Secondary neutron beams and profile parameters

Monochromators

Adjustable lift system is used to hold the monochromators. There are three positions available in the lift. One slot is still empty and will be used in the future. Two other slots are occupied with:

• Bent three silicon single crystals  in special bending holder. Value of bent is adjustable. The best result concerning intensity and peak shape is at the bent to 140µm. Symmetric reflection is from planes (422). By rotation the crystals about 10° is possible to have asymmetric reflection (311) satisfying the Bragg's condition. So this monochromator provides two different wavelength.
• Three mosaic copper crystals adjusted to focus vertically. This monochromator provide one wavelength on planes (220).

Wavelength and secondary beam parameters

Monochromator	Reflection	Wavelength	Minimum Δd/d (x10-3)	Neutron flux (n.cm-2.s-1)	Beam size
3 bent Si single-crystals	(422)	1.271 Å	3.9 (at 56° 2θ)	~8.8x105	2x4 cm2
	(311)	1.877 Å	4.4 (at 59° 2θ)	~8.6x105	2x4 cm2
3 mosaic Cu crystals	(220)	1.460 Å	4.9 (at 59° 2θ)	~3.6x106	4x4 cm2

Other parameters

• 2θ range form 2 to 148°
• adjustable slits in the full range of beam size
• step size down to 0.02° in 2θ
• step delay control strict time or monitor limit

Diffraction pattern of the SiO₂ standard

Measured and calculated spectra of SiO2 standard sample with Si(422) monochromator (λ = 1.271Å).				Part (in 2θ range it correspond to angles between ~42° and ~58°) of the patterns of SiO2 showing the different resolution and intensity of monochromators (all diffraction patterns were collected with the same parameters). At the bottom are the Bragg's positions. The distance between selected reflections is: Δd(022)/(013)=0.012Å, Δd(122)/(023)=0.0068Å, Δd(023)/(031)=0.0035Å.
Evolution of the FWHM (full width in the half maximum) as a function of 2θ angle for all available wavelength represented by monochromators.				Evolution of the Δd/d (resolution) as a function of 2θ angle for all available wavelength represented by monochromators.

Files to download

Here you can find the IRF (Instrument Resolution Files) for the FullProf refinement program.