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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A Comparison of (P,2n) and (P,Pn) Reactions on Cerium-140 at Intermediate Energies

Ruth, Thomas Jean 01 January 1967 (has links)
No description available.
2

Population of low-lying levels in the one-neutron halo nucleus 11Be via the neutron transfer reaction 10Be(d,p)

Schmitt, Kyle Thomas 01 December 2011 (has links)
Historically, measurements of differential cross-sections for the neutron transfer reaction (d, p) on stable targets have been an important tool for extracting spectroscopic information. In particular, it is possible to make orbital angular momentum assignments and extract spectroscopic factors for ground states and excited states by comparing measurements to cross sections calculated for pure single-particle states. In recent years, the advent of rare isotope beams have made it possible to apply this method to increasingly exotic nuclei. As nucleon separation energies decrease along the path to the proton and neutron drip lines, many new reaction channels are opened. Out of the open channels arise complications for theoretical calculations that are not well understood. The archetypal one neutron halo nucleus 11Be has been an important test case for theoretical studies, being within the reach of ab initio theory and relatively near the valley of particle stability while possessing several exotic properties. Although its ground state properties have been studied thoroughly, spectroscopic factors for the first excited state are not well understood. Additionally, little is known about the low-lying resonances. The current study has been performed to provide an extensive data set for the reaction 10Be(d, p) in inverse kinematics, including elastic and inelastic scattering channels important for optical model parameterizations. Differential cross-sections have been measured at equivalent deuteron beam energies of 12, 15, 18, and 21.4 MeV. Results are compared to previous measurements in inverse kinematics at 12 and 25 MeV. The data are also used to evaluate the Distorted Wave Born Approximation and Adiabatic Distorted Wave Approximation methods for cross section calculations and spectroscopic factors are extracted in each case.
3

Monte Carlo Simulations of Ultracold Neutron Velocities

Cox, Isaiah 01 May 2020 (has links)
An electric dipole moment (EDM) in the neutron would indicate a source of CP-violation that is needed to explain the dominance of matter over antimatter in the universe. Several experiments are currently looking for a neutron EDM and so far, the value has been constrained to dn 1.8 x10 26 ecm. Presented here is work supporting the nEDM experiment at Los Alamos National Laboratory which utilizes ultracold neutrons (UCNs) and Ramsey’s separated oscillating fields method. In such an experiment, it is important to understand the velocity of the neutrons due to false EDM signals that can be pro- duced by the presence of a magnetic field. Monte Carlo simulations were used to study the optimal design parameters of a chopper system that would reproduce a given velocity spectrum of a population of neutrons by measuring the time of flight to a detector.
4

Measurement of the Elastic Ep Cross Section at Q2 = 0.66, 1.10, 1.51 and 1.65 Gev2

WANG, YANG 01 June 2017 (has links)
The nucleon form factors have been investigated by physicists for decades because of its fundamental importance. The world data of the proton magnetic form factor GMp shows that the measurements have been focused on Q2 lower than 5 GeV2 and it has large uncertainties at higher GeV2. Experiment E12-07-108 aims to improve the accuracy of the e − p elastic cross section to better than 2% over a Q2 range of 7 − 14 GeV2. From 2015 to 2016, the e − p elastic cross section was measured over a wide range of Q2 from 0.66 − 12.56 GeV2 at the Thomas Jefferson National Accelerator Facility in Virginia, USA. An unpolarized electron beam was scattered off a cryogenic hydrogen target and the scattered electron was detected in the single arm of the high resolution spectrometers (HRS).
5

Determination of the Kinematics of the Qweak Experiment and Investigation of an Atomic Hydrogen Møller Polarimeter

Gray, Valerie Marie 08 February 2017 (has links)
The Qweak experiment has tested the Standard Model through making a precise measurement of the weak charge of the proton (QpW). This was done through measuring the parity-violating asymmetry for polarized electrons scattering off of unpolarized protons. The parity-violating asymmetry measured is directly proportional to the four-momentum transfer (Q^2) from the electron to the proton. The extraction of QpW from the measured asymmetry requires a precise Q^2 determination. The Qweak experiment had a Q^2 = 24.8 ± 0.1 m(GeV^2) which achieved the goal of an uncertainty of ≤ 0.5%. From the measured asymmetry and Q^2 , QpW was determined to be 0.0719 ± 0.0045, which is in good agreement with the Standard Model prediction. This puts a 7.5 TeV lower limit on possible “new physics”. This dissertation describes the analysis of Q^2 for the Qweak experiment. Future parity-violating electron scattering experiments similar to the Qweak experiment will measure asymmetries to high precision in order to test the Standard Model. These measurements will require the beam polarization to be measured to sub-0.5% precision. Presently the electron beam polarization is measured through Møller scattering off of a ferromagnetic foil or through using Compton scattering, both of which can have issues reaching this precision. A novel Atomic Hydrogen Møller Polarimeter has been proposed as a non-invasive way to measure the polarization of an electron beam via Møller scattering off of polarized monatomic hydrogen gas. This dissertation describes the development and initial analysis of a Monte Carlo simulation of an Atomic Hydrogen Møller Polarimeter.
6

Extraction and Parametrization of Isobaric Trinucleon Elastic Cross Sections and Form Factors

Barcus, Scott Kevin 01 January 2019 (has links)
By mining data from Jefferson Lab Hall A experiment E08-014 a new measurement of the 3He elastic cross section at Q^2 ≈ 34 fm^−2 was extracted from a large quasielastic background. This new data point falls approximately halfway between the first and second diffractive minima of the 3He form factors. When combined with recent high Q^2 3He elastic cross section measurements from JLab this new point improves our knowledge of the cross section and form factors at large momentum transfers. The new high Q^2 data motivate a reanalysis of the 3He elastic cross section world data and promise an improved understanding of the magnetic form factor in particular. For this analysis the elastic cross section world data for 3He, and its mirror nuclei 3H, were collected. The world data spans five decades and many different experimental facilities. The world data were then fit using a sum of Gaussians parametrization which allowed for the extraction of both targets’ magnetic and electric form factors, along with charge densities and radii. These new fit results were contrasted with past fit results and compared to modern theoretical predictions.
7

Dihadron Beam Spin Asymmetries On An Unpolarized Hydrogen Target With Clas12

Hayward, Timothy Barton 01 January 2021 (has links) (PDF)
The semi-inclusive deep inelastic scattering process, where an electron scatters off a proton target at high enough energy that the process can be described by the scattering off a single constituent particle, offers targeted access to the internal structure of the nucleon. The process can be described in two phases by parton distribution functions (PDFs), which describe the likelihood of finding a quark or gluon in a particular state inside of the nucleon and then by fragmentation functions (FFs) which describe the likelihood of forming a particular final state particle. One way to study these properties is via the measurement of the beam spin asymmetry, loosely defined as the difference in the production cross section of final state particles from partons with opposite intrinsic angular momenta. The internal physical laws that govern this mechanism are dictated in part by the PDFs and FFs that are of interest. Furthermore, when the final state particles include two hadrons these PDFs are more easily accessed and new and exciting FFs emerge. Azimuthal correlations in the production of hadron pairs in semi-inclusive deep-inelastic scattering provide rich information on nucleon structure. A high precision study of data taken with the newly upgraded CLAS12 detector has been used to extract beam-spin asymmetries for the $\pi^+\pi^-$ channel. The presented data were taken in the fall of 2018 with CLAS12 using a 10.6~GeV longitudinally spin-polarized electron beam delivered by CEBAF incident on a liquid hydrogen target. The wide acceptance and high luminosity of the CLAS12 experiment enable the simultaneous measurement of the scattered electron and multiple final state hadrons with a previously unmatched statistical precision. These data represent the first experimental results obtained with the new CLAS12 system. Beam spin asymmetry amplitudes with respect to the variables $x$, the fraction of longitudinal momentum carried by the struck quark, and $M_{h}$, the invariant mass of the hadron pair, are presented. One extracted asymmetry, sensitive to the azimuthal modulation $\sin(\phir)$, provides the first opportunity to extract the PDF $e(x)$, which provides information about the interaction between gluons and quarks, in a colinear framework. This measurement provides cleaner access to the PDF than alternative methods that also depend on the transverse momentum of the struck quark. A second modulation, sensitive to $\sin(\phih-\phir)$, corresponds to the first ever signal sensitive to the helicity-dependent two-pion fragmentation function $G_1^\perp$. A nonzero signal is reported which describes the dependence of the produced pions on the helicity of the fragmenting quark. A clear sign change is observed around the mass of the $\rho$-meson that appears in model calculations and results from the interference of $s$ and $p$ wave dihadrons. Numerous other asymmetry amplitudes, each sensitive to its own combination of PDFs and FFs, are also extracted.
8

AVERAGE RESONANCE CAPTURE IN COBALT AND MANGANESE USING BORON-10 FILTER TECHNIQUE

Lopez, Armando Macaraeg January 1973 (has links)
<p>The high energy gamma rays from the radiative capture of B¹⁰ filtered neutrons in Mn⁵⁵ and Co⁵⁹ were measured and analyzed in terms of statistical and direct capture model of nuclear reactions. A high resolution NaI(T1)-Ge(Li) pair spectrometer was used to detect the gamma rays. Correlations between (n,Υ) and (d,p) intensities were determined for these nuclei. The distributions of the reduced intensities were also studied and compared with the predictions of the statistical model. Finally an attempt was made to determine a direct capture component in the Co⁶⁰ ground state partial cross-section. It was found that the ground state data could be explained with the resonance amplitudes alone. The following amplitudes were deduced: [equation removed]</p> / Doctor of Philosophy (PhD)
9

A transient model for decomposition and ablation of concrete during a molten core/concrete interaction

Kilic, Arif Nesimi, 1963- January 1991 (has links)
A simple approximation for predicting the concrete erosion rate and depth is derived based on heat balance integral method for conduction with the time dependent boundary conditions. The problem is considered a four-region model including separate, moving heat sinks at the boundaries due to endothermic decomposition reactions. Polynomial temperature profiles are assumed and the results are compared to previous experimental data and other analytical solutions. Since the technique provides an approximate temperature distribution on the average, it does not give the real temperature evaluation but provides a simple prediction of the erosion rates in terms of the parameters that are important during the physical phenomena. Because of its simplicity and reliability, the model might be useful of the larger molten core/concrete interaction models.
10

Fine structure of the Isovector Giant Dipole Resonance: a survey with the (p,p') reaction at zero degrees

Jingo, Maxwell 05 August 2014 (has links)
A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2014. / This investigation involves a survey of the fine structure phenomenon of the Isovector Giant Dipole Resonance (IVGDR) over a wide mass range of nuclei, from 27Al, 40Ca, 56Fe, 58Ni to 208Pb, using inelastic proton scattering at 200 MeV. Proton detection is accomplished using the recently commissioned zero-degree facility of the K600 magnetic spectrometer at iThemba LABS. Inelastic proton experiments at zero degrees are very selective to excitations with low angular momentum transfer, and therefore ideal for studies of the IVGDR. This is because such experiments simplify the analysis of the many contributions to the spectra due to the complex nature of the nuclear interaction. The ability to make precise measurements of the properties of the IVGDR demonstrated by this work opens up new challenges to both experimental and theoretical work in nuclear structure. This is a survey of the (p,p′) reaction at zero degrees as a probe to study properties of the GDR and also the low energy E1 strength with high energy-resolution. Such a data base will provide more stringent tests of nuclear theory and the progress is seen in the details obtained. These tests can only be described by microscopic models including complex degrees-of-freedom. This should lead to new insights into the underlying interactions responsible for the nature of the electric dipole strength in nuclei. In the present study, double-differential cross-sections were converted to equivalent photo-absorption cross-sections and their results compared to previously published photo-absorption data. An excellent correspondence in the excitation-energy region of the Giant Dipole Resonance (GDR) was noticed between the two data sets. The fine structure observed can be described using characteristic energy scales, arising mainly from Landau damping (even though the spreading width may also play a role). The extraction of these characteristic energy scales which are a signature for the decay process was achieved through the use of wavelet analysis. Furthermore, thanks to the recent advances in computational power and techniques, microscopic shell model-based calculations lead to new insights into the underlying properties of the nuclear interaction which are responsible for the collective behaviour evidenced by the existence and properties of the IVGDR. In addition to the extraction of characteristic energy scales, this study also provides level densities of J = 1− states. In order to extract nuclear level densities, there is need to eliminate instrumental background and other contributions to the spectra from (p,p′) scattering using the model-independent Discrete Wavelet Transform (DWT) method. Level densities of J = 1− states are determined using the fluctuation analysis technique and comparisons are made with the phenomenological Back Shifted Fermi Gas (BSFG) model predictions, calculations of the Hartree Fock- Bogoluibov (HFB) microscopic model and Hartree Fock-Bardeen-Cooper-Schrieffer (HF-BCS) predictions. Finally, this survey will simultaneously provide bench-marks on the capabilities and limitations of the new zero-degree facility important for planning of the future experimental work.

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