Scattering of Neutrons of Neutrons Scattering Basics Basics - PDF document

Scattering of Neutrons of Neutrons Scattering Basics Basics Regine Willumeit Willumeit Regine GKSS Research Center 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 are Neutrons Neutrons Produced Produced? ? How Fission 200 MeV n = 2 MeV Natural abundance 0.71 % 1

How are are Neutrons Neutrons Produced Produced? ? How Shut down in Shut down in June June 2010 2010 View of View of the the FRG1 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 Power : Research Reactor Reactor Comparison Power Research [Krümmel] [FRG-1] pressure swimming-pool type UO 2 U 3 Si 2 fuel 3.3-3.5 % <20 % enrichment 840 12 # fuel elements 3690 MW 5 MW therm. power H 2 O H 2 O moderator << 10 14 n/s cm 2 1.4x10 14 n/s cm 2 neutron flux What does does the the flux flux mean mean? ? What ILL:  = 1.5*10 15 n/s cm 2 [Prof R. Scherm]  = 1.5*10 21 n/s m 2 average speed: v = 2000 m/s density =  /v = 6.8*10 17 n/m 3 comparison air: p=10 -7 mbar! 3

How are are Neutrons Neutrons Produced Produced? ? How Spallation Particles with high energy hit a target neutrons come out Protons [H - ] liquid Mercury 1 GeV H + 1 Protons -> 20-30 Neutrons SNS SNS How are are Neutrons Neutrons Produced Produced? ? How European Spallation Source „ESS-I“ Three sites were competing: Lund (S), Bilbao (E) and Debrecen (H) 4

How are are Neutrons Neutrons Produced Produced? ? How European Spallation Source „ESS-I“ Malmö MAX-Lab ESS Comparison of Neutron of Neutron Sources Sources Comparison ESS 5

Correlation between Correlation between Energy and Wave Energy and Wave Length Length pm pm Neutron Properties Neutron Properties no charge 6

Neutron Properties Properties Neutron magnetic moment Neutron Properties 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 H 2 and D 2 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 ... 7

To Remember To Remember: : Neutrons X-Rays Intensity low high H-sensitivity high none Isotope-sensitivity strong none Heavy elements low high Spin-sensitivity strong average Penetration depth high low Sample size/amount large small Measurement time long short Interaction with nuclei electron shell electron shell  Z unsystematic Radiation damage none high Interaction of Radiation Interaction of Radiation with with Matter Matter 8

Interaction of Radiation Radiation with with Matter Matter Interaction of 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) 9

Comparison Comparison Neutron- - and and X X- -ray ray- -scattering scattering length length Neutron [10 - -12 12 cm] some relevant some relevant elements elements [10 cm] n X-ray 1 H -0.37 0.28 2 H 0.67 0.28 12 C 0.66 1.68 14 N 0.94 1.96 16 O 0.58 2.24 31 P 0.51 4.2 32 S 0.28 4.48 56 Fe 0.95 6.72 Neutron Scattering Scattering Length Length Neutron -12 12 cm] of biological biological relevant relevant elements elements [10 [10 - cm] of deuterate whenever possible! [F. Sears (1986), H. Glättli und M. Goldmann (1987)] 10

Contrast Contrast Variation 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 Concept of of Contrast Contrast Variation Variation The Contrast = Difference of Scattering Length Densities 11

X-Ray Scattering Contrast = Difference of Scattering Length Densities Scattering Length Density of the Solute [10 10 cm -2 ] p(R) =  Particle (R) -  LM (R) Neutron Scattering Water Sugar p(R) =  Particle (R) -  LM  (R) = Scattering Length Densitiy = Sum of Scattering Length of Volume Fraction D 2 O all Atoms in a Volume Scattering Length Density of the Solvent [10 10 cm/cm 3 ] Synaptic Arrangement of the Neuroligin/b-Neurexin Complex Revealed by X-Ray and Neutron Scattering . D. Comoletti et al. Structure 15 (2007) 693–705 12

Synaptic Arrangement of the Neuroligin/b-Neurexin Complex Revealed by X- Ray 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% D 2 O We „see“ the deuterated with neutrons and the whole complex with X-rays Deuterated! 14

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 Setup of a SANS Instrument GKSS 15

A A Typical Typical SANS Instrument SANS Instrument Number of plates: 72 Monochromator thickness [mm]: 0.4 Crystal twist angle: 48.27° material: carbon fiber in Selector epoxy with 10 B or Gd 29 cm 25 cm Monochromators: Time of Monochromators : Time of Flight Flight Chopper REFSANS@FRM-II t=0 t=x 16

A A Typical Typical SANS Instrument SANS Instrument Collimation Line A Typical Typical SANS Instrument SANS Instrument A Neutron guides Neutron guides based on total reflection  = atoms / cm 3 k  C  2   b Collimation Line b = scattering length critical angle: sin  c =  /   b/   c [mrad]  c [°] Materials d c [nm] Al 0.81 0.048 62 Ni 1.70 0.10 29 58 Ni 2.03 0.12 25 Fe 1.62 0.095 31 Co 0.86 0.051 58 glass 1.06 0.062 17

A Typical A Typical SANS Instrument SANS Instrument  c [mrad]  c [°] Materials d c [nm] Al 0.81 0.048 62 Ni 1.70 0.10 29 58 Ni 2.03 0.12 25 Fe 1.62 0.095 31 Co 0.86 0.051 58 Detektor glass 1.06 0.062 Collimation Line Sample Position 18

Measurements Raw Data [Chaperonin GroEL] Data Integration Principle Beam center Pixel size 'Mask' measurements 19

Data Integration Solid angle correction Correction: cos 3 (  ) Integration 'pure' I tot / monitor Q [Å -1 ] 20

Measurements Detector response: H 2 O Measurements Detector response Strong incoherent scatterer Water (H 2 O) 1mm Vanadium Plastic Normalization Knowledge about the coherent cross section Water (H 2 O) 1mm Vanadium I(q) / T I(q) norm = for all detector pixels I(q) H2O / T H2O G.D. Wignall, F.S. Bates: Absolute calibration of small angle neutron scattering data. J. Appl. Cryst. (1987) 20 , 28-40 21

Integration 'divided by water' Normalized I tot / monitor 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 22

SANS-1@FRG-1 10 m 10 m Collimator Neutron guide Integration 'with collimation correction' Normalized I tot / monitor 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 Smearing Effects Beam profile Wave length profile Influences on the measured intensity: Smearing Detektor resolution Gauss-distribution W D Influence on medium and large q-range  I(q) = I(q) W D dq m 24

Influences on the measured intensity: Smearing Detektor resolution Finite collimation Gauss-distribution W C Influence on small q-range  I(q) = I(q) W D W C dq m Influences on the measured intensity: Smearing Detektor resolution Finite collimation Wavelength resolution Gauss-distribution W  Influence on medium and large q-range  I(q) = I(q) W D W C W  dq m 25