Gravitational redshift experiments with the high-resolution Moessbauer resonance in 67Zn

A gravitational redshift (GRS) experiment using the high-resolution Moessbauer resonance in 67Zn is described. The tiny Doppler motion of the source can be checked by a dc-SQUID based displacement sensor. The results on the GRS strongly indicate that solid-state effects, which are difficult to control experimentally, finally limit the accuracy that Moessbauer measurements can provide in determining the GRS. We argue that for this reason conventional Moessbauer experiments most probably will not be able to compete with other methods in future GRS measurements of very high precision. (orig.)