NIST SP 1060
COVER: Some partial images of reduced data from NCNR

experiments in 2006. Left to right, material and instrument:

“null” matrix 62NiPt alloy Bragg peaks and diffuse scattering

(disk chopper spectrometer (DCS)); Tb2Ti2O7 magnetic 

002 Bragg peak (DCS, see pp. 18,19); La1.5Sr0.5CoO4

magnon and phonon excitations (thermal triple axis 

spectrometer BT-7); NaCrO2 spin-wave excitations (thermal

triple axis spectrometer BT-9, and DCS, see pp. 16,17).
AND OPPORTUNITIES

NIST Special Publication 1060

Patrick D. Gallagher, Director

Ronald L. Cappelletti, Editor

December 2006

National Institute of Standards and Technology

William A. Jeffrey, Director

Technology Administration

Robert C. Cresanti 

Under Secretary of Commerce for Technology

U.S. Department of Commerce

Carlos M. Gutierrez, Secretary
DISCLAIMER

Certain commercial entities, equipment, or materials may be identified 

in this document in order to describe an experimental procedure or 

concept adequately. Such identification is not intended to imply 

recommendation or endorsement by the National Institute of Standards 

and Technology, nor is it intended to imply that the entities, materials,

or equipment are necessarily the best available for the purpose.

National Institute of Standards

and Technology Special Publication 1060

Natl. Inst. Stand. Technol. Spec. Publ. 1060, 88 pages 

(December 2006)

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE - WASHINGTON: 2006

For sale by the Superintendent of Documents,

U.S. Government Printing Office

Internet: bookstore.gpo.gov ■ Phone: 202.512.1800

Fax: 202.512.2250 ■ Mail: Stop SSOP, Washington, DC 20402-0001 

II
CHEMICAL PHYSICS

6 Enhanced Hydrogen Storage in a Microporous

Metal-Organic Framework 

8 Structure and Hydrogen Bonding in CaSiD1+x:

Is There Covalent Character? 

10 Quantum Rotational Dynamics of Methane in

the Metal-Organic Framework MOF5 

12 Counter-ion Dynamics and the Mechanical

Properties of Fuel Cell Membranes 

CONDENSED MATTER 

14 Novel Magnetic Order in Na0.5CoO2

16 A Two-Dimensional Magnetically Ordered

Phase on a Geometrically Frustrated Lattice 

18 Field-Induced Order and Spin Waves in the

Pyrochlore Antiferromagnet Tb2Ti2O7

20 Resonance Mode in the Electron-Doped

Superconducting Cuprate Pr.88LaCe.12CuO4 

22 Quasiparticle Breakdown in a Quantum 

Spin Liquid 

PHYSICS

24 Radiative Decay Mode of the Free Neutron

SOFT MATTER/POLYMERS

26 Shear-rate Dependent Structure of 

Polymer-stabilized TiO2 Dispersions 

28 Changes in Blood Protein Structure under Static

and Hydrodynamic Shear Conditions 

30 Why are Double-Network Hydrogels So Tough? 

40 Changes of Diphtheria Toxin Bound to Lipid

Membranes 

42 Functional Toxin Pores in Tethered Bilayers

Membrane Association of ·-hemolysin

ENGINEERING PHYSICS

44 Modeling Neutron Measurements on Friction

Stir Welded Steel 

46 High Resolution Depth Profiling in a Plane

Strain Channel Section 

48 Neutron Imaging Facility at BT-2 and

Tomography of Fuel Cells

ADVANCES IN MEASUREMENT

50 Development of New Cold Neutron Sources 

at the NCNR 

51 Improved Analysis of Short-Lived Neutron

Activation Products in Foods 

52 The New SRM 695 for Trace Elements in 

Multi-Nutrient Fertilizer 

53 Residual Stress Determination as a Benchma

for a New Strain Measurement Technique 

54 FACILITY DEVELOPMENTS 

58 THE NCNR EXPANSION INITIATIVE

59 OPERATIONS 

60 AWARDS 2006 

62 SERVING THE SCIENCE AND TECHNOLOGY

COMMUNITY

66 PUBLICATIONS 

80 INSTRUMENTS AND CONTACTS

CONTACTS (inside back cover)
ments to ensure that this strong record of operation will continue long into the future. 

Instrument development at the NCNR has also been very active this year for several reasons. First, a 

upgraded, neutron imaging facility was constructed and commissioned at BT-2 this year. This new, o

facility is optimized for imaging of full-size hydrogen fuel cell systems and is already generating lots 

ment in this research area. There were also continuing efforts on several major on-going projects inc

BT-7 triple axis and the Multi-Analyzer Crystal Spectrometer. And finally, we have been very busy p

some exciting new possibilities for the future! The proposed FY07 budget for NIST that is under con

by Congress at the time of this writing includes funding for a major expansion of the NCNR beginni

that would include a second guide hall, new cold source, and additional instruments. To prepare fo

important opportunity, we have been actively soliciting input from neutron users to collect ideas on 

of new instrumentation can best serve the future research needs of the U.S. research community. A 

of this effort was a workshop held this July in Bethesda, Maryland to provide a forum for discussion 

neutron instrumentation and the associated scientific opportunities they provide. Now we are hard a

digesting the many ideas we received and analyzing the expected performance of various options so 

can promptly begin the project when it is funded. 

The following report contains updates on these and other developments. However, the bulk of this 

centered on the selected highlights from research performed at the NCNR during the past 12 month 

We have tried to select a few examples from each area to represent the large body of exciting resea

conducted at the NCNR. It is my hope that these selections will not only demonstrate the tremendou

depth, and quality of the work done at the NCNR this past year, but also capture the excitement and 

of those performing the research. I also hope that the highlights we selected for this Annual Report 

your interest enough to visit our website at www.ncnr.nist.gov, where you can get additional inform

many other projects that the limited space did not allow us to include. 

I wish to extend my thanks to our users and staff, whose hard work and dedication are celebrated i

for another exciting and successful year. I am already looking forward to seeing what next year will 

IV
storage and retrieval. Atomic motion, especially that

of hydrogen, can be measured and monitored, like

that of water during the setting of cement. Residual

stresses such as those inside stamped steel automobile parts can be mapped. Neutron-based research

covers a broad spectrum of disciplines, including

engineering, biology, materials science, polymers,

chemistry, and physics.

The NCNR’s neutron source provides the intense

beams of neutrons required for these types of measurements. In addition to the thermal neutron beams

from the heavy water or graphite moderators, the

NCNR has a large area liquid hydrogen moderator, or

cold source, that provides intense neutron beams for

the only cold neutron facility presently operating in

the U.S.

There are currently 29 experiment stations: four provide high neutron flux positions for irradiation, and

25 are beam facilities most of which are used for

neutron scattering research. The following pages

show a schematic layout of the beam facilities. More

complete descriptions of instruments can be found at

www.ncnr.nist.gov.

The NCNR supports important NIST research needs,

but is also operated as a major national user facility

with merit-based access made available to the entire

U.S. technological community. Each year, approximately 2000 research participants from all areas of

the country, from industry, academia, and from 

government use the facility for measurements. Beam

time for research to be published in the open 

literature is without cost to the user, but full operating costs are recovered for proprietary research.

Access is gained mainly through a peer-reviewed,

web-based proposal system with beam time allocated

by a Program Advisory Committee twice a year. For

details see www.ncnr.nist.gov/beamtime.html. The

National Science Foundation and NIST co-fund the

Center for High Resolution Neutron Scattering

(CHRNS) that operates six of the world’s most

advanced instruments. Time on CHRNS instruments 

is made available through the proposal system. Some

access to beam time for collaborative measurements

with the NIST science staff can also be arranged on

other instruments.

WHY NEUTRONS?

Neutrons reveal properties not available to other

probes. They can behave like microscopic magnets,

they can diffract like waves, they can set particles

into motion losing or gaining energy and momentum

in the process, and they can be absorbed.

WAVELENGTHS—in practice range from < 0.1 Å to 

< 15 Å (1 Å = 0.1 nm), allowing them to form

observable ripple patterns from structures as small 

as atoms to as large as cells. 

ENERGIES—of millielectronvolts, of the same order as

those of motions of atoms in solids or liquids, waves

in magnetic materials, and vibrations in molecules.

Exchanges of energy between neutrons and matter as

small as nanoelectronvolts and as large as tenths of

electronvolts can be detected. 

SELECTIVITY—in scattering power varies from nucleus

to nucleus somewhat randomly. Specific isotopes can

stand out from other isotopes of the same kind of

atom. Specific light atoms, difficult to observe with xrays, are revealed by neutrons. Hydrogen, especially,

can be distinguished from chemically equivalent deuterium.

MAGNETISM—makes the neutron sensitive to the magnetic spins of both nuclei and electrons, allowing the

behavior of ordinary and exotic magnets to be

detailed precisely. 

NEUTRALITY—of the uncharged neutrons allows them

to penetrate deeply without destroying samples, and

pass through walls controlling a sample’s environment allowing measurements under extreme conditions. Properties ranging from the residual stresses in

steel girders to the unfolding motions of proteins are

amenable to measurement by neutrons.

CAPTURE—characteristic radiation emanating from

specific nuclei capturing incident neutrons can be

used to identify and quantify minute amounts of

material in pollutants or ancient pottery shards.
hydrogenous matter in large components such

as water in fuel cells and lubricants in engines,

in partnership with General Motors.

4. BT-1 Powder Diffractometer with 32 detectors; 

incident wavelengths of 0.208 nm, 0.154 nm, 

and 0.159 nm, with highest resolution of 

δd/d = 8 × 10-4.

ray Activation Analysis Instrument w

tron fluence rate of 3 × 108 /cm2/s u

quantitative elemental analysis of bu

Generally used for the analysis of h

hydrogenous materials (≈ 1 % H) su

oils, and biological materials.

2

5 6

7 8

9 10 11

1

21

22

23

4

3

2

1

The Cold Neutrons for Biology and Technology (CNBT) 

program is a partnership between NIST and a consortium

led by the University of California at Irvine and funded 

by the National Institutes of Health. It focuses on the structure of biological membranes.

The Center for High Resolution Neutron Scattering (CHRNS) 

is a partnership between NIST and the National Science

Foundation that develops and operates neutron scattering

instrumentation for use by the scientific community. 
high throughput at one energy. 

10. NG-1 Advanced Neutron Diffractometer/

Reflectometer (AND/R) a vertical sample 

reflectometer with polarization analysis and offspecular reflection capabilities for measuring

reflectivities down to 10-8, part of the CNBT.

11. NG-1 Vertical Sample Reflectometer instrument

with polarization analysis capability for measuring reflectivities down to 10-8 to determine 

subsurface structure.

12. NG-1 Cold Neutron Depth Profiling instrument

for quantitative profiling of subsurface 

impurities.

15. NG-4 Disk Chopper TOF Spectrometer for studies

of diffusive motions and low energy dynamics 

of materials. Wavelengths from ≈ 0.18 nm to 

> 2.0 nm give corresponding energy resolutions

from ≈ 2 meV to < 10 μeV, part of CHRNS.

16. NG-6 Neutron Physics Station offering three 

cold neutron beams having wavelengths of 

0.5 nm, 0.9 nm, and “white” that are available 

for fundamental neutron physics experiments.

17. NG-7 30 SANS for microstructure measurements,

in partnership with NIST, ExxonMobil, and

CNBT.

18. NG-6 Fermi Chopper Hybrid Time-of-Flight (TOF)

Spectrometer for inelastic scattering measurements with selected incident wavelengths

between 0.23 nm and 0.61 nm.

19. NG-7 Prompt Gamma Activation Analysis cold

neutron fluxes allow detection limit for H of 

1 μg to 10 μg, depending on the matrix. 

Focused beams are available for profiling.

20. NG-5 Spin-Echo Spectrometer for measuring 

dynamics from 100 ns to 10 ps, in partnership

with ExxonMobil, part of CHRNS.

21. NG-5 Spin-Polarized Triple Axis Spectrometer

(SPINS) using cold neutrons with position 

sensitive detector capability for high-resolution

studies, part of CHRNS.

22. NG-7 Neutron Interferometry and Optics Station

with perfect crystal silicon interferometer;

vibration isolation system provides exceptional

phase stability and fringe visibility.

23. NG-7 Horizontal Sample Reflectometer allows 

reflectivity measurements of free surfaces, 

liquid/vapor interfaces, as well as polymer 

coatings.

13

14

15

16 18

17
4

Center: NCNR’s Jack Rush and M

Some NRAN speakers, from top l

Werner (UMo, ret.), Sunny Sinha 

Robert Birgeneau (UCB), Karl Mic

(U Antwerp), Walter Kohn (UCSD)

Dehmer (DOE), John Axe (BNL, re

Weertman (NWU, ret.), Lyle Schw

(AFOSR), Roger Pynn (IUCF).

NCNR’s 

Majkrza

attire, d

Warren 

formal a

the 200

meeting 

NCNR researchers Tatiana

Guidi and Yiming Qiu involved

in a particularly 

complex experimental 

arrangement at DCS 

pause for a photo.

Bob and Toni Carter, seated,

chatting with Karl Michel 

at NRAN. Sadly, Robert S.

Carter, a former director 

of NBSR,passed away in

October, 2005.

NCNR’s 

Chen ho

neutron 

cell at th

instrume
Sushil Satija (front)

demonstrates good

technique to NCNR

Summer School students Andrea Hamill

(USC), Peter

Bowerman (VT), and

Ashish Jha (URI).

Igor Zaliznyak (BNL) 

comments at the NCNR

Expansion Workshop 

in July.

Mike Fitzsimmons

(LANL) leads

a discussion on

polarized beam

methods at the

NCNR Expansion

Workshop.

Students and staff

of the NCNR 2006

Summer School on

Neutron Scattering

gather for a photo.
To maximize the amount of adsorbed H2 accessible

at room temperature and with reasonable applied

pressure, it is thought that a binding energy of 15

kJ/mol is necessary [1]. However, in many materials

typical binding energies are 4 kJ/mol to 7 kJ/mol

between the poorly polarizable H2 molecules and the

pore walls so that cryogenic temperatures are

required to obtain significant H2 uptake. One method

used to enhance H2 binding is to form frameworks

with very narrow pores where overlapping potentials

from two or more pore walls interact to bind a single

H2 molecule. In this way binding energies of up to

9.5 kJ/mol have been observed [2]. A second mechanism has been proposed to use strong metal-H2 interactions with coordinatively-unsaturated metal centers

[3]. We have recently generated a highly porous

framework with exposed Mn2+ coordination sites

leading to a high total H2 uptake of 60 g/L (or 6.9 %

mass fraction) at 77 K and 90 bar. We have demonstrated direct observation of hydrogen binding to the

unsaturated metal center in a metal-organic framework time using neutron powder diffraction. The 

initial H2 binding energy is 10.1 kJ/mol. These numbers represent the highest volumetric capacity and

largest binding energy obtained thus far for a metalorganic framework.

FIGURE 1: 

Schematic crystal structure

showing the

arrangements

of sodalite

cage-like units

with hydrogen

atoms and solvent molecules

omitted for

clarity. 

Sample preparation is discussed elsewhe

gle crystal of the solvated parent compo

lyzed using x-ray diffraction and the resu

work structure is illustrated in Fig. 1. De

ous attempts, evacuation conditions for r

of the remaining solvent without degrad

framework have not yet been discovered 

ual solvent molecules coordinate 83 % o

work Mn2+ ions, leaving only a small fra

these metal centers with open coordinati

From Fig. 1, the high surface area and o

structure of the desolvated material is cle

(N2 isotherms give an estimated surface 

m2/g). The hydrogen storage properties 

ated using volumetric gas adsorption me

The resulting isotherms show fully rever

of 2.2 % mass fraction at 77 K and 1.2 b

highest initial isosteric heat of adsorption 

a metal-organic framework at 10.1 kJ/mo

Neutron powder diffraction experiments, 

BT-1 diffractometer, were performed as a 

check of whether the high binding entha

associated with coordination of H2 at ex

sites. A diffraction pattern was collected 

ed material prior to adding D2. Subseque

analysis indicated the existence of extra 

scattering length density close to the Mn

the framework skeleton, as expected due 

ence of residual methanol molecules. Ac

the extra density was modeled using dis

and C atoms, and this corrected “bare” m

used as a baseline for all subsequent me

involving D2. 

Figure 2 shows the diffraction pattern ob

3.5 K upon adsorption of 12 D2 molecul

mula unit. At this low loading a Fourier 

analysis using the bare material as the in

clearly identifies the two strongest bindin

positions I and II in Fig. 3. Significantly, 

M. Dinca ̆

A. Dailly 5,6

Y. Liu2,3

C.M. Brown2,4

D.A. Neumann2

J.R. Long1

1 University of

California at

Berkeley

Berkeley, CA

94720

2 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

3 University of

Maryland

College Park, MD

20742

4 Indiana University

Cyclotron Facility

Bloomington, IN

47408

5 General Motors

Corporation

Warren, MI 48090

6 Purdue University

West Lafayette, IN

47907

6

H

Y

S I C

S

Evacuation of the solvent molecules entrained in the framework during preparation can lead 

high surface area materials capable of adsorbing hydrogen. 

1
j

work skeleton, providing the first neutron diffraction

evidence for a metal-H2 interaction within a metalorganic framework. To our knowledge, this is also

the first example of H2 binding to a Mn2+ ion. The

D2 molecules at site II are situated inside the

sodalite-like cages, and exhibit van der Waals contacts of 3.49 Å and 3.63 Å with a chloride anion and

four equidistant ligands, respectively. The sum of the

five corresponding attractive interactions is likely

responsible for a significant adsorption enthalpy at

this site as well. Indeed, this site becomes fully 

occupied when the total D2 loading is increased 

to 24 molecules per formula unit.

Increased D2 loadings also permitted identification of

the next strongest binding site, labeled III, and a possible binding site labeled IV in Fig. 3. The D2 molecules at site III are situated inside the larger framework cavities, and have van der Waals contacts of

3.33 Å with two equidistant ligands. At site IV, the 

D2 molecules are located at the interface between the

smaller and larger cavities, and are in closest contact

(3.40 Å) with two carbon atoms from neighboring

ligands, as well as a site partially-occupied by an

extra-framework Mn2+ ion (at 3.21 Å). Filling of sites

III and IV continues when 48 D2 molecules are

loaded per formula unit. Out of 48 D2 molecules

refined from a model derived from the difference

scattering length map, 7.1 reside at site I, 10.7 at 

site II, 24.0 at site III, and 4.9 at site IV.

A key and challenging aspect of hydrogen storage

research is the ability to control the H2 binding energy that governs the adsorption in materials ranging

from microporous solids to metal hydrides. In this

regard, a very attractive property of metal-organic

frameworks is that their pores can be engineered at

the atomic scale, thereby enabling some control over

the H2 binding interaction. The results presented here

show that, on a materials characteristic basis, metalorganic frameworks with unsaturated metal centers

can exceed the 2010 DOE H2 storage targets of 6.0 %

mass fraction and 45 g/L. Meeting these targets for a

complete storage system, however, will require fur

g 

2 

g gy,

such that storage at closer to ambient conditions can

be accomplished. Ultimately, this may be possible in

materials related to those reported here through

adjustment of the electronic structure of the metal

ions and exposure of a higher concentration of 

coordination sites.

REFERENCES

[1] S.K. Bhatia, A.L. Myers, Langmuir 22, 1688 (2006).

[2] M. Dinca ̆, J.R. Long, J. Am. Chem. Soc. 127, 9376 (2005).

[3] B. Chen, N.W. Ockwig, A.R. Millward, D.S. Contreras, 

O.M. Yaghi, Angew. Chem., Int. Ed. 44, 4745 (2005).

[4] M. Dinca ̆, A. Dailly, Y. Liu, C.M. Brown, D.A. Neumann, 

J.R. Long, accepted for publication in J. Am. Chem. Soc..

[5] M. Dinca ̆, J.R. Long, J. Am. Chem. Soc. 127, 9376 (2005).

[6] J.L.C. Rowsell, O.M. Yaghi, J. Am. Chem. Soc. 128, 

1304 (2006).

FIGURE 3: 

Initial D2 adsorption sites. Light blue spheres represent

D2 centroids, while the light orange sphere shows the

position of a partially-occupied, extra-framework Mn2+

ion site. Hydrogen atoms and methanol 

molecules are omitted for clarity.
NPD data were collected for both CaSiD1.2

and CaSiD. No significant structural changes

or phase transformations were evident

from the diffraction

patterns at 10 K and

298 K. Rietveld refinements indicated that

both compounds possessed Pnma symmetry. The refined structures are

shown in Fig. 1. Compared to CaSi, the unit cell of

CaSiD1.2 expands three times along the c axis (the a

axis of CaSi), and the resultant structure has two

kinds of D sites with different nearest neighbors. One

kind of D site is defined by four Ca nearest neighbors (Ca4 sites, 1 per CaSi). Three crystallographically

distinct Ca4 tetrahedra are present and align in a

zigzag fashion along the c direction. 

The second kind of D site is located close to the center of a triangle of three Ca atoms as well as one Si

atom (Ca3Si site, 0.33 per CaSi). Since CaSiD1.2 is a

D-deficient CaSiD1.33 phase, the Ca3Si sites are found

to be partially occupied (59 %), presumably in a disordered fashion. The recent theoretical study of

CaSiH1.3 [2] has concluded that the H atom in the

Ca3Si site is covalently bonded to the Si atom with a

Si-H bond length of 1.58 Å, close to the 1.48 Å bond

length in SiH4. Yet, our results indicate that the Si-D

distance is 1.82 Å (at 298 K), considerably larger 

(by ≈ 0.24 Å) than predicted. Figure 2 indicates that

fixing this Si-D distance at values either increasingly

larger or smaller than 1.82 Å leads to increasing χ2

and Rwp values (i.e., poorer model fits). Similar

results are found for calculated deviations in other

crystallographic directions. Besides being much larger

than the Si-H bond length in SiH4, 1.82 Å is also

larger than that of any Si-H bond reported for various

Si-H cluster, defect, and hydrogenated silicon (1.50 Å

to 1.56 Å) [3]. These new experimental results clearly

call into question the prediction of Si-H covalency by

first-principles calculations [2].

The CaSiD structure (Fig. 1b) reveals an 

Ca3Si site and essentially full occupancie

other three Ca4-type sites in the lattice. C

to CaSiD1.2, CaSiD possesses a slight shri

along the a axis and slight expansions a

b and c axes. 

To further probe the nature of the D bon

CaSiD1+x, we have studied the D vibratio

phases. Figure 3 shows the NV spectra f

pounds measured at 3.5 K. The vibration

H. Wu1,2 

W. Zhou1,3

T.J. Udovic1

J.J. Rush1

T. Yildirim1

1 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

2 University of

Maryland

College Park, MD

20742

3 University of

Pennsylvania

Philadelphia, PA

19104

8

H

Y

S I C

S

FIGURE 

Crystal str

CaSiD1.2 

Blue, pink

spheres re

Si, and D 

tively. Ca4

are in gre

tetrahedra 

FIGURE 2: 

The Rietveld goodness-of-fit parameters χ2 and 

Si-D bond length fixed at various values along th

determined by the refined optimal position of D 

interstices (shown schematically). 
the latter ordered configuration results in a different

symmetry than observed experimentally for CaSiD1.2,

it is useful as a basis for calculating the effect of

vacancies on the local bonding within CaSiD1+x structures where x < 0.33. Starting with the structure

model determined from our NPD data, we obtained

optimized structures for both stoichiometries very

close to the one containing the 1.58 Å Si-H covalent

bonds [2]. It is clear in Fig. 3 that the calculated

CaSiD1+x vibrational spectra are noticeably dependent

on both the occupation and degree of ordering associated with the Ca3Si sites. For example, the calculated CaSiD1.33 spectrum indicates that full occupation

of the Ca3Si sites causes a splitting of the D-associated vibrational modes (parallel to the plane of the Ca3

triads) at around 57.3 meV and 62.6 meV, presumably due to interactions between nearest-neighbor D

atoms occupying these sites. This splitting disappears,

yielding a peak near 60.2 meV for the calculated,

vacancy-ordered CaSiD1.17 spectrum, which possesses

no such nearest-neighbor pairs. The orthogonal Si-D

stretching mode band (corresponding to the 1.58 Å

bond length) is predicted near 142 meV for CaSiD1.33

and 147 meV for CaSiD1.17.

Compared to calculation, the observed CaSiD1.2 spectrum appears to possess a disordered arrangement of

occupied Ca3Si sites as reflected by the significantly

broadened, D-related vibrational mode centered near

63.4 meV. Aware that the calculated CaSiD1.33 and

CaSiD1.17 NV spectra are not expected to be exactly

comparable to that of disordered CaSiD1.2, there are,

nonetheless, notable discrepancies in the 50 meV to

70 meV region (e.g., lower predicted peak energies)

associated with the Ca3Si-occupied D atoms as well

as in the 70 meV to 100 meV region mainly associated with the Ca4-occupied D atoms. Of particular note

is the higher-than-predicted 63.4 meV feature for

CaSiD1.2, which is consistent with a Ca3Si-occupied D

atom that is closer to the Ca3 triad, and therefore, 

farther from the Si atom than calculated by DFT.

Unfortunately, the position of the orthogonal Si-D

stretching mode band for CaSiD1.2 cannot be definitively determined by the present NVS results due to

an overlapping multiphonon band. 

In conclusion, the longer Si-D distance and the 

instability of the Ca3Si site supported by the NPD and

NVS data calls into question the covalent nature of

the Si-H bond suggested in Ref.2. Our neutron

results emphasize the importance of validating theoretical predictions by comparison with experimental

data. It is clear that further theoretical studies are

needed to address the structural and spectroscopic

results and establish the nature of the Si-H bonding

(and related electronic structure) in this CaSi hydride

phase. A fundamental understanding of the Si-H

bonding in the various metal-silicide-based hydrides

is critical for the successful theory-driven development of improved hydrogen-storage materials 

containing Si.

REFERENCES

[1] M. Aoki, N. Ohba, T. Noritake, S. Towata, Appl. Phys. Lett. 85,

387 (2004).

[2] N. Ohba, M. Aoki, T. Noritake, K. Miwa, S. Towata, Phys. Rev. B

72, 075104 (2005).

[3] R.O. Jones, B.W. Clare, P.J. Jennings, Phys. Rev. B 64, 125203

(2001), and references therein. 

FIGURE 3: 

NV spectra of CaSiD1.2 and CaSiD. FWHM instrumental resolutions are depicted by the horizontal bars beneath the spectra. Calculated spectra for CaSiD1.33, CaSiD1.17, and CaSiD

delineating both 1 phonon (dotted line) and 1+2 phonon (solid

line) contributions are shown for comparison. 
Using the difference-Fourier analysis of neutron 

powder diffraction data along with inelastic neutron

scattering (INS) measurements and first-principles

total-energy calculations, we first determined the CH4

adsorption sites in MOF5 (the most widely studied

MOF material, which consists of ZnO4 clusters linked

by 1,4-benzenedicarboxylate (BDC)), and then directly visualized the methane orientation distribution

with increasing temperature and studied the rotational tunnel splitting [3]. 

Due to the large incoherent cross section of hydrogen, both the MOF5 and methane used in this 

experiment are deuterated. The methane loading was

achieved by first filling a well-known dosing-volume

to a target pressure and then exposing it to the

MOF5 sample at 140 K. The sample was then cooled

down to 115 K (the boiling point of methane is 

111 K) at which point the pressure decreased to a 

negligible value as the CD4 was adsorbed. The 

sample was further cooled down to 4 K before the

measurements. 

Figure 1 shows the diffraction pattern obtained on

the BT-1 powder diffractometer at NIST from a MOF5

sample that was loaded with 4CD4 /4Zn. In order to

locate the methane adsorption sites, we first performed a Rietveld structural refinement using the

model for the MOF5 host structure, ignoring the

adsorbed CD4 molecules. The isosurface of the difference-Fourier scattering length density based upon

this model (see Fig.1) clearly indicates that the first

adsorption sites for methane are the cup-sites. This is

the same as the first adsorption site of H2 in MOF5

[2]. Interestingly, the orientation of the methane molecule is well resolved, where one of the CD-bonds is

along the 3-fold axis. Having determined the location

of the first adsorption sites, we then further refined

the structural model, explicitly including the CD4

molecules at the first adsorption site. The final refinement is shown in Fig.1 (solid line). The atomic positions of the CD4 molecule within the MO

obtained from the structural refinement a

shown.

Diffraction data collected at elevated tem

(up to 180 K) further indicate that the fo

atoms do not lose their distinct positions 

the methane molecule remains adsorbed

faces of the difference-Fourier scattering 

ty obtained at sample temperatures of 40 

are shown in Fig. 2 as examples. Clearly

equivalent hydrogen atoms pointing tow

faces are much more resistant to thermal 

than the other hydrogen atom, implying 

different rotation barriers around differen

W. Zhou1,2

T. Yildirim1,2

1 University of

Pennsylvania

Philadelphia, PA

19104 

2 NIST Center for

Neutron Research

National Institute

of Standards and

Technology 

Gaithersburg, MD

20899-8562

10

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S

for practical energy storage applications. 

FIGURE 1: 

The neutron powder diffraction pattern (λ = 2.0

MOF5-4CD4 at 4 K (dots) plus the Rietveld refin

space group Fm3m and a = 25.91 Å, and differ

tom). The inset shows the isosurfaces of the dif

scattering-length density superimposed with the 

the MOF5 host structure, indicating the location 

the first methane adsorption. The well-defined o

adsorbed methane is apparent. The table shows 

tional coordinates of the methane molecule.
atively large energy barriers to rotation. This also

suggests that one may observe quantum rotational

tunneling of a methane molecule between equivalent

orientations, since the methane molecule is a quantum rotor. Such quantum tunnel splitting is very sensitive to the gas-host interaction potential and therefore it is an ideal probe to obtain detailed information about the rotational potential barrier, which is

not available by other means. 

We studied the quantum dynamics of CH4 in MOF

using inelastic neutron scattering (INS). The INS

experiment was carried out using the time-of-flight

Disk Chopper Spectrometer (DCS) at NIST. The lowenergy part of the INS spectrum (after being integrated over the momentum-transfer Q) is shown in Fig.

3. The measured two-dimensional intensity contour

plot in the momentum (Q) and energy (E) plane is

also shown as an inset to Fig.3. Five-transitions originated from the rotational tunnel splitting were clearly

resolved. Despite the rich features of the spectrum,

we are able to fully explain the observed data in

terms of a simple model where the methane molecule is allowed to tunnel around 3-fold axis and 3’-

fold axis (which no longer has 3-fold symmetry due

to the crystal field) as shown in the inset to Fig. 3.

The calculated spectrum (red curve in Fig. 3) is in

excellent agreement with the data in terms of both

the energies and intensities of the peaks. The Qdependencies of the peaks are also in good agreement with the measured spectrum. From this simple

model, we obtained rotational barriers of 41 meV

and 22 meV around the 3-fold and 3’-fold axes,

respectively. We expect that our measured tunnel

splitting spectrum will be a stringent test for 

theoretical models and for testing existing 

intermolecular potentials.

In order to obtain more information about methane

host-lattice interactions and energetics, we also 

performed total energy calculations from density

functional theory (DFT). The calculations were performed within the plane-wave implementation of the

local-density approximation (LDA) to DFT. The binding energy of the “Cup site” is found to be 0.306 eV.

In contrast, the binding energies of the ZnO3 site,

ZnO2 site and Hex site (as found for H2 adsorption

in MOF5 [2]) are all negative for CH4, in agreement

with the experimental observation that these sites are

not favorable for methane. We also calculated the

rotational potentials of CH4 at the MOF5 cup site.

The energy barriers about the 3-fold axis and 3’-fold

axis are found to be 46.3 meV and 28.6 meV, 

respectively, in a reasonable agreement with the

experimental values of 41 and 22 meV.

In conclusion, using Rietveld structural refinement of

neutron powder diffraction data in conjunction with

difference-Fourier (DF) analysis and first-principles

calculations, we have determined the methane

adsorption sites, binding energies, and tunnel splittings in MOF5 [3]. Initial adsorption occurs at the

MOF5 cup site with a well defined CH4 orientation.

The temperature dependent DF-analysis is used to

directly visualize the orientational dynamics of the

absorbed methane molecule with increasing temperature. Using INS, we studied the quantum tunneling of

methane and measured the rotational tunnel splitting.

These results not only hold the key to test theoretical

models of CH4-MOF interactions for energy storage

applications but also suggest that MOFs can be used

as a host lattice to study interesting quantum dynamics of small molecules in a confining potential.

REFERENCES

[1] For more information see

http://www.ncnr.nist.gov/staff/taner/h2. 

[2] T. Yildirim and M.R. Hartman, Phys. Rev. Lett. 94, 175501 (2005).

[3] W. Zhou and T. Yildirim, Phys. Rev. Lett. (in prep., 2006). 

FIGURE 3: 

The rotational tunneling spectrum of CH4 adsorbed at the cup 

site of MOF5. The inset shows the intensity contour plot in Q-E

plane. Five transitions were clearly resolved. The red-plot shows

the calculated spectrum based on a simple tunneling model

around two-axes as shown in the inset.
PFSI’s are copolymers containing runs of tetrafluoroethylene and generally less than 15 mol % of 

perfluorovinyl ether units that are terminated with a

sulfonic acid exchange site. The most widely studied

PFSI and the focus of this study, Nafion, is a product

of the E. I. DuPont Chemical Company (Fig. 1). The

polar perfluoroether side-chains containing the ionic

sulfonate groups aggregate, thus leading to a

nanophase-separated morphology where the ionic

domains, termed clusters, are distributed throughout

the non-polar polytetrafluoroethylene (PTFE) matrix.

This morphology gives a characteristic scattering

peak in small angle x-ray scattering at Q ≈ 0.2 Å-1.

The membranes used in this study have been neutralized with tetramethyl (TMA+) and tetrabutyl (TBA+)

ammonium counter-ions (Fig. 1). The size 

difference between these two counter-ions acts to

change the strength of the electrostatic interactions,

thus changing the chain dynamics and, in turn, the

mechanical properties [1, 2].

Recent studies have shown that the α-relaxation in

dynamic mechanical analysis (DMA) of PFSI materials

is due to the onset of long-range mobility of both the

main and side chains facilitated by a profound weakening of the electrostatic interactions within the ionic

aggregates. At temperatures in the vicinity of the αrelaxation, a significant destabilization of the electrostatic network may be observed, which results in the

activation of a dynamic network facilitated through

an ion-hopping process (Fig. 2). In contrast, the βrelaxation is associated with the onset of segmental

motions (principally backbone motions) within the

framewo

static ph

cross-lin

of chain

Given th

herent s

length of hydrogen (located only on the 

ions), the results obtained from QENS ca

specific information about the counter-io

thus allowing confirmation and character

the ion-hopping process. 

The temperature dependant elastic scatte

Q = 0.25 Å-1 for both TMA+ and TBA+ N

seen in Fig. 3. The elastic scattering for e

is characterized by a distinct drop in inte

is attributed to the onset of mobility of t

ions that have motions roughly on the si

the ionic aggregates. The most striking f

these data is the excellent correlation be

temperature at which there is a transition 

tering intensity and the α-relaxation tem

obtained by DMA for each material. The

show unequivocally that the α-relaxation 

linked to the onset of mobility of the co

thus lending support to the presence of 

ion-hopping process.

K.A. Page 1

R.B. Moore 2

J.K. Park 2

V. Garcia Sakai 3,4

1 Polymers Division

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8542

2 The University of

Southern

Mississippi

Hattiesburg, MS

39406

3 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

4 University of

Maryland

College Park, MD

20742

12

H

Y

S I C

S

understanding of the influence of electrostatic interactions on chain dynamics and developin

gy in PFSI materials. Quasi-elastic neutron scattering (QENS) was used to investigate the co

between counter-ion dynamics and bulk mechanical relaxations in alkyl ammonium neutralize

membranes, thus advancing the current state of understanding of the properties of materia

FIGURE 1: 

Structure of Nafion

and the counter-ions

tetra-methyl (TMA+)

and tetra-butyl (TBA+)

ammonium.

FIGURE 2: 

Depiction of the ion-hopping process, in which io

“hop” from aggregate to aggregate, thus allowin

range mobility of the polymer chains.
0.25 Å-1) showing the correlation between the bulk mechanical α-relaxation and the onset of mobility of the counter-ions.

Further information regarding the dynamics of the

counter-ions was obtained from quasi-elastic scans in

the energy range of ± 17 μeV. By plotting the halfwidth at half maximum Γ of the quasi-elastic 

component of the dynamic structure factor S (Q,ω),

the diffusive nature of the counter-ions has been

ascertained. The data for both TMA+ and TBA+ above

their respective Tαs can be seen in Fig. 4. The nonzero intercept of Γ at low Q values is indicative of

spatially confined diffusion of the counter-ions,

where the rise in Γ at high Q values indicates 

random jump-diffusion within the confined region.

Below the α-relaxation, a drastic decrease in the

mobility of the counter-ions results in less quasielastic broadening, thus Γ becomes relatively flat 

and noisy [4, 5].

FIGURE 4: 

The half-width at half-maximum for TMA+ and TBA+ above their

respective α-relaxation temperatures. The solid lines represent

a fit of a random jump-diffusion model to the data.

Finally, in order to characterize the dynamic length

scales of the counter-ion motions, the elastic incoherent structure factor (EISF) was determined for each

sample over a range of temperatures. The EISFs for

TMA+ and TBA+ at temperatures above and below Tα

are shown in Fig. 5. Considering the vast difference

in counter-ion dynamics above and below Tα, it was

necessary to fit the EISF with a model describing 

diffusion between concentric spheres (i.e., on two

different length scales) [6]. The EISF for both counterions at low temperatures was dominated by diffusion

on a very short length-scale (≈ 1 Å), which means

that the dynamics are dominated by local motions of

the alkyl “arms” of the counter-ions.

At temperatures above Tα, the EISF showed 

contributions from diffusion on a larger length-scale.

The short-range length-scale was again characteristic

of very local diffusive motions, probably facilitated

through motions of the alkyl arms of the counter-ion.

However, the long-range length-scale was found to

be on the order of the size of the counter-ions 

(6 Å to 7 Å). Therefore, within the time-scales 

measured by QENS, the counter-ion motions appear

to be governed by very local motions at temperatures

< Tα. However, at temperatures > Tα the counter-ions

are able to move over a much larger length scale 

on the order of magnitude of the size of the 

counter-ion itself.

In conclusion, using QENS, we have been able to

show explicitly that the α-relaxation in these materials is indeed linked to the onset of mobility of the

counter-ions on the length-scale related to the characteristic ionomer morphology, thus lending support

to the presence of an ion-hopping process. These

data provide further fundamental understanding of

the link between electrostatic interactions and

dynamics in ionomers.

REFERENCES

[1] K. Mauritz, R.B. Moore, Chem. Rev., 104, 4535 (2004).

[2] K.A. Page, K. Cable, R.B. Moore, Macro., 38, 6472 (2005).

[3] K.A. Page, F.A. Landis, A.K. Phillips, R.B. Moore, Macro., 39,

3939 (2006).

[4] M. Bee, Quasielastic Neutron Scattering, Adam Hilger, 1988.

[5] A. Pivovar, B. Pivovar, J. Phys. Chem. B., 109, 785 (2005).

[6] D. Bicout, Phys. Rev. E, 62, 261 (2000).

0 

lines represent the models used to fit the data.
As a function of sodium

doping x, non-hydrated

NaxCoO2 displays a rich

electronic phase diagram,

consisting of a paramagnetic phase for x < 1/2, and

an unusual Curie-Weiss

metallic phase for x > 1/2.

In the half-doped compound (x = 1/2), a unique

state is realized: The Na

ions are chemically

ordered to form zigzag

chains in an orthorhombic

superstructure with twofold symmetry. Based on

resistivity, Hall coefficient,

thermal transport, and

angular magnetoresistance

oscillation measurements, the ground state is

believed to be a magnetically ordered insulator. In

order to further investigate the electronic ground

state of the half-doped CoO2 plane, we have 

performed neutron scattering, susceptibility, and

transport studies on single crystal samples. The 

combination of polarized and unpolarized neutron

scattering data allows us to determine the ordered

spin direction and arrangement. We find that the

ground state is well described by an ordered array 

of stripes of antiferromagnetic spins interleaved with

stripes of non-ordered Co ions.

The samples used in this study were prepared by

electrochemically de-intercalating a floating-zone

grown NaxCoO2 crystal to yield a final concentration

of x ≈ 0.5. The crystal studied was cylindrically

shaped, with mass 2.41 g (Fig.1). Our neutron 

scattering experiments were conducted at the NCNR

using the BT-9 and BT-2 triple-axis spectrometers.

Neutrons interact with the magnetic moments of 

the ions and are an ideal probe for studying 

magnetism in solids.

Figure 2 shows evidenc

netic order below TN = 

obtained by elastic neu

ing. At low temperature

peaks arise that are dis

nuclear reflection peaks

(HHL) reciprocal lattice 

we observe such peaks 

Q = (1/2

1/2 odd) location

perature dependence o

intensities of the (1/2

1/2 

(1/2

1/2 3) peaks are show

2(a). The observed dep

typical for second-orde

phase transitions. Figure

2(c) show reciprocal-spa

through the (1/2

1/2 1) pea

[HH 0] and [00L] directio

tively, at T = 8 K and T 

low temperature peak widths are resolut

indicating a long-range magnetic order ( 

In order to confirm that these peaks orig

magnetic order, we performed polarized 

measurements. This is the clearest way t

magnetic peaks from weak nuclear supe

peaks. We have measured both the spin-

non-spin-flip cross sections with neutron 

tions (P) both parallel and perpendicula

momentum transfer vector (Q). Figure 2(

the scattering measured at T = 8 K with P 

(1/2

1/2 1) peak. In this geometry, all magn

ing occurs in the spin-flip channel (•), a

scattering is non-spin-flip (•). The data s

scattering is entirely spin-flip, i.e., magne

temperature dependence of this scatterin

match the unpolarized data at low T, is d

the filled circles in Fig. 1(a). We see that 

ture dependence is identical. Thus, the s

below 88 K at (1/2

1/2 1) is entirely magne

R.A. Ott1

J.H. Cho 2

F.C. Chou1

Y. Chu1

J.W. Lynn3

Y.S. Lee 1

1 Massachusetts

Institute of

Technology

Cambridge, MA

02139

2 Pusan National

University

Busan 609-735,

Korea

3 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

14

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FIGURE 1: 

The Na0.5CoO2 sample used in our studies,

mounted for neutron scattering measurements in

(HHL) reciprocal lattice plane.

G. Gaˇsparovi ́c1
Neutron polarization analysis is also an extremely

useful method to deduce the direction of the ordered

moment. In Fig. 2(e), we plot the scattering data

measured with P ⊥ Q. In this geometry, magnetic

scattering can occur in the non-spin-flip channel if

the ordered moment has a component parallel to the

polarization direction, whereas a moment along the

c-axis would lead to a large spin-flip component.

Here, the signal predominately occurs in the nonspin-flip channel. Therefore, the direction of the

ordered moments lies within the ab plane, and the

ordered moment along the c axis must be small. The

temperature dependence of the polarized data indicates that the c-axis component remains small at all

measured temperatures below TN = 88 K.

The above information can be combined with measurements of intensities of several nuclear and magnetic Bragg peaks to determine the magnetic structure. Our data are well described by the model

shown in Fig. 3. Within each CoO2 layer, the Co ions

are arranged in alternating rows (or stripes) of mag

, pp

scattering measurements reveal formation of a novel

magnetic order in Na0.5CoO2 below TN = 88 K. The

domains of magnetic order appear to be closely coupled to the domains of Na ion order, consistent with

a twofold symmetric spin arrangement. Within each

domain, the scattering is consistent with an arrangement of alternating rows of ordered and non-ordered

Co ions. Magnetoresistance and anisotropic susceptibility measurements further support this model for

the electronic ground state. Understanding the 

interplay between spin order and charge motion in

this correlated electron system remains an important

issue for further study. 

REFERENCE

[1] See G. Gaˇsparovi ́c, R. Ott, J.H. Cho, F.C. Chou, Y. Chu, 

J.W. Lynn, and Y.S. Lee, Phys. Rev. Lett. 96, 046403 (2006).

FIGURE 2: 

(a) Temperature dependence of the intensities of magnetic

Bragg peaks, measured by elastic neutron scattering. The red

filled triangles denote the integrated intensities, and the blue

filled circles denote the intensities measured using polarized

neutrons, both scaled to match the 8 K peak intensity of 

(1/2 1/2 1). (b) (HH 1) and (c) (1/2 1/2 L) scans through 

(1/2 1/2 1) above (•, T = 120 K) and below ( •, T = 8 K) the

magnetic phase transition. Polarized neutron data with 

(d) P || Q and (e) P ⊥ Q, for spin-flip ( • ) and non-spin-flip ( • )

channels at T = 8 K.

FIGURE 3: 

Model of the spin arrangement in Na0.5CoO2. For clarity, only

Co ions in the two CoO2 layers are shown. The solid circles

represent non-ordered Co ions, and the hollow circles magnetically ordered Co ions with arrows indicating the directions

of the magnetic moments.
Of the many materials that are known to possess

highly 2D magnetic interactions, those that exhibit a

2D long-range ordered (LRO) phase are extremely

rare. This is because even when the inter-plane coupling Jc is much weaker than the in-plane coupling

Jab, 3D order is energetically favorable below a 

temperature Tc at which the in-plane correlation

length ξab is sufficiently large that 

kBTc = Jc(ξab/a)2S 2

where a is the in-plane inter-spin distance and S is

the magnitude of the spin. Therefore a divergence of

ξab that is driven solely by 2D interactions will simultaneously induce 3D LRO. In a neutron scattering

experiment, such behavior is typified by an abrupt

conversion from 2D dynamic scattering, due to 

short-lived in-plane correlations, to 3D Bragg scattering as the system is cooled through the transition

temperature. However, if adjacent lattice planes are

stacked in such a way that inter-plane interactions

cancel out, both the lifetime and spatial extent of 

in-plane correlations may be allowed to grow 

without 3D LRO developing. 

We investigated such a possibility by performing 

neutron scattering measurements on the Mott insulator NaCrO2, in which (S = 3/2) Cr3+ sites form a

rhombohedrally (ABCABC) stacked TL (Fig. 1).

Frustrated inter-plane interactions can arise in this

system provided the exchange couplings are highly

planar and antiferromagnetic. Since this condition

forces the spins in each plane to adopt a 

q = (1/3

1/30) configuration as shown in Fig.1, the

molecular field that a particular spin feels from its

first and second neighboring layers vanis

model for the classical ground state of th

hedrally stacked TLAFM in the limit ⎪Jc / 

solved by Rastelli and Tassi [3]. They sho

instead of rods through q = (1/3

1/3 0) in re

space, as would arise from decoupled 12

planes, the ground state is degenerate al

centered about q = (1/3

1/3 0). Experimenta

particular points along the helices would 

selected via further neighbor interactions 

order-by-disorder. 

Elastic and inelastic neutron scattering m

were carried out on a powder sample of 

using the thermal triple-axis spectromete

the cold neutron Disk Chopper Spectrom

respectively. The magnetic diffraction pr

(Fig. 2b) is well described by a Warren p

tered around q = (1/3

1/30), arising from ro

energy scattering. The Warren peak is re

limited in energy, revealing a correlation 

exceeding 0.4 ns. As shown in Fig. 2d, th

elastic 2D scattering survives over an un

temperature range (Tl = 35 K < T < Tu = 

which ξab grows from 15a to 28a (Fig. 2

the appearance of 3D Bragg peaks. Belo

peaks emerge along the high q tail of th

peak (Fig. 2c) arising from short-range (ξ

inter-plane correlations. The positions of 

cannot be indexed by (1/3

1/3n) where n i

or half-integer, which means that the sta

arrangement of the triangular planes is n

ferromagnetic or antiferromagnetic. A co

drop in the Warren peak position at Tl (F

D. Hsieh1

D. Qian1

M.Z. Hasan1

R.F. Berger 1

R.J. Cava1

B.G. Ueland2

P. Schiffer 2

J.W. Lynn 3

Q. Huang 3

1 Princeton

University

Princeton, NJ

08544

2 Pennsylvania State

University

University Park,

PA 16802

3 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

16

M

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R

-

-

DE

F

D

]F 

]F 

]F  ]F 

]F 

]F 

"

D

E F

FIGURE 1: 

A schematic drawing of the Cr3+ 

NaCrO2 from a (001) projection 

the nearest neighbor in-plane (Jab

neighbor inter-plane (Jc) exchange 

The q = (1/3 1/3 0 ) spin arrangem

on the right which illustrates how 

frustration arises. 
suggests that coupling between planes is instead

established by an in-plane modulation of the 120°

order which relieves the inter-plane frustration. A

departure from purely 120° in-plane order is consistent with a degenerate helix ground state, but the

mechanism that lifts the degeneracy is still unclear. 

The dynamic structure factor of the spin correlations

is shown in Fig. 3a-c. Despite a long in-plane correlation length (ξ ab = 15a) at 40 K, there is strong incoherent inelastic scattering and no finite energy spin

wave modes, indicating that spin correlations are

slowly fluctuating but not truly static. This 2D fluctuation regime is also extended between Tu and Tl (Fig.

3d). Below Tl

, dispersive modes that are both gapped

and gapless at the Brillouin zone center (q = 1.4 Å-1)

begin to appear and are well described by the spin

wave spectrum of a 2D Heisenberg TLAFM with a

single-ion easy-plane anisotropy D = 1.2 meV (Fig.

3e). Such a large value of D is inconsistent with electron paramagnetic resonance measurements on

NaCrO2 which support a

Heisenberg (D ≈ 0) 

character. The origin of the large

effective “D” term can be understood in analogy with square-lattice

Sr2Cu3O4Cl2 [4]. Since NaCrO2 can be separated into

multiple Heisenberg AFM sublattices that can be

rotated relative to each other without costs in 

energy, strong fluctuations can then lift one of the

zero-energy modes to a finite energy. This provides 

support for inter-plane correlations developing 

from an order-by-disorder mechanism. 

Our measurements on NaCrO2 demonstrate that

inter-plane frustration provides a new avenue to 

stabilize 2D magnetic phases in strongly correlated

electron systems. Such a phase can be a host for

exotic superconductors where pairing could be 

mediated by spin fluctuations or the lifted zeromodes upon doping.

REFERENCES

[1] R. Moessner et al., Phys. Rev. Lett. 86, 1881 (2001).

[2] H. Kawamura et al., J. Phys.: Condens. Matter 10, 4707 (1998).

[3] Rastelli et al., J. Appl. Phys. 63, 3823 (1988).

[4] Y. J. Kim et al., Phys. Rev. Lett. 83, 852 (1999).

FIGURE 3: 

(a-c) The dynamic structure factor S(Q,E ) of

NaCrO2 where Q and E are the neutron momentum and energy transfers respectively. (d) shows

the temperature dependence of the Q integrated

dynamic structure factor and the dashed lines

enclose the extended fluctuation regime. (e)

shows the same data as (c) over a larger 

dynamic range. The solid lines are the spin wave

spectrum calculated using the Hamiltonian 

H = -Jab ΣSi.Sj + D Σ(Si

z)2.
Tb2Ti2O7 is a geometrically frustrated cubic

pyrochlore in which magnetic Tb3+ ions are located

at the vertices of a network of corner-sharing tetrahedra. At ambient pressure and zero applied magnetic

field, Tb2Ti2O7 is known to remain a cooperative

paramagnet down to temperatures as low as 20 mK

[1-3]. Calculations of the crystal field levels appropriate to the Tb3+ site predict local [111] Ising anisotropy

such that the spins are oriented either into or out

from the center of each tetrahedron [4].

Both the ground state and first excited

state crystal field levels form doublets

which are separated by ≈ 1.5 meV,

while the next highest levels are at 

≈ 10.5 meV and 14.5 meV [1]. 

Previous studies show that applied pressure and magnetic fields may relieve the

geometric frustration and induce longrange order in Tb2Ti2O7. Neutron studies

have shown an increase in the nuclear

Bragg intensity when a magnetic field is 

along the Ising [111] axis [5]. Also, combi

unidirectional and hydrostatic pressure a

magnetic fields have induced magnetic lo

order at low temperatures and applied fi

More recently, in relatively high applied 

temperatures of 10 K to 20 K, a very slow 

rate to an equilibrium state was observed 

Time-of-flight neutron scattering measure

performed with 5 Å and 9 Å incident neu

NCNR’s disk chopper spectrometer (DCS

1(a–c) show reciprocal space maps in th

plane, integrating over -0.5 meV < < 

energy, and taken at T = 1 K. In zero fie

extensive diffuse magnetic scattering was 

around (002) indicating short-ranged spin 

restricted to distances of about the dimen

of a single tetrahedron. This diffuse scatt

appears to be quasi-elastic or very weakl

with a characteristic extent in energy of ≈ 

(Fig. 1d). In a 2 T applied field, oriented 

[110] direction (Fig. 1b), sharp Bragg inte

observed not only at the allowed nuclear 

but also at 002 which is forbidden within 

space group. Finally, by 8.5 T (Fig. 1c) a 

of magnetic Bragg peaks was observed s

a new ordered state. The strongest of the

field-induced peaks is the 112, as can be 

in Fig. 1c.

hω

hω

hω

K.C. Rule1

J.P.C. Ruff1

B.D. Gaulin1

S.R. Dunsiger 1

J.P. Clancy1

M.J. Lewis1

H.A. Dabkowska1

I. Mirebeau2

P. Manuel3

J.S. Gardner 4

Y. Qiu4

J.R.D. Copley 4

1 McMaster University 

Hamilton, ONT, L8S

4M1, Canada

2 Laboratoire Leon

Brillouin

CEA-CNRS, 

CE-Saclay 

91191 Gif-surYvette, France

3 ISIS Facility

Rutherford Appleton

Laboratory

Didcot, Oxon, OX11

0QX, UK

4 NIST Center for

Neutron Research

National Institute of

Standards and

Technology

Gaithersburg, MD

20899-8562

18

M

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R

FIGURE 1: 

Neutron scattering for - 0.5 meV < < 0.5 meV, and within

the (HHL) plane of Tb2Ti2O7 at T = 1 K is shown for (a) 

B = 0 T, (b) B = 2 T and (c) B = 8.5 T. Fields were applied

along the crystallographic [110] direction. Panel (d) shows high

energy resolution scattering at T = 0.1 K, integrated in 

Q and including the (0 0 2) position. 

hω

FIGU

The i

sity o

0 0 2 

as a 

T = 0

show

the in

elasti

makin

diffus

[HH0]

[00L]
The intensity of the 002 and 112 Bragg peaks were

followed as a function of applied field and 

temperature. In Fig. 2, the intensity of the 002 peak

rises to a maximum by ≈ 0.5 T while the 112 follows

an “S-shaped” increase to saturation at around 8 T.

Figure 3 shows the temperature dependence of both

peaks in applied magnetic fields. At 7 T, the 112

peak falls off sharply with temperature displaying

downward curvature with a phase transition near 

TN ≈ 3 K. In contrast, the 002 at 7 T shows an 

anomaly at TN but remains finite and large up 

to at least 20 K.

Figure 4 shows the inelastic magnetic scattering spectrum taken around the (002) position as a function of

applied field. In zero field (Fig. 4a), quasi-elastic scattering (responsible for the diffuse scattering in Fig.

2a) can be seen at energies less than ≈ 0.3 meV. As

the field was increased, this quasi-elastic scattering

appeared to weaken and finally split from the elastic

scattering by 3 T (Fig. 4d) leaving a clearly resolved

inelastic mode at ≈ 0.3 meV. A broad distribution of

inelastic scattering was also observed in zero field

between 0.8 meV to 1.8 meV. This inelastic magnetic

scattering is also resolved into narrow energy bands

as the magnetic field was increased (Fig. 4b-c). At 

2 T and 3 T, sharp dispersive spin wave excitations

could be seen which appear to have minima in their

dispersion near (001) and (003).

These results suggest the 002 Bragg peak which

appears on application of a very weak [110] magnetic

field, is the signature of a polarized paramagnetic

phase. This is supported by the absence of a well

defined phase transition associated with the 002

Bragg intensity with temperature up to 24 K at a field

of 1 T (Fig. 3), as well as with the absence of collective spin wave excitations in the magnetic inelastic

scattering. In this state, the magnetic Bragg peaks

arise from a single-ion polarization of much of the

paramagnetic moment along the applied field direction. In contrast, the high field magnetically ordered

state shows both well defined spin wave excitations

and a clear phase transition at TN ≈ 3 K. It is evident,

however, that purely [111] Ising spins, as implied by

the crystal field calculations, cannot describe the high

field state as the dispersive spin wave excitations

require continuous spin degrees of freedom. Instead,

a model similar to that reported for the pressure

induced magnetic order [6, 7] is more likely, suggesting that magnetoelastic effects may play a significant

role in the eventual ordering of Tb2Ti2O7.

Our DCS results clearly show how the frustrated

pyrochlore antiferromagnet Tb2Ti2O7 is brought to

order at low temperatures by the application of 

relatively weak magnetic fields applied along [110].

This complex phase behavior and the spin wave dispersion it displays in its high field ordered phase are

expected to motivate theoretical study aimed at a

complete understanding of Tb2Ti2O7 and its 

enigmatic low temperature behavior. 

REFERENCES

[1] J.S. Gardner, et al., Phys. Rev. B 64, 224416 (2001).

[2] J.S. Gardner, et al., Phys. Rev. Lett. 82, 1012 (1999).

[3] J.S. Gardner, et al., Phys. Rev. B 68, 180401 (2003).

[4] M.J.P. Gingras, et al., J. Phys. Chem. Sol. 62, 343 (2001).

[5] Y. Yasui, et al., Phys. Chem. Sol. 62, 343 (2001).

[6] I. Mirebeau, et al., Phys. Rev. Lett. 93, 187204/1 (2004).

[7] I. Mirebeau and I. N. Goncharenko, J. Phys.: Cond. Matt. 17,

S771 (2005).

[8] B.G. Ueland, et al., Phys. Rev. Lett. 96, 27216 (2006).

FIGURE 3: 

The temperature dependence of the 112 Bragg peak in 

B = 7 T, and the 002 Bragg peak in both B = 1 T and 7 T 

is shown. The inset shows the phase diagram for the 

magnetically long-range ordered state in Tb2Ti2O7, as 

determined by time-of-flight and triple axis neutron scattering

and by ac-susceptibility measurements. All lines shown 

are guides-to-the-eye.

FIGURE 4: 

Neutron scattering data within the (00L) – energy plane 

at T = 0.4 K and (a) B = 0, (b) B = 1 T, (c) B = 2 T, and (d)

B = 3 T are shown.

[00L]
The novel phase of high-Tc superconductivity occurs

when charge carriers, either holes or electrons, are

doped into the CuO2 planes of their antiferromagnetically (AF) ordered insulating parent compounds.

This AF order consists of a simple doubling of the

chemical unit cell in the CuO2 planes, with an inplane ordering wave vector Q = (1/2, 1/2). Upon 

doping, long-range AF order is dramatically 

suppressed but strong spin fluctuations persist in all

superconducting concentrations. Experiments probing

these spin fluctuations in hole-doped cuprates have

uncovered a seemingly universal structure of 

dispersion amongst different families of cuprates. 

In these hole-doped systems, including the bilayer

system YBa2Cu3O7-δ and monolayer cuprates 

La2-x(Sr, Ba)xCuO4, low energy magnetic fluctuations

are split away from the commensurate Q = (1/2, 1/2)

wave vector and instead are observed along incommensurate positions Q = (0.5 ± δ, 0.5 ± δ). With

increasing energy transfer these low energy fluctuations disperse inward until they reach the commensurate wave vector Q = (1/2, 1/2), where up

increase in energy transfer they then disp

outward but rotated from their original o

YBa2Cu3O7-δ, at energies where these in

rate fluctuations disperse into a commen

tion, a significant enhancement in the sp

occurs below Tc and a localized magneti

observed. This mode, known as the reso

tation, is strongly coupled to supercondu

appears only below Tc in optimally-dope

The resonance mode has also been disco

variety of hole-doped systems, and the c

energy for this mode, ER, is intrinsically t

superconducting phase of the system thr

universal relation ER = 5.8 kBTc thus sugg

the resonance is linked to the electron-e

ing mechanism in high-Tc materials. 

While the resonance mode and incomme

are seemingly common in the magnetic 

hole-doped cuprates, the question then a

these features also present in the spin ex

the electron-doped cuprates? In order to 

question, we probed the spin dynamics 

mally electron-doped cuprate Pr.88LaCe.1

(PLCCO) with a Tc = 24 K. Using the SPI

S.D. Wilson1

P. Dai1,2

S. Li1

S. Chi 1

H.J. Kang 3,4

J.W. Lynn3

1 The University of

Tennessee

Knoxville,

Tennessee 

37996-1200

2 Center for Neutron

Scattering 

Oak Ridge

National

Laboratory, 

Oak Ridge,

Tennessee 37831

3 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

4 University of

Maryland

College Park, MD

20742

20

M

A T T E

R

ity. We have used the triple-axis spectrometers BT-9 and SPINS at the NCNR to establish a 

excitation mode, known as the “resonance”, as the unifying feature in the spin dynamics bet

and electron-doped cuprates. This resonance is therefore an essential component of superc

in the cuprates [1].

FIGURE 1: 

Low energy neutron scattering results from SPI

stands for monitor counts units and r.l.u. stand

cal lattice units). a) – c) Constant-E scans throu

Q = (1/2 , 1/2 , 0) point at E = 0.5 meV, 1.5 meV

meV, respectively. Scans were taken along the [

tion and show no change from 2 K (black symb

(red symbols). The magnetic scattering centere

much broader than resolution (horizontal bars) 

gapless down to 0.5 meV. d) T-dependence of 1

nel at Q = (1/2 , 1/2 , 0) (black squares) and non

background (yellow triangles). 
neutron triple-axis spectrometer, our investigations of

the low energy excitations of this system reveal that

the spin fluctuations are gapless down to 0.5 meV

and remain commensurate. This contrasts with the

gapped, incommensurate response observed in 

optimally hole-doped cuprates (Fig. 1). Additionally,

these low energy dynamics are independent of the

superconductivity in the system as shown by an

identical response both below Tc (2 K) and above 

Tc (30 K). While the commensurate nature of the 

low energy spin excitations in the electron-doped

cuprates seemingly precludes the incommensurability

seen in hole-type cuprates as universal to all high-Tc,

the question remains as to the existence of the 

resonance mode in the electron-doped cuprates.

In order to investigate the possible presence of the

resonance in PLCCO, we utilized the BT-9 thermal

triple-axis spectrometer, allowing higher energy spin

excitations to be probed. In the range 8 meV ≤ ≤

15 meV the spin dynamics are no longer decoupled

from the onset of superconductivity in the system,

and instead, a localized magnetic mode appears as

the system is cooled below Tc (Fig. 2). This mode

appears centered at ≈ 11 meV and exactly at the

commensurate wave vector (1/2, 1/2). Temperature

scans from another spectrometer, HB-1 at Oak Ridge

National Laboratory, also confirm that this mode

appears only below Tc, and therefore is the 

identical resonance mode feature observed in 

hole-doped cuprates. 

The resonance energy for this electron-doped system

can then be compared to equivalent resonances

observed in hole-doped cuprates, as shown in Fig. 3.

Surprisingly, ER for PLCCO falls exactly onto the universal curve for all systems, thus establishing this

excitation as fundamental to all high-Tc copper

oxides regardless of carrier type. Additionally, the

discovery of the resonance mode in a system with

known commensurate low energy excitations dispersing into it (Fig. 3) implies that there exists no fundamental connection between the resonance energy

and the inward dispersion of incommensurate excitations observed in the hole-doped classes of cuprates.

To fully understand the microscopic origin of the 

resonance mode requires the use of complementary

probes in addition to neutron scattering, such as

angle resolved photoemission or scanning tunneling

electron-microscopy, for which PLCCO is suitable.

Thus, a systematic investigation in a single material is

now possible for the first time using several complementary probes, with inelastic neutron scattering 

providing a foundation for finally deciphering the

microscopic origin of the resonance. 

REFERENCE

[1] S.D. Wilson, P. Dai, S. Li, S. Chi, H.J. Kang, and J.W. Lynn, 

Nature 442, 59 (2006).

hω

FIGURE 3: 

Dispersion relation for PLCCO and universal plot of E R vs. 

Tc. a) Dispersion of the commensurate excitations in PLCCO

with increasing E. Colored bars represent the FWHM of the

measured peak along [HH 0] while the black bars display the

respective instrument’s resolution. b) Universal plot 

showing discovered resonance modes in various classes of

cuprates versus their respective system’s Tc. The new E R for

PLCCO falls exactly onto the universal curve for all systems,

thus signifying a common origin for all resonances in the

high-Tc cuprates regardless of carrier type. The citations in

the figure can be found in Ref.1.
The quasiparticle concept has proven remarkably

successful in describing collective phenomena in

condensed matter, in particular quantum fluids which

are among the most interesting and fundamental condensed matter systems. The study of quasiparticles

which govern the properties of quantum liquids was

pioneered by physicist Lev Landau. Landau explained

a variety of properties of superfluid 4He in terms of a

system of Bose quasiparticles with a spectrum that

has a finite energy minimum (an energy gap) at a

particular wave vector [3]. He also realized that the

presence of such a quantum gap in the excitation

spectrum has dramatic consequences for a quantum

Bose liquid and results in an unusual feature – a singular point where the single-quasiparticle spectrum

terminates [4]. Like unstable elementary particles in

the universe, quasiparticles may not survive beyond

an energy-momentum threshold where certain decays

become allowed by conservation laws, so the quasiparticle spectrum ends at this threshold. Neutron

scattering experiments in 4He indeed indicate that the

spectrum of quasiparticles there (longitudinal acoustic

waves, or phonons) ends at about twice the quantum

gap energy, where phonon quasiparticles start decaying into pairs of near-gap excitations [1,6].

While only two elemental liquids, the helium isotopes 4He and 3He, fail to crystallize at T = 0 K, electrons in metals and superconductors and trapped

ultracold atoms also form quantum liquids, and some

remarkable new examples were recently identified

among quantum spins in magnetic crystals [1,2,5].

The organo-metallic material PHCC provides an

excellent physical realization of a two-dimensional

(2D) quantum spin liquid (QSL). It has Cu2+ spins

coupled through a complex network of interactions

with high degree of frustration, forming a pseudosquare lattice of S = 1/2 dimer pairs in the 

a- c plane [2]. Spin excitations have spec

Δs ≈ 1 meV and a nearly isotropic 2D dis

tion in PHCC’s (h0l) plane, with a bandw

larger than Δs, above the gap. In the abs

external magnetic field, magnetic order i

not occur down to T = 0 K. We explored 

excitations in the 2D QSL in PHCC by in

neutron scattering and found remarkable 

with 4He, particularly where the quasi-pa

sion reaches the threshold for two-partic

interferes destructively with the continuu

also distinctions which can be ascribed t

ent nature of decay interactions in the 2D 

The generality of the physics underlying 

of the quasiparticle spectrum in 4He sug

similar effects may occur in gapped QSL

spin-pair dominated structure factor of P

favorable for probing the interaction of m

siparticles with their two particle continu

(a) we present a series of constant wave 

measurements for energies ≤ 7 meV 

[

1/20l] and [h0-1-h] directions chosen to e

both single-particle and multiparticle exc

the possibility of spectrum termination in 

There is a clear change in the character 

excitation spectrum at Qc = (hc, 0, -1-hc) 

hc ≈ 0.15 near the magnetic Brillouin zon

boundary, where the one-magnon disper

the lower boundary of the two-magnon 

2m(Q) = minq { (q) + (Q-q)}. 

there are two distinct contributions to m

tering, the resolution-limited quasiparticl

lower energy and a broad feature with a 

at higher energy, which we associate wit

particle continuum. For h ≤ 0.15 the qua

hω hω hω

hω

M.B. Stone1 

I.A. Zaliznyak 2

T. Hong 3

C.L. Broholm3

D.H. Reich3

1 Oak Ridge

National

Laboratory

Oak Ridge, TN

37831

2 Brookhaven

National

Laboratory

Upton, NY 

11973-5000

3 The Johns

Hopkins

University 

Baltimore,

Maryland 21218 

22

M

A T T E

R

intensity to the 2-particle continuum and an abrupt development of damping when a thresho

momentum is exceeded.
left. There, the magnon dispersion is weaker, and

single-particle excitation never reaches the boundary

of the 2-magnon continuum and therefore does not

decay. 

Quasiparticles are ubiquitous in nature and quasiparticle spectrum termination as seen in superfluid 4He

can also occur in other condensed matter systems, in

quantum magnets in particular. While this has been

generally expected, the extent of the phenomenon

and how it reveals itself in real materials has not

been clear. Our experiments offer a detailed view of

quasiparticle decays in the 2D quantum spin liquid of

the metallo-organic magnet PHCC. The termination

point predicted from the measured quasiparticle 

dispersion is marked by dramatic changes in the

REFERENCES

[1] M. B. Stone, I. A. Zaliznyak, , T. Hong, C. L. Broholm, D. H.

Reich, Nature 440, 187 (2006).

[2] M. B. Stone, I. Zaliznyak, D. H. Reich and C. Broholm, Phys.

Rev. B 64, 144405 (2001).

[3] L.D. Landau and E. M. Lifshitz, Course of Theoretical Physics:

Statistical Physics, Part 2, by E. M. Lifshitz, and L. P. Pitaevskii,

Vol. 9, 125-139, Pergamon Press, Oxford (1981). 

[4] L. P. Pitaevskii, Sov. Phys. JETP 9, 830 (1959).

[5] M. B. Stone, J. Rittner, Y. Chen, H. Yardimci, D. H. Reich, C.

Broholm, T. Ferraris, and D. V. Lectka, Phys. Rev. B 65, 064423

(2002). 

[6] B. Fåk, and J. Bossy, J. Low Temp. Phys. 112, 1 (1998), and W.

Montfrooij, and E. C. Svensson, J. Low Temp. Phys. 121, 293

(2000). 

FIGURE 1: 

Magnetic excitation spectrum in PHCC

at T = 1.4 K. (a) Background corrected

intensity along [1/2 0 -1-l ] and 

[h 0-1-h ] directions smoothed by a

δ = 0.25 meV running average

applied to each constant wave-vector

scan. Black line is the single-magnon

dispersion [2], white lines are bounds 

of the two-magnon continuum calculated from this dispersion. (b) First frequency moment of measured scattering

intensity integrated over different 

energy ranges, 0.8 hω ≤ 5.5 meV 

hω

(red squares, total), 0.8 ≤ ≤ 3 meV

(black circles, quasiparticle) and 

3 ≤ ≤ 5.5 meV (blue diamonds,

continuum).

hω

hω
electromagnetic interactions. The weak interaction,

however, can convert a down quark into an up

quark through the emission of the W gauge boson

that subsequently decays into an electron and an

antineutrino. This decay is also accompanied by an

inner-bremsstrahlung (IB) photon in the rare process

n→ p + e ̄ +v ̄e+ γ, which is an order-α radiative correction to the main branch. While IB has been measured in nuclear beta decay and electron capture

decays, the mode has never been observed for the

neutron, the fundamental beta decay. A previous

experiment resulted in an upper limit of 6x10-3 (at

the 90 % confidence level) for the branching ratio of

photons between 35 keV and 100 keV [1].

The photon energy spectrum and branching ratio for

neutron radiative decay has been calculated within a

quantum electrodynamics (QED) framework [2] and

recently using heavy baryon chiral perturbation

(HBχPT) theory [3]. The QED calculation takes into

account the IB produced from the electron and 

proton (Figs. 1a and 1b) while the HBχPT approach

includes the photon emission from the weak interaction vertex (Fig. 1c). The latter diagram contributes

less than one percent and creates only a very slight

change in the final photon spectrum and branching

ratio calculations; both the photon energy spectrum

and the photon polarization observables are 

dominated by electron IB. 

The experimental challenge is to distinguish definitively the low rate of radiative decay events in the

large photon background of a neutron beam. The

branching ratio above 15 keV is only about 3x10-3,

which coupled with the long neutron lifetime (about

fundamental physics end-station at the C

Neutron Research at the National Institut

Standards and Technology to search for 

mode. The experiment registers electron

coincidences for electrons followed by a 

proton, thereby reducing the probability 

lated background events. A strong magn

transports charged particles away from th

detector, which increases the solid angle 

detection and minimizes correlated back

electrostatic mirror permits one to chang

electron-proton coincidences with no ch

photon background rate, thus providing 

systematic check on possible background

A cold neutron beam enters parallel to th

magnetic field produced by a supercond

solenoid, as illustrated in Fig. 2. When a 

decays inside the high field region, the c

decay products are confined to move in 

cyclotron orbits typically less than 1 mm 

whose guiding centers are locked to the 

netic field lines. The solenoid has a sligh

the magnetic field direction at one end, 

decay proton and electron to be guided 

beam and into a thick silicon surface bar

(SBD). The SBD is held at a high negativ

(-25 kV) to accelerate the low energy pro

detectable energies. The apparatus was p

employed on NG-6 to measure the neutr

using a proton trap; its mode of operatio

described in detail elsewhere [4].

Nearly all of the decay electrons have m

energy (several hundred keV) and reach 

first, whereas the much slower proton (m

energy of 751 eV) drifts to the detector a 

microseconds later. The electrostatic mirr

constructed in an annular form to permit 

sage of the neutron beam, and it was us

the direction of protons with initial mom

from the detector. Thus, the magnetic fie

electrostatic mirror allow for nearly 2 π s

coverage for the electron detection and u

coverage of the proton detection.

J.S. Nico1

M.S. Dewey1

T.R. Gentile1

H.P. Mumm1

A.K. Thompson1

B.M. Fisher 2

I. Kremsky 2

F.E. Wietfeldt 2

T.E. Chupp 3

R.L. Cooper 3

E.J. Beise 4

K.G. Kiriluk 4

J. Byrne 5

K.J. Coakley 6

1 Ionizing Radiation

Division

National Institute 

of Standards and

Technology

Gaithersburg, MD

20899-8460

2 Tulane University

New Orleans, LA

70118

3 University of

Michigan

Ann Arbor, MI

48109

4 University of

Maryland, College

Park, MD 20742

5 University of

Sussex

BN1 9QH, U.K.

6 Statistical

Engineering

Division

National Institute 

of Standards and

Technology

Boulder, CO 80305

24

FIGURE 1: 

Contributions to radiative neutron decay, showing (a) electron

bremsstrahlung, (b) proton bremsstrahlung, and (c) radiation

directly from the weak vertex.
ing of scintillating crystals coupled to avalanche 

photodiodes was employed. The photon was detected by a single bismuth germanate (BGO) crystal

viewed by a silicon avalanche photodiode (APD) [5].

The gain of the APD increases and its noise decreases as the temperature decreases [6]. In addition, BGO

exhibits increased light output at low temperatures

[7], which reduces the low-energy detection threshold. The BGO crystal was mounted in an aluminum

holder and placed below the neutron beam in the

downstream end of the bore of the solenoid. The

placement of the photon detector well away from the

SBD significantly reduces correlated background from

external bremsstrahlung photons in the SBD. The

photon singles rate, and hence the uncorrelated

background rate, was kept low by using a well-collimated neutron beam and gamma-ray shielding.

If a proton was detected within a 20 μs timing window after an electron, a conversion signal triggered a

computer-based digital oscilloscope board that

recorded the amplified electron-proton coincidence

signal and the preamplifier output of the APD. Figure

3 shows an example of the two waveforms. Protons

are distinguished from electrons based on their pulse

heights. Events attributable to radiative decay photons will occur as prompt events in the timing spec

grounds by varying the electrostatic mirror potential,

which changes the electron-proton coincidence rate.

The available phase space of the neutron’s 4-body

decay does not change linearly with the electronproton rate, in contrast with some sources of correlated backgrounds. Monte Carlo techniques were

used to calculate the expected rates as a function of

mirror potential. For true radiative decay events, it

yields a specific dependence on the neutron decay

kinematics and the detector acceptance, thus 

providing a strong systematic check.

The analysis of the data is in progress; a precise

measurement of the photon spectrum should be 

possible with a straightforward upgrade of the 

detector by covering more of the available solid

angle. A measurement of the spectrum below the 

1 % level would reveal the contributions from the

weak vertex and provide an alternative determination

of the weak coupling constants gV and gA. Similarly,

if the photon’s circular polarization could be 

measured, it would reveal information about the

Dirac structure of the weak current [2,3].

REFERENCES

[1] M. Beck, et al., JETP Lett 76, 392 (2002).

[2] Y. V. Gaponov, R. U. Khafizov, Phys. Atom. Nucl. 59, 1213

(1996); Phys. Lett. B 379, 7 (1996); Nucl. Instrum. Meth. A 440,

557 (2000).

[3] V. Bernard, S. Gardner, U.-G. Meißner, C. Zhang, Phys. Lett. B

593, 105 (2004); Phys. Lett. B 599, 348 (2004).

[4] J.S. Nico, et al., Phys. Rev. C 71, 055502 (2005); M.S. Dewey, 

et al., Phys. Rev. Lett. 91, 152302 (2003).

[5] B.M. Fisher, et al., J. Res. Natl. Inst. Stand. Technol. 110, 421

(2005).

[6] L. Yang, et al., Nucl. Instrum. Meth. A 508, 388 (2003).

[7] H.V.J. Piltingsrud, J. Nucl. Med. 20, 1279 (1979).

FIGURE 3: 

Traces of the digitized waveforms for the two detectors. The

blue line shows the SBD signal for an electron event followed by

a delayed proton; the orange line shows the much slower preamplified output of the APD for a photon event occurring coincident with the electron.

FIGURE 4: 

The electron-photon timing spectrum for a three-day run with

the mirror reflecting all protons. The spectrum shows all photons in a 20 μs window for which the electron start pulse was

accompanied by a delayed proton event. 
pigments and latex emulsions, where all particle

dimensions are in the range of scattering vectors

attainable by light scattering measurements. However,

light scattering studies on coatings formulations are

not possible due to the opacity/turbidity of these

samples. While typical small angle neutron scattering

(SANS) measurements are capable of overcoming the

opacity issues associated with coatings formulations,

the maximum size scale which can be measured by

SANS measurements (typical dmax = 300 nm) is 

smaller than the particles encountered in coatings.

The perfect crystal diffractometer for ultra-high resolution small-angle neutron scattering (USANS) measurements at the NCNR is capable of measuring size

features as large as 104 nm, providing the 

potential for obtaining structural information on 

coatings formulations which was previously

unachievable by other methods.

We measured the shear-rate dependent structure 

of TiO2 dispersions (37 % volume fraction) stabilized

with commercial polymer dispersants in water. The

TiO2 is a commercial grade product with a nominal

particle diameter of approximately 400 nm. The 

solvent compositions were adjusted to the contrast

match point of each dispersant to isolate the behavior of the TiO2. Two different molecular weight

(MW) poly acid dispersants (referred to as “low MW

acrylate polymer salt” and “high MW acrylate polymer salt”) and two different molecular weight alkali

soluble acrylate copolymers (referred to as “low MW

hydrophobic acrylate copolymer salt” and “high MW

hydrophobic acrylate copolymer salt”) were used in

this study. The shear cell that was used is a couette

geometry consisting of double quartz cylinders with 

a 0.5 mm gap. The shear cell was equipped with a

vapor trap which was filled with D2O to prevent

sample drying during the course of the experiment.

All experiments were performed at ambient temperature. Data were collected with the incident radiation

parallel to the shear gradient and the collected scattering pattern is in the flow — vorticity plane. The

shear-rate dependence of the scattering from each

sample was measured at 0.1 s-1, 1 s-1, 10 

and 1000 s-1. After the measurement at 1

scattering was measured at rest. For each 

counting time of 3.4 h was employed to 

counting statistics. All data were correcte

empty cell scattering and slit smearing ef

The shear-rate dependent scattering for e

TiO2 dispersions with a different polyme

contrast matched are shown in Figs. 1-4. 

dispersed with the high MW acrylate pol

shows a decrease in low angle scattering 

increasing shear-rate (Fig. 1), indicating a 

induced breakup of aggregates of TiO2. 

cessation of shear, the low angle scatteri

increases, indicating reaggregation of the 

the high MW acrylate polymer salt. Conv

TiO2 dispersed with the low MW acrylat

salt shows a slight increase in scattering 

increasing shear-rate (Fig. 2). This indica

induced aggregation of TiO2 particles. Th

tion appears to be irreversible, since the 

after cessation of shear has the highest in

A.I. Nakatani1

A. VanDyk1

L. Porcar 2

J.G. Barker 2

1 Rohm and Haas

Company

Spring House, PA

19477

2 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

26

R

/

P

O

L

Y

M

E

R

S

FIGURE 1: 

Smearing-corrected shear-rate dependent scatt

TiO2 dispersion stabilized with a high MW acryl

salt.
The TiO2 dispersed with the high MW hydrophobic

acrylate copolymer salt shows a decrease in low

angle scattering intensity with increasing shear-rate

(Fig. 3). After cessation of shear, the low angle 

scattering appears to increase, but not to the level

observed at the start of the shear history. These

results indicate the TiO2 dispersed with the high MW

hydrophobic acrylate copolymer salt exhibits a shear

induced break up of aggregates and after cessation

of shear, reaggregation of the TiO2 occurs. Finally,

the TiO2 dispersion stabilized with the low MW

We believe these are the first results which demonstrate the sensitivity of dispersions to the molecular

weight and chemistry of the dispersant molecules,

along with the shear-rate dependent behavior of the

dispersions. The unique capabilities of the USANS

instrumentation were a key in obtaining these results.

The complimentary study of these dispersions, in

which the TiO2 has been contrast matched, so the

scattering from the dispersant molecules as a function of shear-rate will be reported separately.

10-5

q (Å-1)

10

102

101

10-4 10-3 10-2

100 s-1

1000 s-1

0 s-1, After Cessation

FIGURE 2: 

Smearing-corrected shear-rate dependent scattering from a TiO2

dispersion stabilized with a low MW acrylate polymer salt.

FIGURE 3: 

Smearing-corrected shear-rate dependent scattering from a

TiO2 dispersion stabilized with a high MW hydrophobic acrylate copolymer salt.



T c

  













 V



 V



 V



 V



 V



 V



 $IWHU &HVVDWLRQ

,QWHQVLW\FP 

FIGURE 4: 

Smearing-corrected shear-rate dependent scattering from a

TiO2 dispersion stabilized with a low MW hydrophobic acrylate copolymer salt. 
Light scattering and small-angle neutron scattering

(SANS) were applied under static (no fluid flow) 

conditions to study the solution structure of human

VWF multimers and protomer. Our observations suggest that these proteins resemble prolate ellipsoids in

solution with radii of gyration (Rg) of ≈ 75 nm and 

≈ 30 nm for the multimer and protomer forms,

respectively. The ellipsoid major and minor axes radii

were of length ≈ 175 nm and ≈ 28 nm for multimers,

and ≈ 70 nm and 9.1 nm for protomers. The multimer is organized into substructural domains at length

scales indicative of the entire protein itself (≈ 75 nm), 

elements of the protomer quarternary structure 

(≈ 16 nm), and individual functional domains 

(≈ 4.5 nm) (Fig. 2a). Individual domains of ≈ 4.5 nm

were also observed in the protomer. Amino acids

occupied a small (≈ 2 %) volume in both multimeric

and protomer VWF ellipsoids, compared to other

proteins like bovine serum albumin (98 %) and fibrinogen (35 %). ADAMTS-13, a metalloprotease that

cleaves VWF, is found in blood, and the absence of

this protease leads to severe bleeding complications.

In our studies, we observed that treatment of VWF

with 1.25M denaturant Guanidine.HCl, which 

increases the susceptibility of VWF to proteolysis by

ADAMTS-13, caused local structural changes at length

scales below 10 nm without altering the protein Rg

(Fig. 2b). Measurements by other methods reveal a

pattern of dimer and trimer units that indicate stable

non-covalent interactions within the multimer.

Since the function of von Willebrand Fac

upon application of fluid forces, VWF iso

blood plasma cryoprecipitate was placed 

couette cell [4] (Fig. 3a) and laminar fluid 

applied in the range from 300/s to 3000/

measurements were simultaneously perfo

assay in situ protein solution structural c

response to hydrodynamic forces. In five 

different experiments performed with dif

of human VWF, we observed changes at 

scales < 10 nm (Fig. 3b) which were rem

the above-mentioned changes in protein 

upon addition of denaturant Guanidine.H

structural changes were irreversible on th

scales studied. Further, even though care

were performed to test the hypothesis th

in protein conformation on a larger scale 

in response to fluid shear, no unequivoc

in support of this view was obtained. Co

were performed to confirm that the obse

conformation change can indeed be attri

VWF in solution and not to VWF bound 

Couette-wall. Our studies also show that 

neutron scattering patterns were specific 

since a smaller protein bovine serum alb

not undergo similar changes in scattering 

upon application of fluid shear.

S. Neelamegham1

I. Singh1

P. Alexandridis1

L. Porcar 2,3

1 State University 

of New York at

Buffalo

Buffalo, NY 14260

2 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

3 University of

Maryland

College Park, MD

20742

28

R

/

P

O

L

Y

M

E

R

S

conformation under two distinct conditions: upon addition of denaturant (Guanidine.HCl) and 

under fluid shear.

FIGURE 1: 

Immobilized von Willebran

(VWF) binding to platelets 

platelet deposition at sites 

injury where the endotheli

is disrupted. High fluid she

may occur in constricted 

regions of the arterial circ

also promote VWF binding 

receptors on blood platele
that stabilize VWF solution structure under static con

FIGURE 2: 

(a) Small angle scattering data were fit to the unified equation

in Ref. 1. This analysis revealed that human VWF has three

distinct structural levels a,b,c within multimeric protein. Level a

is the multimeric molecule, b is an intermediate structure that

likely represents the globular domain at the N-terminus of

VWF, and c represents individual protein domains. Discrete

points represent experimental data while smooth lines are

model fits. (b) SANS data for multimeric VWF before and

after treatment with 1.25M Gd·DCl shows that Gd·DCl does

not affect the Rg of the protein, though it alters structural features at length scales < 10 nm.

FIGURE 3: 

(a) Schematic drawing of a couette shear cell in which VWF

was sheared and protein solution structure was evaluated in

real-time. (b) A representative shear run where the fluid shear

rate was increased from 0/s to 3000/s at a fixed time point.

Increase in scattering intensity is observed in the high q range

and a small decrease is observed at low q.
tough, the unique double-network morphology

should be expected to account for this intriguing

mechanical behavior. Here we highlight the use of

neutron scattering in determining, for the first time,

the structure of DN-gels as well as the structure of

the individual components. To cover a broad range

over four orders-of-magnitude in wavevector q, data

from both ultra-small angle neutron scattering

(USANS) and SANS were collected and compiled

from each sample. The measurements were made

using USANS instrument at BT-5 and the SANS 

diffractometers at NG-3 and NG-7 at the NCNR.

The DN-gels studied in this work were prepared in

situ by polymerizing linear polyacrylamide (PAAm) at

several concentrations within a crosslinked 

poly(2-acrylamide,2-methyl,1-propanesulfonicacid)

(PAMPS) network. The total network structure was

rendered observable using neutron scattering contrast

by immersing the hydrogenated double-networks in

deuterated water. To determine the structure of PAAm

chains within the DN, samples were prepared by

polymerizing deuterium-labeled acrylamide monomer

(d3-PAAm) within the PAMPS network swollen in 

regular water. Matching the neutron contrast of the

d3-PAAm chains with that of a mixture of light and

heavy water then allows us to characterize the

PAMPS network structure within the DN-gels. 

Figure 2 shows the total structure of DN-gels measured over four orders-of-magnitude in wavevector, q.

The scattering intensity at ultra-small angles (I(q), 

q → 0.00001 Å-1), which is related to the extent of

heterogeneity in DN-gels, surprisingly, decreases with

the addition of PAAm to the PAMPS single-network.

This suggests that the PAAm chains are preferentially

situated within the low crosslink density regions of

nized double-network structure with incr

concentration [2]. But the heterogeneity r

some extent for the DN-gel with more th

polyacrylamide. While the initial homoge

the PAMPS network slightly improved the 

of DN-gels prepared at low PAAm conce

toughest of the DN-gels, containing more 

PAAm, is almost as heterogeneous as the 

PAMPS network. However, the individua

structure of PAMPS and PAAm within the 

gets homogenized at high PAAm loading

mined from the USANS results. 

T. Tominaga1,2

V.R. Tirumala1

P. Butler 3

E.K. Lin1

H. Furukawa2

J.P. Gong 2

Y. Osada2 

W-L. Wu1

1 Polymers Division

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8541

2 Hokkaido

University 

Sapporo, Japan

3 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

30

R

/

P

O

L

Y

M

E

R

S

FIGURE 1: 

Pure PAMPS gel breaks down under compressi

by volume (a), but the toughest DN-gel regains 

shape after 90 % compression by volume (b). (

with permission from Ref.1.)
The scattering data at high-q offers insight into the

interactions between the linear PAAm and the PAMPS

network. A well-defined scattering peak resulting

from intrachain correlations is characteristic of a

swollen polyelectrolyte in a polarizable medium [3].

For the present case of the PAMPS primary network

used in DN-gels, this scattering maximum occurs at q

≈ 0.045 Å-1. By making the PAAm network invisible

using contrast matching to the aqueous matrix, the

behavior of the PAMPS network alone can be measured. Figure 3 shows the result of varying the (invisible) PAAm concentration on the PAMPS peak. The

peak position remains constant for DN-gels at all

PAAm concentrations but the peak amplitude diminishes with PAAm loading since the electrostatic repulsion is screened by PAAm. This is noteworthy since

PAAm is not expected to be sufficiently ionized to

screen out the electrostatic repulsions among the

PAMPS, even though water soluble. Regardless of

their origin, the SANS results at high q suggest strong

interactions between PAMPS and PAAm in aqueous

solution. From these results, the structural changes in

the PAMPS gel with the addition of PAAm to form the

toughest DN-gel can be conceptualized as shown in

Fig. 4. We are currently investigating the origin of

these interactions to further determine their effect on

the fracture toughness of DN-gels.

REFERENCES

[1] J.P. Gong, Y. Katsuyama, T. Kurokawa, Y. Osada, Adv. Mater. 15

1155 (2003).

[2] Y.-H. Na, T. Kurokawa, Y. Katsuyama, H. Tsukeshiba, J.P. Gong,

Y. Osada, S. Okabe, T. Karino, M. Shibhayama, Macromolecules

37, 5370 (2004). 

[3] V.M. Prabhu, E.J. Amis, D.P. Bossev, N. Rosov, J. Chem. Phys.

121, 4424 (2004).

FIGURE 2: 

SANS and USANS data from DN-gels prepared at different

PAAm concentrations as shown in the legend. The inset

shows the change in the polyelectrolyte scattering peak with

the addition of PAAm. The data are normalized to the contrast factor.

FIGURE 4: 

Schematic diagram showing the evolution of double-network

structure from the primary PAMPS gel with increase in PAAm

concentration from 0 M to 1 M and 2 M. PAMPS and PAAm

are represented by blue and red colors respectively.

FIGURE 3: 

SANS data from the PAMPS network alone measured from

DN-gels prepared at different PAAm concentrations shown in

the legend. The data are normalized to the contrast factor.

The PAAm network has been rendered invisible by contrastmatching it to the aqueous matrix.
Using the high-resolution quasielastic neutron scattering (QENS) method at the High Flux Backscattering

Spectrometer (HFBS) at the NCNR and the RelaxingCage Model (RCM) [1] for the analysis, we determine

the temperature dependence of the average translational relaxation time, <τT>, for the hydration water.

The dynamic crossover temperature of hydration

water is defined as follows. At high temperatures,

<τT> follows a super-Arrhenius behavior (called a

‘fragile’ behavior [2]) describable approximately by a

Vogel-Fulcher-Tammann (VFT) law: <τT> = τ1

exp[DT0/(T – T0)], where D is a constant providing

the measure of fragility and T0, the ideal glass transition temperature at which the relaxation time appears

to diverge. In reality, however, this divergence is

avoided by the system. Instead, an Arrhenius behavior (called a ‘strong’ behavior [2]) sets in below the

crossover temperature TL where the functional

dependence of the relaxation time switches to a law:

<τT> = τ1 exp[EA/kBT]. In this equation, EA is the activation energy for the relaxation process and kB, the

Boltzmann constant. The crossover temperature TL is

defined by the intersection of these two laws, which

gives 1/TL = 1/T0 - (DkB)/EA. In the case of hydration

water in both lysozyme protein and DNA, we found

TL = 222 ± 2 K, which agrees well with the characteristic transition temperature in protein observed

before [3]. Since the average relaxation time <τT> is a

measure of the mobility of a typical hydration water

molecule, this result implies that the sudden change

in the trend of mobility of water molecules at the

crossover temperature triggers the so-called glass

transition of biomolecules [4-7]. 

Figure 1 shows the mean-squared hydrogen atom

displacements <x2> (calculated from the translational

Debye-Waller factor, SH(Q,ω =0)= exp[-Q2 <x2>])

S-H. Chen1

L. Liu1

X. Chu1

Y. Zhang1

E. Fratini 2

P. Baglioni 2

A. Faraone 3,4

E. Mamontov 3,4

V. Garcia Sakai 3,4

1 Massachusetts

Institute of

Technology 

Cambridge MA

02139 

2 University of

Florence

50019 

Florence, Italy

3 University of

Maryland

College Park, MD

20742 

4 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

32

crossover temperature at 222 ± 2 K with the biomolecules. At the FSC, the structure of hy

water makes a transition from predominantly high-density (more fluid state) to low-density (le

state) forms derived from existence of the second critical point at an elevated pressure.

FIGURE 1: 

Mean-squared atomic displacement <x2> of all 

atoms at 2 ns time scale measured by an elas

resolution of 0.8 μeV (HFBS at NIST), as a fun

ature for H2O hydrated and D2O hydrated prot

and DNA (Panel b). The solid circles represent 

ed by contributions from H atoms in hydration 

empty circles, that dominated by H atoms cont

or DNA molecules. 
obtained by a method of elastic scan in hydrated

lysozyme protein (Panel a) and hydrated DNA (Panel

b), respectively. In both panels, one sees that at low

temperatures up to their respective crossover temperatures, all curves have a gentle linear temperature

dependence. However, at above the crossover temperatures, they rise sharply with different slopes. We

call the crossover temperature of H2O TL, and that of

protein or DNA TC, with both values at approximately 222 ± 2 K. This is to say that the dynamic

crossover phenomenon of both protein and DNA and

that of their hydration water are highly correlated,

and occur at a similar temperature. It is more striking

to note that the TL of H2O hydrated in protein and

that in DNA are close to each other. These results

signal our later conjecture that the dynamic crossover

temperature is independent of the biomolecules. 

To define precisely the TL, we performed dynamic

temperature range from 270 K to 230 K, <τT> obeys

VFT law, a signature of fragile liquid, quite closely.

But at TL = 222 ± 2 K it suddenly switches to an

Arrhenius law, a signature of a strong liquid. So we

have a clear evidence of FSC in a cusp form. It is to

be noted that the crossover temperature of protein

hydration water is sharply defined at TL = 220 K, the

T0 for the fragile liquid turns out to be 176 K, and

the activation energy for the strong liquid, EA = 13.1

kJ/mol, which are slightly lower than in the DNA

case, TL = 222 K, T0 = 186 K, and EA = 14.6 kJ/mol.

In summary, an investigation of the average translational relaxation time, of protein and DNA hydration

water as a function of temperature reveals a hitherto

unnoticed Fragile-to-Strong dynamic crossover at 

TL = 222 ± 2 K, close to the universal dynamic 

transition temperature TC documented for biomolecules in the literature. The coincidence of the dynamic transition temperature TC of biomolecules, signaling the onset of anharmonic molecular motion, and

the FSC temperature TL of the hydration water suggests that the change of mobility of the hydration

water molecules across TL drives the dynamic transition in biomolecules.

REFERENCES

[1] S.-H. Chen, C. Liao, F. Sciortino, P. Gallo, P. Tartaglia, Phys. 

Rev. E 59, 6708 (1999).

[2] C.A. Angell, J. Non-Crys. Sol. 131-133, 13 (1991).

[3] B.F. Rasmussen, A.M. Stock, D. Ringe, G.A. Petsko, Nature 357,

423 (1992). 

[4] W. Doster, S. Cusack, W. Petry, Nature 337, 754 (1989).

[5] W. Doster, S. Cusack, W. Petry, Phys. Rev. Lett. 65, 1080 (1990).

[6] M. Tarek, D.J. Tobias, Phys. Rev. Lett. 88, 138101 (2002). 

[7] D. Vitkup, D. Ringe, G.A. Petsko, M. Karplus, Nat. Struct. Biol. 7,

34 (2000).

[8] S.-H. Chen, L. Liu, X. Chu, Y. Zhang, E. Fratini, P. Baglioni, 

A. Faraone, E. Mamontov, submitted to Phys. Rev. Lett. (2006).

[9] S.-H. Chen, L. Liu, E. Fratini, P. Baglioni, A. Faraone, 

E. Mamontov, to appear in Proc. Nat. Acad. Sci. USA (2006).

FIGURE 2: 

The extracted Q-independent average translational relaxation

time <τT> vs. T0/T from fittings of the quasielastic spectra

plotted on a log scale. Panel (a) is a result from hydrated

DNA [8], whereas Panel (b) is the same quantity measured in

hydrated lysozyme protein [9]. There is clear evidence in both

cases that a well-defined cusp-like dynamic crossover behavior

occurs at TL indicated in the respective figures. The dashed

lines represent fitted curves using the VFT law, while for the

solid lines the fitting is according to the Arrhenius law. TL in

both cases occurs at 222 ± 2 K.
Neutron scattering probes molecular dynamics directly and the observable time scales cover the range of

internal motions occurring in proteins. Incoherent

neutron scattering probes the dynamics of H atoms

because their scattering cross-section is significantly

larger than that of any other atom. H atoms are distributed throughout tRNA and lysozyme, providing

information on their overall motions. Measurements

were performed on the High Flux Backscattering

Spectrometer (HFBS) at the NCNR. Elastic scans were

measured at a heating/cooling rate of 0.7 K/min and

quasielastic scattering measurements were taken

using an energy window of ± 17 μeV (with a resolution of 0.85 μeV).

Figure 1 shows the mean

square hydrogen displacement <u2> of tRNA and

lyzosyme in dry and

hydrated states, obtained

from analyzing the elastic

scattering intensity as a

function of the scattering

wavevector. In both hydrated samples, <u2> increases

sharply above T ≈ 200 K to

220 K, characteristic of the

dynamic transition. Dry

tRNA exhibits a linear

increase in <u2> over the

entire temperature range, a

signature of harmonic

behavior. In contrast, dry

lyzosyme shows an onset of anharmonic

stronger temperature dependence at T ≈ 

In Fig. 2 the resulting quasielastic spectra 

significant broadening relative to the inst

resolution at 300 K for both hydrated tRN

lyzosyme. This indicates a relaxation pro

ring in the 300 ps to 5 ns timescale. Hyd

at 200 K and dry tRNA at 300 K show no 

consistent with the harmonic behavior o

<u2>. In contrast, the spectra of dry lyzo

K and wet lyzosyme at 200 K show quas

broadening, indicating a relaxation proce

at temperatures below the dynamic trans

agreement with the anharmonicity obser

and which is absent in tRNA.

G. Caliskan1,2

R.M. Briber 3

D. Thirumalai 3

V. García Sakai 2,3

S.A. Woodson1

A.P. Sokolov 4

1 Johns Hopkins

University

Baltimore, MD

21218

2 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

3 University of

Maryland

College Park, MD

20472

4 University of

Akron

Akron, OH 44325

34

ences in the architecture and backbone structure of proteins and RNA, hydrated tRNA undergoes the 

transition at the same temperature as hydrated lysozyme, a common protein found in egg-white. This s

ports the idea that the dynamic transition is solvent induced. Our results also suggest that methyl grou

the main contributor to the dynamic transition in biological macromolecules; however, they may explain 

ferences in the dynamics of tRNA and lysozyme observed at low temperatures.

FIGURE 1:

Mean-squared hydrogen displacement as

a function of temperature for lysozyme

(solid symbols) and

tRNA (open symbols)

in hydrated (black)

and dry (red) forms.

Error-bars are smaller than ±0.02 Å2.
The similarity in TD of hydrated tRNA and lyzosyme

indicates that the dynamic transition is not an intrinsic property of the macromolecule. Extensive measurements on various hydrated proteins, DNA and

now tRNA, reveal the dynamic transition in the same

temperature range, despite differences in backbone

chemistry and 3D structure. It has been argued that

the dynamic transition of hydrated biomolecules is

primarily a result of the transition from liquid-like to

solid-like dynamics that occurs in water on molecular

time and length scales. The dynamic crossover for

water occurs at TC ≈ 220 K to 230 K.

Further evidence for a solvent induced transition is

the observation that the dynamic transition of

lyzosyme in glycerol [3] occurs at the same temperature as the dynamic crossover of pure glycerol.

Furthermore, simulations have shown that when the

translational motion of water is artificially restricted,

the protein behaves as if it were below the dynamic

transition even at 300 K [6]. This suggests that arrest

of the translational motion of the solvent molecules

blocks the motion of the biomolecule. 

Based on the similarity of the temperature dependence of <u2> and NMR-determined orientational

order parameter for methyl-bearing side chains, it has

been proposed [5] that the freezing of rotational

relaxation is the cause of the dynamic transition in

proteins. However, the paucity of methyl groups in

suggestion based on MD-simulations is that the 

α-helices in myoglobin become dynamically active

above TD. If this is correct, this type of motion would

require translational motion of water molecules.

The most significant difference between the dynamics

of tRNA and lyzosyme is the absence of anharmonicity in tRNA at low temperatures. An additional 

relaxation process occurs in lyzosyme. It has been

ascribed to methyl group dynamics that contribute

significantly to the scattering spectra. This is consistent with our results for tRNA which lacks this 

relaxation component at low temperatures. 

However, these differences could also be due to 

the different flexibility of the polypeptide and

polynucleotide backbones. 

The present analysis clearly demonstrates that 

neither the 3D structure of biological macromolecules

nor their chemical backbone affect the dynamic 

transition. This conclusion supports the idea [6] that

unfreezing the translation of solvent molecules is 

the main cause of the dynamic transition in biomolecules. Our results also suggest that the rotation of

methyl groups is not the main cause of the dynamic

transition, although they may cause the low-temperature anharmonicity observed in proteins. Understanding the microscopic nature of the motions that

activate in the nanosecond-picosecond time range in

biological macromolecules above TD remains an

important challenge as these motions are intrinsically

linked to biochemical interactions. 

REFERENCES

[1] B.F. Rasmussen, A.M. Stock, D. Ringe, G.A. Petsko, Nature 357,

423 (1992).

[2] H. Lichtenegger, W. Doster, T. Kleinert, A. Birk, B. Sepiol, 

G. Vogl, Biophys. J. 76, 414 (1999).

[3] A.M. Tsai, D.A. Neumann, L.N. Bell, Biophys. J. 79, 2728 (2000).

[4] A.L. Tournier, J. Xu, J.C. Smith, Biophys. J. 85, 1871 (2003).

[5] A.L. Lee, J.Wand, Nature 411, 501 (2001).

[6] M. Tarek, D.J. Tobias, Phys. Rev. Lett. 88, 138101 (2002).

[7] L. Cordone, M. Ferrand, E. Vitrano, G. Zaccai, Biophys. J. 76,

1043 (1999).

FIGURE 2: 

Quasi-elastic scattering spectra of wet tRNA at 300 K (green)

and 200 K (blue) and dry tRNA at 300 K (red) (a). Similar

data for wet lysozyme at 295 K (green) and 200 K (blue) and

dry lysozyme at 320 K (red) (b). The solid gray lines represent

the resolution.
We have used these tools to predict the first fulllength structures of the HIV-1 Gag protein [1]. 

This macromolecule is the major structural protein

element in the virus that causes AIDS. The knowledge of the structure of this protein may allow for

the development of drugs that prevent the assembly

of virus particles in vivo. Additionally, we have 

determined structures of full-length Protein A, which

is the major reagent used to purify antibodies by the

pharmaceutical industry. Knowledge of the structures

that Protein A adopts at thermal equilibrium may

help to improve product yields. These tools, once

mature, may be useful in the study of many intrinsically disordered proteins and the elucidation of

macromolecular interactions in solution.

Proteins are vital components of biological systems

that have a variety of structural and catalytic functional roles. Historically, atomic level structural

knowledge of proteins has relied upon x-ray diffraction and nuclear magnetic resonance (NMR) spectroscopy. These methods have had an immeasurable

impact on the elucidation of many biological problems. Recently, however, it has been estimated that ≈

20 % to 30 % of the proteins encoded by the eukaryotic genome have regions that are structurally illdefined and thus many proteins are intrinsically disordered [2]. These disordered proteins ha

cal function and control mechanisms tha

unclassified. Thus, a less realized role of 

many biological processes has emerged. 

dered proteins have functionality that is 

ed to their flexibility. Due to their inhere

atomic descriptions are not generally ava

entire molecule since the molecules occu

ensemble of interchanging conformations 

Structural data for several regions of the 

protein have been determined by x-ray a

methods. However, the determination of 

structure from either protein crystals or s

not been achieved. The five major region

HIV-1 Gag protein are connected by ami

residues that have been determined by e

J.E. Curtis1

N.F. Berk1

S. Krueger1

P. Coleman2

S.J. Moeller2

R.B. Ross2

S. Datta3

A. Rein3

1 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

2 3M Corporate

Research

Laboratory, USA

3M Center

St. Paul, MN 

55144-1000

3 National Cancer

Institute, NCIFrederick

Frederick, MD

21702-1201

36

SASSIE intended for the NCNR user community.

FIGURE 2: 

Probability density p

allowed structural a

of the individual sub

the HIV-1 Gag prote

regions are colored 

matrix, transparent 

amino-terminal linke

capsid, grey; p2-link

nucleocapsid, green

FIGURE 1: 

Analysis of an ensemble of protein structures of the fulllength HIV-1 Gag protein by comparison of calculated 

patterns with experimentally determined small-angle neutron scattering data. Histogram of Rg values (left panel)

and a comparison of experimental and theoretical SANS

patterns of HIV-1 Gag protein (right panel). The experimental data are shown as points with error bars, while the

best (black) and worst fit (grey) are shown as lines. The

generation and evaluation of millions of Gag-1 structures

indicates that monomeric HIV-1 Gag protein is folded over

and not extended under physiological conditions. This

implies that the protein undergoes a major conformational

change when assembled into the intact virus particle. 
the HIV-1 Gag protein, its nonaggregated state is characterized

by an ensemble of structures. We

have used the 30 m SANS instrument on the NG-3

beamline at the NCNR to determine the structural

characteristics of the HIV-1 Gag protein in the

monomeric state under physiological conditions.

Using atomic positions available from experiment 

as a starting point, we have developed molecular

models of the full-length HIV-1 Gag protein to create

large ensembles of structures for analysis. While not

rigorously exhaustive, the generation of millions of

structures by varying the protein backbone dihedral

angles is reasonably tractable using modest 

computational resources. 

In Fig. 1 we compare the experimentally determined

SANS patterns of monomeric HIV-1 Gag protein to a

few theoretically determined curves from full-length

atomistic models of the protein. Clearly, in all cases,

extended structures have SANS patterns that deviate

significantly from the experimentally determined

data. Thus, in the case of the search for a single 

representative structure of the protein, extended

structures do not have SANS patterns consistent 

with experiment.

In Fig. 2 we show a probability density plot of 

various regions of the HIV-1 Gag protein. The 

density plot was created using a Metropolis importance sampling method to determine representative

linear combinations of structures that are consistent

with the experimental data. As before, the most likely

conformations are those that are folded over and not

extended. Thus, one advantage of these methods 

is that they are useful in ruling out candidate 

structures that do not significantly contribute to 

the observed patterns.

In the native assembled HIV-1 virus particle the Gag

protein is oligomerized to form the outer shell of the

virus. The individual Gag protein molecules have

been shown to align in extended conformation that

is ordered with other Gag protein molecules to form

the concentric shell of the virus. Thus the HIV-1 Gag

protein must undergo a major conformational change

upon virus assembly. A detailed analysis of the

microscopic interactions that are involved in this

oligomerization process from the disordered/foldedover state may potentially lead to the development 

of therapeutic molecules to disrupt this process that

may have value in the treatment of AIDS.

We have condensed the modeling, structure 

generation, and analysis algorithms into a graphical

user interface called SASSIE. In addition to the analysis of structurally disordered proteins, the analysis

package allows for the calculation of SAS

(SAXS/SANS) and reflectivity profiles in real-time as

the user manipulates the molecule(s) on the display.

For example, in Fig. 3, we show the calculation of

the SANS patterns of a single conformation of the

Protein A described above.

In summary, we have developed methods and userfriendly graphical software to aid in the design and

analysis of SANS experiments of disordered molecules. We have applied these methods to study the

conformation of several proteins [1,3]. While the 

individual structural or ensemble solutions may not

be unique, we have found that there is utility in

knowing both what types of structures do and do 

not significantly contribute to a particular patterns.

This knowledge allows for a more systematic analysis

of both single and ensemble conformation structures

that can exist in solution. Therefore, these methods

will have important applications in the use of 

SANS to study the structure and function of 

disordered proteins.

REFERENCES

[1] S.A.K. Datta, J.E. Curtis, W. Ratcliff, P.K. Clark, R.M. Crist, 

J. Lebowitz, S. Krueger, and A. Rein, J. Mol Biol. (submitted).

[2] C.J. Oldfield, Y. Cheng, M.S. Cortese, C.J. Brown, V.N. Uversky,

and A.K. Dunker, Biochemistry 44, 1989-2000 (2005).

[3] D. Lee, et al., Mol. Cell 22, 423-430 (2006), D. Lee, et al., Mol.

Cell (in preparation).
Recent molecular dynamics simulation results [3], as

well as nuclear magnetic resonance studies [4-6], suggest that some acyl chains undergo extreme bending

motions, which bring the methyls close to the bilayer

polar interface. The simulations were aimed at reproducing the complete structure of the DOPC

(dioleoylphosphatidylcholine) bilayer reported by

Wiener and White [7]. Excellent agreement was found

between the simulated and experimental results for

the transbilayer positions and widths of the carbonyl,

glycerol, phosphate, and choline groups, but the

results for the water and the double-bonds showed

significant discrepancies with respect to the experiment. These differences, however, were not as 

dramatic as those observed between the simulated

and experimental terminal methyl group width. 

A much wider terminal methyl distribution was 

predicted by the simulation (Fig. 1). 

Neutron diffraction and specific molecular deuteration were therefore employed in this work to determine the methyl group distribution directly. All the

neutron diffraction experiments were performed at

the Advanced Neutron Diffractometer/Reflectometer

(AND/R) [8] located at the NCNR. High-purity 

terminal-methyl deuterated oleic acid was synthesized and in turn was used to synthesize DOPC with

deuterated terminal methyl groups (d6-DOPC).

Because of the much higher coherent sc

length of deuterium (2H) compared with 

the d6-DOPC allowed direct determinatio

mean transbilayer position and distributio

label. This was accomplished through a 

parison of the profiles obtained for d6-D

with those obtained for the hydrogenous 

similar approach was used to determine 

layer distribution of the waters of hydrat

H2O and 2H2O were used. The water dis

shows the extent of water penetration in

regions of the bilayer. As shown in Fig. 

water distribution can be described by a 

the methyl distribution is characterized b

Gaussian-shaped part accompanied by lo

extend into the polar interface. The area 

tails accounts for ≈ 20 % of the total area 

total methyl profile. 

These experimental results are broadly c

with the prediction of the MD simulation 

analysis of the simulation trajectories of 

methyl groups shows that about 30 % of 

groups eventually visit the polar membra

Most visit the interface for 5 ns or so, bu

percentage stay much longer, 20 ns to 50 

clude that, though the hydrocarbon core 

bilayer is organized into distinct domains

M. Mihailescu1

F. Castro-Roman1

R. Chamberlin1

D.L. Worcester 2

D.J. Tobias1

S.H.White 1

1 University of

California at Irvine

Irvine, CA 92697

2 University of

Missouri at

Columbia

Columbia, MO

65211

38

FIGURE 1: 

Molecular dynamics sim

DOPC bilayer. CHARMM 

fields were used to sim

constituted of dioleoylph

choline (DOPC) lipids hy

5.4 waters/lipid (66 % 

ity). The terminal methy

shown as white beads. 

distribution of the term

groups resulting from t

shown in the bar graph 
chain ends visit the water interface surprisingly often

due to molecular disorder. One can speculate that

this extreme form of disorder could be detrimental to

membrane protein function. Many proteins involved

in signaling, for example, apparently prefer to associate with ordered cholesterol-rich domains [9].

Cholesterol, acting as an important regulator of lipid

bilayer organization may create optimal conditions

for fast dynamical interactions of membrane receptors

with their ligands during signaling.

How does cholesterol affect the terminal-methyl 

distribution? To answer this question, the experiment

of Fig. 1 was repeated with cholesterol in the DOPC

bilayer. Figure 2 reveals that cholesterol causes a

general retraction of the chain ends, because 

cholesterol restricts the motion of the chains due to

the rigidity of its steroid moiety. The retraction of the

chain ends to the center of the bilayer in the presence of cholesterol is a dramatic demonstration of

the ordering and stabilizing role of cholesterol in

lipid bilayers. The results demonstrate unambiguously

that, without the ordering effect of cholesterol, the

terminal methyl groups can explore the space over

the entire hydrocarbon region, and parts of the 

headgroup region. These are unprecedented direct

experimental observations, which were stimulated by

recent progress in neutron diffraction instrumentation

for biological systems [8], molecular dynamics simulation procedures [3], and methods for molecular 

deuterium labelling [10].

ACKNOWLEDGMENTS

This study was carried out as part of the Cold

Neutrons for Biology and Technology project 

supported by the NIH National Center for Research

Resources (RR14812) and The Regents of the

University of California. Additional support was 

provided by a grant from the National Institute of

General Medical Sciences (GM68002).

REFERENCES

[1] K. Simons, and E. Ikonen, Nature 387, 569 (1997).

[2] F.R. Maxfield, and I. Tabas, Nature 438, 612 (2005).

[3] R.W. Benz, F. Castro-Roman, D.J. Tobias, and S.H. White,

Biophys. J. 88, 805 (2005).

[4] Z.-C. Xu, and S. Cafiso, Biophys. J. 49, 779 (1986).

[5] P.E. Godici, and F.R. Landsberger, Biochemistry 13, 362 (1974).

[6] D. Huster, and K.J. Gawrisch, J. Am. Chem. Soc. 121,1992

(1999).

[7] M.C. Wiener, and S.H. White, Biophys. J. 61, 434 (1992).

[8] http://www.ncnr.nist.gov/programs/reflect/ANDR

[9] L. Finegold, Ed., Cholesterol in Membrane Models, CRC Press,

Boca Raton, FL (1993).

[10] R. Chamberlin, et al., unpublished.

[11] S.E. Feller, et al., Biophys. J. 73, 2269 (1997). 

their steroid ring part toward the water

interface.
To begin to address these questions, we performed

neutron reflectivity measurements for diphtheria toxin

(DT) bound to Langmuir monolayers and to tethered

lipid bilayers. We followed pH-dependent conformational changes of the toxin for several bulk DT concentrations. First we examined the structure of DT

(CRM197, a nontoxic mutant) adsorbed to Langmuir

monolayers of dipalmitoylphosphatidylglycerol

(DPPG) at different bulk concentrations. Reflectivity

data are shown in Fig. 1 for a DT concentration of

0.93 μM. In these measurements the lipids and the

proteins were protonated and the subphase was a

phosphate buffer solution in H2O. 

The measurements revealed pH ranges over which

large conformational changes occurred as well as pH

ranges over which little or no observable change

occurred. The main stages of conformational change

are shown in Fig.1. The detailed structure of the

adsorbed layer at each state will be unambiguously

determined only when data for another contrast is

obtained (d-lipids), and so the profiles in Fig. 1b

should not be considered unique. However the qualitative trends are clearly evident in the data. While no

adsorption could be detected at pH 7.6, strong

adsorption occurred at pH 6.5, where the data are

consistent with one principle layer of ≈ 80 Å.

Adsorption continued to increase to pH 6.3, but with

little change in the profile shape (not shown). Below

pH 6.3, the adsorbed amount is nearly constant, and

the changes in the reflectivity data indicate changes

in conformation of the adsorbed protein. At pH 5.81

two layers are resolved. Some segments have penetrated into the lipid tails at this point. With a

decrease in pH to 5.26 the layer adjacent to the lipid

film became thinner and more concentrated in amino

acids whereas the outer layer extended still further

into the subphase. Upon further decreas

4.84, the inner layer became even thinne

concentrated. The outer layer appeared t

somewhat, but this cannot be determine

ously from the present data alone. Overa

decreasing pH it appears that one doma

ably the translocation domain, collapses 

into the membrane, whereas a second d

M.S. Kent1

H. Yim1

J.K. Murton1

S. Satija2

C.F. Majkrzak 2

D.J. McGillivray 2,3

M. Lösche 2,3

1 Sandia National

Laboratories

Albuquerque, NM

87185

2 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

3 Carnegie Mellon

University

Pittsburgh, PA

15213

40

cation may enable means of inhibiting the harmful effects of these toxins. A particularly imp

long-term goal is to mitigate the lethality of botulinum neurotoxin, which is a potential terror

biowarfare agent. While botulinum, tetanus, and diphtheria are extremely potent toxins, the

tremendous potential utility in medicine [1, 3]. Further development of new therapies and ca

treatments based on the re-engineering of the toxins will benefit greatly from a full understa

the enzyme translocation mechanisms. 

FIGURE 1: 

Reflectivity and fitted scattering length density (

for DT binding to Langmuir monolayers of DPPG 
First, no significant adsorption occurs until pH 5.5.

Second, upon initial adsorption the layer is much

thinner (≈ 50 Å) than that at 0.93 μM. This may 

indicate adsorption of monomers at 0.31 μM and

adsorption of dimers at 0.93 μM. The data fitting 

suggests two layers for the protein structure and little

penetration of amino acids into the lipid film, but

these details must be confirmed by acquiring data for

a second contrast. Third, with decreasing pH the

peak simply moves to slightly higher q. A second

peak never appeared at lower q as was the case for

0.93 μM. At 0.31 μM the layer remains thin and simply becomes more concentrated, in contrast to the

results for 0.93 mM. 

A series of measurements was performed for DT

binding to tethered bilayers of dimyristoylphosphatidylglycerol (DMPG) from a 0.31 μM solution in

D2O phosphate buffer. The bilayers were tethered

onto gold-coated wafers using the solvent exchange

method [4]. The tethering molecule and tethering

protocol were supplied by the Cold Neutrons for

Biology and Technology group [4]. Some data for this

series are shown in Fig. 3. Data were obtained to 

qz = 0.3 Å-1, but only the lower qz range where the

effect of the protein is most prominent is shown in

Fig. 3. No adsorption occurred until pH = 5.6, at

which point two layers are required to fit the data.

With decreasing pH the layer expanded substantially,

and three layers are required to fit the data at pH 5.2

and below. The strong expansion with decreasing pH

is similar to the results observed for binding to

Langmuir monolayers of DPPG at 0.93 μM and in

contrast to the results for binding to DPPG at 0.31

μM. Strong insertion into the bilayer did not occur, 

as indicated by the low SLD of the lipid tail region

throughout the series. However, the fitting suggests a

small perturbation of the inner leaflet, which could

indicate helices lying parallel to the headgroups in

that layer. Such a result would be consistent with a

structure proposed previously [5].

In conclusion, this initial work has revealed a rich

variety of structures for DT bound to monolayers and

tethered bilayers as a function of bulk concentration

tinct layers could be resolved within the adsorbed

protein structure, with a large expansion of the outer

layer and strong insertion of the inner layer occurring

with decreasing pH. The large expansion may indicate unfolding of one of the domains, presumably

the catalytic domain. Finally, at the lipid monolayer

and bilayer membranes under the same conditions of

concentration and pH, different adsorbed layer structures resulted. This could be due to the use of gel

versus fluid phase lipids, the constraint of constant

area in the bilayer case versus constant pressure in

the monolayer work, or the obvious structural difference in one versus two leaflets. 

Sandia is a multiprogram laboratory operated by

Sandia Corporation, a Lockheed Martin Company, for

the United States Department of Energy under contract DE-AC04-94AL85000.

REFERENCES

[1] A. Chenal, P. Nizard, and D. Gillet, J. Toxicology Toxin Reviews

21 321 (2002).

[2] G. Lalli, S. Bohnert, K. Deinhardt, C. Verastegui, and G. Schiavo,

Trends in Microbiology 11 431 (2003).

[3] G. Schiavo, M. Matteoli, and C. Montecucco, Physiological

Reviews 80, 717 (2000).

[4] G. Valincius, D.J. McGillivray, W. Febo-Ayala, D.J. Vanderah, J.J.

Kasianowicz, M. Lösche, J. Phys. Chem. B. 110 10213 (2006).

[5] L. Senzel, M. Gordon, R.O. Blaustein, K.J. Oh, R.J. Collier, and A.

Finkelstein, J. Gen. Physiol. 115 421 (2000).

FIGURE 3:

Reflectivity and fitted SLD profiles for DT binding to tethered

bilayers of DMPG at 0.31 μM.
The development of practical biosensors based on

natural membrane proteins, such as αHL, is a subject

of considerable effort. However, many problems

must be overcome in the design of a system suitable

for technical manipulation and measurement while

preserving the biological activity of the protein.

Natural cell membranes are intrinsically complex and

disordered, a specific molecular architecture of lipids,

sterols, proteins, glycolipids, etc., which drives the

development of simpler model systems that are more

amenable to preparation and characterization.

Biosensors must also be robust, preferably reusable,

and allow the behavior of the membrane-associated

protein to be readily probed.

Using a common approach [6] we have a

these issues in developing a solid-suppo

bilayer membrane (tBLM), which can be 

simple fashion on gold-covered surfaces

is surface-decoupled through a controlla

hydrated polymer spacer [7]. The tBLMs 

mized for αHL incorporation using electr

spectroscopy (EIS), a technique that is ca

rapidly probing the ion transport propert

the membrane pore. The increase in the 

admittivity is a function of the number o

pores incorporated (Fig. 1).

The electrical parameters of the toxin in 

can compared with αHL in unsupported 

membranes, where they have been comp

studied [8]. Unfortunately, unsupported l

branes are limited for structural studies o

because of their limited size (≈ 102 mm2

unsuitable for biosensor development as 

fragile, being sensitive to shock and vibr

However, the comparison of the effects o

on pore conductivity [8] and response to 

confirms that the toxin has retained its fu

in the tBLM, with the implication that the 

has also retained its native structure.

Using the optimized conditions, incorpor

into the biomimetic tBLM occurs at a sur

age large enough that its effect is readily 

in the raw neutron reflectivity (Fig. 2). T

can be fitted using a simple layer model

accounts for the most prominent feature 

protein, its large cap domain exterior to 

brane. In order to obtain more informati

interactions between the protein and the 

assumed that the in the tBLM the αHL ch

crystal structure is valid. 

D.J. McGillivray1,2

F. Heinrich1,2

M. Lösche1,2

I. Ignatjev3

G. Valincius3

D.J. Vanderah4

J.J. Kasianowicz5

1 Carnegie Mellon

University

Pittsburgh, PA

15213

2 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

3 Institute of

Biochemistry and

Vilnius Gedimino

Technical

University,

LT-2600, Vilnius

Lithuania

4 Biochemical

Sciences

Laboratory

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8312

5 Electrical and

Electronic

Engineering

Laboratory

National Institute 

of Standards and

Technology

Gaithersburg, MD

20899-8110

This enabled the characterization of the interaction between the membrane and protein usin

reflectometry (NR) at the Cold Neutrons for Biology and Technology’s Advanced Neutron

Reflectometer/Diffractometer (AND/R) [5]. 

42

FIGURE 1: 

Change in tBLM-covered electrode admittivity at ƒ = 5 Hz,

indicative of αHL incorporation, as a function of buffer pH.
the tail region of the lipid bilayer. The extension 

of the stem into the polar headgroup region on the

far side of the membrane also stabilizes the band 

of charged residues that rings the bottom of the 

stem domain.

The NR modeling shows that the protein is incorporated into the bilayer at ≈ 36 % of the estimated maximum possible packing density of the protein. This

packing density, ≈ 1 channel per 310 nm2, is qualitatively similar to that observed in lysed cells [11].

The incorporation of such a large amount of the protein in the bilayer, without bilayer collapse, emphasizes the robustness of the solid-supported system. 

The authors acknowledge useful discussions with Dr

Hirsh Nanda. This work was supported by the NSF

(grant nos. 0555201 and 0457148). ML and AND/R

are supported, through the CNBT, by the NIH under

grant no. 1 R01 RR14812 and by The Regents of the

University of California. JJK is supported in part by

the NIST Office of Law Enforcement Standards and a

NIST Single Molecule Manipulation and Measurement

Competence Award.

REFERENCES

[1] S.M. Bezrukov, J.J. Kasianowicz, Phys. Rev. Lett. 70, 2352 (1993).

[2] J.J. Kasianowicz, S.E. Henrickson, H.H.Weetall, B. Robertson,

Anal. Chem. 73, 2268 (2001).

[3] J.J. Kasianowicz, E. Brandin, D. Branton, D.W. Deamer, Proc.

Natl. Acad. Sci. U.S.A. 93, 13770 (1996).

[4] J.J. Kasianowicz, Nat. Mater. 3, 355 (2004).

[5] J.A. Dura, D. Pierce, C.F. Majkrzak, N. Maliszewskyj, 

D.J. McGillivray, M. Lösche, K.V. O’Donovan, M. Mihailescu, 

U.A. Perez-Salas, D.L. Worcester, S. White, Rev. Sci. Instr. 

(2006), in press.

[6] B.A. Cornell, V.L.B. Braach-Maksvytis, L.G. King, P.D.J. Osman,

B. Raguse, L. Wieczorek, R.J. Pace, Nature 387, 580 (1997).

[7] G. Valincius, D.J. McGillivray, W. Febo-Ayala, D.J. Vanderah, 

J.J. Kasianowicz, M. Lösche, J. Phys. Chem. B 110, 10213 (2006).

[8] S.M. Bezrukov, I. Vodyanoy, R.A. Brutyan, J.J. Kasianowicz,

Macromolecules, 29, 8517 (1996).

[9] J.J. Kasianowicz, S.M. Bezrukov, Biophys. J. 69, 94 (1995).

[10] L.Z. Song, M.R. Hobaugh, C. Shustak, S. Cheley, H. Bayley, 

J.E. Gouaux, Science 274, 1859 (1996).

[11] S. Bhakdi, J. Tranumjensen, Microbiol. Rev. 55, 733 (1991).

FIGURE 2: 

NR and fitted models of the tBLM before and after αHL exposure, measured in D2O. Fits were also constrained to other

water contrasts (not shown).

FIGURE 3: 

(Left) A scaled cartoon of the functional αHL pore incorporated into a tBLM on gold, derived from the neutron scattering

length density (nSLD) profile depicted on the right. (Right) The

nSLD profile derived from simultaneous fitting of data measured in D2O, H2O and a D2O:H2O mixture (CM4) using the 

x-ray crystal structure of the protein. The combination of EIS

and neutron reflectometry on a robust tethered membrane

system has enabled the combined study of the structure and

the functionality of a toxin with potential biotechnology applications. The functionality of the membrane is preserved in the

biomimetic environment, and the neutron reflectometry

reveals that the x-ray crystal structure is well-preserved in the

membrane-bound form of the protein. The scattering also

reveals details of the intimate binding between the protein and

the membrane, confirming predictions based on the toxin

structure.
Design of modern high

performance engineering

components requires

increased understanding

of material response to a

variety of loading conditions. However deformation processing of polycrystalline materials alters

their microstructure and

thus leads to changes in

their macroscopic properties. Therefore, to adequately predict the response of the material to any

loading condition, the ability to represent the

microstructure of the modeled material is key.

Multiscale models, such as polycrystal plasticity based

models, possess the ability to do just that by modeling the response of the individual crystals and their

interactions to accurately predict the macroscopic

response. Moreover, they offer the rare possibility of

direct comparison of simulated crystal deformationderived quantities with those obtained by diffraction.

The importance of this approach cannot be overstated because it offers the rare possibility of direct comparison of simulated crystal deformation-derived

quantities with those obtained by diffraction.

Such an approach is especially suitable for configurations in which nonuniform initial microstructures

cause strength gradients and nonuniform deformations under applied load. The stainless steel friction

stir weld samples studied here are prime examples

with relatively large-grained base material where the

size distribution peaks at 20 μm, followed by a narrow heat affected zone (HAZ) and a fine-grained

weld zone (grain size peak at 4 μm) (Fig. 1). Also,

the crystallite orientation distribution (ODF) in the

base and weld material are different, with the base

material having 

rolling texture 

exhibiting a we

texture compo

The simulation 

gy used here [

for the specim

geneity in two 

by assigning e

element the or

dependent ela

properties of a 

crystal, and second, by a similar finite el

mulation for the continuum scale, for wh

ment properties are derived from the firs

tion. This is done using a polycrystal ave

on a Taylor-like linking assumption. Furt

polycrystal average is not uniform but de

the location in the specimen to account 

scopic property gradients. Model initializ

eters include the initial local ODFs and l

dependent slip system hardness. The latt

such that it accounts for grain size differ

a Hall-Petch relationship. By tracking cer

elements with single crystal properties th

deformation, it is possible to derive certa

such as orientation dependent strain and 

orientation due to rotations. With respec

neutron experiments, the first is compare

dependent lattice strains, the second to c

peak intensities. The peak width — whic

sensitive to dislocation density and there

strain — was not used for comparison b

strongly affected by instrumental parame

deconvolution of instrumental effects on 

broadening will be the subject of future 

D.E. Boyce1

P.R. Dawson1

B. Sidle1

T. Gnäupel-Herold2

H.J. Prask 2

1 Cornell University

Ithaca, NY 14853

2 NIST Center for

Neutron Research

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8562

44

G P

H

Y

S I C

S

deformation of a friction stir welded stainless steel show good agreement with both macros

neutron diffraction data.

FIGURE 1: 

Weld zone of an actual specimen [1]. The grain size in the

weld zone (dark) is approximately 5 times smaller than in the

base material (light). The heat affected zone is not visible but

it extends about 1 mm away from the weld zone.
The diffraction experiments were conducted at the

BT8 Residual Stress Diffractometer. Several specimen

geometries with different gage section shapes were

used. The specimens were deformed in the TD-direction using a screw-driven load frame with 3-4

unloading episodes up to the final extensions > 12

mm, equivalent to more than 20 % strain. Diffraction

peaks were collected for the weld and the base separately using appropriate sampling volumes depending

on the specimen dimensions. Results are presented

for two geometries: specimen A with 6.70 mm 

(ND) × 1.98 mm (RD) and specimen B with 

3.94 mm (ND) × 3.34 mm (RD).

The elastic strains for grains in certain orientations

can be inferred directly from the change in the peak

positions in the neutron data. The results of both

measurement and simulation for weld and base material are shown in Fig. 2.

The overall agreement between simulation and

experiment is very good; if there is a difference then

it is by a constant offset, which is most likely due to

the reference d-spacing chosen to calculate the

experimental lattice strains from the d-spacings. The

results shown here along with results for other reflections [3] indicate that the change in slip system hardness is predicted correctly. Further evidence for the

performance of the simulation is found in the good

estimate of the overall hardening as seen in Fig. 3.

This graph compares the experimental and predicted

extension for a given applied force (at the start of an

unloading episode), showing very good agreement

overall.

The multiscale methodology used here for 

simulation performed well on the microscopic and

on the macroscopic scale. It represents one of the

rare attempts to reconcile microscopic and macroscale behavior in deformation and, as such, illustrates

very well the complexity necessary for the success of

such a model. As a payoff, the model is able to predict many parameters that were equally well matched

by experimental results, such as specimen shape after

deformation, crystallite orientation distribution function, and slip system strength. (For a full account, see

Ref. 3.)

REFERENCES

[1] E. Marin, P. Dawson, Comput. Method Appl. Mech. Eng. 165, 

1 (1998). 

[2] E. Marin, P. Dawson, Comput. Method Appl. Mech. Eng. 165,

23 (1998).

[3] D.E. Boyce, P.R. Dawson, B. Sidle, T. Gnäupel-Herold, accepted

for publication in Computational Materials Science.

FIGURE 3: 

Load-extension curve for specimen B for a series of loadingunloading cycles.

FIGURE 2: 

Lattice strain comparisons for base and weld material. Solid lines are Specimen A. Dashed lines are Specimen B. Black lines are

experiment. Colored lines are simulation. The uncertainties are 1 × 10-4. The symbols ⎢⎢ and ⊥ denote the scattering vector parallel

and perpendicular to the applied stress direction.
Advances in steel production have brought about

new kinds of steel, typically with substantial increases in strength without sacrificing formability. A significant fraction of steels is used in the form of sheet

metal which is usually further processed through

forming operations such as stamping and deep drawing. In order to ensure quality and cost effectiveness

in the application of these processes for production

parts, the simulation of various aspects of forming

has become a key stage in the application of these

materials. In order to characterize forming-related

properties and to compare finite element codes 

used for the simulation, standardized tests are used

in which specimens are deformed by large bi-axial

strains using complex strain paths. For a number of

years now there has been a good tradition of a

strong collaboration between industrial concerns

such as car companies and government/academia

which entails participation in sheet metal forming

benchmark tests. 

Benchmark #3: Channel Draw/Cylindrica

which is a two stage forming test consist

channel draw (Fig. 1), followed by a cup 

channel side walls [1,2]. The concept wa

not only the strain fields achieved during 

stage forming process, but also to test th

numerical models to predict both strain 

fields during multi-stage forming process

numerical results for the first stage formi

springback are essential to guarantee pro

state variables for the subsequent stage s

The main parameter varied in this test w

draw bead penetration which essentially 

magnitude of a bending/unbending cycle 

a pre-strain. The characteristic shape of a 

with draw bead pre-strain is shown in Fi

curvatures of areas A, B and C (opening 

represent the springback and it is caused 

thickness stresses.

T. Gnäupel-Herold1

D.E. Green2

T.B. Stoughton3

M.A. Iadicola4

T. Foecke 4

1 National Institute

of Standards and

Technology

NIST Center for

Neutron Research

Gaithersburg, MD

20899-8562

2 University of

Windsor

Windsor, ONT,

Canada N9B 3P4

3 General Motors

R&D Center 

Warren, MI 

48090-9055

4 National Institute

of Standards and

Technology

Metallurgy Division

Materials Science

and Engineering

Laboratory

Gaithersburg, MD

20899-8553

46

G P

H

Y

S I C

S

FIGURE 1: 

Sketch of the channel draw (first stage).

FIGURE 2: 

Equivalent plastic strain distribution for a chann

back with predicted strains. Neutron measurem

performed in area A.
neutron diffraction, higher spatial resolutions < 0.1

mm become unfeasible due to beam divergence. 

Using this technique, a series of through-thickness

measurements in area A of the channel sidewall was

performed, the results of which are shown in Fig. 4.

The results of the neutron stress measurements highlight the long-known fact that springback decreases

with higher draw bead penetration due to increased

plastic deformation. In this forming experiment

springback is characterized as the curvature of area A

which generally decreases with increasing draw bead

penetration. A similar tendency is visible in the stress

distributions where the magnitude of compressive

stresses at and near the outer surface (Fig. 2) increases with the draw bead penetration. However, the

mechanical equilibrium of both stresses and bending

moments appears to be severely affected, most likely

by intergranular stresses as suggested by the stresses

becoming overall compressive at higher draw bead

penetrations and therefore higher levels of accumulated plastic deformation. Intergranular stresses arise

because when stress is applied grains with a certain

orientation yield at different stresses than neighboring

grains (having different orientations). Upon release 

of the applied stress, grains with different orientations relative to each other are typically at different

states of residual stress. This issue cannot be resolved

from the data present; it requires either the averaging

over different (hkl) or the tracking of the change in 

d-spacing on a specimen with a similar deformation

path but without long-range residual stresses (such 

as through thickness stresses).

The neutron diffraction results presented here,

although incomplete, represent a step forward in the

methodology of making strain measurements at the

highest possible spatial resolution at moderate durations for data acquisition. The demand for such

measurements arises where two requirements have 

to be met at the same time: that for spatial resolution

≈ 0.1 mm and that for good averages, i.e., that the

strains measured are representative for larger areas 

> 10 mm2. The latter is problematic for synchrotron

radiation diffraction but becomes a necessity in 

neutron diffraction due to the need for large 

gage volumes.

REFERENCES

[1] M.C. Oliveira, A.J. Baptista, J.L. Alves, L.F. Menezes, D.E. Green,

T. Gnaeupel-Herold, M.A. Iadicola, T. Foecke, T.B. Stoughton,

Two Stage Forming: Experimental and FE Analysis, Proceedings

of International Deep Drawing Research Group (IDDRG), June

2006, Porto, Portugal.

[2] D.E. Green, T.B. Stoughton, T.Gnaeupel-Herold, M.A. Iadicola, T.

Foecke, Influence of Drawbeads in Deep Drawing of PlaneStrain Channel Sections, Proceedings of IDDRG, June 2006,

Porto, Portugal.

FIGURE 3: 

High spatial resolution strain measurement on sheet metal

specimens. The three reflected beams Q1, Q2, Q3 represent

three different orientations of the specimen. 

FIGURE 4: 

Through-thickness residual stresses (x-direction), measured in

area A.
The Neutron Imaging Facility is a thermal neutron

radiography facility located at BT-2 at the NCNR. 

It is depicted in Figs. 1 and 2. It was built and commissioned in early 2006 after the previous Neutron

Imaging Facility located at BT-6 was decommissioned. This new facility provides ample room to set

up fuel cell experiments

and provides fuel cell testing equipment, hydrogen,

nitrogen, air, deionized

water and chilled water

inside the C100 confinement room. To do this, 

an extensive safety review

was required to understand the hazards associated with the use of hydrogen gas, which is a potential hazard. After extensive

computational fluid

dynamics modeling using

the NIST Fire Dynamics

Simulator (FDS) [5] available through the

Building and Fire

Research Laboratory, it

was determined that

hydrogen accidentally or

purposefully released in

the room would turbulently mix with surrounding air lowering

the concentration below

the flammability limit 

(4 % in air by volume)

at 1.2 m above the

release point at the

maximum release rate of 22.4 L/min. Th

room the concentrations were found to 

lower than the flammability limit. This m

release rate is assured because hydrogen 

facility is produced by an electrolysis un

mum rate of 18.8 L/min. No stored inven

hydrogen are 

the possibilit

accidental re

large amoun

does not exi

Running fuel 

requires accu

over the mas

hydrogen, ai

gen that are 

the fuel cell. 

to controlling 

flow, the hum

gases must a

trolled from 

for a range o

D.L. Jacobson1

D.S. Hussey1

M. Arif 1

J. Gagliardo 2

J. Owejan2

T. Trabold2

1 Ionizing Radiation

Division

National Institute

of Standards and

Technology

Gaithersburg, MD

20899-8461

2 General Motors

Fuel Cell Activities

Honeoye Falls, NY

14472 

48

G P

H

Y

S I C

S

capability widely available to the scientific and engineering communities in the United States, 

in collaboration with the NIST Physics Laboratory Ionizing Radiation Division and General Mo

Cell Activities has built a new facility for neutron radiography that incorporates extensive infr

support for fuel cell experiments. 

FIGURE 1: 

Photo of the Neutron Imaging Facility at BT-2
tures. These functions are performed using a fuel 

cell test stand that incorporates accurate mass flow

control for all gases used by the cell. In addition to

mass flow control, an electronically controlled 

electrical load can also be applied. All of these 

features are automated to allow users to step through

an extensive series of testing protocols. 

Researchers using the facility are only required to

bring fuel cells of their own design to the facility. A

diagram of how a fuel cell works is shown in Fig. 3,

and an example of a fuel cell designed for the purpose of demonstrating tomography is shown in Fig.

4. Fig. 4 also shows the reconstructed 3-D distribution of water in the fuel cell as measured at the facility. Both the anode and the cathode are distinguished, and the water distribution is shown in slices

going from the anode to the cathode. Although water

is produced on the cathode side during cell operation, these data demonstrate that in the steady state,

unexpectedly, the anode side also remains wet.

Water formed on the cathode may be transferred

back to the anode through various mechanisms such

imaging to a variety of non-destructive and in situ

investigations, from the dynamics of two phase fluid

flows to geology and beyond are expected. Future

developments for the facility will produce an order of

magnitude increase in image resolution as well as a

further expansion of fuel cell testing infrastructure to

allow freeze-thaw testing of fuel cells.

REFERENCES

[1] R.J. Bellows, M.Y. Lin, M. Arif, A.K. Thompson, D. Jacobson, 

J. Electrochem. Soc. 146, 1099 (1999).

[2] M.A. Hickner, N.P. Siegel, K.S. Chen, D.N. McBrayer, 

D.S. Hussey, D.L. Jacobson, and M. Arif, J. Electrochem. Soc.

153, A902 (2006).

[3] P.A. Chuang, A. Turhan, A.K. Heller, J.S. Brenizer, T.A. Trabold,

and M.M. Mench, in FUEL CELL 2005, 3rd International

Conference on Fuel Cell Science, Engineering and Technology,

pp. 31–37, ASME Proceedings, New York (2005).

[4] D. Kramer, J. Zhang, R. Shimoi, E. Lehmann, A. Wokaun, 

K. Shinohara, and G. G. Scherer, Electrochim. Acta 50, 

2603 (2005).

[5] NIST Fire Dynamics Simulator and Smokeview

http://fire.nist.gov/fds/.

FIGURE 3: 

Schematic diagram of the operation of a fuel cell.

FIGURE 4: 

Results from neutron tomography of a

fuel cell running in the steady state.

The upper part shows a 3-D drawing of

the cell studied and the lower part displays the tomography data showing

water in slice planes scanned from

anode to cathode on either side of the

membrane electrode assembly (MEA).

A significant finding shown here is that

water is observed distributed on both

the anode and the cathode.
50

N M

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N T 

two for wavelengths greater than 9 Å. The second

source, for the proposed west guide hall, is necessarily a small volume of liquid hydrogen (LH2) installed

in BT-7 that will have the same spectral shape as

Unit 2, but about twice its brightness.

As in the past, the neutron performance and energy

deposition in these sources is simulated using the

Monte Carlo transport code, MCNP. Figure 1, a geometry plot of the MCNP model, shows locations of the

proposed sources. During spring and early summer,

design of the LH2 source has taken priority in preparation for the NCNR Expansion Initiative Workshop,

and the Facility Developments section of this report

contains some information about it. The cryostat

assembly of this source, including the source, insulating vacuum, helium containment and D2O cooling

jacket, must have a diameter of less than 150 mm, so

the moderator vessel has an OD of 110 mm with an

exit cavity of 80 mm ID, and an optimum LH2 thickness of about 4 mm. A 300 W to 400 W nuclear heat

load is expected, not including refrigerator load-line

and condenser losses.

Unlike BT-7, the cryogenic

beam port, CT, has a 560

mm ID thimble, offering

space for a large volume of

LD2. A wide range of sizes

and shapes have been analyzed, from a “small”, 20 L

LD2 vessel (with several percent hydrogen) to the maximum size, 460 mm OD, 60

L, vessel that could be

installed in CT with the

intensity at short wavelengths (Ï < 4 Å). 

to adjust the shape of the LD2 source spe

somewhat, by adding a small amount of 

and using a deeper reentrant hole.

A 35 L, 38 cm x 38 cm vessel was chosen 

promise to mitigate the losses below 4 Å

ent a 2000 W to 2500 W heat load that c

tially be cooled by the existing refrigerato

choices concerning the LD2 source were 

year, however, prior to the announcemen

expansion initiative. A new refrigerator m

required because tests have shown that t

of our refrigerator is likely insufficient for 

tion of the BT-7 source to the Unit 2 load

refrigerator would have the capability of 

the LD2 and BT-7 sources. Full-scale moc

both will be tested to ensure that each ca

with a naturally circulating thermosiphon

operated very reliably in this mode.

Liquid Deuterium

 Cold Source

BT-7

Liquid Hydrogen

 Cold Source

P. Kopetka

R.E. Williams

J.M. Rowe 

NIST Center for

Neutron Research

National Institute 

of Standards and

Technology

Gaithersburg, MD

20899-8560

FIGURE 1: 

Left: northwest 

NBSR core, sho

posed cold neut

(CNS) upgrades

LH2 source in t

be replaced by 

volume, 35 L liq

source, and a n

source, just 0.7

installed in BT-7 

Guide Hall. Righ

comparison of t

CNS to Unit 2. 
the market basket study,

is an ongoing FDA program that determines

levels of various contaminants and nutrients in

foods. FDA’s Laboratory

at the NCNR provides quality assurance instrumental

neutron activation analysis (INAA) for this FDA’s this

program [1]. To improve element limits of detection [2]

(LODs), especially for iodine (recently added to the

TDS Program), a Compton suppression system that

discriminates eliminates against strayscattered background photons by using a coincident signal from a

scintillator surrounding the Ge detector, previously

used for prompt gamma-ray activation analysis, was

converted to an INAA instrument. Combined with new

irradiation and counting procedures, LODs improved

by up to a factor of 4 for 16 elements with short-lived

neutron capture products (half-lives of about 2 min to

1.5 d). Iodine mass fractions (0.075 to 2.03) mg/kg)

were measured in 17 of 40 TDS foods, with LODs

ranging from (0.03 to 1.4) mg I/kg. 

Irradiation facilities at the NCNR, accessed through

“rabbit tubes” (RTs), are highly thermalized. To determine the best irradiation site for iodine measurements

(i.e., which location had the greater epithermal and

fast neutron component), NaCl/KI standards were irradiated in central and peripheral positions in RT1 and

RT4. The central RT1 location was chosen for irradiations because it showed a 16 % enhancement of

iodine activity over Na and Cl activity vs. the RT4

peripheral location. Forty foods from the TDS Program, multielement standards, NaCl fluence/geometry

monitors, blanks, and control portions (NIST SRMs

1572 Citrus Leaves, 1566a Oyster Tissue, 1549 Milk

Powder, and 1846 Infant Formula) were analyzed.

Irradiations were performed for 10 s with counts

beginning 2 to 3 min later. Count times were 30 min,

with spectral data also saved after an initial 10 min

count time for analysis of the short-lived species.

Compton suppression INAA results for TDS foods

were compared to previous INAA procedures that

used RT4 with singles counting and a 9 % relative efficiency Ge detector. (“Singles” are data collected at 

the Ge detector without any reference to coincidence

background reductions.) Figure 1 shows the effect of

Compton suppression for iodine analysis compared to

a simultaneous singles count for the same system and

to the previous procedure. For all foods, an LOD

improvement of about a factor of 4 was observed.

Compton suppression results yielded LODs (and therefore limits of quantitation: LOQs) an average of 40 %

lower than for singles data collected on the same system. A summary of the results for 16 elements in 40

TDS foods is given in Table 1. Greatest improvement

is shown for Cu, K, Mn, and Ca. For control SRMs,

agreement with certified values was found for all elements (All z-scores are < 1.7, where scores < 2 indicate agreement. A z-score of +1.7 corresponds to a

measurement being 1.7 standard deviations above the

mean [3].) 

REFERENCES

[1] Total Diet Study website: 

http://www.cfsan.fda.gov/~comm/tds-toc.html

[2] L.A. Currie, Anal. Chem. 40 (1), 586 (1968).

[3] M. Thompson, R. Wood, J. AOAC Int. 76, 926 (1993).

D.L. A

W.C. 

Eleme

Resea

(HFS-

U.S. F

Admi

Colleg

20740

FIGURE 1. 

Comparison of spectral data (30 min count times) for the

iodine region for TDS food # 177 vanilla ice cream, light. Top

and bottom spectra are from the present study (portion

mass: 2.0 g). Middle spectrum is from previous work (portion

mass 1.6 g).

28Al 1779 2.25 min 0.60-18 1.12 15 7

51Ti 320 5.76 min 0.83-32 1.28 3 3 52V 1434 3.75 min 0.010-0.22 1.42 10 4 87mSr 388 2.81 h 1.0-53 1.36 2 0 76As 559 26.32 h 0.28-15 1.50 0 0

a e.g., for I, 9 of the 17 values > LOD were also > LOQ
E.A. Mackey1

C.N. Fales1

R.R. Greenberg1

M.P. Kronise1

S. Leigh1

S.E. Long1

K.E. Murphy1

R. Oflaz1

J.R. Sieber1

M.S. Rearick1

L.J. Wood1

L.L.Yu1

P.F. Kane 2

W. Hall 3

1 National Institute

of Standards and

Technology

Analytical

Chemistry Division

Gaithersburg, MD

20899-8390

2 Office of Indiana

State Chemist

Purdue University

West Lafayette, IN

47907-2063

3 The Mosaic

Company

Mulberry, FL 

33860

52

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obtained using these methods. A new Standard

Reference Material, SRM 695 Trace Elements in 

Multi-Nutrient Fertilizer, was developed to help meet

these new requirements. SRM 695 has recently been

issued with certified mass fraction values for 17 

elements, reference values for five elements, and

information values for two elements. 

Until 1998, U.S. fertilizer manufacturers generally

were required to guarantee only the nutrient content

of their products. However, the recent discovery of

high levels of As in some iron-based fertilizer materials and high levels of Cd in some zinc-sulfate based

fertilizer materials prompted some states to enact regulations limiting the amount of selected non-nutritive

(potentially toxic) elements in fertilizer materials. To

date, ten states have enacted or proposed regulations,

and other states are expected follow suit. When the

non-nutritive metals As, Cd Co, Hg, Mo, Ni, Pb, Se

and Zn were first limited by regulation in the U.S.,

there were few certified reference materials (CRMs)

available to assist manufacturing and regulatory 

laboratories in method development and measurement validation and none with matrices similar to

typical agricultural or homeowner fertilizer blends.

NIST worked with the members of the manufacturing

and regulatory community to develop the new SRM

695 Trace Elements in Multi-Nutrient Fertilizer. 

The experimental design for certification of SRM 695

was based on the use of two or more independent

analytical techniques performed at NIST to provide

values for all regulated elements and for the nutrient

elements (B, Ca, Cu, Fe, K, Mg, Mn, N, and P) and

other elements if possible. The approach relied on

non-destructive analytical techniques, instrumental

neutron activation analysis (INAA), prompt gamma

ray activation analysis (PGAA) and x-ray fluorescence

spectrometry (XRF) for most elements. A combination

of inductively coupled plasma optical emission 

spectrometry (ICP-OES), ICP-mass spectrometry 

(MS) and cold vapor isotope dilution (CV-ID) 

ICP-MS was used for six elements. 

Expression of Uncertainty in Measuremen

Special Publication 1297 [2,3]. Reference 

provided when only one analytical techn

used or in cases for which there was not 

evaluation of all sources of uncertainty. (

for a complete description of certified, re

information values for SRMs.)

TABLE 2. CERTIFIED AND REFERENCE MA

FRACTION VALUES FOR SRM 695

Element Methods Used Certified V

As INAA (200 ± 5) m

Ca INAA, XRF 2.26 % ± 0

Cd INAA, ID-ICP-MS (16.9 ± 0.2

Co INAA, XRF (65.3 ± 2.4

Cr INAA, XRF (244 ± 6.2) 

Cu ID-MS, ICP-OES, XRF (1225 ± 9) 

Fe INAA, PGAA, XRF 3.99 % ± 0

Hg ID-MS (1.955 ± 0.

K PGAA, XRF 11.65 % ± 

Mg INAA, XRF 1.79 % ± 0

Mn INAA, PGAA, XRF 0.305 % ± 

Mo ICP, XRF (20.0 ± 0.0

Ni ICP, XRF (135 ± 2) m

Pb ICP-OES, XRF (273 ± 17) 

Na INAA, XRF 0.405 % ± 

V INAA, XRF (122 ± 3) m

Zn INAA, XRF 0.325 % ± 

Element Method Reference 

Al INAA, XRF 0.61 % ± 0

B PGAA 0.111 % ± 

N PGAA 13.9 % ± 0

P XRF 7.2 % ± 0.1 

Se INAA (2.1 ± 0.1) 

REFERENCES

[1] M.S. Levenson, D.L. Banks, K.R. Eberhardt, L.M. 

W.F. Guthrie, H.K. Liu, M.G. Vangel, J.H. Yen, N

J. Res. NIST 105, 571 (2000).

[2] Guide to the Expression of Uncertainty in Measu

92-67-10188-9, 1st Ed. ISO, Geneva, Switzerland, 

[3] B.N. Taylor, C.E. Kuyatt, NIST Special Publication 

Guidelines for Evaluating and Expressing the Un

NIST Measurements Results 1994 Edition. 

[4] W.E. May, T.E. Gills, R.Parris, C.M. Beck II, J.D. F

R.J. Gettings, R.R. Greenberg, F.R. Guenther, G. K

B.S. MacDonald, S.A. Wise, Definitions of Terms 

Used at NIST for Value-Assignment of Reference 

Chemical Measurements NIST Special Publication 
has seen remarkable growth in research, develop

ment and application in recent years. This is due to

the ability of FSW to join a variety of alloys that can

be dissimilar, difficult to weld in fusion welding, and

to produce defect free welds with favorable strength

properties without going through a melting process.

FSW is heavily utilized in the aircraft industry where

it offers the possibility of unitized structures made up

of parts of different alloys and joined by FSW, thus

reducing the cost associated with alignment and

assembly. 

A significant potential contributor to the durability

behavior of FSW joints and surrounding material,

however, will be the magnitude and distribution of

residual stresses as an important influence on crack

growth rates. Therefore, knowledge of residual stresses is crucial if accurate property measurements are

required. Neutron diffraction is among the best-established methods for measuring sub-surface, tri-axial

residual stresses which makes it useful as a comparative benchmark for other techniques such as the contour method [1]. The basic idea of this technique is

as follows: One starts with an undisturbed part containing the stresses to be determined. Then, the part

is cut in two which releases stresses and causes distortion on the cut surfaces of the two halves. The

distortions can be measured very precisely by, for

example, confocal laser ranging probes (used here).

specimen was then cut by EDM and the contour

analysis was performed (Fig. 1) using a mesh with

approximately 30 locations per mm2. The stresses

obtained by the two methods are shown in Fig. 2.

There is a general agreement between the two methods, and the findings show the ability of FSW to produce welds with low stress magnitudes (6 % of the

yield strength) even in structures as thick as 25 mm.

The subtle differences can be attributed to variations

of the unstressed d-spacing and to the presence of

intergranular stresses. The first is caused by inhomogenous mixing of the two parent materials [2], creating

mm-sized regions with differing d0, the second is due

to the fact that both parent plates were stretched by

1.5 % prior to welding, thus creating grain-orientation

dependent stresses between grains. The contour

method, while being destructive, demonstrates superior area resolution and it is independent of the two factors affecting the neutron measurements.

REFERENCES

[1] M.B. Prime, Journal of Engineering Materials and Technology

123, 162 (2001).

[2] M.B. Prime, T. Gnäupel-Herold, J.A. Baumann, R.J. Lederich,

D.M. Bowden, R.J. Sebring, accepted for publication in 

Acta Mat.

M.B. 

T. Gn

H.J. P

J.A. B

R.J. L

D.M. 

R.J. S

1 Los 

Nati

Labo

Los 

8754

2 NIST 

Neu

Nati

of S

Tech

Gait

2089

3 The 

Com

St. L

6316

FIGURE 1: 

Elastic finite element of half of test specimen with cut surface

deformed into opposite of measured surface contour.

Displacements magnified by factor of 1000. Part dimensions

before the cut were 162(x) × 54(z) × 25.4(y) (in mm).

FIGURE 2: 

Stresses normal to the mid-plane (Fig.1) at 12.7 mm depth.
ments (B, Li, Cl, N, for

example) provides a

powerful, non-destructive method for determining concentration as

a function of depth

below a surface with

sub-nanometer resolution. In PGAA, the

enhanced probability of

neutron capture that

cold neutrons provide,

translates into increased

sensitivity to elements,

such as hydrogen, that

give off a characteristic

gamma ray essentially

instantaneously after

absorbing a neutron. Specialized instruments for both

techniques have been in operation at the NCNR for

over fifteen years, often at locations with higher than

ideal ambient background radiation. A dedicated

beam line is now under development to alleviate this

situation and provide a more accessible and flexible

sample area for both instruments.

The beam for the NDP and PGAA instruments will

come for a curved supermirror-coated neutron guide

(critical angle = 3x natural nickel) that will direct a 5

cm wide x 4 cm high portion of the NG-7 neutron

guide away from the main beam line to provide a

dedicated beam in a lower background environment

for these instruments. The curved guide is preceded

by a tapered section to increase the flux by compressing the beam size to 3 cm x 3 cm. The compressed beam will then pass through a segmental arc

of 50 cm long guide sections to deflect the beam by

9°. Following the bend is 5 m of straight guide to

homogenize the beam and increase the lateral separation from the main guide (see Fig. 1). 

mounts tha

either instr

easily mov

higher flux 

position. T

space also 

additional 

for future d

The develo

new station

NDP and P

ments is pa

project to re

NG-7 guide 

rate an opti

ilar to that 

the NG-3 gu

serving the CHRNS 30-m SANS instrumen

ation of the optical filter, neutron bender

redesigned space and shielding for the N

PGAA instruments is scheduled for early 

INSTALLATION OF THE HIGH INTENSITY M

COLD NEUTRON SPECTROMETER (MACS) 

The highly innovative multi-axis crystal s

MACS, is being installed in thermal neutr

hall on the one beam line, NG-0, that vie

ent cold neutron source through a nearly 

diameter beam port. This prime location

the instrument’s 1400 cm2 doubly focusi

chromator, promises to make MACS perh

highest flux cold neutron spectrometer in 

Nearly all of the beam conditioning com

for MACS have been installed. These inc

able beam aperture to minimize backgro

control wave vector resolution, a four-po

collimation system to control energy reso

the translating, doubly focusing graphite 

mator. All of these components are hous

helium-filled cask to further reduce back

from air scattering. 

54

FIGURE 1: 

Computer model of the analytical chemistry NDP and PGAA instruments as they will be configured on the new neutron bender to be

installed on the NG-7 neutron guide.
Proceeding in parallel with the beam line installation

has been the detailed engineering of the multi-axis

analyzer/detector section of MACS. This section of

the instrument, shown in the model in Fig. 3, comprises 20 identical detection channels, each with a

vertically-focused, double graphite crystal analyzer

and individual detector tubes, in a common shielded

housing. Fronting the radial array of detection channels will be automatically interchangeable soller collimators and cryogenically cooled beryllium, beryllium

oxide and graphite filters. 

The first beam characterization measurements on

MACS will take place before the end of 2006, while

the multi-axis detection system is being assembled

and tested offline. The first actual experiments with

this system in place are planned for mid-2007. 

In support of the NCNR Expansion Initiative (see

page 58) working groups have been formed to develop conceptual designs and implementation plans for

all aspects of this initiative. One group, made up primarily of staff scientists and engineers, has been

studying the feasibility and projected performance of

the new cold source and neutron guide configuration

that is at the heart of the expansion. Neutron transport calculations have been carried out in conjunction with structural and hydrodynamic calculations to

arrive at a design that achieves high source brightness and optimal guide illumination. The source calculations indicate that a liquid hydrogen source located in a beam tube would have a higher brightness

than the existing large volume source; perhaps by as

much as a factor of two for 15 Å neutrons. The engineering calculations indicate that this performance

can be achieved with the same type of passive thermo-siphon technology used with the present cold

source, which has proven to be highly reliable and

safe to operate. Figure 4 shows a computer model of

one possible configuration of the new source in relation to the geometry of a beam tube.

FIGURE 3:

Model of the assembly of components comprising the 6-axis

sample positioning stage and the 20-channel crystal analyzer/detector section of the MACS spectrometer. 
A second working group has been gathering requirements for upgrades to utilities and other facility infrastructure that would be needed for a second neutron

guide hall and associated office and laboratory space.

Finally, a third group has been exploring and soliciting ideas for new neutron instrumentation and 

scientific opportunities that would be enabled given

the expected performance characteristics of the new

cold source.

IMPROVEMENTS IN SAMPLE ENVIRONMENT

EQUIPMENT

A small but dedicated group of scientists and technicians at the NCNR develops and maintains an ever

expanding variety of sample environment equipment

for neutron scattering experiments. Recent additions

to the inventory of available equipment include:

Top Loading Closed Cycle Refrigerators (TLCCRs)

capable of reaching temperatures from 5 

800 K; upgraded bottom-loading CCRs ca

reaching temperatures from 5 K to 325 

superconducting magnet; and a variety o

sticks” for use with the TLCCRs including 

tomized for gas-loading, high pressure, a

voltage experiments. 

Considerable information on the nanosca

of complex fluids can be derived from S

urements with the fluid subjected to con

steady or oscillatory shear stresses. For s

the NCNR has had a couette shear cell w

been used extensively to explore shear-i

structural changes in colloids and microe

More recently, a commercial research rhe

been adapted for use on the SANS instru

enable rheological data to be collected d

ing measurements. The rheometer cell al

56

FIGURE 4: 

a) A cross sectional view of one possible configuration of the new liquid hydrogen cold source within the BT-7 beam tu

b) Expanded view of the innermost section of the cold source showing the reentrant cylindrical geometry of the liquid 

hydrogen chamber.

FIGURE 5:

Research scientist Lionel Porcar (left) and mechanical engineer Jim Moyer (right) install the new alignment fixtures they designed to improve the accuracy

and reproducibly of the coaxial alignment of the cup

and bob on a commercial fluids rheometer for use

on the NCNR’s SANS instruments.
ette geometry and may be cooled or heated over a

wide range (– 20 °C to 150 °C) by flowing nitrogen

gas. The cell is also equipped with a vapor seal to

inhibit sample evaporation without interfering with

accurate rheological measurements, and an outer

layer of trapped dry cover gas to prevent condensation when measurements are made at temperatures

below the ambient dew point. The latest improvement in this apparatus is a reengineered alignment

system (seen in Fig. 5) that allows the cell to be

readily removed for cleaning and quickly realigned,

thus saving considerable time when changing samples. Included in the cell support is a holder for precisely positioning beam-defining masks for measurements in both radial (beam intersects cylindrical rotation axis of cell) and tangential geometries (beam

passes through gap between coaxial cylinders). 

With the improved shear apparatus, measurements in

both the velocity-vorticity (1-3) and the velocity gradient-vorticity (2-3) planes are possible. However, it

is often desirable to make measurements in any

direction between the velocity and velocity-gradient

directions (1-2 plane). For this purpose a new type of

couette shear cell has been designed, in collaboration

with Prof. Norm Wagner at the University of

Delaware, which allows the beam to be incident

along the vorticity direction. The increased path

length in this cell, 5 mm, for use with deuterated solvents, typically produces enough scattered intensity

distinguish wall effects on the observed scattering

patterns. The prototype cell tested thus far is now

being refined to be easier to use and more robust

and will then be available for user experiments.

INSTRUCTIONAL VIDEOS FOR USERS

To further aid users in preparing for and running an

experiment, the sample environment group has

begun producing freely accessible instructional

videos. The latest video, Fig. 6, takes the mystery out

of refilling cryostats with liquid cryogens. This 6.58

minute movie is a comprehensive supplement to the

short manual found in the equipment booklets. It can

be used as either an introduction to or review of the

art of refilling cryostats. The visual cues and directives are intended to help users avoid common pitfalls and make the refilling process generally less

cumbersome. Available in multiple formats, the

movie as well as other videos on loading and

unloading sample cans can be found under the

“How-to Videos” subsection of the NCNR’s sample

environment website:

http://www.ncnr.nist.gov/equipment/ancequip.html.

REFERENCE

[1] Cook, J.C., Glinka, C.J., Schroder, I.G., Rev. Sci. Instrum. 76,

025108 (2005).
FIGURE 1:

Roland Gähler (ILL) presents his vision for next generation

instrumentation and methods in a plenary session at the

NCNR Expansion Workshop.

The proposed FY07 federal budget includes funding

to begin a major, five-year project to expand the

NIST Center for Neutron Research. Specifically, the

project includes a second guide hall, new cold

source, and five additional instruments. When completed, this project would result in a substantial

expansion in cold neutron measurement capability at

NIST and will allow us to exploit the latest neutron

methods and open up new capabilities to the U.S.

research community. The proposal is making its way

through the congressional budget process as this

report is being prepared.

To prepare for this exciting opportunity, we have

been actively soliciting input from the neutron user

community to collect ideas on what types of new

instrumentation can best serve the future research

needs of the U.S. research community. This effort

neutron researchers from academia, indu

government. Participants at the worksho

ed a broad research community, includin

neutron instrumentation, neutron detecto

optics, polymer science, complex fluids, 

magnetic systems, small molecule system

nuclear physics. In order to stimulate an 

for discussion of new neutron instrumen

the associated scientific opportunities the

participants were asked to provide writte

tions on research opportunities within th

expertise in advance of the workshop. T

began with a general overview of the ex

project, a discussion of how the NCNR e

into the larger U.S. neutron scattering pic

presentation of the expected performanc

cold source. Later, members divided into 

groups covering specific topical areas. T

were charged with producing a summary 

with suggestions in their respective areas

chairs of each group convened on the se

summarizing these suggestions and discu

cutting issues. A final report, based on th

ments gathered by a NIST team, is being 

guide planning for the enhanced facility 

will best meet the needs of the commun

executive summary of this report is post

NCNR website. 

58

FIGURE 2:

The Instrumentation Conc

group at work at the NCN

Workshop. Around the tab

heading back: David Mildn

Roland Gähler (ILL), Mike 

(NCNR), Lee Robertson (O

Georg Ehlers (ORNL), Igor 

(BNL), John Copley (NCNR

Passell (BNL), and Don Pi
FIGURE 3:

Engineer Tony Norbedo places a test module designed to monitor thermal shield performance.

This year, the NIST reactor operated for 266 full

power (20 MW) days or 99 % of the scheduled time.

A typical operating year consists of seven cycles. A

cycle consists of 38 days of continuous, full-power

operation followed by 11 days for maintenance, refueling, and startup preparations. The facility is operated under a license from the U.S. Nuclear Regulatory

Commission (NRC). Currently, an application for

renewal of the license is under consideration by the

NRC, and regulations allow for continued operation

under the original license until there is a final decision on the application. 

FIGURE 4:

Operator Ricky Sprow testing a portion of a newly installed

condensate removal system.

efforts focus on developing detailed plans and equipment for the installation of the new tank. The thermal shield cooling system was fit up with new diagnostic equipment to gauge the effectiveness of

changes to the system, including pump modifications

and the recent addition of a helium gas blanket for

the storage tank water. Major upgrades to the building ventilation system were completed with the

replacement of filters, fans, and controllers using the

newest technology to maintain flows and pressures.

All electrical switchboards in the facility were thermographically inspected and characterized. These

tests are necessary for the future upgrades to the

building’s electrical equipment.

Our engineering team added both an experienced

electrical engineer and mechanical engineer to its

staff. For the first time, reactor operator biennial

requalification was conducted over four separate

training periods instead of one. This eliminated the

need to shutdown the facility to retrain the operations staff. The two operator candidates hired last

year are expected to be licensed by the NRC soon

and recruiting efforts continue to fill expected vacancies. The NCNR continues to work closely with NIST,

local, county, and federal officials in a variety of

areas including environmental management, emergency response, and security.
lished in 1962, recognizes an unusually significant

research contribution to science or engineering that

merits the acclaim of the scientific world and supports NIST’s objectives. This award consists of an

engraved plaque and a $5,000 honorarium. 

TANER YILDIRIM RECEIVES

THE 2006 NSSA SCIENCE

PRIZE 

Taner Yildirim of the NCNR

is the recipient of the 2006

Science Prize of the Neutron

Scattering Society of America

with the citation: “For his

innovative coupling of first principles theory with

neutron scattering to solve critical problems in 

materials science”. The Neutron Scattering Society 

of America (NSSA) established the Science Prize to

recognize a major scientific accomplishment or

important scientific contribution within the last five

years using neutron scattering techniques. The prize

and a $2,500 honorarium were awarded at the June

2006 ACNS meeting in St. Charles, IL.

JOHN BARKER RECOGNIZED

WITH NIST SAFETY AWARD

John Barker of the NCNR 

was awarded the NIST Safety

Award as part of a group

award for superior accomplishments in implementing NISTwide safety activities as articulated in the NIST Safety Plan, and for demonstrating

outstanding leadership by successfully coordinating

these activities among various NIST organizational

units. The Award consists of a framed certificate 

and an honorarium.

users of the NIST Center for Neutron Res

received the award at the annual NIST C

Xi Banquet in May.

DEPARTMENT OF COMMERCE

BRONZE MEDAL AWARDED

TO ROBERT DIMEO

Rob Dimeo of the NCNR,

who is currently serving at

U.S. Office of Science and

Technology Policy, was

awarded the Department of

Commerce’s Bronze Medal “For his leade

development of the DAVE suite of neutron 

data reduction, analysis, and visualizati

tools that are widely used at NIST and at 

research centers around the country” in 

2005. The Bronze Medal recognizes supe

formance characterized by outstanding o

contributions which have increased the e

and effectiveness of NIST. It is the highe

award granted by the NIST Director.

BRIAN TOBY GRANTED DEPARTMENT OF 

COMMERCE BRONZE MEDAL

Brian Toby, who recently moved from th

the Advanced Photon Source, Argonne N

Laboratory, was awarded the Departmen

Commerce’s Bronze Medal “For the deve

a suite of software programs for powder d

crystallography” in December, 2005. The 

Medal recognizes superior performance 

by outstanding or

significant contributions which have

increased the efficiency and effectiveness of NIST. It is

the highest honorary

award granted by

the NIST Director.

60
sionals at the outset of their independent research

careers. The honor was presented at the White

House in July in a ceremony presided over by John

H. Marburger III, Science Advisor to the President

and Director of the White House Office of Science

and Technology Policy.

DIVYA SINGH WINS NSSA THESIS RESEARCH PRIZE

Divya Singh, a graduate student at Johns Hopkins

with Robert Leheny and a guest researcher at the

NCNR, has been awarded the NSSA Prize for

Outstanding Student Research by the Neutron

Scattering Society of America at the June 2006 meeting of the ACNS in St. Charles, IL. The prize recognizes neutron scattering research that has been performed as part of a thesis or degree. The award consists of a certificate, plaque,

and $500. The presented work,

based on collaboration with

NCNR and ORNL scientists, is

entitled “Self-assembly models

for binary phospholipid 

mixtures: Understanding 

bicelle formation”.

HUI WU AWARDED THE S. J. STEIN PRIZE AT THE

UNIVERSITY OF PENNSYLVANIA

Hui Wu, a guest researcher at the NCNR, has been

selected to be the co-recipient of the 2006 S. J. Stein

prize awarded to a Ph.D. degree recipient “for 

superior achievement in the field of new or unique

materials or applications for

materials in electronics” by the

Department of Materials

Science and Engineering at the

University of Pennsylvania. The

recognition includes $500 and

a certificate. Hui worked with

Peter Davies at Penn.

“Membrane structure and assembly” at the meeting of

the Biophysical Society in February. The title of his

poster, based on measurements using AND/R at the

NCNR, was “Determining FGFR3 Transmembrane

Domain Topology Using Neutron Diffraction”.

MATTHEW PAOLETTI RECEIVES

THE APS 2005 APKER AWARD 

Matthew Paoletti, physics graduate of Bucknell University and

currently a physics graduate

fellow at the University of

Maryland at College Park in

nonlinear dynamics, was the

recipient of the 2005 LaRoy Apker Award for

“Experimental Studies of the Effects of Chaotic Mixing

on an Advection-Reaction-Diffusion System” presented at the March meeting of the American Physical

Society. Matt spent two summers at the NCNR as a

SURF student characterizing and developing 

bioencapsulated enzymatic proteins.
PROPOSAL SYSTEM

A significant fraction of the time on NCNR instruments is made available through a competitive, 

peer-review proposal process. The NCNR calls for

proposals approximately twice a year. Proposals are

reviewed at several different levels. First, expert

external referees evaluate each proposal on merit

and provide us with written comments and ratings.

This is a very thorough process where several 

different referees review each proposal. Second, the

proposals are evaluated on technical feasibility and

PARTNERSHIPS

The NCNR may form partnerships with o

institutions to fund the development and 

of selected instruments. These partnershi

“Participating Research Teams”, may hav

as much as 75 % of the available beam t

instrument depending on the share of to

born by the team. A minimum of 25 % o

able beam time is always made available 

the NCNR proposal program to all users. 

are negotiated for a fixed period (usually 

and may be renewed if there is mutual i

a continued need. These partnerships ha

to be an important and effective way to 

research community’s access to NCNR ca

and have been very successful in develo

new instruments. 

COLLABORATION WITH NIST

Some time on all instruments is available 

staff in support of our mission. This tim

to work on NIST research needs, instrum

development, and promoting the widesp

neutron measurements in important rese

particularly by new users. As a result of 

objectives, a significant fraction of the tim

to NIST staff is used collaboratively by e

who often take the lead in the research. 

through such collaborations is managed 

written beam time requests. In contrast 

beam time requests are reviewed and ap

internally by NCNR staff. We encourage 

ested in exploring collaborative research 

ties to contact an appropriate NCNR staff 

62

THE CURRENT PAC MEMBERS ARE:

■ Kenneth Herwig (Oak Ridge National 

Laboratory, chair) 

■ Andrew Allen (NIST Ceramics Division) 

■ Collin Broholm (Johns Hopkins University) 

■ Ken Chen (Sandia National Laboratories)

■ Mark Foster (University of Akron) 

■ Michael Kent (Sandia National Laboratories) 

■ Ramanan Krishnamoorti (University of Houston) 

■ Joanna Krueger (University of North 

Carolina at Charlotte) 

■ Young Lee (Massachusetts Institute 

of Technology) 

■ Robert Leheny (Johns Hopkins University) 

■ Lee Magid (University of Tennesssee, Knoxville) 

■ Janna Maranas (The Pennsylvania State

University) 

■ Dawn Sumner (University of California, Davis)

■ Michael Toney (Stanford Synchrotron 

Radiation Laboratory) 

■ John Tranquada (Brookhaven 

National Laboratory)
RESEARCH PARTICIPATION AT THE NCNR

The NCNR continued its strong record of serving the

U.S. research community this year. Over the 2006 

fiscal year, 2,143 research participants benefited from

use of the NCNR. (Research participants include users

who come to the NCNR to use the facility as well as

active collaborators, including co-proposers of

approved experiments, and co-authors of publications resulting from work performed at the NCNR.)

Research participants represented 241 external institutions, including 140 U.S. universities, 41 national 

laboratories, and 60 U.S. industries. The NCNR is 

a national facility, with participants from 40 states, 

DC, and Puerto Rico. 

2006 NCNR PROPOSAL PROGRAM

Two calls in the past year resulted in the submission

of 600 proposals, a record number, of which 376

were approved and received beam time. The oversubscription, i.e., the ratio of days requested on all

proposals to the days available, was 1.9 on the average, but as high as 2.9 for specific instruments in one

call. Proposal demand has grown constantly since

the NCNR first began accepting proposals in 1991,

and has doubled in the past six years. The following

table shows the data for several instrument classes:

IMAGING FACILITY JOINS USER PROGRAM

In the latest call for proposals, 25 % of the time 

available on the new Neutron Imaging Facility was

offered to the general user community. Twelve proposals were submitted, yielding an oversubscription

of about a factor of two in terms of instrument days.

These proposals covered a wide range of topics 

from archeology to mechanical engineering, and we

foresee that the demand for, and the diverse applications of, neutron imaging will continue to grow in

coming years.

USER GROUP HOLDS FIRST ELECTION

The NCNR User Group (NUG) provides an independent forum for all NCNR users to raise issues or 

concerns to the NCNR. The NUG works through its

executive officers to carry out this function. In

December 2005, it held its first online election of 

officers. The winning candidates are Kalina Hristova

(Johns Hopkins University), Stephan Rosenkranz

(Argonne National Laboratory), Roger Pynn (Indiana

University), and Goran Gaˇsparovi ́c (formerly at MIT,

now at NIST). Other current members of the NUG

executive are Tonya Kuhl (University of California,

Davis), Robert Leheny (Johns Hopkins University),

and Nitash Balsara (University of California,





                    

\HDU

1&1

VW &ROG 6R

TABLE 1

Instrument class Proposals Days requested Days allocated

SANS and USANS 288 979 487

Reflectometers 66 490 399

Spectrometers 234 1607 741

Imaging 12 65 35

TOTAL 600 3141 1662
Berkeley, chair). The NUG executive meets monthly

via a conference call and occasionally meets in person when the opportunity presents itself at national

meetings. In addition, as part of the NCNR Expansion

Workshop held in Bethesda, MD, in July, we held 

the first meeting of the NUG including an open

forum for discussion at the workshop banquet.

Robert Leheny represented the executive officers 

at the meeting. 

NEW PARTNERSHIP WITH GM

NIST and General Motors have joined forces to

exploit the capabilities of neutron imaging for

research on fuel cells for automotive applications. In

2006 a new imaging facility developed under a NISTGM Participating Research Team was commissioned

at BT-2. Because it allows researchers to see the distribution of water directly and in real time, neutron

imaging offers a unique means of evaluating the performance of operating fuel cells. This capability has

recently received independent credit in a report from

the National Academy of Sciences, which states that:

“The NIST effort ... is a considerable achievement

and one of the most significant analytical advances in

the membrane fuel cell realm in decades. The NIST

facility offers the entire fuel cell community unique

research opportunities that previously eluded them.”

THE CENTER FOR HIGH RESOLUTION NEUTRON 

SCATTERING (CHRNS)

The Center for High Resolution Neutron Scattering

(CHRNS) is a national user facility that is jointly 

funded by the National Science Foundation and the

NCNR. The primary aim of this partnership is to

maximize access to state-of-the-art neutron scattering

instrumentation for the academic research community

through the NCNR’s proposal system. Proposals for

use of the CHRNS facilities are considered solely 

on the basis of scientific merit or technological

importance. 

ceramics, magnetic materials, porous me

and gels, and biological molecules. Abou

users of scattering instruments at the NC

instruments that are part of CHRNS and 

40 % of the publications that report scatt

from the NCNR contain research perform

six instruments. 

A particularly important aspect of CHRN

enhanced service it provides to users. Ex

this include staff to maintain and operate 

ed range of sample environment equipm

assist users in well-stocked wet laborator

development of data reduction, visualiza

analysis software through the DAVE pack

CHRNS also supports education and outr

grams that are aimed at strengthening th

community in the U.S. In particular, CH

sors a variety of activities designed to he

next generation of neutron scientists incl

annual CHRNS summer school (see next 

The success of these education and outr

efforts is perhaps best exemplified by th

than 20 Ph.D.’s that are awarded by U.S. 

each year for work done at least in part 

CHRNS instruments.

TWELFTH ANNUAL CHRNS SUMMER SCH

Training young scientists in the theory an

of neutron scattering is an ongoing activ

NCNR. The week-long school that the N

every summer is a very effective way of 

graduate students and postdoctoral resea

neutron scattering. The 2006 summer sc

ed 80 applicants for the 36 available plac

school, sponsored by CHRNS, alternates 

in successive years between dynamical a

methods. This year the school focused o

Following introductory lectures and a fac

“hands-on” groups of six were formed a

though experiments using SANS and USA

to study clay dispersions in water, bicelle

micelles in solution, and void formation 

copper metal, as well as neutron reflecto

64
Figure 3:

NCNR guest researcher David Worcester (U. Mo., left)

provides summer school participants some advice on

reflectometry.

COLD NEUTRONS FOR BIOLOGY AND TECHNOLOGY

(CNBT)

Another major partnership, the CNBT, is dedicated to

studies of biological membrane systems and is funded by the National Institutes of Health (NIH-NCRR)

along with contributions from NIST, the University of

California, Irvine, the University of Pennsylvania, and

Carnegie Mellon University. The CNBT collaboration

maintains the Advanced Neutron Diffractometer/

Reflectometer (AND/R) for structural biology, shares

10 % of the time on the NG-7 30 m SANS 

diffractometer, and operates a fully equipped biology

laboratory as well as two state-of-the-art computer

clusters – one at the NCNR and one at UC Irvine –

for molecular dynamics simulations. This combination

provides a unique and powerful suite of capabilities

to assist U.S. researchers interested in structural 

biology problems involving membranes. 

proposal system. Consortium members conduct 

independent research programs primarily in the area

of large-scale structure in soft matter. For example,

ExxonMobil has used this instrument to deepen 

their understanding of the underlying nature of

ExxonMobil’s products and processes, especially in

the fields of polymers, complex fluids, and petroleum

mixtures. CNBT, which joined in 2001, adds a focus

on biological research, mostly through solution scattering studies that complement the membrane-related

research carried out on the CNBT reflectometer/diffractometer at NG-1.

INTERAGENCY COLLABORATIONS

The Smithsonian Institution’s Nuclear Laboratory for

Archeological Research is part of the Anthropology

Department at the National Museum of Natural

History. It has had a productive 29-year partnership

with the NCNR, during which time it has chemically

analyzed over 32,500 archaeological artifacts by

Instrumental Neutron Activation Analysis (INAA),

drawing extensively on the collections of the

Smithsonian, as well as on those of many other institutions in this country and abroad. Such chemical

analyses provide a means of linking these diverse

collections together in order to study continuity and

change involved in the production of ceramic and

other artifacts. 

The Center for Food Safety and Applied Nutrition,

U.S. Food and Drug Administration (FDA), directs

and maintains a facility at the NCNR that provides

agency-wide analytical support for food safety and

food defense programs. Neutron activation (instrumental, neutron-capture prompt-gamma, and radiochemical), x-ray fluorescence spectrometry, and lowlevel gamma-ray detection techniques provide diverse

multi-element and radiological information about

foods and related materials. Recent studies include

homogeneity determinations following cryogenic

preparation of foods, improved detection capabilities

for iodine and other toxic and nutritional elements in

foods, and rapid screening of food products for dangerous levels of cadmium, lead, mercury, and other

toxic elements.
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Zamyatina, A.A., Zatsepin, G.T., Zlokazov, S.B.,

“Measurement of the Response of a Ga Solar Neutrino

Experiment to Neutrinos From an 37Ar Source,” J. Phys.:

Conf. Ser. 39, 284 (2006).

Abdurashitov, J.N., Gavrin, V.N., Girin, S.V., 

Gorbachev, V.V., Gurkina, P.P., Ibragimova, T.V.,

Kalikhov, A.V., Khairnasov, N.G., Knodel, T.V., Matveev,

V.A., Mirmov, I.N., Shikhin, A.A., Veretenkin, E.P.,

Vermul, V.M., Yants, V.E., Zatsepin, G.T., Bowles, T.J.,

Elliot, S.R., Teasdale, W.A., Cleveland, B.T., Haxton,

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Ahmad, F., Constabel, F., Geckeler, K.E., Seeck, O.H., 

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Air-Water Interface,” Israel J. Chem. 45 (3), 345 (2005).

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Alexandridis, P., Tsianou, M., Antoniou, E., Katori, Y., 

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Allen, A.J., Thomas, J.J., “Analysis of Cement Paste and 

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Anderson, I.S., Cook, J., Felcher, G., Gentile, T.R., 

Greene, G., Klose, F., Koetzle, T., Lelievre-Berna, E.,

Parizzi, A., Pynn, R., Zhao, J., “Polarized Neutrons 

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Babcock, E., Chann, B., Walker, T.G., Chen, W.C., 

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Thermal-Neutron Double-Crystal Diffracto

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Barnes, P.W., Lufaso, M.W., Woodward, P.M., 

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M 3+TaO

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A

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Boyce, D.E., Dawson, P.R., Sidle, B., Gnäupe

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Brown, C.M., Jacques, T.L., Hess, N.J., Daeme

Mamontov, E., Linehan, J.C., Stowe, A.C., 

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Caciuffo, R., Guidi, T., Amoretti, G., Carretta, 

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Castro-Roman, F., Porcar, L., Porte, G., Ligoure, C.,

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Chen, W.-R., Butler, P.D., Magid, L.J., “Incorporating

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Stone, M.B., Lumsden, M.D., Jin, R., Sales, B.C., Mandrus,

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Stone, M.B., Tian, W., Granroth, G.E., Lumsden, M.D.,

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Sturgeon, R.E., Willie, S.N., Yang, L., Greenberg, R., Spatz,

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Sun, Y.P., Huang, Q.Z., Wu, L., He, M., Chen, X.L., 

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Triolo, R., Lo Celso, F., Benfante, V., Gorgoni, C., Barker,

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Tsianou, M., Alexandridis, P., “Molecular Recognition

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Prepr. 46 (2), 1123 (2005).

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Tuteja, A., Mackay, M.E., Hawker, C.J., Van Horn, B., Ho,

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Valincius, G., McGillivray, D.J., Febo-Ayala, W., Vanderah,

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Wang, H., “SANS Study of the Early Stages of

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Wang, H., Christopherson, G.T., Xu, Z.Y., Porcar, L., 

Ho, D.L., Fry, D., Hobbie, E.K., “Shear-SANS Study of

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Wang, H., Xu, Z., Eres, G., “Order in Vertically Aligned

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Wietfeldt, F.E., Huber, M., Black, T.C., Kaiser, H., Arif, M.,

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Wilburn, W.S., Bowman, J.D., Mitchell, G.S., O’Donnell, 

J.M., Penttilä, S.I., Seo, P.-N., Calarco, J.R., Hersmann,

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Young, G.R., De Souza, R.T., Snow, W.M., Desai, D.,

Greene, G.L., Grzywacz, R.K., Frleˇz, E., Poˇcani ́c, D.,

Gentile, T.R., Gudkov, V., Jones, G.L., “Measurement of

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J. Res. Natl. Inst. Stand. Technol. 110 (4), 389 (2005).

Wilking, J.N., Graves, S.M., Chang, C.B., Meleson, K., Lin,

M.Y., Mason, T.G., “Dense Cluster Formation During

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Wilson, K.S., Allen, A.J., Washburn, N.R., Antonucci, J.M.,

“Interphase Effects in Dental Nanocomposites

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Wilson, S.D., Dai, P., Li, S., Chi, S., Kang, H.J., Lynn, J.W.,

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Xiao, Y.G., Huang, Q., Ouyang, Z.W., Lynn, J

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Xu, G., Gehring, P.M., Shirane, G., “Persisten

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Xu, G., Gehring, P.M., Stock, C., Conlon, K., 

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Xu, T., Zvelindovsky, A.V., Sevink, G.J.A., Ly

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Yamaura, K., Huang, Q., Moldovan, M., Youn

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Yamaura, K., Huang, Q., Zhang, L., Takada, 

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Yang, C.C., Lee, S.F., Yao, Y.D., Li, W.-H., L

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78
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Yildirim, T., Harris, A.B., “Magnetic Structure and Spin

Waves in the Kagomé Jarosite Compound

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Yildirim, T., Hartman, M.R., “Direct Observation of

Hydrogen Adsorption Sites and Nanocage Formation 

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Yildirim, T., Íñiguez, J., Ciraci, S., “Molecular and

Dissociative Adsorption of Multiple Hydrogen

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Yim, H., Kent, M.S., Mendez, S., Lopez, G.P., Satija, S.K.,

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Yim, H., Kent, M.S., Sasaki, D.Y., Polizzotti, B.D., Kiick,

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Yim, H., Kent, M.S., Satija, S.K., Mendez, S., Balamurugan,

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Yun, S.I., Briber, R.M., Kee, R.A., Gauthier, M., “DiluteSolution Structure of Charged Arborescent Graft

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Yun, S.I., Terao, K., Hong, K., Melnichenko, Y.B., Wignall,

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Zambrano, E., Kotlarchyk, M., Langner, A., Faraone, A.,

“Isomeric and Concentration Effects of C4-Cosurfactants

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Zank, J., Reynolds, P.A., Jackson, A.J., Baranyai, K.J.,

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“Aggregation in a High Internal Phase Emulsion

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“Local Order and Frustration in the Geometrically

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Zhao, P., Cullen, J., Wuttig, M., Kang, H.J., Lynn, J.W.,

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Zhou, J., Deyhim, A., Krueger, S., Gregurick, S.K., “LORES:

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Zhou, J., Gregurick, S.K., Krueger, S., Schwarz, F.P.,

“Conformational Changes in Single-Strand DNA as a

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Zhou, J., Krueger, S., Gregurick, S.K., “A Coarse Graining

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Zhou, N., Lodge, T.P., Bates, F.S., “Influence of

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Zhu, Z., González, Y.I., Xu, H., Kaler, E.W., Liu, S.,

“Polymerization of Anionic Wormlike Micelles,”

Langmuir 22 (3), 949 (2006).
P.D. Butler (301) 975-2028 butler@nist.gov 

J. Krzywon (301) 975-6650 jeffery.krzywon@nist.gov 

J.G. Barker (301) 975-6732 john.barker@nist.gov 

30-m SANS instrument (NG-3) (CHRNS):

B. Hammouda (301) 975-3961 hammouda@nist.gov 

S.R. Kline (301) 975-6243 steven.kline@nist.gov 

B. Greenwald (301) 975-5797 bryan.greenwald@nist.gov 

J.G. Barker (301) 975-6732 john.barker@nist.gov 

USANS, Perfect Crystal SANS (BT-5) (CHRNS):

A. Jackson (301) 975-3146 Andrew.jackson@nist.gov 

M.-H. Kim (301) 975-6469 man-ho.kim@nist.gov 

P.D. Butler (301) 975-2028 butler@nist.gov 

J.G. Barker (301) 975-6732 john.barker@nist.gov 

Cold neutron reflectometer-vertical 

sample-polarized beam option (NG-1):

C.F. Majkrzak (301) 975-5251 cmajkrzak@nist.gov 

J.A. Dura (301) 975-6251 jdura@nist.gov 

Advanced neutron diffractometer/reflectometer (NG-1):

C. Majkrzak (301) 975-5251 charles.majkrzak@nist.gov

J.A. Dura (301) 975-6251 jdura@nist.gov

Cold neutron reflectometer-horizontal sample (NG-7): 

S.K. Satija (301) 975-5250 satija@nist.gov 

Double-focusing triple-axis spectrometer (BT-7):

Y. Chen (301) 975-6442 ying.chen@nist.gov 

J.W. Lynn (301) 975-6246 jeff.lynn@nist.gov 

Triple-axis spectrometer (BT-9):

W. Ratcliff (301) 975-4316 william.ratcliff@nist.gov

R.W. Erwin (301) 975-6245 rerwin@nist.gov 

J.W. Lynn (301) 975-6246 jeff.lynn@nist.gov 

SPINS, Spin-polarized triple-axis spectrometer (NG-5)

(CHRNS): 

J.-H. Chung (301) 975-8369 jae-ho.chung @nist.gov 

H.-J. Kang (301) 975-4863 hye.kang@nist.gov 

HFBS, High-flux backscattering spectrometer (N

V. Garcia Sakai (301) 975-4404 vicky@nist.

G. Gaˇsparovi ́c (301) 975-8396 goran.gasp

NSE, Neutron spin echo spectrometer (NG-5) (C

A. Faraone (301) 975-5254 antonio.fara

J.S. Gardner (301) 975-8396 jason.gardn

M. Nagao (301) 975-5505 michihiro.n

Prompt-gamma neutron activation analysis (N

R.M. Lindstrom (301) 975-6281 dick.lindstr

R.L. Paul (301) 975-6287 rpaul@nist.

Thermal neutron prompt-gamma activation ana

E.A. Mackey (301) 975-5149 liz.mackey@

Other activation analysis facilities: 

R.R. Greenberg (301) 975-6285 rgreenberg@

Cold neutron depth profiling (NG-1):

G. Downing (301) 975-3782 gregory.dow

Neutron interferometer (NG-7):

D. Jacobson (301) 975-6207 jacobson@n

D. Hussey (301) 975-6465 daniel.huss

M. Arif (301) 975-6303 muhammad

Neutron Imaging Facility (BT-2):

M. Arif (301) 975-6303 muhammad

D. Jacobson (301) 975-6207 jacobson@n

D. Hussey (301) 975-6465 daniel.huss

Fundamental neutron physics station (NG-6): 

NG-6M: M.S. Dewey (301) 975-4843 mdewey@n

NG-6U: H.P. Mumm (301) 975-8355 pieter.mum

NG-6: J. Nico (301) 975-4663 nico@nist.g

Theory and modeling:

T. Yildirim (301) 975-6228 taner@nist.g

N.F. Berk (301) 975-6224 nfb@nist.go

Sample environment: 

J. Leao (301) 975-8867 juscelino.le

D.C. Dender (301) 975-6225, dender@nis

80
the Facility, contact:

Patrick D. Gallagher

(301) 975-6210

patrick.gallagher@nist.gov

Dan Neumann

(301) 975-5252

dan.neumann@nist.gov

To obtain guidelines for preparing prop

to conduct research at the facility, cont

William A. Kamitakahara

(301) 975-6878

william.kamitakahara@nist.gov

Location of all contacts:

NIST Center for Neutron Research

National Institute of Standards and Te

100 Bureau Drive, Mail Stop 8560

Gaithersburg, MD 20899-8560

Copies of this report and other inform

available electronically. Please visit ou

www.ncnr.nist.gov