For a synchrotron radiation facility, for example, the electron beam produces an x-ray beam that then travels down a beamline before reaching the experiment.

Film thicknesses may range from a few nm to several 100 nm, and such thin films are still fully penetrated by the x-ray beam.

The peak spectral radiance and the average spectral radiance are both important properties of an x-ray beam.

In a synchrotron light source, low emittance means that the resulting x-ray beam will be small, and result in higher brightness.

In the early days, radiotherapy was comparatively crude: patients were blasted with x-ray beams from different directions, aimed in such a way as to converge on the tumour.