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