1 / 34

X-rays

Long Wave IR Visible UV X-rays Gamma rays. 10 12 10 6 10 3 10 1 10 -1 10 -3. wavelength (nm). X-rays. Frau R öntgen's hand.

Télécharger la présentation

X-rays

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


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

  2. Long Wave IR Visible UV X-rays Gamma rays 1012 106 103 10 1 10-1 10-3 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. Iconts = AiZV~2 Ichar = Ai(V-Vcrit)~1.5 E >> hc/Kedge E > hc/Kedge E ≈ hc/Kedge X-rays - vary tube voltage Intensity Wavelength

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

  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. X-rays detector filter specimen 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

  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

More Related