The ISO-SWS detectors: Performance trends and space radiation effects

We present a trend analysis of the ISO-SWS detector performance and a study of the space radiation effects on the SWS detectors. In particular, dark c urrents, dark current noise and detector responses have been checked as a f unction of time through the mission and as a function of time in a revoluti on. The results show that these parameters were stable during the mission i n all bands but for band 3 (Si:As). Dark currents and responses were found to be higher in the first hours following the start of the science window, especially in band 2 (Si:Ga). We have studied the impacts of cosmic rays an d radiation belt particles on the SWS detectors, as well as of the only lar ge solar proton event on November 6, 1997, that occurred during the ISO mis sion (operated during solar minimum). The observed glitch rates in all SWS bands are found to be between 2 and 4 times higher than the value predicted by the CREME96 model for the cosmic r ay flux in the period considered. The bands that registered the highest gli tch rates showed also a correlation with the electron fluxes measured on th e GOES 9 spacecraft. From the distribution of glitch heights (voltage jumps in the detector signal), we have derived the deposited energy distribution s of the particles hits. Our results lead to the conclusion that secondary particles produced in the shield and the detectors contributed at least as much as cosmic rays to the observed glitch rate. The effects on the detecto rs of the November 6, 1997 event, which caused that all observations in a r evolution were declared failed, are described in detail.