To investigate giant resonances in the doubly magic nucleus 48Ca, a coincidence experiment of the reaction 48Ca(p,p'n) was performed at the proton accelerator of the National Accelerator Centre, Faure, South Africa. The setup for the detection of neutrons consisted of one 4" x 2" NE213 and five 5" x 2" BC501A scintillation detectors, which were circularly positioned around the scattering center at a distance of 80 cm. These neutron detectors were taken from an existing setup at the S-DALINAC to perform (e,e'n) coincidence experiments. The low radiation background in the environment of the proton accelerator allowed for the use of only the polyethylene collimators of the massive (e,e'n) shielding. These collimators minimized the influence of inscattered neutrons. To investigate the decay of the nucleus 48Ca excited in the reaction (p,p'n), statistcal model calculations were performed. Assuming pure quadrupole excitations, the contribution of nonstatistical decay in the neutron spectra was estimated to be less than 20%. This contribution can be fully explained by knockout reactions. In a former experiment for the investigation of giant resonances in the doubly magic nucleus 40Ca, emitted protons and alpha-particles were detected in coincidence with the scattered proton. Within the scope of this work, experimental angular correlations of the reaction 40Ca(p,p'alpha0), where the ground state of the daughter nucleus 36Ar is populated, were described within a simple model. With the aid of this description, the experimental cross section was unfolded to contributing multipoles. An extension to the more complex p0-decay channel in 40Ca was performed, where again the angular correlations could be described. The limitation of the model became apparent in the reaction 48Ca(p,p'n0), where the isotropic angular correlations could not be described unambiguously. In both nuclei low lying isoscalar quadrupole strength is observed to be heavily fragmented. The E2 strength distribution in 40Ca extracted in the decay channels investigated, are consistent with results from electron scattering and microscopic RPA calculations. In 40Ca, the exhaustion of the isoscalar energy weighted E2-sum rule in the excitation energy range Ex = 11.3 - 16.0 MeV is in the alpha0-decay channel 10.3(2.1)% and in the excitation energy range Ex = 10.9 - 15.8 MeV in the p0-decay channel 17.4(3.5)%. A factor of two more strength in the alpha0-decay channel, found in inelastic alpha-scattering - which has lead to questioning the methods derived for the conversion of hadronic cross sections to transition strength - was not verified. In the n0-decay channel of 48Ca an exhaustion of 11.0(2.2)% of the isoscalar energy weighted E2-sum rule is observed in the excitation energy range Ex = 11.0 - 14.0 MeV. A second part of this thesis was the extension of the Darmstadt (e,e'n) setup: The efficiencies of the neutron detectors were already determined within the framework of former theses, using the well known neutron spectrum of spontaneous fission of 252Cf. However, a comparison to Monte Carlo calculations resulted in a discrepancy in the absolute normalization of 6.5%. Within this thesis, another calibration measurement of the neutron dector having the highest statistics in the former calibration was performed at the low backscattering experimental hall of the Physikalisch-Technische Bundesanstalt, Braunschweig using monoenergetic neutrons. As a result, the actual light output function for protons of the detector calibrated was extracted. In order to describe the efficiencies of the neutron detectors correctly, results of Monte Carlo calculations have to be scaled by 2.5% to higher values. Furthermore, an additional 4" x 2" NE213 detector was calibrated. The existing (e,e'n) setup at Darmstadt was extended by this detector. | English |
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