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x-rays.ppt
- 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
- 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
- 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
- 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