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We suggest a method for probing global properties of clump populations inGiant Molecular Clouds (GMCs) in the case where these act as X-ray reflectionnebulae (XRNe), based on the study of the clumping's overall effect on thereflected X-ray signal, in particular on the Fe K-alpha line's shoulder. Weconsider the particular case of Sgr B2, one of the brightest and most massiveXRN in our Galaxy. We parametrise the gas distribution inside the cloud using asimple clumping model, with the slope of the clump mass function (alpha), theminimum clump mass (m_{min}), the fraction of the cloud's mass contained inclumps (f_{DGMF}), and the mass-size relation of individual clumps as freeparameters, and investigate how these affect the reflected X-ray spectrum. Inthe case of very dense clumps, similar to those presently observed in Sgr B2,these occupy a small volume of the cloud and present a small projected area tothe incoming X-ray radiation. We find that these contribute negligibly to thescattered X-rays. Clump populations with volume filling factors of > 10^{-3},do leave observational signatures, that are sensitive to the clump modelparameters, in the reflected spectrum and polarisation. Future high-resolutionX-ray observations could therefore complement the traditional optical and radioobservations of these GMCs, and prove to be a powerful probe in the study oftheir internal structure. Finally, clumps in GMCs should be visible both asbright spots and regions of heavy absorption in high resolution X-rayobservations. We therefore further study the time-evolution of the X-raymorphology, under illumination by a transient source, as a probe of the 3ddistribution and column density of individual clumps by future X-rayobservatories.

Probing the clumping structure of Giant Molecular Clouds through the spectrum, polarisation and morphology of X-ray Reflection Nebulae