Alpha Particle X-ray Spectrometer onboard Chandrayaan-2 Rover

Alpha Particle X-ray Spectrometer (APXS) is one of the two scientific experiments on Chandrayaan-2 rover named as Pragyan. The primary scientific objective of APXS is to determine the elemental composition of the lunar surface in the surrounding regions of the landing site. This will be achieved by employing the technique of X-ray fluorescence (XRF) spectroscopy using in situ excitation source ²⁴⁴Cm emitting both X-rays and alpha particles. These radiations excite characteristic X-rays of the elements by the processes of particle induced X-ray emission and XRF. The characteristic X-rays are detected by the ‘state-of-the-art’ X-ray detector known as Silicon Drift Detector, which provides high energy resolution, as well as high efficiency in the energy range of 1–25 keV. This enables APXS to detect all major rock forming elements such as, Na, Mg, Al, Si, Ca, Ti and Fe. The flight model of the APXS payload has been completed and tested for various instrument parameters. The APXS provides energy resolution of ~135 eV at 5. 9keV for the detector operating temperature of about –35°C. The design details and the performance measurement of APXS are presented in this paper.