Using tritium and x-ray tubes as x-ray calibration sources for the AXAF CCD imaging spectrometer

Accurate quantum efficiency calibrations for CCDs require stable sources of known cc-ray energies. Radioactive sources are the most stable although some stable commercial cc-ray tubes are available. However, sealed, stable cc-ray tubes include windows which filter low energy cc-rays to which our CCDs are sensitive. Therefore we have developed a windowless radioactive source using the beta spectrum from tritium to fluoresce low-energy x-rays from low Z targets. The potential drawback of tritium outgassing is also investigated. This source is coupled with an additional system based on a stable commercial x-ray tube to produce higher energy x-rays. Together these sources form a system for comparative quantum efficiency measurements with two CCDs mounted on translation stages. We report on the physics and development of these cc-ray sources.