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Long Wave IR Visible UV X-rays Gamma rays wavelength (nm) X-rays Frau Röntgen's hand Visit for more Learning Resources
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X-rays Long Wave IR Visible UV X-rays Gamma rays
Long Wave IR Visible UV X-rays Gamma rays wavelength (nm) X-rays
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X-ray tube
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X-ray tube
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X-rays
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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
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X-rays Mechanism Decelerating charges give off radiation
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X-rays Mechanism Decelerating charges give off radiation
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X-rays Mechanism Decelerating charges give off radiation
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X-rays Mechanism Decelerating charges give off radiation
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X-rays Mechanism Decelerating charges give off radiation
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X-rays Typical tube spectrum
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X-rays - vary tube voltage
Iconts = AiZV~2 Ichar = Ai(V-Vcrit)~1.5 E >> hc/Kedge Intensity E > hc/Kedge E ≈ hc/Kedge Wavelength
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X-rays More electron transitions
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X-rays Cu spectrum
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X-rays Al spectrum
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X-rays Au L spectrum
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X-rays Moseley's law - energy vs. atomic number
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X-ray sources common - Cu, Mo, Fe, Cr, W, Ag
Sealed tubes - Coolidge type common - Cu, Mo, Fe, Cr, W, Ag Ka = (2 Ka1 + Ka2)/3
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X-ray sources common - Cu, Mo, Fe, Cr, W, Ag
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)
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X-ray sources Intensity changes with take-off angle
But resolution decreases with take-off angle
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X-ray sources
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Other X-ray sources Rotating anode high power - 40 kW demountable
various anode types
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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 radians divergence (3-5 4 m) high brilliance wavelength tunable
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Other X-ray sources Synchrotron Advantages 10-4 - 10-5 rad divergence
(3-5 4 m) high brilliance wavelength tunable
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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 rad divergence (3-5 4 m) high brilliance wavelength tunable high signal/noise ratio
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X-ray sources Synchrotron Advantages 10-4 - 10-5 rad divergence
(3-5 4 m) high brilliance wavelength tunable
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X-ray sources Synchrotron Advantages 10-4 - 10-5 rad divergence
(3-5 4 m) high brilliance wavelength tunable
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Beam conditioning Collimation
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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
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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
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Beam conditioning Monochromatization
Crystal monochromators – LiF, SiO2, pyrolytic graphite critical – reflectivity ex: for MoK, LiF 9.4% graphite 54 %
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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°
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For more detail contact us
Beam conditioning Monochromatization Monochromator shape usually flat – problems with divergent beams concentrating type – increases I by factor of 1.5-2 For more detail contact us
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