Complex sentence: If the thickness of the layer formed on the disk is too thick then the lines of the spectrum are broadened, this is because some of the energy of the alpha particles is lost during their movement through the layer of active material.
Split into simpler sentences: If the thickness of the layer formed on the disk is too thick then the lines of the spectrum are broadened. This is because some of the energy of the alpha particles is lost during their movement through the layer of active material.