The High-Energy Celestial X-ray Experiment, a Goddard Space Flight Center effort headed by K. H. Frost, measured the spectrum of X-ray sources in the energy range of 0.01 - 1 MeV and searched for temporal variations in the intensity and spectrum of point sources. In addition, it measured the diffuse component of celestial X-rays over a scanned strip of the sky and set limits on the intensity and isotropy of the 0.511 MeV positron annihilation radiation.
The Soft X-ray Background Radiation experiment of W. L. Kraushaar (U. Wisconsin) studied the galactic latitude dependence of the X-ray background radiation using proportional counters with as narrow a collimation as practical in the region 0.150 - 45 keV. Energy resolution relied largely on selective window transmission rather than pulse height measurement. Viewing was parallel and anti-parallel to the wheel spin direction, so that two single paths across the sky, galactic pole to galactic pole, were carefully surveyed with high statistical accuracy approximately every 6 months.
The Graphite Crystal X-ray Spectrometer, a Columbia University experiment headed by H. L. Kestenbaum, was used to measure continuum profiles over the 2 - 8 keV band with high spectral resolution. During satellite day, solar spectra were obtained. Stellar X-ray sources were observed during satellite night. The spectrometer made use of the wheel rotation to obtain a complete Bragg spectrum every 10 seconds. X-rays transmitted by the slat collimators struck the large graphite crystal panels. Those X-rays which satisfied the Bragg condition for reflection from graphite were reflected into the central bank of detectors. The detectors were double-sided proportional counters with 0.025 mm beryllium windows on each side and contained an argon-xenon gas mixture chosen for its high efficiency over the 2 - 8 keV range. The Graphite Crystal X-ray polarimeter experiment, also out of Columbia University, operated in a similar fashion reflecting X-rays off of a graphite crystal panel into a small proportional counter. The panels reflected preferentially those X-rays polarized perpendicular to the plane defined by the incident and reflected rays.
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