Most elements emit x-rays when properly bombarded with electrons. Heavier
elements (like tungsten) are best because they emit a higher intensity through
bremsstrahlung, but there are plenty of heavy elements to choose from. The
real issue is engineering: Most electrons that hit the tungsten don't do
anything special at all -- no bremsstrahlung, no K-shell emission. All of the
energy from the electrons' impact then goes into heating the tungsten.
Tungsten is used because it can withstand this bombardment, as it has a high
melting point and can conduct heat away very well.
What would happen if you replaced the tungsten with something else?
The bremsstrahlung pattern looks very similar no matter what element you use.
The K-shell emission spectrum is unique and different for each element.
In bremsstrahlung, why is a range of photons emitted instead of just one
The incoming electron is accelerated and strikes the tungsten at a high speed
and has a lot of energy. Recall that we called it "braking radiation." The
electron might be slowed a little or a lot.
Yes, but there is more. If we represent all of the energy of the electron as a
pie, there are bazillions of different ways of cutting up this pie.
No, there is only one cut-off that corresponds to a minimum wavelength. There
is no limit to a maximum wavelength emitted. Go back to the bremsstrahlung
spectrum and see how it fades gradually to zero for long wavelengths.