This document discusses x-rays, including their production via decelerating electrons in an x-ray tube, their wavelength spectrum, and common sources like sealed tubes and synchrotrons. It also covers beam conditioning techniques like collimation, monochromatization using filters or crystal monochromators, and issues affecting resolution and intensity.

1. X-rays
1012 106 103 10 1 10-1 10-3
Long Wave IR Visible UV X-rays Gamma rays
wavelength (nm)
Frau Röntgen's hand

2. 1012 106 103 10 1 10-1 10-3
Long Wave IR Visible UV X-rays Gamma rays
wavelength (nm)
X-rays

3. X-ray tube

4. X-ray tube

5. X-rays

6. X-rays
White radiation
Produced upon "collisions" with electrons in target
Any amount of energy can be lost up to a max. amount
Continuous variation of wavelength
Characteristic radiation
Specific energies absorbed
Specific x-ray wavelengths emitted
Wavelengths characteristic of target atom type

7. X-rays
Mechanism
Decelerating charges give off radiation

8. X-rays
Mechanism
Decelerating charges give off radiation

9. X-rays
Mechanism
Decelerating charges give off radiation

10. X-rays
Mechanism
Decelerating charges give off radiation

11. X-rays
Mechanism
Decelerating charges give off radiation

12. X-rays
Typical tube spectrum

13. X-rays - vary tube voltage
Intensity
Wavelength
E ≈ hc/Kedge
E >> hc/Kedge
E > hc/Kedge
Iconts = AiZV~2
Ichar = Ai(V-Vcrit)~1.5

14. X-rays
More electron transitions

15. X-rays
Cu spectrum

16. X-rays
Al spectrum

17. X-rays
Au L spectrum

18. X-rays
Moseley's law - energy vs. atomic number

19. X-ray sources
Sealed tubes - Coolidge type
common - Cu, Mo, Fe, Cr, W, Ag
Ka = (2 Ka1 + Ka2)/3

20. X-ray sources
Sealed tubes - Coolidge type
common - Cu, Mo, Fe, Cr, W, Ag
intensity limited by cooling requirements (2-2.5kW)
(~99% of energy input converted to heat)

21. X-ray sources
Intensity changes with take-off angle

But resolution decreases with take-off angle

22. X-ray sources

23. Other X-ray sources
Rotating anode
high power - 40 kW
demountable
various anode types

24. Other X-ray sources
Synchrotron
need electron or positron beam orbiting in a ring
beam is bent by magnetic field
x-ray emission at bend
Advantages
10-4 - 10-5 radians
divergence
(3-5 mm @ 4 m)
high brilliance
wavelength tunable

25. Other X-ray sources
Synchrotron
Advantages
10-4 - 10-5 rad
divergence
(3-5 mm @ 4 m)
high brilliance
wavelength tunable

26. Other X-ray sources
Synchrotron
need electron or positron beam orbiting in a ring
beam is bent by magnetic field
x-ray emission at bend
Advantages
10-4 - 10-5 rad
divergence
(3-5 mm @ 4 m)
high brilliance
wavelength tunable
high signal/noise ratio

27. X-ray sources
Synchrotron
Advantages
10-4 - 10-5 rad
divergence
(3-5 mm @ 4 m)
high brilliance
wavelength tunable

28. X-ray sources
Synchrotron
Advantages
10-4 - 10-5 rad
divergence
(3-5 mm @ 4 m)
high brilliance
wavelength tunable

29. Beam conditioning
Collimation

30. Beam conditioning
Monochromatization
-filters – materials have atomic nos. 1 or 2 less than anode
50-60% beam attenuation
placing after specimen/before detector
filters most of specimen fluorescence
allows passage of high intensity & long
wavelength white radiation
X-rays
detector
filter
specimen

31. Beam conditioning
Monochromatization
-filters – materials have atomic nos. 1 or 2 less than anode
50-60% beam attenuation
placing after specimen/before detector
filters most of specimen fluorescence
allows passage of high intensity & long
wavelength white radiation

32. Beam conditioning
Monochromatization
Crystal monochromators – LiF, SiO2, pyrolytic graphite
critical – reflectivity ex: for MoK, LiF 9.4%
graphite 54 %

33. Beam conditioning
Monochromatization
Crystal monochromators – LiF, SiO2, pyrolytic graphite
critical – reflectivity ex: for MoK, LiF 9.4%
graphite 54 %
resolution – determines peak/bkgrd ratio &
spectral purity best - Si – 10"
graphite – 0.52°

34. Beam conditioning
Monochromatization
Monochromator shape
usually flat – problems with divergent beams
concentrating type – increases I by factor of 1.5-2