Presentation on theme: "Incident/Monochromated"— Presentation transcript:
1 Incident/Monochromated Bragg-BrentanodiffractometersJohn and PaulKα1Kα1decelerationradiationKα,β - characteristicradiationPress anybuttonKα2Kβ1Detected spectrumDetectorDetector slitTube spectrumWavelengthWavelengthMonochromatorPrimaryAdjustable energythreshold on detectorIncident/MonochromatedspectrumDiffracted spectrumKα1Kα1Same as incident,unless samplecontains fluorescingelements, e.g. Mn Fe,in which casePress any buttonfor next slideWavelengthWavelength
2 Bragg-Brentano Pete and MINIFLEX diffractometers Kα1 Kβ1 Kα2 Kα1 Kβ1 WavelengthKα1Kα2Kβ1Press anybuttonDetected spectrumDetector slitDetectorβ filterMo X-ray tube (Pete)(MINIFLEX)Adjustable energythreshold on detectorWavelengthKα1Kα2Kβ1Incident spectrumDiffracted spectrumKα1Kα1Same as incident,unless samplecontains fluorescingelements, e.g. Mn Fe,in which casedecelerationradiationKα,β - characteristicradiationKβ1Kα2Kα2Kβ1Press any buttonfor next slideWavelengthWavelength
3 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.θ2θFocusing circlesGoniometer circleReceiving slitX-ray sourceSample containerPowderIdeal 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.AdvantagesHigh intensityNo need inabsorptioncorrectionDisadvantagesDemanding samplepreparationNot suitable for organicsPress any buttonfor next slide
4 No intensity correction required. Bragg-BrentanodiffractometersFixed divergence slit (FDS) – PeteDivergence slitIlluminated length variesIlluminated volume is constantNo intensity correction required.Adjustable divergence slit (ADS) – John, Paul & MINIFLEX𝐼 𝐹𝐷𝑆 𝜃,𝛼 = 𝐼 𝐴𝐷𝑆 𝜃,𝐿 𝑅𝑠𝑖𝑛 𝛼 2 𝐿 ×× 1 𝑠𝑖𝑛 𝜃+ 𝛼 𝑠𝑖𝑛 𝜃− 𝛼 2ADS to FDS correction is available in HighScore Plus software.John&Paul: correcteddata in filename_1.MINIFLEX data correctedduring acquisition.Illuminated length is constantIlluminated volume variesIntensity correction required.
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