There were 4 X-ray detectors in the UCL/MSSL experiment. The main detector was a proportional counter sensitive to the energy range 2.5-10.0 keV (1-3 Å). It had a simple collimation tube with a 2.5 x 3.5 degree FWHM field of view. The effective area was 17.8 cm2 with a sensitivity of about 3 mCrab. The others were two proportional counters and a channeltron, at the foci of grazing incidence telescopes. The channeltron suffered from high UV background and was not scientifically productive. The proportional counters covered the energy range 0.7-1.5 keV and 1.4-4.2 keV (6-18 Å and 3-9 Å). By the clever use of stops at the foci, the fields of view and the effective areas could be set to 10´ (12.3 cm2), 3´ (11.3 cm2), or 1´ (7.6 cm2) and 10´ (3.7 cm2), 6´ (2.4 cm2), or 2´ (1.0 cm2) for the high and low energy systems, respectively. These 2 systems became inoperable in July 1973 due to a failure of a background shutter.
The basic accumulation time was 62.5 seconds, followed by 24 seconds of dead time. Thus, effectively, there was an 86.509 second sampling interval. There was a way to force better time resolution (to multiples of 1.62 s, this mode was named J20), which was used occasionally for observing bright sources, searching for bursts, etc. However this mode was used only on a few occasions and was not scientifically useful.
A six channel Pulse Height Analyzer could be connected to any one of the 3 proportional counters and used to gather spectral information.
The UV Experiment
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