Onboard calibration system for γ-ray spectrometers in space satellites

This paper describes the fabrication method and test results for Co⁶⁰ and Am^{2 4 1} calibration sources to be used in an onboard calibration system for a γ-ray spectrometer and associated x-ray detector to be flown on an earth orbiting satellite. The system consists of radioactive sources loaded into scintillator buttons which-register the charged decay particles (betas and alphas) emitted by the radionuclides in coincidence with γ-rays. The latter are detected by γ-ray and x-ray spectrometers as calibration lines. The scintillator button is viewed by a separate photomultiplier tube so the light pulses resulting from the charged decay particles can be used to gate off the calibration γ-ray lines from the spectrometers during the normal mode of operation. The calibration is achieved by accepting only those pulses which are in coincidence with the pulses from the scintillator button, thus recording the calibration lines from the radioactive source. Some suggestions for future developments are also briefly discussed.