X-Ray Telescope for an Orbiting Solar Observatory

The X-ray experiment described here was designed to monitor the intensity, energy distribution, and time variations of solar X-rays, and to measure the intensity and angular distribution of X-rays over the celestial sphere. The detector, which operates between about 7 to 200 Kev, will also monitor local effects due to cosmic rays, trapped particles, and albedo gamma rays The telescope consisted of a thin NaI (T1) crystal-phototube assembly surrounded by a 10.5-lb cylindrical cup-shaped CsI(T1) shield crystal. The shield, connected in anticoincidence, had a 2-cm wall and defined a field of view of 13 degrees half-angle for the NaI detector. The detector had an area of 9.3 cm2 and a geometry factor of 1.5 sterad-cm2. The charge-energy relationship was divided into eight logarithmically spaced pulse-height channels. Integral rates of the shield crystal were monitored for two thresholds, set at 85 Kev and 3.2 Mev, respectively. Binary and logic circuits provided scaling, storage, and directional information for each channel, and conditioned the data for transmission through the spacecraft telemetry. The experiment is to be flown on the NASA S-57 Orbiting Solar Observatory-C, scheduled for launch in early 1965. The observatory is to be placed in a near circular orbit at 300 nautical miles at an inclination of 33 degrees to the equator. The design lifetime of the instrument is six months. Performance checks with ground observations and with high-altitude balloons indicated the counting rate due to phototube noise to be 3 counts per minute for events > 7 Kev.