Calculation of positron spectra from heavy-ion collisions and study of the line structure

In this thesis the application of the EPOS positron solenoid spectrometer to the measurement of the quasi-atomic positron production in heavy ion collisions as well to the study of line structures is described. For the calculation of positron background contribution originating from nuclear internal pair production with the positron measurement simultaneously measured γ spectra were applied. These were extensively studied concerning their dependence on Zua=Z1+Z2, the incident energy, as well as the ion scattering angles. The multipolarity of the nuclear transitions of the exclusively heavy collisional systems (163 ≤ Zua ≤ 188) could be completely determined under inclusion of theoretical aspects on γ emission in the heavy-ion collision by the comparison of the calculated positron spectra with the experimental data. With the precise knowledge of the nuclear background the quasi-atomic theory is tested and confirmed in dependence on Zua, the incident energy, as well as the scattering angle in a wide range of Zua (163 ≤ Zua ≤ 188) at incident energies at the Coulomb barrier. For the theoretical quasi-atomic production probability a scaling factor fQA=1.0 ± 0.1 is derived. The excellent agreement of the quasi-atomic theory with the experiments allows subsequently the quantitative evaluation of the line structures observed with the EPOS spectrometer. This is performed extensively for the collisional systems 232Th+232Th in dependence on the incident energy as well the scattering angles. An angular distribution is indicated which hints to a connection of the line production with the reaching of the nuclear contact. (orig./HSI)