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Bragg-Brentano diffractometers John and Paul Same as incident, unless sample contains fluorescing elements, e.g. Mn Fe, in which case Diffracted spectrum.

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Presentation on theme: "Bragg-Brentano diffractometers John and Paul Same as incident, unless sample contains fluorescing elements, e.g. Mn Fe, in which case Diffracted spectrum."— Presentation transcript:

1 Bragg-Brentano diffractometers John and Paul Same as incident, unless sample contains fluorescing elements, e.g. Mn Fe, in which case Diffracted spectrum Wavelength Kα1Kα1 Incident/Monochromated spectrum Press any button Detector Detector slit Primary Monochromator Tube spectrum Wavelength Kα1Kα1 Kα2Kα2 Kβ1Kβ1 K α,β - characteristic radiation deceleration radiation Kα1Kα1 Wavelength Kα1Kα1 Detected spectrum Adjustable energy threshold on detector Press any button for next slide

2 Detector slit Detector β filter Mo X-ray tube (Pete) (MINIFLEX) Wavelength Kα1Kα1 Kα2Kα2 Kβ1Kβ1 Bragg-Brentano diffractometers Pete and MINIFLEX Same as incident, unless sample contains fluorescing elements, e.g. Mn Fe, in which case Diffracted spectrum Press any button Detected spectrum Adjustable energy threshold on detector Press any button for next slide Wavelength Incident spectrum Kα1Kα1 Kα2Kα2 Kβ1Kβ1 K α,β - characteristic radiation deceleration radiation Wavelength Kα1Kα1 Kα2Kα2 Kβ1Kβ1 Kα1Kα1 Kα2Kα2 Kβ1Kβ1

3 Bragg-Brentano diffractometers Focusing scheme θ 2θ2θ 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

4 Bragg-Brentano diffractometers Fixed divergence slit (FDS) – Pete Illuminated length varies Illuminated volume is constant No intensity correction required. Adjustable divergence slit (ADS) – John, Paul & MINIFLEX Illuminated length is constant Illuminated volume varies Intensity correction required. Divergence slit ADS to FDS correction is available in HighScore Plus software. John&Paul: corrected data in filename_1. MINIFLEX data corrected during acquisition.


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