Question about X-ray power emitted by the Coolidge tube

[samy4408]

hello i found this equation in a course about x rays , and i couldn't find it anywhere else
they said that it is the theoretical expression of the energy spectrum , and dφ/dE is variation of the power emitted by the Coolidge tube as a function of the energy of the x ray. but i didn't understand it .
can someone point me to another source, where i can find this expression ?
thanks !

 

[gleem]

Google Kramers law or Kramers rule for bremsstrahlung.

 

[samy4408]

Google Kramers law or Kramers rule for bremsstrahlung.

thanks a lot !