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What did I Learn in ’05 Summer?

-- A report on Neutron and X-ray National School

in Argonne National Laboratory

Lu ZouSep. 12th, 2005

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Outline• Introduction to Neutron and X-Ray

Scattering• Introduction to APS and IPNS in

Argonne National Lab• Neutron and X-Ray Detectors and

Instrumentation• Neutron and X-Ray Experiments• Other Information

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1895: Discovery of X-Ray

Wilhelm Conrad Röntgen 1845-1923

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d

2

Scattering GeometryIncident Radiation

(ki, Ei, pi)

Scattered Radiation

(kf, Ef, pf)

Energy Transfer

q = ki - kf

ΔE = Ei – Ef

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Interaction Mechanisms

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Intrinsic Cross Section

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To “see ” 1H with Neutron diffraction,

DEUTORATE ‘H’ to ‘D’

const.dd 2

0

b

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Advanced Photon Source (APS)• e- Gun: Cathode ~1100 oC

• LINAC

• 450 MeV

• >99.999% of C

• Booster Synchrotron

• 7 GeV

• >99.999999% of C

• Electron Storage Ring

• 1104-m-circumference

• > 1,000 electromagnets

• Insertion Devices

• Experiment Hall and Beamlines

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Intense Pulsed Neutron Source (IPNS)50 MeV

450 MeVH-

750 keV

30 Hz

P+

N

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X-Ray Detectors

• Photons can only by “detected” by registering the deposition of energy in the detecting medium

• Therefore, inelastic scattering processes (i.e. those that deposit energy) are relevant.

• Photoelectric effect (Ionization Chambers)

• Compton scattering (Scintillation Detectors)

• Pair (e+, e-) production (Solid State Detectors)

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Neutron Detectors

• To “detect” a neutron, one need to use nuclear reactions to “convert” neutros into charged particles (now, countable)

• Then, use one of many types of charged particle detectors– Gas (3He) proportional counters and ionization

chambers– Scintillation detectors (6Li)– Semiconductor detectors (6Li)

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X-Ray Instrumentation -- Mirror

c

Air (n1 ~ 1)

2

n2

c

Critical Angle for total External Reflection

c = (2)1/2

n2 = 1 - - i

Index of Refraction

Typical values for at 1Å is 10-5 to 10-6, so c is about 10-3 mrads.

R

1

F

F2

R = [2/sin ] [F1 F2/(F1 + F2)]

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X-Ray Instrumentation -- Monochromators• Use Bragg’s Law to select a particular wavelength (or en

ergy since = hc/E), namely: = 2d sin()

• If we differentiate Bragg’s Law, we can determine the energy resolution of the monochromator.

/ = E/E = cot()

• Because of the small angular divergence of the x-ray beam in the vertical direction (and the polarization of the beam - in the plane of the orbit), synchrotron radiation monochromators normally diffract in the vertical plane.

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Double Crystal Monochronmators• The most common arrangement for a monochromator is the double-crystal monochromator. It:

– is non-dispersive, that is all rays that diffract from the first crystal simultaneously diffract from the second crystal (if same crystals with same hkl’s are used)– keeps the beam fixed in space as the energy is changed.

polychromatic

monochromatic

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Neutron Instrumentation• Collimator

• Monochromator

• Analyzer

• …

I didn’t find enough information on this topic …

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Outline for 2nd part

• Small Angle Scattering

• Powder Diffraction

• Reflectometry

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Small Angle Neutron and X-ray Scattering (SANS, SAXS)

• Small Angle X-ray Scattering (SAXS) 0.06 <λ< 0.2 nm

• Small Angle Neutron Scattering (SANS) 0.5 <λ< 2 nm

• Small Angle Light Scattering (LS) 400 <λ< 700 nm

USAXS

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Basic schematics of a SAS experiments

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Incident beamScat

tered beam

P

O

ki·r

kf·r

2 |kf · r - ki· r| = Q · r

Q = |Q| = 4 sin ()

2r

k = 2

Recall Bragg’s Law λ=2dsinθ

d = 2π/Q

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Guinier Plot

• Look at scattering in low-Q regime• Plot the data as ln I(Q) vs Q2

• Needle shaped particles: I(Q) ~ Q-1

• Disk shaped particles: I(Q) ~ Q-2

• Spherical particles: I(Q) ~ Q-3

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“IGOR Pro. 5.03”

• Debye Flexible Gaussian polymer

• Solid Sphere

• Schultz Polydisperse Sphere

• Spherical Shell

• …

Sperical Shell

Schultz Polydisperse Core Sherical Shell

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Small angle scattering is used to study . . . • Polymer materials

– Conformation of polymer molecules in solution and in bulk– Structure of microphase-separated block copolymers– Factors affecting miscibility of polymer blends

• Biomaterials– Organization of biomolecular complexes in solution– Conformational changes affective function of proteins, enzym

es, complexes, membranes, . . . – Pathways for protein folding

• Chemistry– Colloidal suspensions, microemulsions, surfactant micelles– Molecular self-assembly in solution and on surfaces

• Metals and ceramics– Deformation microstructures and precipitation

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Powder Diffraction

• We don’t take a picture of atoms!

• We live in a reciprocal space!

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Sample(capillary)

Detectors

Å(25keV)

2APS

Analyzer

Beam optics = 2dsinVary 2

Parallel beam optics

32-ID powder diffractometer – multi-analyzer/detector

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8 detectors used

sample

Beam pipe

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X-ray Powder Diffraction-- Mixture of Y2O3 and Al2O3

Software : EXPGUI By Dr. R.B. Von DreeleAPS/IPNS Argonne National Laboratory

Gaussian profile

Lorentzian profile

2

2

2)T(2ln4exp2ln4),T(G

2T21

12),T(L

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Summary for Powder Diffraction• Input Data

– Powder scattering pattern data– Trial structure space group and approximate lattice p

arameters and atomic positions– Line shape function and Q-dependence of resolution

• Output Results– Lattice Parameters– Refined atomic positions and occupancies– Thermal parameters for each atom site– Resolution parameters– Background parameters– R factors of fit– Preferential orientation, absorption, etc.

• More than one phase can be separately refined

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Reflectometry

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Scattering Length Density (SLD) ρ(z) = NbN = # of Atoms per unit volume

b = Scattering length

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Reflectometry Applications

• Polymer Interface• Magnetic superlattices and thin films• Langmuir-Blodgett filmes• Biological membranes• Electrochemistry• Superconductivity• Diffusion processes• …

• Langmuir-Blodgett filmes

• Interdiffusion

• Surface and interfacial roughness

• Structures

•Biological membranes

• Lipid layer structure

• Protein adsorption

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Structural studies of Langmuir-Blodgett films

• Dave Wiesler (NIST)• Lev Feigin (Moscow)• Wolfgang Knoll (Planck)• Albert Schmidt (Planck)• Mark Foster et. al. (Akron)• …

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Spallation Neutron Source (SNS)

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U.S. Neutron Scattering Schools• National Neutron and X-ray Scattering Summer School

– Two weeks in August– http://www.dep.anl.gov/nx/– Deadline Apr.30

• NCNR-NIST Summer School– One week in June– http://www.ncnr.nist.gov/summerschool/index.html– Deadline April

• LANSCE Winter School in Neutron Scattering– Topic focus (changes each year)– 7-10 days in January– http://www.lansce.lanl.gov/neutronschool/;– Deadline October

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FissionFission chain reaction continuous flow 1 neutron/fission

SpallationSpallationno chain reactionpulsed operation 30 neutrons/proton

How do we produce neutrons?