Compton scattering and Bragg diffraction

[eoghan]

Hi! I know that x-rays interact with matter (compton effect). But I also know that when X-rays are incident on a crystal, they are diffracted following the Bragg's law.
My question is: why is the x-ray diffracted when it is incident on a crystal, but it isn't scattered by comtpon scattering?

 

[Andrew Mason]

Hi! I know that x-rays interact with matter (compton effect). But I also know that when X-rays are incident on a crystal, they are diffracted following the Bragg's law.
My question is: why is the x-ray diffracted when it is incident on a crystal, but it isn't scattered by comtpon scattering?

Bragg diffraction and Compton effect are two very different phenomena.

If you are wondering why the x-ray does not experience the Compton effect when undergoing Bragg diffraction, it is because the x-ray does not transfer much energy to the crystal. If it strikes an electron, it will impart energy to the electron and this will necessarily reduce the energy of the x-ray as a result. But the crystal has too much mass to absorb much of the x-ray's energy via the compton effect. It is kind of like a ball hitting a brick wall. Compton effect is observed when you have a photon hitting a particle.

AM

 

[eoghan]

Compton effect is observed when you have a photon hitting a particle.

But I've studied that Compton found the effect by the measurements of the x-ray frequencies scattered by graphite block, which is not a particle

 

[Andrew Mason]

But I've studied that Compton found the effect by the measurements of the x-ray frequencies scattered by graphite block, which is not a particle

Well, the x-rays are not scattered by the block or graphite crystals in the block. They are scattered by the electrons in the graphite.

AM

 

[eoghan]

Well, the x-rays are not scattered by the block or graphite crystals in the block. They are scattered by the electrons in the graphite.

AM

but then... why in the bragg diffraction aren't the x-rays scattered by the electrons of the cristal?

 

[Andrew Mason]

but then... why in the bragg diffraction aren't the x-rays scattered by the electrons of the cristal?

I suspect that there is some Compton scattering. Whether Compton scattering occurs for a particular electron may depend on the way the electron is bound to the nucleus. If the energy imparted to the electron by the x-ray photon is less than the energy required to take it to the next energy level, the electron cannot take on the x-ray's energy, so there would not be any change in x-ray energy.

AM