Bragg-Brentano diffractometers John and Paul Same as incident, unless sample contains fluorescing...
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Transcript of Bragg-Brentano diffractometers John and Paul Same as incident, unless sample contains fluorescing...
Bragg-Brentanodiffractometers
John and Paul
Same as incident,unless samplecontains fluorescingelements, e.g. Mn Fe,in which case
Diffracted spectrum
Wavelength
Kα1
Wavelength
Incident/Monochromated spectrum
Press any button
Detector
Detector slitPri
mary
Mon
och
rom
ato
r
Tube spectrum
Wavelength
Kα1
Kα2Kβ1
Kα,β - characteristic
radiationdecelerationradiation
Kα1
Wavelength
Kα1
Dete
cted s
pect
rum
Adjustable energythreshold on detector
Press any button for next slide
Detector slit
Detector
β filter
Mo X-ray tube (Pete)(MINIFLEX)
Wavelength
Kα1
Kα2Kβ1
Bragg-Brentanodiffractometers
Pete and MINIFLEX
Same as incident,unless samplecontains fluorescingelements, e.g. Mn Fe,in which case
Diffracted spectrum
Press any button
Dete
cted s
pect
rum
Adjustable energythreshold on detector
Press any button for next slideWavelength
Incident spectrumKα1
Kα2Kβ1
Kα,β - characteristic
radiationdecelerationradiation
Wavelength
Kα1
Kα2Kβ1
Wavelength
Kα1
Kα2Kβ1
Bragg-Brentanodiffractometers
Focusing scheme
θ 2θ
Focusing circles
Goniometer circle
Receiving slitX-ray source
Sample container
Powder
Note that for simplicity, the scheme has been drawn for a setup with moving receiving slit and X-ray source, while the sample container is stationary (Pete). On John, Paul and MINIFLEX diffractomers the same focusing scheme is achieved with stationary X-ray source and the sample holder turning around the centre of the goniometer circle, in sync with the receiving slit.
Ideal focusing, hence unbiased peak positions and intensities in the diffraction pattern, is achieved ONLY IF the tangent of the focusing circle lies on the surface of the sample and the sample has an infinitely small penetration depth.
The School diffractometers are aligned in such a way that when standard sample containers are filled flush with the surface, the tangent requirement is fulfilled.
Advantages
High intensity No need in absorption correction
Disadvantages Demanding sample preparation Not suitable for organics Press any button
for next slide
Bragg-Brentanodiffractometers
Fixed divergence slit (FDS) – Pete
Illuminated length variesIlluminated volume is constantNo intensity correction required.
Adjustable divergence slit (ADS) – John, Paul & MINIFLEX
Illuminated length is constantIlluminated volume varies
Intensity correction required.
Divergence slit
𝐼𝐹𝐷𝑆 (𝜃 ,𝛼 )= 𝐼𝐴𝐷𝑆 (𝜃 ,𝐿)(𝑅𝑠𝑖𝑛 (𝛼/2 )𝐿 )×
×( 1𝑠𝑖𝑛 (𝜃+𝛼/2 )
+1
𝑠𝑖𝑛 (𝜃−𝛼 /2 ) )ADS to FDS correction is available in HighScore Plus software. John&Paul: corrected data in filename_1. MINIFLEX data corrected during acquisition.