Determination of the Proton Polarizability with an Active Target and Measurement of Dipole Strength in the 235U (gamma,gamma') Reaction up to 4.4 MeV at the S-DALINAC

In the first part of this thesis a new experimental method is presented for a model-independent determination of the energy and angle dependence of the differential cross sections in elastic Compton scattering on the proton. The generated bremsstrahlung is scattered on hydrogen in two special high pressure ionization chambers. The scattered photons are registered in large NaI(Tl) detectors under two angles. In coincidence with the photons the energy and direction of the scattered protons are detected in the high pressure ionization chambers by means of an anode of special geometry. In this work the ionization chambers and electronics were optimized. Two experiments at electron energies of 60 MeV and 79.3 MeV were carried out at the S-DALINAC in 2006 and 2007. The results for the polarizabilities of the proton are presented. In the second part the odd-mass actinide isotope 235U is investigated with the nuclear resonance fluorescence method at the S-DALINAC at endpoint energies of 3.5 MeV and 4.4 MeV under a scattering angle of 135°. In the excitation energy region up to 2.2 MeV seven peaks were identified. In the energy region of scissors mode from 2 MeV up to 4 MeV no discrete transitions were observed. However, a fluctuation analysis of the spectra reveals significant unresolved strength hidden in the background. Assuming a ratio between M1 and E1 transition strength corresponding to the even-mass neighbour isotope 236U a M1 transition strength for 235U of (3.6±1.3) μ2N is extracted. This value is in good agreement with the systematics of even-mass isotopes in this mass-region, where the scissors mode is observed with the total strength 3 μ2N