Vela 5A and 5B
The scintillation X-ray detector (XC) aboard Vela 5A and its twin Vela 5B consisted of two 1 mm thick NaI(Tl) crystals mounted on photomultiplier tubes and covered by a 0.13 mm thick beryllium window. Electronic thresholds provided two energy channels, 3–12 keV and 6–12 keV. In front of each crystal was a slat collimator providing a full width at half maximum (FWHM) aperture of ~6.1 × 6.1 degrees. The effective detector area was ~26 cm2. The detectors scanned a great circle every 60 s, and covered the whole sky every 56 hr. Sensitivity to celestial sources was severely limited by the high intrinsic detector background, equivalent to about 80% of the signal from the Crab Nebula, one of the brightest sources in the sky at these wavelengths.
The Vela 5B satellite X-ray detector remained functional for over ten years.
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