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An Investigation of the Isovector Giant Quadrupole Resonance in 209Bi using Polarized Compton ScatteringHenshaw, Seth January 2010 (has links)
<p><p></p><p>Giant multipole resonances are a fundamental property of nuclei and</p><p>arise from the collective motion of the nucleons inside</p><p>the nucleus. Careful studies of these resonances and their properties provides</p><p>insight into the nature of nuclear matter and constraints</p><p>which can be used to test our theories. </p><p></p></p><p><p></p><p>An investigation of the Isovector Giant Quadrupole Resonance (IVGQR)</p><p>in <sup>209</sup>Bi has been preformed using the High Intensity γ-ray</p><p>Source (HIγS) facility. Intense nearly monochromatic</p><p>polarized γ-rays were incident upon a <sup>209</sup>Bi target producing</p><p>nuclear Compton scattered γ-rays that were detected using the HIγS</p><p>NaI(Tl) Detector Array (HINDA). The HINDA array consists of six</p><p>large (10''x10'') NaI(Tl) core crystals, each surrounded by an</p><p>optically segmented 3'' thick NaI(Tl) annulus. The scattered γ-rays</p><p>both parallel and perpendicular to the plane of polarization were</p><p>detected at scattering angles of 55° and 125° with</p><p>respect to the beam axis. This was motivated by the realization that</p><p>the term representing the interference between the electric dipole</p><p>(E1) and electric quadrupole (E2) amplitudes, which appears in the</p><p>theoretical expression for the ratio of the polarized cross sections,</p><p>has a sign difference between the forward and backward angles and also</p><p>changes sign as the incident γ-ray energy is scanned over the E2</p><p>resonance energy. The ratio of cross sections perpendicular and</p><p>parallel to the plane of polarization of the incident γ-ray were</p><p>measured for thirteen different incident γ-ray energies between 15 and</p><p>26 MeV at these two angles and used to extract the parameters of the</p><p>IVGQR in <sup>209</sup>Bi.</p><p></p></p><p><p></p><p>The polarization ratio was calculated at 55° and</p><p>125° using a model consisting of E1 and E2 giant resonances as</p><p>well as a modified Thomson scattering amplitude. The parameters of the E1 giant</p><p>resonance came from previous measurements of the Giant Dipole</p><p>Resonance (GDR) </p><p>in <sup>209</sup>Bi. The finite size of the nucleus was</p><p>accounted for by introducing a charge form factor in the (modified)</p><p>Thomson amplitude. This form factor was obtained from</p><p>measurements of the charge density in inelastic electron scattering</p><p>experiments. </p><p></p></p><p><p></p><p>The resulting curves were fit to the data by varying the</p><p>E2 parameters until a minimum value of the χ<sup>2</sup> was found.</p><p>The resulting parameters from the fit yield an IVGQR in <sup>209</sup>Bi</p><p>located at E<sub>res</sub>=23.0±0.13(stat)±0.25(sys) MeV</p><p>with a width of Γ=3.9±0.7(stat)±1.3(sys) MeV and a</p><p>strength of 0.56±0.04(stat)±0.10(sys) Isovector Giant</p><p>Quadrupole Energy Weighted Sum Rules (IVQEWSRs).</p><p></p></p><p><p></p><p>The ability to make precise measurements of the parameters of the</p><p>IVGQR demonstrated by this work opens up new challenges to both</p><p>experimental and theoretical work in nuclear structure. A detailed</p><p>search for the missing sum rule strength in the case of <sup>209</sup>Bi should</p><p>be performed. In addition, a systematic study of a number of nuclei</p><p>should be studied with this technique in order to carefully examine</p><p>the A dependence of the energy, width and sum rule strength of the</p><p>IVGQR as a function of the mass number A. The unique properties of</p><p>the HIγS facility makes it the ideal laboratory at which to perform</p><p>these studies.</p><p></p></p><p><p></p><p>Such a data base will provide more stringent tests of nuclear</p><p>theory. The effective parameters of collective models can be fine</p><p>tuned to account for such precision data. This should lead to new</p><p>insights into the underlying interactions responsible for the nature</p><p>of the IVGQR. Furthermore, with the recent advances in computational</p><p>power and techniques, microscopic shell model based calculations</p><p>should be possible and could lead to new insights into the underlying</p><p>properties of nuclear matter which are responsible for the collective</p><p>behavior evidenced by the existence and properties of the IVGQR.</p><p></p></p> / Dissertation
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Scalar Meson Effects In Radiative Decays Of Vector MesonsKerman Solmaz, Saime 01 November 2003 (has links) (PDF)
The role of scalar mesons in radiative vector meson decays is
investigated. The effects of scalar-isoscalar f_{0}(980) and
scalar-isovector a_{0}(980) mesons are studied in the mechanism of the radiative Phi-> / pi{+}pi{-}gamma and
phi-> / pi{0}eta gamma decays, respectively. A
phenomenological approach is used to study the radiative
phi-> / pi{+}p{-}gamma decay by considering the
contributions of sigma-meson, rho-meson and f_{0}-meson.
The interference effects between different contributions are
analyzed and the branching ratio for this decay is calculated. The
radiative phi-> / pi{0}eta gamma decay is studied
within the framework of a phenomenological approach in which the contributions of rho-meson, chiral loop and a_{0}-meson are
considered. The interference effects between different
contributions are examined and the coupling constants g_{phi
a_{0} gamma} and g_{a_{0}K{+}K{-}} are estimated using the experimental branching ratio for the
phi-> / pi{0}eta gamma decay. Furthermore, the
radiative rho{0}pi{+}pi{-}gamma$ and
rho{0}-> / pi{0}pi{0}gamma decays are studied to
investigate the role of scalar-isoscalar sigma-meson. The
branching ratios of the rho{0}-> / pi{+}pi{-}gamma
and rho{0}-> / pi{0}pi{0}gamma decays are
calculated using a phenomenological approach by adding to the
amplitude calculated within the framework of chiral perturbation
theory and vector meson dominance the amplitude of sigma-meson
intermediate state. In all the decays studied the scalar meson
intermediate states make important contributions to the overall
amplitude.
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