Long Wave Gamma rays IR Visible 1012 106

Long Wave Gamma rays IR Visible 1012 106

Long Wave Gamma rays IR Visible 1012 106

103 wavelength (nm) X-rays Frau Rntgen's hand UV

10 X-rays 1 10-1

10-3 Long Wave Gamma rays 1012 IR Visible

106 103 wavelength (nm) X-rays UV

10 X-rays 1 10-1

10-3 X-ray tube target (anode) water inlet

x-ray window filament (cathode)

focusing cup X-ray tube target (anode)

water inlet x-ray window filament

(cathode) focusing cup X-rays 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

X-rays Mechanism Decelerating charges give off radiation X-rays Mechanism Decelerating charges give off radiation X-rays

Mechanism Decelerating charges give off radiation X-rays Mechanism Decelerating charges give off radiation X-rays Mechanism

Decelerating charges give off radiation X-rays Typical tube spectrum X-rays - vary tube voltage Iconts = AiZV~2

Intensity Ichar = Ai(V-Vcrit)~1.5 E >> hc/Kedge E > hc/Kedge E hc/Kedge

Wavelength X-rays More electron transitions X-rays Cu spectrum X-rays

Al spectrum X-rays Au L spectrum X-rays Moseley's law - energy vs. atomic number X-ray sources

Sealed tubes - Coolidge type common - Cu, Mo, Fe, Cr, W, Ag Ka = (2 Ka1 + Ka2)/3 X-ray sources Sealed tubes - Coolidge type common - Cu, Mo, Fe, Cr, W, Ag intensity limited by cooling requirements (22.5kW)

(~99% of energy input converted to heat) X-ray sources Intensity changes with take-off angle But resolution decreases with take-off angle

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

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 Other X-ray sources Synchrotron Advantages 10-4 - 10-5 rad

divergence (3-5 mm @ 4 m) high brilliance wavelength tunable 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

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

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

high brilliance wavelength tunable Beam conditioning Collimation 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 filter specimen

detector 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 Beam conditioning Monochromatization Crystal monochromators LiF, SiO2, pyrolytic graphite critical reflectivity ex: for MoK, LiF 9.4% graphite 54 %

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

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

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