Tripmania

Why does X-Ray diffraction work without a coherent source ? I have an idea about the answer. Maybe the photons do not need to interact with each other. Maybe diffraction also works with a single photon which interacts with itself. However Bragg's equation is always described with multiple photons and different path lengths in the crystal... Moreover, I bthought that X-rays could be used to observed periodicities much larger than the wavelength. Is it possible that a single atom give information about such distances ? Where is the mistake ?