M. J. Burgdorf

The Long-Wavelength Spectrometer (LWS) onboard the Infrared Space Observatory (ISO) covers the 43197 ¯m region with ten doped-Germanium photoconductors that are read out with integrating JF-4 amplifiers. The behaviour of these detector/readout units during some 500 days of operations in space is described. There are no systematic variations of the sensitivity and of the dark current in observations of photometric standard sources in the sky or in measurements with internal illuminators. The effects of ionising radiation do not vary on long timescales, either. It is shown that the impact of the slow response times of the detectors on the accuracy of line scans is small. 1. INTRODUCTION LWS is one of the four experiments on the European Space Agency's ISO satellite [Ref. 1]. Its focal plane unit consists of three subsystems: The optical subsystem, the Fabry-Perot subsystem and the detector subsystem, which is equipped with photoconductive detectors made of Ge:Be to cover the 43-50¯m regi..