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Figure 3.5: The quantum efficiency of the ROSAT PSPC as a function of energy. Included are the window transmission, the average transmission of the window support mesh, and the gas stopping efficiency [ROSAT AO-21991, NRA 91-OSSA-31991]
The quantum efficiency of PSPC-B (the curve for PSPC-C would be nearly identical) as a function of energy is shown in Fig. 3.5. The curve includes the window transmission, average transmission of the window support mesh (79%), and the absorption of the counter gas. The window becomes almost completely transparent by 2 keV, where the counter gas becomes no longer optically thick. The X-ray absorption of the counter gas is close to 100% in the 0.1-2.0 keV band. The fall-off at keV occurs where the effective area of the X-ray mirrors also cuts off (see Fig. 2.5).