Comparison of the production of neutral pions and high-energetic photons in heavy ion collisions at intermediate incident energies

In the present thesis the production of neutral pions and high-energetic photons (Eγ ≥ 50 MeV) in heavy ion collisions at incident energies of 20 and 84 MeV/u was studied. Thereby it was cared much about to detect both samples in the same reactions in order to obtain conclusions on a possible common production mechanism. The spectra of the pions and photons decrease exponentially and are described at fixed projectile energy in all systems studied by the same value for the decreasement parameter. This is compatible with the assumption that their source system consists always of equally much nucleons of the projectile and the target. The maximum possible number of nucleons (in a central collision) is by this determined by the smaller of the contributing nuclei. An experimental hint for this is to be seen in the pion spectra observed under forward (00) and backward (1800) angles which show for a source system moving with half of the beam rapidity the same exponential decreasing. Also the angular distribution of the photons under the assumption of the emission from such a system is symmetric relative to the 900 direction. A corresponding representation of the angular distribution of the pions doesn't show this symmetry because it is influenced by the absorption of the pions in the surrounding nuclear matter. From the contribution in the cross section missing at the side of the larger of the two nuclei the strength of the absorption can be determined. It represents a large contribution of the measured yield, for instance in the system 18O + Ta about 70% of the measured value are lossed by absorption. (orig./HSI)