X-ray crystallography. What tools do we have to ID minerals so far?. How do we know atomic structure of minerals?. Atoms are 1-5Å apart so how do we see this?. X-rays. Between 0.1 and 10Å (1Å = 0.1 nm). X-rays. Amplitude Wavelength. X-ray interference. Constructive is in phase.
Constructive is in phase
Destructive if out of phase
Interference and diffraction
If a wave encounters a barrier with several holes, the
propagating wave will have sharper peaks of intensity at
Table 2-1: Wavelengths in Nanometer Units of Characteristic Emission Lines for Selected Elements.
Element K[alpha] K[alpha]1 K[alpha]2 K[beta]1 L[alpha]1
Cr 0.229092 0.228962 0.229351 0.228480 ****
Cu 0.154178 0.154051 0.1544330 0.139217 1.3357
Mo 0.071069 0.070926 0.071354 0.063225 0.54062
W 0.021060 0.020899 0.021381 0.018436 0.14763
Destructive and constructive interference of waves
nl=2dsinq n is the “order”
As soon as the crystal is rotated, the beam ceases (This is diffraction, not reflection)
Only get diffraction at certain angles!
Relation between l and d and q