The COS NUV dark rate is monitored regularly by taking 2 1330s dark exposures every 2 weeks. These exposures, after excluding thosethat graze the SAA, are used to determine the dark rate trend with time. Background counts in FUV observations can come from a variety of sources including radioactive decay of atoms in the detector glass, external charged particles, scattered light, and phosphorescence from the detector window.
For more information on the COS NUV dark rate see ISR 2010_12: COS NUV Detector Dark Rates During SMOV and Cycle 17
Dark Rate vs. Time
Most Recent Dark Monitoring Exposures: