Hard Solar X-Ray Monitoring

Description

The UCSD solar X-ray experiment was designed to accomplish two principal objectives: (1) to study, with good temporal and energy resolution, the solar X-ray emission over the energy interval 2-300 keV and (2) to monitor the local radiation environment (cosmic rays, trapped protons and electrons, and cosmic and local X-rays), thereby allowing for a clean interpretation of the primary results. The charged particle data from solid-state detectors were read out each 15.36 s. The instrument was located in the rotating wheel section of the spacecraft. The three detector systems in the instruments were: (1) a collimated proportional counter (2-15 keV), (2) a NaI(Tl) scintillation counter (10-300 keV), and (3) three silicon surface-barrier, charged-particle devices. The proportional counter consisted of an aluminum collimator (20 by 90 deg), a 2-mm-thick Be window, and an aluminum-lined counter filled to one atm with xenon and carbon dioxide in a nine to one ratio. The detector was provided with a weak Fe(55) source for inflight calibration. The basic element in the hard X-ray detector was a 1-cm thick by 3.5-cm diameter NaI(Tl) scintillator directly coupled to an RCA photomultiplier tube (PMT). A two-segment CsI(Na) anticoincidence shield surrounded the aluminum cylinder subassembly. Each segment of the shield was polished, wrapped in aluminum foil to provide efficient light reflection to an end-mounted PMT, covered by a layer of lead foil, and placed in an aluminum housing. The shield-detector unit had a 90-deg response in the wheel-rotation plane and a plus/minus 10-deg response in the perpendicular direction. The detector output was analyzed and loaded into nine energy-channel counters. Inflight calibration for the system was provided by monitoring the outputs from a series of suitably placed Am(241) sources. For more details, see T. M. Harrington et al., IEEE. Trans. Nucl. Sci., v. NS-19, p. 596, 1972.