Scattering of Neutrons
Basics
Regine Willumeit
GKSS Research Center
1.11.2010: Helmholtz Zentrum Geesthacht
Zentrum für Material und Küstenforschung
How are neutrons produced?
What are the properties of neutrons?
The concept of contrast variation
Experimental set up of a SANS instrument
Data analysis: what is different to X-rays
How are Neutrons Produced?
Fission
200 MeV
n = 2 MeV
Natural abundance 0.71 %
1
How are Neutrons Produced?
Sh
ut
do
wn
in
Ju
ne
20
10
View of the FRG1
Schematic picture of FRG-1
controll center
Reactor hall
experimental hall
warm water
second pool
reactor pool
beryllium reflector
beamlines
reactor core
first cooling system
second cooling system
Heat exchanger
2
Comparison Power : Research Reactor
Power
[Krümmel]
Research
[FRG-1]
type
pressure
swimming-pool
fuel
enrichment
UO2
3.3-3.5 %
U3Si2
<20 %
840
12
3690 MW
5 MW
H2O
H2O
# fuel elements
therm. power
moderator
neutron flux
<< 1014 n/s cm2
1.4x1014 n/s cm2
What does the flux mean?
ILL:  = 1.5*1015 n/s cm2
[Prof R. Scherm]
 = 1.5*1021 n/s m2
average speed: v = 2000 m/s
density = /v = 6.8*1017 n/m3
comparison air: p=10-7 mbar!
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How are Neutrons Produced?
Spallation
Particles with high energy hit a target
neutrons come out
Protons
[H-]
liquid
Mercury
1 GeV H+
1 Protons -> 20-30 Neutrons
SNS
How are Neutrons Produced?
European Spallation Source „ESS-I“
Three sites were competing:
Lund (S), Bilbao (E)
and Debrecen (H)
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How are Neutrons Produced?
European Spallation Source „ESS-I“
Malmö
MAX-Lab
ESS
Comparison of Neutron Sources
ESS
5
Correlation between Energy and Wave Length
pm
pm
Neutron Properties
no charge
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Neutron Properties
magnetic moment
Neutron Properties
Deep Penetration
residual stress, texture, cavities, precipitates, cracks ...
deep inside materials or technical components
Strong Magnetic Interaction
magnetic structure on atomic scale, domane structures ...
magnetic surface and bulk structures ...
Strong Interaction with H2 and D2
Soft matter research: polymers, colloids, biological macromolecules ...
surface and bulk structures, ordered layers, solution ...
Nuclear Reactions
-Spectrum => nuclear activation analysis
chemical analysis of more than 50 elements in bulk ...
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To Remember:
Neutrons
X-Rays
Intensity
low
high
H-sensitivity
high
none
strong
none
Heavy elements
low
high
Spin-sensitivity
strong
average
Penetration depth
high
low
Sample size/amount
large
small
Measurement time
long
short
nuclei
electron shell
Isotope-sensitivity
Interaction with
electron shell
Radiation damage
unsystematic
Z
none
high
Interaction of Radiation with Matter
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Interaction of Radiation with Matter
Light scattering
Interaction with electrons
X-ray scattering
Interaction with electrons
Scattering ‘strength’ is proportional to Z
Interaction with electron spin possible
Neutron scattering
Interaction with nuclei (protons and neutrons)
Scattering ‘strength’ does not vary systematically
Interaction with nuclear spin possible
Interaction with electrons and electron spin possible
Atomic Scattering factors / length
X-Rays
Neutrons
H
atomic mass / g mol-1
R.Winter, F. Noll: Methoden der biophysikalischen Chemie, Teubner (1998)
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Comparison
Neutron- and X-ray-scattering length
some relevant elements [10-12 cm]
1H
2H
12C
14N
16O
31P
32S
56Fe
n
-0.37
0.67
0.66
0.94
0.58
0.51
0.28
0.95
X-ray
0.28
0.28
1.68
1.96
2.24
4.2
4.48
6.72
Neutron Scattering Length
of biological relevant elements [10-12 cm]
deuterate whenever possible!
[F. Sears (1986), H. Glättli und M. Goldmann (1987)]
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Contrast
Variation
When the monster came,
Lola, like the peppered
moth and the arctic hare,
remained motionless and
undetected.
Harold of course, was
immediately devoured.
The Concept of Contrast Variation
Contrast = Difference of Scattering Length Densities
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X-Ray Scattering
Scattering Length Density of the Solute [1010 cm-2]
Contrast =
Difference of
Scattering Length Densities
p(R) =
Particle(R) - LM(R)
Neutron Scattering
Water
Sugar
p(R) =
Particle(R) - LM
(R) =
Volume Fraction D2O
Scattering Length Densitiy =
Sum of Scattering Length of
all Atoms in a Volume
Scattering Length Density of the Solvent [1010 cm/cm3]
Synaptic Arrangement of the Neuroligin/b-Neurexin Complex Revealed
by X-Ray and Neutron Scattering. D. Comoletti et al. Structure 15 (2007) 693–705
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Synaptic Arrangement of
the Neuroligin/b-Neurexin
Complex Revealed by XRay and Neutron
Scattering. D. Comoletti et al.
Structure 15 (2007) 693–705
Synaptic Arrangement of the Neuroligin/b-Neurexin Complex Revealed
by X-Ray and Neutron Scattering. D. Comoletti et al. Structure 15 (2007) 693–705
Impossible to crystallize
13
Synaptic Arrangement of the Neuroligin/b-Neurexin Complex Revealed
by X-Ray andNeutron Scattering. D. Comoletti et al. Structure 15 (2007) 693–705
Deuterated!
Synaptic Arrangement of the Neuroligin/b-Neurexin Complex Revealed
by X-Ray andNeutron Scattering. D. Comoletti et al. Structure 15 (2007) 693–705
42% D2O
We „see“ the deuterated with neutrons
and the whole complex with X-rays
Deuterated!
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Synaptic Arrangement of the Neuroligin/b-Neurexin Complex Revealed
by X-Ray andNeutron Scattering. D. Comoletti et al. Structure 15 (2007) 693–705
Distance Distribution
Setup of a SANS Instrument
GKSS
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A Typical SANS Instrument
Monochromator
Crystal
Selector
Number of plates: 72
thickness [mm]:
0.4
twist angle:
48.27°
material: carbon fiber in
epoxy with 10B or Gd
29 cm
25 cm
Monochromators: Time of Flight
Chopper
REFSANS@FRM-II
t=0
t=x
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A Typical SANS Instrument
Collimation Line
A Typical SANS Instrument
Neutron guides
based on total reflection
3
kC  2 
b
Collimation
Line = atoms / cm
b = scattering length
critical angle: sin c =  /  b/ 
Materials c [mrad]
Al
0.81
Ni
1.70
58Ni
2.03
Fe
1.62
Co
0.86
glass
1.06
c [°]
0.048
0.10
0.12
0.095
0.051
0.062
dc [nm]
62
29
25
31
58
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A Typical SANS Instrument
Materials
Al
Ni
58Ni
Fe
Co
glass
c [mrad]
0.81
1.70
2.03
1.62
0.86
1.06
c [°]
0.048
0.10
0.12
0.095
0.051
0.062
dc [nm]
62
29
25
31
58
Detektor
Collimation Line
Sample Position
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Measurements Raw Data [Chaperonin GroEL]
Data Integration
Principle
Beam center
Pixel size
'Mask' measurements
19
Data Integration
Solid angle correction
Correction: cos3()
'pure'
Itot / monitor
Integration
Q [Å-1]
20
Measurements
Detector response: H2O
Measurements
Detector response
Strong incoherent scatterer
Water (H2O) 1mm
Vanadium
Plastic
Normalization
Knowledge about the coherent cross section
Water (H2O) 1mm
Vanadium
I(q)norm =
I(q) / T
I(q)H2O / T H2O
for all detector pixels
G.D. Wignall, F.S. Bates: Absolute calibration of small angle neutron
scattering data. J. Appl. Cryst. (1987) 20, 28-40
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'divided by water'
Normalized Itot / monitor
Integration
Q [Å-1]
SANS-1@FRG-1
10 m
10 m
SANS-2@FRG-1: 2 x 20 m
D11@ILL: 2 x 40 m
Rule of thumb:
collimation length = sample-detector distance
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SANS-1@FRG-1
10 m
Neutron guide
Collimator
'with collimation correction'
Normalized Itot / monitor
Integration
10 m
Q [Å-1]
23
Considerations about Scattering data
We considered so far:
solid angle correction
detector response (division by water)
flux reduction by collimation
We still have to consider:
Sample concentration, dark current, backgroud
subtraction (cuvette), dead time corrections
Detektor resolution
Beam profile
Smearing Effects
Wave length profile
Influences on the measured intensity: Smearing
Detektor resolution
Gauss-distribution WD
Influence on medium
and large q-range
I(q)m=
I(q) W
D
dq
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Influences on the measured intensity: Smearing
Detektor resolution
Finite collimation
Gauss-distribution WC
Influence on small
q-range
I(q) =
m
 I(q) W
D
WC dq
Influences on the measured intensity: Smearing
Detektor resolution
Finite collimation
Wavelength resolution
Gauss-distribution W
Influence on medium
and large q-range
I(q) =
m
 I(q) W
D
WC W dq
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Influences on the measured intensity: Smearing
Thank your for
your Attention!
Argonne National Lab
http://www.neutron.anl.gov/
http://pathfinder.neutron-eu.net/idb
http://ess-scandinavia.eu/about-esss
http://www.ill.fr/
http://www.isis.stfc.ac.uk/
http://sni-portal.uni-kiel.de/kfn/
Neutron Scattering Home Page
The Neutron Pathfinder
ESS Scandinavia
ILL home
ISIS
Komitee Forschung mit Neutronen
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