NIST/NRC Postdoctoral Fellowship Research

1
SANS with Magnetic Contrast
neutron magnetic moment
Neutrons are scattered by inhomogeneities in the
scattering length density of a material
Chemical contrast
matrix
particle
And, by inhomogeneities in the magnetization
(magnetic moment per unit volume) of a material
Magnetic contrast
2
SANS with Magnetic Contrast

I(Q-)
-
Q
Inhomogeneities in magnitude and direction of M
produce scattering, e.g. domain walls
I(Q?)
Sample with randomly oriented Magnetic domains
Magnetic contrast
3
SANS with Magnetic Contrast


By aligning magnetic domains with an applied
magnetic field, domain wall scattering is
eliminated
I(Q?)
Sample with randomly oriented Magnetic domains
Magnetic contrast
4
SANS with Magnetic Contrast (unpolarized
neutrons)
I(Q-)
I(Q?)
similar terms for each species
5
SANS with Magnetic Contrast (unpolarized
neutrons)
I(Q-)
I(Q?)
similar terms for each species
Magnetic scattering comes From
only!
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Using SANS to Correlate Radiation Dose with
Microstructural Changes in Reactor Pressure
Vessel Steels
G. R. Odette, G. Lucas, et al. (U. California at
Santa Barbara)
Reactor Vessel
Measurements aimed at determining what factors
and mechanisms cause reactor vessels to embrittle

SANS is particularly useful because of its
sensitivity to both chemical and magnetic
inhomogeneities
7
Typical SANS Patterns for Reactor Pressure Vessel
Steels
Irradiated sample
Irradiated sample
11 for pure Cu
1.5 for voids
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Type II Superconductor
Mixed state
Normal state
normal conductor
mixed
state
Complete flux penetration
Meissner state
Complete magnetic flux exclusion
9
SANS 2D detector
Diffraction from fluxoid lattices
Neutron diffraction reveals

• fluxoid size, shape and interface thickness
• fluxoid lattice symmetry
• fluxoid interactions
• details of phase tranisitions
• strength of pinning centers

Sample in mixed state with magnetic field along
beam direction
n
10
Vortex Matter in Superconductor Nb
Real space depiction of vortex lattice
X. S. Ling and S.-R. Park (Brown
University) S.-M Choi, D. Dender and J. Lynn,
(NCNR/NIST)
11
Characterization of Protein/RNA Complexes
Contrast Variation
Deborah Kuzmanovic, Catherine O Connell, NIST
Biotech. Div. Susan Krueger, NIST NCNR Charles
Wick, Aberdeen Proving Ground
MS2 Bacteriophage
12
Small Angle Scattering from Macromolecules in
Solution



Macromolecule in Solvent

















?s ?(0)

-




13
SANS Data Analysis
Low Angles QRg 1
I(0)/c constant x Mw

• Not model specific
• Simple shape models from Rg, Mw and V

14
Distance Distribution Function
4?P(r) ? number of distances within the molecule
Dmax ? maximum distance within the molecule
P(0) 0 P(2r?Dmax) 0
15
Standard Assays for Diseases

• Commercially available model recombinant non-
• infectious virus can be used as a RNA carrier
• Any gene (RNA) for a disease of interest can be
• incorporated for use in clinical assays.

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Samples for SANS Measurements

• WT MS2 phage (3500bp)
• Wild-type
• Found in nature
• Infectious (to bacteria only)
• Empty capsid (0bp)

• Recombinant RNA samples
• Lambda phage (1000bp)
• HCV (500bp)

IS there one RNA per capsid?
17
Capsid and WT MS2 Protein
Capsid and WT MS2 protein structures look similar
when measured in 65 D2O solvent, where I(Q)RNA
0.
18
Contrast Variation of MS2 Complexes
Contrast (??)
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Structure and Mw Determination
Scattered intensity and Mw from protein and RNA
components can be determined separately by making
measurements at several contrasts.
I(q) ??12 I1(q) ??1 ??2I12(q) ??22 I2(q)
20
Structure and Mw of WT MS2 Phage
RNA in core packs tightly within a radius of
80Å.
21
Structure of MS2 Complexes
Wild-type MS2
HCV Armored RNATM
0 and 10 D2O RNA scattering is strongest 100
D2O RNA scattering is weaker 85 D2O RNA
scattering is weakest
22
Structure of MS2 Complexes
Protein shell is less well-defined in HCV
particles. RNA is not as tightly packed in HCV
particles.
23
Conclusions

• Empty capsid and WT MS2 protein shell have
  similar structures.
• Protein shell is thicker and less well-defined in
  HCV and ? particles.
• RNA is WT MS2 is tightly packed within a radius
  of 80Å.
• RNA is not as tightly packed in HCV and ?
  particles.
• Mw measurements confirmed the known amounts of
  protein and RNA in WT MS2.
• Freshly prepared HCV and ? particles likely
  contain more than one RNA per capsid.