The effects of radiation damage on the spectral resolution of the Chandrayaan-1 X-ray Spectrometer

The Chandrayaan-1 X-ray Spectrometer (C1XS) was launched onboard the Indian Space Research Organisation (ISRO) Chandrayaan-1 lunar mission in October 2008. The instrument consisted of 24 swept-charge device silicon X-ray detectors providing a total collecting area of similar to 24 cm(2), corresponding to a 14 degrees field of view (FWHM), with the ability to measure X-rays from 0.8 - 10 keV. During the 10 months the spacecraft was located in orbit around the Moon a number of solar flare X-ray events were detected, along with calibration data from X-ray sources housed inside the movable door of the instrument. This paper presents a study of the degradation in spectral resolution of the measured X-ray calibration lines, comparing those recorded mid way through the mission lifetime with ground based calibration data collected prior to the launch of the instrument. The radiation environment the detectors were subjected to is discussed in light of the actual radiation damage effects on the spectral resolution observed in flight.