JEM-X consists of two identical coded-aperture mask telescopes co-aligned with the other instruments on INTEGRAL . The photon detection system consists of high-pressure imaging Microstrip Gas Chambers (MSGC) located at a distance of 3.4 m from each coded mask. Figure 2 shows a schematic diagram of one JEM-X unit. A single JEM-X unit comprises 3 major subsystems: the detector, the associated electronics and the coded mask.
The two JEM-X units have been used alternatively in the past, and are currently operated simultaneously. The decision to use only one instrument at a time was made about three months after launch when a gradual loss in sensitivity had been observed in both JEM-X units, due to the erosion of the microstrip anodes inside the detector. By lowering the operating voltage, and thereby the gain of the detectors, the anode damage rate has now been reduced to a level where the survival time of the detectors seems to be assured for a further five year period. Only 6 anodes have been lost on JEM-X1 in all of 2006. Another 7 anode strips have been lost on JEM-X1 in the first 8 months of 2007. For the complete, updated list of dead anodes see http://outer.space.dtu.dk/users/oxborrow/sdast/InstrConfig/JC.BadAnodes.txt
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