Production of Eta-Mesons in Collisions of Nucleons and Delta-Resonances

We calculate the cross section for the production of $\eta$-mesons via \mbox{$\Delta N \to N N \eta$} in a relativistic One-Boson-Exchange-Model. Using this cross section we then determine the probability for the production of an $\eta$-meson by a $\Delta$-resonance moving in nuclear matter. The result is compared to prescriptions in BUU-calculations in which \et-production proceeds both through a direct channel and through the sequential process $\Delta \to N \pi ; \pi N \to N \eta$.Comment: revised version: large parts have been rewritten, there are two new figures. A discusion of effects of multi-body reactions of the intermediate pion on our results has been adde