu/record/uuid:bf11f50f-0349-425a-81c3-d433bd752765

► Models of the r-process are extremely sensitive to the rate of production of 9Be, because the alpha(alpha n gamma)superscript9Be reaction is the primary mechanism for… (more)

Subjects/Keywords: College of Arts and Sciences; Department of Physics and Astronomy

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APA (6^th Edition):

Arnold, C. W. (2011). A New Absolute Total Cross-Section for Photodisintegration of Beryllium-9. (Thesis). University of North Carolina. Retrieved from https://cdr.lib.unc.edu/record/uuid:bf11f50f-0349-425a-81c3-d433bd752765

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Arnold, Charles William. “A New Absolute Total Cross-Section for Photodisintegration of Beryllium-9.” 2011. Thesis, University of North Carolina. Accessed March 03, 2021. https://cdr.lib.unc.edu/record/uuid:bf11f50f-0349-425a-81c3-d433bd752765.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Arnold, Charles William. “A New Absolute Total Cross-Section for Photodisintegration of Beryllium-9.” 2011. Web. 03 Mar 2021.

Vancouver:

Arnold CW. A New Absolute Total Cross-Section for Photodisintegration of Beryllium-9. [Internet] [Thesis]. University of North Carolina; 2011. [cited 2021 Mar 03]. Available from: https://cdr.lib.unc.edu/record/uuid:bf11f50f-0349-425a-81c3-d433bd752765.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Arnold CW. A New Absolute Total Cross-Section for Photodisintegration of Beryllium-9. [Thesis]. University of North Carolina; 2011. Available from: https://cdr.lib.unc.edu/record/uuid:bf11f50f-0349-425a-81c3-d433bd752765

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of North Carolina

3. Lin, Lin. Characterization of the Water Transport Properties of the Active Layers of Polyamide Reverse Osmosis and Nanofiltration Membranes.

Degree: Environmental Sciences and Engineering, 2015, University of North Carolina

URL: https://cdr.lib.unc.edu/record/uuid:8ead5fe9-6886-4daf-a5c3-79c7eac2c91b

► The overall objective of this study was to elucidate which parameter among water partitioning, water diffusion and active layer thickness accounts for the differences in… (more)

▼ The overall objective of this study was to elucidate which parameter among water partitioning, water diffusion and active layer thickness accounts for the differences in water permeability among polyamide reverse osmosis (RO) and nanofiltration (NF) membranes. To achieve this overall objective, the following specific objectives were pursued: (i) to identify appropriate methods (facile and accurate) for measuring active layer thickness in RO/NF membranes; (ii) to ascertain the existence of voids within the polyamide active layers of RO/NF membranes and develop methods to quantify void volume fraction in active layers; (iii) to measure the partition coefficient of water into membrane active layers, and calculate the diffusion coefficient of water in active layers based on measurements of membrane water permeability (A), active layer thickness (δ), and water partition coefficient (K); and (iv) to correlate membrane water permeability (A) to active layer thickness (δ), water partition coefficient (K) and water diffusion coefficient (D) for a group of polyamide RO/NF membranes with a broad range of performance levels. The following major conclusions were drawn through this dissertation: (i) atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), quartz crystal microbalance (QCM), profilometry and ellipsometry produce consistent active layer thickness results among each other and likely provide the most accurate results of active layer thickness of RO/NF membranes; (ii) scanning electron microscopy (SEM) and transmission electron microscopy (TEM) likely overestimate active layer thickness; (iii) voids with sizes in the ≈10-100 nm range commonly exist in the active layers of RO/NF membranes, occupy a significant volume fraction of the active layers, and are filled with water when the membranes are in contact with water (e.g., when they are being used for water purification); (iii) among active layer thickness, water partition coefficient and water diffusion coefficient, the differences in water permeabilities among RO/NF membranes were mostly accounted for by the differences in the water diffusion coefficients in their active layers; (iv) the presence of the voids in the active layer increases the membrane water permeance; and (v) there was not a clear correlation between void volume fraction and water permeance, water partition coefficient or water diffusion coefficient. Advisors/Committee Members: Lin, Lin, Coronell, Orlando, Aitken, Michael, Characklis, Gregory, Clegg, Thomas, Dewan, Prasun, Lopez, Rene.

Subjects/Keywords: Environmental engineering; Environmental sciences; Gillings School of Global Public Health; Department of Environmental Sciences and Engineering

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APA (6^th Edition):

Lin, L. (2015). Characterization of the Water Transport Properties of the Active Layers of Polyamide Reverse Osmosis and Nanofiltration Membranes. (Thesis). University of North Carolina. Retrieved from https://cdr.lib.unc.edu/record/uuid:8ead5fe9-6886-4daf-a5c3-79c7eac2c91b

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Lin, Lin. “Characterization of the Water Transport Properties of the Active Layers of Polyamide Reverse Osmosis and Nanofiltration Membranes.” 2015. Thesis, University of North Carolina. Accessed March 03, 2021. https://cdr.lib.unc.edu/record/uuid:8ead5fe9-6886-4daf-a5c3-79c7eac2c91b.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Lin, Lin. “Characterization of the Water Transport Properties of the Active Layers of Polyamide Reverse Osmosis and Nanofiltration Membranes.” 2015. Web. 03 Mar 2021.

Vancouver:

Lin L. Characterization of the Water Transport Properties of the Active Layers of Polyamide Reverse Osmosis and Nanofiltration Membranes. [Internet] [Thesis]. University of North Carolina; 2015. [cited 2021 Mar 03]. Available from: https://cdr.lib.unc.edu/record/uuid:8ead5fe9-6886-4daf-a5c3-79c7eac2c91b.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Lin L. Characterization of the Water Transport Properties of the Active Layers of Polyamide Reverse Osmosis and Nanofiltration Membranes. [Thesis]. University of North Carolina; 2015. Available from: https://cdr.lib.unc.edu/record/uuid:8ead5fe9-6886-4daf-a5c3-79c7eac2c91b

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of North Carolina

4. Sandor, Magdalena. NMR Study of Local Magnetism, Anelastic Deformation, and Liquid Behavior of Bulk Metallic Glasses.

Degree: Physics and Astronomy, 2012, University of North Carolina

URL: https://cdr.lib.unc.edu/record/uuid:6ea6e6c5-615a-4d66-91ca-b88e67e5faf2

► In this dissertation, 27Al NMR studies of CuZr- and La-based metallic glasses were carried out to investigate local magnetic properties, the mechanism of anelastic deformation,… (more)

▼ In this dissertation, 27Al NMR studies of CuZr- and La-based metallic glasses were carried out to investigate local magnetic properties, the mechanism of anelastic deformation, and liquid state behavior. The first part of this dissertation will cover magnetization properties of (CuZr)93-xAl7Gdx bulk metallic glasses (BMGs) from temperature dependent 27Al NMR spectroscopy and magnetic susceptibility measurements. Significant nonlinear line broadening of 27Al spectra commencing at high temperatures is attributed to a local magnetic susceptibility distribution. Magnetization measurements confirm linewidth enhancement caused by the strong frustrated development of antiferromagnetic magnetic short-range order. The next section of this dissertation concerns constant-compression experiments that were carried out at room temperature to study the anelastic response of La50Ni15Al35 bulk metallic glasses with varying compression time and stress. 27Al NMR nutation experiments were used to measure changes of the quadrupolar interaction in order to probe local structural changes induced by anelastic recovery. It was observed that anelastic deformation results in enhanced local symmetry at Al sites and that the changes of local structure are proportional to the magnitude of stress and compression time. Modulated differential calorimetry studies were also performed to understand the correspondence between local structure changes observed and changes in free volume. These results can be further reconciled within the theory of atomic level stresses. The last topic addressed in this dissertation is temperature-dependent 27Al nuclear magnetic resonance (NMR) experiments above the liquid temperature in La-based metallic glasses. The coexistence of two liquid states was observed from phase separation driven by differences of density or chemical potential. In addition, nonlinear liquid behavior also emerged and indicates a first-order-like phase transition. The nonlinear behavior was verified in the spectroscopy and spectral linewidths. Annealing tests show that features of phase separation can be controlled, which may be significant for processing applications of metallic glasses. These NMR results provide important thermodynamic insight for the understanding different mechanisms that drive phase separation and the underlying relevance of potential energy landscape theory. Advisors/Committee Members: Sandor, Magdalena, Sandor, Magdalena, Wu, Yue, Sen, Pabitra, McNeil, Laurie, Clegg, Thomas, Qin, Lu-Chang.

Subjects/Keywords: College of Arts and Sciences; Department of Physics and Astronomy

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APA (6^th Edition):

Sandor, M. (2012). NMR Study of Local Magnetism, Anelastic Deformation, and Liquid Behavior of Bulk Metallic Glasses. (Thesis). University of North Carolina. Retrieved from https://cdr.lib.unc.edu/record/uuid:6ea6e6c5-615a-4d66-91ca-b88e67e5faf2

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Sandor, Magdalena. “NMR Study of Local Magnetism, Anelastic Deformation, and Liquid Behavior of Bulk Metallic Glasses.” 2012. Thesis, University of North Carolina. Accessed March 03, 2021. https://cdr.lib.unc.edu/record/uuid:6ea6e6c5-615a-4d66-91ca-b88e67e5faf2.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Sandor, Magdalena. “NMR Study of Local Magnetism, Anelastic Deformation, and Liquid Behavior of Bulk Metallic Glasses.” 2012. Web. 03 Mar 2021.

Vancouver:

Sandor M. NMR Study of Local Magnetism, Anelastic Deformation, and Liquid Behavior of Bulk Metallic Glasses. [Internet] [Thesis]. University of North Carolina; 2012. [cited 2021 Mar 03]. Available from: https://cdr.lib.unc.edu/record/uuid:6ea6e6c5-615a-4d66-91ca-b88e67e5faf2.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Sandor M. NMR Study of Local Magnetism, Anelastic Deformation, and Liquid Behavior of Bulk Metallic Glasses. [Thesis]. University of North Carolina; 2012. Available from: https://cdr.lib.unc.edu/record/uuid:6ea6e6c5-615a-4d66-91ca-b88e67e5faf2

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of North Carolina

5. Silano, Jack. Sub-barrier Photofission Measurements in 238U and 232Th.

Degree: Physics and Astronomy, 2016, University of North Carolina

URL: https://cdr.lib.unc.edu/record/uuid:b6b4f9a1-eb77-4214-a7ba-98700c2eb141

► A study of photofission of ²³²Th and ²³⁸U was performed using quasi-monoenergetic, linearly-polarized γ-ray beams from the High Intensity γ-ray source at TUNL. The prompt… (more)

Subjects/Keywords: College of Arts and Sciences; Department of Physics and Astronomy

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APA (6^th Edition):

Silano, J. (2016). Sub-barrier Photofission Measurements in 238U and 232Th. (Thesis). University of North Carolina. Retrieved from https://cdr.lib.unc.edu/record/uuid:b6b4f9a1-eb77-4214-a7ba-98700c2eb141

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Silano, Jack. “Sub-barrier Photofission Measurements in 238U and 232Th.” 2016. Thesis, University of North Carolina. Accessed March 03, 2021. https://cdr.lib.unc.edu/record/uuid:b6b4f9a1-eb77-4214-a7ba-98700c2eb141.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Silano, Jack. “Sub-barrier Photofission Measurements in 238U and 232Th.” 2016. Web. 03 Mar 2021.

Vancouver:

Silano J. Sub-barrier Photofission Measurements in 238U and 232Th. [Internet] [Thesis]. University of North Carolina; 2016. [cited 2021 Mar 03]. Available from: https://cdr.lib.unc.edu/record/uuid:b6b4f9a1-eb77-4214-a7ba-98700c2eb141.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Silano J. Sub-barrier Photofission Measurements in 238U and 232Th. [Thesis]. University of North Carolina; 2016. Available from: https://cdr.lib.unc.edu/record/uuid:b6b4f9a1-eb77-4214-a7ba-98700c2eb141

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of North Carolina

6. Burant, Alex. Characterizing Hyperpolarized Xenon-129 Depolarization Mechanisms During Continuous-flow Spin Exchange Optical Pumping and as a Source of Image Contrast.

Degree: Physics and Astronomy, 2018, University of North Carolina

URL: https://cdr.lib.unc.edu/record/uuid:d55aa0a8-dcfb-42d4-b575-b6b1b9c23712

► Xenon-129 has become the isotope of choice for applications of hyperpolarized (HP) noble gases in magnetic resonance imaging (MRI) and spectroscopy due to its lower… (more)

▼ Xenon-129 has become the isotope of choice for applications of hyperpolarized (HP) noble gases in magnetic resonance imaging (MRI) and spectroscopy due to its lower cost and higher availability compared to helium-3, relatively high tissue solubility, and wide range of chemical shifts. As the signal achieved in HP gas MRI is directly related to the nuclear spin polarization, the production of large volumes of highly polarized xenon-129 is paramount. While near unity levels of xenon polarization have been achieved in optical cells using stopped-flow spin exchange optical pumping (SEOP), continuous-flow SEOP is the most widely used method for clinical applications as it enables the production of large volumes of hyperpolarized gas, which are necessary for imaging applications in humans. However, polarization levels achieved via continuous-flow SEOP are well below the theoretically predicted values. In this dissertation, xenon-129 relaxation mechanisms that are often ignored during continuous-flow SEOP are investigated, through both simulations and experiments, to quantify their effects. First, computational fluid dynamics simulations are used to better characterize the SEOP process inside the optical cells. This work reveals turbulence inside the optical cell occurs at much lower flow rates than previously predicted. Turbulence leads to a wide distribution of xenon residency times in the cell, previously assumed to be constant for a given flow rate. This could be a cause for the discrepancy between the theoretical model for the final xenon polarization and the levels achieved experimentally. Then, the effect of diffusion-mediated depolarization of xenon-129 gas in magnetic field inhomogeneities during continuous-flow SEOP is determined. The results indicate that xenon diffusion in regions in which the magnetic field abruptly changes strength and direction can be a major source of depolarization during continuous-flow SEOP. As such, care should be taken in the design of the SEOP setup to avoid these gradients in the flow path of the HP gas. In the absence of such large magnetic field gradients, wall collisions remain the major contributing factor to gas-phase spin relaxation. Depolarization in magnetic field gradients can also be a source of image contrast for magnetic resonance imaging. To this end, the effects of longitudinal and transverse spin relaxation are separated and characterized for hyperpolarized xenon-129 diffusing near SPIONs using finite element analysis and Monte Carlo simulations. Simulations demonstrate that signal loss near SPIONs is dominated by transverse relaxation, with little contribution from longitudinal relaxation. In addition, experimental and computational work clearly show that the high diffusion coefficient of xenon does not provide appreciable sensitivity enhancement to SPIONs at the length scales typically probed by MRI. This work provides a better understanding of often-ignored relaxation mechanisms during continuous-flow hyperpolarization and will aid… Advisors/Committee Members: Burant, Alex, Branca, Rosa, Clegg, Thomas, Henning, Reyco, McNeil, Laurie, Ng, Jack.

Subjects/Keywords: College of Arts and Sciences; Department of Physics and Astronomy

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APA (6^th Edition):

Burant, A. (2018). Characterizing Hyperpolarized Xenon-129 Depolarization Mechanisms During Continuous-flow Spin Exchange Optical Pumping and as a Source of Image Contrast. (Thesis). University of North Carolina. Retrieved from https://cdr.lib.unc.edu/record/uuid:d55aa0a8-dcfb-42d4-b575-b6b1b9c23712

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Burant, Alex. “Characterizing Hyperpolarized Xenon-129 Depolarization Mechanisms During Continuous-flow Spin Exchange Optical Pumping and as a Source of Image Contrast.” 2018. Thesis, University of North Carolina. Accessed March 03, 2021. https://cdr.lib.unc.edu/record/uuid:d55aa0a8-dcfb-42d4-b575-b6b1b9c23712.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Burant, Alex. “Characterizing Hyperpolarized Xenon-129 Depolarization Mechanisms During Continuous-flow Spin Exchange Optical Pumping and as a Source of Image Contrast.” 2018. Web. 03 Mar 2021.

Vancouver:

Burant A. Characterizing Hyperpolarized Xenon-129 Depolarization Mechanisms During Continuous-flow Spin Exchange Optical Pumping and as a Source of Image Contrast. [Internet] [Thesis]. University of North Carolina; 2018. [cited 2021 Mar 03]. Available from: https://cdr.lib.unc.edu/record/uuid:d55aa0a8-dcfb-42d4-b575-b6b1b9c23712.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Burant A. Characterizing Hyperpolarized Xenon-129 Depolarization Mechanisms During Continuous-flow Spin Exchange Optical Pumping and as a Source of Image Contrast. [Thesis]. University of North Carolina; 2018. Available from: https://cdr.lib.unc.edu/record/uuid:d55aa0a8-dcfb-42d4-b575-b6b1b9c23712

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of North Carolina

7. Buckner, Matthew. Hydrogen Burning of the Rare Oxygen Isotopes.

Degree: Physics and Astronomy, 2014, University of North Carolina

URL: https://cdr.lib.unc.edu/record/uuid:876509f7-86a6-4773-a854-00420c972e7a

► At the Laboratory for Experimental Nuclear Astrophysics (LENA), two rare oxygen isotope proton capture studies were performed at low energies – ¹⁸O(p,γ)¹⁹F and ¹⁷O(p,γ)¹⁸F. The goal… (more)

▼ At the Laboratory for Experimental Nuclear Astrophysics (LENA), two rare oxygen isotope proton capture studies were performed at low energies – ¹⁸O(p,γ)¹⁹F and ¹⁷O(p,γ)¹⁸F. The goal of each study was to improve thermonuclear reaction rates at stellar plasma temperatures relevant to ¹⁸O and ¹⁷O destruction, respectively. The stellar nucleosynthesis temperature regime corresponds to very low proton bombarding energies. At these low energies, the Coulomb barrier suppresses the reaction yield in the laboratory, and environmental backgrounds dominate the detected signal, making it difficult to differentiate the γ-cascade from background. At LENA, the electron cyclotron resonance (ECR) ion source produces intense, low-energy proton beam, and these high currents boost the reaction yield. LENA, a "sea-level" facility dedicated to nuclear astrophysics, also has a coincidence detector setup that reduces environmental background contributions and boosts signal-to-noise. The sensitivity afforded by γγ-coincidence and high beam current allowed these rare oxygen isotope reactions to be probed at energies that correspond to stellar plasma temperatures. For stars with masses between 0.8 M_⊙ < M < 8.0 M_⊙, nucleosynthesis enters its final phase during the asymptotic giant branch (AGB) stage. This is an evolutionary period characterized by grain condensation that occurs in the stellar atmosphere; the star also experiences significant mass loss during this period of instability. Presolar grain production can often be attributed to this unique stellar environment. A subset of presolar oxide grains features dramatic ¹⁸O depletion that can not be explained by the standard asymptotic giant star burning stages and dredge-up models. An extra mixing process for low-mass asymptotic giant branch stars, known as cool bottom processing (CBP), was used in the literature to explain this and other anomalies. Cool bottom processing can also occur during the red giant branch (RGB) phase, but it is not thought to contribute to the extreme ¹⁸O depletion observed within certain stellar environments and within presolar grain samples. However, intense depletion could result from the ¹⁸O + p processes during cool bottom processing in low-mass AGB stars. A portion of this dissertation describes a study of the ¹⁸O(p,γ)¹⁹F reaction at low energies performed at LENA. Based on these new results, it was found that the resonance at E_R = 95 keV has a negligible effect on the reaction rate at the temperatures associated with cool bottom processing when compared to the (p,α) reaction. It was also observed that the direct capture S-factor is almost a factor of 2 lower than the previously recommended value at low energies. The product of this research is a new thermonuclear reaction rate for… Advisors/Committee Members: Buckner, Matthew, Iliadis, Christian, Cecil, Gerald, Champagne, Arthur, Clegg, Thomas, Heitsch, Fabian.

Subjects/Keywords: Nuclear physics; Astronomy; College of Arts and Sciences; Department of Physics and Astronomy

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APA (6^th Edition):

Buckner, M. (2014). Hydrogen Burning of the Rare Oxygen Isotopes. (Thesis). University of North Carolina. Retrieved from https://cdr.lib.unc.edu/record/uuid:876509f7-86a6-4773-a854-00420c972e7a

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Buckner, Matthew. “Hydrogen Burning of the Rare Oxygen Isotopes.” 2014. Thesis, University of North Carolina. Accessed March 03, 2021. https://cdr.lib.unc.edu/record/uuid:876509f7-86a6-4773-a854-00420c972e7a.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Buckner, Matthew. “Hydrogen Burning of the Rare Oxygen Isotopes.” 2014. Web. 03 Mar 2021.

Vancouver:

Buckner M. Hydrogen Burning of the Rare Oxygen Isotopes. [Internet] [Thesis]. University of North Carolina; 2014. [cited 2021 Mar 03]. Available from: https://cdr.lib.unc.edu/record/uuid:876509f7-86a6-4773-a854-00420c972e7a.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Buckner M. Hydrogen Burning of the Rare Oxygen Isotopes. [Thesis]. University of North Carolina; 2014. Available from: https://cdr.lib.unc.edu/record/uuid:876509f7-86a6-4773-a854-00420c972e7a

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of North Carolina

8. Kelly, Keegan. Nuclear Reaction Rate Uncertainties and the 22Ne(p,γ)23Na Reaction: Classical Novae and Globular Clusters.

Degree: Physics and Astronomy, 2016, University of North Carolina

URL: https://cdr.lib.unc.edu/record/uuid:c5bd94e5-fca2-440a-9419-dbf33edd4150

► The overall theme of this thesis is the advancement of nuclear astrophysics via the analysis of stellar processes in the presence of varying levels of… (more)

▼ The overall theme of this thesis is the advancement of nuclear astrophysics via the analysis of stellar processes in the presence of varying levels of precision in the available nuclear data. With regard to classical novae, the level of mixing that occurs between the outer layers of the white dwarf core and the solar accreted material in oxygen-neon novae is presently undetermined by stellar models, but the nuclear data relevant to these explosive phenomena are fairly precise. This precision allowed for the identification of a series of elemental ratios indicative of the level of mixing occurring in novae. Direct comparisons of the modelled elemental ratios to observations showed that there is likely to be much less of this mixing than was previously assumed. Thus, our understanding of classical novae was altered via the investigation of the nuclear reactions relevant to this phenomenon. However, this level of experimental precision is rare and large nuclear reaction uncertainties can hinder our understanding of certain astrophysical phenomena. For example, it is commonly believed that uncertainties in the 22Ne(p,g)23Na reaction rate at temperatures relevant to thermally-pulsing asymptotic giant branch stars are largely responsible for our inability to explain the observed sodium-oxygen anti-correlation in globular clusters. With this motivation, resonances in the 22Ne(p,g)23Na reaction at E_c.m. = 458, 417, 178, and 151 keV were measured. The direct-capture contribution was also measured at E_lab = 425 keV. It was determined that the 22Ne(p,g)23Na reaction rate in the astrophysically relevant temperature range is dominated by the resonances at 178 and 151 keV and that the total reaction rate is greater than the previously assumed rate by a factor of approximately 40 at 0.15 GK. This increased reaction rate impacts the expected nucleosynthesis that occurs in these stars and will shed light onto the origin of this anti-correlation as it is incorporated into sophisticated stellar models in the future. In both of these cases the available nuclear data were used to probe stellar processes. This analysis of stellar processes through nuclear reactions is an extremely useful technique that is crucial for the advancement of astrophysics. Advisors/Committee Members: Kelly, Keegan, Champagne, Arthur, Iliadis, Christian, Clegg, Thomas, Heitsch, Fabian, Law, Nicholas.

Subjects/Keywords: College of Arts and Sciences; Department of Physics and Astronomy

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Kelly, K. (2016). Nuclear Reaction Rate Uncertainties and the 22Ne(p,γ)23Na Reaction: Classical Novae and Globular Clusters. (Thesis). University of North Carolina. Retrieved from https://cdr.lib.unc.edu/record/uuid:c5bd94e5-fca2-440a-9419-dbf33edd4150

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Kelly, Keegan. “Nuclear Reaction Rate Uncertainties and the 22Ne(p,γ)23Na Reaction: Classical Novae and Globular Clusters.” 2016. Thesis, University of North Carolina. Accessed March 03, 2021. https://cdr.lib.unc.edu/record/uuid:c5bd94e5-fca2-440a-9419-dbf33edd4150.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Kelly, Keegan. “Nuclear Reaction Rate Uncertainties and the 22Ne(p,γ)23Na Reaction: Classical Novae and Globular Clusters.” 2016. Web. 03 Mar 2021.

Vancouver:

Kelly K. Nuclear Reaction Rate Uncertainties and the 22Ne(p,γ)23Na Reaction: Classical Novae and Globular Clusters. [Internet] [Thesis]. University of North Carolina; 2016. [cited 2021 Mar 03]. Available from: https://cdr.lib.unc.edu/record/uuid:c5bd94e5-fca2-440a-9419-dbf33edd4150.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Kelly K. Nuclear Reaction Rate Uncertainties and the 22Ne(p,γ)23Na Reaction: Classical Novae and Globular Clusters. [Thesis]. University of North Carolina; 2016. Available from: https://cdr.lib.unc.edu/record/uuid:c5bd94e5-fca2-440a-9419-dbf33edd4150

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of North Carolina

9. Daniels, Timothy Vaughn. Spin-correlation coefficients and phase-shift analysis for p+3He elastic scattering.

Degree: Physics and Astronomy, 2009, University of North Carolina

URL: https://cdr.lib.unc.edu/record/uuid:517d74d7-03f8-4e85-8e93-07529e2432cd

► A new spin-exchange optical pumping polarized 3He target has been used to measure angular distributions of A0y , Ayy , and Axx for p+3He elastic… (more)

Subjects/Keywords: College of Arts and Sciences; Department of Physics and Astronomy

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Daniels, T. V. (2009). Spin-correlation coefficients and phase-shift analysis for p+3He elastic scattering. (Thesis). University of North Carolina. Retrieved from https://cdr.lib.unc.edu/record/uuid:517d74d7-03f8-4e85-8e93-07529e2432cd

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Daniels, Timothy Vaughn. “Spin-correlation coefficients and phase-shift analysis for p+3He elastic scattering.” 2009. Thesis, University of North Carolina. Accessed March 03, 2021. https://cdr.lib.unc.edu/record/uuid:517d74d7-03f8-4e85-8e93-07529e2432cd.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Daniels, Timothy Vaughn. “Spin-correlation coefficients and phase-shift analysis for p+3He elastic scattering.” 2009. Web. 03 Mar 2021.

Vancouver:

Daniels TV. Spin-correlation coefficients and phase-shift analysis for p+3He elastic scattering. [Internet] [Thesis]. University of North Carolina; 2009. [cited 2021 Mar 03]. Available from: https://cdr.lib.unc.edu/record/uuid:517d74d7-03f8-4e85-8e93-07529e2432cd.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Daniels TV. Spin-correlation coefficients and phase-shift analysis for p+3He elastic scattering. [Thesis]. University of North Carolina; 2009. Available from: https://cdr.lib.unc.edu/record/uuid:517d74d7-03f8-4e85-8e93-07529e2432cd

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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