Neutron Instrumentation

Oxford School on Neutron Scattering 5th September 2019

Ken Andersen Summary

2 The time-of-flight (TOF) method distance

Δt time Diffraction: Bragg’s Law Diffraction: Bragg’s Law Diffraction: Bragg’s Law Diffraction: Bragg’s Law Diffraction: Bragg’s Law Diffraction: Bragg’s Law λ = 2d sinθ Diffraction: Bragg’s Law λ = 2d sinθ

2θ Reflection: Snell’s Law incident reflected n=1 θ θ’ refracted n’<1 Reflection: Snell’s Law incident reflected n=1 θ θ’ refracted θ’=0: critical angle of total n’<1 reflection θc Reflection: Snell’s Law incident reflected n=1 θ θ’ refracted θ’=0: critical angle of total n’<1 reflection θc

cosθc = n' n = n' Nλ2b  n' = 1−  ⇒ θc = λ Nb/π 2π  ≈ − 2 cosθc 1 θc 2 Reflection: Snell’s Law incident reflected n=1 θ θ’ refracted θ’=0: critical angle of total n’<1 reflection θc

cosθc = n' n = n' 2 for natural Ni, Nλ b  n' = 1−  ⇒ θc = λ Nb/π 2π  θc = λ[Å]×0.1° cosθ ≈ 1− θ2 2 c c  -1 Qc = 0.0218 Å Neutron Supermirrors

Courtesy of J. Stahn, PSI Neutron Supermirrors

λ Reflection: θc(Ni) = λ[Å] × 0.10° c λ 1 Multilayer: θc(SM) = m × λ[Å] × 0.10°

λ 2

λ 3

λ 4

} d 1 } d 2 } d3 } d4

18 Neutron Supermirrors

λ Reflection: θc(Ni) = λ[Å] × 0.10° c λ 1 Multilayer: θc(SM) = m × λ[Å] × 0.10°

λ 2

λ 3

λ 4 “m-number” Supermirror critical angle } d 1 } d 2 } d3 } d4

19 State-of-the-art Supermirrors

Mirrotron

20 State-of-the-art Supermirrors

Mirrotron

Swiss Neutronics

21 Neutron guides

WISH @ ISIS

Swiss Neutronics guides for NIST DistributionNeutron Guides:by Guides Creating space for instruments Background Reduction

Guides can be used to reduce background • Distance: – move away from fast- neutron source ~ 1/R2 Background Reduction

Guides can be used to reduce background • Distance: – move away from fast- neutron source ~ 1/R2 • Curved Guides: – avoid direct line-of-sight – avoid gammas – avoid fast neutrons Focusing

Guides can also be used to increase flux

Converging guide increases flux, but increases divergence

26 Shielding

• Shielding functions: – allow safe operation – keep background down – reduce activation • Radiation components: – Slow neutrons – Fast neutrons – Gammas

27 Shielding: radiation units and numbers

Unit Description Examples Dose Curies Decay rate: 3.7×1010 Bq (decays/s) Dental x-ray 10 μSv Gray Energy dose: J/kg Abdominal CAT scan 10 mSv Sievert Biological effect of radiation Airline flight crew members 10 mSv/year Roentgen, rad, rem – legacy units 50% probability of death 5 Sv

Average Person Dose Neutron experimental halls < 3 μSv/hour × 2000 hours: < 6 mSv/year Radon 2 mSv/year Cosmic 0.28 mSv/year Terrestrial 0.28 mSv/year Internal 0.4 mSv/year Medical x-rays 0.39 mSv/year Nuclear medical 0.14 mSv/year Consumer products 0.1 mSv/year Other 0.03 mSv/year Total 3.62 mSv/year 28 Source: Günter Muhrer, Los Alamos, New Mexico ISIS-TS2 Shielding: slow & fast neutrons

• Slow neutrons – easy to absorb (few mm B, Cd, Gd, ..) – emit gammas when absorbed – easily detected • Fast neutrons

cold thermal – can require several m of material for slow epithermal fast absorption – alternatively, thermalise using hydrogenous material (e.g. wax or ESS Target Monolith: 11m diameter polyethylene) then absorb – both require multiple (10s) of collisions – visualise as a gas, filling both solids and air – difficult to detect • Gammas – high-energy photons – absorbed by any material – absorption length scales inversely 3 with density: Pb 11.3 kg/m , steel29 7.9 WISH @ ISIS-TS2 kg/m3, concrete 2.4 kg/m3 -1 Wavevector Q [Å ] 10-3 10- 10-1 1 101 102 103 2 10-15 103

TOF & Crystal 10-12 1 Spectroscopy

10-9 10-3 Backscattering Energy [meV] Energy Time[s] Spin-echo

10-6 Length [m] 10-6 10-1 10-2 10-3 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-14 10-15

SANS Imaging Diffraction Particle Physics Reflectometry -1 Wavevector Q [Å ] 10-3 10- 10-1 1 101 102 103 2 UV & X-ray FEL: Pump & Probe studies 10-15 103 Inelastic X-ray Scattering X-ray Spec. Infrared -12 Light TOF & Crystal 10

1 Spectroscopy red Infra -

FTIR -9 Raman Backscattering 10 10-3 Brillouin Energy [meV] Energy Time[s] Visible Light Visible Spin-echo Dynamic Light Scattering SR NMR µ

Dielectric Spec. 10-6 -6 Length [m] 10 Laser PCS X-ray PCS 10-1 10-2 10-3 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-14 10-15

SANS Imaging Diffraction Particle Physics Reflectometry

X-ray Imaging SAXS, X-ray Refl. X-ray Diffraction EXAFS & XANES X-rays

NMR Imaging Triangulation NMR NMR

Optical Microscopy Optical Nanoscopy Electron Microscopy Microscopy

SNOM AFM STM Scanning Techniques -1 Wavevector Q [Å ] 10-3 10- 10-1 1 101 102 103 2 UV & X-ray FEL: Pump & Probe studies 10-15 103 Inelastic X-ray Scattering X-ray Spec. Infrared -12 Light TOF & Crystal 10

1 Spectroscopy red Infra -

FTIR -9 Raman Backscattering 10 10-3 Brillouin Energy [meV] Energy Time[s] Visible Light Visible Spin-echo Dynamic Light Scattering SR NMR µ

Dielectric Spec. 10-6 -6 Length [m] 10 Laser PCS X-ray PCS 10-1 10-2 10-3 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-14 10-15

SANS Imaging Diffraction Particle Physics Reflectometry

X-ray Imaging SAXS, X-ray Refl. X-ray Diffraction EXAFS & XANES X-rays

NMR Imaging Triangulation NMR NMR

Optical Microscopy Optical Nanoscopy Electron Microscopy Microscopy

SNOM AFM STM Scanning Techniques Diffractometers

• Measure structures (d-spacings) • Very general method: – crystals – powders – polycrystalline materials – liquids – large molecules or structures – surfaces • Ideal diffractometer:

– measure ki of each incident neutron – measure kf of the same neutrons

𝑓𝑓 𝑘𝑘 33 𝑘𝑘𝑖𝑖 Diffractometers

• Measure structures (d-spacings) • Very general method: – crystals – powders – polycrystalline materials – liquids – large molecules or structures – surfaces • Real diffractometer:

– measure ki or kf of the beam • time-of-flight • Bragg diffraction

– assume ki = kf 𝑓𝑓 𝑘𝑘 34 𝑘𝑘𝑖𝑖 Powder diffractometers

• Measure crystal structure using Bragg’s law – Rietveld refinement • Large single crystals are rarely available Polycrystal

2π Q = λ = 2d sinθ d Time-of-flight (TOF) Method

distance

detector λ = 2d sinθ sample

Δt time Time-of-flight (TOF) Method

distance

detector λ = 2d sinθ sample

Δt time Time-of-flight (TOF) Method

distance

detector λ = 2d sinθ sample

Δt time Time-of-flight Resolution

2 2 λ 2  ∂d   ∂d  d = (∆d ) =  ∆λ  +  ∆θ  2sinθ  ∂λ   ∂θ 

Δt time Time-of-flight Resolution

2 2 λ 2  ∂d   ∂d  d = (∆d ) =  ∆λ  +  ∆θ  2sinθ  ∂λ   ∂θ  To improve the resolution: • increase the length: long guide • move to a sharper moderator • reduce the beam divergence

Δt time Time-of-flight (TOF) Method

WISH @ ISIS TS2 Crystal Monochromators

Graphite 002 Copper 200

d-spacing Germanium 333 1.089 Å Copper 200 1.807 Å Silicon 111 3.135 Å Graphite 002 3.355 Å Pulsed source time structures (λ=5Å)

short pulse

0 100μ ILL 57MW

Intensity@λ =5Å) 1 s ISIS-TS1 128kW ISIS-TS2 32kW log(

0.1

0.01 43

0 20 40 time ( m s ) 80 100 120 Pulsed source time structures (λ=5Å)

short pulse

0 100μ ILL 57MW

Intensity@λ =5Å) 1 s ISIS-TS1 128kW ISIS-TS2 32kW log(

0.1

0.01 44

0 20 40 time ( m s ) 80 100 120 Constant-Wavelength Diffraction

D1B @ ILL Rietveld refinement

Debye-Scherrer cone 2θ The Diffractometer Family

• Powder diffraction – chemical crystallography – disordered materials – engineering: strain scanning • Single-crystal diffraction – magnetic ordering – diffuse scattering – large unit cells – protein crystallography • Small Angle Neutron Scattering (SANS) – soft matter – macromolecules in solution – nanomaterials • Reflectometry – surfaces and interfaces – both planar and in-plane structures

46 Sample environment

• neutron penetration: good • sample volume: bad SNS pressure cell • range as varied as the science – magnetic fields – low temperatures – high temperatures – pressure cells (TiZr) – sample changers – stress rigs – in-situ chemistry – flow cells ILL 15mK dilution cryostat ILL adsorption trough – Langmuir troughs – …

ISIS Cryomagnets

47 Neutron Spectroscopy

• Excitations: vibrations and other motions – lattice vibrations – magnetic excitations – quasi-elastic scattering: diffusion & relaxation

48 Neutron Spectroscopy

• Excitations: vibrations and other motions – lattice vibrations – magnetic excitations – quasi-elastic scattering: diffusion & relaxation • Ideal spectrometer:

– measure ki of each incident neutron – measure kf of the same neutrons

𝑓𝑓 𝑘𝑘 49 𝑘𝑘𝑖𝑖 Neutron Spectroscopy

• Excitations: vibrations and other motions – lattice vibrations – magnetic excitations – quasi-elastic scattering: diffusion & relaxation • Real spectrometer:

– measure ki and kf of the beam • time-of-flight • Bragg diffraction • Larmor precession

– Fix ki and scan through kf – “direct geometry” – Fix kf and scan through ki – “indirect geometry”

𝑓𝑓 𝑘𝑘 50 𝑘𝑘𝑖𝑖 Chopper Spectrometers

Direct geometry:

fix ki by chopper phasing distance scan through kf by time-of-flight detector

sample chopper

0 time Neutron Choppers

Fermi choppers Disk choppers

f < 600 Hz f < 300 Hz Δt > 1μs Δt > 10μs Chopper Spectrometers

• General-Purpose Spectrometers – Incident energy ranges from 1meV to 1eV • Huge position-sensitive detector arrays – Single-crystal samples Detectors

3He gas tubes Scintillators n + 3He  3H + 1H + 0.764 MeV n + 6Li  4He + 3H + 4.79 MeV >1mm resolution <1mm resolution High efficiency Medium efficiency Low gamma-sensitivity Some gamma-sensitivity 3He supply problem Magnetic-field sensitivity Detectors

10B detectors n + 10B  7Li + 4He + 0.48 MeV massive development programme none yet in operation many different types

inclined blades

boron layer thickness limited to ~ 1 μm => ~ 5% efficiency perpendicular blades Direct-Geometry Kinematics

ki 2θ

kf Q

𝑄𝑄 𝑘𝑘𝑖𝑖 − 𝑘𝑘𝑓𝑓

56 Direct-Geometry Kinematics

ki 2θ

kf Q

𝑖𝑖 𝑓𝑓 𝑄𝑄 = 𝑘𝑘 −=𝑘𝑘 2 2 22 2 𝑝𝑝 ℏ 𝑘𝑘 𝐸𝐸 𝑚𝑚 𝑚𝑚

57 Direct-Geometry Kinematics

ki 2θ

kf Q

𝑖𝑖 𝑓𝑓 𝑄𝑄 = 𝑘𝑘 −=𝑘𝑘 2 2 22 2 𝑝𝑝 ℏ 𝑘𝑘 𝐸𝐸 𝑚𝑚 𝑚𝑚

58 Direct-Geometry Kinematics

ki 2θ f E

kf - Q i E

𝑖𝑖 𝑓𝑓 𝑄𝑄 = 𝑘𝑘 −=𝑘𝑘 2 2 2

2 2 = Energy Transfer 𝑝𝑝 ℏ 𝑘𝑘 𝐸𝐸 𝑚𝑚 𝑚𝑚

Momentum transfer Q 59 Alternative to Direct Geometry

Indirect geometry:

fix kf – usually by analyser crystals distance scan through ki by time-of-flight detector

analyser

sample

0 time Indirect-Geometry Kinematics f E - i E Energy Transfer = Energy Transfer ki 2θ

kf Q

Momentum transfer Q 61 Vibrational Spectroscopy

TOSCA@ISIS

Density-of-states measurements

62 High Resolution 1: Backscattering

π λ = 2d sinθ θ → 2 ∆λ ∆d ⇒ = + cotθ∆θ cosθ λ cotθ = → 0 d sinθ

Use single crystals in as close to backscattering as

possible to define kf. Scan through ki with as good energy resolution. Backscattering

BASIS@SNS Si111 3μeV

OSIRIS@ISIS PG002 25μeV High Resolution 2: Neutron Spin Echo

High energy resolution < 1 μeV

Larmor precessions encode energy transfer θ ϕ

B0 B1

Pz π-flipper

L0 L1 Triple-Axis Spectrometers

• Single-crystal excitations • Very flexible • Measures a single point in Q -E space at a time • Scans:  – Constant Q : Scan E at constant ki or kf  – Constant E: Scan Q in any direction Collimation

• TAS E and Q resolution adjusted by collimation

Soller collimator Collimation

• TAS E and Q resolution adjusted by collimation • SANS resolution also adjusted by collimation Soller collimator

Pin-holes separated by distance

5 cm < 30 m 5 cm > 0.1° 68 TAS with multiplexing

IN20 flat-cone multi-analyser

Top view Side view

sample

31 channels 75º angular range -1 -1 kf = 3 Å kf = 1.5 Å Neutron Imaging

70 neutron x-ray Summary

• Neutron instrument concepts – time-of-flight – Bragg’s law • Neutron Instrumentation – guides – monochromators – shielding – detectors – choppers – sample environment – collimation • Neutron diffractometers – powder diffraction • Neutron spectrometers – direct and indirect geometry time-of-flight – backscattering – triple-axis – spin-echo • Imaging

71 Thank you!

5th June72 2015