In X-ray production, one usually distinguishes between bremsstrahlung (continuous spectrum) and characteristic lines. The brilliance of X-ray sources is calculated as
$B = \frac{N}{t \cdot A \cdot \Omega \cdot \frac{\Delta \lambda}{\lambda}}$
where $\frac{\Delta\lambda}{\lambda}$ is the spectral bandwidth of the radiation in question. This makes total sense for continuous spectra, but I wonder, how this can hold true for characteristic lines. So, I basically have two questions:
- How is the spectral bandwidth defined for characteristic lines?
- Where does the spectral brodening stem from for characteristic lines (if any)?