COS-B carried a single large experiment the design and provision of which have been the responsibility of a group of research laboratories known as the Caravane Collaboration. The characteristics of the instrument are described below. The Gamma-Ray Telescope performed well throughout the mission: the only complication being the occasional erratic performance of the spark-chamber and the inevitable reduction in performance as the spark chamber gas aged. This aging was, however, minimized by means of a gas-replenishment system that permitted emptying and refilling of the spark chamber. As the rate of gas deterioration decreased with time, it became possible to increase the interval between flushing from its initial value of once every 6 weeks to about once every 36 weeks before the final flushing in November 1981. The spark chamber was still performing creditably at the end of the mission in April 1982.
A comparison of data from overlapping observation periods enabled longterm sensitivity changes of COS-B to be estimated. For the first three years of the mission, the sensitivity was virtually stable. However, a slow fall-off began to develop. From careful monitoring, curves for the empirical correction factors were derived. Over time, the level of the background component increased. This increase was due largely to the interaction of cosmic rays with the massive parts of the satellite and surrounding subsystems. Significant reductions were achieved by increasing the modulation of the cosmic rays with the approach of the solar maximum. This effect served to counter-balance the reduction in detector sensitivity.
The originally foreseen duration of the mission was two years, but in fact COS-B was finally switched off on 25th April 1982, having functioned successfully for 6 years and 8 months.
Beneath the telescope was an energy calorimeter, which absorbed the secondary particles produced by the incident photons. For on-axis incidence, the effective detector area reached a maximum value of ~50 cm2 at ~400 MeV. The energy resolution had its best value (~40% FWHM) at about 150 MeV and was better than 100% up to at least 3 GeV. The experiment was described in detail by Bignami et al. (1975).
Alongside the Gamma-Ray Telescope was mounted a proportional counter sensitive to 2-12 keV X-rays. This detector was intended to provide synchronization of possible pulsed gamma-ray emission from pulsating X-ray sources. The pulsar synchronizer was also used for monitoring the intensity of radiation from X-ray sources.
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