In my text book, I came across this question:

What is the equation used to determine the shortest wavelenght of the bremsstrahlung spectrum of x-rays?

The answer was:

λ = hc/eV. (Where: h is planck constant, c is the speed of light, e is the electron charge and V is the voltage across the cathod and the anode in Coolidge tube.

I thought the above equation is used to determine the shortest wavelength of the charecteristic spectrum of x-rays, so why it is used here? Could some ome clarify things for me, please?


1 Answer 1


That represents all the kinetic energy gained by an electron $eV$ becoming a photon of energy $\frac {hc}{\lambda}$.

If electrons do not have enough energy to produce a characteristic X-ray photon then none such photons will be produced.

enter image description here

If the cut off wavelength for the continuous spectrum was $1\,\rm Å$ (corresponding to an electron energy of approximately $12 \,\rm kV$) then the K-lines would be produced from the Copper target but not from the Molybdenum target. So the shortest wavelength of the continuous spectrum must be less than the wavelength of a characteristic X-ray line.
In the case of Molybdenum the minimum energy of the incoming electron has be be approximately $18 \,\rm kV$ (photon wavelength $0.7\,\rm Å$) to produce a K-line.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.