Payloads : 4. X-ray fluorescence spectrometer (LEX)

An X-ray spectrometer, sensitive in the 1 to 10 keVregion will determine the major element compositionof the lunar surface material, by determiningthe flux of the characteristic Kƒ¿ X-rays of variouselements like Mg, Al, Si, Ca and Fe. Since fluorescentX-rays are excited by the solar flare X-rayflux, a solar X-ray monitor (SXM), consisting oftwo Si pin diodes, orthogonally placed, each coveringa field of view of 90. will monitor the Sun all thetime. The frequency and energy spectrum of thesolar flares depend on the phase of the solar cycle.Distribution of Mg, Al and Si and, possibly Ca, Tiand Fe during energetic X-ray flares, can be measuredusing this technique. A spectrometer similarto the one onboard Smart-1 mission (DCIXS, Foinget al 2004; Grande et al 2003) having an active areaof 50 cm2 should be quite suitable for this purpose.The spectrometer uses a swept charge device foroptimizing the signal to background ratio. Witha 5. collimator, it is expected to have a spatialresolution of 20 km. Since the operation of the Xrayspectrometer depends on solar illumination, animaging strategy has been developed, although itwill provide useful data only during flare time.