Week 2 - X-ray Diffraction

X-Rays

High energy EM radiation

Usually wavelengths in the Amstrong range 10^-10m

Production of X-Rays

Bombardment of target with energetic electrons which undergo collisions and scattering, resulting in the production of X-rays

Bremsstrahlung X-rays

Continuous X-ray which results from electrons changing direction when travelling in proximity to the target nucleus

Kinetic energy of incoming electron - energy of emitted X-ray photon  

Characteristic X-ray 

Result from incoming electron knocking out electron from atomic shell of target 

KE incoming e- > binding energy of shell e- 

Vacancy filled with e- from outer shell resulting in the emission of X-ray photon with characteristic energy equal to the difference in binding energies of shells involved

Characteristic X ray series between shells 

Diffraction

Interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/opening

Constructive interference

2 sets of waves meet in phase

Path difference between 2 waves is nλ

Destructive interference 

2 sets of waves meet completely out of phase 

Path difference is (n+1/2)λ

Fraunhofer single slit diffraction 

Diffraction from crystal lattice planes

Diffraction with monochromatic beam

Angularly dispersive XRD

Diffraction with white light

Energy dispersive XRD

Single crystal XRD

Detailed information about internal lattice of crystaline substances to provide a mineral IDP

Powder XRD

Can analyse single crystal or rock powder with lots of randomly oriented fragments so sample doesn’t need to be rotated

Example of powder XRD

Peaks correspond to diffraction on different lattice planes

Key equations