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

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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.