General properties of the X-ray spectrum for beam K = 400 keV (red) and K = 800 keV (blue). Top: ratio of the luminosity radiated from the rear of the cloud and the hot spot at the front as a function of the density of the cloud. Middle: luminosity of the spectra as a function of the density. Bottom: dependence of the centroid of the X-ray energy distribution on the cloud density. The continuous and dashed lines refer to data from the transmitted and backscattered spectra. The kinetic energy of the e-beam is fully absorbed within the cloud for particle densities above 10¹⁴ cm⁻³.