Kramers' law

Kramers' law is a formula for the spectral distribution of X-rays produced by an electron hitting a solid target. The formula concerns only bremsstrahlung radiation, not the element specific characteristic radiation. It is named after its discoverer, the Dutch physicist Hendrik Anthony Kramers.

The formula for Kramers' law is usually given as the distribution of intensity (photon count) ${\displaystyle I}$ against the wavelength ${\displaystyle \lambda }$ of the emitted radiation:

The constant K is proportional to the atomic number of the target element, and ${\displaystyle \lambda _{min}}$ is the minimum wavelength given by the Duane–Hunt law.

...
Wikipedia