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

Stephen E. Jones, Marshall Bautz, Steven Kissel, and Michael Pivovaroff
Center for Space Research, Massachusetts Institute of Technology
Cambridge, Massachusetts, 02139


Accurate quantum efficiency calibrations for CCDs require stable sources of known x-ray energies. Radioactive sources are the most stable although some stable commercial x-ray tubes are available. However, sealed, stable x-ray tubes include windows which filter low energy x-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 x-ray sources.

KEYWORDS: ACIS, AXAF, calibration, CCD, tritium, x-ray source