Calibration of the C1XS instrument on Chandrayaan-1

The Chandrayaan-1 X-ray spectrometer (C1XS) experiment on the Chandrayaan-1 mission was designed to carry out spectroscopic observations in the 1-10 keV range for deriving lunar chemistry. We present results from the ground calibration of the Swept Charge Devices (SCDs) on C1XS at the RESIK X-ray beam facility at Rutherford Appleton Laboratory, Chilton, UK. The spectral redistribution function of the SCDs are determined in the energy range from 2.3-8 keV using discrete line energies from a monochromatic X-ray beam. The detection efficiency of the SCDs are determined relative to a reference Si-PIN detector. The Si-PIN detector itself has been calibrated at the beamlines of the synchrotron facility at PTB/BESSY II. A non-Gaussian response matrix which includes probability for partial absorption events in the SCD is constructed using instrument parameters obtained from ground calibration. The calibration spectra from the 55Fe radioactive isotopes obtained from C1XS while in the lunar orbit, are used to validate the response matrix derived on ground.