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The NISTNSF Center for High Resolution Neutron Scattering at NISTs Center for Neutron Research Gaith

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Title: The NISTNSF Center for High Resolution Neutron Scattering at NISTs Center for Neutron Research Gaith


1
The NIST/NSF Center for High Resolution Neutron
Scatteringat NISTs Center for Neutron
ResearchGaithersburg, Maryland
  • 2003 Highlights of Activities Supported by
  • DMR-9986442, Charles Glinka, PI
  • DMR-0086210, Dan Neumann, PI

2
Depletion Interactions in Colloid-Polymer Mixtures
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When non-adsorbing polymers are added to stable
colloidal suspensions the particles experience an
induced depletion attraction due to an
unbalanced osmotic pressure arising from the
exclusion of polymer molecules from the region
between colloids. Understanding these
interactions is key to controlling the
microstructure and properties colloidal
suspensions for applications ranging from paints
to environmentally responsive smart gels.
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Small-Angle Neutron Scattering (SANS) is
exquisitely sensitive to the influence of polymer
induced depletion interactions on the solution
thermodynamics and phase behavior of colloidal
suspensions. Shown here are CHRNS SANS data (by
C.F. Zukoskis group at U. Illinois) showing the
development of clustering as the polymer
concentration is increased in a suspension of
silica particles.
S. A. Shah, Y. L. Chen, K. S. Schweizer and C. F.
Zukoski, J. Chem. Phys. 118, 3350 (2003)
Langmuir 19(12), 5128 (2003) J. Phys. Condensed
Matter 15(27), 4751 (2003).
3
Tours of the National Institute of Standards and
Technologys Center for Neutron Research for High
School Science Classes
Charles Glinka, NIST, DMR-9986442
The NIST Center for Neutron Research (NCNR)
invites high school science classes to tour its
facilities on the NIST campus in Gaithersburg,
Maryland, and learn about some of the ways beams
of neutrons are used in research on the
microscopic structure of advanced materials. The
tour of the Center is preceded by a lecture, with
demonstrations developed specifically for upper
level high school students, that introduces some
of the basic concepts of neutron physics through
analogous optical and wave phenomena. Up to 40
students and accompanying teachers may be
accommodated for a lecture and tour that
typically take about two hours to complete.
Information about the NCNR is available on its
web site at http//www.ncnr.nist.gov.
Neutron Guide Hall
4
A Multicritical Point in Superconducting Niobium
An applied magnetic field will penetrate a
type-II superconductor and form an ordered
magnetic vortex lattice at low temperatures.
Small-Angle Neutron Scattering (SANS) is the
technique of choice for probing the phase
behavior of vortex lattices in bulk
superconductors.
SANS patterns showing the disordering (melting)
of the hexagonal magnetic vortex lattice in
niobium.
In 2001, scientists at Brown U. discovered a
solid-to-liquid-like transition, in which
vortices become disordered, in niobium via SANS
measurements at CHRNS.
By carrying out in situ ac magnetic
susceptibility measurements, this same group has
now found that the degree of hysteresis
associated with the melting transition is
strongly field dependent, and disappears at low
fields. Detailed SANS and susceptibility data
have led to the phase diagram on the right which
shows the location of a multicritical point. New
theory is needed to explain this phenomenon in
type-II superconductors.
X.S. Ling, S.R. Park et al. Phys. Rev. Lett. 86,
712 (2001) Submitted to Phys. Rev.Lett. (2003).
5
A Piece of the Protein Folding Puzzle

Proteins are ubiquitous in biological processes
including the folding of proteins! Proteins that
mediate this essential function are called
chaperonins and their role in catalyzing the
proper folding of proteins has been a subject of
intense study for years.
Through the use of deuterium labeling to vary
scattering contrast, Small-Angle Neutron
Scattering (SANS), combined with results from x
ray crystallography and nmr, has provided key
insights into the organization of polypeptide
chains complexed with chaperonins.
For example, scientists at NIST and the Center
for Advanced Research in Biotechnology (CARB)
have constructed the model shown of the tertiary
structure of a polypeptide (the nonnative
subtilisin variant, PJ9) that forms a metastable
complex with the chaperonins GroEL and GroES.
SANS data collected at CHRNS directly provides
the relative location, size and approximate shape
of the trapped polypeptide. Subsequent modeling
using the known crystallographic coordinates of
the individual chaperonins yields the model of
the complex shown in the figure.
S. Krueger, S.K. Gregurick, J. Zondlo, E.
Eisenstein, J. Struct. Biol. 141, 240 (2003).
6
SURF Students - 2003
CHRNS participates in the NIST/NSF REU Summer
Undergraduate Research Fellowship (SURF) program
by hosting four SURF students each year.
  • In 2003, CHRNS staff mentored student projects
    in
  • characterizing bioencapsu-lated proteins
  • analyzing small-angle neutron scattering from
    peptides in cell membranes
  • optimizing the metallurgical characteristics of a
    bismuth filter for neutron vibration spectroscopy
  • investigating factors causing aggregation of
    polymers in aqueous solutions.

Jamaal Sanders U.C. Irvine
Matt Paoletti Bucknell U.
Ramsey Zeitoun U. Maryland
Andrew Rockwell Johns Hopkins
7
Summer School on Methods and Applications of
Neutron Spectroscopy June 9-13, 2003
CHRNS holds a week long course on neutron
scattering each summer - usually in June. These
courses are aimed at potential new users of the
neutron instruments at the NCNR and emphasize
hands-on training at the instruments where
participants carry out experiments and analyze
data
In 2003, 32 graduate students and postdocs from
23 institutions attended the 9th CHRNS summer
school which emphasized cold neutron techniques
for probing the motions of molecules in materials
using 4 CHRNS spectrometers that together probe
time scales from 10-7s to 10-12 s.
CHRNS Summer School Class of 2003
8
Elementary excitations in a 1-D spin chain
No matter how strong the nearest neighbor
antiferromagnetic interactions, quantum
fluctuations prevent static long-range order
within an infinite line of spin-1/2 quantum
moments. What at first blush appears to be the
simplest possible antiferromagnet, thus turns out
to be a unique correlated spin liquid in which
the elementary excitations are spinons carrying
fractionalized spin.
Using inelastic neutron scattering, researchers
from Johns Hopkins University and NIST have
revealed that spinons get confined under the
influence of staggered fields into particles with
finite mass the equivalent of solitons and
breathers in the framework of the quantum
sine-Gordon model. This enabled the quantitative
confirmation of predictions for this exactly
solvable model which were made more than 20 years
ago. M. Kenzelmann, Y. Chen, C. Broholm, D.H.
Reich, and Y. Qiu, Phys. Rev. Lett., in press.
9
Polar nanoregions in relaxor ferroelectrics
Relaxor ferroelectrics, such as Pb(Mg1/3Nb2/3)O3
(PMN), exhibit record piezoelectric properties,
which make them ideal materials for transducers
and actuators. Researchers from Brookhaven
National Laboratory and NIST have used diffuse
elastic neutron scattering to characterize the
formation of the polar nanoregions that are
responsible for their remarkable properties.
The figure shows the neutron diffuse scattering
around a (100) peak in the (hk0) plane at four
different temperatures for PMN. Compared with
x-ray measurements, almost all phonon
contributions can be removed by integrating the
scattering over an appropriate energy range.
G. Xu, G. Shirane, J.R.D. Copley and P.M.
Gehring, Phys. Rev. B (in press).
10
Vibrational enhancement at the nanoscale in
glasses
Disordered materials ranging from common silica
glasses to metallic glasses, to polymers and even
to proteins, display an enhancement of the
vibrations in the low frequency (10s of cm-1)
range. Researchers from Arizona State University
and their collaborators have utilized the unique
ability of inelastic neutron scattering to
simultaneously probe frequency and length scales,
to show that this enhancement is greatest on the
nanoscale. The top figure shows the measured
vibrational density of states for three different
glassy states of rockwool and the ordered
crystalline state averaged over a wide range of
length scales. Note the low frequency
enhancement in the glassy systems. The bottom
panel shows the same thing for a length scale of
1 nm. C.A. Angell, Y.-Z. Yue, L.-M. Wang,
J.R.D. Copley, S. Borick and S. Mossa, J. Phys.
Condens. Matter 15, S1051 (2003).
11
Cholesterol stiffens phopholipid vesicles A
model system for cell walls
Vesicles, one of the many phases that
phospholipids form in solution, provide a nearly
ideal model system for the cell walls of living
tissue. Neutron spin echo spectroscopy has shown
that the stiffness of these vesicles increases
substantially (by 2) when cholesterol is
incorporated into the vesicle wall.
Effective diffusion coefficient of DMPC vesicles,
scaled by the solvent viscosity and temperature
and normalized to that at 35 C. This quantitiy is
inversely related to the wall stiffness. The red
symbols indicate the results for the vesicle
walls in the absence of cholesterol while the
blue symbols show the effect of adding
cholesterol. (D. Bossev and N. Rosov,
unpublished)
12
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