Time of Flight instrumentation for powder diffraction :

Size: px

Start display at page:

Download "Time of Flight instrumentation for powder diffraction :"

Jonathan Tyler
5 years ago
Views:

$powder diffraction : techniques,$ applications and new perspectives.

1 Time of Flight instrumentation for powder diffraction : techniques, applications and new perspectives. Paolo G. Radaelli ISIS Facility, Rutherford Appleton Laboratory Les Rencontres de Saint-Aubin, Mar

2 TS-I TS-II

3 Views of the Moderator Engineering Vane of poisoned moderator Target Water Jacket Paolo G. Radaelli

4 S-CH 4 L-H 2 λ = 2 Å S-CH 4 L-H 2 λ = 4 Å τ (µsec) τ (µsec)

6 A generic TOF powder diffractometer Moderator Sample Tank Detector Disk Choppers Nimonic Chopper Neutron Guide Collimator Monitors Beam Stop Monitor Monitors

7 Distance (m) Distance (m) time (sec) time (sec) 10 Hz -40m -20m 20 Hz-40m time (sec)

8 Decoupled Moderator Wavelength (Å) τ (µsec) Flightpath (m) d/d (10-3 ) Coupled Moderator Wavelength (Å) τ (µsec) Flightpath (m) d/d (10-3 )

9 Diffractometers: Flux on Sample Optical efficiency Dispersive Source Resolution solid angle Φ = Ω ε P ρ sam dis s λ ( λ) λ Σ P= n sec sterad cm ν τ Incident spectrum Peak Brilliance Repetition Pulse width rate

10 Diffractometers: Dispersive resolution ρ ρ ρ dis dis dis = = t t v v λ = λ * TOF Velocity Selector Monochromator

11 Peak Brilliance Pulsed Steady State time

Supermirrors Direct view of the moderator : - Resolution depends on L - Φ α solid angle α 1/L 2 so the distance is a limiting factor Using optics : - Can transport beam up to very large distance.

12 Supermirrors Direct view of the moderator : - Resolution depends on L - Φ α solid angle α 1/L 2 so the distance is a limiting factor Using optics : - Can transport beam up to very large distance. - However reflectivity drops rapidly in the supermirror region Reflectivity (%) (Measurements from Mirrotron). - m=1,reflectivity about 99% - above m=1, loose around 10% per extra m θ C = m.λ 0.1m.λ m ~ 0.1 at 1 Å

13 Powder cross section σ Ω coh = n c (2π ) v 0 3 τ δ ( 3 ) 2 2 ( q τ) F( τ) [ cm ] δ δ = ( 3 ) ( x) ( r ) δ( θ ) δ( φ ) r 2 sinθ ( ( )) δ f x ( ) f x = x 1 ( ) δ x σ Ω pow coh = N (2π ) 4π v 0 3 τ δ ( q τ ) q 2 F 2 2 () τ [ cm ] δ 1 = k cosθ 2 λ 4π sinθ ( q) δ ( 2θ ) = δ ( λ) Angle-dispersive Wavelength-dispersive pow 3 σ N (2 π) δ ( 2θ 2θτ ) 2 d2θ= mτ F 2 () τ d2θ Ω pow 3 2 4π v kq cosθ λ δ ( λ λ ) coh N λ 2 = m τ F () τ 4π v 0 2sinθsin2θ 1 N 3 2 m 2 = τ { 2 d tan θ} F () τ [cm ] 4π v σ N (2 π) 2 dλ = m F() τ dλ Ω coh τ τ 2 4π v0 4πq sinθ N λ = = 4 8sin 4 N mτ F 3 () τ mτ{ d θ} F() τ π v0 θ π v0 2 sin [cm A ]

14 Powder cross section (TOF) pow 0 ( ) 2 λ δ λ λτ 2 3 σ (2 ) 2 N π dλ = mτ F() τ dλ Ω 4π v 4πq sinθ coh N λ = = 4 8sin 4 N mτ F 3 () τ mτ{ d θ} F() τ π v0 θ π v0 2 sin [cm A ] pow 0 ( ) 3 2 σ N (2 π) λ δ λ λτ 2 dλ = mτ F 2 () τ dλ Ω 4π v 4πq sinθ coh N λ = = 4 8sin 4 N mτ F 3 () τ mτ{ d θ} F() τ π v0 θ π v0 2 sin [cm A ]

15 TOF Instrument designs GEM HRPD

16 Resolution HRPD

17 TOF data structure Y 2 O 3 powder 3 g 1 min run θ = θ = θ = θ = d-spacing (Å) d-spacing (Å)

18 The classic design Decoupled Poisoned Moderator Disk Choppers Nimonic Chopper Jaws Monitors + Direct view of the moderator (no losses) + High flux at short wavelengths. + Good bandwidth ( λ=3957/ν/l tot ). - Problem to cool moderator below 100 K - long wavelengths. - No focussing = relatively low flux. Can recover with solid angle but - Fragmented data structure.

22 80 cm

23 Location of adsorbed species in NO-reduction catalysts Refined data from pristine Cu-exchanged zeolite Y at 77 K collected in only 30 mins using all current detector banks on GEM. The structural evolution of the framework and of the adsorbed NO ligands was studied as a function of temperature and NO gas overpressure. G C Hardy, M J Rosseinsky, Dept. of Chemistry, University of Liverpool & R M Ibberson, P G Radaelli, ISIS.

24 La1-xSrxCoO3

Multiferroics: REMn 2 O 5 (b) H=0 T 40 E pole //+b H//a (ZFC) 20 P (nc/cm 2 ) 0-20 P 40 0 P 1 P 2 40 T H=9 T -40 1. N. Hur et al.

25 Multiferroics: REMn 2 O 5 (b) H=0 T 40 E pole //+b H//a (ZFC) 20 P (nc/cm 2 ) 0-20 P 40 0 P 1 P 2 40 T H=9 T N. Hur et al. Nature, 429, 392 (2004) 2. L.C. Chapon et al., Phys. Rev. Lett. 93, (2004) 3. G. Blake et al., Phys. Rev. B 71, (2005) T (K) 0

kh z w a r m in g ε 30 25 0 T 1 T 3 T 5 T

//a ( Z F C ) II I 20 P (nc/cm 2 ) 0-2 0

26 REMn 2 O 5 : temperature and field dependence (a) 35 E //b, H //a (F C ) 1 kh z w a r m in g ε T 1 T 3 T 5 T 7 T 9 T (b ) IV III E pole //+ b H //a ( Z F C ) II I 20 P (nc/cm 2 ) P 40 0 P 1 P 2 40 T T (K) 0

27 Hydrogen sorption of Nb-catalysed, nanostructured Mg F M Mulder, H G Schimmel (TU-Delft, The Netherlands), J Huot (Université du Québec à Trois-Rivières, Canada) and L C Chapon (ISIS)

28 17th/19th century iron armour plates Sylvia Leever, J. Dik TU Delft, NL D. Visser ISIS&NWO,NL wt%: 99.9 Fe, 0.2 Fe 3 C, 0.2 FeO wt% C wt%: 97.3 Fe, 2.5 Fe 3 C, 0.2 Fe 3 O wt% C

29 The long uns HRPD Decoupled Poisoned Moderator or Unpoisoned/Coupled Curved neutron guide ( 58 Ni or SM) up to 100 m Disk Choppers Jaws Monitor + Sharp pulse structure w. poisoned moderator can reach particle size limit in backscattering + Resolution truly independent on d-spacing in backscattering + Can accommodate focussing. + Coupled moderators can be colder (20 K) - Need to reduce the repetition rate to archive sufficient BW -> TS2. - Need to transport neutrons efficiently optics.

30 High Pressure studies: Epsom salt on the moons of Jupiter A D Fortes, M Alfredsson, J P Brodholt, L Vocùadlo, I G Wood, (University College London) and K S Knight (ISIS) ISIS Annual Report 2004.

1200 1000 800 1500 MPa 1000 800 600 600 400 0 1 2 3 4 5 z/mm R/mm -2-1 0 1 2 800 600 800

31 Inertia friction welding Rolls-Royce plc. Compressor rotor factory (CRF) As welded Conventional PWHT Modified PWHT R/mm MPa z/mm R/mm h 760 C MPa unacceptable z/mm R/mm h 810 C z/mm

32 OSIRIS

33 Intensity (arb. un.) Gem: 80 m OSIRIS: 3 h GEM-OSIRIS Comparison Magnetic Diffraction Bank 4 Bank 2 1/5 Bank 3 Bank 1 Osiris d-spacing (Å)

$GOALS of the WISH project To build the first world-leading magnetic diffractometer at a pulsed source. TOF instruments are naturally focussed in backscattering.$

34 GOALS of the WISH project To build the first world-leading magnetic diffractometer at a pulsed source. TOF instruments are naturally focussed in backscattering. Therefore, our main strength has to be towards the higher resolutions. Need cold neutrons, wide λ and good resolution. Perfect match with general aims of ISIS TS-II Status: funded and under construction Paolo G. Radaelli

35 WISH scientific themes Magnetism in ionic and covalent systems. Model and designer magnetic systems. Metallic magnets. Magnetic clusters and nano-particles. Magnetism under extreme conditions (pressure, magnetic field). Large unit-cell structures. Initial requirements : WISH is primarily a powder diffractometer to be optimised for magnetic studies, but with a full 2D detector for SX studies. Dedicated 15 Tesla magnet Phase 2 construction upgrade: Polarization device, flipping ratios, spin-density distributions

36 WISH Overview Moderator Incident Wavelengths Single-frame bandwidth d-spacing range L1 L2 Flight path Choppers Detectors Beam size Optimal frequency Sample/detector tank Sample environment Decoupled, Unpoisoned Solid Methane, broad side Å 8 Å Å 40m m Elliptical guide+ tunable divergence (slit collimation) 3 disc choppers (50-10Hz) 3 He linear PSD detectors covering all scattering angles between 10º and 175º. 20 mm x 40mm (unfocussed) to 1 mm x 1mm (super-focussed) 10 Hz Radial Collimator, 2m diameter vacuum tank All standard equipment + dedicated 15 T cryomagnet

37 Guide 120 mm Guide entrance : 40 x 80 mm Guide exit : 22 x 44 mm Moderator and sample positioned at ellipse extremes 0.5 m sections with 0.5 mm breaks every 1.5 m.

WISH Detector 3 He tubes PSD, 8mm diameter 125 pixels (8 mm resolution) 1 m long detectors ( 28 degrees azimuthal angle ) at 2.2 m from sample position. Insensitive to magnetic field.

38 WISH Detector 3 He tubes PSD, 8mm diameter 125 pixels (8 mm resolution) 1 m long detectors ( 28 degrees azimuthal angle ) at 2.2 m from sample position. Insensitive to magnetic field. Need good vertical resolution to reconstruct Debye-Scherrer cones. This option will enable single-crystal studies. Cover degrees 2θ on both sides (~1200 tubes). Tubes on a 10 mm pitch. Initially considered secondary flight path under vacuum Current Design : Secondary flight path under Ar atmosphere

39 Flux at sample position Integrated flux is n/cm 2 /s at sample position (50 times GEM). Peak flux 200 times GEM at 4 Å in high divergence mode Peak flux 20 times GEM at 4 Å with same horizontal divergence Intensity at sample position (n.cm -2.s -1.Å -1 ) 1E WISH-0.16deg Hdiv WISH-high div λ (Å) GEM Intensity at sample position (n.cm -2.s -1.Å -1 ) 1E7 x WISH-high div GEM λ (Å)

40 Moderator Sample Tank Detector Disk Choppers Nimonic Chopper Neutron Guide Collimator Monitors Beam Stop Monitor Monitors

Neutron Instruments I & II. Ken Andersen ESS Instruments Division

Neutron Instruments I & II. Ken Andersen ESS Instruments Division Neutron Instruments I & II ESS Instruments Division Neutron Instruments I & II Overview of source characteristics Bragg s Law Elastic scattering: diffractometers Continuous sources Pulsed sources Inelastic