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Title: The asymmetry of the ¹²C(γ→,pn) reaction
Author: Franczuk, Stefan
ISNI:       0000 0001 3482 2086
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1998
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The work presented in this thesis describes the first experimental study of the ¹²C(γ→,pn) reaction using linearly polarised tagged photons in the energy range 150 MeV to 360 MeV. The experiment was carried out using the MAMI-B c.w. electron accelerator at the Institut fur Kernphysik, Mainz, Germany. Linearly polarised Bremsstrahlung photons were produced by a diamond radiator and are tagged by momentum analysing the recoiling electrons using the Glasgow tagging spectrometer. The tagger has an energy resolution of 2MeV and can tag photon fluxes of up to ~10⁸s⁻¹. The ¹²C target was in the form of a 2mm thick graphite sheet, placed at an angle of 30° to the photon beam line. A plastic scintillator hodoscope PiP was used to detect the protons from the target, and covered polar angles from 51° to 129°, with a resolution of ~4.5° and azimuthal angles from -22.8° to +22.8°. The coincident neutrons were detected in 6 banks of plastic time-of-flight (TOP) scintillator detectors, each made up of 2 layers. These were positioned opposite PiP, covering polar angles from 10° to 175° with a resolution of ~2°, and azimuthal angles in the range 160° to 200°. The detector system has a missing energy resolution of ~7.5 MeV for allowing nucleon breakup from the (1p1p) shells and (1s1p) shells to be distinguished. Direct knockout events were selected on the basis of angular correlation and missing energy. Photon asymmetries and parallel and perpendicular cross sections were measured in 12 photon energy bins, each of width 20 MeV. Within each bin asymmetries were measured for 3 missing energy regions, (20-40 MeV), (40-70 MeV) and (>70 MeV), corresponding to the ejection of nucleons from (1p1p ), (1p1s) shells and multiparticle processes respectively. Systematics of the asymmetries were studied by measuring those asymmetries as a function of recoil momentum for the 20-40 MeV and the 40-70 MeV missing energy regions. W ithin the 20-40 MeV region photon asymmetries were also measured as a function of proton polar angle. Differential cross sections were also m easured for both the parallel and perpendicular directions of polarisation, in the 20-40 MeV missing energy region. Comparisons have been made with results on lighter nuclei from previous experiments, which aUow some clear trends to be identified. The data have been shown to be consistent with direct 2N knockout for missing energies up to 70 MeV. The data have also been compared to predictions of asymmetry from the theory developed by the Gent group, and good agreements have been found in the 20-40 MeV missing energy region, at photon energies above 200 MeV. Differences were found between data and theory in the 40-70 MeV missing energy region, and for the 20-40 MeV region below 200 MeV.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Polarised photons; Photoabsorption; Detectors