Lu Zou Sep. 12 th , 2005
description
Transcript of Lu Zou Sep. 12 th , 2005
1
What did I Learn in ’05 Summer?
-- A report on Neutron and X-ray National School
in Argonne National Laboratory
Lu ZouSep. 12th, 2005
2
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
3
1895: Discovery of X-Ray
Wilhelm Conrad Röntgen 1845-1923
4
d
2
Scattering GeometryIncident Radiation
(ki, Ei, pi)
Scattered Radiation
(kf, Ef, pf)
Energy Transfer
q = ki - kf
ΔE = Ei – Ef
5
Interaction Mechanisms
6
Intrinsic Cross Section
7
To “see ” 1H with Neutron diffraction,
DEUTORATE ‘H’ to ‘D’
const.dd 2
0
b
8
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
9
Intense Pulsed Neutron Source (IPNS)50 MeV
450 MeVH-
750 keV
30 Hz
P+
N
10
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)
11
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)
12
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)]
13
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.
14
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
15
Neutron Instrumentation• Collimator
• Monochromator
• Analyzer
• …
I didn’t find enough information on this topic …
16
17
Outline for 2nd part
• Small Angle Scattering
• Powder Diffraction
• Reflectometry
18
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
19
Basic schematics of a SAS experiments
20
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
21
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
22
“IGOR Pro. 5.03”
• Debye Flexible Gaussian polymer
• Solid Sphere
• Schultz Polydisperse Sphere
• Spherical Shell
• …
Sperical Shell
Schultz Polydisperse Core Sherical Shell
23
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
24
Powder Diffraction
• We don’t take a picture of atoms!
• We live in a reciprocal space!
25
26
27
Sample(capillary)
Detectors
Å(25keV)
2APS
Analyzer
Beam optics = 2dsinVary 2
Parallel beam optics
32-ID powder diffractometer – multi-analyzer/detector
28
8 detectors used
sample
Beam pipe
29
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
30
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
31
Reflectometry
32
Scattering Length Density (SLD) ρ(z) = NbN = # of Atoms per unit volume
b = Scattering length
33
34
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
35
Structural studies of Langmuir-Blodgett films
• Dave Wiesler (NIST)• Lev Feigin (Moscow)• Wolfgang Knoll (Planck)• Albert Schmidt (Planck)• Mark Foster et. al. (Akron)• …
36
Spallation Neutron Source (SNS)
37
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
38
FissionFission chain reaction continuous flow 1 neutron/fission
SpallationSpallationno chain reactionpulsed operation 30 neutrons/proton
How do we produce neutrons?