A Ring Imaging Cherenkov (RICH) detector system has been built and is
now in full operation within the DELPHI experiment. Large data samples
of Z(O) decays are being collected with good resolution on the observ
ed Cherenkov angles. Several studies of Z(O) decays using the RICH hav
e already been performed on limited samples. Disturbance of the detect
or operation caused by shrinkage of polymeric construction materials a
nd by migration of radiator substance is reported. These effects have
been counteracted and do not endanger the quality of the data.