X-raysX-rays

1012 106 103 10 1 10-1 10-3

Long Wave IR Visible UV X-rays Gamma rays

wavelength (nm)

Frau Röntgen's handFrau Röntgen's hand

1012 106 103 10 1 10-1 10-3

Long Wave IR Visible UV X-rays Gamma rays

wavelength (nm)

X-raysX-rays

X-ray tubeX-ray tube

water inlet

filament (cathode)

target (anode)

x-ray window

focusing cup

water inlet

filament (cathode)

target (anode)

x-ray window

focusing cup

X-ray tubeX-ray tube

X-raysX-rays

X-raysX-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

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

X-raysX-rays

Mechanism

Decelerating charges give off radiation

Mechanism

Decelerating charges give off radiation

X-raysX-rays

Mechanism

Decelerating charges give off radiation

Mechanism

Decelerating charges give off radiation

X-raysX-rays

Mechanism

Decelerating charges give off radiation

Mechanism

Decelerating charges give off radiation

X-raysX-rays

Mechanism

Decelerating charges give off radiation

Mechanism

Decelerating charges give off radiation

X-raysX-rays

Mechanism

Decelerating charges give off radiation

Mechanism

Decelerating charges give off radiation

X-raysX-rays

Typical tube spectrumTypical tube spectrum

X-rays - vary tube voltageX-rays - vary tube voltage

Inte

nsi

ty

Wavelength

E ≈ hc/Kedge

E >> hc/Kedge

E > hc/Kedge

Iconts = AiZV~2

Ichar = Ai(V-Vcrit)~1.5

X-raysX-rays

More electron transitionsMore electron transitions

X-raysX-rays

Cu spectrumCu spectrum

X-raysX-rays

Al spectrumAl spectrum

X-raysX-rays

Au L spectrumAu L spectrum

X-raysX-rays

Moseley's law - energy vs. atomic numberMoseley's law - energy vs. atomic number

X-ray sourcesX-ray sources

Sealed tubes - Coolidge typecommon - Cu, Mo, Fe, Cr, W, Ag

Sealed tubes - Coolidge typecommon - Cu, Mo, Fe, Cr, W, Ag

Ka = (2 Ka1 + Ka2)/3Ka = (2 Ka1 + Ka2)/3

X-ray sourcesX-ray sources

Sealed tubes - Coolidge typecommon - Cu, Mo, Fe, Cr, W, Agintensity limited by cooling requirements (2-

2.5kW)(~99% of energy input converted to

heat)

Sealed tubes - Coolidge typecommon - Cu, Mo, Fe, Cr, W, Agintensity limited by cooling requirements (2-

2.5kW)(~99% of energy input converted to

heat)

X-ray sourcesX-ray sources

Intensity changes with take-off angleIntensity changes with take-off angle

But resolution decreases with take-off angleBut resolution decreases with take-off angle

X-ray sourcesX-ray sources

Other X-ray sourcesOther X-ray sources

Rotating anode

high power - 40 kWdemountablevarious anode types

Rotating anode

high power - 40 kWdemountablevarious anode types

Other X-ray sourcesOther X-ray sources

Synchrotron need electron or positron beam orbiting in a

ringbeam is bent by magnetic field

x-ray emission at bend

Synchrotron need electron or positron beam orbiting in a

ringbeam is bent by magnetic field

x-ray emission at bend

Advantages

10-4 - 10-5 radians divergence (3-5 mm @ 4 m)

Advantages

10-4 - 10-5 radians divergence (3-5 mm @ 4 m)

high brilliancewavelength tunablehigh brilliancewavelength tunable

Other X-ray sourcesOther X-ray sources

Synchrotron

Advantages

10-4 - 10-5 rad divergence (3-5 mm @ 4 m)

high brilliancewavelength tunable

Synchrotron

Advantages

10-4 - 10-5 rad divergence (3-5 mm @ 4 m)

high brilliancewavelength tunable

Other X-ray sourcesOther X-ray sources

Synchrotron need electron or positron beam orbiting in a

ringbeam is bent by magnetic field

x-ray emission at bend

Advantages

10-4 - 10-5 rad divergence (3-5 mm @ 4 m)

high brilliancewavelength tunable

high signal/noise ratio

Synchrotron need electron or positron beam orbiting in a

ringbeam is bent by magnetic field

x-ray emission at bend

Advantages

10-4 - 10-5 rad divergence (3-5 mm @ 4 m)

high brilliancewavelength tunable

high signal/noise ratio

X-ray sourcesX-ray sources

Synchrotron

Advantages

10-4 - 10-5 rad divergence (3-5 mm @ 4 m)

high brilliancewavelength tunable

Synchrotron

Advantages

10-4 - 10-5 rad divergence (3-5 mm @ 4 m)

high brilliancewavelength tunable

X-ray sourcesX-ray sources

Synchrotron

Advantages

10-4 - 10-5 rad divergence (3-5 mm @ 4 m)

high brilliancewavelength tunable

Synchrotron

Advantages

10-4 - 10-5 rad divergence (3-5 mm @ 4 m)

high brilliancewavelength tunable

Beam conditioningBeam conditioning

CollimationCollimation

Beam conditioningBeam conditioning

Monochromatization

-filters – materials have atomic nos. 1 or 2 less than anode

50-60% beam attenuationplacing after specimen/before detector

filters most of specimen fluorescenceallows passage of high intensity & long

wavelength white radiation

Monochromatization

-filters – materials have atomic nos. 1 or 2 less than anode

50-60% beam attenuationplacing after specimen/before detector

filters most of specimen fluorescenceallows passage of high intensity & long

wavelength white radiation

X-raysX-rays

detectordetectorfilterfilter

specimenspecimen

Beam conditioningBeam conditioning

Monochromatization

-filters – materials have atomic nos. 1 or 2 less than anode

50-60% beam attenuationplacing after specimen/before detector

filters most of specimen fluorescenceallows passage of high intensity & long

wavelength white radiation

Monochromatization

-filters – materials have atomic nos. 1 or 2 less than anode

50-60% beam attenuationplacing after specimen/before detector

filters most of specimen fluorescenceallows passage of high intensity & long

wavelength white radiation

Beam conditioningBeam conditioning

Monochromatization

Crystal monochromators – LiF, SiO2, pyrolytic graphite

critical – reflectivity ex: for MoK, LiF 9.4% graphite 54 %

Monochromatization

Crystal monochromators – LiF, SiO2, pyrolytic graphite

critical – reflectivity ex: for MoK, LiF 9.4% graphite 54 %

Beam conditioningBeam 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°

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°

Beam conditioningBeam conditioning

Monochromatization

Monochromator shape

usually flat – problems with divergent beams

concentrating type – increases I by factor of 1.5-2

Monochromatization

Monochromator shape

usually flat – problems with divergent beams

concentrating type – increases I by factor of 1.5-2