Alpha Particle X-Ray Spectrometer (APXS) On-board Chandrayaan-2 Rover -- Pragyan

TL;DR

The APXS instrument on Chandrayaan-2's Pragyan rover uses X-ray fluorescence spectroscopy with a Cm-244 source and Silicon Drift Detector to determine lunar surface elemental composition, achieving high resolution and efficiency.

Contribution

This paper presents the design, development, and performance testing of the APXS instrument for lunar surface elemental analysis on Chandrayaan-2.

Findings

APXS detects major rock-forming elements like Na, Mg, Al, Si, Ca, Ti, Fe.

The instrument achieves 135 eV energy resolution at 5.9 keV.

Flight Model of APXS has been successfully tested.

Abstract

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 spectroscopy using in-situ excitation source Cm-244 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 (PIXE) and X-ray fluorescence (XRF). The characteristic X-rays are detected by the state-of-the-art X-ray detector known as Silicon Drift Detector (SDD), which provides high energy resolution as well as high efficiency in the energy range of 1 to 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 (FM) of the APXS payload has been completed and tested for various instrument parameters. The APXS provides energy resolution of 135 eV at 5.9 keV for the detector operating temperature of about -35 deg C. The design details and the performance measurement of APXS are presented in this paper.