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Incident/Monochromated
Bragg-Brentano diffractometers John and Paul Kα1 Kα1 deceleration radiation Kα,β - characteristic radiation Press any button Kα2 Kβ1 Detected spectrum Detector Detector slit Tube spectrum Wavelength Wavelength Monochromator Primary Adjustable energy threshold on detector Incident/Monochromated spectrum Diffracted spectrum Kα1 Kα1 Same as incident, unless sample contains fluorescing elements, e.g. Mn Fe, in which case Press any button for next slide Wavelength Wavelength
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Bragg-Brentano Pete and MINIFLEX diffractometers Kα1 Kβ1 Kα2 Kα1 Kβ1
Wavelength Kα1 Kα2 Kβ1 Press any button Detected spectrum Detector slit Detector β filter Mo X-ray tube (Pete) (MINIFLEX) Adjustable energy threshold on detector Wavelength Kα1 Kα2 Kβ1 Incident spectrum Diffracted spectrum Kα1 Kα1 Same as incident, unless sample contains fluorescing elements, e.g. Mn Fe, in which case deceleration radiation Kα,β - characteristic radiation Kβ1 Kα2 Kα2 Kβ1 Press any button for next slide Wavelength Wavelength
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2θ θ Bragg-Brentano Focusing scheme diffractometers Focusing circles
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. θ 2θ Focusing circles Goniometer circle Receiving slit X-ray source Sample container Powder 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
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No intensity correction required.
Bragg-Brentano diffractometers Fixed divergence slit (FDS) – Pete Divergence slit Illuminated length varies Illuminated volume is constant No intensity correction required. Adjustable divergence slit (ADS) – John, Paul & MINIFLEX 𝐼 𝐹𝐷𝑆 𝜃,𝛼 = 𝐼 𝐴𝐷𝑆 𝜃,𝐿 𝑅𝑠𝑖𝑛 𝛼 2 𝐿 × × 1 𝑠𝑖𝑛 𝜃+ 𝛼 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. Illuminated length is constant Illuminated volume varies Intensity correction required.
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