I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 1 1 THE EUROPEAN NEUTRON SOURCE

INSTITUT LAUE LANGEVIN

NeutronOp+cs

P.CourtoisServiceforNeutronOp4cs

Cremlin14-15May2018

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 2

Basicconceptsandop+calcomponentsØ Reflec+ngOp+cs Mirrors&Super-MirrorsØ Diffrac+ngOp+cs MosaiccrystalsØ Filters Crystals,polycrystallinematerialsØ PolarizingOp+cs Super-Mirrors,crystals,3Hespinfilters

Ø Someexamplesofapplica+onsatI.L.L.

Neutron Optics Neutrons have wave-like properties…

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 3

§ Mirror&Super-Mirrorareusedtoconstructefficientneutronguides§  CollimatordeterminesincidentandscaReredneutrondirec+ons-Angularresolu+on§  Filterselectsoutunwantedneutrons§  CrystalMonochromator/BraggMirrordeterminesincidentwavelengths(Energies)§  CrystalAnalyzerdeterminesscaReredwavelengths(Energies)

Wavelengthresolu+on(Energyresolu+on)§  Crystal/Super-Mirror/3Hespinfilterareusedtopolarizeneutronbeams

Orienta+onoftheneutronspin

Ø InstrumentPerformancesarethendeterminedbyNeutronOp7cs!

Why do we need neutron optics Neutron Optics are key components for neutron instrumentation

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 4

Neutron Mirrors Reflection/Refraction at Surfaces

πλθ coh

cNb

=

incident reflected

refracted

Nbcoh=ScaReringLengthDensityN=atoms/cm3bcoh=coherentsca<eringlength

fornaturalNi:θc(°)= 0.1 x λ (Å)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

λ = 5 Å

refle

ctivi

ty

θ [°]

θc

Nimirror

θ

Material Nb(x1038/m2) θc(mrad)

58Nickel 13.31 2.03

Nickel 9.41 1.7

Iron 8.2 1.62

Copper 6.7 1.39

Silicon 2.08 0.81

Aluminium 2.08 0.81

Totalreflec7onforθ<θc

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 5

Periodic Multilayers Reflection/Refraction at Surfaces

Totalreflec+onforθ<θc+

addi+onalBraggpeakatθB≈λ/2d

R∝ 4N 2d 4 N1b1 - N2b2( )2

π 2n4

Totalreflec+on

Braggpeak

Totalreflec+on

θc

NeutronReflec+vity

Wavelengthband

θΒ ≈ λ / 2d

Δλλ

= 2d2 N1b1−N2b2

π

d

θ

substrate(glass,Si…)

Nbcoh=ScaReringLengthDensityN:numberofbilayersn:orderofthereflec4on

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 6

Super-Mirrors

substrate(glass,Si…)

d3

d2 d1

θ

Sequenceofbi-layersofvariablethicknessesdTotalreflec+onforθ<θc+addi+onalBraggpeaks

m =θc

SM

θcNi

G=θc

sm

θcNi

⎛

⎝⎜⎜

⎞

⎠⎟⎟

2

∝m2

0.00 0.25 0.50 0.75 1.00 1.250.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.00.0 0.5 1.0 1.5 2.0 2.5

m - value

λ = 5 Å

refle

ctivit

y

θ [°]

regimeofsupermirror

regimeoftotal

reflec+on

How to increase angular acceptance of mirrors

→ significantincreaseincri7calangle(θc = λ / 2dmin)

mSuper-Mirror

Gaininneutronflux

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 7

Ni/Ti Super-Mirrors Properties

NeutronReflec7vityR∝(N1b1-N2b2)2 Highcontrast→highreflec4vity!

•  Ni Nb=9.40(10-6Å-2)•  Ti Nb=-1.95(10-6Å-2)

Reflec4vityprofilesofNi/Tisuper-mirrorsfor4≤m ≤ 7(sources:www.swissneutronics.ch)

m=4Performances

§ R>80%form=4Ni/Ti

Ø Gainfactor/Nimirror=16(2D)

Ø buttransmissionT∝Rn!!

eg:fora100mlongguide,atleastten

reflec+ons→Transmission<10%...

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 8

Ni/Ti Super-Mirrors Deposition : Reactive DC Magnetron Sputtering

Applica7onsØ  Neutronguides(previouspresenta+on)Ø  Collima+onØ  Filters(SANSinstruments)Ø  LargeBandmonochromators(Laue

Diffrac+on)

Spu<eringmachine(ILL)-Produc4on0.8m2/day

Produc7onØ  m=4:1600layers!Ø  Substrate:0.5cmthickSiwafersor0.2cmthickGlass/Si/Sapphire

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 9

m Super-Mirrors Long wavelength cut-off filters on D33 at I.L.L. (SANS instrument)

Whitebeam Transmi<edλ <λC

reflectedλ >λC

Θ = 2.2°λc=20Å

§  toselectoutunwantedneutronsofwavelengths>λc(3availablewavelengthbands)m=1.1SMNiV/Tion0.5cmthickSisubstratemountedatanangleθinaneutronguide

Borofloatglassm=0.65

0.84m

Nic

c mθθ

λ =

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 10

m Super-Mirrors Long wavelength cut-off filters on D33 at I.L.L. (SANS instrument)

Whitebeam Transmi<edλ <λC

reflectedλ >λC

Θ = 2.2°λc=20Å

Θ = 1.32°λc=12Å

Nic

c mθθ

λ =

§  toselectoutunwantedneutronsofwavelengths>λc(3availablewavelengthbands)m=1.1SMNiV/Tion0.5cmthickSisubstratemountedatanangleθinaneutronguide

Borofloatglassm=0.65

0.84m

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 11

m Super-Mirrors Long wavelength cut-off filters on D33 at I.L.L. (SANS instrument)

Whitebeam Transmi<edλ <λC

reflectedλ >λC

Θ = 2.2°λc=20Å

Θ = 1.32°λc=12Å

Nic

c mθθ

λ =

§  toselectoutunwantedneutronsofwavelengths>λc(3availablewavelengthbands)m=1.1SMNiV/Tion0.5cmthickSisubstratemountedatanangleθinaneutronguide

Borofloatglassm=0.65

0.84m

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 12

m Super-Mirrors Long wavelength cut-off filters on D33 at I.L.L. (SANS instrument)

NeutronFluxatthesampleposi4ononD33

C.D.Dewhurstetal.,J.Appl.Cryst.(2016).49,1-14

no filter

λc=20Å

λc=12Å

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 13

Bragg Mirrors Large wavelength band Monochromator on LADI (Laue diffractometer for Protein crystallography)

guide

Ø  toproducea«monochroma7c»beamat3.5ÅwithabandwidthΔλ/λ =20%

Θ

Stacked Multilayer monochromator§  Beamwidth=20mm§  θB=1.25°->d0=80ŧ  Δλ/λ =20%->gradedd-spacing74-90ŧ  Beamsize>>Samplesize(1mm)->Focusingdevice(fangeometry)

• mirrorlength=25mm• thickness0.5mm• 40mirrorsNi/Ti• Sisubstrate(lowa<enua4onfactor)

monochromatorsample

Lmono-sample=2135mm

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 14

Bragg Mirrors

guide

Θ

monochromator

sample

monochromator

neutrons

directbeam

reflectedbeam§  λ0≈3.5Å

§  Δλ/λ ≈20%

§  Reflec+vity≈75%

TOFspectraonLADI

Large wavelength band Monochromator on LADI (Laue diffractometer for Protein crystallography)

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 15

Polarizing Co/Ti Super-Mirrors Analyzer for wide angle spin echo spectrometer (WASP)

Co/Tim=2.8

Teta(°)

R+

R-

P

§  Cbender-op7mizedfor λ=[4-12Å]§  Neutronspropagateintoair§  CurvatureR=7mtoavoiddirectlineofsight:atleastonreflec+on!§  Doublesidedmirrors(h141xw254mm2)

Cbender

substrate

absorbinglayer

Co/TiSM

0.2cmthickBoratedglasssubstrate

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 16

Polarizing Co/Ti Super-Mirrors Analyzer for wide angle spin echo spectrometer (WASP)

90°analyzer

WASPspectrometer

Analyzer1°=37CoTiSMs

CoTiSuperMirror

(coildiameter≈6m)

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 17

Polarizing Fe/Si Super-Mirrors at I.L.L.

Ø  toproduceapolarizedcoldneutronbeam

S bender Polarizer for neutron reflectometer D17

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3

0 0.5 1 1.5 2 2.5 3 3.5 4

Re

fle

cti

vit

y

Omega

m=θ / θc(Ni)

m=3.8Fe/SiR+>80%

R+

R-

P

m=3.8Fe/SiSMson0.2cmthickSisubstrate

§ Spin⎪↑>transmiRed§ Stackof60blades(l50mm;h160mm;w10mm)§ Pneutrons>95%(5.5Å)§ T~40%ofthegoodneutrons

200 µm Si channel

B

Polarizing supermirrors

⎪↑>

neutrons

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 18

Mosaic Crystals Bragg Diffraction – Monochromators & Analyzers

UseofsinglecrystalstoselectagivenwavelengthbandaccordingtotheBragg’sLaw

polychromatic

beam

monochromatic beam

λ0

crystal

2 dhkl sinθΒ = nλ0d=distanceofthelasce(hkl)planesθΒ =Braggangle

Ifα~β,theresolu+onandintensityaresaidtobeop+misedØ  MosaicCrystal,i.e.crystalwithdefectssuchasdisloca+ons,

mustbeusedtomatchthedivergenceαofprimarybeamwhichistypically0.2°-0.8°

§  Therela+vebandwidthΔλ/λisgivenforGaussiandistribu+onsbyΔλ/λ = (α 2 + β 2)1/2cotθB α:divergenceoftheprimarybeamβ:fullwidthathalfmaximumoftheneutron“rockingcurve”orneutronmosaicspread

n/s

β θ

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 19

Mosaic Crystals Good Materials should have

q Highneutronreflec.vity∝sca<eringpowerQØ  LargestructurefactorFhklØ  HighcoherentscaReringlengthbcoh(Fhkl∝bcoh)Ø  SmallunitcellVolume&compactstructures=Cubic,DiamondØ  d-spacingop+mizedforagivenwavelength(d~λ)

q lowincoherentscaReringlength→lowbackgroundq lowabsorp+oncrosssec+ons→smalla<enua4onq Nohigherorders

Bθλ /sin2/V)e(F=Q 32-Whkl

Ø Availabilityoflargesinglecrystalswithsuitablewidthanduniformmosaicblockdistribu4on!

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 20

Mosaic crystals for neutron monochromators

Crystal orienta7on CrystalMosaic

NeutronEnergy Applica7on Supplier

HOPG(C)d002=3.35Å

HOPG(002) 0.5°-3° ColdThermal Highflux

Panasonic,Op4graph,Momen4ve

Cud111=2.08Å

(111)(220)(200)… 0.01°-3° Hot

Thermal

Highresolu+onorhighflux

I.L.L.(or?)

Sid111=3.13Å

(111)(113)… Perfect Cold

ThermalHigh

resolu+onmany!

Ged111=3.26Å

(111)(113)… <0.4° Cold

ThermalHigh

resolu+onI.L.L.(or?)

KC8d002=5.3Å

(002) 2°-5° Cold Highflux I.L.L.

HeuslerCu2MnAl (111) 0.2–0.6° Hot

ThermalPolarizedneutrons

I.L.L.

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 21

crystalAnvil

Hea4ngelement

FWHM=0.15°

FWHM=0.45°FWHM=1°

Mosaic Crystals Control of the mosaic distribution by plastic deformation (I.L.L.)

FWHM=0.4°Perfectcrystal

Ge111

Cu200

Peakreflec+vityatλ=3.4ÅRexp=50-55%(FWHM=0.4°)

Rexp≈70%ofRth

Peakreflec+vityatλ=1.1ÅRexp=40-45%(FWHM=0.3°)

Rexp≈80-90%ofRth

T=800°C

P=1MPa

as-growncrystal

Cu200 P,T

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 22

Mosaic Crystals Bent perfect Silicon crystals (I.L.L.)

Effec+vemosaicδ (rad)δ = cot(θB) t / R t=totalcrystalthicknessR=radiusofcurvatureθB=Braggangle

<hkl>R

θΒ

PerfectSicrystal

neutrons

Stackofthinwaferstoallowbending§  waferthickness=1mm§  10waferstogett=10mm(ormore)§  Curvature:flattoRH≈2m

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 23

Monochromators

HOPGD19 •  Large effective area to cover the direct beam

Assembly of mosaic crystals •  FWHM ~ beam divergence 0.2 < FWHM < 0.6 ° •  Crystal size ~ Sample size (1 to 10 cm2) •  Crystals fixed onto specific mechanics •  10B4C is used to reduce background and activation •  Orientation accuracy ± 0.03° •  Vertical Focusing •  Horizontal Focusing (Triple axis spectrometers)

crystal

AlB4C

crystal+support

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 24

Focusing devices Divergentbeamflux~1010n/cm2/s

α=2θcSampleS~1cm2Neutronsource(guide,

beamtube)

BeamsizeS~100cm2

lostneutrons!

Ø  Focusingdevicesareusedtoincreasetheneutronfluxatthesampleposi+on.However,theincrease of neutron flux implies a degrada+on of the angular resolu+on. (Liouville’stheorem!)

H1H2H1α1=H2α2Divergence α1

α2

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 25

Focusing Devices Principles

Ver7calFocusing§  Imagesize~crystalsize(height)§  Gaininflux∝compressionfactorØ Increaseofver7calangulardivergenceØ Rv∝λ

HorizontalFocusing§  HorizontalfocusingaffectsQresolu7on§  Rh∝1/λ

Sample

1Rv

=1

2sinθ1L1

+1L2

⎛

⎝⎜

⎞

⎠⎟

1RH

=sinθ

21L1

+1L2

⎛

⎝⎜

⎞

⎠⎟

RvSource

Sample

L2

L1

θ

L2L1Source

Sample

RHθ

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 26

Focusing Devices Monochromators for neutron Diffractometers

Production of a fixed neutron wavelength at a given take-off angle

Ge(335)-λ=1.6Åcrystalmosaic=0.2°

HighResolu4on

D2B

D20

Ge(111)-λ=3.15Åcrystalmosaic=0.4°

HighResolu4on

D20

Gemonochromatoriswellsuitedforhighresolu7onneutrondiffractometers

D20 (high intensity difffratometer with variableresolu+on)-D2B&D1B(powderdiffractometers)§  LargedimensionsHeigth300mmWidth50-120mm§  noλ/2contamina7on(oddreflec7ons)§  Fixedver+calfocusingRv=2LMSsinθB D20:Rv=3200mm

D2B:Rv=4600mm

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 27

D20

SinglecrystaldiffractometerHOPG(002)-λ=2.4Åcrystalmosaic=0.5°

HighFlux

D19

SinglecrystaldiffractometerCu(200)-λ=1.2Åcrystalmosaic=0.2°

HighResolu4on

D10

HOPGmonochromator•  Provides high neutron flux (thermal & cold

neutrons)§  λ/2contamina+on(002reflec+ons)Ø  UseofHOPGFilter!§  Fixedver+calfocusing

Cumonochromator§  provideshighneutronfluxorhighresolu+on

(hot&thermalneutrons)§  λ/2contamina+onØ  useofHOPGFilter!Ø  thermalneutronguidecut-off

Focusing Devices Monochromators for neutron Diffractometers

28 THE EUROPEAN NEUTRON SOURCE

Ø  Optimization of instrument performances for a wide energy range Ø  Variable horizontal and vertical curvature Ø  Focusing monochromator is used in combination with focusing guide (virtual

source) see previous presentation from J. Kulda !

Cremlin14-15May2018

Focusing Devices Monochromators for Triple Axis Spectrometers

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 29

D20

HOPG(002)monochromatorcrystalmosaic=0.5°

coldneutrons

Cu(200)monochromatorcrystalmosaic=0.3°

HighFlux–Thermalneutrons

Si(113)monochromatorbentperfectcrystals

Hotneutrons

Thales IN8C IN1

Focusing Devices Monochromators for Triple Axis Spectrometers

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 30

Monochromator for polarized neutrons Heusler Cu2MnAl mosaic crystals

• (111)reflec+on F111N=-F111M• Mosaic 0.2°<fwhm<0.6°

• Reflec+vity Rexp≈Rtheor

• Polariza+on P>92%THALES

(3-Axisforlowenergyspectroscopy)IN20

(Thermalneutron3axisspectrometer)

FixedVer+calCurvature–VariableHorizontalCurvature

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 31

Neutron Filters Neutron filters are used to select out unwanted neutrons

θ

PolycristallineBerylliumat77Kisusedtoselectoutneutronsofλ<4Å

(Cut-offatλ=2dBemax)

PerfectSaphirrecrystalisusedtoselectoutfastneutronsof λ <0.5Å

Ø Reduc+onofbackground

T~ 5%

T~ 80%

n λ >λcut

λ <λcut

Cut-off

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 32

Neutron Filters Neutron filters are used to select out unwanted neutrons

θ

λ=1.2Å

λ=2.4Å

Wavelengthλ (Å)

transm

ission

λ0 / 2

HOPG crystal (Highly Oriented Pyroli7cGraphite) is commonly used for elimina+ngh i g h e r - o r d e r c o n t a m i n a + o n o f amonochromatedneutronbeamPG filter has strong aRenua+on at 1.2 Å butpasses2.4Å•  T>80% at2.4Å•  T<1% at1.2Å

λ=0.8Å

λ0 =2.4Å λ0 =2.4Å + λ0 /2 =1.2Å

HOPGfilter,4cmthick

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 33

Neutron Filters – Polarized Neutrons 3He spin filters at I.L.L.

B

3Hespinfiltercell

P

§  For fully polarized 3He (PHe = 1), one spin state goes through the filter with zeroabsorp+on. The other spin state is almost fully absorbed since σ = 6000 barns →polarizedneutronbeam

§  Absorp7oncrosssec7onof3HeliumnucleiØ IfthenuclearspinofHeandtheneutronspinareparallel,σa↑↑≈0Ø IfthenuclearspinofHeandtheneutronspinarean+-parallel,σa↑↓≈6000barns

I N S T I T U T M A X V O N L A U E - P A U L L A N G E V I N 34

Neutron Filters – Polarized Neutrons 3He spin filters at I.L.L.

Ø  Polariza+onofneutronbeams(hot,thermal,cold)Ø 3HespinfiltersprovideanuniquetooltoperformXYZpolariza+onanalysis

Polariza+onof3He:P(t)=exp(-t/T1)and

§  Toperformpolarizedneutronsexperiments:T1>100hØ Highquality3Hespinfilters(Polariza+on,Tw)Ø Homogeneousmagne+cfield

]b[750]h[P

Td = h 400200−≈wT Tm[h] =P[b]7000

∂B /∂r[cm]B

"

#$

%

&'−2

1T1

= 1Td

+ 1Tw

+ 1Tm

35 THE EUROPEAN NEUTRON SOURCE

Production of 3He spin filters at I.L.L. Metastability Exchange Optical Pumping (MEOP)

§  Produc+onrate>1bar-litre/h§  Finalpressureupto4bar§  Polariza+onof3He≈80%

3Hefillingsta4onatI.L.L.

Developmentof3Hecells§  Bananashaped§  Coverageangleupto125°§  Siwindows:Reduc+onofbackground§  Cscoa+ng§  Tw>200h

Cremlin14-15May2018

36 THE EUROPEAN NEUTRON SOURCE

Conclusion §  NeutronOp7csdefinebeamproper7es

-  Direc+on,Divergence,Wavelength,Energy,Polariza+on-  AngularResolu+on,Wavelengthresolu+on,Energyresolu+on

§  Ver+calfocusingdevicesallowtheop+miza+onoftheneutronfluxatthesampleposi+on§  Doublevariablefocusingdevicesallowtheop+miza+onofinstrumentperformancesforawideenergyrange

Ø Sincethepowerofthesourceislow,neutronop7calcomponentsmustbeofhighqualityandproperlydesigned

Ø NeutronOp+csobeytoLiouville’sTheorem:Itcostsfluxtoincreaseresolu+onanditcostsresolu+ontoincreaseflux

Theop7miza7onofinstrumentperformancesisalwaysacompromisebetweenfluxandresolu7on

37 THE EUROPEAN NEUTRON SOURCE

ThankYouforyouraRen+on

Cremlin14-15May2018