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)
The constant K is proportional to the atomic number of the target element, and
The intensity described above is a particle flux and not an energy flux as can be seen by the fact that the integral over values from
To obtain a simple expression for the energy flux, first change variables from
The energy flux, which we will call
for
for
It is a linear function that is zero at the maximum energy