NAT'L INST. OF STAND & TECH R.I.C.

A111D3 STTD3E

NISI

PUBLICATIONS

NIST TECHNICAL NOTE 1272

U.S. DEPARTMENT OF COMMERCE/National Institute of Standards and Technology

NIST Reactor:

Summary of Activities

July 1988 Through June 1989

QC

100

.U5753

NO. 1272

1989
NATIONAL INSTITUTE OF STANDARDS &

I TECHNOLOGY

'.- Research Information Center

I Gaithersburg, MD 20899
NIST Technical Note 1272

'^lK%3

NIST ReactoK /?^?

Summary of Activities <^ /

July 1988 Through June 1989

Carol O'Connor, Editor

Reactor Radiation Division

Institute for Materials Science and Engineering

National Institute of Standards and Technology

Gaithersburg, MD 20899

December 1989

*"(f WW ^ Sit r*

e

U.S. Department of Commerce

Robert A. Mosbacher, Secretary

National Institute of Standards and Technology

Raymond G. Kanimer, Acting Director
National Institute of Standards and Technology Technical Note 1272

Natl. Inst. Stand. Technol. Tech. Note 1272, 324 pages (Dec. 1989)

CODEN: NTNOEF

U.S. GOVERNMENT PRINTING OFFICE

WASfflNGTON: 1989

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
FOREWORD

The National Institute of Standards and Technology (NIST) research reactor

serves the needs of NIST, other government agencies, universities, and

industries as a national center for the application of neutron methods to a broad range of problems of national interest. The Reactor Radiation Division

has a threefold mission: to operate the reactor in the most cost effective

manner possible while protecting the public safety; to perform research on a broad range of problems in materials-related science and to develop new or improved methods for the application of neutrons; and to operate a national user center, providing state-of-the-art neutron measurement capabilities to

U.S. researchers. The Division staff works closely with many other organizations both within NIST and outside on research of mutual interest. The

extent of these cooperative and collaborative programs has expanded steadily

since the reactor came on line. They can be expected to grow even further as the Cold Neutron Research Facility, which will provide 15 additional

instruments, comes on line over the next 3 years.

The reactor operates at 20 MW and supports over 25 research facilities, with

an additional 15 becoming available as part of the Cold Neutron Project.

During the period covered by this report, over 1160 irradiations were

performed, and more than 350 researchers made use of the facilities, in spite

of an operating schedule that was seriously curtailed as a result of

construction activities.

This report summarizes the work done which is dependent on the reactor

including a large number of programs outside the Division. The first section

summarizes the programs carried out by scientists in the Reactor Radiation

Division and their collaborators. The second section summarizes NIST work

originating outside NIST for which the Division provides reactor facilities

and irradiation services. The remaining sections are self-explanatory.

Appreciation is extended to C. O'Connor for her contributions to the editing,

organization, and preparation of this report; E. Altman, N. Repetti, J.

Spillman, and S. von Feck for typing the manuscripts.

Finally, this is the first report in the history of the Division prepared by

anyone but Dr. R. S. Carter, who retired in December 1988. All that has been

accomplished over the years is a direct result of the foresight and

dedication of Bob. We wish him well in his retirement.

J. Michael Rowe, Chief

Reactor Radiation Division

National Institute of Standards

and Technology

111
ABSTRACT

This report summarizes all those programs which use the NIST reactor.

It covers the period for July 1988 through June 1989. The programs range

from the use of neutron beams to study the structure and dynamics of

materials through nuclear physics and neutron standards to sample

irradiations for activation analysis, isotope production, neutron

radiography, and nondestructive evaluation.

KEY WORDS: activation analysis; cold neutrons; crystal structure;

diffraction; isotopes; molecular dynamics; neutron; neutron

radiography; nondestructive evaluation; nuclear reactor;

radiation.

DISCLAIMER

Certain trade names and company products are identified in order to

adequately specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the National Institute

of Standards and Technology, nor does it imply that the products are necessarily the best available for the purpose.

IV
CONTENTS

FOREWORD iii

ABSTRACT iv

A. REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS 1 Neutron Scattering Study of the Vibrations and Dynamics of

Trimethylsilyl Adsorbates on Silica 1 Hydrogen Vibrational Modes and Anisotropic Potential in a-ScH . . 3

Neutron Spectroscopic Studies of Adsorbates on Ruthenium

Sulfide Catalysts 6

Neutron Scattering Study of the Molecular Dynamics of

Ammonium Fluoroberyllate 8

Inelastic Neutron Scattering Studies of Nonlinear Optical

Materials: p-Nitroaniline Adsorbed in ALPO-5 9

Dynamics of Molecular Hydrogen Adsorbed in Transition-Metal

Exchanged Zeolites _ 11

The Dependence of the OH'Librations on the Octahedral Site

Occupancies in 2:1 Layered Silicates 12

Neutron Scattering Studies of Tri methyl ammonium Pillared

Vermiculite Clays 14

Structural Studies of Stage 1 Metal -Dichloride Graphite

Intercalation Compounds 17

Application of Maximum Entropy to Phase Refinement in

Macromolecular Crystallography 18

Background Contributions and Quantitative Phase Determination

in Rietveld Structure Refinement 21

Neutron Rietveld Analysis of Anion and Cation Disorder in the

Fast-Ion Conducting Pyrochlore System Y^CZr Ti, )20y .... 23

Crystal Structure of ll,23-di-tert-butyl-l,9,ll,13,21,23-hexaazapentacyclo[19.3.1^'^.l^'-^"^.l^^'^^.]octacosa-3,5,7{28),

15,17,19 (26)-hexaene-25,27-dione, (C3QH42Ng02) 24

Neutron Diffraction Studies of the Martensitic Transformation

in Sodium Metal 26

Structure of AlCuFe Alloys Exhibiting the Icosahedral Phase ... 29

Evolution of the Magnetic Structure in Tb Y, Ag 32

Magnetic Order in A Tbp rDyg ^ Single Crystal 34

Orientation Dependence of the Magnetic Structure in Dy/Y

Superlattices 35

Magnetoelasticity in Rare-Earth Superlattices and Films 37

Neutron Diffraction Studies of Cd, Mn Se Films and

ZnSe/MnSe Multilayers 42

Exchange Interactions in Co-Based II-VI Diluted Magnetic

Semiconductors 45
CONTENTS

Characterization of the Quasicrystalline State of AK^Mn^jSig

From Neutron Scattering Experiments 47

Ant i ferromagnetic Order in YBa^Cu-, Co Og 49

Oxygen Dependence of the Magnetic Phase Transitions in

YBa2CU2.8CO0.2Vy 52

Magnetic Properties of BipA^TOg: A = MSr,Ca and T = Co,Mn 54

The Defective Structures of Ba^YCu-Og and

Ba2YCu3 M Og^^ (M = Fe, Co, Al , Ga) 56

Magnetic Order of Nd in NdBa2Cu20g 57

Two- and Three-Dimensional Magnetic Behavior of Er in ErBa^Cu^O^ . 59

Effect of Superconductivity on the Small Angle Neutron

Scattering in ErBapCu^O, 63

Magnetic Order of Pr in PrBa^Cu-O, 67

Pressure Dependence of the Cu Magnetic Order in ^^a^Cu^Og . ... 70

Two- and Three-Dimensional Magnetic Order in /?Ba2Cu.0g 73

Magnetic Order of the Cu Planes and Chains in ^Ba^Cu-Og 76

Anti ferromagnetic Order of the Cu in NdpCuO. 82

Superconducting TK nBa^ nC^^fi+S* ^ ^^^^ Resolution

Neutron Powder Investigation 85

Neutron Powder Diffraction Study of Pb^Sr^YCu^Og, The

Prototype of a New Family of Superconductors 89

Sans Study of YBa^Cu-O^ Sol -Gel Processing 89

Interplanar-Boson-Exchange Models of High-Temperature

Superconductivity--Theoretical Comparisons and Possible

Experimental Tests 90

Texture Study of Magnetically Aligned YBa^Cu^O, by Neutron

Diffraction 95

Grazing-Angle Neutron Diffraction Study of Cr/Nb/AKO^Film .... 97

Neutron Reflectivity Study of GD-Y Interface 99

Determination of Hydrogen Density Profiles in Thin Films and

Multilayers by Neutron Reflection 101

The Morphology of Symmetric Di block Copolymers as Revealed by

Neutron Reflectivity 102

Temperature Dependence of the Morphology of Thin Di block

Copolymer Films as Revealed by Neutron Reflectivity 109

Neutron Reflectivity Study of the Density Profile of an Adsorbed

Diblock Copolymer at the Solution-Quartz Interface 115

SANS Studies of Blends of Crossl inked PSD With Linear PSH .... 119

The Effect of Radiation Crossl inking on the Scattering Function

in Weakly Interacting Miscible Polymer Blends 121

Grafted Interpenetrating Polymer Networks 123

Microstructure and Isotopic Labeling Effects on the Miscibility

of Polybutadiene Blends Studied by the Small Angle Neutron

Scattering Technique 125

VI
CONTENTS

Shear Effects on the Phase Separation Behavior of a Polymer Blend

in Solution by Small Angle Neutron Scattering 132

Concentration Fluctuations in Mixtures of Linear and Star

Shaped Polymers 137

Chain Conformation of a Block Polymer in a Microphase-Separated

Structure 138

SANS Study of Order and Disorder in a Model Diblock Copolymer . . 144

Molecular Structure of Bimodal Polymer Network 146

Small Angle Neutron Scattering Studies on Chain Asymmetry of

Coextruded Poly{Vinylalcohol) Film 150

In-Situ Neutron Diffraction on Deuterium Loaded Palladium in an Electrochemical Cell 151

Comments on Cold Fusion in Metals 155

Cavity Growth Rates in Fatigued Copper 155

Textures of Specially Fabricated Metals 158

Residual Stress Measurements in Metallurgical Samples 162

Microstresses in Ceramic Composites 166

Multiple Small Angle Neutron Scattering Characterization of the

Densification of Alumina 168

Neutron Scattering and Its Effect on Reaction Rates in

Neutron Absorption Experiments . . 171

Characterization of Molecular Network of Epoxies Using

Neutron Scattering 174

Shearing Apparatus for SANS: Preliminary Results From Sheared

Colloidal Suspensions 177

Analysis of SANS From Controlled Pore Glasses 180

Physical Gels of Aqueous Polyvinylalcohol Solutions

- A Small Angle Neutron Scattering Study 182

Small Angle Neutron Scattering From Bacterial Magnetite 183

SANS Study of Mixed Lecithin-Bile Salt Micelles and Vesicles ... 187

NIST Crystal Data Center 189

A New Method for Identification of Solid-State Materials 190

Autoradiography Study of Paintings 192

Cold Neutron Project 195

Center for High Resolution Neutron Scattering 198

Spin Polarized Inelastic Neutron Scattering Spectometer (SPINS). . 199

Cold Neutron Triple Axis Spectrometer 200

High Resolution Time-of-Fl ight Spectrometer 201

Analytical Calculations of the Performance of Neutron

Guide Systems 202

On the Use of Multiply Channeled Guides to Increase Intensity on the Sample in a Multiple Disk Chopper Time-of-Fl ight

Spectrometer 207

Focused Neutron Beams for Materials Analysis 211

Design Studies for the Prompt Gamma-Ray Activation Analysis

Instrument 212

Cold Neutron Depth Profiling 214

High Resolution Small Angle Scattering Spectrometer 215

Design of Cold Neutron Backscattering Spectrometer 217

Supermirror Development 218

Vll
CONTENTS

B. NON-RRD PROGRAMS 219

Neutron Interactions and Dosimetry Group 219

Nuclear Methods Group: Overview 233

INAA Homogeneity Measurements on the New NIST Leaf

Reference Materials 238

Prompt Gamma Activation Analysis of Gaseous Samples 244

Instrumental Neutron Activation Analysis of Marine Samples .... 246

Determination of B and Li in Dietary Samples using NA-MS 249

Exhumation Confirms Lead Analyses Results ... 250

Instrumental Neutron Activation Analysis of Microscopic Samples. . 251

Low-Background Gamma Ray Assay Laboratory for Activation

Analysis 252

Investigation of Reported Cold Nuclear Fusion 258

Facilities for Activation Analysis 261

Atmospheric, Environmental Biological Studies by Instrumental and

Neutron-Capture Prompt 7-Ray Activation Analysis 262

Effects of Neutron Scattering by Hydrogen on Neutron-Capture

Prompt 7-Ray Activation Analysis (PGAA) 263

Submicrometer Size Distributions of Airborne Particles Bearing

Various Trace Elements 265

California Air Resources Board Air-Filter Samples 269

Stable Isotope Tracing of Zinc in Infants 271

128 Investigation of the Gamma-Ray Spectrum for the Te(n,g) and

^^°Te(n,g) Reactions 274

Fundamental Physics 275

Neutron Activation Analysis at the Food and Drug Administration . 275

Germanium Detector Optimization of MDA for Efficiency vs. Low

Intrinsic Background . 278

C. REACTOR OPERATIONS AND ENGINEERING SERVICES 280

Reactor Operations and Services 280

Reactor Operations and Engineering 281

D. PERSONNEL ROSTER 284

E. PUBLICATIONS 295

Vlll
A. REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SCATTERING STUDY OF THE VIBRATIONS AND DYNAMICS OF

TRIMETHYLSILYL ADSORBATES ON SILICA

T. J. Udovic, D. A. Neumann, and J. J. Rush

L. C. Sander

(Organic Analytical Research Division)

and

I. S. Anderson

(Paul Scherrer Institut, Villigen, Switzerland)

The nature of trimethylsilyl ((CH2)3Si-, TMS) adsorbates bonded to

silica surface oxygens, via the reaction of trimethylchlorosilane with

surface silanol groups, has been probed using neutron scattering methods.

The TMS vibrational spectra in the range 10 - 230 meV were obtained as a function of temperature by incoherent inelastic neutron scattering (IINS)

using the BT-4 triple-axis spectrometer with both the Be-filter and Begraphite-Be-filter analyzers. The region below 12 meV was investigated using

the cold-neutron time-of-flight (TOP) spectrometer in order to characterize

the temperature dependence of both low-energy vibrational transitions and

quasielastic neutron scattering processes.

Figure 1 shows high-resolution vibrational spectra of TMS/SiO^ at 4 and

80 K. Both spectra reflect the same general features: an intense mode at ~ 20 meV due to the methyl torsional modes, weak scattering intensity between

30 and 80 meV due to the different skeletal modes, and the more pronounced

peaks between 80 and 120 meV due mainly to the Si-C-H bending modes.

Additional scattering features at ~ 160 and 180 meV observed under lowresolution conditions (i.e., Be-filter analysis, spectrum not illustrated)

are representative of H-C-H bending modes. Acceptable spectral fits by

normal coordinate analysis required the inclusion of off-diagonal forceconstant matrix elements (i.e., intramolecular interactions). The IINS

spectral features at 80 K are noticeably broader than the corresponding

features at 4 K, indicative of significant TMS rotational motions on a neutron timescale down to 80 K or below.

Figure 2 shows the corrected TOF spectra of TMS/SiO^ at 4 and 10 K on an energy scale. An energy loss feature at ca. 2.5 meV at 4 K shows up as both
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

energy loss and energy gain features at 10 K due to the population of the

2.5 meV level above the ground state as the temperature is raised. This lowenergy feature is assigned to the torsional vibration of the entire

trimethylsilyl group around the 0-Si axis, since the relatively large moment

of inertia of this group would predict torsional modes in this region.

Quasielastic neutron scattering spectra between 4 and 300 K confirm that

trimethylsilyl group rotational motions are responsible for the broadening of

the I INS vibrational features at 80 K, with the methyl group rotational

motions (observable at higher temperatures) already virtually frozen out

(t> 10' s) at this temperature.

1 1 1 1 1 1 1

^, TMS/SiOg

%

*

n

o

*>A»v*/^' « c

o *> u•—> 2

\ s

4 . * ^ ^

4K -

1 ' ! ' 1 1 1

1 1 1 TMS/Si02

1 1 1

c

3

cS

p2

O lOK

^

*

4

4K £

1 1 40 80 120 Energy Loss (meV)

160 -12 -6 6 Energy Transfer (meV)

12

Figure 1. (left) IINS spectra of TMS/SiOp as a function of temperature taken

on the BT-4 spectrometer using the Be-graphite-Be-filter analyzer.

Figure 2. (right) Low-energy IINS spectra of TMS/SiOp as a function of

temperature taken on the TOF spectrometer with 13.8 meV incident

energy. Positive energy transfers correspond to neutron energy

loss.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

HYDROGEN VIBRATIONAL NODES AND ANISOTROPIC POTENTIAL IN a-ScH

T. J. Udovic and J. J. Rush

I. S. Anderson

(Paul Scherrer Institut, Villigen, Switzerland)

and

R. G. Barnes

(Iowa State University, Ames, lA)

The hydrogen vibrational spectra of single-crystal a-ScH (x = 0.05,

0.16, and 0.25) have been measured using incoherent inelastic neutron

scattering (IINS) methods in order to characterize the bonding potential of

hydrogen in the tetrahedral interstices (i.e., t sites) of the Sc metal

lattice. Alignment of the momentum transfer vector Q either perpendicular or parallel to the c-axis permitted selective enhancement of the scattering

sensitivity of the different hydrogen normal modes. Low-resolution IINS

spectra, obtained using the BT-4 spectrometer with the Be-filter analyzer,

show that the c-axis vibration peak (at ~ 103 meV) is over 30% lower in

energy than the doubly-degenerate basal -plane modes (at - 148 meV) and

is substantially anharmonic, as reflected by the ratio (1.76) of the secondto first-excited-state energies.

High-resolution IINS spectra of the c-axis mode at the different

hydrogen concentrations, obtained using the BT-4 spectrometer with the Begraphite-Be-filter analyzer, are shown in figure 1. The observed downward

shift of the c-axis mode from 102.9 meV at x > 0.16 to 101 meV at x = 0.05 is

similar to the hydrogen concentration dependence of the c-axis mode found for

tt-YH [1], which has been attributed to the relaxation of coherent strain

ordering as the hydrogen concentration decreases, resulting in a larger

average metal -hydrogen separation as more alternative hydrogen configurations

become accessible. All hydrogen concentrations reveal a peak that is much

broader (~ 14 meV fwhm intrinsic linewidth, x = 0.25) than the instrumental

resolution. The peak, however, is devoid of any resolved fine structure

indicative of a distinct local -mode splitting induced by the dynamic coupling

of hydrogen pairs across metal atoms along the c-axis, as was observed

previously for a-YH [1].

A comparison of the high-resolution spectra of the c-axis mode for a- ScHq 25 and a-YHQ ,g in figure 2 illustrates the difference in lineshapes.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In contrast to the Gaussian-shaped peak for o-ScHq ^r* ^ definite 4 meV

splitting is observed for a-YHg ,g, despite its narrower apparent overall

linewidth. Even if a splitting is present for qi-ScHq «c> it would not

necessarily be observable if the component peaks were considerably broadened.

Indeed, the c-ScHq 25 spectrum can be fit just as well with two broad

Gaussian components, each ~ 10 meV fwhm and separated by 4 meV at positions

of 102.9 ± 2 meV. In contrast, the visible splitting in the YHq ,g

spectrum, necessitates the presence of much narrower component peaks.

Attempts to fit the complex-shaped spectrum with two Gaussians required

peakwidths of ~ 4 meV to reproduce the degree of observed separation in the

central portion of the spectrum.

In short, the overall broadness of the a-ScH spectra is consistent with

the presence of H pairing across Sc atoms along the c-axis, similar to the

hydrogen pairing that occurs in a-YH . The lack of visible splitting in the

a-ScH spectra suggests that the individual components of the c-axis spectra

are more broadened than in a-YH due to a larger distribution of H-pair

environments (i.e., less extended ordering of H pairs in the c-direction) or

a greater variety of intra- and interline arrangements. Thus, it appears

that the hydrogen pairs in a-ScH are more disordered than in a-YH , which is

consistent with the suggestion from recent NMR studies [2] that the hydrogen

arrangements in a-ScH are, in some sense, akin to a "proton glass."

Previous vibrational spectroscopic measurements of o-YDq j^Hq Q,g [1],

in which the H atoms are sufficiently dilute that they can effectively pair

only with D atoms across an Y atom, yielded a single narrowed peak at 100 meV

instead of the expected doublet at 99 and 103 meV found for H-H pairs in a- YHq jg. This observed behavior confirmed that the c-axis mode splitting in

a-YH is caused by a dynamic coupling mechanism rather than by vibrations in

a local potential statically perturbed by pairing. Similar isotope dilution

experiments, utilizing qi-ScDq «c doped with a small percentage of H, are planned in order to further probe the nature of dynamically-coupled hydrogen

pairing in this system. Experiments are also under way to study the local c- axis diffusion of hydrogen in the a-ScH system.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

c3

ou

c

ou2

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J ! I L J L

0.05

90 100 110 120 Energy Loss (meV)

c

3

ou

c

o

uZ

T

1

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1 r

.• c-axis mode

^ S

\ ^ ii a-ScH.

F+

a-YH,0.18 (8K)

J \ 1 I \ \ L 90 100 110 120 Energy Loss (meV)

Figure 1. (left) High-resolution IINS spectra of the c-axis mode at

T < 10 K for a-ScH as a function of H concentration. The

instrumental resolution (fwhm) is illustrated by the horizontal

bar beneath the spectra.

Figure 2. (right) High-resolution IINS spectra of the c-axis mode at

T < 10 K for single-crystals of qi-ScHq ^c ^i"^ ^"^^n 18 '^'* '^^^ instrumental resolution (fwhm) is illustrated by the horizontal

bar beneath the spectra.

References

[1] Anderson, I. S.; Berk, N. F.; Rush, J. J.; Udovic, T. J. Phys. Rev.

B37, 4358 (1988).

[2] Lichty, L. R.; Han, J.-W.; Ibanez-Meier, R.; Torgeson, D. R.; Barnes, R. G.; Seymour, E. F. W.; Sholl, C. A. Phys. Rev. B39, 2012 (1989).
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SPECTROSCOPIC STUDIES OF ADSORBATES ON RUTHENIUM SULFIDE CATALYSTS

T. J. Udovic and J. J. Rush

and

B. J. Tatarchuk

(Auburn University, Auburn, AL)

Ruthenium sulfide (RuS^) is an active catalyst for hydrodesulfurization

(HDS) reactions. As a result, there has been interest in investigating the

adsorption properties of this material, particularly with respect to

hydrogen. A previous incoherent inelastic neutron scattering (IINS) study

[1] of hydrogen adsorption on RuS^ has indicated that hydrogen adsorbs

dissociatively forming surface sulfhydryl (SH) groups. The likely sites for

hydrogen dissociation and adsorption are coordinatively unsaturated S-S anion

pairs which provide both the necessary electron density and dual -site

geometry. The H/RUS2 vibrational spectrum at 80 K is shown in figure la.

The main scattering feature, assigned to the Ru-S-H bending modes, appears as

a complex doublet at 74 and 88 meV with the corresponding second harmonics

evident at higher energy.

A corresponding isotope dilution experiment [1] utilizing a 15% H2/85%

Dp adsorbate mixture yielded the H/RuSp spectrum at 80 K in figure lb,

indicating no significant change in the H vibrational peak structure except

for some additional increase in scattering intensity at -104 meV. Assuming

that complete isotopic mixing of H and D occurred, this spectrum would be a measure of isolated SH groups surrounded by SD groups, effectively breaking

up any possible H-H dynamic coupling. Hence, the conclusion from the isotope

dilution experiment would be that the complex peakshape in figures la and lb

is due to a distribution of bending-mode energies rather than the phonon

dispersion of a single bending mode via H-H dynamic coupling interactions.

Recent secondary ion mass spectrometry (SIMS) data at Auburn University

have suggested that, contrary to the original assumption, no significant

isotopic mixing occurs when H^ and D^ are coadsorbed on RuS^, even at 373 K.

In other words, the dissociation and adsorption of H-H and D-D onto the S-S

anion pairs results in a stable configuration of (H)S-S(H) and (D)S-S(D)

groups with no (H)S-S(D) groups created by exchange processes. This suggests

that the complex bending-mode peakshape may be due to H-H interactions
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

between hydrogens on the same S-S anion pair and clouds the conclusions of

the previous isotope dilution results.

To investigate this further, another isotope experiment was performed by

measuring the vibrational spectrum after adsorption of HD onto the RuSp

surface. This would ensure that the amount of (H)S-S(D) groups is maximized.

The resulting IINS spectrum is shown in figure Ic, again indicating no significant changes in the H vibrational peak structure except for additional

scattering intensity at 104 meV. Hence, it still appears that the complex

peakshape is due to a distribution of bending-mode energies rather than a dispersion effect induced by dynamic coupling interactions between near- neighbor hydrogens. The origin of the 104 meV feature is still under

investigation but may be due to the presence of impurity atoms which lead

to the formation of surface OH groups possessing bending mode energies in

this region.

Experiments are in progress for investigating other adsorbates on RuS^,

such as thiophene, which are of interest from the viewpoint of HDS surface

chemistry.

50 100 150 Energy Loss (meV)

200

Figure 1. IINS spectra of RuSp at 80 K taken on the BT-4 spectrometer using

the Be-filter analyzer after saturation adsorption of H^ (a),

15% H2/85% D2 (b), and HD (c).
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Reference

[1] Heise, W. H.; Lu, K.; Kuo, Y.-J.; Udovic, T. J.; Rush, J. J.; Tatarchuk,

B. J. J. Phys. Chem. 92, 5184 (1988).

NEUTRON SCATTERING STUDY OF THE MOLECULAR DYNAMICS OF

AMMONIUM FLUOROBERYLLATE

M. Davidovid

("Boris Kidri^" Institute of Nuclear Sciences, Vincl(, Belgrade, Yugoslavia)

and

T. J. Udovic and J. J. Rush

Inelastic neutron scattering experiments were performed to investigate

the molecular dynamics of both the protonated and deuterated forms of

ammonium fluoroberyllate ((NH-)2BeF^ and {ND,)2BeF.), an ammonium salt with a ferroelectric phase transition at ~ 180 K. The BT-4 triple-axis spectrometer

with the Be-graphite-Be-filter analyzer was used to collect the density-ofstates spectrum between 10 and 80 meV of both isotopic forms as a function of

temperature: namely, above, at, and below the ferroelectric transition

temperature. Complementary spectra covering the low-energy region below 12

meV were collected using the TOP spectrometer with 13.8 meV incident energy.

Data analysis is in progress to characterize any subtle changes in the

molecular dynamics accompanying the incommensurate structural phase

transition which occurs upon transformation from the paraelectric to the

ferroelectric state.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

INELASTIC NEUTRON SCATTERING STUDIES OF NONLINEAR OPTICAL MATERIALS:

p-NITROANILINE ADSORBED IN ALPO-5

J. M. Nicol

(University of Maryland, College Park, MD and Reactor Radiation Division)

T. J. Udovic and J. J. Rush

and

S. D. Cox and G. D. Stucky

(University of California, Santa Barbara, CA)

Inclusion of a guest species into a host framework is a relatively new method by which new nonlinear optical materials for second harmonic

generation (SHG) can be synthesized. SHG is very sensitive to symmetry

restrictions; thus, for a material to exhibit SHG the crystal structure must

be noncentrosymmetric. In inclusion chemistry this symmetry restriction can

be imposed on a guest molecule by an acentric host or created by guest-host

interactions. Therefore by careful size and shape selection of the host and

guest, the inclusion of a guest molecule in a host framework can result in

molecular alignment and optimization of the SHG coefficient and create a system with nonlinear optical properties that are very different from those

of either the individual guest molecules or the host framework.

Recently the adsorption of para-nitroaniline (p-NA) into the channels of

the molecular sieve ALPO-5 has been shown to produce SHG effects ten times

larger than that of any previously reported organic or organometallic

inclusion complex [1]. The acentric molecular sieve ALPO-5 has a neutral

framework composed of alternating AlO. and PO, tetrahedra linked by oxygen

bridges to form an array of one-dimensional 12-ring channels, into which p-NA

is adsorbed.

We have used incoherent inelastic neutron scattering (I INS) to

characterize the vibrational spectroscopy (below 2000 cm' ) of p-NA adsorbed

in ALPO-5 at both 3 and 13 wt % which represent the onset of and the maximum

in the nonlinear optical coefficient, respectively. In addition, the spectra

of pure p-NA and ALPO-5 were obtained for comparison.

The IINS scattering data were measured using the BT-4 spectrometer with

either a Be or Be-graphite-Be filter analyzer and a Cu(220) monochromator

with 40' -40' collimation before and after the monochromator or a graphite
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(002) monochromator with 40' -20' collimation. Data were collected over the

energy range 10-220 meV at a temperature of 80 K.

Figure 1 illustrates data in the 35-230 meV region for 3 and 13 wt %

p-NA adsorbed in ALPO-5. Analysis of these data and that obtained for pure

Na and ALPO-5 are currently under way. Spectral differences in the region of

30-60 and 100-150 meV are clearly seen. These differences may arise from

differences in the alignment, ordering and hydrogen bonding of the p-NA

molecules inside the confines of the ALPO-5 channels. From IR data [1] it is

known that the extent of hydrogen bonding of p-NA in ALPO-5 is different in

the low and high loading samples. The possibility also exists for clustering

of p-NA in the channels. Further studies of the system are planned using

quasielastic neutron scattering, SANS and neutron diffraction.

' ' ' '^

T T" 1 1 1

,

(b)

i < A \ A 13 \ \

\ \J\

1 I \ ^^ \ 4 s

l\ \ \l \ A ^h V W\ 1 lit \x ?> / »

I

Z, ^^\a

V

yv, . . .

1 1 1 1 i_ 110 150 190 230 30 70 110 160 100 230

Figure 1. The IINS of (a) 3 wt % and (b) 13 wt % p-nitroaniline adsorbed in

ALPO-5 at 80 K.

Reference

[1] Cox, S. D.; Gier, T. E.; Stucky, G. D.; Bierlein, J.

110 , 2986 (1988).

J. Am. Chem. Soc,

10
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

DYNAMICS OF MOLECULAR HYDROGEN ADSORBED IN TRANSITION-METAL

EXCHANGED ZEOLITES

J. M. Nicol

(University of Maryland, College Park, MD and Reactor Radiation Division)

J. Eckert

(Los Alamos National Laboratory, Los Alamos, NM)

and

J. Howard

(Imperial Chemical Industries, Wilton, England)

The sensitivity of incoherent inelastic neutron scattering (IINS) to the

rotational and vibrational transitions of molecular hydrogen, as well as the

ability of neutrons to induce transitions within the librational ground state

by nulear spin flips that are generally not allowed in optical spectroscopies, makes IINS a partically useful probe of bound hydrogen. We have

previously studied the rotational and vibrational transitions of molecular

hydrogen adsorbed in the cavities of partially cobalt-exchanged type A

zeolite by IINS [1]. Transitions due to both rotational and vibrational

excitations of the adsorbed hydrogen were identified in the spectra.

Analysis of the data revealed the barrier height to rotation and details of

2+

end-on coordination of hydrogen to the Co cations. This work has now been

extended to other transition-metal ion-exchanged zeolites.

IINS spectra have been obtained for molecular hydrogen adsorbed in the

cavities of partially Zn-exchanged type A zeolite as a function of both

temperature and coverage. Neutron scattering data were collected in the

energy-transfer range 1-12 meV using the time-of-flight (TOP) spectrometer at

an incident energy of 13.8 meV. Hydrogen was adsorbed to coverages of 0.5,

1.0, and 2.0 molecules per supercage in the fully dehydrated zeolite at 50 K.

The sample was then annealed at 80 K before being cooled to the data

collection temperature of either 4, 50, or 80 K.

The data reveal two transitions in both neutron energy loss and gain at - 4 and 8.4 meV. The intensities and temperature dependence of these peaks,

as well as their frequency shifts, are being analyzed to establish their

origin in terms of rotational and vibrational transitions of the hydrogen

molecules interacting with the cations (Zn and Na) in the framework. As in

the CoNa-A case, a number of potential force fields of different symmetry are being considered; i.e., end-on vs. side-on adsorption geometry.

11
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Reference

[1] Nicol, J. M.; Eckert, J.; Howard, J. J. Phys. Chem. 92, 7117 (1988).

THE DEPENDENCE OF THE 0H~ LIBRATIONS ON THE OCTAHEDRAL

SITE OCCUPANCIES IN 2:1 LAYERED SILICATES

D. A. Neumann

and

J. M. Nicol

(University of Maryland, College Park, MD and Reactor Radiation Division)

4-

Most layered silicates are composed of two basic building blocks: SiO.

3-

tetrahedra which are corner-joined, and Al(OH)g octahedra which are edgejoined. Different minerals are formed by the isomorphous substitutions of

either or both of the Al and Si ions and by different stacking arrangements

of the tetrahedrally and octahedrally coordinated layers. For instance, a 2:1 layered silicate is composed of a tetrahedral layer followed by an octahedral layer followed by another tetrahedral layer which are joined by

shared atoms. Members of this class of minerals include the micas,

vermiculite, the smectites, and talc. The vastly different properties of

these substances are due to the charge density on the layers which arises

from the various substitutions in the octahedral sites, tetrahedral sites, or both. This charge is compensated by cations residing in the interlayer

galleries. These minerals are further classified according to the degree to

which the octahedral sites are occupied. If all of the octahedral sites are occupied, the mineral is referred to as trioctahedral , while if 2/3 of the

these sites are occupied it is called dioctahedral . Talc and vermiculite are examples of trioctahedral 2:1 layered silicates. Muscovite, which is a mica,

and montmorillonite, a smectite, are dioctahedral minerals.

Using the Be-graphite-Be filter analyzer on the BT-4 spectrometer, we

have begun inelastic neutron scattering measurements on members of this class

of silicates in order to determine the dependence of the OH" librations on the occupancy of the octahedral site. This information will provide valuable

experimental input for currently developing models of the dynamics of these

minerals and may be important for the characterization of the host material

in pillared clays which show promise as tailored catalysts and molecular

sieves.

12
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1 shows the inelastic spectra for talc between 20 and 140 meV.

Talc is trioctahedral with an ideal chemical formula of Mg^Si .0,q(0H)2. The

Mg has been substituted for the Al in the octahedral sites causing the charge

density on the layers to be zero. Thus there are no gallery cations in talc.

Here a dominant peak is observed at about 85 meV which is due to the OH'

librations. A smaller peak is observed at about 65 meV. The inelastic

spectra of muscovite is shown in figure 2 over the same energy range.

Muscovite is dioctahedral with an ideal chemical composition of

KAl2{AlSi3)0,Q(0H)2. The K is the gallery ion which compensates the net

negative charge which arises from the substitution of Al for Si on the

tetrahedral sites. Here we observe essentially three peaks of comparable

intensity at about 60, 80, and 115 meV. Clearly the two spectra are vastly

different.

To ascertain the degree to which charge density on the layers and

tetrahedral site substitutions affect the OH' librations in these minerals,

we plan to do similar measurements on phlogopite which is a trioctahedral

mica with an ideal compostion of KMg2{AlSi2)0,Q(0H)2 and pyrophyllite which

is dioctahedral mineral with composition Al2Si^0,Q(0H)2. Like talc,

pyrophyllite has no net charge on the layers, so there is no gallery cation.

In addition, efforts are being made to model our results using programs

written by J. Gales and S. D. Mahanti of Michigan State University.

S

§

b

Sz

1 1 "i r r; 1 1 II

TALC •

•

•

•

• •

•

• A . • -y-Y-^-- ,V 1 1 1 1

a

oh

2

—1 1 r

MUSCOVITE

-1

r-

.V A

20 44 68 92 116 Energy Loss (meV)

J 1 I L

140 20 44 68 92 116 Energy Loss (meV)

J 1 1 I 140

Figure 1. (left) Inelastic scattering spectra of talc taken at 80 K.

Figure 2. (right) Orientationally averaged inelastic scattering spectra of

muscovite taken at 80 K.

13
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SCAHERING STUDIES OF TRINETHYUVMONIUM

PILLARED VERMICULITE CLAYS

D. A. Neumann

Y. B. Fan, H. Kim, S. A. Solin, and T. J. Pinnavaia

(Michigan State University, East Lansing, MI)

and

S. F. Trevino

(ARDEC, Picatinny Arsenal, NJ and Reactor Radiation Division)

Layered silicates such as vermiculite are unique among lamellar solids

because of their ability to be pillared by robust intercalated guest ions

which occupy sites within the interlayer galleries. The enormous free volume

of accessible interior space that is created by pillaring has significant

practical implications for tailored catalysts and molecular sieves. In spite

of this, relatively little information is available concerning the structure

and dynamics of these potentially important materials. We have therefore

undertaken a neutron scattering study of trimethyl ammonium pillared

vermiculite.

The measurements were performed on the BT-4 spectrometer using the

conventional triple-axis arrangement for the elastic scans and the Begraphite-Be filter analyzer for collection of the inelastic scattering data.

The samples were fabricated from natural Mg- vermiculite from Llano, Texas

which were ground until the crystallites were a few microns in size to ensure

that the ion exchange process would occur within a reasonable time. After

the Mg ions were exchanged for tetramethyl ammonium in the presence of the

EDTA anion, the resulting material was sedimented onto a glass plate to form

a self-supported, oriented film. This film was then dried for 12 hours at

100 °C and cut into smaller pieces which were stacked so that their c-axes were aligned. The resulting samples had mosaics of about 30°.

Table 1 shows the total scattering lengths of the individual layers

obtained by fitting the measured (00^) intensities compared to the scattering

lengths expected for a unit cell composition of [(CH2)3NH"'"]2-

(AIq 3jFeQ 03^95 66^2^^^5 73^^2 27^^20^^^^* ^^^ important point is that all

of the fit scattering lengths correspond closely to the expected ones, except

for those of the gallery ions. Varying other parameters in the system (i.e.,

bond lengths and Debye-Waller factors) does not alter this conclusion. This

14
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

implies that the tri methyl ammonium ions have not completely exchanged with

the original gallery ions. In fact, this data is consistent with an exchange

of only about 30%. Thus the available gallery space in these materials may

not be uniform, a result which has implications for the possible use of these

materials as catalysts, catalyst supports, and molecular sieves.

Table 1. Comparison of the total scattering lengths B. per layer per unit

cell which were derived from a fit of the (00£) intensities to

those expected for Llano vermiculite intercalated with trimethylammonium

Layer B.(fit) B. (calculated)

Mg 5.90 6.15

0(1) 2.83 2.73

Si/Al 1.89 1.60

0(2) 3.37 3.48

(CH3)3NH"^ 2.63 -1.63

(CD3)3ND'*" 8.50 19.19

The inelastic scattering spectra for the (CH3)3NH intercalated sample

are shown in figure 1 for two different orientations. Here the open symbols

are data taken with the graphite monochromator and collimations of 40' -20'

before and after the monochromator, respectively, and the open symbols refer

to data taken with the Cu(220) monochromator and collimations of 60' -40'. In

the energy range between 20 and 100 meV, four peaks were identified as being

due to internal modes of the trimethyl ammonium ion. The symmetric and

antisymmetric torsional excitations of the methyl groups were observed at

28.8 and 36.8 meV, respectively, while two bending modes were observed at

energies of 51.1 and 58.0 meV. Since the data showed obvious orientational

dependence, we have also performed a normal mode calculation for the

trimethyl ammonium ion in order to determine its orientation. The best

representation of the experimental data, after taking the clay modes into

account, was obtained when the N-H bond was parallel to the c-axis. The

result of this calculation was convoluted with the resolution and is plotted

as the solid line in figure 1. Modes not reproduced by the calculation are due to excitations of the host material and mainly result from motion of the

H in the OH" groups. These features are also present in the (CD3)3ND''"

15
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

intercalated sample. The only one of these peaks which has been clearly

identified is the one at 80 meV which arises from the OH' librations. The

identification of the other modes requires a detailed lattice-dynamical

calculation of the host material.

570

d

O

o 370

170

570-

O

o 370

170

40 60 80

Energy (meV)

100

Figure 1. Inelastic neutron scattering spectra of trimethyl ammonium pillared

vermiculite for in-plane and out-of-plane excitations taken at

80 K. The solid line represents a normal mode calculation for the

trimethyl ammonium ion assuming that the C-H bond is oriented along

the c-axis.

16
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STRUCTURAL STUDIES OF STAGE 1 NETAL-DICHLORIDE GRAPHITE

INTERCALATION COMPOUNDS

J. S. Speck, B. J. Wuensch, and M. S. Dresselhaus

(Massachusetts Institute of Technology, Cambridge, MA)

and

E. Prince

Metal -dichlorides such as CuCK or CoCl^ intercalated into graphite

usually form incommensurate structures. The intercalate layer in these

compounds consists of a chlorine/metal/chlorine sandwich similar to that

found in the CdCl^ structure. We have carried out extensive x-ray

photographic and diffractometer studies on a series of stage 1 and stage 2

metal -dichloride graphite intercalation compounds (GICs). Although the

intercalant and carbon have incommensurate in-plane structures, both species

form long-range ordered three-dimensional crystals for the stage 1 compounds.

In the stage 2 compounds the interlayer intercalant interactions are sufficiently attenuated by the carbon that there is no layer stacking

structure. We have found that the CdCK structure is preserved for CoCl«,

MnClp, and NiCK in the stage 1 compounds. CuCl^ intercalated in graphite

has the structure of copper cations sitting in the octahedral sites of

distorted chlorine layers. In this case the CuClp stacks in an ot$ sequence.

The single crystal GICs used for these studies have a fwhm mosaic spread

of - 5° in the best case. This is because the intercalation processes causes

a ~ 300% expansion of the graphite crystals perpendicular to the layer

planes. Hence the quality of data for single crystal structure refinement

will be poor. To overcome this problem, we have prepared stage 1 CuCK and

CoClp-GICs in graphite powder. We have obtained neutron powder diffraction

data on the Neutron Beam Split-core (NBS) reactor in order to carry out a Rietveld structure refinement. The data analysis is currently in progress.

The goal of the analysis is to refine the atomic positions, site occupancies,

and thermal parameters. The current limitation in the analysis is that the

carbon and intercalant have distinct reciprocal lattices and hence their

respective structures must be refined separately. Additionally, different

parameters are necessary to describe the linewidths of different families of

reflections.

17
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

APPLICATION OF MAXIMUM ENTROPY TO PHASE REFINEMENT

IN MACRONOLECULAR CRYSTALLOGRAPHY

E. Prince

L. Sjolin

(Chalmers University of Technology, Goteborg, Sweden)

and

D. M. Collins

(Naval Research Laboratory, Washington, DC)

A procedure was previously described [1] for finding an everywherepositive density distribution whose Fourier transform is in agreement with an arbitrarily large set of observed diffraction intensities. This procedure

has been applied to improving the phases, and thereby elucidating details, of

the crystal structures of several proteins, ribonuclease A complexed with

uridine vanadate, calcium containing fragment 1 of bovine prothrombin, and

Mojave toxin.

In each case the starting map was one that had been produced with phases

obtained from a partial (Mojave toxin) or complete (ribonuclease and bovine

prothrombin) solution of the structure of the protein molecule obtained by

other means. In Mojave toxin there are two molecular subunits, in one of

which the chain was well refined, while in the other it was not. After 50

cycles of sequential maximum entropy fitting of blocks of the 100 worst

fitting reflections, the resulting map showed an alternative path for a part

of the poorly fitting chain. Interestingly, a molecular dynamics calculation

[2] of the minimum energy conformation of the chain suggests a similar

alternative path.

In ribonuclease the protein chain was well refined, but details of the

solvent and, particularly, the uridine vanadate complex, which was believed,

on biochemical grounds, to be bound at the active site, were missing. After

a maximum entropy fit of the 30 worst fitting reflections, the resulting map

revealed that one region of previously uncertain density was clearly a molecule of t-butanol, that several previously located water molecules should

be moved, and, most importantly, a clear picture of the uridine vanadate

complex. Figure 1 shows this region of the maximum entropy map, with the

uridine molecule and a nearby histidine side chain in the active site of the

protein molecule.

18
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The protein chain of calcium containing fragment 1 of bovine prothrombin

was also fairly well defined, but a substantial proportion (25%) of the

contents of the unit cell is carbohydrate, which had not been located, and

the location of the calcium atom was also unclear. A maximum entropy fit to

the 30 worst fitting reflections gave a clear picture of the calcium atom,

bound, as had been expected, to a group of four residues of the unusual amino

acid 7-carboxy glutamic acid on the surface of the molecule, and also

revealed numerous regions of density that could be fit with carbohydrate.

Figure 2a shows one of these regions, and figure 2b shows the calcium site.

His 12

Figure 1. The electron density of the uridine vanadate complex in the active

site of ribonuclease A, as calculated by maximum entropy methods.

A histidine ring (His 12) from the protein molecule is also shown.

19
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2a 2b

Figure 2. Electron density maps from calcium containing fragment 1 of bovine

prothrombin, calculated using maximum entropy methods. Figure 2a

shows extended density attached to a nitrogen atom of asparagine

77 that binds the protein to carbohydate. Figure 2b shows the

calcium site, near the rare amino acid residue -y-carboxy glutamic

acid.

References

[1] Prince, E. Acta Cryst. A45, 200-203 (1989).

[2] Brunger, A. T. J. Mol . Biol. 203, 803-816 (1988).

20
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

BACKGROUND CONTRIBUTIONS AND QUANTITATIVE PHASE DETERMINATION

IN RIETVELD STRUCTURE REFINEMENT

J. K. Stalick and E. Prince

Accurate treatment of background contributions is important in the

Rietveld method of structure refinement, particularly when one is attempting

to determine small structural features such as occupancies of crystallographic sites or the amount of site substitution by different elements. For

partial site substitution or site occupancy, the average scattering length,

b, for a given site is actually determined. In the case of 10% substitution

of Zn for Cu, for example, one is looking for a very small difference: b = 0.772 X lO'-^^cm for Cu, and 0.752 x lO'^^cm for 90% Cu, 10% Zn. It is

important to treat the pattern background scattering as carefully as possible

to augment the significance level of the resulting atomic site occupancies.

To this effect, two strategies have been employed: (1) inclusion of higherorder polynomial terms in the background function to enable the use of lowangle peaks in the refinement, and (2) inclusion of the scattering due to

impurity phases as a contribution to background.

In order to determine adequately the amount of substituent on a given

crystal lographic site, it is important that the data cover as large an angular range as possible to decouple the occupancy parameters from the

thermal parameters in the refinement. Since a linear approximation to

background is not adequate for materials with relatively large unit cells,

additional background parameters were added to the NIST version of the

Rietveld refinement program in the form of Chebychev polynomial coefficients

[1]. The use of the orthogonal Chebychev polynomials instead of a power

series eliminates any problems with correlations in the refinement, as adding

additional terms to improve the approximation does not affect the values of

the coefficients of the preceding terms. Figure 1 shows the agreement of

calculated and observed data, along with a residual plot, for YBapCu^O, in

the low-angle region. A six-parameter Chebychev polynomial function provided

an adequate fit of the background.

The Rietveld refinement program has also been modified to include

scattering from up to five impurity phases as contributions to background.

In order to include impurity phases, the impurities must first be identified

from peak positions and intensities. The known structure of the impurity

phase is used to obtain a calculated pattern, assuming the same zero point

21
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

and range of data as the main phase, and a scale factor k. is refined for

each impurity phase according to the equation

(1/c ) Y.(calc) + B. + 2 kjY.j = Y.(obs)

where B. is the background intensity defined by the Chebychev polynomial

coefficients and Y.. is the calculated intensity of impurity phase j at point

i. The ratio l/c:k. gives the main phase : impurity phase ratio.

c

LINEAR BACKGROUND

.#1

P^ag^ii^

^^^f,

° 'j^i*'', .'jj i' jtJijJ'' L''*i iUii i iV''i-'.ii»>t'i<aH3«a"S^tt<ii^g»j^5jgirir>j^ «W.T(»i«%^'i.

4.0 8.0 12.0 16.0

chi

"in ""

C

id20.0 24.0 Anele

28.0

Chebychev polynomial background

iJiWwjjw

i tfHjiawaiWiMi'i^^Va^^wia i

i Wi ,-ie»aiij«;;^

4.0 8.0 12.0 16.0 20.0 24.0 28.0 Angle

Figure 1. Agreement between calculated and observed intensities for

YBa2Cu30g9Q.

Reference

[1] Prince, E. Mathematical techniques in crystallography and materials

science. Springer-Verlag, New York, 1982.

22
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON RIETVELD ANALYSIS OF ANION AND CATION DISORDER

IN THE FAST- ION CONDUCTING PYROCHLORE SYSTEM ^z^r^J^ 1.^)2^7

S. M. Haile and B. J. Wuensch

(Massachusetts Institute of Technology, Cambridge, MA)

and

E. Prince

The cubic pyrochlore structure type, A^BpOy, space group Fd3m, is a superstructure with lattice constant double that of a fluorite-like array of

ions. Cations A and B order in positions 16c 000 and 16d 1/2 1/2 1/2; oxygen

ions are ordered in 48f x 1/8 1/8 and 8a 1/8 1/8 1/8, leaving an anion

vacancy (relative to a fluorite array) at 8b 3/8 3/8 3/8. YpTipO, is a fully-ordered pyrochlore, whereas Y^Zr^O, is fully disordered and

statistically has the fluorite structure. Intermediate solid solutions have

partial order. A progressive increase in ionic conductivity by two and one- half orders of magnitude (1.6 10"^ to 5.0 10"^ ohm'-^cm"-^ at 1000 "C)

accompanies the disorder [1].

High quality powders have been synthesized for compositions

^2^^^x^M-x^2^7 '^^^''"9 X = 0, 0.3, 0.45, 0.60, and 0.90 to permit correlation

of structure with oxygen ion conductivity with the aid of Rietveld powder

profile analysis. Data have been recorded with 1.5530 A thermal neutrons for

the samples with x = and 0.90. Refinement has been sucessfully completed

for the former composition providing as residuals RDy,ann "^ 2.17%, R^p = 9.96%

and R^ = 7.36%.

Most of the information on ordering is contained in the superstructure

intensities. Identically zero in the disordered fluorite state, the

magnitudes of the superstructure intensities are determined by the amount of

displacement of the 48f oxygen ion from the ideal value of x = 3/8

(relaxation toward the oxygen vacancy occurs) and, secondly, by the

difference between the scattering length of the cation species which order in

the A or B site, and the average cation scattering length for a given

composition. The scattering length of Ti is negative (-0.3438) relative to

values 0.775 and 0.716 for Y and Zr, respectively. The average cation

scattering length is small, therefore, and the difference between individual

and average cation scattering lengths is unusually large. The superstructure

maxima are thus as much as three times more intense than the fluorite-type

23
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

substructure intensities that appear in the powder diffraction pattern.

Neutron scattering is, accordingly, an especially sensitive measure of order

in the present system.

Reference

[1] Moon, P. K.; Tuller, H. L. Solid State Ionics 28-30 , 470 (1988).

CRYSTAL STRUCTURE OF 11, 23-DI-TERT-BUTYL-l, 9,11, 13,21, 23-HEXAAZAPEMTACYCL0[19. 3.1^'^. l^»^^.l^^*^^.]0CTAC0SA-3, 5,7(28), 15, 17, 19(26)-

HEXAENE-25,27-DI0NE, {^2q\^^2^^^2^

H. L. Ammon

(University of Maryland, College Park, MD)

and

C. S. Choi

(ARDEC, Picatinny Arsenal, NJ and Reactor Radiation Division)

The crystal structure of the titled compound was determined by x-ray

diffraction, using the ENRAF-NONIUS CAD4 diffractometer at the x-ray

laboratory of the Department of Chemistry, University of Maryland. The

crystals were synthesized and grown by P. R. Dave of Geo-Centers, Inc.,

Hopatcong, NJ. The compound crystallizes in the triclinic Pi space group

with unit cell dimensions of a = 11.2931(9), b = 12.4655(8), c = 13.0891(8),

0! = 68.820(7), ^ = 71.056(6), 7 = 74.530(6), containing two formula units of

the titled compound and an acetonitrile molecule per unit cell. The

structure was solved with the MITHRIL direct methods link, and was refined to

the final R-factors of R = 0.065 and R. , = 0.092. • w There are two independent centrosymmetric molecules in the crystal,

namely molecule A and molecule B, as shown in figure 1. The two molecules

have virtually identical molecular conformations. The benzene ring and their

methylene substituents are planar within experimental error. The

heterocyclic six-membered rings are bent into two planar parts, along the

C1...N3 line in molecule A and C21...N23 in molecule B. The intramolecular

distances across the center of the molecular rings are 5 A or longer in both

molecules. Hydrogen atoms H6 and H6' (molecule A) and H26' and H26'

(molecule B) point into the 5 A cavity.

24
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A three atom moiety, which we have interpreted as acetonitrile

(crystallization solvent), is rather poorly defined because of the large

thermal motions and, subsequently, the methyl hydrogens were not modeled.

The shortest intermolecular distances are C43...01 = 3.147(9) and C43...02 = 3.29(1) A. There are no other contacts within 5 A distances.

A.

^1 CIS ^^ 4hm^i C2

B.

Q O

.0- o ^A A

O

o

O'

Figure 1. ORTEP drawings of molecules A and B,

25
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON DIFFRACTION STUDIES OF THE NARTENSITIC

TRANSFORMATION IN SODIUN METAL

R. Berliner

(University of Missouri, Columbia, MO)

H. G. Smith

(Oak Ridge National Laboratory, Oak Ridge, TN)

J. R. D. Copley

and

J. Trivisonno

(John Carroll University, Cleveland, OH)

Recent neutron diffraction experiments on single crystals of sodium,

using the BT-9 spectrometer, have improved our understanding of the structure

of this metal at low temperatures [1]. We now have ample evidence that

sodium, after passing through the martensitic transformation, adopts a structure similar to that of the low temperature form of lithium, i.e., the

9R (Sm-type) trigonal structure [2]. The transformation in sodium is

observed to occur abruptly at about 35 K, where about 40% of the specimen

transforms to the trigonal form, with the c-axis of the 9R structure aligned

to within a few degrees of the original bcc [110] direction. Each bcc [110]

direction is associated with four variants of the 9R structure, located

symmetrically about the bcc [110] at (1.018,0.92,16) and (0.92, 1.018, ±5), S

being of the order of 0.06. The low-temperature diffraction pattern is

considerably complicated by the presence of these 24 variants. Elastic

diffraction scans along the trigonal [10£] and [20£] directions show that the

diffraction peaks are both shifted and broadened in a manner characteristic

of layer defects (typically stacking faults) [3]. The shifting and

broadening are consistent with the presence of a "double-twin" layer defect,

a defect which is created whenever the 9R stacking order, . .ABCBCACAB. . , is

altered at a layer such that the stacking sequence reverses for a single

layer and then proceeds forward again, e.g., . .ABCBCBCACAB. . . The

correspondence between the model diffraction calculations and the (10£)

elastic scans is shown in figure 1. This type of defect is similar to the

defect predicted by Gooding and Krumhansl [4] in their analysis of the

martensitic transformation in lithium.

26
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In addition to the broadened and shifted 9R diffraction peaks, the

diffraction pattern shows evidence of another phase, tentatively identified

as hep. The extra peaks appear near the (±1,0, ±4. 5) and (±1,0,0) reciprocal

lattice points. The intensities of the hep and 9R peaks were monitored as the temperature of the specimen was changed, as shown in figure 2. We find

that the 9R phase reverts to the bcc near 55 K whereas the hep phase remains,

transforming to bcc at a somewhat higher temperature. The shifts in position

of the hep diffraction peaks, from their ideal (9R index) positions of

(±1,0, ±4. 5) and (±1,0,0), are not yet understood.

1 1 1

(104)

-\ \ 1 r -

(105) Na.30K

PJXPERIMENT

(1.0.13)

(«w),

Ooh

(1.0.10)

(f"^) (I07)j

(7o/) f

^'%oo)

(102)

(1.0.14)

(«M)J

(1.0.8)

-12 -6 12

I I T^

r CALCULATION

iv I A ' - I iv I Aj ^J ILj Aj—=-J—11

-12 -6 6 12

Miller index 1

Figure 1. Upper figure: the measured (10^) diffraction pattern for sodium

at 30 K. Both 9R and hep peaks are shown: the hep peak labels are indicated in italics. Measured peak shifts range from -0.11, for

the (-1,0,-13) 9R peak, to +0.17 for the (-1,0,-1) and (-1,0,3)

hep peaks. Unassigned peaks are believed to be associated with

additional variants in the sample.

Lower figure: the calculated diffraction pattern for a 9R sodium

lattice with 10% single layer "double-twin" stacking faults. The

theoretical diffraction pattern repeats every nine units in £.

The calculated peak shifts are in reasonable agreement with

experiment.

27
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

-

1

-

1

32

45

50

K

K

K

1 1 1 1 T-

>%

"" / 1 ^

_._ _ 55 K / 1 CO \ l"^ 1 — 11 K

*i [;.,\

C ///

'•'

// ii 73 _ /'\- '? ,^ 0) /f ^N a N

/ 6

— £ ^ 1

— u

o */J - /

*x^

\: M

-

*fJ

f

rs r>e -•_[-

1 1 I I ^•1—-

^

-4.8 -4.4 -4.0

. Miner index 1

-3.6

Figure 2. A series of (10^) scans from ^ = -5 to -3.5, normalized to the same neutron monitor count, which demonstrate the existence of a second low temperature phase in sodium. The shifted (104) peak,

which is associated with the 9R phase, was observed to disappear

rapidly (though not completely} as the temperature was increased

from 32 to 55 K, whereas the (101) hep peak, at (-1,0,-4.5) in the

9R notation, remained. The shifted 9R (104) peak reappeared, with

increased intensity, when the sample was cooled to 11 K.

References

[1] Berliner, R.; Smith, H. G.; Copley, J. R. D.; Trivisonno, J. NIST Tech.

Note 1257, C. O'Connor, ed. p. 69 (1989); Bull. Am. Phys. Soc. 34, 769

(1989).

[2] Berliner, R.; Fajen, 0.; Smith, H. G.; Hitterman, R. J. Phys. Rev. (in

press).

[3] Berliner, R.; Werner, S. A. Phys. Rev. B34» 3586 (1986).

[4] Gooding, R. J.; Krumhansl , J. A. Bull. Am. Phys. Soc. 33, 615 (1988).

28
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STRUCTURE OF AlCuFe ALLOYS EXHIBITIKG THE ICOSAHEDRAL PHASE

Y. Calvayrac, M. Cornier-Quiquandon, D. Gratias, and A. Quivy

(C.E.C.M./C.N.R.S.)

R. Bellissent

(C.E.N.-Saclay)

F. Biancaniello, F. W. Gayle, and R. Schaefer

(Metallurgy Division)

J. W. Cahn

(Institute for Materials Science and Engineering)

and

B. Mozer

AlCuFe alloys have been shown to form a stable icosahedral phase [1].

Particular alloys of this phase have been produced which form yery perfect

singly oriented specimens exhibiting very narrow line widths in their x-ray

diffraction patterns [2]. Some of these singly oriented specimens are of

sufficient size to yield precise neutron diffraction patterns [3].

We have obtained both x-ray and powder neutron diffraction patterns on several specimens of ^^63^"25'^^12 P^^pared according to the procedure

determined by some of us [2] which produced the pure icosahedral phase.

Figure 1 shows the x-ray diffraction patterns taken of our specimens. One

observes the narrowness of the peaks of the pattern where many of the peak

widths are essentially determined by the instrumental resolution. The lines

are very well indexed by the procedure for powders given by Cahn, Gratias,

and Shechtman for a 5-d fee reciprocal lattice [4] and show that this alloy

belongs to the face centered icosahedral lattice, different from the

primative icosahedral lattice of our other alloy systems. Neutron diffraction data were taken on only the alloy prepared as an ingot. Figure 2 shows

both the x-ray and neutron diffraction pattern for this alloy. Here again, one observes the very narrow line shapes in the neutron diffraction pattern

that has not been obtained in any other icosahedral system. The x-ray and

neutron diffraction patterns are very similar for this alloy in contrast with

the patterns observed for AlMnSi alloys which have the primative icosahedral

lattice and where the manganese has a negative scattering length which

produces large differences in the relative intensities of the peaks.

29
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

wvJy^'W^^^

(a)

SW^M^M^^t^^HiwV*^ l.li. ~Lt .

68 97 58

7 SB IS 37 Se 45 ee 52 58 68 I ANG

e? 58 ?S 88 82 58 98 88 97 58

Figure 1. X-ray diffraction patterns of AlggCu^rFejp prepared by (a) rapid

solidification, powdering, and annealing; and (b) melting an ingot

in the arc furnace, powdering a small piece cut from the ingot,

and then annealing.

30
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(a)

W^ii-Ww

? se 15 ee 22 sa 3e 1 3> sa 45 ea 525a sai ANC

6^ sa ?5~

62 sa 9B

iiL._^

(b)

OvK

7 SB IS 22 sa 3a ae 3V sa 4b aa 52 sa nNC

68 ee £7 sa ?s ee 82 sa 9a ee 9r sa

Figure 2. A comparison of the x-ray and neutron diffraction patterns of the

alloy prepared as in figure lb. (a) X-ray pattern with good

statistics, and (b) neutron diffraction of the annealed ingot not

powdered

.

31
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

These preliminary studies are part of an international cooperation

between the three laboratories to determine the boundaries of the icosahedral

phase of the ternary phase diagram, to determine the procedure for producing

a unique phase of isotopically substituted alloys, and to use these alloys in

x-ray and neutron diffraction to determine the structure of each constituent

element of these alloys so that a precise model for the atomic distribution

of an icosahedral alloy can be determined.

References

[1] Tsai, A.; Inoue, A.; Masumoto, T. J. Appl . Phys. (Japan), L1505 (1987).

[2] Devaud-Rzepski , J.; Quivy, A.; Calvayrac, Y.; Cornier-Quiquandon, M.;

Gratias, D. Phil. Mag. (to be published).

[3] Bellissent, R. et al . ; private communication.

[4] Cahn, J.; Gratias, D.; Shechtman, D. J. Mater. Res. 1, 13 (1986).

EVOLUTION OF THE KAGNETIC STRUCTURE IN Tb^Yj ^^g

J. A. Gotaas

M. R. Said and J. S. Kouvel

(University of Illinois, Chicago, IL)

and

T. 0. Brun

(Argonne National Laboratory, Argonne, IL)

As the nonmagnetic yttrium ion is substituted for terbium, the cubic

intermetallic compound TbAg changes from a conventional antiferromagnet into

a complex magnetic system with components of both commensurate and

incommensurate spin structures and bulk magnetic properties typical of spin

glass behavior for Tb concentrations less than 50%. We have carried out

neutron diffraction experiments on polycrystalline samples of Tb Y, Ag with

X = 0.15, 0.5, and 1.0 to complement our earlier studies for x = 0.3 [1].

For X = 1.0, the magnetic structure is the (ttttO) anti ferromagnetic

structure observed in many of the CsCl-type RAg (R = rare earth) compounds,

with ferromagnetically aligned [110] -type planes of rare-earth magnetic

moments which are antiferromagnetically coupled. T^, is found to be

32
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

approximately 106 K, and there is no evidence for a change in magnetic

structure on cooling as has been suggested recently on the basis of crystal

field considerations [2].

For X = 0.5, the system orders at Tj^ « 58 K into the mixed structure

observed for x = 0.3, with a peak corresponding to the commensurate (ttttO)

magnetic structure at the (1/2, 1/2, 0) position and asymmetric satellites

arising from an incommensurate modulation of the basic {ttttO) structure. In

this case, however, the (1/2, 1/2, 0) peak is much sharper, and on cooling

below 40 K the incommensurate peaks almost disappear, remaining only as lowintensity shoulders of the commensurate peak at the lowest temperature

measured (T = 4 K). Hysteresis is observed in the relative intensity of the

two components of the structure between 45 and 55 K.

For X = 0.15, the system orders at 1^ =s 18 K into the two component

structure, but with the (1/2, 1/2, 0) peak much broader than the

incommensurate satellite peaks, indicating that the commensurate spin

correlations are an order of magnitude shorter than that of the modulated

structure. The two components have an approximately constant intensity ratio

and show no evidence of hysteresis, similar to the behavior found for x =

0.3. Thus, as the Tb concentration decreases, the relative stability of the

commensurate and incommensurate structures appears to change. In the case of

X = 0.5, the balance is so close that the structure changes from mixed

commensurate/incommensurate to primarily commensurate as the magnetic moment

develops. For x = 0.3 and 0.15, on the other hand, the incommensurate

component exists over larger distances, but the commensurate component

remains in coexistence down to the lowest temperatures measured.

References

[1] Gotaas, J. A.; Said, M. R.; Kouvel , J. S.; Brun, T. 0. J. Phys. 49, C8-

1103 (1988).

[2] Aleonard, R.; Morin, P.; Rouchy, J. J. Phys. 49, C8-395 (1988).

33
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC ORDER IN A Tb^ ^Dy^ ^ SINGLE CRYSTAL

M. L. Spano

(Naval Surface Warfare Center, Silver Spring, MD)

and

J. A. Gotaas and J. J. Rhyne

The rare-earth elements Tb and Dy both order magnetically with

decreasing temperature into a basal -plane helical state, followed at lower

temperatures by a transition to a basal -plane ferromagnetic state. In the

low-temperature ferromagnetic phase, the b-axis is the magnetic easy axis for

Tb, while the a-axis is the easy axis in the case of Dy. In the mixed alloy

system, the competition of the different basal -plane anisotropies leads to

temperature-dependent changes in the easy-axis direction, as indicated by

magnetostriction results [1]. We have utilized neutron diffraction to study

the nature of the magnetic ordering in a single crystal of TbQ rDy^ r at the

NIST reactor.

Measurements were performed on the crystal with the b-axis oriented

perpendicular to the scattering plane, primarily on the (0002) peak and the

satellites observed along the c-axis in the helical phase. On cooling from

the high-temperature paramagnetic phase, the crystal orders into the helical

phase with magnetic peaks observed at (0002 ± 8) at Tj^ « 206 K. In the

vicinity of 170 K, second harmonics begin to appear at (0002 ± 25), arising

from bunching of the moments prior to the ferromagnetic ordering which

appears at T^ ~ 152 K. At this temperature, there is an abrupt reduction in

the intensity of the satellite peaks at 6, while the harmonics at 2 6

effectively vanish, as the ferromagnetic intensity increases sharply at the

(0002) position. Some intensity remains at the satellite positions down to

approximately 130-135 K.

We also observe a Lorentzian peak underlying the (0002) which appears as the moments order into the helical phase. As the temperature decreases, the

width of this Lorentzian decreases and the intensity grows, showing a peak in

the vicinity of 152 K before decreasing again. This may indicate the

presence of critical scattering in the helical -ferromagnetic phase

transition, which would be quite unusual. Further experimental work may be

able to clarify this situation.

34
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In the ferromagnetic phase, the magnetostriction measurements indicate

that the easy magnetic axis changes from the b to the a direction in the

basal plane at about 100 K. In principle, this leads to a rotation of the

ferromagnetically aligned moments from the b to the a axis in the vicinity of

this temperature, which can be observed via neutron diffraction by looking at

the (lOTO) or (1120) reflections. However, in the absence of an applied

magnetic field, there will be domain formation such that the domain-averaged

intensity would be the same whether the moments lie along the a- or b-axis,

making a zero-field measurement insensitive to this transition. It may be

possible to apply a field sufficient to form a single domain, yet weak enough

to allow the moments to rotate when the sample cools enough. This experiment

will be attempted in the future.

Reference

[1] Spano, M. L.; Clark, A. E.; Teter, J. P.; Cullen, J. R. J. Phys. 49,

C8-347 (1988).

ORIENTATION DEPENDENCE OF THE MAGNETIC STRUCTURE IN Dy/Y SUPERLATTICES

F. Tsui, C.P. Flynn, and M. B. Salamon

(University of Illinois at Urbana-Champaign, Urbana, IL)

and

R. W. Erwin and J. J. Rhyne

The dependence of the magnetic structure on growth direction has been

investigated in superlattices made from alternating layers of Dy and Y metals. Using new molecular beam epitaxy techniques we have succeeded in

growing high quality single crystal materials with structural coherence

lengths > 500 A and with the growth direction oriented along the a, b, or c crystal lographic axes. In earlier work we showed that, in c-axis samples, Dy

layers order coherently via RKKY-like interactions propagated through Y layers up to about 150 A thick [1].

In figure 1 we show neutron diffraction data for a b-axis superlattice

[Dy^glYg]. The nuclear superlattice satellites, here enhanced by inducing a ferromagnetic state in the sample, are clearly visible. However, the

magnetic scattering is not resolvable into separate superlattice peaks, and

35
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

furthermore the width of the magnetic peak suggests that the magnetic

coherence is confined to a single Dy layer.

One possible explanation is due to the anisotropy of the interaction

length in yttrium as related to the structure of the conduction electron

susceptibility x(q)- Alternatively, the lack of long-range order might be

related to frustration effects which could be observed in a compositionally

modulated b-axis sample.

240-

"180

COC 120 oo

Figure 1

60-

b-[Dy26^o] -"' -"^ <

(0 f 2)

0- -0.06 -0.02 0.02 0.06

t

Magnetic and structural peaks of the b-axis superlattice

[DypglYg]. The open circles are an (f 2-k) scan across one of

the magnetic peaks and the closed circles are an (f 2) scan in

a field of 2.5 Tesla to show the structural satellites of (0

2). The inset shows a comparable scan through a magnetic group of

the c-axis superlattice [Dyj.|Yg] having long-range order.

Reference

[1] Rhyne, J. J.; Erwin, R. W.; Borchers, J.; Sinha, S.; Salamon, M. B.;

Du, R.; Flynn, C. P. J. Appl . Phys. 61, 4043 (1987).

36
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETOELASTICITY IN RARE-EARTH SUPERLATTICES AND FILMS

R. W. Erwin and J. J. Rhyne

and

J. Borchers, R. Du, M. B. Salamon, and C. P. Flynn

(University of Illinois at Urbana-Champaign, Urbana, IL)

Recently developed techniques for growing epitaxial rare-earth

superlattices and thin films have afforded a unique opportunity to study the

interactions responsible for the complex magnetic orderings in these

materials. In particular, it has been possible to measure the range,

strength, and nature of rare-earth exchange interactions by interleaving

dissimilar layers of rare earths with and without local magnetic moments [1],

thereby fine-tuning the already well developed and successful theoretical

framework for rare-earth magnetism [2].

We have been focusing on investigations of the role of magneto-elastic

energetics in determining the magnetic structure. These energetics are modified by the constraints imposed by epitaxy of the magnetic lattice to

nonmagnetic interlayers and the substrate. Because magnetostriction is large

in magnetic rare earths, approaching one percent, we can expect that the role

of magnetoelastic energetics in determining the magnetic structure will be

emphasized in these highly strained materials.

Neutron diffraction data from a Dy thin film and a [Dy|Y] superlattice

are shown in figure 1. These data were collected at the NIST reactor using a beam of 13.5 meV neutrons and wave vector resolution of 0.02 A" at wave vector transfers near 2 A' . The magnetic structure of Dy [3] is a basal

plane helix modulated along the c-axis of the hep structure. This structure

is also found in the films and superlattices. This magnetic order is thus

described by the single parameter w, the precession angle of the basal -plane

moments from one atomic plane to the next.

The data for a 4000 A Dy film shown in figure la, are quite similar to

those obtained for the bulk material. The helimagnetic structure collapses

in a first-order phase transition to a ferromagnetic state just below Tp = 80 K (compared to 85 K for the bulk). However, the temperature hysteresis

for this transition is about 15 K (compared to 5 K for bulk Dy), and on cooling the transition may require as long as one hour for completion.

37
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The diffraction from a superlattice consisting of bilayers of 16 atomic

planes of Dy alternated with 9 atomic planes of Y is compared to the film in

figure lb. Although the initial ordering temperature, T|^, is within 7 K of

the bulk and film values (185 K), there is evidently no collapse to the

ferromagnetic state down to 5 K. The temperature dependence of w obtained

for the Dy layers is shown in figure 2b for three different superlattices,

while the result for bulk Dy is shown in figure 2a for comparison.

100

•E3

Dy film

4000 A

[l^yielYg]

2.1 2.3 2.1 2.3

Qz (A-')

2.5

Figure 1. (a) The neutron diffraction scan along the (OOOO direction

determines the magnetic structure in a 4000 A film as a function

of temperature. The intensity associated with the helimagnetic

state collapses onto the (0002) Bragg peak below about 80K, but

the width of this magnetic scattering is not resolution limited.

This zero field ferromagnetic correlation length is about 200 A.

In (b) the same scans at the same temperatures for a [Dy^glYg]

superlattice show that the ferromagnetic transition is suppressed,

although weak magnetic satellites appear about the (0002)

position.

As a first step towards understanding the magnetic structure in the Dy

films and superlattices, we apply the theories developed to explain the

ordering in bulk Dy [2]. The elastic energy is quadratic in the strains and

the magnetoelastic energy is linear,

^me 2 ^^iri ^ ^22^2 ^ ^ S^ ^1^1 ^2^2 - Vt (1)

38
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The c's are the elastic constants and the K's are the magnetoelastic coupling

parameters in a hexagonal symmetry basis. The magnetoelastic energy obtained

experimentally from the elastic constants and the anomalous strains as obtained by Rosen et al . [4], is reproduced in figure 2c. The discontinuous

decrease of the magnetoelastic energy at T^ drives the transition by

overcoming the exchange energy difference between the ferromagnetic and

helimagnetic states. The 7-mode associated with an orthorhombic distortion

is the part of the magnetoelastic energy which is primarily responsible for

the ferromagnetic transition, and this magnetoelastic energy can only be

gained when u = (the clamping effect).

Figure 2.

40-

_ _ 1 1 1

bulk Dy /

•^ 20- y

3

n-

(a)

1 1

* • • 1

[Dy|Y] c-axis

(b)

o

-^

(c) ^

^

-6-

10- 1 -i 1 100 200

T (K)

100 200

The turn angles, w, are compared as a function of temperature for

bulk Dy (a) and the c-axis superlattices (b). The superlattice

values are greater than in the bulk, remaining at or above 30°

down to the lowest temperatures. The solid curve in (b) is the

calculation for the completely "clamped" film or superlattice.

The measured magnetoelastic energy for bulk Dy, obtained from the

elastic constants and anomalous strains is shown in (c), while the

calculation for the "clamped" material is shown in (d).

Two mechanisms [2] have been proposed to explain the decrease of w as the temperature is lowered. Either the position of the minimum of the

exchange energy shifts, possibly due to the creation of magnetic super-zone

gaps, or the temperature and w dependence of the magnetoelastic energy

produces a shift in the minimum of the total energy. The w dependence of the

39
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

magnetoelastic energy arises from the strain derivative of the exchange

energy and produces a cosw term. To model the effect of the a-modes on the

temperature dependence of above Tp we use a parabolic approximation for the

exchange energy near u so the turn angle which minimizes the energy

satisfies

s2j"(w^) (cosw - cosWq) = K^ . (2)

The more rapid temperature dependence of the magnetoelastic coefficient K

2 compared to S drives the turn angle towards zero in this model.

At this point we can transfer the analytic result for the exchange of

bulk Dy directly to the superlattices. The epitaxial constraints can be

built into the equilibrium magnetoelastic energy expression for the c-axis

growth direction materials to show that the strains in the growth plane are reduced by the factor l/(l+r), where r is the ratio of nonmagnetic to

magnetic material, and the contribution of those strains to the magnetoelastic energy is also reduced by this same factor. The nonmagnetic strain

along the z-axis is determined solely by Poisson's ratio, while the magnetic

z-axis strain includes the z-axis magnetoelastic contribution K /c^o.

A calculation of the temperature dependence of w based on this model is

shown in figure 2b, showing a reasonable agreement with the observed values

in the superlattices.

The energy difference between the helimagnetic and ferromagnetic states

in the superlattice is calculated to be roughly 2 K/atom at 10 K, compared to

the 4 K/atom jump at Tp in the bulk. This difference corresponds to a critical field of 2 K/atom ~ 3.5 kOe on 10 /ig. Magnetization measurements in

fact show the low temperature critical fields are 3 kOe or less.

The above predictions are in sharp disagreement with the observation for

the Dy film where Tp was only suppressed by 5 K. In the ferromagnetic state

we have applied a saturating field of 25 kOe along the easy a-axis direction

to insure that we are not measuring a domain averaged lattice parameter. The

application of the magnetic field was observed to sharpen the (0002) Bragg

peak to a resolution limited width, consistent with the formation of a single

domain. We then measured the change in the b-axis lattice parameter from

just above Tp in zero field to below Tp with the field applied. The

resulting anomalous strain was found to be only about 1/3 of the

40
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

discontinuity at Tp in bulk Dy. This is a peculiar result since it suggests

that the 7-mode driving energy is also reduced by 1/3, yet the ferromagnetic

transition still occurs. Furthermore, we found that the Nb buffer layer

undergoes no anomalous strains at all. This indicates that anelastic

processes are involved, probably at the interface between the rare earths and

the Nb.

As the magnetic structures in Er are more complicated than in Dy, so are the theories which attempt to explain them. This makes the transfer of these

theoretical ideas to the superlattices and films a more difficult and less

certain procedure. For example, the magnetoelastic energy can be treated

with the same formalism outlined for Dy. Using the measured elastic

constants and anomalous strains in bulk Er, we estimate the magnetoelastic

driving energy for the ferromagnetic transition to be 2.2 K/atom in agreement

with the original calculation of Rosen et al . [4]. Assuming complete

clamping in the growth (basal) plane as before, we find that the magnetoelastic driving energy should be reduced to about 1.4 K/atom. While this

might explain qualitatively the suppression of the ferromagnetic transition,

it fails to explain quantitativley the magnitude of the critical field

measured in the superlattices and films by Borchers et al . [5]. It also

doesn't explain the dependence of the critical field on sample thickness

observed in these materials [5]. It requires a 1 micron thick film before

the energy associated with the critical field becomes roughly equivalent to

the calculated magnetoelastic energy for the completely "clamped" material.

In summary, the magnetic structure of Dy films and superlattices when

compared to that of bulk Dy suggests that magnetoelastic interactions

predominantly control the temperature dependence of the turn angle.

Quantitative calculations of the magnetoelastic energies are also in

agreement with the observed critical fields in these materials. The

energetics determining the magnetic structure in the Er films and superlattices cannot be explained by magnetoelasticity alone, and additional work

is in progress on these materials.

References

[1] Rhyne, J. J.; Erwin, R. W.; Shantanu Sinha; Borchers, J.; Salamon, M

B.; Du, R.; Flynn, C. P. J. Appl . Phys. 61, 4043 (1987); Salamon, M

B.; Shantanu Sinha; Rhyne, J. J.; Cunningham, J. E.; Erwin, R. W.

Borchers, J.; Flynn, C. P. Phys. Rev. Lett. 56, 259 (1986); Erwin, R

W.; Rhyne, J. J.; Salamon, M. B.; Borchers, J.; Shantanu Sinha; Du, R.

41
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Cunningham, J. E.; Flynn, C. P. Phys. Rev. B35, 6808 (1987); Majkrzak,

C. F.; Gibbs, D.; Boni, P.; Goldman, A. I.; Kwo, J.; Hong, M.; Hsieh, T.

C; Fleming, R. M.; McWhan, D. B.; Yafet, Y.; Cable, J. W.; Bohr, J.;

Grimm, H.; Chien, C. L. J. Appl . Phys. 63, 3447 (1988).

[2] Cooper, B. R. Phys. Rev. Lett. 19, 900 (1967); Phys. Rev. 169, 281

(1968); Evenson, W. E.; Liu, S. H. Phys. Rev. 178, 783 (1969);

Elliot, R. J.; Wedgwood, F. A. Proc. Phys. Soc. (London) 81, 846

(1963).

[3] Wilkinson, M. K.; Koehler, W. C; Wollan, E. 0.; Cable, J. W. J. Appl.

Phys. 32, 48S (1961).

[4] Rosen, M.; Klimer, H. Phys. Rev. Bl, 3748 (1970); Rosen, M.; Kalir,

D.; Klimer, H. Phys. Rev. B8, 4399 (1973).

[5] Borchers, J.; Salamon, M. B.; Du, R.; Flynn, C. P.; Erwin, R. W.;

Rhyne, J. J. J. de Physique (to be published); Borchers, J.; Salamon,

M. B.; Du, R.; Flynn, C. P.; Erwin, R. W.; Rhyne, J. J. J. Appl. Phys.

61, 4050 (1987); J. Appl. Phys. 63, 3458 (1988).

NEUTRON DIFFRACTION STUDIES OF Cdj^Mfij^Se FILMS AND ZnSe/MnSe MULTILAYERS

T. M. Giebultowicz, P. Klosowski, N. Samarth, H. Luo, and J. K. Furdyna

(University of Notre Dame, Notre Dame, IN)

and

J. J. Rhyne

We have begun neutron diffraction studies of new diluted magnetic semiconductor (DMS) films and superlattices grown by molecular beam epitaxy

(MBE). This technique makes possible the preparation of entirely new DMS

systems that do not form in the bulk. One of the latest achievements in this

field [1] has been the growth of zinc-blende (ZB) type Cd, Mn Se epilayers

on (100) GaAs substrates with Mn concentrations up to x = 0.75 and

thicknesses up to 2 /zm. In the bulk form, Cd, Mn Se can be obtained only in

the wurtzite structure with x < 0.50. In samples with x = 0.70 and 0.75 we have observed additional diffraction maxima at low temperatures clearly

indicating the Type III ant i ferromagnetic structure (AF III). This type of

order, which is associated with doubling of the crystal lographic unit cell

along one of the cubic axes, also occurs in two other alloys from the

II VI

^l-x^"x^ DMS series, Cdj_^MnJe and Zn^^^MnJe, which form bulk ZB-type

crystals. However, in striking contrast with the short-range nature of the

42
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

spin correlations seen in those materials, our data from Cd, Mn Se epilayers

indicate a formation of long-range ordered AF III domains. Such domains have

the doubling direction parallel to the epilayer surface, whereas for the

third domain orientation the order remains of a short range (see fig. 1).

The reasons for such an anisotropic behavior are not yet clear, considering

that the epilayers exhibit no significant tetragonal distortion.

Another example of new MBE-grown DMS systems are ZnSe/MnSe multilayers

[2]. The Mnse and ZnSe layers grow both in the ZB structure, although bulk

MnSe forms only NaCl-type crystals. We have investigated superlattices

containing 100-200 ZnSe/MnSe bilayers with thicknesses 60-105 A, and the MnSe

layer thicknesses 22-50 A. Nuclear diffraction patterns from the multilayers

exhibit a number of satellite lines well resolved from the GaAs substrate

reflections, in good agreement with theoretical calculations. At low T we have observed additional peaks, clearly indicating an AF III spin structure

in the MnSe layers. However, in contrast to the behavior observed in the

Cd, Mn Se epilayers, the tetragonal axes of the domains are oriented in the

direction perpendicular to the layers. The magnetic reflections were

strongly broadened in the growth directions, showing that the AF III order

does not propagate through the non-magnetic ZnSe layers, which is consistent

with the short-range nature of the exchange interactions in a semiconducting

crystal. The data obtained from supperlattices with MnSe thickness 22 A

(i.e., corresponding to about 7 nanomolecular layers) exhibit no indication

of ant i ferromagnetic order breakdown which is expected in the 2D limit,

confirming previous conclusions that films with such thicknesses can be still

treated as three-dimensional systems.

43
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

750

500

250

t->W

a 750 a

-" 500

>5 250

"oj

iX

Q =^(1.0.0

200

100

Q=¥(i.f.o)

Q = ¥(e.i.o)

X^ $ I

mM^

0.4 0.5 0.6 Wavevecl.or component ^ (redLiced units)

Figure 1. Diffraction scans through AF III reflection points

(lO^), (l20),and (^lO) for a Cd^ 3MnQ ^Se epilayer at 4.2 K. The

three points correspond to AF III domains with the doubling

directions oriented, respectively, along the z, y, and x crystal lographic axes, as shown in the insets. Note the striking

difference between the the peak widths and intensities for the inplane and normal -to-the-plane domain orientations.

References

[1] Samarth, N.; Luo, H.; Furdyna, J. K. Appl . Phys. Lett, (in press).

[2] Kolodziejski, L. A.; Gunshor, L. A.; Otsuka, N.; Gu, B. P.; Hefetz, Y.;

Nurmikko, A. V. ibidem, 4Z, 1482 (1986).

44
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

EXCHANGE INTERACTIONS IN Co-BASED II-VI DILUTED MAGNETIC SEMICONDUCTORS

T. M. Giebultowicz, P. Klosowski, and J. K. Furdyna

(University of Notre Dame, Notre Dame, IN)

and

J. J. Rhyne and T. J. Udovic

The nature of the basic magnetic exchange interactions between substitutional magnetic ions in host semiconducting lattices (such systems are referred to as Diluted Magnetic Semiconductors (DMS)) continues to receive

strong attention from both experimentalists and theorists. Significant progress has been recently made [1,2] in understanding the Mn-Mn interaction in

DMS materials belonging to the A, „Mn B class (where A = Zn, Cd, or Hg, WT i-x X and B = S, Se, or Te; e.g., Cd, Mn Te, or Zn, Mn Se). In contrast, very

little is still known about the exchange interactions in II-VI DMS alloys

containing transition metal atoms other than Mn. Progress in experimental

studies of such systems has been limited due to the lack of high quality

crystals. However, new opportunities have opened up in this field thanks to

recent developments in sample preparation techniques. For instance, the use of high-pressure inert gas furnaces, as well as the adaptation of ceramic

techniques, have made it possible to prepare an entirely new line of Co-based

II-VI DMS compounds.

We have carried out the first direct measurements of the nearestneighbor (NN) anti ferromagnetic exchange constant J|^|^ in three of the new

alloys (Zn, Co S, Zn, Co Se, and Zn, Co Te) using neutron scattering

methods. Measurements performed on samples with x = 0.01 - 0.06 at low T

revealed distinct inelastic scattering maxima corresponding to transitions

between the excited states of isolated NN Co-Co pairs. In II-VI lattices the

2+ orbital momentum of the Co ion (L = 3) is quenched by the tetrahedral

crystal field, and the Co-Co interaction can be treated, to a very good

approximation, as a Heisenberg-type exchange between two S = 3/2 spins. Such

a pair, normally possessing a ground state with total spin Sj = 0, has three

excited levels with Sj = 1, 2, or 3, and with energies 2J|^j., 6J|^|^, and 12Jmm,

respectively. The selection rules for neutron scattering allow transitions

between adjacent levels only (ASj = + 1), so that the inelastic maxima occur

at E = 2J|^|^, 4J|^j^, and ^^k,ki- One of the clear signatures of this process is

the temperature behavior of the maxima. At low T the excited levels are not

45
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

populated, and one observes only a single maximum at E = 20^,^. corresponding

to a transition from the ground state to the first excited state (|0 >-* |1>).

As T is raised, the population of the Sj = 1 level gradually increases,

giving rise to a |1 >-^ |2> peak at E = 40^,,.. At the same time, the first

maximum decreases in intensity. An example of the Zn, Co S data

illustrating such behavior is displayed in figure 1. From the positions of

the |0 >^ |1> maxima

systems investigated are 4.1 ± 0.05, 4.2 ± 0.1, and 3.3 ± 0.1 meV,

respectively. The exchange interaction in all three systems is decidedly

stronger, and exhibits a different chemical trend than the interactions in

their Mn-based counterparts. This latter fact cannot be understood in light

of the presently existing theory of II-VI DMS systems [1].

Ziio94CooogS, Q=1.347x27T/a

1 r

we have established that the 0^^ values for the three

10 15

Energy (rneV)

Figure 1 Inelastic scattering spectra from polycrystalline ZnQ qa^^q qc^S at

three different temperatures, showing the |0 >^ |1> and 1 1 >-^ |2>

transition peaks from NN Co-Co pairs. The broad feature at E « 11

meV, which is seen also in pure ZnS (see the inset), can be

attributed to phonon scattering.

References

[1] Larson, B. E.; Mass, K. C; Ehrenreich, H.; Carlsson, A. E. Rev. B37,

4137 (1988).

[2] For review of experimental studies of Mn-based II-VI DMS, see, eg.,

Fudyna, J. K. J. App. Phys. 64, R29 (1988).

46
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CHARACTERIZATION OF THE QUASICRYSTALLINE STATE OF A1^3Mn2jSig

FROM NEUTRON SCATTERING EXPERIMENTS

A. Goldman

(Iowa State University, Ames, lA)

M. Bessiere, Y. Calvayrac, D. Gratias, S. Lefebvre, and A. Quivy

(C.E.C.M./C.N.R.S. Vitry, France)

and

B. Mozer

Neutron scattering experiments were used to help characterize the

magnetic state observed at low temperatures in the icosahedral phase of the

alloy Aly-Mn^jSig which was prepared at C.E.C.M./CN.R.S. , Vitry. Measurements were performed at the NIST research reactor on the powder diffraction

instrument, BT-1, at room temperature and at low temperature below the

magnetic transition to observe if there were any changes in the relative

intensities of the diffraction peaks. The diffraction peaks observed for

this alloy show narrow peaks but they still exhibit evidence of disorder.

Preliminary analysis of the data indicates no significant changes in the peak

intensities associated with the magnetic ordering and do not show any

evidence of new peaks which might indicate a possible ferro- or antiferromagnetic transition. Polarized neutron scattering experiments were then

performed on the triple-axis spectrometer H8 at Brookhaven National

Laboratory using polarized neutrons and polarization analysis. The

spectrometer was used in the spin-flip mode of operation so as to observe

only the magnetic contribution to the scattering from our powder sample. The

collimation of the instrument and the incoming energy were chosen so as to

insure that all energies of the scattered neutrons were included in the

acceptance angles of the analyzer-detector when used in the elastic

scattering mode.

Spin-flip measurements were taken on the sample at temperatures of 9 K

and 150 K as a function of the wave vector difference (q) for values of q

from 0.40 to 2.84 A' . A spin-flip measurement at constant q, 0.40, as a function of the temperature was taken for temperatures from 9 K to 280 K. Figure 1 shows the form factor for the magnetic scattering of our icosahedral

alloy at the two different temperatures. The form factor at the lowest

temperature is the same as that measured by one of us [1] on the icosahedral

47
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

alloy AKMn. This form factor is very different from that observed for

manganese in metal alloys or compounds. The higher temperature form factor

is much different than would be expected for a paramagnetic scatterer as observed by K. R. A. Ziebeck and P. J. Brown [2] and still seems to show some magnetic ordering.

2500

2000 -

§1500

0) ^ 1000

Q.

I 1. 500

CO

Figure 1. The spin-flip differential scattering from the icosahedral phase

of AU^MnpiSig as a function of q = 47rsin5/X at 9 K and 150 K.

References

[1] Goldman, A.; Zabel , H. private communication.

[2] Ziebeck, K. R. A.; Brown, P. J. J. Phys: Metal Phys. 10, 2015 (1980).

48
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

ANTI FERROMAGNETIC ORDER IN YBagCUj^^COj^Og

P. F. Miceli, J. M. Tarascon, L. H. Greene, P. Barboux, and M. Giroud

(Bell Communications Research, Red Bank, NJ)

and

D. A. Neumann and J. J. Rhyne

and

L. F. Schneemeyer and J. V. Waszczak

(AT&T Bell Laboratories, Murray Hill, NJ)

While the mechanism responsible for superconductivity in the high

temperature superconducting oxides is still not understood, current theories

suggest that electron pairing may arise from ant i ferromagnetic correlations.

This viewpoint is supported by the discovery of long-range antiferromagnetic

order in the nonsuperconducting parent compounds, La^CuO. and YBaCu^Og,

which suggests that antiferromagnetic correlations may indeed exist in the

superconducting phases. It is therefore of interest to understand how

substitutions for Cu, particularly by other magnetic ions such as Co, affect

the magnetic properties of the parent compounds. Thus we have undertaken a neutron diffraction study of magnetic order in oxygen deficient

YBa^CUg, Co Og for two powder samples, one with x = 0.2 and y = 0.45, and

the other having x = 0.8 and y = 0.91.

The results show that the x = 0.2 sample orders antiferromagnetically in

a two step process. Below T-.^ 211 K, {^H) reflections exist for both

integral and half-integral values of £ (fig. la). For temperatures between

T-. and and a second transition at T = 415 K, only peaks corresponding to

integral i remain (fig. lb). Above T long-range magnetic order disappears.

The appearance of (H£) reflections is characteristic of a structure

consisting of antiferromagnetic sheets ordered with spins alternately along

[110] and [TTO], while the absence of a (f^O) peak indicates that the net

spin is zero when summed along the c-axis. In order to further determine the

stacking of the antiferromagnetic sheets, structure factor calculations have

been performed for the 5 K data. For integral i, the best fit to the

observed intensities was obtained using a model in which the moment on the

single "chain" site is zero, while the moments on the two "plane" sites are 0.41 /fg. The stacking sequence can then be represented as +0 - +0 - where

49
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the + and - refer to the moments on the "plane" sites. For half-integral H it was necessary to also include a nonzero moment on the "chain" site and an angle of ~ 111" between the spins on the different types of sites in order to

obtain an acceptable fit to the observed intensities. The stacking sequence

can then be represented as +r + -r' - where the + and - again refer to the

spins on the "plane" sites and r refers to the moment on the "chain" site

which has been rotated in the basal plane (r' denotes a spin which is

antiparallel to that denoted by r). The best fit moments were 0.18 /ig and

0.62 Hd for the "plane" and "chain" sites respectively. The total magnetic

structure for the x = 0.2 sample is then simply the vector sum of the

structures determined for the above two cases. A substantially different magnetic structure is found for the x = 0.8

sample. Here only half-integral H peaks are observed between 5 K and a single magnetic transition at T-.^ 435 K (fig. 2). This immediately implies

that the moments on the two types of sites are equal. An excellent fit to

the intensities measured at 5 K was obtained for a moment of 0.68 Hn and a simple stacking of +-+-+-.

Thus the presence of Co substantially alters the antiferromagnetic

structure of oxygen deficient YBa^Cu^, Co Og by enhancing the half-integral

H type of ordering. This implies an increased magnetic coupling between the

"plane" and "chain" sites upon the substitution of Co, which resides

principally on the "chain" sites. However, it is not possible to decouple

the effects of concentration from those due to differing Co concentrations

with the present data. Further studies are planned to clarify the effects of

concentration on the magnetic properties of these materials.

50
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

3000 —

2500

e 2000

= 2500

1500

1 I i i I Y Ba.Cu.,Co, jO„5

T=5K

I I T=300K

ri|i 'Y'

I I

(b)

' '"rijr W^»H '*^/i#'

I I I

I

O 40G0

2000

YBa,CUj_,Co„.30,.3 —. (11

- \2 2

200400 600 8001000

T[KT

'.''«'.«'-'sS'*"i-d'i

1.2 1.3 1.4 1.1 1.2 1.3 1.4 QtA']

Figure 1. (left)

Figure 2.

YBa2Cu2. 8^0.206. 45'

Ant i ferromagnetic diffraction peaks for

(a) The occurrence of peaks of the form

(1/2, 1/2, i') where H' is half integral indicates the occurrence

of anti ferromagnetic spin ordering on the chain Cu,Co-0 sites

below T, ~ 211 K in addition to order on the Cu-0 plane sites

manifested by the integral £ (1/2, 1/2, £) peaks. (b) At

temperatures above T,, but below the upper N6el temperature T «

415 K, only integral H peaks occur indicating that the chain site

moments have become disordered. Within each Cu-0 layer (chain or plane) spins are oriented antiparallel with a propagation vector

along [110].

(right) In the more full Co substituted compound

YBapCUp oCOq 8^6 9 °"^^ half- integral H' peaks are observed over

the full temperature range below Tjg ~ 435 K. This indicates that

the additional Co has enhanced the exchange coupling and produces

essentially similar moments on both chain and plane sites.

51
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

OXYGEN DEPENDENCE OF THE MAGNETIC PHASE TRANSITIONS IN YBa2Cu2 gCo^ ^0^^

P. F. Miceli, J. M. Tarascon, P. Barboux, L. H. Greene, and M. Giroud

(Bell Communications Research, Red Bank, NJ)

and

D. A. Neumann and J. J. Rhyne

A complete understanding of high-temperature superconductivity must

include the interesting magnetic properties of the Cu oxide based

superconductors, which are either superconducting or antiferromagnetic

depending on the composition. An important tool for probing the basic

physical properties, in particular the magnetic properties, of these systems

is the isomorphous substitution of magnetic ions such as Co for Cu. Previous

work has shown that Co preferentially occupies the "chain" site in these

materials [1] and that two antiferromagnetic transitions exist for y = 0.45

corresponding to magnetic ordering first on the "plane" sites (AFl) followed

by ordering on the "chain" sites as well as the "planes" (AF2) [2]. At

higher oxygen concentrations the samples become superconducting. Thus, this

system exhibits all of the essential magnetic and superconducting features

which are present in the parent compound YBa^Cu^Og . We have therefore

performed neutron scattering studies in order to determine the oxygen

dependence of these transitions in YBa^Cu^ qCOq p^e+v'

These experiments were performed on six powder samples, each weighing

about 10 grams, prepared by standard solid-state reaction techniques. Powder

diffraction measurements were performed using the BT-1 spectrometer which

allowed the determination of the content to ± 0.02 using Rietveld analysis.

The magnetic structures were then determined as a function of temperature

using the triple-axis spectrometers at BT-2 and BT-9. AC susceptibility

showed that only the sample with y = 1.0 was superconducting with a T = 60 K.

The oxygen dependence of the two magnetic phase transitions determined

from the temperature dependence of the whole and half integer H is shown in

figure 1. Here 1^ and T^, refer to the transition to the antiferromagnetic

phase which displays "plane" site ordering only (integer H) and to the phase

which displays ordered moments on both "chain" and "plane" sites (halfinteger i)y respectively. The solid and dashed lines serve as guides to the

eye; however, the dashed lines are not intended to be used for interpolation.

52
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

500

400-

300

YBa^Cu^gCo^^Og^^

T(K)

Figure 1.

200

100-

0.2 " 0.4 0.6 0.8

Oxygen Concentration: y

Oxygen dependence of the two magnetic phase transition temperatures in YBa^CUp gCo^ p^s+v* ^^^ results are presented

schematically in the inset.

It is seen that both transition temperatures increase with decreasing oxygen

content until y = 0.32 where both "chains" and "planes" order at a single

temperature. No magnetic ordering has been found at y = 1. The inset is a schematic diagram showing the regions of paramagnetic (PARA), superconducting

(SC), and ant i ferromagnetic behavior. We have also performed a similar

experiment on a sample with a Co concentration of 0.8 which displayed only

half-integer i peaks for all concentrations [2]. Thus the effect of adding

Co is to raise the "chain" site ordering temperature T

N,

""til T„^= T„^.

These results provide a direct test for theoretical models which make

predictions concerning the electronic and magnetic interactions in these

materials.

References

[1] Miceli, P. P.; Tarascon, J. M.; Greene, L. H.; Barboux, P.; Rotella, F. J.; and Jorgensen, J. D.; Phys. Rev. B3Z, 5932 (1988).

[2] Miceli, P. F.; Tarascon, J. M.; Greene, L. H.; Barboux, P.; Giroud, M.;

Neumann, D. A.; Rhyne, J. J.; Schneemeyer, L. F.; and Waszczak, J. V.;

Phys. Rev. B38, 9209 (1988).

53
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC PROPERTIES OF Bi2A2TOg: A = MSr.Ca AND T = Co,Mn

P. F. Miceli, J. M. Tarascon, P. Barboux, G. W. Hull, and L. H. Greene

(Bell Communications Research, Red Bank, NJ)

and

J. J. Rhyne and D. A. Neumann

Bi^Sr^CuOg belongs to the general class of high-temperature superconductors of the form BioSr^Ca jCu with n = 1, 2, 3 where n is the

number of CuO^ layers. Ant i ferromagnetic interactions are believed to be

important to all Cu oxide superconductors; however, unlike La^, Sr CuO, and

YBapCu^Og , there has been no clear experimental verification of a crossover

from anti ferromagnetic order to superconductivity in the Bi based Cu oxide

systems due to the difficulties in varying the composition of these

materials. Therefore we have begun neutron scattering studies of Bi^Sr^CoOg,

Bi^Sr^MnOg, and Bi^Ca^MnOg to investigate the magnetic properties, which

directly reflect the electronic structure, of this general class of

compounds. These materials also exhibit a structural modulation and it is of

considerable fundamental interest to understand how the modulation impacts

the magnetic properties. Recent magnetic susceptibility studies have

suggested the presence of weak ferromagnetic and/or spin canting behavior.

The magnetic neutron diffraction results obtained by subtracting high

temperature data from that at 6 K are shown in figures 1-3. The intensities

of the peaks can be reproduced with simple spin structures. For Bi^Sr^CoOg,

the spins are antiferromagnetically ordered in the a-b plane, while in both

of the Mn compounds, the spins are antiferromagnetically ordered along the c- axis. These powder diffraction results suggest that there is an average spin

structure in these compounds which is unaffected by the modulation. In

contrast, very recent measurements performed on single crystals of BipSr^MnOg

have shown an interesting field dependence as well as yery weak magnetic

satellite peaks which indicates that the average spin structure is indeed

perturbed by the modulation.

54
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. Magnetic neutron diffraction scan for Bi^Sr^CoOg at 6 K.

4000

2000

6000

—: : 1 1 1

(101)

T

4 (012) 2 2 6

4000

(010).

•

•

(1C3)

•

2000 t

•

i i (014)

;• , (105) (016)

n J uUwwA--**^

1.5 1.7 1.9 Q (inv. Angstroms)

1.1 1.3 1.5 1.7 1.9

Q (inv. Angstronns)

2.1

Figure 2. (left) Magnetic neutron diffraction scan for Bi2Ca2MnOg at 6 K,

Figure 3. (right) Magnetic neutron diffraction scan for Bi2Sr2MnOg.

55
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE DEFECTIVE STRUCTURES OF Ba2YCu30g^^ AND Ba2YCu3 M Og^^

(M = Fe, Co, Al, Ga)

A. Santoro

A knowledge of the oxygen distribution in the basal planes of

BapYCu-Og and B^p'^^^^S-v^v^B+z ^^ ^ prerequisite to an understanding of

the superconducting properties of these materials. Models for the oxygen

ordering and the defect structure in ^^2^^^2^6+x ^"^ ^''2^^^3-v^v^6+z ^^^ ^®

derived from a study of the twinning present in the orthorhombic phase of

these compounds, from an analysis of the possible structures at the twin

boundaries, from the coordinations available to the copper and M ions for

various models, etc. It has been shown [1] that the twin laws operating in

this system are (110) , (110) , and [001]gQo and that there is a strong

relationship between twin boundaries and the oxygen stoichiometry. In

addition, it seems that the most probable structure of the twin walls is one

in which the copper ions at the boundary have a distorted tetrahedral

coordination. By eliminating from this model the oxygen atoms so that small

chains with different crystallographic orientations are formed, it is

possible to derive configurations for the defect oxygen compositions in which

the number of copper ions in three-fold coordination is miniminized, or reduced to zero. Similar considerations, and essentially the same oxygen

configurations, are used to build models of the defect structures of the M

substituted compounds, ^^2^^^2-\/^\/^6+7' ^" these cases, the type and the

degree of the substitution depend yery strongly on the size and the

coordination of the M cations replacing the copper ions on the basal plane.

Reference

[1] Hodeau et al . Solid State Commun. 64, 1349-1352 (1987).

56
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC ORDER OF Nd IN NdBa2Cu30g^j^

W.-H. Li and J. W. Lynn

(University of Maryland, College Park, MD and Reactor Radiation Division)

R. W. Erwin

and

K. N. Yang, J. M. Ferreira, B. W. Lee, and M. B. Maple

(University of California San Diego, La Jolla, CA)

The nature of the magnetic ordering of the rare earth ions R in the

f^^^2^^2^6+yc ^y^^^^ ^^^ ^^^ identity of the dominant interaction, exchange or dipolar, has become somewhat controversial. Specific heat measurements [1] on the Nd system show that at full oxygen stoichiometry (x = 1) the anomaly

associated with magnetic ordering at Tj^ == 0.5 K can be analyzed

quantitatively on the basis of the 2-d anisotropic Ising model, indicating

that the interactions are highly anisotropic, while at x ~ the anomaly is

much broader, and occurs at a temperature which is three times higher. In

the related Er system we have recently shown [2] that the magnetic

interactions are indeed 2-d in nature, even though 3-d Bragg peaks are observed below the Neel temperature.

To determine the spin configuration of the Nd ordering in this system,

neutron powder diffraction measurements were taken on a standard triple-axis

spectrometer, with the conventional experimental setup of employing a pyrolytic graphite PG(002) monochromator and PG filter, and a wavelength of

2.355 A. The sample was mounted in a top-loading dilution refrigerator with

a low temperature capability of -25 mK. A complete magnetic diffraction

pattern was obtained by using the subtraction technique, in which data taken

at high temperatures are subtracted from data taken well below 1^: only the

magnetic contribution to the scattering will survive the subtraction

procedure.

The data obtained are quite similar to other systems we have studied

recently, and hence we will only summarize the results. The observed widths

of the magnetic peaks are consistent with the instrumental resolution, thus

indicating that the system exhibits 3-d long-range magnetic order, with the

magnetic unit cell just double the chemical unit cell along all three

crystallographic directions. This is a simple magnetic structure in which

nearest neighbor spins in all three directions are aligned antiparallel , and

57
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

is the same type of structure which has been found for the Dy [3], Gd [4],

and Pr[5] systems. The low-temperature ordered moment we obtain from our data is <Hj> = (1.07 ± 0.07) /Xp, with the direction along the c-axis. This

3+

value is substantially smaller than the free-ion moment of 2.14 /in for Nd . The anti ferromagnetic transition temperature is also very sensitive to

the value of the oxygen concentration, as shown in figure 1. The shape of

the intensity versus temperature curves are yery similar for the two samples,

and yields an estimate for the critical exponent p ~ 1/3, typical for a 3-d

transition, but the ordering temperature varies by a factor of three between

the two samples. Crystal field effects could no doubt be important in

causing this behavior, and inelastic neutron scattering measurements as a function of x are planned to determine the crystal field splittings in this

system.

2 3 6 + x

m

o

1.2n

1.0

0.8

0.6

0.4

0.2

0.0

-0.2L_x_.

TtJt.t (1/2. 1/2. 1/2)

{

I

I

h

km

-1 1 1 L I I I U 0.5 1.0 1.5 2.0

Temperature (K)

Figure 1. Temperature dependence of the (1/2 1/2 1/2} peak intensity,

showing the variation of the square of the staggered magnetization

with temperature. The Neel temperature for the system with x = 0.9 (triangles) is -1/2 K, while T|. for x = 0.3 (solid circles) is

1.5 K.

References

[1] Yang, K. N.; Ferreira, J. M.; Lee, B. W.; Maple, M. Lynn, J. W.; Erwin, R. W. (submitted for publication).

B.; Li, W.-H.;

58
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

[2] Lynn, J. W.; Clinton, T. W.; Li, W.-H.; Erwin, R. W.; Liu, J. Z.;

Shelton, R. N.; Klavins. P. (to be published); Lynn, J. W.; Li, W.-H.;

Li, Q.; Ku, H. C; Yang, H. D.; Shelton, R. N. Phys. Rev. B36, 2374

(1987).

[3] Goldman, A. I.; Yang, B. X.; Tranquada, J.; Crow, J. E.; Jee, C.-S.

Phys. Rev. B36, 7234 (1987).

[4] Paul, D. McK.; Mook, H. A.; Hewat, A. W.; Sales, B. C; Boatner, L. A.;

Thompson, J. R.; Mostoller, M. Phys. Rev. B37, 2341 (1987).

Chattopadhyay, T.; Maletta, H.; Wirgen, W.; Fischer, K.; Brown, P. J.

Phys. Rev. B38, 838 (1988). Mook, H. A.; Paul, D. McK.; Sales, B. C;

Boatner, L. A.; Cussen, L. Phys. Rev. B38, 12008 (1988).

[5] Li, W.-H.; Lynn, J. W.; Skanthakumar, S.; Clinton, T. W.; Kebede, A.;

Crow, J. E.; Mihalisin, T. Phys. Rev. B: {Rapid Communications), (to

be published).

TWO- AND THREE-DIMENSIONAL MAGNETIC BEHAVIOR OF Er IN ErBa2Cu30^

J. W. Lynn, T. W. Clinton, and W.-H. Li

(University of Maryland, College Park, MD and Reactor Radiation Division)

R. W. Erwin

J. Z. Liu and K. Vandervoort

(Argonne National Laboratory, Argonne, IL)

and

R. N. Shelton

(University of California, Davis, CA)

The magnetic properties of the rare earth ions R in the RBapCu^Oy

superconductors are of interest because of experiments which have shown that

the superconductivity is not significantly affected by the substitution of

several rare earth ions [1-2]. The RBa^Cu^Oy materials order antiferromagnetically, where the system is orthorhombic and superconducting. The magnetic

interactions are wery weak, yielding ordering temperatures (Tj^ -IK) well

below the superconducting transition temperature (T ~ 92 K), making these

materials good examples for investigating the competing interactions of

superconductivity and magnetism. The first neutron experiments on ErBa^Cu-Oy

[3] powder showed a magnetic phase transition at 1^ ~ 0.6 K, which agreed

with the specific heat data [4-5]. The Er moments exhibited a twodimensional character in the a-b plane, while there were no significant

59
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

magnetic correlations detected along the c-axis down to the lowest

temperatures achieved (0.33 K) . This anisotropic behavior was expected since

the interactions are primarily dipolar in origin, and the spacing between Er

ions along the c-axis is three times longer than along the a-b directions.

Additional powder measurements found that the system ordered three

dimensionally at lower temperatures (140 mK)

.

Recently we have made measurements on a high quality single crystal.

Above the 3-d ordering temperature (Tj^ = 0.618 K) we observe a rod of

scattering along (1/2,0, £) which demonstrates the expected strong anisotropy

of the magnetic interactions and the concomitant 2-d character of the system.

Figure 1 shows three scans through the rod and one scan along the rod just

above the 3-d ordering temperature. The scans through the rod have a width

which is limited by the instrument resolution, while the scan along the rod

shows that there are no significant spin correlations between adjacent a-b

layers.

Below the 3-d Neel temperature we find that two magnetic structures

can occur at low T, one characterized by a wave vector (1/2,0,0) and the

other by (1/2,0,1/2). The spin structure for the (1/2,0,1/2) configuration

consists of ferromagnetic chains of spins along the b direction, with

adjacent chains in the a-b plane coupled antiferromagnetically. Along the c- axis the spins are antiparallel . The spin structure for the (1/2,0,0)

configuration corresponds to parallel spins along the c-axis. Both of these

structures are observed in our powder samples, while only the (1/2,0,1/2)

structure is found in our single crystal sample. We thus believe that the

(1/2,0,1/2) structure represents the true ground state configuration. The

two structures probably occur because the dipolar energies of these

configurations are almost identical, as calculated by Felsteiner [7] for the

Gd system, and the energetics may be influenced by the detailed metallurgical

properties of the crystallites such as strains, grain and twin boundaries,

etc.

The temperature dependence of the (1/2,0,1/2) peak is shown in figure

2. Both specific heat [4-5] and inelastic neutron scattering [8] reveal that

the ground state is a doublet, so that S = 1/2 is appropriate. In addition,

in an orthorhombic structure with such a low Neel temperature we might expect

the anisotropy to be large compared to the magnetic interactions, thus

defining a unique spin direction. This corresponds to a 2-d Ising model,

60
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

which is the only one exhibits long-range magnetic order in 2-d. The solid curve is a fit to the Onsager's exact solution for S = 1/2 2-d Ising model

[9] which is seen to provide an excellent description of the data. In addition, if we analyze the data in the reduced temperature range 1 x 10' <

(T|^ - T)/T,^ < 0.11, we obtain $ = 0.122 ± 0.004, in good agreement with the

theoretical result $ = 1/8. It should be noted that our data are very

similar to the prototypical S = 1/2 2-d Ising system K2CoF^ [10]. Thus, we believe that the physics of the rare earth ordering in these materials is

controlled by the 2-d like character, with the 3-d ordering being induced as

a necessary consequence of the onset of long range order within the a-b

planes.

brBa.fufi-y

c

-M

E

O

CDn

m

\-

z

Z)

o

u

750 - (0^0,0.5) T=0.B7K

650 / N 550 / \

450 / \

350

P5n '.j±y

1>in 1 1 _1, 1 1 0.41 0.44 0.47 0.50 0.53 0.56 0.59

750 - (0^0,0.85) T=0.67K

650 -

550 M 450 { \ 350

250

1»in -J* , . . 1 1

0.41 0.44 0.47 0.50 0.53 0.56 0.59

1350 "(0.5,0. Q^) T=0.B7K

1150 -

950 -

750

550 V*^*-*- 1 . ix f**j '*-

350

, _.J. ...L. J _J . .J.. i 0.41 0.44 0.47 0.50 0.53 0.56 0.59 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 Q

Figure 1. Three scans across the rod of scattering in reciprocal space,

showing the 2-d character just above Tj^ = 0.618 K. The fourth

scan shows that the scattering intensity does not vary

significantly along the rod, indicating that there are no significant spin correlations between planes.

61
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1.2

O

? 1.0

0.8

n 0.6

<N^ 0.4

LUI 0.2

(1/2. 0. 1/2)

Tm •= 0.618 K

-e-e—o—e0.2 0.4 0.6 0.8 i.O 1.2

Temperature T/T^

Figure 2. Sublattice magnetization versus temperature. The solid curve is a fit to the Onsager exact solution for the S = 1/2 2-d Ising model.

References

[1] Wu, M. K.; Ashburn, J. R.; Torng, C. J.; Hor, P. H.; Meng, R. L.; Gao,

L.; Huang, Z. J.; Wang, Y. Q.; Chu, C. W. Phys. Rev. Lett. 58, 908

(1987).

[2] Hor, P. H.; Meng, R. L.; Wang, Y. Q.; Gao, L.; Huang, Z. J.; Bechtold,

J.; Forster, K.; Chu, C. W. Phys. Rev. Lett. 58, 1891 (1987).

[3] Lynn, J. W.; Li, W.-H.; Li. Q.; Ku, H. C; Yang, H. D.; Shelton, R. N.

Phys. Rev. B36, 2374, (1987).

[4] See Brown, S. E.; Thompson, J. D.; Willis, J. 0.; Aikin, R. M.

Zirgiebl, E.; Smith, J. L.; Fisk, Z.; Schwarz, R. B. Phys. Rev. B36

2298 (1987). Dunlap, B. D.; Slaski, M.; Hinks, D. G.; Soderholm, L. Beno, M.; Zhang, K.; Segre, C; Crabtree, G. W.; Kwok, W. K.; Malik, S

K.; Schuller, I. K.; Jorgensen, J. D.; Sungaila, Z. J. Mag. Mag

Matrl. 68, 1139 (1987). Lee, B. W.; Ferreira, J. M.; Dalichaouch, Y. Torikachvili, M. S.; Yang, K. N.; Maple, M. B. Phys. Rev. B3Z, 2368

(1988). Van Der Muelen, H. P.; Franse, J. J. M.; Tarnawski, Z. Kawdowaki , K.; Klaasse, J. C. P.; Menovsky, A. A. Physica C 152, 65

(1988).

[5] van den Berg, J.; van der Beek, C. J.; Kes, P. H.; Mydosh, J. A.;

Nieuwenhuys, G. J.; de Jongh, L. J. Solid State Commun. 64, 699 (1987).

Simizu, S.; Friedberg, S. A.; Hayri, E. A.; Greenblatt, M. Phys. Rev.

B36, 7129 (1987). Dirken, M. W. ; de Jongh, L. J. Solid State Commun.

64, 1201 (1987).

62
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

[6] Chattopadhyay, T.; Brown, P. J.; Bonnenberg, D.; Ewert, S.; Maletta, H. Europhys. Lett. 6, 363 (1988).

[7] Felsteiner, F. Phys. Rev. B39, 7248 (1989).

[8] Walter, U.; Fahyl , S.; Zettl , A.; Louie, S. G.; Cohen, M. L.; Tejedor,

P.; Stacy, A. M. Phys. Rev. BM, 8899 (1987). Furrer, A.; Bruesch, P.;

Unternahreh, T. Phys. Rev. B38, 4616 (1988). Goldman, A. I.; Gao, Y.;

Ting, S. T.; Crow, J. E.; Li, W.-H.; Lynn, J. W. J. Mag. Mag. Matrl

.

76-77 . 607 (1988) (to be published).

[9] Onsager, L. Phys. Rev. 65, 117 (1944).

[10] Ikeda, H.; Hirakawa, K. Solid State Commun. 14, 529 (1974).

EFFECT OF SUPERCONDUCTIVITY

ON THE SMALL ANGLE NEUTRON SCATTERING IN ErBa2Cu30^

J. W. Lynn, H. Zhang, and W.-H. Li

(University of Maryland, College Park, MD and Reactor Radiation Division)

M. Yethiraj

(Los Alamos National Laboratory, Los Alamos, NM)

and

J. Z. Liu

(Argonne National Laboratory, Argonne, IL)

The central issue for the oxide superconductors is to understand the

origin of the superconducting state. One aspect concerns the basic character

and symmetry of the superconducting state itself; that is, whether it

develops in the usual BCS way as a result of an instability of the Fermi

liquid, or perhaps entails a different mechanism such as RVB. The second

basic question involves the identification of the interaction responsible for

the electron pairing. Since the discovery that the Cu ions carry a magnetic

moment, some of the leading contenders have been theories in which the spin

degree of freedom plays a fundamental role, thus making the magnetic

properties of these systems of special interest [1].

In the "parent" insulating phases such as La^CuO., Nd^CuO., and

RBdiJ^^j^B ^^ '^ ^^^^ earth), long-range antiferromagnetic order has been

observed, and considerable information has been obtained about the spin

dynamics both by neutron [2-4] and Raman [5] scattering. For the La^CuO. and

YBa^Cu^Og ordered antiferromagnets, the measurements reveal that the exchange

63
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

interactions within the Cu-0 planes are very much larger than between the

layers, which gives rise to 2-d magnetic behavior above the ordering

temperatures, and an overall energy scale which is much larger than the

ordering temperatures would suggest. The essential question then is whether

the Cu magnetic moments, and the \/ery strong spin energetics, survive into

the superconducting state. A number of experiments have been performed which

provide evidence that the spin fluctuations do indeed exist --n the superconducting state, in particular in the La^, Sr CuO., YBa^Cu^O,, and

Bi^Sr^CaCu^Og superconducting phases. The correlation range is found to be

quite short in the superconducting state, but the amplitude of the magnetic

moment appears not to be diminished substantially. In addition, the magnetic

fluctuations which are observed in the superconducting region of the phase

diagram have been found by Raman scattering [5] and our own small angle

neutron scattering (SANS) measurements [4] to be suppressed by superconductivity. One expected suppression effect [6] in SANS is the screening of the

magnetic fluctuations by the superconducting electrons, at wavelengths > X,

,

where A. is the London penetration dep h. This suppression comes from the

electromagnetic interactions: there is a magnetic field B(q) associated with

the magnetic fluctuations, and the supercurrents will screen these

fluctuations at small wave vectors. However, the length scale which was obtained from the data is only 22 A, which is much too short to be

interpreted as a London penetration depth. A second effect is expected from

the reduction of the spin susceptibility of the superconducting electrons

themselves [6], which is caused by the formation of Cooper pairs. The length

scale associated with this effect is the coherence length f. In the

traditional "magnetic superconductors" the superconducting electrons do not

have a spin component, and hence the conduction electron spin susceptibility

is too small to be observed. But in the oxide superconductors the Cu ions

carry a spin in the superconducting phase.

Our early SANS results on polycrystalline samples showed [4] that the

intensity at small wave vectors q did in fact decrease when the sample became

superconducting, with a characteristic length scale -20 A. Thus we could

interpret this as a reduction of the paramagnetic spin susceptibility of the

Cu ions, with a length scale ~ f. However, the signal-to-noise ratio for

these powder data was not very good. To improve the experimental data we have redone this experiment with single crystal specimens. Approximately 15

64
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

single crystals (T ~ 93 K) were mounted on a perfect single crystal of Si,

to minimize SANS from the sample holder. Each crystal was aligned with its

c-axis parallel to the beam, and the data were taken at 10.5 A to minimize

multiple Bragg scattering. The total volume of the sample was -0.08 gm.

This is more than an order of magnitude smaller than our powder sample, but

the signal-to-noise was dramatically improved since the metallurgical SANS

was drastically reduced. The sample was put in physical contact with the

cold finger of the cryostat and allowed to equilibrate in temperature. Hence

no exchange gas was used in order that we might eliminate any possible

concern about the exchange gas condensing [7] on the sample and changing the

SANS signal

.

Some data, shown in figure 1, were taken with the SANS instrument in

the "coarse" resolution mode. Data obtained at 120 K were used as "background," and subtracted from the data taken at lower temperatures. The

intensity has been summed over the region of Q from 0.023 A" to 0.038 A' to

improve statistics, as we had done previously [5]. We see that the

scattering clearly decreases with decreasing temperature below T , quite

similar to our previous data on the polycrystalline sample. Hence we have

demonstrated that the SANS scattering does in fact decrease below the

superconducting transition.

Although these preliminary results on single crystals are suggestive,

much more work needs to be done. Since these are not polarized SANS

experiments, experimentally we can only say that there is a decrease in

overall scattering, which we assume is magnetic in origin. We also have

assumed that since the length scale is short (-20 A) that the Cu ions are involved. One obvious experiment to do is to repeat thes^e SANS studies on a sample of YBa^Cu^Oy. Hopefully we can obtain a much larger sample volume, so that the shape of the curve and the temperature dependence can be obtained

much more accurately, and without the complication of having Er in the

sample. Further work is in progress.

65
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Er Baa CU3 O7

j^-^''

>.«

5

-r y^

A" c y

0) 10 c -

a> /

Z 15 y

^ y

20

1 1 1 1 1 1 1 1 10 20 30 40 SO 60 70 80 90 T(K)

Figure 1. Temperature dependence of the net small angle neutron scattering,

integrated over the Q range from 0.023 A" to 0.038 A . The

"background" data at 120 K have been subtracted from the data at

lower temperatures. The scattering is seen to decrease below the

superconducting transition temperature. The dashed curve is a guide to the eye.

References

[1] For a recent review, see chapter 8 of High temperature superconductivity. J. W. Lynn, ed. Springer-Verlag, New York, 1989.

[2] Endoh, Y. et al . Phys. Rev. B37, 7443 (1988). Birgeneau, R. J. et al

Phys. Rev. B38, 6614 (1988).

[3] Sato, M. et al . Phys. Rev. Lett. 61, 1317 (1988). Mezei, F. et al

Physica C153-155, 1669 (1988).

[4] Lynn, J. W. et al . Phys. Rev. B36, 2374 (1987).

[5] Lyons, K. B.; Fleury, P. A. J. Appl . Phys. 64, 6075 (1988).

[6] See, for example, Fulde, P.; Keller, J. in Topics in Current Physics 34,

Chapter 9, Fisher, 0.; Maple, M. B.; eds. Springer-Verlag, New York,

1983.

[7] Lynn, J. W. Physica B 136, 117 (1986).

66
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC ORDER OF Pr IN PrBa2Cu30^

W.-H. Li, J. W. Lynn, S. Skanthakumar, and T. W. Clinton

(University of Maryland, College Park, MD and Reactor Radiation Division)

and

A. Kebede, C.-S. Jee, J. E. Crow, and T. Mihalisin

(Temple University, Philadelphia, PA).

The superconducting transition temperature of the Y, /? Ba^Cu-O, (/? = rare earth) compounds does not depend significantly on the concentration x of trivalent rare earths in the material. An important exception to this

behavior is Pr, which forms the same orthorhombic structure but is thought to

be strongly mixed valency, and close to the tetravalent ionic state. The

superconductivity is found to be strongly suppressed as a function of Pr

concentration [1,2] with a behavior which is consistent with the classical

Abrikosov-Gorkov depairing theory [7], and superconductivity is lost for Pr

concentration x > 0.6. On the Pr-rich end, on the other hand, there is

evidence in specific heat and susceptibility of a magnetic phase transition,

with a Neel temperature which is strongly x dependent and maximizes at 17 K

for x = 1. The purpose of our measurements was to determine if indeed these

anomalies originated from magnetic ordering, and if so, to determine the

nature of the ordering.

The samples were made by the usual solid state reaction technique.

Both x-ray diffraction and high resolution neutron profile refinement

measurements were used to characterize the samples prepared for these

measurements. From the neutron measurements, the nominal oxygen

concentration was determined to be 7.00 ± 0.08, and any impurity phases were

found to be less than 1% of the sample.

Two magnetic Bragg reflections have been identified, and may be indexed

as (1/2, 1/2, 1/2} and (1/2, 1/2, 3/2) reflections, on the orthorhombic

chemical unit cell. Since all three Miller indices are half-integer, the

magnetic unit cell is just double the chemical unit cell along all three

crystal lographic directions as shown in the insert in figure 1. Hence the

underlying magnetic structure consists of nearest neighbor spins in all three

directions which are aligned antiparallel, and is the same type of structure

as has been found for the Dy, Gd, and Nd systems. The observed intensity for

the (1/2, 1/2, 2/3} peak is considerably weaker than that for the (1/2, 1/2,

67
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1/2} peak which then suggests that the moment direction in the system is

predominantly along the c-axis direction. However, in the present case there

are only two observable peaks due to the small value of the magnetic moment

(as discussed below), and hence we should only consider this spin direction

as tentative.

The low- temperature ordered moment we obtain from our data is

<Hj> = (0.74 ± 0.08) /ip. This value is much smaller than the free-ion moment

of 2.14 Mg for Pr^'^(J = 5/2) or 3.18 /Zg for Pr^'^(J = 4). Crystal field (CF)

effects may be important in reducing the value of <fi > below the free- ion

result. An ordered moment of 0.71 /Xp would be expected for the most likely

CF ground state (| ± 1/2 > doublet) of Pr^"*". For Pr^"^, on the other hand,

the orthorhombic distortion would totally remove the nine-fold degeneracy

[3], concomitantly reducing Tj^,, the ordered moment, and the entropy removal

at Tjg, which is inconsistent with our data.

Figure 1 shows the temperature dependence of the (1/2, 1/2, 1/2} peak

intensity, and reveals a typical order parameter with a Neel temperature of

Tjg ~ 17 K. The temperature dependence of the specific heat C(T) for this

compound is shown in figure 2, where a clear anomaly in the vicinity of 17 K

is evident. The magnetic entropy associated with this transition is -5.0

J/mole-K [2], and is somewhat smaller than the expected entropy change due to

the ordering of a CF doublet ground state; i.e., 5.7 J/mole-K.

The essential difference in the magnetic ordering between the present

nonsuperconducting PrBa^Cu-O^ system and the trivalent superconducting

/JBa^CUgOy systems is their Neel temperatures T»,, and the values of the

ordered moment. If we scale these temperatures with respect to either the

size of the (free ion) magnetic moment of Pr, or the spin of the Pr via a possible Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction, then we would expect a transition temperature for PrBa^Cu^Oy which is an order of

magnitude smaller than for OdBa^Cu^Oy. The observed transition is of course

about an order of magnitude larger than these trivalent rare earths. In

addition, the ordered moments for the heavy rare earth materials Er, Dy, and

Gd were found to be 4.9, 7.2, and 7.4 /ig, respectively, while the Pr moment

is only 0.74 /Xg. Thus the higher ionic state for the Pr affects not only the

electronic and superconducting properties of the Cu-0 layers (e.g., the

suppression of T ), but also the electronic and magnetic properties of the Pr

sublattice. The present specific heat and neutron data taken together

68
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

indicate that the 4f level for the Pr ions hybridize strongly with the

electrons at the Fermi level.

en

o

75000

74000

73000

72000

71000

PnBa^CUgO^

5 10 15 20 25 30

Temperature (K)

I0)

1-1 o

3 5 -

15

10 -

.... ., , I

Tm- /

'^K 1 5 10 15 20

Temperature [K]

Figure 1. (left) Temperature dependence of the (1/2, 1/2, 1/2} peak

intensity, showing the variation of the square of the staggered

magnetization with temperature. The Neel temperature for this

system is -17 K based on these data as well as on the specific

heat data. The solid curve is a guide to the eye. The insert

shows the magnetic configuration of the Pr spins.

Figure 2. (right) Measurements of the specific heat at low temperatures for

?r^diJi\xJi-j^ showing the magnetic transition at T^, = 17 K.

References

[1] Dalichaouch, Y.; Torikackvili , M. S.; Early, E. A.; Lee, B. W.; Seaman,

C. L.; Yang, K. N.; Zhou, H.; Maple, M. B. Solid State Commun. 65, 1001

(1988).

[2] Jee, C.-S.; Kebede, A.; Nichols, D.; Crow, J. E.; Mihalisin, T.; Myer,

G. H.; Perez, I.; Salomon, R. E.; Schlottmann, P. Solid State Commun.

(in press).

[3] A recent theoretical calculation predicts a Tl singlet as ground state,

and an overall energy splitting of ~ 110 meV for Pr ions: Nekvasil, V.;

Stehno, J.; Sebek, J,; Havela, L.; Sechovsky, V.; Svoboda, P. J. de

Physique (in press)

[4] See, for example, Stewart, G. R. Rev. Mod. Phys. 56» 755 (1984).

Fisk, Z.; Hess, D. W.; Pethick, C. J.; Pines, D.; Smith, J. L.;

Thompson, J. D.; Willis, J. 0. Science 239, 33 (1988).

69
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PRESSURE DEPENDENCE OF THE Cu MAGNETIC ORDER IN li^^2^^3%+x

J. W. Lynn and W.-H. Li,

(University of Maryland, College Park, MD and Reactor Radiation Division)

S. F. Trevino

(EWD, ARDEC, and Reactor Radiation Division)

and

Z. Fisk

(Los Alamos National Laboratory, Los Alamos, NM)

The paramagnetic-antiferromagnetic ordering temperature of the

/?Ba2Cu~0g (/? = rare earth) compounds was found to be very sensitive to the

oxygen concentration x in the chain layers. We have studied the magnetic

order of the Cu spins in two single crystals of composition NdBa^Cu-Og -c and

NdBa^CUgOg , as a function of hydrostatic pressure. The temperature

dependence of the magnetic intensity of the (1/2, 1/2, 2) Bragg peak for the

NdBa^Cu-Og ^c crystal is shown in figure 1 at a series of pressures. At zero pressure the ordering temperature is 230 K [1]. With increasing pressure

the curves are seen to shift rapidly to higher temperatures, indicating that

the ordering temperature 1^. is increasing.

In this temperature regime the intensity is approximately linearly

dependent on temperature [1], and to obtain an estimate of Tj^, we have simply

least squares fit a straight line (solid curves) to the data (symbols). The

transition temperatures which have been obtained from these fits increase

approximately linearly with pressure at the rate of (23 ± 3) K/kbar up to an applied pressure of 4 kbars. This rate of increase is more than two ordersof-magnitude higher than the rate of 0.05 K/kbar observed for the

superconducting transition temperature T for YBa^Cu^Oy, and is also two

orders-of-magnitude larger than the calculated shift in T^.

The pressure dependence of the Bragg scattering associated with the

lower transition temperature Tj.^* which is where the Cu chain spins order, is

shown in figure 2. There is a small increase in the maximum value of the

intensity, but only a very little shift in T^.^. We believe that this weak

pressure dependence is representative of the fact that when the chain ions

order, then the spacing between the Cu ions in the a, 6, and c directions is

about equal and we have a fully 3-d magnetic structure with simple

anti ferromagnetic nearest neighbor interactions, in contrast to the situation

70
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

at Tj.j as discussed below. At Tj.^ the magnitude of the pressure effect is

typical of 3-d phase transitions.

The Neel temperature T^., is known to be quite sensitive to the oxygen

concentration, so that the pressure effect we see might be explained by the

removal of oxygen from the sample. However, below room temperature the

oxygen will not reenter the sample, and we find no evidence for any irreversible effects in our data. We therefore discard this as a possibility. We

have also measured the pressure dependence of the lattice parameters, and

find a smooth decrease of -0.03%/kbar, which translates into a -13 -1

compressibility of 7.5*10 Pa . We detect no anomalies or abrupt changes

in the lattice over the pressure range explored.

The most likely explanation for the strong pressure sensitivity of T|^,

is in terms of the large magnetic anisotropy and competing exchange

interactions which are present when the Cu chain spins are disordered in the

/JBa^Cu-Og system. The magnetic exchange interaction J within the Cu-Op

layers is very large, and thus in the vicinity of l^,-, there are very strong

magnetic correlations within the Cu-Op planes. Hence we have 2-d like

magnetic behavior, with the preferred spin direction in the tetragonal plane,

and since there is no 2-d long range order [2] above T^., an x-y model should

be appropriate. The 3-d phase transition is then driven by the weak

effective interaction J' between layers. Since the in-plane exchange J is

already very large, it is likely that J is near a maximum versus ionic

separation and thus will not be particularly sensitive to pressure. On the

other hand, the effective interaction J', which is mediated through the spindisordered Cu chain layer, results from an overlap of wavefunctions on ions

which are well separated. The overlap integral should then depend

exponentially on separation, and a substantial increase in J' with pressure

can be expected. A calculation [3] based on spin wave fluctuations gives T,^, - Jin' {J/J') for large J/J' , which would yield a linear dependence of 1^, on

P as observed. However, T.,, would be a weak function of J/J' and hence this

scenario would then require a large change in J' to explain the data. Such a large change could be the result of a significant pressure-induced change in

the electronic structure, similar to the change in 1^, caused by oxygen

variation, or it could be due to some competing interactions caused by the

disordered spins on the chain layers.

71
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A second possibility is that the anisotropy within the plane increases

with pressure, which would increase the in-plane correlations and eventually

produce a phase transition with long-range order in 2-d [4]. Indeed, if

there were a tendency for pressure to cause an orthorhombic distortion, for

example, then the magnetic behavior of the layers would crossover to a 2-d

Ising system (with long range order), and T|^j could increase dramatically.

However, so far we have found no indication experimentally of an orthorhombic

distortion.

NdBaXu.O,

1000 'i^"»"i'|| i'"i i"i"i"i I'i'i I'l I I I I ri I [1/2. 1/2.2) o P=0

^ P=1.25 kbarl

Kbar

ar

140 190 340 290 Temperature (K)

340

NdBa .c U3O6.,

(1/2. 1/2. 3/2)

. • •

I B p=0 ^-; " • B aP=i kbar

5000 ^ • I o dP=2 kbar . CO

1 ) ^ P=3 kbar

d op=4 kbar

ID • P=5 kbar

CJ o CJ 3000 -

-1 > " i QJ • ^_

1000

o i

•

*!;,.,

-1000 1 25 50 75 125 Temperature (K)

Figure 1. (left) Temperature dependence of the (1/2, 1/2, 2) Bragg peak

intensity in the vicinity of Tj^, for the NdBa^Cu^Og ~r crystal at

a series of pressures. The solid lines are fits to the data to

obtain Ta.,.

Figure 2. Intensity of the (1/2, 1/2, 3/2) Bragg peak from the NdBa2Cu20g

j crystal at a series of pressures.

References

[1] Li, W.-H.; Lynn, J. W.; Mook, H. A.; Sales, B. C; Fisk, Z. Phys. Rev.

B37 , 9844 (1988). Lynn, J. W.; Li, W.-H.; Mook, H. A.; Sales, B. C;

Fisk, Z. Phys. Rev. Lett. 60, 2781 (1988) (to be published). Lynn, J.

W.; Li, W.-H. J. Appl. Phys. 64, 6065 (1988). Lynn, J. W.; Li, W.-H.;

Trevino, S. F.; Fisk, Z. Phys. Rev. B. (to be published).

[2] Shirane, G.; Endoh, Y.; Birgeneau, R. J.; Kastner, M. A.; Hidaka, Y.;

Oda, M.; Suzuki, M.; Murakami, T. Phys. Rev. Lett. 59, 1613 (1987).

Lyons, K. B.; Fleury, P. A.; Remeika, J. P.; Cooper, A. S.; Negran, T.

J. Phys. Rev. B3Z, 7443 (1988).

[3] Ferrel, R. A. (private communication).

72
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

[4] See, for example, Kosterlitz, J. M.; Thouless, D. J. J. Phys. C 6, 1181

(1973). Jose, J. v.; Kadanoff, L. P.; Kirkpatrick, S.; Nelson, D. R. Phys. Rev. B 16, 1217 (1977).

TWO- AND THREE-DIMENSIONAL MAGNETIC ORDER IN /^Ba^Cu^Og

H. Zhang, J. W. Lynn, W.-H. Li, and T. W. Clinton

(University of Maryland, College Park, MD and Reactor Radiation Division)

and

D. E. Morris and R. Sid

(Lawrence Berkeley Laboratory, Berkeley, CA)

The magnetic properties of the oxide superconductors have been of

particular interest for two reasons. One is that the Cu magnetism may be

related in a fundamental way to the pairing mechanism in these materials, and

the second is that these are ideal systems in which to investigate the

electromagnetic coupling between the rare earth magnetic and superconducting

order parameters. In this latter regard we have been systematically

investigating the nature of the rare earth ordering in the ^^^ip^^S^S+x

systems, and have found [1,2] that they are prototypical two-dimensional

magnetic systems. We are now extending these measurements to the RBa^CiiflOo

class of materials, which is similar to the 1-2-3 system except that the

(orthorhombic) c-axis is approximately twice as long, with two rare earth

ions in the chemical unit cell [3].

The diffraction data were collected with the BT-2 triple-axis

spectrometer using the standard subtraction technique, in which the

scattering well • above the ordering temperature is subtracted from the

scattering at low T, to isolate the magnetic response of the system. A

dilution refrigerator was employed to cool the powder samples down as low as 0.05 K. Two polycrystalline samples were investigated, with compositions

ErBa2Cu^0g and DyBa2Cu40g.

For the ErBa^Cu^Og system, the data reveal three dimensional Bragg

peaks at low temperatures, which may be easily indexed on the chemical unit

cell. The magnetic spin configuration is shown in figure 1, and the system

has a Neel temperature of 0.43 K. Just above T,,, we also found evidence of

two-dimensional behavior similar to the behavior found [1,2] in the

ErBa^Cu^O, system.

73
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The data for the DyBa^Cu^Og system was quite different. Figure 2a

shows the diffraction profile observed at low temperatures. The skewed

lineshape is characteristic of a system with two-dimensional behavior, and in

fact the solid curve is the theoretical calculation assuming long-range order

in the a-b planes, with no correlations between the spins along the c-axis

[4]. The theory is seen to provide a good description of the data. In the

bottom part of the figure is a plot of the observed intensity at the peak

position as a function of temperature, and is quite typical of an order

parameter, with a Neel temperature of -0.74 K.

The lack of any 3-d order in the DyBa^Cu-Og material is quite

surprising. In the conventional two-dimensional systems such as K^CoF. [5],

K2NiF- [6] and more recently ErBa^Cu^O, [2], the 2-d ordering and the 3-d

ordering occur at (essentially) the same temperature. The reason for the

close proximity of the two transitions is that when the system develops a

2

static moment in the layers, then there is an energy ± JA between the

layers, where J is the exchange interaction between planes and A is the

average size of a domain in the layer. The - sign is for layers that are properly matched (e.g., antiferromagnet if J < 0) and + is for layers that

are out of phase. Thus even if the interlayer coupling is very weak, there

2 is an energy difference 2JA between the "correct" and the "wrong" spin

configurations, which can be quite large since A is large: Hence the layers

will order along the c-axis producing 3-d Bragg peaks. In the present

DyBa2Cu40g system these interplanar correlations appear to be disrupted,

leaving only 2-d order. Further work will be needed to isolate the origin of

this unusual behavior.

74
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. Ground state magnetic spin configuration of the Er spins in

ErBapCu.Og.

DyBa2Cu40g

DyBa^u,Oa

22 23 24 2; 26 27 28 29 38 31 32 33 34 35

Scattering Angle (2^)

0.25 0,50 0.75 Temperature (K)

1.00

2 a) 2 b)

Figure 2. a) Magnetic scattering profile of DyBa2Cu^0g at T=0.05 K. The

solid curve is a theoretical fit to a two-dimensional ly ordered

system, b) Intensity versus temperature for the (1/2, 1/2,0)

peak, revealing a Neel temperature 1^ ^ 0.74 K.

75
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[1] Lynn, J. W.; Li, W.-H.; Li, Q.; Ku, H. C; Yang, H. D.; Shelton, R. N.

Phys. Rev. B36, 2374 (1987).

[2] Lynn, J. W.; Clinton, T. W.; Li, W.-H.; Erwin, R. W.; Liu, J. Z.;

Vandervoort, K.; Shelton, R. N. (to be published).

[3] See, for example, Morris, D. E.; Nickel, J. H.; Wei, J. Y. T.; Asmar, N.

G.; Scott, J. S.; Scheven, U. M.; Hultgren, C. T.; Markelz, A. G.;

Post, J. E.; Heaney, P. J.; Veblen, D. R.; Hazen, R. M. Phys. Rev. B39,

7347 (1989)

[4] Warren, B. E. Phys. Rev. 59, 693 (1941).

[5] Ikeda, H.; Hirakawa, K. Solid State Commun. 14, 529 (1974).

[6] Birgeneau, R. J.; Guggenheim, H. J.; Shirane, G. Phys. Rev. Bl, 2211

(1970).

MAGNETIC ORDER OF THE Cu PLANES AND CHAINS IN RBi^Cu^O^^^

W.-H. Li and J. W. Lynn

(University of Maryland, College Park, MD and Reactor Radiation Division)

Z. Risk

(Los Alamos National Laboratory, Los Alamos, NM)

and

H. A. Mook and B. C. Sales

(Oak Ridge National Laboratory, Oak Ridge, TN)

Both the magnetic and superconducting properties of the ^^^ipCu^Og

(/? = rare earth) compounds are very sensitive to the oxygen concentration x in the "chain" layers. In the small x regime, where the materials are tetragonal and semiconducting, the Cu "plane" layers were found [1,2] to

order antiferromagnetically with a Neel temperature T^g as high as 500 K. At

lower temperatures the spins on the Cu "chain" sites have also been observed

[3,4] to order antiferromagnetically. This additional ordering causes an interplanar competition between the "plane" and the "chain" layers, and

results in a rich behavior of the magnetic structure as a function of

temperature.

76
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The spins in all three layers turn out to be coupled antiferromagnetically within the tetragonal layers. For the unit cell along the c- axis, there are two types of ordering that have been observed. At low

temperatures both the "chain" layers and the "plane" layers can be ordered,

with an ant i ferromagnetic sequence along the c-axis like (+-+-+- ...) as shown in figure 1(a). This yields a magnetic unit cell double the

chemical one along all three crystallographic directions. Magnetic Bragg

reflections with all three Miller indices half integral are then expected.

We refer to these peaks as "half-integral peaks."

In the high-T phase, the "chain" moments disorder while the "plane"

moments reorient themselves into a new ant i ferromagnetic configuration, and we have an ordering sequence like ( + - + - ...) along the c-axis as shown in figure 1(b). In this case the magnetic and chemical unit cells are the same in this direction and S. will be integral. We refer to these peaks

as "whole-integral peaks."

Measurements were made on four different samples with different oxygen

concentrations. Two samples were polycrystalline, with compositions

YBa^Cu-Og ,- and NdBa^Cu-Og q^' ^^^ weighing ~9 g each. The other two

samples were single crystals, one with composition NdBa2Cu20g 35and weighing

-9.5 mg, and a second one with composition NdBa^Cu^Og , and weighing -45 mg.

The Rutherford backscattering measurements on the single crystals revealed a ratio of Nd:Ba:Cu = 1:2:3, indicating that there is no significant substitution of the rare earth onto the Ba site.

The temperature dependence of the strongest of the two types of peaks

is shown in figure 2 for the x = 0.1 crystals. The data obtained from the

X = 0.35 crystal show identical behavior, except that the magnetic transition

temperatures Tj^,, and T^.^ are of course different due to the different oxygen

content. The decrease in the intensity of the (1/2 1/2 2) peak at low T is

accompanied by the development of intensity at the (1/2 1/2 3/2) peak

position. Both changes mark the onset of the "low-T phase" at Tj^p. Our

measurements indicate that 1^, = 430 K and T^.^ = 80 K for the x = 0.1

crystal, and 1^^ == 230 K and 1^^ = 10 K for the x = 0.35 crystal.

77
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(a) (b)

r^ /".^

Figure 1. The basic spin structure for the Cu moments at (a) low T and (b)

high T. There is a substantial moment on the Cu ions in the

oxygen deficient planes (small circles) in the low-T phase. These

Cu "chain" ions in the oxygen deficient planes become disordered

at the high-T phase.

Since the half-integral and whole-integral Bragg reflections correspond

to separate Fourier components, they can be treated separately, and if we

make the physically reasonable assumption that the magnitude of the moments

on the two "plane" layers are the same, then the angle between the two

components of the spin structure must be 90°. There are, therefore, three

adjustable spin parameters we have taken in our model MCM, and

so that Mo = Mnii + Md

P P|| Pi

M , where Mp and Mp are the moments on the "chain" and the "plane" layers,

respectively. The || and x represent moment directions parallel and

perpendicular, respectively, to the moment direction on the "chain" layers,

A qualitative survey of the observed intensities

shows that the spin direction must lie in the tetragonal plane.

At high temperatures for T < T^., , only whole-integral reflections were

observed. Upon cooling from the paramagnetic state, as T reaches Tj^, the Cu

spins on the "plane" layers start to align, and the value of Mp starts to

develop. We note that the "flattening" of the order parameter at lower

temperatures has been observed in a number of crystals. The maximum

78
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

intensity occurs at about 100 K for the x = 0.1 crystal. We use the value of

the moment obtained from our powder results (where extinction is not a problem), and that is determined to be 0.64 ± 0.06 /in for the saturated Mp .

Upon further cooling, the system undergoes a change in its spin

structure which is characterized by the coexistence of the whole- integral and

half-integral peaks. For the x = 0.1 crystal, at T = 100 K the wholeintegral reflections dominate the scattering. As the temperature is

decreased, the half-integral reflections become more intense while the

intensities for the whole- integral reflections decrease. At T = 20 K, the

half-integral reflections are much stronger than the whole-integral

reflections.

As the temperature is decreased, Mp decreases together with a

development of both Mp and Mpii. The spin structure along the c-axis is a superposition of two orthogonal collinear sequences of + Mp , 0, - Mp ,

+ Mp , 0, - Mp , and - Mpii, + Mp, - Pipii, + j^pii, - Mp, + h^pii, which results in

a noncollinear structure along this axis. Along both directions in the

tetragonal planes, the structure remains a collinear arrangements of + F^p,

- Mp, and + Mp, - Mp in the "plane" and "chain" layers, respectively.

A relative moment of Mp/Mpii = 0.43 is deduced from our data taken on the x = 0.1 crystal at T = 10 K. The values of the ordered moments that we obtained at low temperatures are Mp = 0.81 ± 0.08 /Xg for the "plane" layers

and Mp = 0.35 ± 0.06 jUg for the "chain" layers. The temperature dependence

of the moments on the Cu ions for the x = 0.1 crystal is shown in figure 3.

The relatively large moment observed in the "chain" layers is somewhat

surprising. As the temperature is raised, the thermal agitation randomizes

the spins and results in a reduction of the (average) moments: both Mp and

Mp decrease with increasing temperature, with Mp decreasing faster than Mp

does. As the temperature reaches Tj^«, Mp drops to zero and the Cu spins in

the "chain" layers become completely disordered, while a moment of as high as -0.65 /Ltg still remains on the Cu ions in the "plane" layers.

The 43 independent magnetic reflections that we observed on the single

crystals of NdBa^Cu^Og , and NdBa^Cu-Og ^c aJ^e well explained by the

assumption of a 3-d magnetic form factor on the Cu ions with no need for a significant moment on any of the oxygen ions. The essential difference

between the low- and high-T spin structures is of course the moment Mp on the

79
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

"chain" layers which develops below l^,^. The unexpectedly large value of M^

which we have observed on the Cu "chain" layers demonstrates that the Cu

state is not an appropriate description of the electronic configuration of

the "chain" layers in these materials. There must be strong hybridization of

the (band) electronic wave functions within all three Cu layers. It is quite

clear that the "plane" layers are intimately involved in both the magnetism

and superconductivity, and the oxygen plays a determinative role in the

system.

cn -M

C

O

u

2000

= 1000 \-

NgEcJZujOp.

'empenature (K)

NdEa^uA.i

7500

1

' 'J

; ••. (i/a 1/2. 3/a i

5000

^ \ 1

1 S500

1

n "••••••• ] 100 200 Temperature (K)

Figure 2. (left)

NdBa2Cu30g

Temperature dependence of the magnetic intensities for the

J crystal. The onset of magnetic order for this oxygen

concentration is 1^, = 430 K as revealed by the intensity of the

(1/2 1/2 2) peak shown in (a).

(right) The sharp downturn in the (1/2 1/2 2) intensity at low

temperatures is accompanied by new Bragg peaks at positions such

as (1/2 1/2 3/2) as shown in (b), indicating that the spins are undergoing a change

concentration is == 80 K.

in structure.

Nl

for this oxygen

80
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NdBa^u^B.i

+-' C

QJE

O

U

•M

-P

CDC

CD

fD

-1—1—1 ' 1

' r - - J^ (Mpfi-Mp^^ 1/2

20 40 60 80 100 120 Temperature (K)

Figure 3. Temperature dependence of the ordered moment on the Cu ions for

the X = 0.1 crystal. Mp is the moment on the "chain" layers, Mpii

and Mp are the components of the moments on the "plane" layers

that are || and i, respectively, to Mp. At low temperatures, the

moment on the "chain" layers is about 40% of that on the "plane"

layers. At T = Tj^^, Mp drops to zero, and only the spins of the

Cu in the "plane" layers remain ordered. The solid curves are guides to the eye.

References

[1] Tranquada, J. M.; Cox, D. E.; Kunnmann, W.; Moudden, A. H.; Shirane, G.;

Suenaga, M.; Zolliker, P.; Vaknin, D.; Sinha, S. K.; Alvarez, M. S.;

Jacobson, A. J.; Johnston, D. C. Phys. Rev. Lett. 60, 156 (1988).

[2] Li, W-H.; Lynn, J. W.; Mook, H. A.; Sales, B. C; Bull. Am. Phys. Soc.

33, (1988); Li, W.-H.; Lynn, J. W.; Mook, H. A.; Sales, B. C; Fisk, Z. Phys. Rev. B3Z, 9844 (1988).

[3] Kadowaki , H.; Nishi, M.; Yamada, Y.; Takeya, H.; Takei, H.; Shapiro, S.;

Shirane, G. Phys. Rev. B3Z, 7932 (1988).

[4] Lynn, J. W.; Li, W.-H.; Mook, H. A.; Sales, B. C; Fisk, Z. Phys. Rev.

Lett. 60, 2781 (1988); Lynn, J. W.; Li, W.-H. J. Appl . Phys. 64, 6065

(1988).

81
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

ANTIFERROMAGNETIC ORDER OF THE Cu IN Nd^CuO^

S. Skanthakumar, H. Zhang, T. W. Clinton, W.-H. Li, and J. W. Lynn

(University of Maryland, College Park, MD and Reactor Radiation Division)

and

Z. Risk and S.-W. Cheong

(Los Alamos National Laboratory, Los Alamos, NM)

The magnetic properties of the oxide superconductors are of particular

interest because of the intimate relationship between the magnetic and superconducting properties, which raises the possibility that the copper magnetism

may play an important role in Cooper pairing. The structures of the La^CuO.

and YBapCu-Oy classes of materials consist of strongly bound planes of CuO^

ions, which results in highly anisotropic magnetic and superconducting

properties [1]. Recently, electron superconductors have been discovered [2],

typified by the parent material Nd^CuO., where charge carriers are electrons

rather than holes. Their existence places important constraints on any

theory which is successful in describing the overall behavior of these

systems. It is interesting in this regard to establish the nature of the

magnetic ordering in the parent material. In the present work we report

neutron and x-ray scattering experiments, in which we find a relatively

simple magnetic spin arrangement.

Unpolarized diffraction data were taken with a wavelength of 2.359 A

and a pyrolytic graphite monochromator and filter, at the BT-2 triple-axis

spectrometer. Polarized neutron measurements were taken at approximately the same wavelength, with a Heusler alloy monochromator, and a multilayer

polarizing analyzer. The polarization analysis measurements were essential

in establishing that the spin structures are noncollinear.

The magnetic behavior of this system turns out to be rather

complicated; we have in fact already found five magnetic transitions. The

magnetic peaks can be indexed as (h/2,k/2,^), with h,k odd integers, which is

the same indexing as found for La^CuO. [3,4] and related compounds [5]. The

half-integral values for the first two Miller's indices signify that the unit

cell is doubled in size in the (pseudo)tetragonal a and b directions, while

in the c direction the unit cell above and below Tj^ is the same size. The

temperature dependence of some reflections is shown in figure 1. All the

(1/2 1/2 H) type reflections increase in intensity with decreasing

82
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

temperature, and reveal a Neel temperature 1^ = 245 K. Peaks with i even are observed to have quite different intensities compared to those with i odd.

The (1/2 1/2 0) peak is found to have negligible intensity except in the

temperature region between 30 K and 75 K. In the high temperature phase

(75 K < T < 245 K) we found that the ratios of the spin-flip scattering of

polarized neutrons for the even-integral peaks were quite large (~6), while

the odd-integral peaks we measured had ratios near unity. These data lead us to the spin structure proposed in figure Ic. Note that the spins within each

Cu-0 layer are antiferromagnetically coupled. At 78 K essentially the full

Cu moment has ordered, and we obtain a saturated moment of ~ 0.4 fin. The data in figure la and lb also show that at 75 K the intensity of

the odd-integral peaks suddenly drops, while the even integral peaks increase

abruptly in intensity. We interpret this as a spin reorientation transition,

in which the sense of the spin direction changes from [110] to [lIO]. This

then reverses the character of the spin-flip ratios observed in the polarized

beam data. A similar type of transition has been observed recently for

La^CoO, [5], but the structure is different in that case. At 30 K another

abrupt spin reorientation takes place, where the spins rotate back to the

original spin sense as indicated by the negligible intensity for T < 30 K of

the (1/2 1/2 0) peak. At low temperatures (1.5 K), the Nd ions also order

antiferromagnetically and we find a fifth transition of a continuous nature

at 0.15 K [6].

Our neutron (above T^,) and x-ray scattering data gave evidence for a small distortion in this material from the tetragonal crystal structure [7].

The x-ray intensities were found to be essentially independent of temperature

over the range from 100 K to 300 K and we conclude that the structural and

magnetic peaks behave independently over this temperature range.

83
Figure 1

REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

c)

C

in

in

c

_j

o

u

1 N V_i^_-i_iv_;4

1600 ^Jl.

a)

:200 #

^i jij (l/'2 1/2 1) sB

800 ^

%

I JOO I

•

•

1".•.-.•-

n

,

2500

2000

100 200 30

-

i

b)

(i/'2 1/2 a

1500

1

I

•

1000

:00

ni

1

•

••.

• •

100 200 TemperETiLre (K)

=00

{a),(b) The intensity of the (1/2 1/2 1) and (1/2 1/2 2) peaks as

a function of temperature. Below the Neel temperature of 245 K

the intensity of all the peaks increase with decreasing T. At 75

K there is a sudden spin reorientation, in which the even-integral

peaks [(h/2, k/2, 2n)] increase in intensity while the oddintegral peaks [(h/2, k/2, 2n+l)] decrease in intensity. At 30 K

a second spin reorientation takes place in which the spin

directions return to their original directions,

(c) Magnetic spin configuration of the Cu spins in Nd^CuO..

References

[1] For a general review see High temperature superconductivity,

Lynn, J.W, ed. Springer, New York, 1989.

[2] Tokura, Y.; Takagi, H.; Uchida, S. Nature 337, 345 (1989).

[3] Vaknin, D.; Sinha, S. K.; Moncton, D. E.; Johnston, D. C; Newsam, J.

M.; Safinya, C. R.; King, Jr., H. E. Phys. Rev. Lett. 58, 2802 (1987)

[4] La^CuO. is orthorhombic, and the crystallographic notation is different

than in the present case. The (1/2 1/2 0) peak in the present notation

corresponds to the (100) magnetic peak in LapCuO-.

[5] Yamada, K.; Matsuda, M.; Endoh, Y.; Keimer, B.; Birgeneau, R. J.;

Onodera, S.; Mizuaski, J.; Matsuura, T.; Shirane, G. Phys. Rev. B39,

2336 (1989).

84
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

[6] Li, W.-H.; Skanthakumar, S.; Sumarlin, I. W.; Lynn, J. W.; Shelton, R. N.; Peng, J. L.; Cheong, S.-W.; Fisk, Z. (private communication).

[7] Skanthakumar, S.; Zhang, H.; Clinton, T. W.; Li, W.-H.; Lynn, J. W.;

Fisk, Z.; Cheong, S.-W. Physica C (to be published).

SUPERCONDUCTING TI2 QBa2 o^"°6+5'

A HIGH RESOLUTION NEUTRON POWDER INVESTIGATION

J. B. Parise and M. A. Subramanian

(E. I. du Pont de Nemours & Company, Wilmington, DE)

and

E. Prince

Preliminary reports of the new family of thallium based superconductors

[1-3] have led to a windfall of investigations designed to reveal the

structural features unique to this new class of materials.

Perhaps the most enigmatic of this family is TlpBa^CuOg (fig. 1). It

has been variously described as a nonsuperconductor [4], low-T superconductor [5], moderate-T (<70 K) superconductor [5,6], and high-T (>90 K)

superconductor [3,7]. The composition as written implies a formal oxidation

state for Cu of 2+ (or of 2- for the single CuO^-sheet, and this composition,

containing no excess of holes or electrons, would not be expected to superconduct on the basis of comparison with other Cu-0 based superconductors [8].

Several suggestions have been advanced as possible mechanisms for the

production of the holes in the CuO^ sheets [3,8]. These include internal

redox mechanisms, metal nonstoichiometry, and oxygen nonstoichiometry;

recently the presence of oxygen defects has been revealed in a study of the

related bismuth system [9]. Gross metal vacancies have also been proposed in

Tl2Ba2CuOg [6] as a means of introducing holes in the CuOp sheets. This

suggestion, in particular, requires investigation since it proposes that as many as 12% of the available thallium sites are vacant; a precise single

crystal x-ray investigation [3] found no evidence for such vacancies.

Our results on this system provide evidence that neither Tl -vacancies

nor tetragonal symmetry are necessary conditions for superconductivity in

TlpBa^CuOg. The structure of the orthorhombic form of TKBa^CuOg^ (T = 90 K), synthesized in sealed gold tubes using Ba02, has been refined using

high resolution neutron powder diffraction data collected at 4 K. No

85
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

significant deficiency in metal stoichi omet ry could be inferred from the

crystal structure analysis. The space group (Fmmm) used in this study gives

essentially the same results as the alternatives (Abma, Amaa) proposed in

earlier work. The large amount of disorder that exists in the TKO^'-slab is

mirrored in the large thermal parameters for this structural unit compared to

those for the CuOp sheet (tables 1 and 2). A site at (1/4 1/4 1/4) is

occupied by an amount of oxygen to give overall stoichiometry Tl2Ba2CuOg ,q,

suggesting that oxygen nonstoichiometry plays an important role in producing

high T superconductivity in this system as has recently been reported [10]

in the cadmium doped system ^^2-)S'^)c^^2^^^6+8'

Tl/Cd

-Tl/Cd

Figure 1. A view of the structure of TKBapCuOg, Oxygen atoms are at the corners of corner sharing or edge sharing octahedra. Copper and

thallium atoms are in the octahedral holes in the planes

indicated.

86
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

at 4 K. The usual Table 1. Refined parameters for

discrepancy indexes [11] are reported

^^2^V°6.10

Atom Site

Ceil parameters (A)

a = 5.4604 (2)

b = 5.4848 (2)

c = 23.2038 (6)

R,^ = 0.049

Sp2= 2.26

R = 0.076

wp

B(A2)

Ba

Cu

0(1)

0(2)

16m

8i4a

8e

8i

1/2

1/4

-0.025(1)

3/4

0.2024(1)

0.0828(1)

0.1163(1)

0.43(5)

0.48(6)

0.41(5)

0.45(5)

0.59(5)

0(3)'''^ 16m -0.059(1) 0.2895(2) 3.6(2)d

0{4f 8f 1/4 1/4 1/4 7(2)

(a) Space group Fmmm (no. 69).

(b) Close to ideal site (8i: 0,0,2); half occupancy of site 16m.

(c) Refined occupancy: 0.98(1 ) atom/site.

(d) Equivalent isotropic B. This atom refined with anisotropic thermal parameters:

B^ ^ = 7.2(3), B22 =3.3(5). B33 = 0.2(1 ), 833= -0.2(2);

exp [-0.25(8-1 ih2a*2....+2(Bi2hka*b*...)]

(e) Refined occupation: 0.07(1) atom/site.

(f) a and b reversed from reference [10].

87
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 2. Selected interatomic distances^ for TlpBa^CuOg ,q

Cu -0(1) (x4) 1.9349(1)

-0(2) (x2) 2.698(3)

Ba -0(1) (x4) 2.723(2)

-0(2) (x2) 2.838(1)

-0(2) (x2) 2.850(1)

-0(3) (X1) 2.981(6)

TI -0(2) (X1) 2.004(3)

-0(3) (XI) 2.028-2.073(4)

-0(3) (x2) 2.284-2.932(9)

0(3) (x2) 2.213-2.566(9)

-0(3) (x4) 2.776-2.743(9)

-0(4) 2.144-2.317(5)

0(4) - 0(3) 1.949(4)-2.361(4)

a Those distances involving 0(3) and Tl have been calculated for both

partially occupied sites (at Oyz and 0-yz). When these are not equivalent,

a range is shown.

References

[1

[2

[3

[4

[5

[6

[7

[8

[9

Sheng, Z. Z.; Hermann, A. M. Nature 332, 138 (1988).

Hazen, R. M. et al . Phys. Rev. Lett. 60, 1657 (1988).

Torardi, C. C. et al . Phys. Rev. B38, 225 (1988).

Parkin, S. S. P. et al . Phys. Rev. B38, 6531 (1988).

Shimakawa, Y. et al . Physica C (in press).

Hewat, A. W. et al . Physica C 156, 369 (1988).

Parise, J. B. et al . J. Solid State Chem. 76, 432 (1988).

Sleight, A. W. Science 242, 1519 (1988).

Torardi, C. C. et al . Physica C 157, 115 (1989).

[10] Parise, J. B. et al . Physica C 159, 255 (1989).

[11] Young, P. A. et al . J. Appl . Cryst. 15, 357 (1982).

88
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON POWDER DIFFRACTION STUDY OF Pb2Sr2YCu30Q, THE PROTOTYPE OF A NEW

FAMILY OF SUPERCONDUCTORS

R. J. Cava, M. Marezio, J. J. Krajewski, and W. F. Peck, Jr.

(AT&T Bell Laboratories, Murray Hill, NJ)

and

A. Santoro and F. Beech

The structure of Pb^Sr^YCu^Og has been analyzed with powder neutron

diffraction techniques and profile analysis. The results of this study

confirm the general structural features determined by x-ray single-crystal

methods. The material has pseudo tetragonal symmetry, but is orthorhombic,

space group Cmmm with lattice parameters a = 5.3933(2), b = 5.4311(2), and

c = 15.7334(6) A. The orthorhombic distortion is caused by the disordering

in the ab plane of the oxygen atoms of the PbO layers over the general

position of the space group, with x = 0.275(5) and y = 0.402(5) A. The

structure of this compound can be derived from that of YBa^Cu^Og by

substituting the Cu layers with blocks of . . .PbO.Cu.PbO Of the two Cu

atoms in the asymmetric unit, one has twofold coordination while the other

has fivefold pyramidal coordination with the apex elongated along the c-axis.

SANS STUDY OF YBa2Cu30^ ^^ SOL-GEL PROCESSING

G. Moore, G. Kordas, and M. B. Salamon

(University of Illinois, Urbana, IL)

J. Hayter

(Oak Ridge National Laboratory, Oak Ridge, TN)

and

C. J. Glinka

Sol -gel methods offer a novel route to the fabrication of hightemperature superconducting materials. They offer the advantage of mixing at

the atomic level, synthesis at ordinary temperatures, and possible routes to

thin films and wires without high temperature processing. The chemistry of

this process has been studied at the University of Illinois (G. Kordas) who

has found that alkoxides of Cu, Ba, and Y can be dissoved in suitable

89
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

solvents (e.g., methyl ethyl ketone), dried, and converted to the superconducting phase after processing in oxygen. The purpose of these SANS experiments

was to monitor the development of the gel by determining the fractal

dimensionality of the structure.

A preliminary experiment was performed in February, while the cold source was not in operation. Evidence for the development of fractal

structures was seen in this work, but the range of accessible q-values was

too small to give definitive results. We were able, however, to determine

the optimal solvent conditions and to assure that the component materials

were in the sol phase.

A second 2-day run was carried out in May. Very good evidence for

fractal structure formation was observed and complements SAXS results taken

on similar gels. The data are presently being analyzed for inclusion in the

dissertation of G. Moore, and will be prepared for publication in the near

future. The effects of differing solvents (mixtures of MEK with toluene, for

example) were also studied, and show that solvent conditions can strongly

affect the microstructure of the resultant gel.

INTERPLANAR-BOSON-EXCHANGE MODELS OF HIGH-TEMPERATURE SUPERCONDUCTIVITYTHEORETICAL COMPARISONS AND POSSIBLE EXPERIMENTAL TESTS

R. C. Casella

I have generalized my earlier attempts to understand high-T superconductivity in the layered CUO2 compounds in terms of the exchange of

(unspecified) high-energy (w » w . ) intermediate bosons (IB) between

different CuOp planes [1]. The earlier work was limited to IB exchange

between only two CuOp layers. In order to include systems such as the li and

Bi compounds, the analysis has been extended to include IB exchange between a number n of closely spaced CUO2 layers in a cluster, as well as between

members of different nearby clusters [2]. While limited to IB exchange

between only two layers, the earlier analysis involved IB exchange between

pairs of carriers, which pairs lie in two distinct types of quasi-twodimensional bands, leading to various two-gap scenarios [1]. In the

extension to n-clusters the analysis is simplified by considering only a single band type, whence, under appropriate averaging procedures, a singlegap parameter A(n) emerges [2]. A(n) and the critical temperature T (n)

90
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

depend upon the number n of CuO^ layers per cluster for a given compound. In

the coupled-gap equations employed in the formalism, IB penetration of

several layers is allowed under the assumption that the IB couples weakly to

the paired carriers in the CuO^ layers [1,2]. (The predicted values of T (n)

for n > 3, given experimental values for smaller n, do not depend upon the

absolute scale of the effective coupling parameters g within the formalism,

but only on the ratios C= g /g,.) In common with other theoretical models

[3], I find a rapid saturation of T (n) with increasing n for the IH^ and Bi

compounds. I also obtain the possibility of a diminution of T (n) for n > 3

in the T^^ systems, as illustrated in table 1. Results are presented for two

models. In model #1 the coupled equations in reference [2] lead to an effective coupling parameter of the form

Qp = (n - 1) A^ + (2n)Ap. (1)

Here A^, is the average effective four-fermion coupling resulting from IB

exchange between pairs residing in distinct layers of the same cluster and

Ar, that between a CuO^ layer in a given cluster with each of the n layers in

either of the two immediately adjacent clusters. The factor (n - 1) in the

intracluster term is a consequence of the basic assumption [1,2] that IB

exchange between pairs in the same CuO^ layer (if occurring) does not

contribute to g . In model #2 assumed fixed ranges delineate IB exchange

leading to near (N) and far (F) components Vj^ and Vr of the otherwise

averaged four-fermion interaction potential V. As shown in table 1, both

models lead to rapid saturation of T (n) with increasing n. The possibility

of a diminution of T (n) for n > 3 in the IH^ systems exists in model #2 when

one assumes a high value for T (n = 1) within the range £ ^A^^ £ 85 K

reported by various experimental groups [6,7]. However, this case leads to

technical difficulties in matching the two models at small values of n where

physically one expects them to coalesce. Whether the difficulty encountered

for this case is due to the crude cut-off and averaging procedures employed

or is endemic to IB exchange models if the ratio T (1)/T (2) is not

sufficiently small, is presently unclear.

I have recently considered the possibility that, even under optimal

doping, T (1) <^ 10 K for the T^, and T^^ systems, a possibility which one might reconcile with the higher values reported if the latter were due to.

91
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

say, otherwise undetected small inclusions of materials with clusters having

n > 1. A value of T in this low range need not be considered as requiring a special mechanism such as high-energy interlayer IB exchange. Therefore,

within the context of these models, I have replaced the possible condition

T (1) £ 10 K by the formal assumption T (1) =. [4,5]. This has led to

modifications of models #1 and #2. These are, respectively, models #1' and

#2' in which gj = Ar = 0, whence the predicted values of T (n) for n > 3

depend only upon the ratios f

' = gVgo of^ the couplings. In model #1' only

intracluster IB exchange coupling occurs, and in model #2' IB exchange occurs only between CuO^ layers separated by distances < 0.9 nm for the T£, and li^

systems. Results obtained for these systems are presented in table 2 and

table 3, respectively. These tables include results for yet another model

(#3) in which only nearest-layer intracluster exchange is allowed despite the

assumed weakness of the IB coupling. Comparison of the results for models

#1' and #3 given in the tables shows that they are equal. This equality is

demonstrated analytically in reference [5] and complicates the task of

separating the two experimentally.

The assumption that the effective range for IB exchange along the c axis

is approximately the same in the T^, and T^p series {- 0.9 nm, with

comparable values in the LaSr, LaBa, Bi, and the 1-2-3 yttrium compounds),

allows an understanding of the relatively low values for T (1) reported for

the lH-. and Bi systems, while allowing T == 92 K in the 1-2-3 compound (where

n = 2) and the somewhat reduced but still high values for T in the LaSr and

LaBa systems (where n = 1, but c/2 < 0.9 nm). Hence, resolving the

experimental situation with good single crystals of the T£,, T^^ ^"^ ^i

layered CuO^ compounds with only one CuO^ layer per cluster is of

considerable importance.

92
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Values of T^(n) for n = 4,5,6 for T«2^^n-1^^2^^"°2^n°4+x

as predicted by models #1 and #2

n \

(n)[K]

1 83^ lo''

2 109^ 102^

3 122^ 122^

model #1 model #2 model #1 model #2

4

5

6

130

135

139

121

118

112

130

135

138

130

132

134

^Input from reference [6].

Averages over ranges quoted in reference [7].

Table 2. Values of T (n) for n = 4,5,6 for T^,Ca jBapCCuOp) 0- as predicted by models #1', #2', and #3 when T^(l) <^ 10 K

n Tc(^i)[K]

1 0^

2

75*^

3 105^

model #1' model #2' model #3

4 117 112 117

5 124 116 124

6 128 117 128

^Formal assumption when T (1) < 10 K, the latter implied by

the data of reference [7].

Averages over ranges quoted in reference [7].

93
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 3. Values of T^(n) for n = 4,5,6 for

"''^2^^n-1^^2^^"°2^n°4+x

as predicted by models #r, #2', and #3 when T (1) <^ 10 K.

n T^.(n)[K]

1 0^

2

102*'

3

122''

model #1' model #2' model #3

4

5

6

130

133

136

126

128

130

130

133

136

^Formal assumption when T (1) <^ 10 K, the latter compatible

with the data of reference [7].

Averages over ranges quoted in reference [7].

References

[1] Casella, R. C. Nuovo Cimento D 10, 1439 (1988).

[2] Casella, R. C. Solid State Commun. 70, 75 (1989).

[3] Wheatley, J. M.; Hsu, T. C; Anderson, P. W. Nature 333, 121 (1988);

Birman, J. L.; Lu, J. P. Phys. Rev. B39, 2238 (1989).

[4] Casella, R. C. Post-deadline poster presented at the March meeting of

the American Physical Society, St. Louis, MO (1989).

[5] Casella, R. C. Appl . Phys. Lett, (in press).

[6] Torardi, C. et al . Science 240, 631 (1988).

[7] Parkin, S. et al . Phys. Rev. Lett. 61, 750 (1988).

94
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

TEXTURE STUDY OF MAGNETICALLY ALIGNED YBa2Cu30^ BY NEUTRON DIFFRACTION

C. S. Choi

(ARDEC, Picatinny Arsenal, NJ and Reactor Radiation Division)

H. J. Prask

and

C. P. Ostertag

(Ceramic Division)

Crystals of YBa^CUoOg high-T superconducting materials have a layer

type structure, consisting of sheets of CuO , BaO, and CuO^, oriented

perpendicular to the c-axis, and hence, their superconducting properties are extremely anisotropic. The critical current density along the direction

parallel to the basal plane (i.e., 001 plane) is more than 10 times larger

than that in the direction perpendicular to the plane (or c-axis direction)

in a single crystal sample, with approximately 3 x 10 A/cm at 45 K in the

favorable directions of the crystal. However, the current densities of

polycrystalline materials are about two orders of magnitude less, which is

attributed to random orientation and grain boundary effects. Therefore, a higher degree of alignment of the crystallites along the c-axis is an important factor for a polycrystalline material to achieve higher current

density.

The crystallite orientation distributions of two magnetically aligned

samples: YBa^Cu^Og aligned in the tetragonal phase followed by oxidation for

orthorhombic conversion (YBaCuO-153), and orthorhombic YBapCu-O^ (YBaCuO151), were studied by neutron pole figure measurements. The intensity

distributions of (004) over the entire orientation hemisphere, with the (f>- angle ranging from -180 to 180 and x-angle from 90 to in 5° intervals, were measured using the single-crystal neutron diffractometer. The observed pole

figures of the two samples, which are shown in figure 1, show a fiber texture

with the c-axis parallel to the applied magnetic field direction. The

orientation distributions of the fiber axes could be described quite

satisfactorily with Lorentzian or March distribution functions, as shown in

table 1. The sample aligned in the tetragonal phase had distinctly better

alignment than that aligned in the orthorhombic phase, with FWHMs of 19.3(3)°

and 37.8(7)° respectively. The contour lines of the pole figures showed

95
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

irregularities which could be attributed to the presence of coarse grains in

the samples.

Table 1. Results of the nonlinear least squares fits of the x-angular

distributions of the fiber axes to Lorentzian (L) and March (M)

function. The functions used are in the form:

L = A{l+4(C-x)W}"^ and

M = S(r^cos^(C-x) + r"-^sin^(C-x))""^/^ with r < 1

The peak height (A) and FWHM (W) of M function were calculated by,

A = S(r"^) and FWHM = 2arcsin{(4^/"^-l)/(l-r^))^/^.

The GL function is a linear combination of Gaussian and Lorentzian with

the same FWHM, and with the best-fitted scale ratio of Gaussian/Lorentzian =

1.3(4).

Sample/function type AmDlitude(A) FWHM(W) Position(C) RSD

YBaCuO-151/L 681(9) 37.8(7) 76.1(2) 0.053

YBaCuO-151/M 673(15) 38.7(4) 76.1(3) 0.059

YBaCuO-153/L 1720(18) 19.3(3) 83.5(1) 0.045

YBaCuO-153/M 1667(49) 21.0(2) 83.5(9) 0.061

YBACUO-151 (004) YBACUO-153 (004)

Figure 1. Observed 004 pole figures of YBaCuO-151 and YBaCuO-153. The

contour lines below 1 m.r.d. levels are deleted. The step

intervals are 0.3 m.r.d. for the 151 samples and 1 m.r.d. for 153.

96
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

GRAZING-ANGLE NEUTRON DIFFRACTION STUDY OF Cr/Nb/Al203 FILM

J. F. Ankner, H. Zabel , J. A. Dura, and C. P. Flynn

(University of Illinois, Urbana, IL)

and

D. A. Neumann and C. F. Majkrzak

Grazing-angle diffraction is a powerful tool in the study of surfaces

and interfaces. The development of synchrotron sources in the decade since

the first demonstration of grazing-angle diffraction has led to a broad

application of the method as an x-ray structural probe. The comparatively

low flux of conventional neutron sources had, until recently, prevented a similar use of the technique in neutron experiments. We first demonstrated

the feasibility of grazing-angle neutron diffraction using a large perfect

silicon crystal [1] and have now extended the technique to the study of

ideally imperfect crystals, using Cr/Nb/AKO^ as a test case [2]. These

experiments pave the way for the use of grazing-angle neutron diffraction in

studies of those materials to which neutrons are uniquely sensitive (e.g.,

magnetic and hydrogen-rich interfaces, surfaces, and films).

The essence of the grazing-angle diffraction technique is the excitation

of a diffracted beam under conditions of total external reflection of the

incident beam. Figure 1 shows the wave-vectors external to the crystal in

the grazing-angle geometry. A neutron beam (k) strikes the sample at an angle (f> with respect to the surface and is specularly reflected (k , 0); the

sample is oriented such that an in-plane reflection (kg) is excited at

glancing angle 0g. The total reflection occurring simultaneously with the

diffraction process ensures that the diffracted intensity originates in that

portion of the sample which lies close to the surface.

To demonstrate grazing-angle neutron diffraction in the kinematical

regime, we studied an molecular-beam epitaxy (MBE)-grown film consisting of

3200 A Cr(llO) on a 400 A Nb(llO) buffer layer atop an Al2O3(1120) substrate.

The Cr and Nb layers were crystalline with mosaic spreads of 0.3°. Figure 2 shows the intensity distributions of the specularly reflected (solid curve)

and the grazing-angle diffracted beams for two different in-plane Bragg

reflections: Cr(li2) (dashed) and Nb(220) (dotted). The diffracted curves were recorded with collimations 0p and 9 relaxed (see fig. 1) to maximize

intensity. The incident beam (0) had 0.017° angular divergence and was

97
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

scanned (Q » 47r0/A) up through the critical angles for total external

reflection of the layers; the intensity of the specularly reflected beam

(solid) drops off as the critical Q of the sapphire substrate

(Q = 0.016 A' ) is reached. The intensities of the grazing-angle diffracted

beams increase with Q below Q as the neutron beam penetrates deeper into the

sample; above Q (less than that of the substrate for both Cr and Nb) the

intensity falls off as the in-crystal wave vector no longer satisfies the

diffraction condition. This behavior occurs for both the Cr(li2) and Nb(220) scans and is the signature of grazing-angle diffraction.

In summary, we have modified a triple-axis diffractometer so that it can

be used for grazing-angle neutron diffraction and demonstrated the

applicability of the method to imperfect crystals. The application of

grazing-angle neutron diffraction to studies of magnetic and hydrogen-rich

materials promises to enhance our understanding of surface and interfacial

physics by utilizing the unique sensitivity of neutrons to these systems.

nA

Figure 1. Grazing angle diffraction geometry.

incident, specularly reflected, and

vectors.

k, K and k. ^s' "•" 'G

ref1 ected-di ffracted

are the wave

98
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

d

£

o

3 50

c

o^

25

c

K T T——

0.00 0.01 0.02 0.03

Figure 2.

References

Grazing-angle reflectivity scans. Solid line is specularly

reflected intensity (scaled down by a factorof 100), dashed

Cr(li2) reflected-diffracted, and dotted Nb(220) reflecteddiffracted.

[1] Ankner, J. P.; Zabel , H.; Neumann, D. A.; Majkrzak, C. F. Phys. Rev.

B40, 792 (1989).

[2] Ankner, J. F.; Zabel, H.; Neumann, D. A.; Majkrzak, C. F.; Dura, J. A.;

Flynn, C. P. J. Phys. (submitted for publication).

NEUTRON REFLECTIVITY STUDY OF GD-Y INTERFACE

J. F. Ankner, H. Zabel, A. Matheny, J. A. Dura, and C. P. Flynn

(University of Illinois, Urbana, IL)

and

D. A. Neumann and C. F. Majkrzak

In recent years, there has been a great deal of interest in surface,

interface, and thin-film magnetism. Using neutron reflectometry and grazingangle diffraction, one can determine the magnetic structure of surface and

subsurface layers in these types of systems. We have studied, using spinpolarized neutron reflectometry, the interface between Y(OOOl) and Gd(OOOl)

films grown by molecular beam epitaxy (MBE).

99
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Bulk gadolinium is a ferromagnet with T = 293 K. Recent measurements

by Weller et al . [1], on the magnetism of Gd (Gd/vacuum interface) have

indicated that a surface magnetic moment persists as much as 20 K above T . We have therefore been interested in the nature of the magnetism in other

interfacial Gd systems, a first example of which is the interface with non- magnetic yttrium. Both Gd and Y are hep metals, with approximately the same lattice constants at room temperature. The film we studied consists of a 100 A Y(OOOl) cap layer on 1000 A of Gd(OOOl) atop a 300 A Y(OOOl) seed

layer, which grows on a 1000 A Nb(llO) buffer layer and an Al202(1120)

substrate. The mosaics of the metal layers range from 0.1-0.4". Figure 1 shows the neutron reflectivity of the film at T = 151 K with the incident

neutron beam polarized parallel (closed circles) and antiparallel (open

circles) to the magnetic moment in the Gd. At this temperature (well below

T ), the Gd layer is fully magnetized. By careful analysis of these

reflectivity profiles and comparison with x-ray reflectivity data, we will be

able to determine the depth-dependence of the magnetization at the topmost

Gd-Y interface. We have also searched for an interfacial magnetic state

above T (at T = 295 K) and find, within experimental uncertainty, no net

moment at the Gd-Y interface. This result is in agreement with results

obtained for Gd-Y superlattices studied by polarized neutron diffraction and

suggests that the Gd-Y interface is indeed different from the surface of Gd

in vacuum. We plan to study Gd interfaces with nonmetallic compounds and to use grazing-angle neutron diffraction to determine the spin orientation and

crystal structure of these interfacial regions.

100
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

4

0.02 0.04 0!06

Figure 1. Neutron reflectivity of Y/Gd/Y/Nb/Al 2O3 film at 151 K. Closed

circles have neutron polarized parallel to sample moment, open

antiparallel

.

Reference

[1] Weller, D.; Alvarado, S. F.; Gudat, W.; Schroder, K.; Campagna, M.

Phys. Rev. Lett. 54, 1555 (1985).

DETERMINATION OF HYDROGEN DENSITY PROFILES IN THIN FILMS AND

MULTILAYERS BY NEUTRON REFLECTION

C. F. Majkrzak, S. K. Satija, D. A. Neumann, and J. J. Rush

D. Lashmore and C. Johnson

(Metallurgy Division)

J. Bradshaw

(Optoline, Andover, MA)

and

L. Passell and R. DiNardo

(Brookhaven National Laboratory, Upton, NY)

The density of hydrogen in thin films or multilayers of metal hydrides

can be inferred from an expansion of the host lattice as measured by

conventional x-ray diffraction techniques. However, because hydrogen and

deuterium have scattering lengths for neutrons that are comparable to those

of most metal nuclei, unlike the corresponding case for x-ray atomic

scattering amplitudes, the hydrogen density profile normal to the surface of

101
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

a flat, thin film can be determined directly from neutron reflectivity

measurements. The hydrogen density modulation in an artificial superlattice

along the growth direction can also be determined in this manner. Furthermore, the thin films or multilayers need be neither crystalline nor metallic;

for example, the H composition profile in a H-Si superlattice created by

chemical vapor deposition can be obtained by neutron reflection [1].

Often hydrogen can be loaded into a film or multilayer in either a gas

cell or electrolytically, in situ, thereby making possible real-time

measurements of hydrogen concentration profiles in active electrodes. The

latter configuration can be realized in practice by using a single-crystal

substrate (e.g., silicon), which is nearly transparent to neutrons, as the

incident medium. Several thin-film metal hydride systems are currently being

studied, including a Ni-Ti multilayer electrolytically charged with H and D.

Reference

[1] Abeles, B.; Yang, L.; Leta, D.; Majkrzak, C. F. J. of Non-Crystalline

Solids 97 and 98 , 353 (1987).

THE MORPHOLOGY OF SYMMETRIC DIBLOCK COPOLYMERS AS

REVEALED BY NEUTRON REFLECTIVITY

S. H. Anastasiadis and T. P. Russell

(IBM Research Division, San Jose, CA)

and

S. K. Satija and C. F. Majkrzak

Recently, it has been shown that symmetric diblock copolymers of

polystyrene (PS) and polymethylmethacrylate (PMMA) when prepared as thin

films (5000 A or less) on silicon substrates, exhibit a strong orientation of

the lamellar microdomains parallel to the surface of the substrate [1,2].

This orientation occurs when the copolymer films are annealed at temperatures

above the glass transition temperatures of the PS and PMMA blocks and results

from the interactions of the two blocks with the air and substrate

interfaces. PMMA, the more polar species, preferentially resides at the

silicon (silicon oxide)/copolymer interfaces, whereas PS, the lower surface

energy component, preferentially segregates to the air/copolymer interface.

102
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

These interactions, coupled with the chemical connectivity of the PS and PMMA

blocks, result in the observed multi layered structure.

In this report the details of the lamellar morphology for a series of PS

and PMMA, symmetric di block copolymers is reported where the molecular weight

of the copolymer is varied. It is shown that neutron reflectivity provides

the key means by which the exact nature of the interface between the

copolymer microdomains can be investigated. It is also shown that the interface between homopolymers of PS and PMMA is identical to that seen in the

copolymers.

Symmetric, diblock copolymers of PS and PMMA, denoted P(S-b-MMA), were purchased from Polymer Laboratories and were prepared by a successive anionic

polymerization process. The complete characterization of the copolymers is

shown in table 1. As can be seen, the copolymers have narrow molecular

weight distributions and styrene contents close to the desired 50%. It

should also be noted that either the PS or PMMA block in the copolymer was perdeuterated which provided the contrast necessary for the neutron

reflectivity studies.

Samples of the copolymers were prepared on 10 cm diam, polished Si

substrates. The substrates were ~ 5 mm in thickness to ensure that the

substrate did not bow or bend when mounted in the sample holder. Solutions

of the copolymer were prepared in toluene with the concentration being varied

to produce the desired sample thickness. The substrates were fully coated

with copolymer solutions and spun at 2000 rpm to produce a film with a uniform thickness. The spinning process also served to evaporate most of the

solvent in the film. The substrates were then placed under vacuum at 80 "C

for 24 h to remove the remaining solvent and then were heated to 170 °C for

72 h to produce the oriented lamellar morphology. The specimens were then

cooled to room temperature and investigated without further heating.

Neutron reflectivity measurements were performed on the BT-4 triple-axis

diffractometer at the NIST reactor. Details of the experimental geometry can

be found elsewhere [7]. Experiments were performed with neutrons of

wavelength X = 2.35 A over an angular range of 29 = 0° to 1.7°. This

translates into a neutron momentum, k range from to -0.1 A" where

k = (27r/^) sin 9. Under such condition reflectivities down to 10" could be

measured which proved to be crucial to these studies [7,8].

103
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The neutron reflectivity profile measured for the P{S-b-d-MMA) diblock

copolymer, where the molecular weight of each block is ~ 15,000, after

annealing at 170 "C for 72 h is shown in figure 1. As can be seen at small

values of the neutron momentum, total external reflection is seen below the

critical angle. Above this the reflectivity drops by nearly two orders of

magnitude whereupon a strong first-order Bragg reflection at k = 0.0195 A'

is seen. This is followed by a further decrease in the reflectivity with the

appearance of second- and third-order reflections at k 's of 0.0375 and

0.0540 A' , respectively. The Bragg reflections are directly attributable to

the layering of the lamellar morphology parallel to the surface of the film

and the positions of the Bragg reflections yield directly the period of the

lamellar microdomain morphology. In this case the period is 175 A which is

comprised of a PS microdomain with a size of 91 A and a PMMA microdomain of

84 A. More importantly, the interface between the PS and PMMA microdomains

is found to be 50 ± 3 A. Using this model for the variation in the neutron

scattering length density normal to the film surface, the calculated

reflectivity profile, indicated by the solid line in figure 1, is obtained.

The agreement between the calculated and measured reflectivity profile is

very good over the entire k range and over 5.5 orders of the reflectivity.

Variation of the parameters outside of the stated values produces

reflectivity profiles that do not agree with the experimentally measured

profile. It must be emphasized that such precision on the width of the

interface between the two microdomains was, heretofore, impossible.

Increasing the molecular weight of the blocks to ~ 50,000 per block

produces dramatic changes in the neutron reflectivity profiles. Shown in

figure 2 is the measured reflectivity profile of the P(d-S-b-MMA) diblock

copolymer after annealing at 170 °C for 72 h under vacuum. As with the lower

molecular weight specimen, at small values of k total external reflection.

However, at higher k at least five orders of Bragg reflections are evident

which yield a period of 398 A which is comprised of PS and PMMA microdomain

sizes of 210 A and 188 A, respectively. As expected, the period of the

lamellar morphology has increased with the increase in the molecular weight

of the copolymer. The large number of Bragg reflections also provides a high

sensitivity to the interface between the copolymer microdomains. Shown in

figure 2 by the solid line is the calculated reflectivity profile where the

interface is described by a hyperbolic tangent function where the effective

104
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

width of the interface is 50 ± 3 A. This describes the observed reflectivity

quite well over the entire measured k range. Using this functional form for

the interface, variation of the interface width outside of these limits

produces an unacceptable description of the measured reflectivity profile.

Also shown in figure 2 as the dashed line, is the calculated reflectivity

profile where a simple linear gradient of the neutron scattering length

density was used to describe the concentration variation across the interface

between the PS and PMMA microdomains. As can be seen, this model describes

the data reasonably well over the entire k range, but does not produce as good a fit to the data as the hyperbolic tangent function. Consequently, the

neutron reflectivity results clearly show that whatever the functional form

of the concentration gradient across the interface is, it must closely follow

the hyperbolic tangent functional form. Such details on the morphology of

block copolymers were previously unattainable by other techniques.

Similar studies have been performed on the P{S-b-d-MMA) diblock

copolymer where the molecular weight of each block is ~ 50,000. In this case

the neutron reflectivity profile yields a period of 512 A comprised of a PS

and PMMA microdomains with sizes of 268 A and 244 A. As with the P(d-S-bMMA) copolymer the interface was well described by a hyperbolic tangent

function with an effective width of 47 ± 4 A. Thus, with the exception of

the variation in the length of the period due to the increase in the

molecular weight, these results are identical to the other cases. Finally, a P(d-S-b-MMA) diblock copolymer where the molecular weight of

each block was ~ 150,000 was investigated. It has been found that the rate

at which the copolymer microdomains orient parallel to the film surface

depends strongly upon the molecular weight of the copolymer. For such high

molecular weights the time required for the lamellar orientation is quite

long. Therefore, a copolymer film was prepared where the total thickness of

the specimen corresponded to one-half of the period size. This specimen was annealed for 240 h at 170 "C. The neutron reflectivity profile obtained from

this specimen is shown in figure 3. As can be seen, periodic oscillations

are seen in the data with at least two different characteristic frequencies.

The frequencies correspond to the total thickness of the specimen and the

thickness of the deuterated PS microdomain. The reflectivity results could

be well described by the scattering length density profile shown in the inset

of the figure. This model is comprised of a 225 A layer of deuterated PS on

105
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

top of a 156 A layer of PMMA. The two layers are separated by an interface

with a composition variation across the interface that is given by a hyperbolic tangent function with an effective width of 50 ± 4 A.

Therefore, the clear picture that emerges from the combined results of

these studies is that the period of the lamellar microdomain morphology

increase with the molecular weight of the copolymer. If N is the total

number of segments in the copolymer, then these results indicate that L, the

period, varies with N

* which agrees with theories describing copolymers in

the strong segregation limit. The width of the interface is found to be

independent of the copolymer molecular weight, and, for the P{S-b-MMA)

copolymers, is found to be 50 A. Independent studies on bilayers of PS and

PMMA homopolymers [7,9] have shown that the interface between the homopolymers is well described by a hyperbolic tangent function (or other

functions that closely follow this form) with an effective width of 50 A in

precise agreement with the copolymer results. From the measured values of

the interaction parameter between PS and PMMA [10] and the values of the

statistical segment lengths of PS and PMMA, the width of the interface can be

calculated theoretically. These calculations yield a value of the interface

of 21 A. Unfortunately, this value is more than a factor of two smaller than

the measured value. This discrepancy is well outside of any experimental errors in the reflectivity results or errors associated with the interaction

parameter or the statistical segment lengths and, in our opinion, points to a significant shortcoming of current theoretical treatments of the interface

between homopolymers and copolymer microdomains.

Table 1. Temperature dependence of PS/PMMA parameters

Copolymer Mps Mp,^,^^ M^M^ f

P(S-b-d-MMA) 14,670 15,107 1.10 0.50

P(d-S-b-MMA) 52,900 48,000 1.07 0.50

P(S-b-d-MMA) 56,300 65,000 1.12 0.47

P(d-S-b-MMA) 169,500 131,900 1.08 0.53

106
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

0.00 0.02 0.04 0.06

k,(A- )

0.08

Figure 1. Neutron reflectivity profile of a P(S-b-d-MMA) diblock copolymer

film annealed on a Si substrate for 72 h at 170 °C where the total

copolymer molecular weight is ~ 30,000. The points are the

measured reflectivity profile whereas the solid line is the

calculated reflectivity profile using the scattering length

density profile shown in the inset.

10

0.00 0.02 0.04 0.06 0.08

k„(A-l)

Figure 2. Neutron reflectivity profile of

film on a Si substrate annealed

copolymer molecular weight is

measured reflectivity profi

reflectivity profile using the

describe the interface between

dashed line is that calculated

the microdomains. The models

profiles are shown in the inset

a P(d-S-b-MMA) diblock copolymer

for 72 h at 170 'C where the total

~ 100,000. The points are the

le the line is the calculated

hyperbolic tangent function to

the copolymer microdomains and the

assuming a linear gradient between

used to calculate the reflectivity

107
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

^0

G.04

—.—1—

1

. •

- A

- V

n " I.I. I

J (K) 200 300

?(A) 400 500 -

1 1 %^

0.06 0.08

Figure 3. Neutron reflectivity profile for a P(d-S-b-MMA) diblock copolymer

annealed for 240 h at 170 °C where the total molecular weight of

the copolymer is - 300,000. The solid line is the calculated

reflectivity profile using the scattering length density profile

shown in the inset.

References

[1] Coulon, G.; Russell, T. P.; Deline V. R.; Green P. F. Macromol . 22,

2581 (1989).

[2] Russell, T. P.; Coulon, G.; Deline, V. R.; Miller, D. C. Macromol. (in

press)

.

[3] Helfand, E.; Wasserman, Z. R. Developments in block copolymers - 1.

I. Goodman, ed. Appl . Sci . Pub., New York (1982).

[4] Meier, D. J. Thermoplastic elastomers--research and development. N.

Legge, G. Holden, H. Schroeder, eds. Hanser Pub., Germany (1988).

[5] Ohta, T.; Kawasaki, K. Macromol. 19, 2621 (1986).

[6] Semenov, A. N. Zh. Eksp. Teor. Fiz. 88, 1242 (1985).

[7] Anastasiadis, S. H.; Russell, T. P.; Satija, S. K.; Majkrzak, C. F. J. Chem. Phys. (submitted for publication).

[8] Anastasiadis, S. H.; Russell, T. P.; Satija, S. K.;

Phys. Rev. Lett. 62, 1852 (1989).

Majkrzak, C. F.

[9] Fernandez, M. L.; Higgins, J. S.; Penfold, J.; Ward, R. C; Shackleton,

C; Walsh, D. J. Polymer 29, 1923 (1988).

[10] Russell, T. P.; Hjelm, R. P.; Seeger, P. A. Macromol. (submitted for

publication).

108
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

TEMPERATURE DEPENDENCE OF THE MORPHOLOGY OF THIN DIBLOCK

COPOLYMER FILMS AS REVEALED BY NEUTRON REFLECTIVITY

T. P. Russell and S. H. Anastasiadis

(IBM Research Division, San Jose, CA)

and

S. K. Satija and C. F. Majkrzak

Thin films of symmetric diblock copolymers on solid substrates have been

shown to exhibit a strong orientation of the lamellar microdomains parallel

to the surface of the substrate upon heating to temperatures above the glass

temperature [1-4]. Specular neutron reflectivity measurements [3,4] clearly

show that this orientation is parallel to the surface of the substrate over

large lateral length scales. Consequently, the morphology produced by simply

annealing the films above the glass transition temperature is that of a perfect multilayer. This behavior is found provided the annealing temperature is below the microphase separation transition temperature (MST) where a transition from an ordered to a disordered morphology occurs. For perfectly

symmetric diblock copolymers the MST occurs when xN = 10.5 where x is the

Flory-Huggins interaction parameter and N is the total number of segments in

the copolymer chain. For thin films of symmetric diblock copolymers annealed

at temperatures above the MST, recent neutron reflectivity studies [3] have

shown that there is a preferential segregation of one of the components to

the air/copolymer and the copolymer/substrate interfaces. Due to the

connectivity of the blocks this excess surface concentration induces an oscillatory variation in the composition of the two components normal to the

interface that is exponentially damped. This behavior has been shown to be

in agreement with recent theoretical arguments [5].

In this report neutron reflectivity studies on the temperature

dependence of the morphology of diblock copolymers in the vicinity of the MST

are discussed. At temperatures below the MST the ordered multi layered

lamellar morphology is found to penetrate through the entire specimen. At

temperatures above the MST the periodic variation in the composition of the

components is maintained but a clear dissipation of the order is found with

increasing distance from either the air/copolymer or copolymer/substrate

interfaces. An exponentially damped squared cosine function from both

interfaces is found to well describe the reflectivity results. The

109
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

characteristic decay length is found to decrease with increasing temperature

in accordance with mean field arguments. Results from two different

copolymers with two different molecular weights and, consequently, two

different MST's are found to be identical on a reduced temperature scale.

Symmetric, di block copolymers of PS and PMMA, denoted P(S-b-MMA), were purchased from Polymer Laboratories and were prepared by a successive anionic

polymerization process. The P(S-b-d-MMA) copolymer, where the methacrylate

block is perdeuterated, had a PS block molecular weight of 14,670 and a PMMA

block molecular weight of 15,107. The total copolymer had an M /M of 1.1

and the fraction of PS in the copolymer was 0.5. The P(d-S-b-MMA) copolymer

had a total molecular weight of 27,600 with M /M = 1.08 and a PS fraction of

0.43.

Samples of the copolymers were prepared on 10 cm diam, polished Si

substrates. The substrates were ~ 5 mm in thickness to ensure that the

substrate did not bow or bend when being mounted in the sample holder.

Solutions of the copolymer were prepared in toluene with the concentration

being varied to produce the desired sample thickness. The substrates were

fully coated with the copolymer solutions and spun at 2000 rpm to produce a film with a uniform thickness. The spinning process also served to evaporate

most of the solvent in the film. The substrates were then placed under vacuum at 80 "C for 24 hours to remove the remaining solvent.

Neutron reflectivity measurements were performed on the BT-4 triple-axis

diffractometer at the NIST reactor experimental hall. Details of the

experimental geometry can be found elsewhere [4]. Experiments were performed

with neutrons of wavelength A = 2.35 A over an angular range of 28 = to

1.7°. This translates into a neutron momentum k range from to ~ 0.1 A'

where k = (27r/A) sin 5.

Experiments were performed at temperature by heating the cast, dried

specimen under vacuum in a heated sample stage on the spectrometer. It is

important to note that experiments were performed initially at temperatures

above the MST of the copolymers to prevent a complete ordering of the

copolymer films. It was found that heating the samples to temperatures below

the MST initially, followed by heating to temperatures above the MST was not

successful. It appeared as if the specimens required a substantial amount of

time to reach equilibrium; i.e., to lose completely the ordering induced at

the lower temperature.

110
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The neutron reflectivity profile measured for the P{S-b-d-MMA) diblock

copolymer, where the molecular weight of each block is ~ 15,000, at 155 "C is

shown in figure 1. As can be seen at small values of the neutron momentum

total external reflection is seen below the critical angle. Above this the

reflectivity is seen to drop by nearly two orders of magnitude where upon a strong first-order Bragg reflection at k = 0.0195 A' is seen. At higher

values of k a second-order reflection and a diffuse third-order reflection

are evident. The solid line in the figure is the calculated reflectivity

profile using the scattering length density profile shown in the inset where

the period is 175 A and the effective width of the interface between the PS

rich and PMMA rich microdomains is 50 A. For the P{S-b-d-MMA) copolymer

investigated here the MST, calculated from the molecular weight of the

copolymer and the temperature dependent interaction parameter [6], is 179 °C.

0.08

Figure 1. Neutron reflectivity profile of a P(S-b-d-MMA) diblock copolymer

film on a Si substrate at 155 "C. "

reflectivity profile, the line

profile using scattering length

inset.

The points are the measured

is the calculated reflectivity

density profile shown in the

Thus, at 155 °C the copolymer is below, but near, the MST. In keeping with

this, the two microphases in the lamellar morphology are not pure PS or PMMA

but are only rich in either component and the total fraction of the specimen

that is occupied by the interface is ~ 0.65. Consequently, while the

oriented lamellar morhology propagates through the entire specimen, it is

yery diffuse due to the proximity of the MST.

Ill
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Experiments were performed at several temperatures above the MST. As an example of a typical reflectivity result, the data for the experiment

performed at 200 "C is shown is figure 2. In general, at temperatures not

too far above the MST, the first order Bragg reflection persists but is

broader and less intense than that seen at temperatures below the MST. In

addition, the higher order reflections become much more diffuse. The solid

line in this figure represents the reflectivity profile calculated using the

scattering length density profile shown in the inset. Here the scattering

length density as a function of the distance z from either interface is given

2 by b + brexp (-z/f) cos (ttz/L), where b is the average scattering length

density of the specimen, br is the excess scattering length density at the

interface, f is the correlation length characterizing the damping of the

oscillatory composition profile and L is the period. For this measurement at

200 "C, f is 600 ± 50 A and L is 162 A. The results for the other measurment

temperatures above the MST are given in table 1. Also shown in table 1 are the results for the P(d-S-b-MMA) specimen which was annealed at 170 "C and

quenched to room temperature. Detailed discussions of these data can be

found elsewhere [3]. It is important to note that the MST for this copolymer

is 40 "C which results from the difference in the molecular weight.

10^^0

10 -1

10-2

R 10-3

10

10

-4 -

10'

: ^J 1

1 ' 1 ' 1 i

~#^^fl) . A

CD l

' 1 1 _ V cf 6 f\ n \ < A A A

";

rk /\ A A \ \ _ ^ l\ ^ ^ \ \f\ \ \

Xk- A^ p Y

X

/ yy v v/ \/ \ \ — ^^^ ' V ^

/ v V y

\ ~

; \ — ^ V ^ -

- \ 1 I _

) 400 B(in 12(>o _

- v^ z(A)

-

- -

: ^s^i-N^ :

-

1 1 1 1 1

Oodn o

1 On

5 -

0.02 0.04

k„{A-')

0.06 0.08

Figure 2. Neutron reflectivity profile for a P(S-b-d-MMA) diblock copolymer

at 200 "C. The solid line is the calculated reflectivity profile

using the scattering length density profile shown in the inset.

112
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Temperature dependence of PS/PMMA parameters

Copolymer TC clM IXAi

P{d-S-b-MMA) 170 95 ± 7 150

P(S-b-d-MMA) 185 1100 ± 100 166

P(S-b-d-MMA) 195 800 ± 75 161

P(S-b-d-MMA) 200 600 ± 50 162

The results in table 1 clearly show that the period above the MST is

lower than that found for the copolymers at temperature below the MT and is

not a strong function of the temperature. Secondly, as the temperature is

increased above the MST, the correlation length is seen to decrease

dramatically.

These results can be understood in terms of the recent mean field

arguments of Fredrickson [5]. In his treatment the surface induced ordering

can be described by an exponentially damped cosine function which is

identical in form to the function used here to describe the scattering length

density profile from the interface. According to Fredrickson [5] the

correlation length f is given by

1 = ( 6f(l - f) [(xN). - {xN)])^/2 (1)

f Nb2

where f is the fraction of one component in the copolymer, N is the total

number of segments in the copolymer, b is the average statistical segment

length of the copolymer, (xN)r is the value of (xN) at the MST and (xN) is

the value of (xN) at the measurement temperature. These parameters are available from previous studies for the copolymers of interest here [3,6].

As shown previously, x is of the form A + B/T where T is the absolute

temperature. Therefore, eq (1) can be rewritten as

2 = ~i (l/T. - VT) . (2)

f{l - f)Br'^ b"^ ^

From this equation it is seen that, at temperatures above the MST, as the measurement temperature approaches the MST, f gets larger and at the MST

f becomes infinite. This merely states that as the MST is approached, the

ordering induced by the surface propagates further into the specimen and at

the MST and below the ordering completely saturates the specimen.

113
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

This behavior is precisely what is seen in the experiments reported

here. However, direct application of eq (2), taking into account the

differences in the molecular weights and fractions of PS in the copolymers,

does not yield the expected linear behavior. This results from the precision

to which X must be known for this copolymer since x has a very weak

temperature dependence. Adjusting x by only 2% brings the data into align

with the theoretical arguments. It is not possible, at this time, to measure

X with better precision. However, variation of x by this small amount brings

the data for both the P(S-b-d-MMA) and the P(d-S-b-MMA), which have different

molecular weights, fraction of PS, and MST's, into very good agreement with

each other. It is clear from this that the mean field theoretical arguments

describe the behavior seen for these copolymers well, within the experimental

limitations.

References

[1] Coulon, G.; Russell, T. P.; Deline, V. R.; Green, P. F. Macromol . 22,

2581 (1989).

[2] Russell, T. P.; Coulon, G.; Deline V. R.; Miller, D. C. Macromol.

(accepted for publication).

[3] Anastasiadis, S. I.; Russell, T. P.; Satija, S. K.; Majkrzak, C. F. Phys. Rev. Lett. 62, 1852 (1989).

[4] Anastasiadis, S. H.; Russell, T. P.; Satija, S. K.; Majkrzak, C. F. J. Chem. Phys. (submitted for publication).

[5] Fredrickson, G. H. Macromol. 20, 2535 (1987).

[6] Russell, T. P.; Hjelm, R. P.; Seeger, P. A. Macromol. (submitted for

publication)

.

114
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON REFLECTIVITY STUDY OF THE DENSITY PROFILE OF AN ADSORBED

DIBLOCK COPOLYMER AT THE SOLUTION-QUARTZ INTERFACE

S. K. Satija and C. F. Majkrzak

S. K. Sinha, E. B. Sirota, and J. Hughes

(Exxon Research and Engineering Co., Annandale, NJ)

and

T. P. Russell

(IBM Almaden Research Center, San Jose, CA)

Adsorption of polymers at a solid-liquid interface is of considerable

practical importance. There has been a considerable amount of work done to

gain understanding of the conformations of adsorbed polymers from a solution near a solid surface. This work has involved various different techniques

including, ellipsometry [1], surface force measurement [2,3], and x-ray

fluorescence [4]. A large body of theoretical work [5,6] has also been

carried out to understand the equilibrium concentration profiles for a polymer solution near a solid wall. Despite this work a detailed

understanding of the problem is still lacking.

We present results of neutron reflectivity measurement on solutions of

Poly (styrene-b-methymethacrylate), PS-PMMA, di block copolymers near a quartz

wall. By utilizing all four combinations of hydrogenated and deuterated

blocks, we are able to determine the density profile of the PMMA blocks

adsorbed on to the quartz wall. The concentration of polystyrene segments

beyond this initial layer of PMMA block seems to be too small to be seen by our experiments.

The cell used for the experiment is shown in figure 1 and is similar in

design to a cell used by Kitchens et al . [7] for their quartz/liquid-helium

interface experiment. It consists of a large single crystal of quartz (B)

3

(200 X 75 X 25 mm ) which was optically polished on one face (C). The quartz

crystal was clamped with brass bolts between a pair of rigid stainless steel

plates (A). An 0.5 mm teflon gasket was used as a seal between the quartz

crystal and top steel plate. The gap provided by the teflon gasket was used

as the cell volume for the polymer solutions. The cell was filled through

two small openings (G) in the top steel plate. The neutron beam was transmitted through the quartz and reflected internally at the liquid interface with the reflected beam coming out through the quartz on the other side.

115
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figures 2 and 3 show neutron reflectivity profiles from all four

combinations of block copolymers used for the present experiments. In each case the reflection cell was allowed to adsorb the polymer for 1 hour before

taking reflectivity data. Each profile took 12 hours to complete and no time-dependent effects were seen. This was confirmed by rerunning the entire

profile in two cases and rerunning selected portions of the profile in the

other cases. For three of the copolymer solutions reruns were also done

starting with fresh cleaned cell and polymer solutions. No difference was noted between the two runs. The profiles shown in figures 2 and 3 are thus

reproducible.

The first thing to be noticed from figures 2 and 3 is that deuteration

of the PS block does not change the reflectivity profile in any significant

way. For example, profiles of hPS-hPMMA and dPS-hPMMA are similar in figure

2 and profiles of hPS-dPMMA and dPS-dPMMA are similar in figure 3.

Deuteration of PMMA block, however, changes the reflectivity profile

significantly at wavevectors higher than .02 A' as shown in figure 4 for

hPS-hPMMA and hPS-dPMMA.

Analysis of the data was done by only varying the concentration of PMMA

segments near the quartz surface assuming the concentration of PS to be zero. Many different scattering density profiles were tried in order to fit the

reflectivity data for all four samples simultaneously. The density profile

of PMMA that best seems to fit the data is as follows. According to this

profile, near the quartz surface the density is given by

^ = Vpmma " (1 ^s^^CCl^

with the volume fraction of PMMA, ^ = 0.42. The volume fraction of PMMA

then goes down in a parabolic manner with a functional form.

05 * (D^ - z2)/d2

with D = 45 A. This is equivalent to a collapsed PMMA film of -30 A

thickness. Similar fits to the data could be obtained with a PMMA film of

30 A thickness with a 15 A Gaussian smearing at the polymer solvent

interface.

116
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The thickness of 30 A means that quartz surface is covered by flattened

disks of PMMA blocks whose thickness is roughly equal to R dmma' ^^^ radius

of gyration of the PMMA block in CCl,. Thus the PS-PMMA copolymer adsorbs

rather strongly to the quartz surface by virtue of the affinity of PMMA block

to the quartz surface and the PS blocks extend from the PMMA blocks in a stretched configuration. This picture is similar to the one obtained by

Hadziioannou et al . [3] from their experiment of forces between surfaces of

PS-PV2P block copolymers adsorbed on mica. Hadziioannou et al ., however, had

to postulate the existence of a PV2P layer near the mica surface, whereas the

reflectivity measurements do indeed show that there is an initial compacted

layer of PMMA near the quartz surface.

In summary, we have shown that neutron reflectivity is a useful

technique for the study of polymer-solution interfacial density profiles. In

particular, the results of neutron reflectivity measurements, when combined

with other techniques such as force measurements, x-ray reflectivity, etc.,

should lead to a good understanding of this long standing problem.

Reflected neutron beam

Stainless

steel plate

Solution

chamber

Incident neutron beam

Filling port

-2

-4

1 1 1 1 1 1

%

:vX

'''^^v.'a, .«

1 1

•

1 1 1

•

1 Polished surface of

(|uartz crystal

(i 0.000 0.032 O.OO'I O(A')

09(>

Figure 1. (left) Schematic diagram of the solution scattering cell used in

these experiments. Details of the cell are discussed in the text.

Figure 2. (right) Neutron reflectivity profiles for P(S-b-MMA) [o] and P(dS-b-MMA) [o] copolymers dissolved in CCl^ at a concentration of

0.4g/100 cm-^.

117
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

0.000

"Is.V"^Vr. . .

_L

0.032 O.OGI Q(A-')

0.09(3 0.000 0.032 0.064 Q(A-')

0.096

Figure 3. (left) Neutron reflectivity profiles for P(S-b-MMA) [o] and

P(cl-S-b-d-MMA) [o] copolymers dissolved in CCl. at a concentration

Figure 4.

of 0.4g/100 cm"^.

(right) Comparison of the neutron reflectivity profiles obtained

for P(S-b-MMA) [o] and P(S-b-d-MMA) [o] where only the labeling of

the MMA block was varied and the concentrations of both copolymers

3

in solution is 0.4g/100 cm .

References

[1] Kawaguchi, M.; Takahashi, A. J. J. Polym. Sci. Polym. Phys. Ed 18,

2069 (1980).

[2] Klein, J. J. Chem. Soc, Faraday Trans. 79, 99 (1983)

[3] Hadziioannou, G.; Patel , S.; Granick S.; Tirrell, M.

108 , 2869 (1986).

J. Am. Chem. Soc.

[4] Bloch, J. M.; Sansone, M.; Rondelez, F.; Peiffer, B. G.; Pincus, P.; Kim

M. W.; Eisenberger, P. Phys. Rev. Lett 54, 1039 (1985).

[5] deGennes, P. G. Macromol . 14, 1637 (1981) and references therein.

[6] Milner, S. T.; Witten, T. A.; Cates, M. E. Macromol. 21, 2160 (1988).

[7] Kitchens, T. A.; Overshizen, T.; Passell, L.; Schermer, R. I. Phys. Rev.

Lett. 32, 791 (1974).

118
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SANS STUDIES OF BLENDS OF CROSSLINKED PSD WITH LINEAR PSH

R. M. Briber and B. J. Bauer

(Polymers Division)

Small angle neutron scattering (SANS) has been used to study the

scattering function and thermodynamics of blends of linear protonated

polystyrene (PSH) and crossl inked deuterated polystyrene (PSD). Two series

of samples were synthesized. In both cases the linear PSH was dissolved in

deuterated (dg) styrene monomer containing a small amount of di vinyl benzene

as a crossl inker. The styrene/di vinyl benzene mixture was then polymerized

using a free radical initiator to form the PSD network around the linear PSH

chains. The samples were all made at a concentration of 50/50 by weight

PSD/PSH. Series 1 is a set of samples with the same network (N = 387, where

N is the average number of monomer units between crosslinks) varying the

length of the linear chain (N^^ = 91, 308, 422, 981, 1711, and 3413, where N.

is the number of monomer units in the linear chain). Series 2 is a set of

samples containing the same length linear chain (N, = 422) varying the

network density systematically (N = oo, 960, 475, 345, 260, and 158).

In the series 1 samples as the length of the linear chain is increased

the SANS scattering increases as the sample approaches phase separation.

-1 2

The data were plotted in the form S(q) versus q which yields a linear

relation and allows extrapolation to q = and hence gives S(0). S(0) is

2 2 related to the second derivative of the free energy of the system, d Af/50 , which is composed of terms relating to the entropy and enthalpy of mixing of

the linear chains in the network and the elasticity of the network. For H/D

blends the enthalpy of mixing (i.e., the Flory-Huggins interaction parameter)

-4

is small (x -1.5 x 10 ). As the length of the linear chain increases the

entropy of mixing decreases until it can no longer balance the unfavorable

elastic contribution from the network and phase separation occurs. Indeed it was found that the sample with the longest linear -12chain length (N, = 3413)

has a negative intercept when plotted as S(q) versus q indicating that the

sample was phase separated.

In the series 2 samples the scattering increases as the network density

increases (N decreases). The elastic contribution to the free energy

increases as N decreases until it overwhelms the mixing -12 portion of the free

energy and phase separation occurs. Again a plot of S(q) versus q gave a straight line which allowed extrapolation to q = to obtain S(0). At the

119
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

highest crosslink density (N = 158) the intercept was negative indicating

that phase separation had occurred. Assuming additivity of the elastic and

mixing terms in the free energy, the second derivative of the elastic

contribution to the free energy can be calculated from S(0). The values of

2 2

d Af„T,./30 obtained for the series 2 samples are given in table 1. A

e I as 1 1 plot of S(0)" versus N

" should allow the extrapolation to the value of N

1 c c where S{0)' = corresponding the value of N where the system phase

separates. Such a plot is show in figure 1. The extrapolated value of N

where phase separation occurs is N = 160, agreeing closely with the value of

N = 158 for the sample which was found to be phase separated.

In conclusion, it has been found that linear chains can be incorporated

into networks formed by sequential polymerization of the network around the

linear component (i.e., single phase blend of linear and crossl inked

polymers) if the network density is kept low (N > 150). This result helps

to explain why similar systems studied in the past at higher crosslink

densities have almost always phase separated at some point during the

synthesis. SANS can be used as a tool to study the thermodynamics of these

systems and values for the elastic contribution to the free energy can be

calculated from the extrapolated zero angle scattering.

Table 1. Number of monomers between crosslinks, zero angle scattering,

2 2 correlation length, k /S(0) {= d A^to+a-i/^^ )' ^^^ the elastic

contribtion to the second derivative to the free energy

2 2 (3 (Af/kT)/30 elastic) for the series 2 samples.

Series 2 (N^^ = 422)

"c

S(0) cm"^ eA-i

eo 79.0 51.9

960 65.9 60.0

475 113 66.3

345 127 93.6

260 227 111

158t *** ***

k^/S(0) a^(Af/kT)/a0^ elastic

3 6 3 7 mole/cm molecule xlO mole/cm molecule xlO

5.2

4.3 4.4

3.6 - 61

3.2 -101

1.8 -243 *** ***

fThe sample with N = 158 was phase separated

120
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2 3 4 5

Figure 1. Plot of S(0)" versus N for the series 2 samples,

THE EFFECT OF RADIATION CROSSLINKING ON THE SCATTERING

FUNCTION IN WEAKLY INTERACTING MISCIBLE POLYMER BLENDS

R. M. Briber and B. J. Bauer

(Polymers Division)

Using small angle neutron scattering (SANS) the scattering function in

the single phase region of the phase diagram was measured for the weakly

interacting polymer blend system of protonated polystyrene (PSH) and

deuterated polystyrene (PSD) which had been crossl inked by gamma rays from a cobalt 60 source. A theory presented by de Gennes [1] for the critical

scattering from crossl inked blends and the effect of crossl inking on the

phase diagram had been tested previously using SANS with the strongly

interacting blend system poly(vinylmethylether)/PSD [2]. In the PVME/PSD

system the theory was found to describe the behavior of the observed

scattering function qualitatively (the scattering function for a crossl inked

* polymer blend develops a peak at a nonzero q vector, q ). The measured

behavior of q was found to agree with theory with q scaling with the

average radius of gyration between crosslinks. The divergence of the

scattering intensity at q , S(q ), was found to be mean field within

experimental error with S(q )' - (x_ - x)^ where 7 = 1.0 (x is the FloryHuggins interaction parameter and x^ is the value of x at the spinodal). The

121
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

* peak observed in the scattering function at q was not present at the

temperature of crossl inking but only became apparent upon raising the

temperature (changing x)

g

A blend of high molecular weight PSD and PSH (each with M = 10 ) was

60

crossl inked using gamma rays from a Co source. Samples with doses of

(control), 55, 125, and 200 MRad were prepared. The corresponding number of

monomers between crosslinks, N , calculated for these samples are «, 1800,

700, and 500, respectively. In the crossl inked PSH/PSD system the measured

scattering function was found to be essentially unchanged from the scattering

function measured for the uncrossl inked system (see fig. 1). The predictions

for the uncrossl inked and crossl inked system N = 700 is shown in figure 2.

Other values of N gave similar results. Clearly the data shown in figure 1 does not agree with the prediction from the theory as shown in figure 2.

There is no peak present as predicted by the theory, although there is a small decrease in S(0) after crossl inking. The same results were observed

initially with the PVME/PSD system though a peak did subsequently appear upon

changing the temperature (changing x)- In the PSD/PSH system there is almost

no temperature dependence of x* Combining these observations with the

results from the PVME/PSD system the conclusion can be drawn that the theory

does not predict the scattering observed after crossl inking if x remains

roughly constant but does predict the observed behavior qualitatively when x

is subsequently changed.

I

100

75

S

" 50

25

1 B-i O

1 —1 100

a

o

(? a UncroflaUnlced 75

*. CroaaUsked (No='700) 1

- i 50

1 ! 1 1

25

n

0.00 0.02 0.04 0.06 0.08 0.10

q A

-1

0.00 0.02 0.04 0.06 0.08 0.10

q A-'

Figure 1. (left) SANS scattering for the crossl inked PSD/PSH blends (circles:

125 MRad, N = 700, squares: MRad, N = «, (uncrossl inked))

.

Figure 2. (right) Calculated scattering curves for the samples shown in

figure 1.

122
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[1] de Gennes, P. G. J. Phys. (Les Ulis, Fr.) 40, L-49 (1979)

[2] Briber, R. M.; Bauer, B. J. Macromol . 21, 3296 (1988)

GRAFTED INTERPENETRATING POLYMER NETWORKS

B. J. Bauer and R. M. Briber

(Polymers Division)

Interpenetrating polymer networks (IPN) are two component polymeric

systems in which one polymer is swollen with monomer of a different type and

polymerization of the monomer forms the second polymer. One or both of the

polymers is crossl inked to itself, but crosslinks between the two different

polymers are not present. Previous work at NIST [1] has shown that IPNs

promote phase separation; i.e., mixtures of polymers that would form a single

phase blend can be made to phase separate in a crossl inked IPN. When

compatible blends are radiation crossl inked, forming crosslinks between the

two different polymers, the single phase region is greatly enhanced, and a peak appears in the scattering, indicating that microphase separation would

occur, forming domains of approximately 100 A [2].

We have explored an alternate method of introducing bonds between the

two polymers by use of macromonomers. Macromonomers are polymers with one

end containing a functionality such as a methacrylate group that can copolymerize with the monomer that forms the second polymer, thereby grafting

it to the crossl inked network. Figure 1 gives the scattering intensity from

standard semi -II IPNs of 13,000 dalton polystyrene and crossl inked

polystyrene-d with 0.2 and 0.5% divinylbenzene (DVB). As has been previously

seen, added DVB increases the scattering intensity, pushing it towards phase

separation. The three lower curves are for samples with 0.2, 0.5, and 1.0%

DVB for the system of grafted polystyrene. The symbol at q = is the

calculated intensity for a blend of equivalent molecular weight. While a standard IPN structure promotes phase separation, the grafted IPN inhibits

phase separation.

Figure 2 shows the results from a similar system except polymethylmethacrylate is grafted onto a network containing 0.5 and 1.0% DVB. In this

polymer combination there is a small positive interaction parameter which

123
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

promotes phase separation. Prominent peaks can be seen in both scattering

curves similar to the radiation crossl inked blends [2]. This type of grafted

IPN would microphase separate into a system of domains. Therefore, by

controlling the crossl inking reaction, the resulting morphology of

crossl inked polymers can be easily controlled.

12

48

40

32

ao 24

16

1 1 o

o

1 1 1 1 PSH/PMMA Semi-II IPN

o Ungrafted and Grafted

o D 0.2 % Ungrafted

o

o o 0.5 % Ungrafted

o

o A 0.2 % Grafted

o 0.5 % Grafted

1.0 % Grafted

1 1 1 1

10 -

e a

4

-

2

-

1 1 1 PMMA/PSD

r<X^ Grafted IPN.

O

r \

D \-

- u 0.0 % DVU

"

1 1

O 1.0 % DVB.

1 0.00 0.02 0.04 q(A"')

0.06 0.08 0.00 0.02 0.04 0.06 0.08

Figure 1. (left) SANS results for PSH/PSD grafted and ungrafted semi -II IPNs,

Figure 2. (right) SANS results for PMMA/PSD grafted semi -II IPNs.

References

[1] Bauer, B. J.; Briber, R. M.; Han, C. C. Macromol . 22, 940 (1989).

[2] Briber, R. M.; Bauer, B. J. Macromol. 21, 3296 (1988).

124
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MICROSTRUCTURE AND ISOTOPIC LABELING EFFECTS ON THE MISCIBILITY OF

POLYBUTADIENE BLENDS STUDIED BY THE SMALL ANGLE NEUTRON SCATTERING TECHNIQUE

S. Sakurai, H. Hasegawa, and T. Hashimoto

(Kyoto University, Kyoto, Japan)

I. G. Hargis and S. L. Aggarwal

(Gen Corp, Akron, OH)

and

C. C. Han

(Polymers Division)

Polybutadiene blends of various microstructures are widely used in the

rubber industry to tailor properties to applications. Such blends offer an ideal system to study the fundamentals of binary interaction parameters of

butadiene monomers with different microstructures.

Small angle neutron scattering (SANS) should be the tool to use to

study this microstructure effect. Unfortunately, the deuterium labeling of

one of the components which is needed for SANS introduces a repulsive

interaction [1] between the two components. This has prevented a straightforward measurement of the binary interaction parameter, x> between a 1,2-

unit and a 1,4-unit.

In this work, an attempt has been made to separate the isotope effect

from the microstructure effect through a systematic SANS study of blends of

deuterated polybutadiene (PBD) and protonated polybutadiene (PBH) with

various vinyl contents. Random copolymer theory was used to carry out this

separation.

All SANS data are analyzed with a nonlinear regression fitting routine

according to the random phase approxmation calculation of deGennes which can

be written as follows:

S(q) = K^/ 1 + 1 - 2^ (la)

^A<Vn V9d(^)a>w V^B>n ^B <%^^h\ %

with S(q)rvp = S(q) + baseline. (lb)

125
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In figure 1, typical SANS data from a miscible blend, in this case the

VBRD6/VBRH6 (deuterated polybutzdiene with 63% 1,2-content and M = 134 K,

M /M = 2.0, hydrogenated polybutadiene with 68% 1,2-content and M„ = 135 K, w n n MP/M = 1.8) with volume fraction of ^ugnnc = 0.278 and at room temperature,

is displayed together with the best fitted line according to eq (1). A

normalized deviation plot is also displayed in the lower half of figure 1.

The static structure factors for VBRD6/VBRH6 with ^ugnng = 0.375 at various

temperatures are shown in figure 2. It is clear from figure 2 that S(q)

decreases with increasing temperature. This implies the existence of an UCST

below room temperature. SANS results for various compositions of VBRD6/VBRH6

series and VBRD6/CisBR7k (deuterated polybutadiene as defined

above/hydrogenated polybutadiene with 7% 1,2-content and M = 6.9 K, M /M =

1.5) series at different temperature have also been analyzed. The

interaction parameter, x» zero wave number structure factor, S(q = 0) and the

correlation length, ^, have been extracted for all experimental conditions.

Since polymer/polymer blends can be described by the mean-field theory,

spinodal or the critical temperature can be obtained through the

-1 -2 -1 -2

extrapolation of x> S(q = o) or £ vs 1/T to x

= X^* S(o) ^ or ^ -^0,

respectively. Where x^ is the x at the spinodal temperature T . In figure

3, x» S(q = o)"-^ and C^ are plotted vs 1/T for the VBRD6/VBRH6

(^ygR^Qg

=

0.474) blend. T of -37.2 "C is obtained consistently from the

extrapolations of all three sets of results. A similar procedure has been

carried out for all data sets of both the VBRD6/VBRH6 and the VBRD6/CisBR7k

series of blends.

Besides the isotope effect which could cause incompatibility [1], the

microstructure effect has to be properly accounted for in order to understand

the phase behavior of rubber/rubber blends. If we define deuterated 1,2-

butadiene, deuterated 1,4-butadiene, protonated 1,2-butadiene and protonated

1,4-butadiene monomers as A, B, C, and D, respectively, then for a blend of

A-B copolymer with C-D copolymer, the free energy of mixing can be written

as:

126
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A£ = (0i/Nj)«n 0j + (02/N2)«n (f>^ + 0^02 ^biend ^2)

RT

""'^^ ^blend = ^y % ' ^1-^)^ % ^ ^(1-y) ^,AD

+ (1-x) (1-y) XgD - x{l-x) x^B " ^(1"^) X qd (^)

where x is the number fraction of A in A-B copolymer and y is the number

fraction of C in C-D copolymer, x and y refer to the number fraction of

repeat units in the lattice theory of blends. We equated number fractions to

volume fraction for this work.

By neglecting the difference between trans and cis-1,4 polybutadiene

and assuming polybutadiene is a simple random copolymer, we should be able to

obtain all six x-pai^aiieters if we have six sets of data for blends with

different microstructure variations. We do not have six sets of data.

Nonetheless, using the data from Bates et al . [1] and making a few

assumptions about the interaction parameters, we shall demonstrate a scheme

of separating various interaction parameters.

First, let us assume Xap = Xgn = Xo- This assumption implies identical

isotope effect between 1,2-pairs and between 1,4-pairs of different isotopes.

Without knowledge of the exact intermolecular potential energy function

between two isotopically labeled microstructure pairs the severity of this

assumption cannot be assessed. Once we have made the above assumption, we

can then assume Xad = Xrn = Xi and XAn = Xgr = Xp- These two assumptions

imply that pure microstructure effect (interaction between either protonated

or deuterated 1,2- and 1,4-butadiene pairs) is independent of the isotope

used and consequently that the cross (isotope labeled) microstructure effect

is independent of which one of the two monomers is labeled. Actually, these

two assumptions are implied from the previous assumption that identical

isotope effects prevail between 1,2-pairs and 1,4-pairs.

We are now in a position to calculate the three interaction parameters

Xj, X2» and Xo for three sets of PBD/PBH blends. As noted before, we have

two sets of X data from this study, and we will also employ the literature

127
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

value of Bates et al . [1], which was reported for a PBD/PBH system with 11%

of 1,2-unit for both components and with ^pnrj = 0.31.

Thus, three simultaneous equations can be obtained from equation 3 as

X (VBRD6/VBRH6) = - 0.451Xj + 0.454x2 "^ ^'^^% (^a)

X (VBRD6/CisBR7k) = - 0.307Xj + O.6IOX2 + O.39OX3 (4b)

X (Bates et al.) = - 0.196xj + 0.196x2 "^ 0-804x3 ^^^^

Values of Xp Xn' ^^^ ^3 obtained are displayed in figure 4 as a

function of 1/T.

In figure 5, x values obtained from SANS measurements of a separate set

of blends, H-19/H-16 (H-19 with Mn = 71 k and 28% of 1,2-unit; H-16 with Mn =

281 k and 40% of 1,2-units are displayed as a function of 1/T, together with

the predicted values (solid line) which were calculated according to equation

3 and Xi» X2' and X3 values obtained before. Although the predicted numbers

are slightly lower than the experimental values, considering the assumptions

and errors involved in the calculation, in this analysis, in sample

preparation, and in SANS experiments, this agreement may be considered to be

excellent.

We should point out that the main contribution for miscibility in a blend of a A-B copolymer with a C-D copolymer is due to the interaction

between the intramolecular pairs of A/B and C/D which has a negative

coefficient as indicated in equation 3. Actually, in order to maximize this

negative contribution (in magnitude) to the total interaction, Xu-igpfj*

copolymers of equal constituents (x. = Xg = 0.5, Yr = yn = 0-5) should be

used. If we examine figure 3 again with these intramolecular interactions in

mind, then it becomes clear why negative x's have been obtained for

deuterated polybutadiene/protonated polybutadiene blends, which lack any

specific attractive interaction.

128
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

VBRD6/VBRH6 (tvbrd*" 0.278) Blends at Room Ttmp.

X

M

•S

0.12

"3

as

o

4

3

•

2

1

•

I I I I I I

0.00

-aQ».

e o

e a "r-%»—5—

o

0.02 0.04 0.06. O.OB 0.10 0.12

RJLS. Residuals = 5.716Z-02

Figure 1. Normalized SANS intensity S(q) of VBRD6/VBRH6 with volume fraction

^VBRD6

^ 0-278 at room temperature is displayed in logarithmic

scale as a function of scattering vector q together with the best

fitted line according to eq (1). Normalized deviation is plotted

in the lower half of the graph.

129
Figure 2,

Figure 3,

REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

VBRD6/VBRH6 Blends (*>VBRDa=0-375)

150

120 -

1 (D) 23.0'C

2(o) 60.0*C

3(4) 90.0 *C

* (») 120. 'C 5(a) 150.°C

6(0) 180. 'C

u

SANS data from the VBRD6/VBRH6 series with <l>y^^QQ = 0.375 at

various temperatures (shown in the graph) is plotted as S{q) vs.

q. Data are shifted along the 45 " line for clarity.

VBRU6/VBRH6 (y^^BRD6=0.474)

o

il zr

c

X

0.003 0.004 0.005

1

0.006

SANS results of x[o], S(q = 0) ^ [A] and £ ""[n] from non-linear

regression analysis for the VBRD6/VBRH6 (^wDonc = 0.474) are plotted against 1/T. A dotted-and-broken (-•-) horizontal line

displays x^ value for this system. Linear extrapolation are performed simultaneously for all three plots to obtain the

spinodal temperature, T

= -37.2 "C.

s' The scales

in a consistent manner. In this case labeled on the ordinate is for y

values. The scales for S{q = 0)' is from 0.0 to 0.006 with

interval of 0.001 and for ^ is from 0.0 to 0.00024 with interval

of 4x10"^ A"^.

130
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

H-19/H-16 (vapB^O.-'S?) 10 VDPB = 0.3

9 ^^^.--^

8 ^^-^"^^^^

•)o

*

7

6

5

^^

-**

-*- ^ - " "

^2

4

•

3

2

-

1 ^3

1 1 ' 1 1 1 2.0 2*-l 3^-^-1

T

* • 10^ (K ^)

3.2

Figure 4. (left) Xj, Xg and X3 presented as a function of 1/T.

Figure 5. (right) Measured x values [0] for series H-19/H-16 (PBD/PBH) at

volume fraction of 0.757 of H-19 (PBD) is plotted against I/T

together with the predicted x values in solid line which was calculated by using eq (4) and the Xj, Xg and X3 values from

table 3.

Reference

[1] Bates, F. S.; Dierker, S. B.; Wignall, G. D. Macromol . 19, 1938 (1986).

131
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SHEAR EFFECTS ON THE PHASE SEPARATION BEHAVIOR OF A POLYMER BLEND

IN SOLUTION BY SMALL ANGLE NEUTRON SCATTERING

A. I. Nakatani, H. Kim, and C. C. Han

(Polymers Division)

and

Y. Takahashi

(Nagoya University, Japan)

The effect of shear on the phase separation of polymer blends has been

examined extensively [1-5] and is of dual importance for polymer mixtures.

First, a basic understanding of the behavior of polymer blends is required

for optimization of process parameters. Second, the study of the phase

behavior of quiescent polymer blends has been of paramount importance in the

development and testing of theories of critical phenomena. Experimental

studies have primarily utilized light scattering techniques to examine the

size and shape of concentration fluctuations of the order of 1000 A. Further

studies using shorter wavelength radiation such as neutrons to understand the

influence of flow fields on smaller critical fluctuations as the system

approaches instability from the one-phase state have not been performed. In this communication we report preliminary results on the small angle neutron

scattering (SANS) behavior of a solution of two homopolymers under shear.

Observations were made at various combinations of temperature and shear rate

for two samples representing compositions close to and far from the critical

composition.

For miscible polymer blends, the structure factor, S(q), can be analyzed

according to the random phase approximation calculated by deGennes [6]. For

small q (q = (47r/X)sin(^/2)) , the structure factor is identical to the

Ornstein-Zernike form of a Lorentzian function as follows:

S(q) = [S(q = 0)/(l + eV)] . (1)

The concentration correlation length is given by the variable, ^. The

correlation length is related to the spi nodal temperature by the following

relation:

£ « (I/T3P - 1/T)-^ (2)

132
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

where u is predicted to be 1/2 for a mean field system and 2/3 for an Ising

system. Therefore by fitting the structure factor to equation 1, the

correlation length, C, and S(q = 0) can be obtained. By plotting £ versus

the reciprocal of the temperature, the spinodal temperature may also be

estimated for a mean field system.

The system chosen for study in these experiments was a solution of

linear polystyrene-dg (PSD) and linear polybutadiene (PB) in dioctyl

phthalate (DOP). Two different PSD samples were used: 1) M = 27,000, M /M

= 1.06, and 2) M^ = 85,000, M^M^ = 1.02. The polybutadiene sample had a M^

of 24,000, with M^M^ = 1.07.

Two different samples were prepared. The first sample contained 8%

total polymer by weight with a composition of 35% of the 85,000 molecular

weight PSD and 65% of th PB in DOP (sample designation = 088535). The second

solution contained 12% total polymer by weight and had a composition of 50%

of the 27,000 molecular weight PSD and 50% of the PB (sample designation = 122750). The first sample has a composition close to the critical

composition while the second sample is off-critical. Total polymer

concentration was selected to give transitions from the two phase to one phase region around 40 "C.

A couette-geometry shear cell was designed and constructed to fit within

the constraints of the SANS instrument at the NIST reactor. The geometry of

the cell is similar to that described by Lindner and Oberthur [7]. An

incident wavelength of 9 A was used and sector averages of the data parallel

(horizontal) and perpendicular (vertical) to the flow directions were obtained in 10° arcs. Both 088535 and 122750 were tested at and 600 s"-^ between 30 and

60 °C. Both solutions exhibit UCST behavior and optical cloud points of the

solutions were 40.6 °C for 088535 and 34.8 "C for 122750.

For both samples at s" , the scattering intensity increased as temperature decreased in the one-phase region. In the two-phase region, the

scattering intensity then decreased with decreasing temperature as expected

for a phase separated system. The maximum scattering intensity was observed

at between the horizontal and vertical sector averages. An example of the

temperature dependence of the scattering intensity at zero shear in the

horizontal direction is shown in figure 1 for 088535.

133
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

T = 31 "C, 3 T = 33 'C, s" T = 35 °C. a" T = 37 "C. s" T = 39 "C, s" T = 41 "C. a' T = 43 'C, s~ T = 45 °C, a' T = 50 °C, a' T = 60 'C. s'

000 015 0.030 0.045 0.060

Figure 1. S(q) versus q at s" as a function of temperature for 088535.

Curves represent nonlinear regression fits to data. Data points

are the horizontal sector averages.

The temperature dependence of the scattering at 600 s' for 088535 in

the direction parallel to the flow is shown in figure 2. As observed in the

static case, the scattering intensity increased as temperature decreased in

the one-phase region and continues to increase in the two-phase region.

Similar behavior is observed in the direction perpendicular to the flow.

The increase in S(q) with shear at temperatures which are below the

static cloud point is taken to be evidence for the disruption of large

droplets due to shear. This effect will cause increased scattering intensity

in the wavelength range of our SANS experiments due to smaller droplet

structures and increased sample transmission.

Correlation lengths were obtained by fitting the experimental SANS data

_2

to eq (1) using a nonlinear regression routine. For points of ^ versus

_2

1/T, extrapolation to ^ =0 was performed using a linear regression routine

utilizing the points in the one-phase region only (43 to 60 'C for 088535).

Examples of these plots for 088535 are shown in figures 3 and 4. The extrapolated spinodal temperatures in the sheared and unsheared case for the

134
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

T = 31 "C. 600 s T = 33 °C, 600 s T = 35 °C, 600 s T = 37 °C, 600 s T = 39 "C, 600 s T = 41 °C. 600 s T = 43 °C, 600 s T = 45 °C, cOO s T = 50 "C, 600 s T = 60 "C, 600 s

0.000 0.01 s 0.030 0.045 q(A-')

Figure 2. S(q) versus q at 600 s' as a function of temperature for 088535.

Curves represent nonlinear regression fits to the data. Data

points are the horizontal sector averages.

IB.O

16.0

M.O ^ 12.0

(VJ

Ii 100 o

X 6

0.02 90

a - 088535. s , Verlicsl

A - 086535, 600 3~

' . Vertical

3 00 3 10 3 20 3.30 1/T XIO^ (K"')

IB.O

16.0

M.O 0BB53S, 9, Horizontal 0BB53S. 600 9~

' . Ilorizonta

1/T xlO-' (K'')

-2

Figure 3. (left) C versus temperature at and 600 s perpendicular (vertical) to the flow. Solid

_2

linear regression fits extrapolated to ^ =0.

1 in the direction

lines represent

Figure 4, (right)

parallel

-2 -1 ^ versus temperature at and 600 s in the

(horizontal) to the flow

direction

Solid lines represent linear

regression fits extrapolated to £' = 0.

135
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

horizontal and vertical sector averages are given in table 1. For both

samples, the spinodal temperature determined from the vertical and horizontal

sector averages at rest and the spinodal temperature in the direction

perpendicular to the flow direction are equal within experimental error. The

spinodal temperature determined from the horizontal sector averages during

shear are much lower. At this time, we do not have enough data to determine

the shear rate dependence of the spinodal temperature. However, the limited

existing data seem to indicate that the magnitude of the depression of the

spinodal temperature increases with increasing shear rate. Additional

experiments are being planned to confirm this effect.

The above observations are qualitatively consistent with the notion of

shear stabilization and decoupling of the flow field to its orthogonal

directions proposed by Onuki [8-10]. As the shear field is applied to the

system, very large concentration fluctuations are suppressed in the one-phase

region along the shear direction causing a decrease in the scattering

intensity as well as the correlation length. This effect is more pronounced

as the system is brought closer to the phase boundary; consequently, the

Table 1. Spinodal temperatures

Condition T ( °C)

088535, s'-^, Vertical 36.2

088535, s"-^. Horizontal 35.9

088535, 600 s'^ Vertical 36.6

088535, 600 s"^ Horizontal 23.4

122750, s'-^, Vertical 39.2

122750, Os '^ Horizontal 37.5

122750, 600 s'-^, Vertical 35.2

122750, 600 s"-^. Horizontal 13.3

phase transition temperature is depressed by the shear field. The question

of whether the concentration fluctuations in a shear field will still follow

the conventional scattering of eq (2) has yet to be determined. In the

analysis of this work, we have assumed the system follows mean-field behavior

although both samples are in the semi-dilute regime. While the mean-field

136
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

assumption is not quantitatively justified, the qualitative features of the

phenomena and conclusions we present here will not change.

References

[1] Hashimoto, T.; Takebe, T; Suehiro, S. J. Chem. Phys. 88, 5874 (1988).

[2] Takebe, T.; Hashimoto, T. Polym. Commun. 29, 227 (1988).

[3] Lyngaae-Jorgensen, J.; Sondergaard, K. Polym. Eng. Sci. 27, 344 (1987).

[4] Wolf, B. A. Macromol. 17, 615 (1984).

[5] Rangel-Nafaile, C; Metzner, A. B.; Wissbrun, K. F. Macromol. 17, 1187

(1984).

[6] deGennes, P. G. Scaling concepts in polymer physics. Cornell University

Press, Ithaca, New York (1979).

[7] Lindner, P.; Oberthur, R. C. Revue Appl . Phys. 19, 759 (1984).

[8] Onuki, A. Physica 140A, 204 (1986).

[9] Onuki, A. Phys. Rev. AM, 3528 (1986).

[10] Onuki, A. Phys. Rev. A35, 5149 (1987).

CONCENTRATION FLUCTUATIONS IN MIXTURES OF LINEAR AND STAR SHAPED POLYMERS

T. P. Russell

(IBM, San Jose, CA)

L. J. Fetters

(Exxon Research and Engineering Co., Annandale, NJ)

and

J. C. Clark, B. J. Bauer, and C. C. Han

(Polymers Division)

Mixtures of linear polyvinylmethylether (PVME) with four armed star

polystyrene (PS) were studied to evaluate the effect of chain topology on the

critical fluctuations in homogeneous polymer mixtures. It was found that the

cloud-point curve of the PS/PVME mixtures was elevated by about 10 °C over

that of the corresponding linear mixtures. The use of deuterated PS (PSD)

elevated the cloud point about 10 "C beyond that of hydrogen containing PS

(PSH). SANS studies of blends of PSH and PSD stars were used to measure the

137
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

single chain structure factor of the stars, and were found to be in excellent

agreement with the theories of Benoit [1] and Burchard [2]. This structure

factor was then used to analyze the concentration fluctuations of PSD/PVME

blends over a range of compositions and temperatures.

The inverse of the zero-angle scattering vector, S(0)' , extrapolated

linearly with inverse temperature to yield the spinodal temperature, T . The correlation length, ^, was found to depend upon [{T - T )/T ] where

A S S u = 0.5. C was also linearly dependent on inverse temperature yielding

values of T in close agreement with the S(0)" results. |o, the bare

correlation length, was found to depend upon composition in a manner similar

to a previous study. The Flory-Huggins interaction parameter was also

measured and found to vary linearly with inverse temperature and to be a function of concentration.

References

[1] Benoit, H. J. Polym. Sci'. 11, 561 (1953).

[2] Burchard, W. Macromol . 10, 919 (1977).

CHAIN CONFORMATION OF A BLOCK POLYMER IN A NICROPHASE-SEPARATED STRUCTURE

Y. Matsushita, K. Mori, Y. Mogi, R. Saguchi, I. Noda, and M. Nagasawa

(Nagoya University, Nagoya, Japan)

T. Chang and C. C. Han

(Polymers Division)

and

C. J. Glinka

It is important to study the single-chain conformation of polymers in

order to understand their physical properties at the molecular level. In

dilute solutions it is well established that the chain conformation is

Gaussian in G-solvents; i. e., v = 0.5 in the molecular weight dependence of

2 2 2i/ mean square radius of gyration, <s >; that is, <s > « M , while it is non- Gaussian; i. e., i/~ 0.6 in good solvents [1]. In condensed polymer systems,

such as concentrated solutions and melts, it was found by small angle neutron

scattering (SANS) that the chain conformation is Gaussian as predicted by

Flory [1,2,11]. In microphase-separated structures, where the block polymers

138
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

are confined anisotropically, however, their conformations should be

distorted, as suggested by the molecular weight dependence of domain spacing,

D; i.e., D « M ^ [3-5]. Therefore, it will be very interesting to study the

conformation of a block polymer chain not merely because it could lead to the

understanding of the microphase-separated structure at the molecular level

but because it could clarify the difference between conformations of polymer

chains in free space and in anisotropic domains.

Typical microdomain structures of block copolymers are lamellar,

cylindrical, and spherical structures of which the first one is the most

suitable microdomain for the study of a single-chain conformation because

this structure can be assumed to be in an equilibrium state but not the other

two structures [5,6]. If the lamellar structure is oriented along the

direction parallel to the surface of a film specimen, moreover, we can measure dimensions of a polymer chain along the orthogonal axes as we will

mention later. Two experimental works have been published so far on conformations of block polymers in lamellar structures using styrene-isoprene

block copolymers [7,8]. They reported that the dimension of a block polymer

extends along the direction perpendicular to the lamellae, while it shrinks

along the direction parallel to the lamellae. The extension of a block

polymer along the perpendicular direction can be understood by the theories

of Meier and Helfand for microphase-separated structures [3,4]. However, the reason for the shrinkage of block polymer along the parallel direction

remains unknown. As usually carried out in the study of chain conformation

in dilute solutions, the molecular weight dependence of polymer dimensions in

microphase-separated structures should be studied in order to have a definite

and quantitative conclusion on this problem. In this work, therefore, we prepared diblock copolymers of deuterated styrene-2-vinylpyridine with

different molecular weights and studied molecular weight dependences of radii

of gyration of the polystyrene block along the orthogonal axes in lamellar

structures by SANS. These samples are considered particularly suitable for

the SANS study, because the scattering length of poly(2-vinylpyridine) is

between those of labeled and unlabeled polystyrenes. Therefore, we could

make a contrast matching between two domains to extract a single chain

scattering if the labeled and unlabeled polystyrene blocks would be randomly

mixed. Moreover, it is noted that the statistical segment lengths of both

block polymers are almost the same.

139
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

As reported in a previous paper [9], a contrast matching between two

domains is required to extract a single-chain scattering of a block polymer

along the perpendicular direction, though it is not required along the

parallel direction since the lamellae are predominantly oriented along the

direction parallel to a film surface. However, we could not achieve a contrast matching except for a low molecular weight sample. Hence, we measured the radius of gyration along the perpendicular direction only for

the low molecular weight sample and assumed that the radii of gyration along

the perpendicular direction for the higher molecular weight samples are proportional to thier domain spacings determined by small angle x-ray

scattering (SAXS) [10].

Since the lamellae are predominantly oriented along the direction

parallel to the film surface, only single chain scattering was observed at

the through view, while the strong diffractions from the lamellae were observed together with a single chain scattering at the edge view.

Therefore, the contrast matching is necessary to extract the single chain

scattering at the edge view. Figure 1 shows the single chain scattering of a typical sample pair at the through view after the incoherent scattering

intensity was subtracted. The corresponding Guinier plot is displayed in

figure 2. For other sample pairs similar figures are obtained. Radii of

gyration for different molecular weight pairs in the X and Z directions

(parallel to the lamella surface) have been evaluated from these Guinier

plots.

As mentioned before, we could achieve a contrast matching only for the

low molecular weight sample pair, (II), therefore, this is the only sample

pair with radii of gyration measured in all three X, Y (perpendicular to

lamella surface) and Z directions.

Figure 3 shows molecular weight dependences of radii of gyration of

block polymer along x-axis, that is, along the direction perpendicular to

lamellae. Here, we assumed that the radius of gyration along y-axis

increases with increasing molecular weight according to the same power law as the molecular weight dependence of the domain spacing, D

D = 0.332 M^^-^"^ (A). (1)

140
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

From figure 3, we have the molecular weight dependences of radii of

gyration of a block polymer along x-, y- and z- axis as

f^g.x = Rg,z = 0-289 M°-^3 (A). (2)

Rg^y = 0.0453 M ^-^^(A). (3)

On the other hand, since deuterium-labeled polystyrene chains in bulk were determined to have the conformation of the ideal chain as [11]

Rg Q

= 0.275 M°-^ (A). (4a)

so that we can obtain the following relationship between unperturbed

dimension along an axis, R .p., and the molecular weight using the condition

2 2 9 > "^^ "g.O = ^''g.kO

•

I'g.kO = 0-159 m'^^- (lb)

This relationship is also shown in figure 3. Comparing equations 2, 3 and

4b, we find that the shrinking ratio along the direction parallel to lamellae

is lower than the extending ratio along the direction perpendicular to the

lamellae.

If we assume that the shapes of deformed polymer chain in lamellar

structures and undeformed polymer chain in melts are an ellipsoid of

revolution and a sphere, respectively, and their radii are proportional to

the corresponding radii of gyration, the volumes of the ellipsoid of

revolution V^ and the sphere V can be written as:

e '^ s

VeMW3)Rg^,Rg^/g^, = 0.16Ml-5 (5)

V3 « (47r/3)Rg

i^Q^ = 0.017 M^'^ (6)

141
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The comparison between eqs (5) and (6) reveals that not only the

molecular weight dependences but also the pre-factors of the volumes occupied

by a single chain are almost the same in melts and in lamellar structures.

That is, there is no change in the volume occupied by a block polymer; i.e, no change of degree of coil -overlapping, when a block polymer is brought into

lamellar structures. This implies that block polymers shrink along the

direction parallel to the lamellae to preserve the same intermolecular

interactions in lamellar structures as in disordered states.

0.00 0.05 O.IO q (1/A)

0.15 q^ * 10^ (1/A^)

Figure 1. (left) Typical plots of coherent scattering intensity versus the

magnitude of the scattering vector for a blend of labeled and

unlabeled block copolymers with a highly oriented lamellar

structure at the through-view. Intensities were obtained by a circular average of the two-dimensional data. Sample; DP-33/SP33, mixing ratio; 12/88 by weight.

Figure 2. (right) Guinier plot of the data in figure 2. Dotted vertical

line indicates the limit of Guinier's region described in the

text.

142
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

LOG M

Figure 3. Double logarithmic plots of the radii of gyration along x-axis (0)

and y-axis (0) against the molecular weight of labeled polystyrenes in block copolymers. The solid, chain and dotted lines

denote eqs (3), (4), and (4b), respectively.

References:

[1] Flory, P. J. Principle of polymer chemistry. Cornell University Press,

Ithaca, NY (1953).

[2] Higgins, J. S.; Stein, R. S. J. of Appl . Cryst. 11, 346 (1978).

[3] Meier, D. J. J. Polym. Sci., Part C, 26, 81 (1969). Meier, D. J.

Block and graft copolymers. J. J. Burke and V. Weiss, eds. Syracus

University, NY (1973).

[4] Helfand, E.; Wasserman, Z. R. Macromol . 9, 879 (1976).

[5] Hashimoto, T.; Shibayama, J.; Kawai, H. Macromol. 13, 1237 (1980).

[6] Hashimoto, T.; Fujimura, M.; Kawai, H. Macromol. 13, 116 (1980).

[7] Hadziioannou, G.; Picot, C; Skoulios, A.; lonescu, M.-L.; Mathis, A.;

Duplessix, R.; Gallot, Y.; Lingelser, J. -P. Macromol. 15, 263 (1982).

[8] Hasegawa, H.; Hashimoto, T.; Kawai, H.; Lodge, T. P.;

Glinka, C. J.; Han, C. C. Macromol. 18, 67 (1985).

[9] Matsushita, Y.; Nakao, Y.; Saguchi, R.; Mori, K.; Choshi.

Y.; Noda, I.; Nagasawa, M.; Chang, T.; Glinka, C,

Macromol. 21, 1802 (1988).

[10] Matsushita, Y. (to be published).

Amis, E. J,

H.; Murogoa,

J.; Han, C. C.

[11] Cotton, J. P.; Decker, D.; Benoit, H.; Farnoux, B.; Higgins, J.;

Jannink, G.; Ober, R.; Picot, C; des Cloizeaux, J. Macromol. 6, 863

(1974).

143
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SANS STUDY OF ORDER AND DISORDER IN A MODEL DIBLOCK COPOLYMER

F. S. Bates, J. H. Rosedale, and G. H. Fredrickson

(AT&T Bell Laboratories, Murray Hill, NJ)

and

C. J. Glinka

A partially deuterated poly(ethylenepropylene)-poly(ethylethylene) (PEPPEE) diblock copolymer containing 55% by volume PEP was studied by small

angle neutron scattering (SANS). Two series of measurements were conducted,

separately addressing the disordered and ordered states of this material. As

described in a recent publication [1], the order-disorder transition (also

referred to as the microphase-separation transition (MST)) for this diblock

copolymer occurs at T»oj =125+1 °C

The first set of SANS experiments on this sample was designed to examine

the significance of fluctuations above T»^-r. Recent theory [2] predicts non- mean-field behavior for disordered block copolymers well above the MST. By

precisely measuring the SANS peak intensity between 126 and 181 °C, we were

able to conclusively demonstrate that fluctuation effects play a dominant

role in determining the location of the MST. In addition, these measurements

provide the first quantitative test of the fluctuation-induced first-order

transition theory of Braovskii [3], which finds application in various areas of physics.

The second set of SANS measurements addressed the ordered state. For

the nearly symmetric composition characterizing our sample, a lamellar phase

is anticipated [2] at temperatures below T»^j. However, simply cooling the

sample produces a macroscopically isotropic (i.e., "powdered") material, and

accordingly a Debye-Scherer scattering pattern. We have found that shearing

this material on a dynamic mechanical spectrometer produces dramatic changes

in the rheological properties which we attributed to the development of long

range order, i.e., orientation. In order to test this hypothesis, specimens were sheared, and subsequently studied on the SANS instrument. As illustrated in figure 1, this shearing in fact results in the spectacular

alignment of lamellae, which is preserved over long times at room temperature

(fig. lA). As this sample is heated towards T»^-j- the initial anisotropy

begins to decrease (fig. IB) due to the influence of the fluctuations already

demonstrated to be significant above T^^-r [1] (see above). The residual

144
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

anisotropy evident at 123 °C (fig. IC) clearly disappears with heating

through Tj^^^ to 127 °C (fig. ID).

Through these SANS studies we are developing a qualitatively new understanding of the behavior of block copolymers near the order-disorder

transition.

-^/^'^^Sj^^^^fe^^^-^-^rK^i^^&IS*^:^

Figure 1. Relative SANS intensity {all scaled to equal magnitude) recorded

on a two-dimensional detector for a shear-oriented PEP-PEE diblock

copolymer: A) as prepared, 22 °C heating to B) 99 °C, C) 123 °C,

and D) 127 °C. The loss of anisotropy between 123 and 127 °C

results from passing through the microphase separation transition.

References

[1] Bates, F. S.; Rosedale, J. H.; Fredrickson, G. H.; Glinka, C. J. Phys.

Rev. Lett. 61, 2229 (1988).

[2] Fredrickson, G. H.; Helfand, E. J. Chem. Phys. 8Z, 697 (1987).

[3] Brazovskii, S. A. Sov. Phys. JETP 41, 85 (1975).

145
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MOLECULAR STRUCTURE OF BIMODAL POLYMER NETVORK

W.-L. Wu and L. D. Coyne

(Polymers Division)

and

L. Jong, A. Hanyu, and R. S. Stein

(University of Massachusetts, Amherst, MA)

Model polymer networks have been prepared by reacting polymer chains

exclusively at their ends. The chain length distribution of the resultant

network is thus identical to that before crossl inking. It was observed that

for polydimethylsiloxane (PDMS) the networks prepared with a bimodal

molecular weight distribution exhibited some unique features compared to the

unimodal networks [1]. The most noticeable difference is the ultimate

strength before break; the bimodal networks are much stronger or tougher than

the unimodal ones. Progress has been made toward the understanding of the

molecular origins of this difference in network properties. Stress-strain,

stress-birefringence and stress-temperature measurements were conducted to

elucidate the cause of this unusual feature in bimodal networks [2].

However, experiments which can provide a direct characterization of the

molecular structure in these networks have not been carried out.

In this report, a set of preliminary results from small angle neutron

scattering (SANS) of bimodal polytetrahydrofuran (PTHF) network will be

presented. The question to be addressed is whether the short and the long

chains are deposited randomly in the bimodal network. A random disposition

of the long and the short chains within an average network is the obvious

choice, and is also assumed in all the previous work, at least implicitly.

However, in an early work with an epoxide-amine reaction as the crossl inking

mechanism, SANS results indicated that the short and the long chains were segregated [3]. The definition of segregation needs to be clarified; it does

not necessarily imply the existence of long-chain and short-chain domain

structure as for the cases of segregated block copolymer. Such segregation

will be called as phase segregation. The other segregation to be emphasized

in this work is defined as follows: the makeup of the chemical neighbors of

a short chain (or a long one) is not statistically random. In an early work,

the chemical neighbors of a short chain were found to be a long one and vice versa [3]. Such segregation will be called the molecular segregation. The

146
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

linear chain analog of a molecular segregated network is a block copolymer;

the short chain (S) and long chain (L) after crossl inking forms (S-L) or other block-like structures with certain regularity.

For all the SANS specimens, every short chain is deuterated while the

long one is hydrogenated. The synthesis of the di functional PTHF with narrow

molecular weight distribution was carried out according to the method of

Smith and Hubin. The GPC results of the prepolymers used in this work is

given in table 1; two pairs of prepolymers were used and they were denoted by

the subscripts 1 and 2, respectively. The polydispersity of these

prepolymers is in the range of 1.1 to 1.3. The details of the synthesis can

be found elsewhere [4].

Pentaerithritol tetrakis (3-mercaptopropionate) was used as the

crossl inking agent and a stoichiometric amount of it was used for all the

samples. The reaction was initiated with benzopinacole which was stable at

ambient temperature, by heating to 80 °C or above this compound would be

activated to start the crosslink process. Two sets of samples were prepared

using prepolymer pair 1; one contained 0.19% wt. initiator and the other with

0.16% wt. For both sets of the samples the molar ratio of the long to short

chain was kept at 1.1. The third set of samples was prepared with prepolymer

pair 2 with a molar ratio of long to short chain at 3:7. The initiator

concentration used was 0.6% wt. The specifications of the samples are given

in table 2.

For each of the three sets of samples, SANS measurements were conducted

on the uncured, the completely cured and a few intermediately cured samples.

The SANS facility at the NIST reactor was used. The sample temperature was

kept at 50 °C, a few degrees above the melting point of PTHF, throughout the

SANS measurements. The wavelength of the incident neutrons was set at 12 A

and the q range covered was from 0.005 to 0.08 A' . After subtracting the

incoherent component and the empty cell background, the scattered neutron

intensity was reduced to its absolute scale with a silica gel sample as a secondary scattering standard.

The SANS results of sample set A are given in figure 1. For the uncured

sample (curve a), the I(q -+ 0) is estimated to be 0.7 cm" which is very

close to the theoretical value of 0.74 for the prepolymer pair assuming an ideal mixing. This result strongly suggests that the mixing of the long and

the short chains in the uncured state approaches that of an ideal solution.

147
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

If cure or crosslink does not induce either molecular or phase

segregation between the hydrogenated long chains and the deuterated short

chains, the scattering intensity will stay unchanged. However, as illustrated in curve b, a dramatic increase in intensity occurred in the

small q range. This provides an unequivocal evidence for segregation.

However, from curve b alone one can not yet determine that the type of

segregation is of the phase type or the molecular one. As cure proceeds to its completion, the scattering intensity, especially

in the low q region, exhibits a remarkable decrease. In addition, a weak

maximum appeared around q of 0.04 A" in the scattering intensity for the

cured sample (curves c and d).

This trend was also observed in sample sets B and C. The weak maximum

resembles that observed for regular block copolymer. The intensity at the

maximum is only a few times greater than that of the uncured sample. This

tends to suggest that the segregation is of the molecular type instead of the

phase type.

At the present time we cannot rationalize all the findings and more work

is apparently needed. Nevertheless, the SANS results covered in this note

strongly suggests that crosslink can induce segregation in bimodal network.

This result is consistent with the early finding of the epoxy-amine system.

In light of this new discovery, some of the earlier observations made on bimodal network needs to be re-examined.

Table 1. Molecular weight of PTHF prepolymers

Mn

Lj 8286

Sj 995

L2 10034

So 1018

Table 2. Speci fications of SANS sampl es Initiator Molar Ratio

Desiqnat ion Preoolvmers Concentration "/i wt. L:S

A 4' h0.19 1:1

B Lj, Sj 0.14 1:1

C Lg, Sg 0.6 3:7

148
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

3.2

2.4

1.6

0.8

'^ 0.0

-0.8

1.6

a A

ax °B

- \. '^ 1 \ ^°

n«5%5%aiPlJnm^^

- a

0.00 0.02 0.04 0.06

Figure 1. SANS results of PTHF at different levels of Crosslinking--

A, uncrosslink; B, C, intermediate; D, completely crossl inked.

References

[1] Mark, J. E. Advances in Polym. Sci. 44, 1 (1982).

[2] Mark, J. E.; Andrady, A. L. Rubber Chem. Teh. 54, 366 (1981).

[3] Wu, W.; Bauer, B. J. Macromol . 19(6) 1613 (1986).

[4] Jong, L. Doctor Dissertation, University of Massachusetts (1989).

149
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SHALL ANGLE NEUTRON SCATTERING STUDIES ON CHAIN ASYMIETRY

OF COEXTRUDED POLY(VINYLALCOHOL) FILM

M. Shibayama, H. Kurokawa, and S. Nomura

(Kyoto Institute of Technology, Kyoto, Japan)

S. Roy

(Polaroid Corporation, Norwood, MA)

R. S. Stein

(University of Massachusetts, Amherst, MA)

and

W.-L. Wu

(Polymers Division)

Poly(vinylalcohol) (PVA) is a crystalline polymer for which the local

conformation is not well understood. Fringed-micelle type structure has been

accepted for a long time for PVA film prepared from aqueous solution. On the

other hand, folded chain crystals are observed if it is solidified from an organic solvent [1]. It is natural to expect that intra- and inter-chain

hydrogen bonding play an important role in local chain organization. On

deformation, these hydrogen bonds may work as crossl inking points or entanglements. Since PVA is a polymer widely used in industry [2]; e.g.,

fibers, staples, asbestos alternatives, sheet, high oxygen barrier film, and

so on, it is worthwhile to explore chain asymmetry of deformed PVA fibers

and/or films.

In this work, we examine the radii of gyration of solid state co- extruded PVA film cast from aqueous solution in both the extension and the

perpendicular directions by small angle neutron scattering. Deutereous and

hydrogenous poly(vinylalcohol)s were supplied by Kuraray Co., Ltd. Those are coded as d-PVA and h-PVA followed by the viscosity-average degree of

polymerization, respectively. A 50/50 (by weight) mixture of d-PVA and h-PVA

powder was dissolved in boiling distilled water. The solution of ~ 10 wt.%

was stirred for a few hours at 90 °C then cooled gradually to room temperature. Films of the PVA mixture were prepared by solution casting onto

a glass plate at 60 °C. The thickness of the films was around several

hundred microns.

The films were coextruded with a polyoxymethylene billet at 165-170 'C

at a crosshead speed of 1 mm/s. The extension draw ratio (EDR) was varied by

150
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

changing aspect ratio of the conical die. Coextrusion with EDR larger than 5 was difficult because of the extruded film becoming inhomogeneous.

The SANS results can be summarized as follows: the statistical segment

length for PVA is found to be 5.76 A. Chain asymmetry of solid-state

coextruded PVA was examined by both small -angle neutron scattering and

birefringence measurements. It was found that PVA chains were affinely

deformed for extension up to EDR = ~ 5. Birefringence measurements also show

the affine nature of the deformation of PVA chains. Birefringence

measurements show that PVA is more effectively deformed than polystyrene,

which is explained by a positive effect of hydrogen bonding on extension.

References

[1] Tuboi, K.; Mochizuki, T. Kobunshi Kagaku 23, 636 (1966); 24, 433

(1967).

[2] For example, Sakurada, I. Polyvinyl alcohol fibers. Marcel Dekker,

NY (1985).

IN-SITU NEUTRON DIFFRACTION ON DEUTERIUM LOADED PALLADIUM

IN AN ELECTROCHEMICAL CELL

S. K. Satija, D. A. Neumann, C. F. Majkrzak, and J. J. Rush

D. Lashmore and C. Johnson

(Metallurgy Division)

and

R. M. Lindstrom

(Inorganic Analytical Research Division)

The phase diagram of the palladium/hydrogen system is well known. At room temperature and low concentration of hydrogen (or deuterium) the system

exists in the a-phase with a lattice constant very similar to that of pure

palladium. At higher concentrations of H(D) there exists a $ phase with a considerably expanded lattice where the H(D) atoms are located in the

octahedral interstitial sites [1].

We report here in-situ neutron diffraction measurements on palladium in an electrochemical cell. This was done in order to investigate whether

tetrahedral interstitial sites could be filled with D by the electrolysis

process. The electrolysis cell was made out of thin walled teflon sheet.

151
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The electrolyte used was 0.1 M LiOH in DpO (99.5%). The palladium electrode

was in the form of a sheet .4 mm thick. The other electrode was a thin sheet

of platinum. During the diffraction data collection the cell was rotated by

180° in order to average out the effect of any preferred orientation of

crystallites in the original palladium sample.

Figure 1 shows the neutron diffraction pattern (taken with 1.53 A

neutrons) from Pd before electrolysis. All the Pd peaks are labeled in the

figure. The other peaks are from the teflon cell. The Pd peak intensities

(after correction for the Lorentz factors) are in good agreement with what is

expected from pure FCC palladium. The palladium was first loaded with D by

applying a current of 1 A for 12 h before taking the diffraction data. The same current of 1 A was kept on while collecting the diffraction data. The

lower part of figure 1 shows the diffraction pattern from D loaded Pd under

the conditions described above. All of the peaks shift to lower angles due

to expansion of the lattice. The even hkl peaks increased in intensity and

all the odd hkl peaks decreased in intensity. For clarity, two of the

diffraction peaks (311) and (222) before and after electrolysis are shown in

figure 2.

The lattice constant of the cell after electrolysis was found to be

4.035 A. This is similar to what is reported for ;3-phase Pd-D(H) in the

literature [1]. Our attempts to fit the data to a ^-phase Pd-D cell, in

which D atoms are located in octahedral sites, resulted in an octahedral site

occupancy of only 0.32 as opposed to the known value of -0.7. The results of

such a fit are shown in table 1. The rms displacement of D atoms was found

to be 0.21 A in wery good agreement with earlier results [1]. Any attempts

to fit the data by partially or fully filling the tetrahedral sites was unsuccessful

An occupancy factor of only 0.32 for D loaded sample points to the fact

that there is a considerable amount of H along with D in the electrolysed

palladium. Assuming a filling factor of 0.7 for octahedral sites, one can calculate the amount of H present in the D loaded Pd sample. This turns out

to be H(0.35) and D(0.65). Even though the electrolytes used contained at

most 1-1.5% H, the final loaded Pd contains nearly 35% H. Higher solubility

of H (as compared to D) in Pd under electrolysis is quite well known [2].

However the separation factor

S„,etal/l1q'("/'"metal/("/°>liq = 35

152
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

that we obtain seems to be much higher than the highest values reported in

literature (of the order of 10-13). A neutron activation analysis of the

electrolysed Pd sample also confirmed our estimate of about 30% H in the

sample.

Table 1. Measured and calculated ratios of the integrated intensities of the

observed peaks after the sample was loaded to those of the pristine

sample. The calculated values were obtained using an octahedral

site occupancy of 0.32 D/Pd and an rms displacement of 0.21 A for

the octahedral atoms

Peak Measured Ratio Calculated Ratio

(111) 0.40 ± 0.03 0.48

(200) 1.68 + 0.08 1.67

(220) 1.49 ± 0.07 1.52

(311) 0.47 + 0.03 0.64

(222) 1.14 ± 0.17 1.41

(400) 1.44 ± 0.12 1.33

(331) 0.51 ± 0.07 0.76

(420) 1.11 ± 0.08 1.26

The electrolysis of Pd in nearly 99% deuterated electrolysis solution

leads to substantial amounts of H isotope being incorporated in the Pd

sample. No evidence for incorporation of D (or H) into the tetrahedral sites

was seen. It seems, therefore, that in the recent experiments on cold fusion

done by many groups a large amount of H along with D was present in the Pd

electrodes.

153
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

60-

SO

80

601-

: V

2

= 40

20-

(111)

T 1 1 1 1 r

Pd

(200)

(220)

(311)

1 1 1 r

(200) Pd with D(H)

(111)

'•'V'

(220)

C

(311)

>. (228)

0L_

35 55 75 95 29 (deg) US 135

T r 1 r

• Pd

» Pd yrith D(H)

?^^'

80 84

Ze (deg) 92

Figure 1. (left) In-situ neutron diffraction patterns of Pd before and

after electrolysis. The neutron wavelength used was 1.53 A. Both

Pd and Pd D(H) peaks are marked in the figure. The other peaks

are from the teflon cell.

Figure 2. (right) A selected section of in-situ neutron diffraction pattern

of Pd before and after electrolysis. The lines are fit to the

data with gaussian line shapes.

References

[1] Worsham, J. E.; Wilkinson, M. K.; Shull, C. G. J. Phys. Chem. Solids 3,

303 (1957).

[2] See e.g., Lewis, F. A. The Palladium-Hydrogen System, Academic Press

(1967).

154
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COMMENTS ON COLD FUSION IN METALS

R. C. Casella

I spent some time thinking about (and discussing with other NIST

scientists [1]) possible low-temperature fusion of deuterons in Pd and Ti

metals [2]. Two qualitative conclusions were drawn, (i) The idea that a condensed-matter quasiparticle of large effective mass m* in metallic Pd or

Ti could play a role analogous to that of the muon in the known muon-induced

fusion process by drawing the deuterons very close together in a solid (a

theoretical motivation discussed by Jones et al . [2]) is incorrect. The

concept of effective mass applies when reckoning the response of a quasiparticle in a solid to potentials which vary slowly over distances of the

order of a lattice constant--not rapidly on the scale of tenths of angstroms.

For example, one uses the free-electron mass to compute the core levels of

heavy atoms in the solid state, not the effective mass of some band-like or quasi-localized electron contributing to the conduction process, (ii) A

three-body DDPd process (suggested by M. Danos [3]) involving a recoiling Pd

nucleus, which allows direct production of a fast-moving (23 MeV) a particle

in its internal ground state, should lead to the production of host-metal x- rays by the heavily ionizing a's as they are stopped in the solid. (The

Danos mechanism proceeds by exchange of off-shell 7's and yields no final

state proton, neutron or on-shell 7, unlike the two-body DD fusion process.)

The x-rays produced by the stopping a's ought to be observed in experiments

originally designed to look for host-metal x-rays generated by the stopping

protons, which are produced with branching ratio ~ 50% in two-body DD fusion.

To my knowledge, such x-rays have not been detected. The absence of a signal

in the charged modes, coupled with the serious background problems associated

with the minuscule neutron counting rates [2] implies that considerable

effort will be required to place reliable quantitative bounds on (or to

detect) cold fusion in metals, including the three-body amplitude in

question.

References

[1] Berger, M.; Berk, N.; Danos, M.; Fleming, R.; Gilliam, D.; Lamaze, G.;

Lashmore, D.; Lindstrom, R.; Majkrzak, C; Neumann, D.; O'Connell, J.;

Rush, J.; Satija, S.; Schrack, R.; Stone, C; Wasson, 0. private

communications (unpublished).

155
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

[2] Jones, S.; Palmer, E.; Czirr, J.; Decker, D.; Jensen, G.; Thorne, J.;

Taylor, S.; Rafelski, J. Nature 338, 737 (1989).

[3] Danos, M. Post -deadline paper presented at the spring meeting of the

American Physical Society, Baltimore, MD (1989) and private

communication.

CAVITY GROVfTH RATES IN FATIGUED COPPER

J. G. Barker and J. R. Weertman

(Northwestern University, Evanston, IL)

Materials stressed at high temperatures, (0.4 - 0.7) T , fail by the

nucleation, growth, and coalascence of grain boundary cavities. Diffusional

growth of cavities in materials under static stress has been adequately

described [1], but predicts no net growth under fully reversed fatigue

conditions. By including a second order stress dependence of grain boundary

diffusivity, a small net growth rate is expected [2], but in practice, the

cavity growth rate under fatigue matches or exceeds that under creep

conditions. Other mechanisms involving plastic strain or gas stabilization

have also been proposed [3-5].

The present study separates the stress and plastic strain effects by

measuring cavity growth as a function of fatigue frequency. A weighted

3 2 cavity size, R = <R >/<R >, is measured by combining precision density

measurements to determine cavity volume fraction, V , with SANS measurements

in the Porod region to determine cavity surface area, S . A characteristic

3 cavity volume is defined as: Vp = 4/37rR ; R = 3V /S ; a characteristic

cavity number as: N = ^w/^nVp and N will give estimates of cavity growth and nucleation,

respectively. The cavity volume, V , measures a weighted cavity growth; due

to the distribution of cavity sizes, N is also affected. The true cavity

size and number are measured only with a monodisperse size distribution.

The 99.999% pure copper samples were tested at 405 "C temperature and

-5

34.4 MPa stress amplitude. The cavity volume fraction varied from 10 x 10

-5 -1

to 600 X 10 and the cavity surface area varied from 8 to 250 cm . A

series of samples were tested at 17 Hz frequency with varied number of

cycles. The cavity growth rate was found to be constant, dV /dt = -23 3-1 " 7.5 X 10 m s (see fig. la). The nucleation appears to be mostly

completed within the first 10% of sample life, (N^ = 810,000). Snowden [6]

156
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

et al . also claim nucleation is completed within 20% of fatigue life, but

during creep nucleation has been found to be continuous.

Another series of samples were tested with fixed number of cycles,

(100,000), but with the frequency varied from 2 to 100 Hz. The growth rate was found to increase with increased frequency. Weertman's theory predicts

growth should be independent of fatigue frequency. Since the plastic strain

amplitude is constant over this frequency range, the growth rate should be

linear with respect to frequency if plastic strain was controlling the growth

process. The total number of cavities also increases with increased

frequency (see fig. 2b).

In summary, by combining RDM and SANS measurements, a characteristic

cavity size and number can be estimated. Measurements completed on fatigued

copper samples indicate:

Most cavities are nucleated early in sample life.

The cavity growth rate is constant at fixed frequency.

Growth rate increases with increased frequency.

Number of cavities increases with increased frequency.

100 200

cycles (10x3)

!,l I i"

I

cycles (10x3)

Figure 1. All samples in the figure were tested at 17 Hz, 405

MPa. Left

C, and 34.4

figure plots cavity volume V as a function of number

of fatigue samples. Right figure plots number of cavities Np as a function of number of cycles. Points denoted as A and B

correspond to samples with a 200 micron grain size, explaining the

low Np values, all other samples have a 50 micron grain size.

157
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1S. i.s«

Puqnenc; (III) Frr«|iM*iit:y (11/.)

Figure 2. All samples in the figure were tested at 405 C, 34.4 MPa, and

100,000 cycles. Left figure plots cavity growth rate dV /dt, as a function of fatigue frequency. The right figure plot cavity

number versus fatigue frequency.

References

[11 Speight, M. V.; Beere, W. J. Met. Sci . 9, 190 (1975).

[2] Weertman, J. Met. Trans. 5, 1743 (1974).

[3] Skelton, R. P. Phil. Mag. 14, 563 (1966).

[4] Gittins, A. J. Met. Sci. 2, 51 (1968).

[5] Trinkaus, H. Scripta Met. 15, 825 (1981).

[6] Snowden, K. U.; Stathers, P. A.; Hughes, D. S. Res. Mechanica 1, 129

(1980).

TEXTURES OF SPECIALLY FABRICATED METALS

C. S. Choi

(ARDEC, Picatinny Arsenal, NJ and Reactor Radiation Division)

and

H. J. Prask

During the reporting period, the textures of three specially fabricated

metal samples were studied. They are a Ta sheet provided by the Naval

Surface Warfare Center, a hemispherical Ti shell fabricated at Los Alamos

National Laboratory, and DU tensile specimens with 7% and 20% tensile strains

158
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

provided by the Army Materials Technology Laboratory. The measurements of

the Ti and DU tensile samples will be continued in FY 90 with new samples.

Ta Sheet . The samples were prepared from a cylindrical ingot by

applying a series of thermomechanical treatments: upset forge, reforge to

original cylinder, rolling to a plate form, and annealing at high temperature. The sample used was a large triangular piece with edge lengths of

3 approximately 7.6 x 10.2 x 12.7 cm . Since the sample was much larger than

the neutron beam cross section, the exposure volume was limited by covering

the surface with a thin Cd sheet (0.25 mm thick), leaving a circular exposure

hole (12.7 mm diam) at the center of the sample. The texture was measured

over the partial orientation hemisphere ranging from x

= 90° to 20°, <f> = -180° to 180°, using the reflection method. The 110, 200, 211, and 222 pole

figures were measured. In this nondestructive method, the exposed volume

varies as a function of scattering angles and of x-angles. Therefore, the

data were normalized to the calculated exposure volume, then were converted

to the pole density in the units of multiples of a random distribution

(m.r.d.). Among the four pole figures, 220 and 222 are shown in figure 1.

The pole figures could be interpreted as having three preferential orientations, each with the slip plane (pole in the normal direction) of 111, 100,

and 113, respectively. The corresponding pole-density peak positions based

on the three-texture model are marked in the pole figures.

Ti Hemispherical Shell . The textures of two samples, labeled E and P,

which were cut from a quarter-sphere sample, were measured by neutron

diffraction. Sample E is approximately a rectangle cut from the equatorial

region, with approximate dimensions of 10 mm x 8 mm x 2 mm. Sample P is

approximately a rhombus cut from the pole region, with side edges approximately 8 mm long and the short diagonal, 7 mm long. The samples were mounted

on the goniometer of the x-circle cradle, with the sample rotation axis (0-

axis) perpendicular to the sample surface. Due to the scheduled shutdown of

the reactor, only three pole figures (100, 101, and 110) were measured from

sample P, and only two (100 and 101) from sample E. The diffraction

intensities were measured over an entire hemisphere using 1.275 A wavelength

neutrons. The observed intensities were converted to the pole density in

m.r.d. units, and are presented in equal -area type pole figures, using

established procedures. The 101 pole figures are shown in figure 2.

Comparing the pole figures of the two samples, some texture gradients are

159
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

evident in going from equator to pole of the hemispherical sample. At the

pole, a fiber-texture distribution is clear in all patterns, which in the

equator pole figures, becomes a sheet-texture type.

DU Tensile Samples . The textures of four uranium samples, labeled A,

WR, A2, and WR2, were measured by neutron diffraction methods. Sample A was prepared by annealing at a high temperature to reduce the texture. Sample WR

was prepared by a warm rolling of cast ingot. Sample A2 was prepared by

applying 7% tensile deformation to the annealed sample, and WR2 by applying

20% tensile strain to the warm-rolled sample. Each sample was cut into two

3 identical -sized pieces (1.9 x 1.9 x 0.25 cm ), which were stacked with the

rolling directions aligned in the same direction to make a square plate.

Four pole figures, 020, 111, 112 and 131, were measured using the normal

procedures, with 1.275 A wavelength neutrons. The absorption corrections

were calculated by assuming that the effect of the 0-angular orientation is

negligibly small. The observed pole figures of the WR2 sample are given in

figure 3. The 020 pole figure indicates clearly that the crystallites in the

warm-rolled tensile sample are highly oriented with the 010 poles concen- trated in the rolling direction, with the maximum pole densities of 11

m.r.d.. The pole figures of the WR samples are quite similar to those of

WR2, which indicates that the two samples have essentially an identical

texture. Since the 010 poles are concentrated in the rolling direction, the

preferential poles in the normal direction must consist of one or more of

hOl-type poles. An examination of the 111, 112, and 131 pole figures

suggested that the preferential pole in the normal direction is the 103 pole.

Based on the (103) [010] slip model, the peak positions in the four pole

figures were calculated and marked on the corresponding pole figures to

compare with the observed pole densities.

The four pole figures of the annealed blank showed no particular texture

except the several well-defined isolated peaks in the 020 pole figure, which

suggests the presence of several large grains in the annealed blank. The

annealed tensile sample with 7% strain (A2) showed very weak texture. The

general features of the pole figures showed some similarity with the

corresponding pole figure of WR or WR2 samples.

160
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

TA-5590 (220) TA-5590 (222)

Figure 1. The 220 and 222 pole figures of the Ta sheet. The center of the

pole figures correspond to the normal direction (x = 90°) and the

periphery to x = 20°. The calculated pole density peak positions

based on the three preferential slips were indicated with, squares

for 100 slip plane, triangles for the 111 slip plane and x's for

the 113 slip plane model. The contour levels of 1 m.r.d. or higher are given in steps of 0.5 m.r.d.

P-101 E-101

ZSTEP = 10

Figure 2. The 101 pole figures of the Ti samples S, P, and E. The center of

each pole figure corresponds to the normal direction to the sample

surface. The symbol LD in the pole figures of sample E indicates

the longitudinal direction of the sample hemisphere, and in sample

P it indicates the direction of the long diagonal of the rhombic

shape. The densities lower than random intensity are shown by

dotted contours, the lowest solid contour lines corresponding to

"random." The contour intervals, in 0.1 m.r.d. units, are shown

by the symbol ZSTEP in each pole figure.

161
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

WR 020

ZSTEP =5.0

WR2 111

ZSTEP =2.0

Figure 3. The 020 and 111 pole figures of the WR2 DU sample. The center of

the pole figure corresponds to the normal direction of the sample.

The calculated pole density peak positions based on a (103) [010]

slip model are indicated with shaded circles.

RESIDUAL STRESS MEASUREMENTS IN METALLURGICAL SAMPLES

H. Prask

and

C. Choi

(ARDEC, Picatinny Arsenal, NJ and Reactor Radiation Division)

Energy-dispersive neutron diffraction was used to nondestructively

determine subsurface residual stress distributions in three types of

technologically important samples: plastically deformed U-0.75 wt% Ti rods,

7075-T6 aluminum nose cones ("ogives") for 155 mm shells, and an inductionhardened steel axle--a test specimen for the Society of Automotive Engineers.

The first two represent new work in long-term programs which have been

reported on previously; the last is a new effort.

In the U-0.75 Ti project, samples with different types of plastic

deformation were provided to the Army by Battel le Pacifac Northwest Labs.

The residual stress distribution in these samples is of interest because of

their susceptibility to stress corrosion cracking and because of the effect

of stresses on yield strength. Of particular interest in this case is the

162
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

separation of pseudo macrostresses produced by plastic deformation (i.e.,

microstresses which cause changes in d-spacings like long-range stresses) and

the macrostresses of engineering interest. Initial measurements on small

specimens cut from the samples of interest suggest that direction-dependent,

measured effective do-spacings may provide a means for removing the pseudo

macrostress contribution from measured strains. This work is in progress.

Earlier residual stress measurements on two types of ogives suggested

that a cold-sizing operation in the fabrication of one type induced tensile

residual stresses which reduced the effective strength and led to documented

failures. In the present effort pre- and post-sizing samples of the failureprone type were examined by energy-dispersive neutron diffraction to

determine changes in the residual stress distributions. A beam spot of

3

4 X 4 X 4 mm was used to determine the stresses at four positions through

the 18.2 mm thickness in the region where the failures occur. The results

are summarized in the table 1.

Comparison of the hoop stress distributions for sized and unsized ogive

blanks shows that sizing significantly affects the stresses. In the axial

direction the final machining steps remove more than half of the starting

material in the region of interest, and could necessitate a major

redistribution of stresses to maintain balance over the equilibrium plane.

However, the a distribution in the non-removal region (ID to ID + 8.6 mm)

has the appearance of the finished ogive for both the sized and the unsized

blanks. This suggests that the steps which produce the significant

differences in the failing and nonfailing ogive axial stress distributions

occur before the cold sizing.

In this reporting period a feasibility study was made for the SAE

Fatigue Design and Evaluation (FD&E) Committee to determine the applicability

of the neutron diffraction technique to residual stress determination in a multiaxial fatigue lifetime prediction project. Specifically, the project is

part of an integrated engineering approach for design analysis and validation

of components for vehicles in which test spindles, shown in figure 1, will be

tested for fatigue life, characterized for materials properties--including

residual stress, and modeled by finite element techniques. Depth-profiling

of residual stresses had been done by x-ray diffraction with layer removal,

about which the FD&E Committee felt some uncertainty.

163
REACTOR RAPIATION PIVISION ANP COLLABORATIVE PROGRAMS

Table 1 Residual stresses from neutron diffraction measurements

Unsized Sized

0" 180" 0" 180°

OP - 2.25 mm^

^r -33(14)MPa 27(9)^ -70(14) -82(11)

""ee -21(26) 16(13) -178(27) -219(19)

^zz -104(16) -37(10) -85(15) -107(12)

OP - a

rr

6.75 mm

-34(11) -1(7) 9(10) 18(12)

°ee 54(22) 81(13) -38(21) -30(21)

^zz 36(14) 76(9) 23(13) 45(14)

OP - ^rr

11.25 mm

-25(13) -25(10) 49(10) -13(14)

""60 40(25) 138(19) -30(19) -126(27)

^zz 53(15) 90(12) 82(12) 5(16)

OP - ^r

15.75 mm

-23(12) -72(11) -1(10) -4(9)

^ee

-21(24) -2(22) -96(19) -81(17)

ff,. -50(14) -49(13) 30(11) 29(11)

Position of center of beam spot

'standard deviation due to counting statistics

Figure 1. Schematic of SAE fatigue test specimen and neutron beam spot.

The axle diameter at "P" is 40 mm.

164
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

For the initial neutron measurements, a simplified procedure was employed in which d-spacings were measured only for probe directions in the

r-B plane; i.e., with Q perpendicular to the cylinder axis. The beam-spot

employed was 1 mm x 1 mm x 12 mm in size, oriented such that the long

dimension was always parallel to the cylinder axis. Measurements were made

with the center of the 1 mm x 1 mm cross section at 1.3, 3.3, and 6.3 mm below the 40 mm diam surface, which allows a relatively quick determination

of

(^rr"*^^^^' ^^^ "°^ °^ ^^^ individual stress components. Several

measurements were made at each of three depths along single radii with the

center of the 12 mm length at positions "B" and "D" of figure 1, at which a finite element analysis (FEA) had been done.

From information provided and neglecting stress gradients in the axial

direction, an FEA-(a -a^^) can be determined and compared to the neutron

results (fig. 2). It is clear that the FEA-(a -aaa) changes much more sharply with depth than the measured values for both positions.

I uuu -

900 - \ ^

800 - \

as Q. 700 - \

s: 600 - \\

«& 600 - \\

b" 400 - V—3C S- 300 - \

^

300 -

100 -

- \ 10 DEPTH (mm)

Figure 2. Comparison of (o^y,^,-^^^^) at points B and D of figure 1, as measured

by neutron diffraction and as calculated; x = neutron, = FEA.

With regard to the x-ray results, a direct comparison cannot be made

since the x-ray measurements cannot determine a . However, it is worth

noting that both the x-ray and the neutron results are in reasonably good

agreement with the FEA calculations at a depth of ~3 mm, and in poor

165
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

agreement at ~6 mm. At ~1 mm the neutron results are in rather poor

agreement with the FEA, whereas the x-ray/FEA agreement is variable. The

FD&E Committee has requested continuation of the neutron measurements since a reliable determination of the triaxial stress distribution is not available

to them and is essential for further refinement of FEA models.

MICROSTRESSES IN CERAMIC COMPOSITES

H. Prask

C. Choi

(ARDEC, Picatinny Arsenal, NJ and Reactor Radiation Division)

E. Fuller and R. Krause

(Ceramics Division)

Micro residual stresses occurring between constituents of a composite,

e.g., between particles or fibers and matrix, are prime factors in

determining the physical and mechanical properties (e.g., fracture toughness)

of these materials. X-ray diffraction provides the best-established method

for determination of residual stresses and has been used for the study of

ceramic composites. In the x-ray case, however, surface macrostresses

contribute to peak shifts and complicate the analysis. Neutron diffraction

parallels x-ray diffraction for residual stress determination, but because

neutrons in the diffraction-wavelength regime penetrate, typically, three

orders of magnitude deeper than x-rays, either depth-profiling or total

sample averaging of stresses is possible. When a sample is totally immersed

in the neutron beam, the macrostress contribution to peak shifts averages to zero.

In the present measurements, AKO^ reinforced with 30 vol% SiC{whisker)

was studied. To elucidate the effect of whisker size and mean spacing on the

development of microstresses during processing, two different types of

whiskers were used: Tokai TWS 100 (-0.4 /Ltm diameter, -10 jLtm long) and Tokai

TWS 400 (-1.1 /zm diameter, -50 iim long). With each whisker type, processing

into the composite was the same: hot-pressing into a disk 5 cm in diameter

and 1,3 cm thick, at 42 MPa at 1700 °C for 30 min. The samples for neutron

study were cut from the center of the pressed disks and ground to cubes 1 cm

on a side.

166
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The diffraction pattern of the pure SiC whiskers indicates that it is in

the cubic form. In the composite, the most favorable SiC peak--based on intensity and overlap considerations--is the (311); AKO^ peaks with similar

d-spacings are the (300) and (125), of which the (300) is much more intense.

The unstressed d-spacings were taken to be the values for the initial

materials. Energy-dispersive neutron diffraction was used to determine the

average d-spacings of each sample, totally immersed in the beam, for eight

different orientations of each, from which strains were calculated using the

assumed unstressed d-spacings. Stresses were calculated from the strains in

the standard way, using an average of Reuss and Voigt diffraction elastic

constants for SiC(311) and the elastic isotropic values for Al202(300). The

results are shown in the table 1, in which a corresponds to the pressing

direction.

Table 1. Average microstresses in AI2O2/30 vol% SiC(wh.)

a

XX

a

yy

a

XX

"yy

"zz

TWS 100 TWS 400

373(4)*MPa

AI2O3

301(4) MPa

336(6) 310(5)

273(5)

SiC

202(6)

-1018(6) -1023(5)

-1055(9) -1013(6)

-990(7) -909(6)

*Standard deviations due to counting statistics only.

For both samples it is clear that the pressing direction is unique, with

significantly less average stress than is observed in the orthogonal

directions. As one would expect from the difference in thermal expansion

coefficients and as has been observed elsewhere, the whiskers are in a state

of high compression, the matrix in tension. Of particular interest is the

fact that the TWS 400 composite, on the average, shows lower stress

magnitudes than the TWS 100 material, which is possibly indicative of the

different mean-spacing between fibers in the two samples.

167
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MULTIPLE SMALL ANGLE NEUTRON SCATTERING CHARACTERIZATION

OF THE DENSIFICATION OF ALUMINA

G. G. Long

(Ceramics Division)

S. Krueger

(Polymers Division)

and

R. A. Page

(Southwest Research Institute, San Antonio, TX)

Over the past two decades, clear associations between microstructural

character and performance capabilities have been identified for a number of

ceramic systems. Progress toward achieving an improved process model and

improved process control will be achieved when a better understanding of the

relationships between processing variables and the resulting microstructure

is obtained. Toward this end, we have been investigating the microstructure

evolution as a function of thermal processing in well -characterized systems

with precisely defined chemistries.

Until now, it has been very difficult to perform quantitative

microstructure studies of ceramics in the early and intermediate stages of

sintering because the relevant size range (0.08-10 /xm) is beyond the

resolution of standard techniques, and the density is between 55% and 90% of

theoretical. The multiple scattering formalism developed by Berk and

Hardman-Rhyne at NIST successfully addresses these issues [1]. Their

formalism has been applied by us to the problem of microstructure evolution

during the sintering of pure alumina and has led to the first detection of

the transition from one sintering mechanism to another by small angle neutron

scattering.

The samples were made by conventional sintering of Baikowski alumina

2 powder (CR6, 6m /g) that had been slipcast to an average green density of 53%

theoretical density (TD). Samples were removed from the furnace at different

times during the sintering process to yield examples of material between 56.5

and 98.9% TD.

Using the multiple scattering analysis formalism, the radius of

curvature was determined as a function of neutron wavelength for each of

eight samples. Figure 1 shows the radii of curvature measured (symbols) and

the theoretical radii (solid lines). The densities measured volumetrically

168
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

and those determined by the neutron scattering are shown in the inset to the

figure.

20

18

15

14

12

10

%TD

^^?asu^?<i Zil A 55.5 D 57.0 O 79.1

85.4 O 90.8 89.0 Q 94.5 92.5 O 97.1 95.5

98.9 98.0

5 -

0.5 0.8 1.0 1.2 1.4 1.5

Neutron Wavelengtii, nm

Figure 1. Measured radii of curvature (symbols) and the theoretical radii

(solid lines) as a function of neutron wavelength. The inset

identifies the sample symbols by their measured densities and

shows the densities fitted by the theory, where different.

Figure 2 shows the effective average pore radius for the alumina samples

as a function of percent theoretical density determined from the multiple

scattering formalism (R i:/r(0)) and from the single particle Porod measurement

(R^^(<»)). The multiple scattering determinations, which are strongly

weighted to the larger volume particles [2] indicate that the average

effective pore radius for the distribution within the alumina decreases in

the intermediate sintering stage and increases sharply in the final stage.

The Porod determinations, which are made from the total surface scattering

area, indicate an average effective pore radius that is slowly increasing

during the intermediate stage of sintering and rapidly increasing during the

final stage. Both methods show a break between the intermediate stage

169
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

processes, in which the pores are believed to be open, and the final stage

processes, in which the pores become sealed off. The multiple scattering and

the Porod analyses are combined to model the total pore size distribution

during each step of thermal processing.

O.'l

0.2

0.1

1 O W..t(0)

K.b(oo)

Wl GO 70 80 90 100

Percent of'ilicorclicnl Dcnsily

Figure 2. Effective pore radius (in micrometers) as a function of percent TD

determined from the multiple scattering formalism (circles) and

from the Porod analysis (squares).

This work was supported in part (GGL) by the U.S. Army Research Office

under Grant No. 26123-MS.

References

[1] Berk, N. P.; Hardman-Rhyne, K. A. Analysis of SAS DATA dominated by

multiple scattering. J. Appl . Cryst. 21, 645-651 (1988).

[2] Long, G. G.; Krueger, S. Multiple small angle neutron scattering

characterization of the densification of ceramics: application to

microporous silica. J. Appl. Cryst. (to be published).

170
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SCATTERING AND ITS EFFECT ON REACTION RATES

IN NEUTRON ABSORPTION EXPERIMENTS

J. R. D. Copley

and

C. A. Stone

(Center for Analytical Chemistry)

In general there is a systematic error in the results of any inbeam

neutron absorption experiment because of scattering in the sample [1]. The

error is largest when scattering predominates over absorption, when the

transmission of the sample is small, and when the lateral dimensions of the

sample are large compared with its thickness. The ratio of the reaction rate

in the sample (R), to the rate calculated ignoring both scattering and selfshielding due to absorption (R), may be significantly less than or greater

than unity, depending on the scattering properties of the sample and its size

and shape.

These conclusions are derived from Monte Carlo calculations based on a very general expression for the rate of a neutron absorption reaction in a sample which scatters and absorbs neutrons. This expression is written as a sum over orders of scattering within the sample, as illustrated in figure 1,

and was obtained using the technique adopted by Sears [2] in his study of

multiple scattering effects in neutron scattering experiments. The first

term in the series, R , may be written as Re , where R is defined in figure 1 and c is the self-shielding factor appropriate to neutron absorption

experiments: for slab samples c = (1 - e"'^) / t, where the optical

thickness t is the product of the slab thickness t and the total macroscopic

cross section 2j. Each of the remaining terms R. (j > 1) may be similarly

written as R c., where c. is in general a {4j + 3)-dimensional integral whose

integrand is the product of j differential scattering cross sections (for the

j scattering events), an overall attenuation factor, and a factor which

expresses the departure of 2n from (1/v) dependence. Complete details are given in reference [1].

In figures 2 and 3 we present the results of calculations of the

correction factor C = R/R, performed for slab samples of thickness t and

lateral dimension ^, placed in a very narrow, monoenergetic, monodirectional

neutron beam. The assumed scattering cross section was both isotropic and

171
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

R = €) + €) -^ 4) +

^ +•••

Rf

R = Xi^ = ovsR

c= JR —

I

Figure 1. The reaction rate R in a macroscopic sample is written as a sum of

contributions from different orders of scattering. The first term,

R , represents neutrons which enter the sample and undergo the

Figure 2

Figure 3

absorption reaction of interest. Subsequent terms R. represent

neutrons which are scattered j times and then undergo the reaction

of interest. Attenuation of the beam, due to scattering and

absorption, is included. The quantity R is the reaction rate

calculated in the approximation that both scattering and

attenuation (by scattering and absorption) are ignored: is the mean incident neutron flux, V is the sample volume, and 2^ is the

macroscopic cross section for the reaction. The correction factor

C is simply (R/R).

a=1020_js.^=-=

1.5

l.Ol

0.5

O.OL

^

1

1

._l/4

. i/id" -

""**• — * —. .

1 Optical

2 thickness

3 4 T

1 2 Optical thickness r

(left) Correction factors C for slab samples with aspect ratio a = 4, for different values of the ratio Xc = ^s^^T' ^^^ points

represent the results of the Monte Carlo calculations whereas the

lines are guides to the eye.

(right) Correction factors C for purely scattering slab samples

with different aspect ratios a. The points represent the results

of the Monte Carlo calculations whereas the lines are guides to

the eye. The self-shielding factor c^ is also shown.

172
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

static ("elastic" in the language of the thermal neutron scattering

community), meaning that no change in neutron energy was permitted to occur within the sample. Figure 2 shows C as a function of t, for different

choices of the cross section ratio Xc = (2^/2j), 2^ being the total

macroscopic scattering cross section of the sample. The calculations are for

samples with H = 4t; i.e., samples with an aspect ratio a = i/t of 4. When

Xq = 0, the only contribution to C is the self-shielding term c , and the

specific reaction rate (R/V) drops with increasing sample thickness. On the

other hand (R/V) increases dramatically with increasing t in the limit that

Xr tends to unity. In this limit it is also wery sensitive to Xc at constant

T.

In figure 3 we show C as a function of r, in the limit that Xc tends to

unity, for various choices of a. When a is much less than unity, i.e., for

pencil -shaped samples, scattering mostly removes neutrons from the sample, so that C drops with increasing t. In the opposite limit, that of a slab with

infinite lateral dimensions, scattering increases the mean path length of

neutrons in the sample and therefore enhances (R/V).

We are presently investigating the dependence of specific reaction rate

on t, keeping i fixed, in order to decide whether or not experimental

measurements can be reliably extrapolated to zero thickness to correct for

the effects of scattering (and absorption). We are also developing methods

to calculate correction factors in samples of other shapes, such as disks and

spheres. Our recent results suggest that extrapolations to zero thickness

can be problematic, since C is a nonanalytic function of t.

In conclusion, we believe that changes in the mean distance travelled by

a neutron, due to scattering, rather than changes in the mean reaction cross

section, due to spectral moderation, are the principal cause of hitherto

unexplained variations in observed reaction rates in largely hydrogenous

samples.

References

[1] Copley, J. R. D.; Stone, C. A. Nucl . Instrum. Meth. A281 . 593 (1989).

[2] Sears, V. F. Adv. Phys. 24, 1 (1975).

173
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CHARACTERIZATION OF MOLECULAR NETWORK OF EPOXIES USING NEUTRON SCATTERING

W.-L. Wu

(Polymers Division)

Neutron scattering has been used extensively to study the chain

conformation of thermoplastics in bulk and in solution. The basic scheme

used is to blend deuterium labeled chains with the protonated chains. The

conformation of individual chains can be extracted from the scattering

results [1]. The first successful attempt to use neutron scattering to

investigate the network structure in thermosets was made by Wu and Bauer [2].

The basic approach of their work was to have all the monomer partially

deuterated. The material after cure or crosslink resembles, in a linear

chain analogue, a multiple block copolymer of (H - D)^, where H stands for

the protonated portion of the monomer or repeating unit and D stands for the

deuterated portion. The corresponding symbol for networks is therefore

^^(H - D)u"^ , where the branches on each side of the monomer denote the

multi -functionality nature of the junction point.

For a multi -block linear polymer in bulk, the scattering intensity has

been modeled using the results of the random phase approximation (RPA) [3].

For linear and flexible chains, only a modest amount of change in scattering

behavior is observed as the value of N increases from one to infinity. In

other words, the scattering behavior of a di -block copolymer is almost the same as that of a multi-block one. This is not a surprising result since the

position correlation between blocks of the same chain diminishes rapidly as the contour distance between these blocks increases. This is just the nature

of a flexible chain. However, for multi-block rigid rod molecules, the width

of the scattering peak gets narrower as the value of N increases, albeit the

application of RPA to an ensemble of rigid rod molecules is rather

questionable.

For thermosets, RPA calculations based on a simplified network model

have been carried out [2]. The result indicates that the peak width depends

strongly on the rigidity of the network. The early neutron scattering

results of partially deuterated diglycidyl ether of bisphenol A (DGEBA) cured

with Jeffamines can be fitted quantitatively with the RPA scheme. However,

the presence of amines tends to muddle the experimental results; in the

uncured mixtures the correlation hole peak from the partially deuterated

DGEBA almost disappears due to the presence of amines. They also make the

174
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

data interpretation more complicated; e.g., the H portion in the notation

(H - D)», for cured materials now denotes a combination of the amine and the

protonated portion of DGEBA. Although the fit between the calculation and

the neutron scattering results on Jeffamine/DGEBA is quite satisfactory [3],

the question concerning the sensitivity of neutron scattering for elucidating

the network structure still remains. In other words, if the starting

monomers give rise to a clear correlation hole peak in scattering intensity,

will crossl inking result in a significant change in this peak?

To answer this question, the following experiment was conducted. The

partially deuterated DGEBA (d-DGEBA) was cured without any amines. It is

well known that homopolymerization of DGEBA will occur at elevated

temperature especially in the presence of some catalysts [4]. Piperidine (5

pph) was added to d-DGEBA at room temperature and served as a catalyst. The

material was cured at 160 °C for 20 hours. Infrared results on the amplitude

of the epoxide band at 915 cm' indicated that the cure was almost complete.

Neutron scattering measurements were conducted using the BT-6 spectrometer. With the analyzer crystal in front of the detector, only the elastic

scattering component was recorded. The results for the monomer and the cured

sample are given in figure 1. The thickness for both samples was identical

(2 mm) and the beam apertures for these two measurements were also kept the

same. Consequently a direct comparison can be made between these two

scattering curves. The most striking feature observed for these scattering results is the

down shift of the peak position upon curing. This implies that the average

radius of gyration of the monomer increases upon crossl inking. This result

is rather surprising in light of our current understanding of rubber

elasticity theory which was developed for materials with large molecular

weight between crosslinks. In the present case, the length of the linkage

between crosslinks is rather short, in the range of - (10 - 20) A. The

increase in monomer size upon crossl inking might be interpreted as the

straightening effect of chain ends as they join at a crosslink point. This

phenomenon is similar to what occurs in star shape molecules; the radius of

gyration of an individual arm is larger than that of an equivalent free

chain. This effect can be rather pronounced in star molecules with a large

number of arms. In homopolymerized epoxy, the functionality of the junctions

175
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

can be rather high. Hence this chain end effect could play an important role

in the increase in the monomer size upon crossl inking.

DEUTERATED DGEBA NEUTRON DATA

CT 170

Figure 1

140

O 110-

^ 80

1 1 1 1 1 1

_ CROSSLINKED

%

^

"" ^

° -A "

n^ /* \o"! "l/^ t^

— 0^ ^ ^A, MONOMERS

r

0.0 0.4 0.8 1.2

Neutron scattering results of partially deuterated DGEBA monomer

and the crossl inked material.

The sharpening of the scattering peak is the other interesting feature

caused by crossl inking. The half widths of the peaks shown in figure 1 are 0.25 A" and 0.36 A' for the cured sample and monomer, respectively. In

addition, the ratios of the half-widths to the peak positions are 0.69 and

0.76 for the cured and the uncured materials, respectively. According to a calculation based on RPA, this ratio stays the same for linear chains of

different size. In other words this sharpening effect cannot be attributed

just to the increase in the radius of gyration of monomers. Therefore, this

sharpening of the scattering peak suggests that the crossl inking results in

additional changes which must be of an inter-monomer nature.

As demonstrated in the work by Wu and Bauer [3], for multi-block

copolymer in bulk the half-width of the scattering peak decreases as the

number of repeats N increase. This result has now been extended to

crossl inked polymers to accommodate the observation mentioned above.

In summary, the crossl inking process in thermosets results in pronounced

changes in the scattering behavior. These changes indicate 1) an increase in

the radius of gyration of the monomer upon crossl inking, 2) an enhancement of

the inter-monomer correlation.

176
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[1] For review article see: Wignall, G. D. Encyclopedia of polymer science

and engineering. Second ed. Wiley-Interscience (1985).

[2] Wu, W.; Bauer, B. J. Polym. Commun. 26, 39 (1985), Polym. 27, 169

(1986).

[3] Wu, W.; Bauer, B. J. Macromol . 19(6) , 1613 (1986).

[4] Riew, C. K.; Rowe, E. H.; Siebert, A. R. Advances in chemistry series

(ACS) No. 154, 326 (1976).

SHEARING APPARATUS FOR SANS: PRELIMINARY RESULTS

FROM SHEARED COLLOIDAL SUSPENSIONS

G. C. Straty and H. J. M. Hanley

(Thermophysics Division)

and

C. J. Glinka

The aooaratus . We have constructed and tested a couette-type concentric

cylinder apparatus to investigate liquids at equilibrium and under shear.

The apparatus is intended to be available to SANS users as a general purpose

tool. Design features include a) versatility and a rugged construction, b) a wide range of shear rates and operating temperatures, and c) fully automated

computer controlled and programmable functions.

An outline of the apparatus has been presented by Straty [1] and details

will be provided in a forthcoming publication. The cell is a stationary

cylindrical quartz glass stator surrounded by a rotating cylindrical quartz

glass rotor. The cell used for testing has a mean diameter of 56.5 mm with

an annular gap of 0.5 mm. Thermostating fluid is circulated within the

stator for temperature control. The nominal operating temperature range is

at present 245-373 K. The outer cylinder is driven by a dc brushless servo motor that is programmed to allow for any inputed combination of velocity,

acceleration, direction of motion, delay, or other operating parameters.

Test results: shear-induced changes in the microstructure of

polystyrene colloidal suspensions . An ongoing project at NIST is to try to

understand why liquids behave as they do. A key to this understanding is to

investigate the microstructure of liquids, particularly distortions in the

177
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

pair correlation function, or the structure factor, when the liquid is

perturbed away from equilibrium [2]. Colloidal suspensions are attractive

candidate systems for study because we have demonstrated the parallel between

suspensions and simple atomic liquids [3], and it is well known that the

structure factor of colloidal suspensions obtained by light, x-rays, or neutrons is relatively straightforward to interpret.

Solutions of 6% to 30% by weight 98 nm diam polystyrene suspensions in

deionized H^O and in H^O/D^O mixtures were prepared. The solutions were placed in the shearing cell and the neutron intensity-wave vector (Q) pattern

observed for the systems at rest and when subjected to a shear. A dramatic

difference in the intensity plots, and hence the structure factor, was evident. Typical results are shown in figure 1 for the 30% sample. The

initial lattice structure is very evident. It is surmised that the colloidal

crystal distorts under low shear allowing layers to slip relative to one another until, at sufficient shear, the slippage creates a liquid-like

structure factor. Whether the suspension is actually a liquid is an open

question. The temperature of the experiments was a nominal 22 K. One rpm is

equivalent to a shear rate of about 6 Hz. The distortion sequence is

reproducible and reversible.

178
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SHEAR INDUCED MELTING OF

POLYSTYRENE COLLOIDAL SUSPENSIONS

RPM 12 RPM

980A PARTICLES

30% VOLmiE IT.ACTICN

60 RPM 300 RPM

Figure 1. Change in the neutron scattered intensity pattern for a sheared colloidal suspension as a function of shear-rate.

Note the shear induced melting to a liquid structure.

References

[1] Straty, G. C. J. Res. Natl. Inst. Stand. Technol . 94, 259 (1989).

[2] Hanley, H. J. M. Lectures on thermodynamics and statistical mechanics,

A. E. Gonzales and C. Varea, eds. World Scientific Press, 109 p, (1988).

[3] Hanley, H. J. M.; Rainwater, J. C; Clark, N. A.; Anderson, B. J,

J. Chem. Phys. 79, 4448 (1983).

179
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

ANALYSIS OF SANS FROM CONTROLLED PORE GLASSES

N. F. Berk and C, J. Glinka

W. Haller

(Ceramic Division)

and

L. C. Sander

(Organic Analytical Research Division)

Small angle neutron scattering (SANS) measurements have been performed

on several samples of silica controlled pore glasses with pore sizes ranging

from roughly 70 to 300 A. The scattering intensity is strongly peaked at

small Q and shows approximate Porod law behavior at large Q. Contrast

variation measurements have shown that the pore space in these samples is

entirely interconnected and thus forms a bicontinuous microstructure. The

scattering data have been analyzed using the leveled wave method based on an early scheme for representing two-phase microstructures resulting from

spinodal decomposition. In this approach [11, interfaces are modeled by the

contours of a stochastic standing wave composed of plane wave components

propagating in random directions with random phases and having wave numbers

distributed according to a given probability density, P(k). We have

determined model P(k) functions by fitting the SANS data with the leveled

wave scattering function and then used these to construct leveled wave images

of the corresponding porous structures (fig. 1). The average pore sizes

obtained by measuring chord lengths in the computer models turn out to agree

with the values determined for these glasses by mercury porosimetry.

180
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1

Reference

Simulated "TEM" views of controlled pore glass structure as determined from analysis of SANS using the leveled wave model.

Each image corresponds to a particular porosity, <f>, and average

pore size, D, according to: a) = 68%, D = 255 A; b) = 66%,

D = 156 A; c) = 63%, D = 116 A; d) = 51%, D = 70 A. The four

views are shown on a constant length scale.

[1] Berk, N. F. Scattering properties of a model bicontinuous structure

with a well defined length scale. Phys. Rev. Lett. 58, 2718 (1987).

181
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PHYSICAL GELS OF AQUEOUS POLYVINYLALCOHOL SOLUTIONS

- A SMALL ANGLE NEUTRON SCATTERING STUDY

W.-L. Wu and L. D. Coyne

(Polymers Division)

M. Shibayama, H. Kurokawa, and S. Nomura

(Kyoto Institute of Technology, Kyoto, Japan)

S. Roy

(Polaroid Corporation, Norwood, MA)

and

R. S. Stein

(University of Massachusetts, Amherst, MA)

Physical gelation in various polymer solutions has been a subject of

interest to many researchers. Poly(vinylalcohol) (PVA) in water is one of

the physical gel systems studied rather extensively; after all, PVA fibers

have been produced commercially from aqueous PVA solutions for many years.

Compared to chemical gelation, the gelation process in physical gels has not

been widely studied by scattering techniques. This does not imply that other

transitions, e.g., liquid-liquid phase transitions in physical gels, have not

been studied using scattering techniques. For instance, the spinodal

transition in PVA-water has been determined via an elastic light scattering

technique.

For the sol -gel transition problem the change in the cluster size or molecular weight distribution during gelation is an essential parameter to

monitor. The sol -gel transition is defined as the point at which the average

cluster size goes to infinity. To measure the molecular weight or the

cluster size distribution with either chromatographic or scattering

techniques, the material must be diluted. However, dilution will cause

physical gels to be highly disturbed or even completely dissolved.

Consequently, scattering and other techniques in which dilution is a prerequisite are applicable only in studying the sol -gel transition in

chemical gels. However, as will be shown, it is possible to study certain

aspects of physical gelation without resorting to a dilution scheme.

SANS data were collected on PVA gels as they were heated through their

sol -gel transition temperature. The PVA solutions with concentration across

0*, the concentration threshold at which the polymer chains start to overlap, were investigated. Mass fractal dimension and correlation length were

182

i
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

extracted from the SANS data. Very little change in these two quantities

were observed for these solutions with their concentration greater than 0* as they went through a sol -gel transition.

For the solution at 0* concentration, a maximum was observed in both the

correlation length and the zero-angle scattering intensity as it went through

the transition temperature. The origin of this maximum is interpreted

successfully in terms of a two-phase weak aggregate model.

SMALL ANGLE NEUTRON SCATTERING FROM BACTERIAL MAGNETITE

S. Krueger, G. J. Olson, and J. J. Rhyne,

and

R. P. Blakemore, Y. A. Gorby, and N. Blakemore

(University of New Hampshire, Durham, NH)

Magnetotactic bacteria were discovered and described by Blakemore [1].

The bacterial cells accumulate iron intracellularly, to a significant

fraction of their dry weight (2-4%), in the form of membrane-bounded

magnetite (Fe-O.) crystals [2], termed magnetosomes. The magnetosomes in

Aquaspirillum magnetot act i cum, the most thoroughly studied magnetotactic

bacterium, are usually cuboidal to octahedral in shape, with a diameter of

400-500 A, and are arranged in a chain that longitudinally traverses the

cell [3]. An average of 20 single domain magnetic iron oxide particles form

the chain, which carries a net magnetic dipole moment equal to the vector sum of the individual particle moments and which is sufficient to orient the cell

in the geomagnetic field [4]. The feasibility of applying the small angle

neutron scattering (SANS) technique for studies of metal accumulation or deposition by living cells was explored using A. magnet ot act i cum as a model

system.

Aquaspirillum magnetotacticum strains MS-1 and MS-2 were grown at the

University of New Hampshire in continuous culture [2]. Iron was supplied as ferric quinate (FeQ). The total background iron content of the medium (no

FeQ added) was 0.35 /iM, which was the concentration at which "low iron" cells

of MS-1 were grown. "High iron" cells were grown in 40 /iM FeQ, and "normal

iron" cells in 20 /xM. Cells were shipped cold to MIST where they were stored

at 2 °C until analysis (within 2-3 days).

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The scattering from MS-1, grown under "normal iron" conditions, was measured in both 100% D^O and in 30% D^O buffers in an applied horizontal

magnetic field of 25 Gauss using a neutron wavelength, A, of 6 A with a wavelength spread AA/X = 0.25. The results, in the form of constant

intensity contour plots are presented in figure 1. In 100% D^O (fig. la),

the scattering from the bacterium itself is large compared to that from the

magnetite particles. The scattering pattern is highly elliptical and extends

to larger Q values, where Q = 47rsin(5)/X and is the Bragg scattering angle.

The elliptical shape of the intensity contours confirm that the bacteria are oriented by the magnetic field.

On the other hand, the scattering from MS-1 in 30% D^O (fig. lb) arises

mainly from the magnetite particles themselves. While the pattern is still

slightly elliptical, it is confined to much smaller Q. This scattering is a result of interaction of the neutron magnetic moment with that of the

magnetite particles and can be described in the form [5]

I(Q,a) = B(Q) ± C(Q)cos2a, (1)

where a is the angle between the magnetic field direction in the plane of the

detector and the scattering vector, Q. The negative sign applies for a ferromagnet and the positive sign for a super-paramagnetic system.

Additional SANS measurements were performed, in an applied magnetic

field of 25 Gauss, on MS-1, grown under both "high iron" and "low iron"

conditions, as well as on MS-2, grown under "normal iron" conditions. In all

three cases, the solvent contained 30% D^O, permitting studies of the

magnetite particles in the living cells. Slightly elliptical intensity

contours, similar to those shown in figure lb, were obtained in each case. The intensity contours from both the "high iron" and "normal iron" samples

had the major axis of the ellipse in the direction perpendicular to that of

the magnetic field (negative sign in eq (1)), indicating that the magnetosomes behaved as ferromagnetic particles. On the other hand, the contours

from the "low iron" sample showed elongation in the direction of the magnetic

field (positive sign in eq (1)), consistent with a superparamagnetic system.

The data were averaged in sectors of width 30' about the horizontal (0')

and vertical (90°) directions. The transverse and longitudinal spin

scattering components were separated as B(Q) + C(Q) and B(Q) - C(Q),

184
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

respectively [6]. Each component was fit to a Lorentzian plus Lorentzian

squared equation of the form [6]

I(Q) = E/(q2 + /Cj2)2 + f/(q2 + t,^) (2)

corresponding to a spin correlation term <S.|S.> = exp{-K;r..}. The

coefficients E and F as well as the inverse correlation lengths, /c, and k^ were found as given in table 1.

The longitudinal inverse correlation length, Kj(1), for the "low iron"

sample as well as the transverse inverse correlation lengths, K;,(t), for all

three samples are zero. Derived from the Lorentzian squared term, k,

describes static spin correlation lengths, ^,(1) and £j(t), which are long

range. However, since the amplitude coefficient E is nonzero, these

correlation lengths and thus, the sizes of the magnetic domains, must be just

beyond the resolution limits of the SANS instrument under the present

experimental conditions, and are listed in table 1 as greater than 300 A.

Values well within the resolution limits of the SANS instrument were obtained for KpCl), in the "low iron" case, and for kA^) in all three cases. Since k^ is associated with the Lorentzian term describing the dynamic spin

fluctuations, the results indicate dynamic spin correlation lengths, ^^f^)

and CoC^)* 0" the order of 50 A, which are superposed on a static magnetic

cluster size several times larger.

Table 1. Summary of SANS results

Lorentzian Souared Term

Sampl

>-8 E (10"°) Ci (A)

Lorentzian Term

F (10"^) ^2 (A)

'high iron" (t) 11.0 > 300 2.3 60 ± 10

'normal iron" (t) 9.6 > 300 2.4 38 ± 4

"low iron" (t)

(1)

2.5

3.2

> 300

> 300

0.9

3.1

38 ± 4

20 + 4

(t) = transverse spin component

(1) = longitudinal spin component

185
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure la, Figure lb.

Figure 1. Constant intensity SANS contours from l\. magnetotacticum with an applied horizontal magnetic field of 25 Gauss a) in 100% D^O,

where the bacteria themselves scatter strongly, and b) in 30% 0^0,

where the scattering from the magnetite particles dominates.

References

[1] Blakemore, R. P. Science 190, 377 (1975).

[2] Blakemore, R. P.; Maratea, D.; Wolfe, R. S. J. Bacterid. HO, 720

(1979).

[3] Balkwill, D. L.; Maratea, D.; Blakemore, R. P. J. Bacteriol. 141, 1399

(1980).

[4] Frankel, R. B. Ann. Rev. Biophys. Bioeng. 13, 85 (1984).

[5] Cywinski, R.; Booth, J. G.; Rainford, B. D. J. Phys. F. 7, No. 12,

2567 (1977).

[6] Rhyne, J. J. Physica B 130, 253 (1985).

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SANS STUDY OF MIXED LECITHIN-BILE SALT MICELLES AND VESICLES

E. W. Kaler and J. F. Billman

(University of Washington, Seattle, WA)

We have carried out a series of experiments to investigate the effect of

bile salt on lecithin vesicles and mixed micelles. One of the most

straightforward ways to follow a micelle-to-vesicle structural transition in

model bile is simply to dilute a mixed micelle solution with buffer. If a 5.0 g/dl mixture with a lecithin/taurodeoxycholate ratio of 0.4 (which is

initially a mixed micellar solution) is diluted with 0.15 M NaCl buffer, a series of size changes is detected with quasielastic light scattering (QLS).

Initially, the solution has an apparent radius of 42 A. Apparent sizes in

sequentially diluted samples increase monotonically until a 16x-diluted

sample demonstrates a radius of 435 A. Further dilution produces a monotonic

decrease in size to an apparent radius of 118 A after a 144 dilution. This

progression of sizes has been postulated to be the result of micelle growth

cumulating in micelle aggregation into rod-like structures (in samples

demonstrating the largest sizes), followed by aggregate breakup and the

formation of vesicles at the highest dilutions.

To test this hypothesis, we have made SANS measurements along such a path (fig. 1). Several features are clear. First, the scattering from the

least dilute sample is consistent with that of mixed micelles as observed by

us in other systems. Second, there is a qualitative difference between the

form of the scattering curve of the least and most dilute samples; in

particular the most dilute samples have substantial periodicity in the

scattering curves and are consistent with the scattering from vesicles.

Finally, it is clear that the periodicity increases as the dilution increases

from 36 to 144. This last feature is consistent with a coexistence of

vesicular and micellar aggregates. An example of the fit of a vesicle form

factor to the 144 dilution data is shown in figure 2. Note that excellent

agreement with QLS measurements is obtained along with new information about

bilayer thickness. An exact fit of the data can be gotten after accounting

for polydispersity of the vesicle population.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1.5

log(D

3.0

Q(l/A)

Dilution Factor (Co = 5g/dl)

r—as—*—'144

f>V //a ^—,60

r%»*r-r*r—^ 48 ^

A 36

'24

12

-.4

0.1

Figure 1. SANS patterns of samples generated by sequential dilution with

0.15 M NaCl buffer of a 5.0 g/dl mixture with a lecithin/

taurodeoxycholate ratio of 0.4. The initial solution contains

mixed micelles, and the final sample is vesicular.

0.5

Dilution Factor = 144

(Co = 5 g/dl)

Log(I)

-3.0

Figure 2. Fit of SANS pattern from the 144x dilution shown in figure 1. The

solid line is the fitted value for a monodispersed population of

vesicles with outer radii of 118 A and bilayer thickness of 40 A.

The radius as determined by QLS is 118 A.

188
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NISI CRYSTAL DATA CENTER

A. D. Mighell and V. L. Himes

and

M. Mrose

(U.S. Geological Survey)

The NIST Crystal Data Center is concerned with the collection, evaluation and dissemination of data on solid-state materials. The data center

maintains a comprehensive database with chemical, physical, and crystallographic information on all types of well -characterized substances. These

materials fall into the following categories: inorganics, organics,

organometallics, metals, intermetall ics, and minerals. The data are made

available to the scientific community through computer oriented modes of

dissemination and through printed products. Two major databases are produced: NIST CRYSTAL DATA [11 and the NIST/Sandia/ICDD Electron

Diffraction database [2]. These databases have many uses including materials

design, materials characterization, and phase identification by neutron, x- ray, and electron diffraction.

During the year, work has focused on the following areas: the development of a new analytical tool by integrating the Electron Diffraction

Database into the analytical electron microscopes that are marketed by

several different commercial companies; the publication of a new book for

phase identification of materials based on d-spacing/element type matching

techniques; the production of a CRYSTAL DATA CD-ROM and accompanying software; the design of algorithms and software to be used in the automation of

diffractometers with respect to accurate symmetry determination; and the

preparation of the annual update to the master database (currently 142,000

entries).

As the databases now contain large collections of evaluated data, the

development of efficient dissemination methods is critical to the utilization

of the information for research and analysis. Recently, it has become

apparent that three principal methods for the computerized delivery of

scientific data are rapidly evolving. All three are now used by the data

center with the first two being initiated during this year. The first is a desktop method in which the database on CD-ROM is used in conjunction with a PC. The second is the incorporation of the database into a scientific

189
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

instrument where the combination represents a new analytical tool. The third

is the distribution of data through international on-line systems.

The on-line method permits the data center to provide rapidly the

general scientific community with up-to-date data and with extensive software

tools to retrieve and manipulate the information. All that is required to access the system is a terminal, a modem, and a local call. To build and

maintain the on-line system in the most efficient manner, NIST and the

National Research Council (Canada) have formally agreed to pool their

resources. The objective is a long-term collaboration not only to broaden

the scope of the existing CRYSTDAT System (= on-line version of NIST CRYSTAL

DATA), but also to expand the system to include databases in related fields

to create an interdisciplinary materials database system. Such a system will

utilize a high performance computer environment including supercomputing

resources, networks, and the applications of new software technologies.

References

[1] NIST CRYSTAL DATA (1989). A database of chemical, physical, and

crystal lographic data (142,000 entries). Compiled and evaluated by the

NIST Crystal Data Center, National Institute of Standards and

Technology, Gaithersburg, MD 20899.

[2] NIST/Sandia/ICDD Electron Diffraction Database (1988). A database

designed for phase characterization by electron diffraction. Prepared

by the NIST Crystal Data Center (in collaboration with the Sandia

National Laboratories and the International Centre for Diffraction

Data), National Institute of Standards and Technology, Gaithersburg, MD

20899.

Both standard reference databases are leased to the scientific community in

two forms: CD-ROM and magnetic tape.

A NEW METHOD FOR IDENTIFICATION OF SOLID-STATE MATERIALS

V. L. Himes and A. D. Mighell

As a result of a long-term basic research program supported by the

Reactor Radiation Division and the Office of Standard Reference Data, the

Crystal Data Center has developed a highly accurate analytical procedure that

will greatly extend identification techniques, particularly for electron

diffractionists. The method opens new opportunities in the identification of

solid-state materials, in that crystalline samples in the size range of 10 /xm

to 10 A can be accurately characterized.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Research with NIST CRYSTAL DATA (a large database with chemical,

physical and crystal lographic data on solid-state materials) has proved that

a material can be uniquely characterized on the basis of its lattice and

chemical composition. To characterize a material, it is sufficient to

determine any primitive cell of the lattice and the element types present.

Using a modern analytical electron microscope (AEM), the experimentalist can collect the required data on an unknown sample. The lattice information is

obtained by rotation of the sample to obtain two planes of data, from which a unit cell defining the lattice can be deduced. The chemical data are determined by energy dispersive spectroscopy (EDS) or electron energy loss

spectroscopy (EELS).

Once the experimental data are measured, the unknown can be identified

against the database of knowns using lattice/element- type matching

techniques. The basic strategy consists of three steps (fig. 1). First, the

unknown lattice is searched against the database to find all lattices that

are the same or related; the results of this search are kept in SET 1.

Second, the unknown is searched against the database to find all materials

with the same or similar element types; the results of this search are kept

in SET 2. Finally, SET 1 and SET 2 are combined using the BOOLEAN .AND.

operation to obtain SET 3 which is the answer set. Experience has proved

that the procedure is selective and accurate.

Rapid and accurate identification of the unknown against lattices in the

database with 140,000 entries is due: a) to the development of a universal

classification scheme for all lattices independent of crystal system and

lattice centering; b) to theoretical work that has led to algorithms that can deduce the relationship, if it exists, between any pair of lattices; and c)

to the creation of computer algorithms and search software to carry out

lattice matching in an efficient manner when an extremely large number of

lattices is involved.

Plans are under way to build this procedure directly into the work

stations associated with commercial analytical electron microscopes through

technology transfer with private-sector groups. This strategy, then,

provides an automated identification technique since data collection, NIST

CRYSTAL DATA, and the identification software will all be integrated into the same instrument. *The methodology is also useful for the identification of

unknowns by means of neutron and x-ray diffraction data.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

LATTICE/ ELEMENT-TYPE MATCHING

w '^ w

SET 1: LATTICE SET 2: ELEMENT TYPE SET 3: LATTICE / ELEMENT TYPE

SET1

AND SET 1, SET 2 SET 2

SET 1 = The SET of compounas resulting from lattice matching.

SET 2 = The SET of compounds resulting from element-type matching.

SET 3 = AND SET 1 , SET 2 = the compounds in the NISI CRYSTAL DATA

file that have the same or related lattice/element-type as

the unknown.

Figure 1. Phase identification by lattice/element- type matching

AUTORADIOGRAPHY STUDY OF PAINTINGS

Y. T. Cheng and J. S. Olin

(Smithsonian Institution, Washington, DC and Reactor Radiation Division)

The first phase of autoradiography study on paintings of Thomas Wilner

Dewing has been completed. A manuscript titled "Thomas Wilner Dewing: An

Ebauche or Sketch of His Painting Technique" has been prepared and accepted

by the "Smithsonian Studies in American Art" for publication. The work

comprises the study on 11 of Dewing's paintings and is the result of a close

collaboration among scientists, art historians and painting conservators.

The collaboration is needed because the study is not only to reveal how the

artist achieved his painterly effects, but also to seek the meaning which he

purposed to convey. The autoradiographs suggest the technique that the

artist employed in his creative process by registering brush marks, pigment

distributions, and form changes. These radiographic images were analyzed in

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

conjunction with other analytical tools at our disposal such as the scanning

electron microscope, gas chromatography mass spectrometer as well as more conventional means of painting examination--x-ray radiography, microscopy,

and infrared photography. Extensive literature research and personal interviews have also contributed to the interpretation of the autoradiographs and

understanding of each of the paintings. They often provided information

about changes in the painting which were subsequently revealed in the

autoradiographs.

Dewing is a good subject for such an investigation for in many ways he was a painter's painter, recognized in his own day for his technical ability.

Not one to work routinely, Dewing varied his paint applications from picture

to picture, blending his individual style with a repertory of images that he

drew from sources as diverse as Jean-Baptiste-Simeon Chardin, Jan Vermeer,

Gerard ter Borch, the American expatriate James McNeill Whistler, and the old

masters. To our fascination, we find that throughout his career. Dewing

continued to employ the classical ebauche that he had learned while a student

in Paris. This technique ordained the method whereby he laid in his work,

establishing its light and dark passages which were clearly revealed by the

autoradiographs.

Gamma ray spectroscopy was conducted in parallel to the autoradiography

2 process. Table 1 lists the surface density in mg/cm of the various elements

detected by neutron activation in Dewing's paintings.

The work to examine paintings of another American artists Albert P. Ryder by neutron activation autoradiography continued. Thus far, 10 of his

works from the collections in the National Museum of American Art (NMAA),

including his master work "Jonah", have been studied. Portions of the study

have been included in the catalog, and will be on display during the Ryder

exhibition to be inaugurated in 1990 at NMAA.

To more accurately analyze the radiographic information generated in the

study, calibration references are being established. The calibration

procedure involves first measuring the film responses of selected known

materials that were subjected to the same painting neutron activation

condition. The film responses as a function of time in the autoradiographic

sequence are stored in computer and serve as standards against which one can compare the digitized results of painting autoradiographs.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Surface density of the elements in Dewing 's paintings as determined by neutron activation analysis

PAINTING

ELEMENT ALMATHAYER HOUSTON

LADY LISTENING NECKLACE NUDE SPINETLADY IN WHITE #1 LADY IN WHITE #2

SODIUM 0.67 0.11 0.16 0.97 0.07 1.79 0.12 0.17

MAGNESIUM * * 0.54 * * * 0.46 *

ALUMINIUM 0.57 0.35 0.40 0.38 0.35 0.82 0.43 0.95

CHLORINE 1.02 0.22 0.41 0.82 1.32 2.97 0.14 0.33

POTASSIUM 0.08 0.06 0.02 0.21 0.21 1.21 0.49 0.61

CALCIUM 6.45 1.54 7.44 3.65 3.73 14.89 7.58 2.80

CHROMIUM 0.02 0.10 0.31 0.22 0.02 0.08 * 0.03

MANGANESE 0.02 0.09 0.03 0.01 0.10 0.07 0.10 0.20

IRON 0.47 6.77 0.93 * 2.05 * 4.35 7.51

COBALT 0.02 0.11 * * 0.09 * * 0.01

COPPER * 0.26 * * * * * 0.09

ZINC 1.62 0.38 9.40 7.81 0.34 2.95 5.11 16.26

ARSENIC * 0.06 * * 0.01 0.01 * 0.01

CADMIUM 0.16 0.57 0.08 0.09 * 0.65 0.17 0.08

ANTIMONY 0.02 0.25 0.30 * 0.02 0.12 * *

BARIUM 1.75 0.26 0.07 1.61 0.03 3.01 * 0.97

MERCURY 0.55 1.14 0.29 0.34 * 21.16 * 0.02

indicates element was not detected

194
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COLD NEUTRON PROJECT

J. R. D. Copley, C. J. Glinka, J. A. Gotaas, G. Greene, W. Knill,

J. LaRock, C. J. Majkrzak, C. O'Connor, D. Pierce, H. J. Prask,

J. M. Rowe, S. Satija, I. G. Schroder, T. J. Udovic, and R. Williams

The neutron guide hall and office/laboratory building construction

contract was awarded in the fall of 1987. The bids received indicated that

the design package was good, and the successful bidder proved to be

responsible and reliable; construction began in November 1987.

On January 12, 1989, the Cold Neutron Research Facility (CNRF) was officially dedicated by the Secretary of Commerce, C. William Verity. Among

the many representatives of government, industry, and universities present were former Deputy Secretary of Commerce Clarence J. Brown and Acting UnderSecretary of Commerce for Technology, Ernest Ambler. Dr. Ambler, Raymond

Kammer, Acting Director of NIST, and Institute for Materials Science and

Engineering Director, Lyle Schwartz also spoke at the ceremonies.

In his address. Secretary Verity stressed that the CNRF represents the

imminent arrival in this country of an important set of new tools for

scientists and engineers, and that the development of new polymers, new ceramics, new catalysts, and better semiconductor devices all involve

problems that may only be solved by cold neutron probes. He mentioned the

report of the National Research Council, which placed the project at the top

of its list of urgently needed improvements, and the economic importance of

the tools that the project would provide. He also praised the cost

effectivness and rapidity of the construction and the foresight of the NIST

scientists who designed the reactor and made provision for the addition of a large cold-neutron source. The new office space associated with the CNRF was occupied in early

March 1989, and the current state of facility construction is as follows.

The neutron guide tubes are being fabricated by Cilas-Alcatel of France, with

the first delivery in the spring of 1989, and all guides for NG 5, 6, and 7 now on-site; guides for NG 3 have been ordered. Penetration of the 7-m thick

exterior wall for guide-tube installation began in late June, following the

end of the last reactor cycle in early June. Fabrication of the guide

support system is being done in the NIST shops, and is on schedule.

Construction of the automatic shutter system began in early 1989; delivery of

195
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the first (for testing) took place in May, and delivery of the remaining six

is expected on schedule.

In the first stage of instrumentation, the three guides that run along

the east side of the guide hall will be installed and developed. The

remaining four guides will be installed later, possibly at the same time as a new cold source, which is presently being designed, is ready. This schedule

has been chosen to minimize reactor down time, while allowing for an orderly

development of the full complement of instruments. The layout of the initial

three guides and instruments is shown in figure 1.

NG-1 NG-2

NG-3

NG-(

NG-5

NG-6

NG-7

////^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^v///^^^^^^^^^^^^^^^^^^^^^^^^^^v/////////;^y/////^^^^^^^^^^^wy^

fH//h'/f,','f/ffHffffh</ff//ffHHffNfff,>,>f,'/,<f//ff?f/ffff/}fff/,>ffff//,<ffffh>,>,<fh<h>fffh</ffh>/ft/^ffH ' AA

1. REFLECTRONETER

2. INTERFEROHETER

3. 30 METER SANS

k. TOE

5. 8 METER SANS

6. PROMPT GAMMA SPECTROMETER

7.. NEUTRON LIFETIME EXPERIMENT

-200 FT. Figure 1. Cold Neutron Research Facility layout showing initial

instrumentation complex.

The design and construction of the first instruments are under way, with

different instruments at different stages. Two of the instruments shown, the

8-m small angle neutron scattering facility (SANS) and the time-of-flight

(TOF) spectrometer, have been moved from the reactor building to the guide

hall. As the new instruments come on line, these two will be replaced, but

in the development stage, they will be available for research. The port

previously allocated to the TOF machine in the reactor hall will be modified

to become a new neutron depth profiling station, installation of which will

follow immediately on guide installation. Within the guide hall, the

196
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Exxon/NIST 30 m high-resolution SANS will be ready for installation early in

1990, as will the prompt gamma-ray activation analysis station. Also to be

placed on-line at that time will be the neutron lifetime experiment--a

University of Sussex(UK)/NIST collaboration.

Among the other instruments to be installed on the first three guides,

fabrication of a cold neutron triple-axis spectrometer will begin soon,

whereas a neutron reflectometer is entering the detailed-design stage. Both

of these instruments should be completed in early 1990. A neutron interferometer is in the design and initial construction stage, with an expected

installation date of 1992. Not shown on the floor plan is a second 30 m SANS

and a spin-polarized crystal spectrometer, to be built under the National

Science Foundation (NSF)/NIST sponsorship as described below; the fabrication

of the SANS is now under way. Also in the design stage for commissioning in

1992 are a high resolution cold neutron time-of-flight spectrometer and a back-reflection spectrometer. Descriptions of the current state of

development of some of the instruments are given in separate subsections of

this report.

Relating to instrument development, the following major collaborations

have been initiated in 1989. NIST and NSF have announced plans to develop a Center for High Resolution Neutron Scattering (CHRNS) for research in

chemistry, physics, biology, and materials science at the CNRF. The Center,

to be built around two state-of-the-art neutron research instruments to be

designed and constructed by NIST with funding from NSF, will be managed as a national user facility, open to use by U.S. universities, industries, and

government agencies. Proposals for research time will be evaluated on the

basis of scientific merit by a program advisory committee. The new instruments will be a 30-m SANS spectrometer and a spin-polarized inelastic

neutron scattering (SPINS) spectrometer.

The Organic and Electronic Materials Department of Sandia National

Laboratories (SNL) has entered into a long-term cooperative research

agreement with the CNRF. SNL will provide partial funding for development

and support costs of the new high-resolution TOF and the new back-reflection

spectrometer. SNL will also provide a post-doc to participate in instrument

development and to perform research of interest to SNL and NIST.

In early March the initial members of the Program Advisory Committee for

the CNRF were officially welcomed to the committee. Dr. David Price of

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Argonne National Laboratory, Professor E. A. Schweikert of Texas A&M

University, Dr. Sunil Sinha of Brookhaven National Laboratory, and Professor

Hyuk Yu of the University of Wisconsin, have generously agreed to serve. The

first PAC meeting is planned for the fall.

Two workshops were conducted during the reporting period. A workshop on Neutron Methods for High T Superconductors was held at NIST November 3-4,

1988. This workshop was designed to provide interested DARPA contractors

with an in-depth view of neutron methods as applied to superconductor

characterization. Presentations were made by NIST and guest scientists on total -profile analysis, SANS, inelastic neutron scattering, neutron

activation analysis, and neutron microstructure characterization. A workshop

on the Utilization of Cold Neutron Beams for Prompt Gamma Neutron Activation

Analysis and Neutron Depth Profiling was held on May 22-23, 1989. It

focussed on applications of neutron-induced nuclear reactions in chemical

analysis, materials science, and physics research.

In May the first issue of the Neutron Standard, the Reactor Radiation

Division and CNRF newsletter, was printed and sent to approximately 16,000

scientists and engineers from specialities which the CNRF could benefit.

News of the dedication, facility development, and special events--such as workshops--was presented. A detailed description of instruments and a request for proposals is planned for inclusion in the next newsletter.

CENTER FOR HIGH RESOLUTION NEUTRON SCATTERING

J. J. Rhyne

The National Science Foundation provided a grant for a Center for High

Resolution Neutron Scattering (CHRNS), which will include the development of

two instruments in the Cold Neutron Research Facility. These instruments, a 30-m SANS and a Spin Polarized Inelastic Neutron Spectrometer (SPINS), to be

jointly developed by NIST and NSF, will operate as a user facility open to

qualified research workers from universities, national laboratories, and

industry. The CNRF program committee will evaluate proposals for beam time.

The 30-m SANS will occupy an end-guide position in the guide hall and

will provide the highest resolution available in the United States (minimum Q

of 0.001 A" with a sample flux of approximately 10 n/sec on a 2 cm diam

198
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

sample), and will incorporate a high counting rate two-dimensional detector.

The detector will move inside a 15-m evacuated flight path. Provision will

be made for a second detector to move along an arc at a fixed radial distance

of 1.5-m thereby extending the Q-range of the instrument to 1 A' . The plan

is to provide for a polarized neutron capability using a polarizing filter or multilayer reflection crystals.

The neutron monochromator will be a variable pitch velocity selector

providing wavelength tunability over the range 4 to 25 A with a variable

wavelength spread, AX/X, from about 5 to 25%.

The design and procurement of electronic and mechanical components for

the SANS instrument is under way, and it is anticipated it will be available

for use in March 1991 with the SPINS, described in more detail below,

available approximately a year later.

SPIN POLARIZED INELASTIC NEUTRON SCAHERING SPECTROMETER (SPINS)

C. F. Majkrzak

Design work on this new instrument for the NIST Cold Neutron Research

Facility and CHRNS is currently under way. As described in detail elsewhere

[1], the use of efficient broad-band polarizers and novel energy-dependent,

spin-flipping devices will make it possible, in principle, to achieve high

energy resolution without prohibitive restrictions on beam divergence.

Measurement of energy transfers with a resolution approaching 10 jueV should

be obtainable. Because the actual efficiencies of the polarizers and

flippers ultimately limit the performance of the instrument, priority is now

being given to the development of these component devices. Various types of

polarizers are being fabricated and tested, including supermirrors and curved

Soller arrays of mirrors or benders. Detailed calculations of the

performance of energy-dependent spin-flipping devices are also being done in

order to determine the optimal spatial current distribution.

Reference

[1] Majkrzak, C. F.; Glinka, C. J.; Satija, S. K. SPIE Conf. Proc.

No. 983, p. 129, SPIE, Bellingham, WA, 1989.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COLD NEUTRON TRIPLE AXIS SPECTROMETER

S. F. Trevino

(ARDEC, Picatinny Arsenal, NJ and Reactor Radiation Division)

Two cold neutron triple axis spectrometers will be installed on guide

tubes at the Cold Neutron Research Facility. The conceptual design of one of

these instruments is completed and detailed engineering is in progress. We

hope that the first of these instruments will be installed in the summer of

1990.

Capabilities common to the two instruments are:

-- monochromator scattering angle from 30 to 150 deg;

-- vertical focusing of the monochromator;

-- shielded filters between monochromator and sample (cold Be and Pg);

-- sample scattering angles from -150 to +150 deg;

-- shielded filters between sample and analyzer;

-- vertical focusing of the analyzer;

-- interchangeable collimators with angular acceptance between 5

and 60 min of arc between monochromator-sample, sample-analyzer,

and analyzer-detector;

-- the sample environment includes temperature control from 3 mk

to 2000 K deg., pressures to 10 kbar, and magnetic fields to

60 kgauss; and

-- the mechanical support of the sample and analyzer tables will be

accomplished with air pads.

One of the spectrometers will be capable of neutron polarization

analysis of the beam before and after the sample by the use of either multilayer or mirror technology or both.

The second machine will utilize the Drabkin resonance flipper for energy

analysis (see C. F. Majkrzak in this report).

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

HIGH RESOLUTION TIME-OF-FLIGHT SPECTROMETER

J. R. D. Copley

The high resolution time-of-flight spectrometer will use two pairs of

counter-rotating disk choppers to produce a pulsed beam of monochromatic

neutrons at the sample position. Either two or three additional choppers

will be used to remove higher orders, and to reduce the burst frequency in

order to minimize frame overlap problems at the detector. We expect to award

a contract in October for the design and construction of the complete chopper

system, comprising motors, bearings, disks, vacuum housings, and a standalone microprocessor-based control system. The height of the slots in the

choppers will be 100 mm whereas a choice of at least three distinct slot

widths will be available, depending on the desired resolution. In order to

increase the intensity on the sample under conditions of high resolution, we expect to (a) include an arrangement of two closely spaced slots in at least

one of the pairs of counter-rotating choppers [1], and (b) use a multiplychanneled guide which restricts the lateral motion of the neutrons after they

leave the first chopper pair [2].

The instrument will probably be located on guide NG-1, which will

hopefully have supermirror-coated horizontal surfaces in order to increase

the intensity at the sample. It is likely that we shall include an option to use an inclined multilayer-coated plate or plates, placed before the first

chopper, to remove very long wavelength neutrons from the incident beam:

this device will be particularly attractive if it turns out to obviate the

need for a seventh chopper.

References

[1] Copley, J. R. D. Nucl . Inst. Meth. A2Z3, 67 (1988).

[2] Copley, J. R. D. On the use of multiply channelled guides to increase

intensity on the sample in a multiple disk chopper time-of-flight

spectrometer, elsewhere in this report.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

ANALYTICAL CALCULATIONS OF THE PERFORMANCE OF NEUTRON GUIDE SYSTEMS

J. R. D. Copley

Our previous work in this area [1] has been considerably extended over

the past 12 months [2,3]. The emphasis lately has been on analytical

calculations of the performance of moderately complicated straight-sided

guide systems. Acceptance diagrams at various points within a guide system

are computed and plotted using a computer program developed in collaboration

with G. Greene of this Division. These diagrams show the y-/3 distribution of

the neutrons at the location of interest, where y is the spatial coordinate

normal to the direction of the guide, and ^ measures the angle between the

neutron direction and the guide direction. The acceptance diagrams in turn

enable us to compute integrated intensities and related properties.

In the following paragraphs we discuss some of the guide system problems

which we have attacked using the analytical technique:

(1) It is likely that the horizontal surfaces of some of the guides in

the new hall will have supermirror coatings. In contrast, all guide surfaces

within the biological shield of the reactor will almost definitely be nickelcoated, because of uncertainties with regard to the long-term stability of

supermirror coatings in high radiation fields. We have investigated the idea

of tapering the nickel -coated guide section in order to increase the

intensity of neutrons at the exit of the guide. Our results, shown in figure

1, show that the expected increase is of order 10 to 15% at long wavelengths.

(2) A supermirror-coated guide which is preceded by a nickel -coated

guide is, in general, incompletely illuminated because of the lower critical

angle of nickel. In addition the intensity of neutrons in the guide

decreases with increasing distance from the source because the supermirror

coating has less than 100% reflectivity above the nickel critical angle.

These statements have been placed on a quantitative basis as illustrated in

figure 2. We conclude that intensity gains of order 30 to 50% may be

achieved, for wavelengths up to about 6 A, using supermirror-coated guides

which start just outside the biological shield of the reactor. These

calculations are clearly of importance in view of the very significant

additional cost of supermirror-coated guides.

(3) We have investigated the performance of a vertically curved

monochromator placed in a neutron guide, with particular reference to effects

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

due to changes in the critical angle of the guide coating. The mosaic spread

of the monochromator was appropriately convoluted into the acceptance diagram

calculations. The results were independently confirmed by Monte Carlo

calculations [4]. In figure 3 we show cumulative intensity distributions

computed as a function of vertical distance from the sample center for

various choices of mosaic spread r}, for nickel- and supermirror coated

guides. When rj is small an increase in the critical angle of the guide

results in an increase in the height of the beam at the sample. On the other

hand a large mosaic spread has the effect of increasing the intensity at all

points along the sample.

(4) One of the more important features of our calculational method is

that we can track neutrons which are transmitted through a non-absorbing

guide surface. This has enabled us to compute the filtering properties of

the device illustrated in the inset to figure 4. Our results, shown in

figure 4, are in good agreement with Monte Carlo calculations by Mezei [5]

for the case that the inclined plate's critical angle is twice that of the

guide. It is possible that a device of this sort will be placed before the

first chopper of the high resolution time-of-flight spectrometer (see

elsewhere in this report), in order to remove very long wavelength neutrons

which might otherwise contaminate the beam at the sample. Note that the

actual transmission will be somewhat reduced because the transmitted beam

must pass through the inclined plate.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1

20 24

Guide entreince height 2H (cm)

20 40 60 SM or Ni-58 Gmde Length L (m)

80

(left) Results of 2-dimensional calculations of the intensity at

the exit of a long supermirror guide placed immediately following

58

a converging Ni guide, as shown in the inset. The supermirror

guide is long in the sense that its acceptance angle (i.e., its

height/length) is less than the critical angle for all wavelengths

CO

considered in the calculations. The Ni guide entrance is 120 cm from the source and 160 cm long. The source is 30 cm high, the

CO

entrance height of the Ni guide is 2H, and its exit height is 15 cm. The supermirror guide height is 15 cm. The intensity I is

expressed as a ratio to the maximum intensity !« which is obtained

if the supermirror guide is fully illuminated. In these

CO

calculations the critical wave vectors Qp for

supermirror material were 0.025 and 0.042 A' respectively. The

supermirror was assumed to have 100% reflectivity up to the

critical wave vector.

Ni and for the

Figure 2. (right) Calculated ratios of the intensities I^^. and Im^.co at

the exits of guides of length L coated with supermirror material

CO

and with Ni respectively. In both cases the guide is preceded

CO

by a parallel 160 cm long Ni guide whose entrance is 120 cm from

the source (cf the inset to fig. 1). The source is 30 cm high and

CO

the guides are 15 cm high. The Ni has a critical wave vector Qof 0.025 A' whereas the reflectivity of the supermirror is 100%

up to 0.021 A' (the critical wave vector of natural Ni), falling

gradually to 85% at 0.042 A : therafter, it is zero. The

vertical dashed lines indicate, very approximately, values of L corresponding to the closest and most distant positions where

beams can be extracted from guides in the guide hall.

204
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

40

H (mm)

Figure 3. Cumulative intensity distributions in the focal plane of a vertically curved monochromator crystal placed in a guide. The

neutron wavelength is 4 A, the monochromator d-spacing is 3.35 A,

and its radius of curvature is 1.791 m. The focal plane (for

neutrons in the guide) is therefore 1.50 m from the monochromator.

The full height of the guide (and monochromator) is 15 cm, and it

CO _ 1 is coated either with Ni (Qp = 0.025 A" ) or with supermirror

material (Qp = 0.043 A' ). The ordinate is proportional to the

integrated intensity on a sample of half-height H. Its maximum

value, when H is large, is the product (2Hp)(2^p) where 2Hg is the

height of the guide and ^p is its critical angle.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

0.00 0.01 0.02 0.03 0.04

Figure 4. The calculated transmission of the device shown in the inset,

which is basically a plate inclined at an angle a to the mean beam

direction, coated with material of critical wave vector Qp. The

critical wave vector of the guide, Q^, is 0.025 A' , i.e., that of

CO

Ni, and the filter is designed to have 100% transmission up to

10 A, i.e., for 6^ < 0.02. This is achieved by making a equal to

0.02 (1 + Qp/Q(,).

References

[1] Copley, J. R. D. NIST Tech. Note 1257, O'Connor, C, ed. p. 151 (1989).

[2] Copley, J. R. D. Advanced Neutron Sources , Physics Conference Series

Vol. 97, Institute of Physics Publishing, London, 1989 (in press).

[3] Copley, J. R. D. Nucl . Instrum. Meth. (submitted).

[4] The Monte Carlo calculations were performed by D. A. Neumann.

[5] Mezei, F. Thin-film optical devices: mirrors, supermirrors, multilayer

monochromators, polarizers, and beam guides. Majkrzak, C. F., ed. Proc.

SPIE 983, 10 (1989).

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

ON THE USE OF MULTIPLY CHANNELED GUIDES TO INCREASE INTENSITY

ON THE SAMPLE IN A MULTIPLE DISK CHOPPER TIME-OF-FLIGHT SPECTROMETER

J. R. D. Copley

A conventional direct geometry inelastic scattering time-of-flight

spectrometer (at a reactor) necessarily has at least two choppers: the first

pulses the beam and the second selects a wavelength from the pulsed beam. If

disk choppers are used, significant advantages accrue when each of the two

choppers is replaced by a pair of counter-rotating choppers, as illustrated

in figure 1. A neutron guide is generally placed before, between, and

sometimes following the chopper pairs, in order to increase the intensity of

neutrons on the sample. (In a real instrument there are additional choppers,

to remove unwanted orders and to reduce frame overlap, but these choppers are of no concern to us in the present discussion.)

The intensity distribution immediately following the first chopper pair,

for the setup illustrated in figure 1, is a triangular function of the

transverse spatial coordinate y. It rapidly develops into a roughly

rectangular distribution as the neutrons progress down the guide, as illustrated in figure 2 for the case that 2W, = 2Wg (see the caption to

fig. 1). In what follows, we shall assume that the intensity in any guide

placed between the chopper pairs of a time-of-flight (TOF) spectrometer is

independent of y by the time the neutrons reach the second chopper pair.

The transmission of the second chopper pair, integrated over time, is

again a triangular function of y, and the number of neutrons which pass

through the second chopper pair, per pulse, is given by

I2 = (dlj/dA) (W2/Wg) (h/mL) (W2/V), (1)

where the number of neutrons transmitted by the first chopper pair, per

pulse, per unit wavelength interval, is

(dIj/dX) = f^ (2 Wj2/v) (2Hg) (2 e^)'^. (2)

In these equations § is the intensity of the incident beam before the first

2 chopper pair (typically expressed in units of neutrons/cm /sec/ster/A) , v is

the tangential velocity of the choppers, 2Hq is the height of the guide (and

of the slots in the choppers), 6^ is the (wavelength-dependent) critical

207
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

angle of the guide material (assumed identical for all surfaces), L is the

distance between the chopper pairs, h is Planck's constant, and m is the mass

of the neutron.

Suppose that it were possible to completely prevent motion of neutrons

in the y direction, so that the intensity distribution just before the second

chopper pair was still triangular (rather than rectangular). In this case

the transmitted intensity K, for the special case that 2W, = 2W2 = 2Wg,

would be increased to (4/3) of its value in the absence of the constraint on

y. The increase occurs because a greater proportion of the neutrons are located close to the guide centre, where the transmission of the second

chopper pair is relatively high. This result suggests the use of multiply

channeled guides to restrict the lateral motion of the neutrons, and thereby

increase the intensity on the sample, in a multiple disk chopper

spectrometer. This concept is illustrated in figure 3. Calculated gains for

several choices of chopper slot width and number of channels are presented in

table 1. Note that gains are particularly dramatic when the chopper slot

widths are much smaller than the guide width. This is the case when an instrument is in its higher resolution modes of operation, under

circumstances where any method of increasing intensity on the sample is

particularly welcome.

In order to decide whether multiply channeled guides should be used in a given instrument we must determine their effect on its resolution. We will

then be able to estimate intensity gains at constant resolution. This work

has just been started. Our preliminary calculations indicate that intensity

gains at constant resolution can still be significant, though somewhat less

dramatic than the numbers given in table 1.

The gain in intensity in any practical realization of this concept will

clearly be somewhat smaller than the theoretical gain, because of the finite

thickness of the channel plates, losses due to misalignments, and reflectivity losses due to the increased number of reflections. Nevertheless, we believe that significant overall gains can result, and we are likely to

incorporate this concept into the design of the new high resolution TOP

spectrometer (described elsewhere in this report).

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Calculated gains for various choices of the ratios (Wj/Wg) and

(Wo/Wg) as a function of N, the number of channels into which the

guide is (equally) divided. The relative intensity per pulse

(R.I.), in the third column, is in units of [^q (2 Wg^v) (2Hg) (2

2

^p) (h/mL) (Wq/v)]. Note that (for symmetry reasons) there is no gain if N = 2

(W^/Wg) (Wg/Wg) R.I. Gains, relative to N = 1 N = 3 N = 4 N = 8 N = 16 N = «

1.0 1.0 1 1.222 1.250 1.313 1.328 1.333

1.0 0.5 1/4 1.556 1.500 1.625 1.656 1.667

0.5 0.5 1/16 2.389 2.000 2.500 2.625 2.667

0.5 0.25 1/64 2.667 2.000 3.000 3.250 3.333

0.25 0.25 1/256 3.000 2.000 4.000 5.000 5.333

Figure 1. Two closely spaced counter-rotating chopper pairs arranged to

pulse and monochromate a beam of neutrons in a guide tube of width

2Wg and height 2Hg. The slots in the choppers have linear

velocity v, and the distance between chopper pairs is L. The

widths of the slots in the first and second chopper pairs are 2Wj

and 2W2, respectively. The height of all slots is 2Hg. The

coordinate system is indicated.

209
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CP#1

CP#1

N=l

i

N=3

CP#2

1/4

CP#2 u i Ti

2/9 1 1/24 5/9 2 2/3

2/9 3 1/24

Figure 2. (left) A three-dimensional plot illustrating the evolution of an initially triangular spatial neutron distribution with base width

2W (at X = 0), as it progresses along a guide of the same width

and critical angle 6^. The distribution is flat, i.e., independent of y, at the nodes x = (nW/^-) where n is a positive integer:

these positions are indicated by the tick marks along the x axis.

At the antinodes, x = (nW/5p) with n = 1/2, 3/2, 5/2, etc., the

extremum values of the intensity•^ are I ^,^(1 ± l/4n) where

mean^ ' ' !»,«,« is the mean intensity. The underside of the surface is not mean •' shown.

Figure 3. (right) The concept of a channeled guide is illustrated with

reference to the case that (W,/Wg) = 1 and (W^/Wg) = 1/2. To the

left and right of the guide are shown relative intensity

distributions transmitted by the first and second chopper pairs

(CP#1 and CP#2) respectively. The quantity f. is the fraction of

the intensity transmitted by the first chopper pair, (dIj/dA),

which enters channel i. The quantity T. is the mean transmission

of the second chopper pair for neutrons in channel i, relative to

the peak transmission at y = 0. The number of neutrons per pulse

after the second chopper pair may be written as [(dlj/dX) { 2

(f^T.)} AX^], where (dIj/dA) is defined in the text and AA^ =

(h/mL) (2W2/V) is the maximum wavelength interval transmitted by

the second chopper pair (at y = 0). The gain of the three-channel

arrangement is the ratio of the sums 2(f.T.), i.e., [(7/18)/(l/4)]

= (14/9) (cf. Table 1).

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

FOCUSED NEUTRON BEANS FOR MATERIALS ANALYSIS

D. F. R. Mildner

(Center for Analytical Chemistry)

The Cold Neutron Research Facility at NIST combined with advanced

research in neutron optics offers the possibility for developing an analytical microprobe for techniques which are dependent only on the reaction

rate, not on the collimation, such as prompt-gamma activation analysis and

neutron depth profiling analysis. Previous work involving converging guides

of nickel -titanium supermirrors [1] looks promising, though there are problems with undulations of the layer profile as the film thickness

increases. However, intensity gains are only about three in one dimension,

caused by the increase of the angle that the neutron makes with the device

axis on successive reflections.

Stacked curved microguides overcome this limitation of any mirror

system by the superposition of outputs from many individual elements each of

which point to a focus. Their ends slightly overlap each other, rather like

a shifted stack of playing cards. The device is best understood by analogy

with a strong focusing optical lens. The maximum intensity gain with the

smallest possible focal area is obtained with a large number of microguides,

each with a large radius of curvature and a short focal length. The

thickness of the microguides relative to their length requires some optimization, though it may be dictated by practical considerations.

The principle was first demonstrated with 45 overlapping nickel coated

glass mirrors, over a meter long, giving a gain of nearly two [2]. In

another effort, 100 layers of alternating aluminum (3200 A) and nickel

(500 A) were placed on a convex surface of length about 1 cm [3]. This

device demonstrated the bending of neutrons, but no attempt was made to

measure any intensity gain, if any. Surprisingly, this idea has remained

dormant until last year at JUlich, where 10 bilayers of aluminum (10,000 A)

and nickel (1000 A), of length 11 mm, were used to focus a beam of dimensions

2

0.01 X 25 mm into a circular spot of 3 mm half width at a distance of 23 cm. The method to be adopted at NIST uses 25 /xm thick, 5 cm diam nickel

coated silicon wafers. Single crystal silicon has about the same neutron

properties as aluminum for the substrate for the nickel. Silicon wafers of a thickness of about .001 in are now commercially available, and can easily be

coated with nickel (1000 A) on one side. The wafers will be loaded into a

211
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

cassette, fabricated to ensure overlapping, and to enable a small curvature

to be maintained.

A method using acceptance diagrams [4] has been developed for analyzing

the transmission properties of continuous curved neutron guides [5], such as beam benders and microguides. The method allows analytic expressions for the

intensity and spatial and angular distributions of neutrons transmitted along

a one-dimensional guide. The acceptance area for curved guides is parabolic

in shape, and shows the asymmetry in the spatial distribution. From these

formulations the average number of reflections can be determined as a function of wavelength. This is important for the microguides since

reflectivity losses increase with the average number of reflections in the

exponent.

References

[1] Copley, J. R. D.; Majkrjak, C. F. Thin-film neutron optical devices:

mirrors, supermirrors, multilayer monochromators, polarizers and beam

guides. C. F. Majkrjak, ed. SPIE Proc, pp 93-104, August 1988, San

Diego.

[2] Friedmann, M.; Rauch, H. Nucl . Instrum. Meth. 86, 55-59 (1970).

[3] Marx, D. Nucl. Instrum. Meth. 94, 533-536 (1971).

[4] Carpenter, J. M.; Mildner, D. F. R. Nucl. Instrum. Meth. 196, 341-348

(1982).

[5] Mildner, D. F. R. Nucl. Instrum. Meth. (submitted).

DESIGN STUDIES FOR THE PROMPT GAMMA-RAY ACTIVATION ANALYSIS INSTRUMENT

C. A. Stone and R. Zeisler

(Center for Analytical Chemistry)

Development of the prompt gamma-ray instrument has focused attention on the neutron and gamma-ray background near the instrument. Characteristics of

the background were studied using the prompt gamma-ray instrument at the ELLA

Cold Neutron Research Facility, KFA Julich. Experiments showed that much of

the background activity is due to neutrons which scatter off of the samples

and are captured by materials which can be viewed by the detectors. An

especially important experiment showed that the gamma-ray background due to

boron in the neutron guides will degrade the performance of the instrument.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In these experiments a gamma-ray detector and a piece of borated glass were

placed outside of the neutron beam such that the detector could view both the

glass and a sample which was placed in the neutron beam. When a sample which

scattered neutrons, i.e., an hydrogenous sample, was placed in the neutron

beam, a very intense boron peak was observed in the prompt gamma-ray spectra.

Moreover, the intensity of the boron peak was a function of the total neutron

scattering cross section of the sample. An important concern here lies in

the placement of the NIST prompt gamma-ray instrument at a mid-point along

the NG-7 neutron guide. The neutron guide is split at the instrument with a neutron guide continuing to the SANS instrument: prompt gamma-ray analyses

are thus performed underneath this continuing guide. As a result of these

studies, the neutron guide near the prompt gamma-ray instrument has been

designed using boron-free glass.

Support and shielding materials were shown to contribute significantly

to the prompt gamma-ray instrument at KFA Julich. Neutron capture in the

aluminum from the sample supports, from the table which supported the

detector, and from other miscellaneous components all contributed to the

background in the gamma-ray spectra. Another major source of background was from the lead used to shield the detectors from the background! Although

lead itself has a low neutron-capture cross-section, it is large for the

impurities within the lead (antimony, for example). Thus an important part

of the shielding for the prompt gamma-ray instrument includes quickly

attenuating neutrons which scatter from the sample and thereby preventing

them from striking material surrounding the instrument.

One promising material for neutron shielding is Li-containing glass.

Samples of this glass have been fabricated with up to 37 mole-percent of

LipO. The primary component of this glass is SiO^ (59 mole-percent) but it

also contains small amount of AKO^ as a stabilizer. This glass is easily

made and can be ground into any desired shape. The large Li concentration

gives the glass the ability to quickly absorb the neutrons: 1 mm is

sufficient to attenuate 85% of the neutron beam. Plates of this glass will

be incorporated into the shielding of the detectors and the general shielding

in the instrument.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COLD NEUTRON DEPTH PROFILING

G. P. Lamaze, R. G. Downing, J. K. Langland, and B. L. Grazman

(Nuclear Methods Group)

The design of the new Cold Neutron Depth Profiling (CNDP) Facility has

been completed and the major components have been ordered. This includes a new 61 cm diam stainless-steel chamber, vacuum system, detectors,

electronics, and data acquisition system. The new depth-profiling chamber

will be capable of operating at UHV pressures and incorporates many design

features that enhance the capabilities that currently exist at the thermal

depth-profiling instrument at BT-3. The chamber will have an XY positioning

system that will allow computer controlled scanning of up to 15 cm diam

samples. The computer will also be capable of rotating both the sample and

the detectors to adjust the sensitivity of the depth-profiling probe. The

ability to use time-of-flight depth profiling techniques has also been

incorporated into the chamber design. An electron gun for in-situ surface

etching of samples will also be available.

The cold neutron beam will be filtered by 24 cm of single crystal

sapphire to remove most of the fast neutrons. The expected neutron fluence

9 -2-1

rate at the sample position is 7 x 10 n cm s with a cadmium ratio of

-4

about 10 . The peak energy of the beam is calculated to be 5.6 meV, which,

for a 1/v cross-section reaction gives an effective cross section of 1.9

times the thermal value. This yields an increased sensitivity of about 20

times that of the present facility at BT-3 for the same efficiency particle

detectors. Pancake type uranium fission chambers will be used for monitoring

the neutron fluence. Both the beam and the target chamber are expected to be

available in early October 1989.

A second chamber is being designed that will be placed downstream from

the above chamber. This will have a computer-controlled sample changing

capability for processing of batches of study materials. While this chamber

will be less sophisticated than the chamber described above, it will allow

higher sample throughput for routine analyses. This chamber will also be

operated at UHV pressures and in-situ surface etching may also be available.

This chamber is expected to be available in the spring of 1990.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

HIGH RESOLUTION SMALL ANGLE SCATTERING SPECTROMETER

C. J. Glinka, J. Moyer, and A. Heald

and

S. K. Sinha

(Exxon Research and Engineering Company, Annandale, NJ)

Much of the vacuum flight path for the 30-m long, high resolution SANS

spectrometer, being built jointly by NIST and the Exxon Research and

Engineering Co., has been constructed and assembly of the instrument is now under way. The 15-m long post-sample section of the flight path, shown in

figure 1, is designed to house two large area position-sensitive detectors;

one that can be positioned within the main cylindrical section of the flight

path at any distance from 4 to 15 m from the sample, and a second identical

detector that moves along a circular arc at a fixed distance of 2 meters from

the sample. Together the two detectors will span a Q-range from roughly

0.001 to 1 A' . The 15-m long pre-sample flight path, which is still under

construction, has provision for the insertion of neutron guide sections to

allow the effective source-to-sample distance to be varied in steps from 5 to

15 m to match the beam collimation to the chosen sample-to-detector distance.

The neutron velocity selectors, purchased for the instrument from the

Central Institute for Physics in Budapest, Hungary, have been received and

tested and do meet all of their design specifications. In particular, the

wavelength bandpass of these selectors has been measured by time-of-flight

and can be varied from 10 to 25% (AX/X FWHM) by inclining the axis of the

rotor to the beam direction.

A novel feature of this instrument will be the use of a doubly curved,

grazing incidence mirror, 2.4 m long, to focus the incident beam onto the

detector. If successful, such a mirror would provide up to a fourfold

increase in flux on the sample, for a given minimum Q-value, over what can be

obtained with either single or multi-beam converging pinhole collimation. As

currently planned this mirror will consist of eight, 30 cm long x 5 cm high,

concave cylindrical segments that will be aligned tangent to an arc 1700 m in

radius. Each segment will be slightly bent to conform approximately to this

1700 m arc to achieve focusing in the horizontal plane. We recently received

and tested the first 30 cm segment of the planned mirror which had a measured

215
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

S.A.N.6. SPECTROMETER

POST-SAMPLE FLIGHT PATH

Figure 1. Isometric view of the post-sample vacuum flight path for the

NIST/Exxon high resolution SANS spectrometer. The flight path will

house two detectors, one that is moveable along the axis of the

long cylindrical section and another within the angled section near

the sample to extend the angular range of the instrument.

surface roughness' of between 5 to 10 A (rms). The profile of a slitcol limated neutron beam reflected from the surface of this mirror was observed to be free of any stray scattering due to the residual surface

_3

roughness at least to the 10 level which was the signal-to-noise limit of

the measurement. Based on these results, we are proceeding to order the

remaining sections needed for the full mirror.

The NIST/Exxon SANS instrument is expected to begin operation during the

early part of 1990 with implementation of all of its planned features,

including the focusing mirror and polarized beam options, continuing

throughout next year.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

DESIGN OF A COLD NEUTRON BACKSCATTERING SPECTROMETER

D. A. Neumann

The cold neutron backscattering spectrometer will be the first ultrahigh energy resolution spectrometer to be built in the United States. This

excellent resolution (= 0.5 /ieV) is achieved by reflecting the neutrons from

perfect Si monochromator and analyzer at a Bragg angle of - 90". The major

drawback of this approach is the low intensity due to the narrow energy slice

which is accepted and to the small divergence of the incident beam imposed by

the guide. Since the narrow energy slice is necessary to obtain the desired

resolution, the only way to improve the intensity is to increase the

divergence of the incident beam. Several features are planned in order to

CO

accomplish this. First the instrument will be placed on a Ni guide with

the possibility still open of having supermirror coatings on the top and

bottom of the guide. There will also be a converging supermirror nose to

2 compress the beam from 6 x 15 cm to the sample size which will probably be

2 3 X 3 cm , necessary because the sample size has a second-order affect on the

resolution.

The most novel feature intended to increase the divergence of the

incident beam is the implementation of the phase-space transform idea of

Schelten and Alefeld [1]. Here a crystal with a relatively large mosaic is

placed on a disk chopper so that the crystal moves perpendicularly to the

average scattering vector. Then neutrons that have larger Bragg angles than

the nominal one are Doppler shifted to larger energies and vice versa; i.e.,

neutrons that are moving too slowly are sped up and those moving too fast are slowed down. Simulations [2] have shown that a gain of a factor of 5-6 can

be realized using this technique. We are preparing tests to determine if the

crystal can be spun fast enough to realize this anticipated gain in practice.

Another possible problem with using this technique is that the sample must be

placed next to the direct beam which leads to concerns about the background.

Since it is not possible to accurately gauge the severity of this problem,

the instrument will be built so that the beam can be deflected away from the

main beam before striking the phase-space chopper.

Another important feature planned for the backscattering spectrometer

which will reduce the counting time for some experiments is a hydraulic

Doppler drive for varying the incident energy distribution. This device,

217
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

pioneered at JUlich, allows the experimenter to vary the incident energy

distribution so that the majority of time can be spent in a region of

particular interest; e.g., in the vicinity of a rotational tunneling line.

In addition, this device will extend the dynamical range of the instrument

out to at least 100 /xeV, if the experimenter chooses to do so. With the

inclusion of these features which should increase the neutron current density

5 2 on the sample to 10 n/sec-cm and provide a great deal of flexibility to the

user, this spectrometer will open up a wide range of experiments in condensed

matter chemistry and physics that are at present impossible to perform in the

United States.

References

[1] Schelten, J. and Alefeld, B.; in Proc. Workshop on Neutron Scattering

Instrumentation for SNQ, Maria Laach, 3-5 September 1984, Scherm, R. and

Stiller, H. H., eds. report JUl-1954 (1984).

[2] Neumann, D. A.; in NBS Reactor: Summary of Activities July 1987 Through

June 1988, O'Connor, C, ed. NIST Tech Note 1257, p. 141.

SUPERHIRROR DEVELOPMENT

C. F. Majkrzak, D. A. Neumann, and J. R. D. Copley

The program of systematic development of supermirror coatings for

neutron guide tubes, described in last year's report, continues. Significant

progress has been made. Two private companies have been fabricating the

supermirrors which are evaluated by us here at the NIST reactor. Specifically, to overcome the progressive roughening of layers which typically

occurs in the conventional Ni-Ti supermirrors [1], a number of amorphous

alloy multilayer systems such as Ni C, - Ti Mn, have been investigated

and improved supermirror reflectivities have in fact been obtained. However,

because the companies involved in the research will probably bid for a contract to coat some of the guide tubes in the new NIST Cold Neutron

Research Facility, the actual neutron reflectivity profiles, as well as detailed information regarding the deposition processes, are of a proprietary

nature and cannot be revealed at this time.

Reference

[1] Keem, J. E. et al . Neutron and X-ray Scattering and TEM studies of NiTi multilayers. Proc. of the SPIE, Vol. 983 . C. F. Majkrzak, ed. SPIE,

Bellingham, WA, 1989, p. 38.

218
B. NON-RRD PROGRAMS

NEUTRON INTERACTIONS AND DOSIMETRY GROUP

J. A. Grundl

(Ionizing Radiation Division)

The Neutron Interactions and Dosimetry Group develops and applies wellcharacterized neutron fields and related capabilities for neutron dosimetry

methods evaluation and standardization, for detector development and

calibration, and for reaction cross-section measurements. Involvement with

outside organizations, both in the federal and private sectors includes many

types of research and technology assistance programs as well as leadership

roles on national and international standards and radiation policy making

bodies.

A selection of accomplishments for FY 89 with emphasis on NIST reactor

related activities are outlined below in titled paragraphs grouped under four

projects.

DOSIMETRY FOR MATERIAL PERFORMANCE ASSESSMENT . (E. D. McGarry, D.

Gilliam, C. Eisenhauer, and G. Lamaze). Dosimetry methods for monitoring the

degradation of materials in high fluence neutron exposures are diverse. This

project provides some form of measurement assurance, standardization, or methods development for nearly every approach to materials dosimetry employed

in the United States. Interlaboratory measurement cooperation with

substantial International participation are an important feature of this

project.

NIST/Nuclear Regulatory Commission (NRC) Contract . The 1977 Rancho

Seco Reactor incident demonstrated that it was possible for a nuclear

pressure vessel subjected to thermal shock to also experience significant

pressure loading. This was of particular importance to subsequent studies

that showed that relatively small flaws subject to pressurized thermal shock

(PTS) could lead to failure of the pressure vessel. The possibility of small

flaw development increases with hardening and loss of ductility of the

pressure vessel, which takes place in carbon steels subjected to neutron

irradiation. By law. Title 10 of the Code of Federal Regulations, Appendix

G and H require that a program, involving irradiation of metallurgy test

specimens and dosimeters, be <:arried out for the surveillance of pressure

219
NON-RRD PROGRAMS

vessel embrittlement damage. Consequently, the NRC in late 1977 identified

the need for improved surveillance of reactor pressure vessels. In practice

this means more and better fast neutron dosimetry and improved fluence

calculational capability. Improvement implies better methods as well as better assessment of the uncertainties of derived parameters. The NRC

carried out an 11-year international program (1977-1988), the Light Water

Reactor Pressure Vessel Surveillance Dosimetry Improvement Program (LWR-PVSDIP), dedicated to this task. NIST participated in activities to benchmark

reference dosimetry measurements and calculations, and continues as consultant to the NRC.

NRC Regulatory Guide Preparation . A regulatory guide to provide

guidance for improving and benchmarking neutron transport calculations is

being drafted. The guide is in the form of instructions on important aspects

of calculations, on dosimetry needed to validate the calculations, and on the reconciliation of differences between measurement and calculation

including the assignment of uncertainties. NIST is a major participant in

the formulation of this document, the preparation of which will continue into

FY 90.

Neutron surveillance dosimetry measurements are generally made in

special capsules containing dosimeters and metallurgy test samples. They are located in the water between the reactor core and the pressure vessel.

Calculations are necessary to extrapolate results from these capsules to the

one-quarter thickness of the pressure vessel, the established point of

interest for reactor licensing. The extrapolation is carried out after the

calculations have been confirmed by, or normalized to, the measurements in

the surveillance capsule.

ASTM Benchmark Standard Balloted . Another draft of an ASTM Standard

Guide for benchmark referencing of neutron dosimetry for reactor pressure

vessel surveillance, E706IIIB [1], was prepared by NIST and was accepted for

ballot after revision by the ASTM E10.05 Subcommittee meeting in Orlando,

Florida, January 1989. A revised draft was balloted at the June 1989 E10.05

Meeting in Scottsdale, Arizona.

NIST/Westinqhouse Cooperative Agreement . Measurement assurance activities with respect to Solid State Track Recorders (SSTRs) developed by

Westinghouse Science and Technology Center (formerly Westinghouse Research)

continues. The trend in the nuclear power industry to implement SSTR

220
NON-RRD PROGRAMS

dosimetry in ex-vessel cavities also continues. The bulk of these interests

centers around work taking place in Westinghouse PWRs and in the B&W Owner's

Group Davis Besse Dosimetry Benchmark Experiment. NIST is specifically

interested in problems associated with establishing reliable masses for the

SSTR fissionable deposits which are in the pico-gram to nano-gram range.

Generally, mass uncertainties in conventional dosimeters are not

significant. At the picogram and nanogram level in SSTR dosimeters, however,

the amount of material and the uniformity of the fissionable deposit present

difficulties. The latter, in particular, is not always distinguishable from

the effects of neutron fluence gradients. Westinghouse has largely circumvented the latter problem by using a readout system that provides two and

three dimensional graphics of the fission track density over the whole

surface of the SSTR. The problem of total mass is less easily solved. NIST

has taken on the task of providing a basis for establishing mass scales of

237j^p^ 235y^ 238^^ ^^^ 239p^ ultra-lightweight deposits in Westinghouse SSTR

dosimeters. This involves exposing the heavier of the lightweight deposits

235

to known neutron fluences. These irradiations are carried out in the U

Cavity Fission Source at the NIST Reactor to an accuracy of about 2.5% (la).

238

Initial results for U suggest that there is a 5% discrepancy between masses assigned on this basis and those determined at Westinghouse by spiking

and alpha counting techniques.

The IAEA Advisory Group Meeting on Nuclear Data for Radiation Damage

Assessment and Related Safety Aspects will meet in September 1989 in Vienna,

Austria. NIST will co-author a paper with Westinghouse Research entitled,

"Benchmark Referencing of Ultra Low-Mass, Solid State Track Recorder Neutron

Dosimeters in NIST Standards Neutron Fields."

Calibration of BELGIAN Cavity Fission Source . NIST personnel traveled

to Mol , Belgium in December 1988 to re-establish the tie between the NIST and

235

CEN/SCK fission neutron fluences in their respective U Cavity Fission

Sources. The basic calibration measurements were made with a NIST dual

fission chamber containing fissionable deposits identical to those used in

the calibration accomplished at Mol by NIST (then NBS) in 1983. Measured

fission rates agreed to about ± 1% (la). This is a significant result

because in the interim NIST had to repair and re-calibrate the run-to-run

monitor used to maintain the absolute fluence scale of the Belgian Cavity

Fission Source.

221
NON-RRD PROGRAMS

235

The calibration of the Belgian U fission field also affects the NIST

235

U Cavity Fission Source calibration because of complementary features of

235

the two sources. The NIST U fission source strength is almost two orders

of magnitude higher than the Belgian source but the volume available for

experiments is much smaller. The larger experimental volume in the Belgian

source is more appropriate for NIST fission chambers and hence the direct

fission chamber calibration in Belgium may be transferred back to the NIST source with some reduction in uncertainty. This cycle of calibration was completed in December 1988.

VENUS Benchmark Participation . The most active use of the Belgian

Cavity Fission Source for the past several years has been to calibrate

miniature fission chambers for active dosimetry in the Belgian LWR-PV

Benchmark Experiment, VENUS, at their CEN/SCK Laboratory in Mol , Belgium.

The VENUS series of PV benchmark experiments confirm neutron transport

calculations of dosimetry measurements in the vicinity of fuel corners and

out through the pressure vessel into the ex-vessel cavity. Additional checks

involve ex-core calculations associated with matters of high fuel burnup.

The VENUS experiments started in 1983 and have just been completed this year.

The primary NIST function has been to provide supplementary benchmark calibrations and "hands-on" verification of the CEN/SCK benchmark referencing.

VENUS Absolute Power Calibrations . NIST became involved in the VENUS

235

power determination when the U mass of in a commercial miniature fission

chamber was determined at the reactor thermal column [2]. These small sealed

fission chambers make it possible to probe down in between the fuel plates in

a low-power core and, without disturbing the thermal fluence rate, make

vertical and horizontal scans of the absolute fission rate over the core

volume. This powerful technique for determining absolute core-power levels

235 was first employed in pool critical assembly (PCA) [3]. The reported U mass of 4.72 ± 2% /xg was determined by comparing fission rates with a known- mass deposit from the NIST inventory.

Corrections for gradients, relative spatial locations, and thermal

fluence perturbations have made this measurement the subject of extensive

discussions on both sides of the Atlantic. The matter was of some importance

because the chambers involved were also used to determine the absolute core power of the earlier benchmark, PCA, operated at Oak Ridge National

Laboratory (ORNL).

222
NON-RRD PROGRAMS

Now, after 8 years of additional work in which the Belgians have

considerably advanced the state-of-the-art in the determination of absolute

power levels in experimental reactor facilities, the "4.72 ng U mass"

stands as the constant that links three expensive VENUS campaigns to PCA.

The reason is that through 10 years of effort the NIST calibrated miniature

fission chamber was the common instrument used in all experimental

configurations.

Dosimetry Methods Development for Reactor Support Structures . An NRC

priority effort in the Heavy Section Steel Technology (HSST) Program this

year was evaluation of the implication of low-temperature low-fluence-rate

embrittlement on reactor vessel support structures. This issue arose from

findings of higher than expected embrittlement in the High Flux Isotope

Reactor (HFIR), at ORNL, and in the reactor shield tank from the Shippingport

Reactor. The HSST staff studied and categorized all LWRs [4] into support

structure types, and then selected two specific plants for detailed review.

One aspect of this review will be to obtain dosimetry measurements and

neutron transport calculations near critical support structures in two

operating reactors. NIST is responsible for consultation and contracting for

the dosimetry measurements and for benchmarking these measurements against

NIST standard neutron fields. The benchmarked dosimetry will be used to

adjust the calculations at the dosimeter locations. The calculations will be

used then to specify the radiation damage exposure at the support structures.

Dosimetry at the Tro.ian Reactor . Two commercial power reactor

installations have been selected for plant-specific evaluation of major

reactor support integrity. They are the Trojan Reactor in Oregon and the

Turkey Point Reactor in Florida. Current preparations for ex-vessel

dosimetry experiments in Trojan are under NIST direction and will include a measurement assurance component. The plan is to place dosimetry packages as close as possible to a support structure buried in the concrete of the

biological shield. These measurements will then be used to normalize or adjust neutron transport calculations used to predict cumulative exposures at

critical flaw depths in the support structure. Contracts will be let for the

dosimetry in FY 89 and the irradiation will take place in 1990. All

dosimeter-evaluation systems must be benchmarked prior to obtaining the

Trojan measured results in 1991.

223
NON-RRD PROGRAMS

PUD Neutron Sensors for Out-of-Core Reactor Dosimetry . Second only to

237

the fission of Np for good spectrum coverage of neutron with energies E > 238

1.0 MeV, U is the desirable reaction for PV surveillance dosimetry.

However, in such partially thermal ized spectra, the fission in small concen- trations of U remaining in depleted U can require a significant

correction. Avoiding this correction by using highly depleted uranium is

expensive and the material is becoming scarce. The Paired Uranium Detector

(PUD) dosimetry technique was developed at NIST to circumvent the need for

' 238 ?3*i 238

the highly depleted U material and to obtain a measure of the U/ U

fission ratio, an important neutron spectrum index.

The technique involves simultaneous irradiation of moderately depleted

23R ?^R

uranium (approximately 200 pm U) along with natural uranium as the U

detector. Both materials are readily available. The small concentration of

U in natural uranium (0.7%), with low self-absorption, gives the U

response correction for the depleted uranium detector and a reasonable value

of the 235^j^238^j spectral index. The ^"^^U detector of the PUD pair can be

235 directly calibrated in the U fission neutron spectrum of the Cavity

Fission Source at the NIST Reactor and the quality assurance of the depletion

can be checked in a thermal neutron beam. The uncertainty enhancement

associated with the composite response in each detector has been documented.

Energy Response of Innovative Electronic-Hardware Dosimeter . The

Nuclear Effects Directorates (NED) at the Aberdeen Proving Ground has been

evaluating a new personnel dosimetry system for battlefield use by the Army.

Special NIST neutron-field facilities were used to establish the neutron

energy sensitivity of this semiconductor device. Multiple irradiations were performed for NED in a thermal neutron beam, in the 2-keV scandium filtered

beam, in the 24-keV iron filtered beam, and at the 144-keV silicon filtered

beam, all at the NIST Reactor, and at several Van de Graaff beams, and

finally at the NIST ^^^Cf source. Applications of PUDs in Benchmark Experiments . PUD detectors, furnished

by NIST, were first employed in the ORNL/PSF Surveillance Capsule Perturbation Experiment and in the ORNL/SDMF-4 Dosimetry-Method Comparison

Experiment [4]. In the latter experiment, detector pairs, furnished by NIST, were placed along with conventional single isotope radiometric fission

detectors front, back, and inside of a pressure vessel wall simulator. The

results are reasonably consistent among the three fission products counted,

224
NON-RRD PROGRAMS

103 including the sometimes troublesome Ru fission product activity. The

poo 0'i<^ observed spectral indexes ( U/ U) indicate an expected spectrum hardening

in going from the front water/steel interface to the vessel quarter thickness

as epithermal neutrons from the water are absorbed. Continued degradation of

the spectrum occurs deeper in the steel as inelastic scattering in iron

238 transfers neutrons to below the U response threshold.

Following these ORNL pressure-vessel simulator benchmarks, PUDs were

used to back up SSTR measurements in the first low-level leakage core measurements at the H. B. Robinson commercial power plant. The NIST/PUD

measurements were made in both the surveillance capsule and in the ex-vessel

cavity to confirm generic through-wall transport calculations and decreased

fluence-rates in low-leakage cores. Following these benchmark measurements, PUDs have become useful as ex- vessel cavity fluence dosimeters in commercial power plants. These include

the Diablo Canyon, Turkey Point, and the Zion reactors. All of this is

carried out as part of the NIST/Westinghouse cooperative agreement.

PERSONNEL DOSIMETRY (R. Schwartz, C. Eisenhauer, J. Coyne, and E. Boswell). Standard neutron fields are used to calibrate radiation protection

instrumentation and to investigate and test new types of dose measuring

techniques. Responsibilities in national and international dosimetry methods

research focuses on tissue dose modeling, and tissue equivalent proportional

counter (TEPC) measurements, and the development of written standards.

Calibration Service . Approximately 60 neutron radiation protection

instruments were calibrated this year. Although the majority of the

calibrations were done for commercial nuclear power plants, our "customers"

also included institutions as diverse as Redstone Arsenal and the M. D. Anderson Cancer Center. For the past year we have also been performing tests

of the "electronics package," before performing the actual neutron calibration. This allows us to detect nonlinearities or instabilities which are difficult to pin down using neutron sources alone.

Performance Tests of "Bubble Dosimeter." The new "bubble," or superheated drop detectors represent a new and promising approach to neutron

dosimetry. We are involved in a joint project to determine the relevant

properties of these detectors. The other "players" include the Naval Surface

225
NON-RRD PROGRAMS

Warfare Center, the U.S. Naval Academy, the Naval Research Laboratory, and

the National Physical Laboratory (NPL) in England.

While we still have many data to analyze, it so far appears that the

"bubble dosimeter" (supplied by Bubble Technology, Inc., (BTI)) has high

sensitivity, a good dose equivalent response, and is quite linear up to the

point where the bubbles can no longer be accurately counted. Fewer data have

been analyzed for the SDD-P (a pen-sized neutron personnel dosimeter supplied

by Apfel Enterprises, Inc.,) but this device also seems to have a good dose

equivalent response. Although intrinsically less sensitive than the "bubble

dosimeter," it is much easier to read. We are currently analyzing the large

amount of energy response data taken at a recent visit to NPL, and will

shortly be measuring the response as a function of temperature for several of

these devices.

TEPC Dose Measurement for Neutron RBE . The Armed Forces Radiobiology

Research Institute (AFRRI) recently obtained very surprising results in

experiments which examined the relative biological efficiency (RBE) for

lethality in mice exposed to reactor radiations. In brief, the experiments

indicated that a slight (5%) addition of neutron dose, into a pure gamma-ray

field, decreased the lethal dose for the mice by almost 40%. The neutron and

gamma-ray dose components were determined by conventional AFRRI ion chamber

dosimetry. In an effort to shed some light on this totally unexpected

result, we measured the linear energy transfer (LET) spectra in some of the

AFRRI fields, using a tissue-equivalent proportional counter (TEPC). The

results of this measurement disagreed with the AFRRI ion chamber dosimetry.

Specifically, our results indicated that the supposedly 5% neutron field

actually had a neutron dose approximately equal to the gamma-ray dose; i.e.,

the field was ~ 50% neutrons. If the dosimetry derived from our TEPC results

is used to interpret the data from the "mouse experiments," then there are no longer any surprises. It should be pointed out that since the efficiency of

the TEPC is very high, the reactor had to be run at very low power, and our experiments were limited to measurement of the neutron-gamma ratios for

various configurations similar to those used in the mouse experiments. There

was no attempt made to determine the absolute doses used in the actual

experiments. We are currently trying to understand this difference in

dosimetry, and, in particular, we are running the TEPC in known neutron,

226
NON-RRD PROGRAMS

gamma-ray, and mixed neutron-gamma fields to establish the accuracy and

reliability of the system.

Catalog of Neutron Spectra for AFRRI . A catalog of neutron spectra

requested by the Armed Forces Radiobiological Research Institute has been

completed. This catalog gives tabulations and plots of calculated fluence

spectra, plots of calculated and measured energy deposition spectra, reaction

rates measured with neturon activation foils and neutron fission chambers,

neutron kerma rates measured with ionization chambers, and comparisons of

measured and calculated quantities.

ICRU Publication on Practical Determination of Dose Equivalent . In a landmark publication ("Determination of Dose Equivalents Resulting from

External Radiation Sources," ICRU Report 39 (February 1, 1985)), the

International Commission on Radiation Units and Measurements (ICRU)

recommended a new system for determining the dose equivalents resulting from

exposure to external radiation sources. The advantages of the new system

included a uniform approach to dose equivalent determination and reporting

for gamma-rays, electrons, and neutrons, as well as a close link with the

fundamental limiting quantity, effective dose equivalent (as defined in ICRP

Publication 26). ICRU 39 is, however, a very terse document, giving little more than the definitions of the new dose equivalent quantities. Accordingly,

another report committee was set up by the Commission to produce a document

on practical determination of dose equivalents; i.e., how one uses the new quantities in practical radiation protection measurements and calibrations.

In the rather short time--as these things go--of just over 2 years from our first organizational meeting, an "almost-final" draft was submitted to the

Commission for its preliminary approval. Unfortunately, it does appear that

we are shooting at a moving target. At a recent meeting, the Commission

decided that the document should be split into two separate reports: the

first on gamma-rays and electrons, and a second, separate publication on neutrons. This, despite the fact that one of the advantages of the new system was the unification of the dose equivalent definitions for the three

types of radiations, and the fact that the draft text was carefully crafted

to emphasize this unification. In addition, some Commission members are questioning the definitions of some of the quantities, -and the phantom,

specified in ICRU 39. We anticipate further interesting developments.

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NON-RRD PROGRAMS

Radiation Protection Policy Committee Work . C. Eisenhauer serves as chairman of a subpanel of the Science Panel of the Committee on Interagency

Radiation Research and Policy Coordination (CIRRPC). The subpanel has

produced a report on the desirability of planning for research on human

health effects in the event of a nuclear accident. The subpanel recommended

a follow-up effort to recommend ways of implementing such planning.

RESEARCH AND TECHNOLOGY ASSISTANCE (all group members). Research and

technology assistance are strongly coupled in neutron dosimetry. A multiplicity of institutional involvements, drawn to the group by the availability

of unique irradiation facilities and measurement capabilities, encourages a variety of attractive projects and unavoidable responsibilities.

Neutron Lifetime--Abso1ute Neutron Counting . An overview of the NIST

involvement in measurement of the free neutron lifetime is given in the

Fundamental Physics section of the NON-RRD program reports. The paragraphs

in this section will discuss only one aspect of the experiment--the

improvements in the absolute neutron counting under development for the

upcoming new phase of the project at the NIST guide hall. In the measure- ments made at the Institut Laue-Langevin during the past year, the neutron

density determination was made by employing a B-10(n,a7) detector whose mass- thickness had been determined by isotope dilution mass spectrometry. In the new phase of the project at NIST, calibration of the neutron monitor will be

made by two new methods which do not depend on either the B-10 sample mass

nor the B-10 reaction cross section. The new methods are alpha-gamma

coincidence and calorimetry.

A new alpha-gamma coincidence counter for thermal and cold neutrons has

been built [2], based on the counting of prompt gamma rays from a boron

target which totally absorbs the impinging neutrons. In the calibration of

the gamma detectors, the totally-absorbing B-10 target is replaced by a thin

B-IO target and the alpha-gamma coincidence method is employed to establish

the efficiency of the gamma detectors. Alternatively, the gamma efficiency

can be determined by calibration with a standard alpha source with reference

to the well-known branching ratio for the B-10(n,Q!7) reaction. Both of the

calibration methods are believed to have the potential for approaching the

0.1% accuracy level, and a comparison of these two calibration techniques

228
NON-RRD PROGRAMS

will provide a test of consistency in assessing the accuracy actually

achieved. Figure 1 shows a photograph of the new apparatus.

Figure 1. The new alpha-gamma coincidence system.

In collaboration with scientists from Los Alamos National Laboratory

(LANL) and Harvard University, a Li-6 calorimeter was given initial testing

in a beam from the thermal column. This neutron counter operates by

measuring the heat derived from totally absorbing a beam of neutrons in a LiPb target. The observed thermal power and derived neutron flux were compared

with the flux derived from fission chamber measurements. These results were

found to agree within the ± 3% uncertainty of the fission chamber measurements. Future intercomparisons at more demanding accuracy levels are planned

with respect to the alpha-gamma coincidence method.

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NON-RRD PROGRAMS

Benchmark Measurements for Critical itv Safety . In collaboration with

the Department of Energy sponsored groups at LANL and ORNL, an experimental

program has been undertaken to improve the understanding of neutron leakage

from aqueous systems which are representative of situations occurring in

chemical processing of isotopes for nuclear weapons production. There has

been a long-standing difficulty in the field of critical ity safety analysis

in calculating critical ity of systems composed of multiple subcritical

assemblies. One possible explanation for the difficulty is that the

calculations are incorrectly predicting the neutron leakage from the

individual assemblies. The present program compares calculations by two of

the best Monte Carlo codes with state-of-the-art measurements for spherical

252

aqueous systems driven by Cf neutron sources. Fission ionization chambers

with fissionable deposits from the NIST collection of Fissionable Isotope

Mass Standards (FIMS) are employed to make the neutron leakage measurements.

Working deposits from the FIMS collection are calibrated with respect to the

reference deposits by comparisons made in beams from the reactor thermal

column and in other NIST neutron fields.

Measurements have been completed at one of two prescribed radii outside

a water-filled sphere of 4-in (10.16 cm) diam, including fission rates for

four different nuclides: ^^^U, ^^^U, ^^^Pu, and ^^^Np. It has been possible

to determine the ratios of count rates for the water-filled sphere relative

to the count rates for the empty sphere to an accuracy of the order of 1%,

because these ratios are independent of uncertainties in the source strength,

the deposit masses, and the detector positions (so long as they remain

fixed). The calculations and experiments are in good agreement for these

238 237 235 239 wet/dry counting ratios for U and Np. However, for U and Pu,

these wet/dry ratios are calculated to be 5 to 8% (respectively) higher than

measured. These results must be considered as preliminary until perturbation

studies of temperature variations and geometrical uncertainties have been

completed; but if sustained, these results could provide valuable guidance in

improving critical ity safety calculations.

Radiation Shielding Calculations for NIST Cold Neutron Research

Facility (CNRF) . Calculations have been made to determine shielding

necessary for two shutters to be installed at the CNRF. The first shutter

will be placed at the exterior face of the biological shield. Calculations

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NON-RRD PROGRAMS

were made for G. Lamaze using the discrete ordinates method, (ANISN computer

code.) Various combinations of iron, tungsten, borated polyethylene, and

lead were explored to determine an optimum configuration. The final

configuration was designed by G. Lamaze on the basis of these calculations

and the criterion that the dose equivalent rate due to neutrons and photons

emerging from the shield be less than 100 mrem/h.

The second type of shutter will be placed at the wall of the reactor

room. Calculations were made for I. Schrflder using both the discrete

ordinates and Monte Carlo methods. One area of concern in this case is the area near the shutter when the shutter is closed and acts like a beam stop.

Another area of concern is the area on the other side of the wall, which is

the interior face of a wall in the Guide Hall. Monte Carlo calculations were

used when the geometry was critical and discrete ordinate calculations for

thick-shield calculations. These calculations were used to design shield in

both areas. Neutron Penetration in Slabs of Finite Extent . Monte Carlo calculations

of neutron transmission through slabs have been performed to help the U.S.

Navy estimate shielding of personnel on submarines carrying nuclear missiles.

These calculations demonstrate that neutron and gamma-ray penetration is

insensitive to the position of a slab between a localized (point) source and

detector. Furthermore, an angular parameter can be specified such that the

relative contribution of neutrons or photons within that angle is also

insensitive to the slab position. This is equivalent to quantifying the

increase in scattered particles as one moves from a narrow-beam to a broadbeam configuration. A paper on this subject will be submitted for

publication in Nuclear Science and Engineering.

Nuclear Energy Exhibit at National Atomic Museum . The National Atomic

Museum in Albuquerque, NM, is developing a nuclear energy exhibit around an operating replica of Lady Godiva, an early experimental nuclear reactor and

nuclear historic landmark. The aim of the exhibit, summed up in its title:

Lady Godiva and the Realities of Nuclear Energy, is to engage public

perception of nuclear energy by means of an eminently displayable and

historically important nuclear reactor. A group member with unique

experience in this area of nuclear technology is a consultant for the

exhibit. Efforts this year have focused on the preparation and review of

texts for exhibit labeling and an introductory video.

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IRRADIATION AND CALIBRATION FACILITIES (E. D. McGarry, J. Grundl , C.

Eisenhauer, and E. Boswell). Well -characterized neutron fields built and

maintained as permanent irradiation facilities, provide certified fluences of

pure fission neutrons, sub-MeV distributions, monoenergetic keV beams, and

thermal neutrons. Passive and active detectors are exposed in these neutron

fields for response calibrations, for cross-section measurements, and for the

investigation of new measurement techniques. A multi-purpose fission rate

measurement capability is centered around the NIST "go anywhere" double

fission chambers and the NIST set of fissionable isotope mass standards

(FIMS). The Manganous Sulfate Bath is the primary neutron source strength

calibration facility for the United States. Absolute neutron fluences for

all fission-neutron-driven standard neutron fields at NIST are derived from source strength calibrations at this facility.

Fission Neutron Irradiation Operations . Spreadsheets and test reports

for certified fission neutron fluence irradiations have been reworked and

updated and are now on PC computers. The new general purpose shield cave for

storing high- and intermediate-level radioactive components is moving toward

completion. The shield walls and top section are finished and on the reactor

floor. Hardware for the rolling door is in hand. When complete, this shield cave will greatly simplify irradiation operations at the reactor thermal, not

only for the cavity fission source but also for the Intermediate-Energy

Standard Neutron Field (ISNF).

References

[1] McElroy, W. N.; McGarry, E. D., eds. LWR-PV-SDIP: service laboratory

procedures: verification and surveillance capsule perturbations.

NUREG/CR-3321, WHC-EP-0205, NRC, Washington, DC, December 1988.

235

[2] McGarry, E. D. Determination of the effective mass of U in the

fission chambers used for absolute core-power measurements in PCA.

Light Water Reactor Pressure Vessel Irradiation Surveillance Program , Quarterly Progress Report for the April, May, June 1980 Quarter.

[3] McElroy, W. N., ed. LWR-PV-SDIF: PCA experiments, blind test, and

physics-dosimetry support for the PSF experiments. NUREG/CR-3318, HEDLTME 84-1, NRC, Washington, DC, September 1984.

[4] Cheverton, R. D.; Pennell, W. E.; Robinson, G. C; Naust, R. K. Impact

of radiation embrittlement on integrity of pressure vessel supports for

two PWR plants. NUREG/CR-5320, January 1989.

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NUCLEAR METHODS GROUP: OVERVIEW

R. R. Greenberg

(Center for Analytical Chemistry)

The development and application of nuclear analytical techniques for

greater accuracy, higher sensitivity, and better selectivity are the goals of

the Nuclear Methods Group. A high level of competence has been developed in

both instrumental and radiochemical neutron activation analysis (INAA and

RNAA). In addition, the group has the unique capability of using neutron

beams as analytical probes for both prompt gamma activation analysis (PGAA)

and neutron depth profiling (NOP). NDP determines elemental (isotopic)

concentrations versus depth profiles within the first few micrometers of a surface by the energy analysis of the prompt charged-particles emitted during

neutron bombardment. PGAA, on the other hand, measures the total amount of

an analyte present throughout a sample by the analysis of the prompt gammarays emitted during neutron capture. These techniques (INAA, RNAA, PGAA and

NDP) provide a powerful combination of tools to address a wide variety of

analytical problems of great importance in science and technology.

The group has continued to contribute to the Standard Reference Material

(SRM) certification effort; this year's efforts include multielement

determinations performed on a number of SRMs including: Total Diet, Apple

Leaves, Peach Leaves, Oyster Tissue, Coal, and Marine Sediment. Group

members are serving as Technical Champions for many of these new SRMs, and as such are responsible for scientific decisions made throughout the production

and certification processes of these materials. Additionally, RNAA

measurements are currently under way to determine Hg in Bovine Serum and Se

in Buffalo River Sediment. This will allow the certification of two

additional, highly-important elements in these existing SRMs. A homogeneity

study has been completed on the new Apple and Peach Leaves SRMs which showed

that many elements were homogeneous to about 1% in 100 mg samples. In

collaboration with members from other groups in the Inorganic Analytical

Research Division, a study of these leaf materials has been undertaken to

identifying problems in the dissolution of these materials which can lead to

analytical errors during the certification analyses. A new ability to

quantify nitrogen in biological samples will result from this year's research

in developing an RNAA-liquid scintillation beta counting technique which

14 14 exploits the thermal neutron reaction N(n,p) C, and measures the activity

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of (radioactive) COp upon sample processing. This project is being done in

collaboration with the University of Illinois.

The International Conference on Nuclear Analytical Methods in the Life

Sciences, held at NIST from April 17-21, 1989, was organized by members of

the Nuclear Methods Group. At this conference, 144 participants from 32

countries presented papers and posters detailing recent advances of nuclear

analytical methodology in the life sciences. The conference pointed to the

continuing, essential role of nuclear methods in the life sciences, and

provided new emphasis for the group's research program in this field.

Recent applications of Neutron Activation Analysis (NAA) in the life

sciences by the group include "nonclassical" detection and determination of

"tags" associated with biological macromolecules such as proteins, enzymes,

and antibodies. In one application, an activatable tag has been attached to

an antibody used in a medical diagnostic test. The INAA determination of the

activatable tag is then used as the detection step of the diagnostic

analysis. Research is continuing on the polyacryl amide gel electrophoresis

neutron activation analysis technique (PAGE-NAA). The activation and

subsequent determination of phosphorus in phosphoproteins has already been

demonstrated. Research to extend this technique to the determination of

other elements in specific macromolecules is under way. Such advanced uses of NAA in the life sciences may open a wide variety of applications for

nuclear analytical chemistry.

The Biomonitoring Specimen Bank Research Project continued its research

support for other agencies' monitoring programs. These programs included the

Environmental Protection Agency's human liver project, the National Oceanic

and Atmospheric Administration (NOAA)'s National Status and Trends (NS&T)

program, the National Cancer Institute's micronutrient program, the

International Atomic Energy Agency (IAEA)/NIST/Food and Drug Administration

(FDA)/U.S. Department of Agriculture (USDA) Total Diet Study, and most

recently, the NOAA Alaska Marine Mammal Project. Research has centered on specimen banking protocols and improved analytical methodology. The group's

participation in intercalibration exercises with the project participants and

the development of QA materials for various marine analyses helped to enhance

the quality of the analytical results used in the assessment of the

environmental health of the nation. Of major importance this year has been

the analysis of samples from 30 NOAA NS&T sites. Both essential and

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pollutant elements have been studied to assess the effects of anthropogenic

inputs to the environment.

The joint NIST/FDA/USDA study of trace elements in human diet, sponsored

by the IAEA, has completed its fifth year. A total of 120 diets from

different countries have been analyzed to date for minor and trace elements.

Nine diets from different regions of the United States have also been

collected, and thus far, six have been analyzed. The data obtained from the

U.S. diet composites have confirmed daily intake results for some of the

elements investigated by the FDA (based on individual food analysis), as well

as established reliable daily dietary intakes for additional elements

including B, Cr, Cs, Li, and Sn. In the case of Li, the observed intake

values are considerably lower than earlier published results. The group

has taken an active role in the NIST program on high-temperature

superconductivity research, both in the measurement of impurities in starting

materials and final products, and the determination of the actual

stoichiometry of the metallic constituents. The effort this year has

centered on the development of accurate, rapid measurements of these

materials by both NAA and PGAA. An effort to establish an accurate, monitor

activation analysis technique for further study of high-temperature

superconductors at NIST is under way.

Nearly a decade ago, a systematic error for PGAA was observed in which

elemental sensitivities (counts/j[tg-s) increased with increasing hydrogen

concentration. Sensitivities in hydrogenous samples have been observed to

increase by up to approximately 25% relative to samples with little H. This

error was handled previously by matching H concentrations in samples and

standards without any real understanding of the problem. During the last

year, substantial progress has been made in understanding the problem on a theoretical level. In addition, systematic, experimental solutions to this

problem are currently under investigation. The sensitivity enhancement seems

to be caused predominantly by neutron scattering. This scattering can increase the neutron path length within the sample for some sample

geometries, and thus may enhance the probability of neutron absorption.

Measurements have been made which demonstrate this sensitivity enhancement as

a function of H concentration for 11 elements in samples of constant size and

shape. In a second set of measurements made on a series of disk-shaped

pellets with constant H concentration but varying thicknesses (shapes),

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elemental sensitivities were observed to increase with decreasing sample

thickness. These general trends have been predicted by theoretical

calculations. Our current understanding of this problem indicates that

effects of scattering on sensitivities can be minimized or perhaps eliminated

by irradiating spherical samples. A final series of measurements made on spherical samples with constant H concentration, and varying diameters (and

thus masses), has indicated that the use of a spherical geometry greatly

reduces, and perhaps eliminates, this problem.

A novel technique of PGAA analysis of gas samples has been developed

using both the currently available thermal neutron beam at the NIST reactor

and the ELLA Cold Neutron Facility at KFA, Jlilich. Feasibility studies

involving noble gases and gas mixtures indicate that sensitivities in the

sub-ppm range for a number of elements should be achievable using the new NIST cold-source PGAA instrument which will be operational in FY 90. The

development of a nuclear technique for gas analysis will establish an independent analytical method for reference material certification.

During the past year, a large part of the group's efforts has been

directed at the exploitation of the analytical applications of cold neutrons.

These efforts are needed to take full advantage of the guided beams of cold

neutrons soon to be available at the new Cold Neutron Research Facility

(CNRF). Plans are underway to include both PGAA and NOP experimental

systems in the first phase of implementation. The group's involvement

includes the design and construction of state-of-the-art instruments for both

PGAA and NOP. Last year, the cold source itself was installed and became

operational, and construction of the guide hall was completed during the

first part of this year. The group's efforts have been aided substantially

by its ability to use the existing cold neutron beams at the KFA JUlich

facility. A major grant from the Eastman Kodak Company is contributing to

the timely development of the NOP cold-neutron instrument. In order to

introduce these new instruments to the potential user community outside of

NIST, the Nuclear Methods Group organized a workshop on Analytical

Measurements with Cold Neutron Beams, which was held May 22-23, 1989. This was the third in an ongoing series of workshops on the uses of cold neutrons

organized by NIST.

Research on the new recoil -nucleus time-of-flight NOP technique has

focused on the problem of detecting (with good energy resolution) the low

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energy heavy nuclei which are emitted along with the light nuclei used in

conventional NDP. These heavy nuclei can be used to provide very high

resolution depth profiling capabilities in the sample region \/ery close to

the surface. Initial measurements appear to have validated this approach,

and efforts are under way to determine how closely the actual depth

resolution measured will approach the calculated values.

A long-range program to explore and develop the analytical applications

of focused beams of cold neutrons has been initiated within the group. The

ultimate goal of this research is to produce beams of neutrons which have

intensities several orders of magnitude greater than previously available.

Such beams will greatly enhance the capabilities of both PGAA and NDP, and

may ultimately lead to a neutron milliprobe or even microprobe. The neutron

microguide appears to be the most promising approach to achieve analytically

useful focused neutrons, and as a first approach, a device will be developed

and tested using a stack of nickel -coated single-crystal silicon wafers as focusing elements.

The strong interaction with industrial scientists using NDP, PGAA, and

NAA has continued this year with a growing number of guest workers, research

associates, and joint publications. An important development has been the

demonstration of two-parameter coincidence spectroscopy (in NDP) for thin

samples, in collaboration with the NDP group at the University of North

Carolina and with Eastman Kodak. For appropriate samples, this technique

provides an increase in sensitivity equivalent to more than a tenfold

increase in reactor neutron flux. The measurement of distributions of

lithium and boron in metals, glasses, and polymers continues to produce

important results.

The Nuclear Methods Group is collaborating with scientists from the NIST

Center for Atomic Molecular and Optical Physics, the NIST Center for

Radiation Research, and the University of Sussex in a new measurement of the

neutron lifetime. The goal of this research is to provide a new value for

the neutron lifetime with an uncertainty of less than 0.3%. The current

uncertainty for the neutron lifetime is about 0.6%. The technique used

involves detecting the protons which decay in a neutron beam passing through

a superconducting-magnet proton trap. Such measurements have been made with

a cold neutron beam at the Institut Laue-Langevin in Grenoble, and additional

measurements will be made at the new NIST CNRF next year.

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During the coming year the group will continue to improve the accuracy,

productivity, and sensitivity of nuclear methods as applied to elemental

measurements. Problems to be addressed include those inherent in sample

preparation, irradiation, radiochemical separation, counting, and data

reduction, with the goal of minimizing and quantifying various sources of

random and systematic errors in analysis by nuclear methods. Maintaining

full accuracy at high count rates using current-generation data-acquisition

electronics is the goal of our count-rate-dependent studies. Accurate

quantification of gamma-ray self-absorption and measurement of the shape of

the efficiency curve are required for accuracy in monitor activation analysis

(since matching of sample with primary standards is not done). The development of monitor activation analysis is part of the high-temperature

superconductivity effort to achieve rapid sample turnaround with minimum

sacrifice of accuracy; however, the approach will also provide good quality

control when used in parallel with traditional primary standard NAA.

INAA HOMOGENEITY MEASUREMENTS ON THE NEW NIST LEAF REFERENCE MATERIALS

D. A. Becker

(Center for Analytical Chemistry)

The first natural matrix, widely distributed reference material was Bowen's kale, produced and evaluated by Humphrey J. M. Bowen of Reading

University, U. K. [1]. This material demonstrated to the scientific

community the usefulness of such reference materials, and shortly afterwards

the National Bureau of Standards (NBS) brought forth the first such material

to be certified for trace elemental content [2]. Eventually, SRM 1571

Orchard Leaves was certified by NBS for 25 elements, with information values

and/or compiled literature values for 42 additional elements [3], for a total

of 67 elements. The Orchard Leaves SRM has been out of stock for a number of

years, and was replaced by SRM 1572, Citrus Leaves. The Citrus Leaves were certified by NBS for 22 elements, with information values and/or compiled

literature values for 35 additional elements, for a total of 57 elements.

NIST has obtained and prepared a new "orchard leaves" reference material

to be certified for elemental content. Actually, the previous orchard leaves

are being replaced by two new leaf materials: Apple Leaves, SRM 1515 and

Peach Leaves, SRM 1547. These two materials have been obtained and prepared

238
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for certification work, and this paper discusses some of the work on these

materials to date.

Since the intent was to improve these new leaf SRMs in relation to the

old leaf SRMs as well as other currently available botanical reference

materials, a number of new or revised procedures were developed to better

evaluate the SRM preparation procedures. These included the following:

handpicking of the apple leaves followed by washing prior to grinding, to

help remove dirt and siliceous material (a significant problem with the

Orchard Leaves; washing was not done with the peach leaves, to determine

differences, if any); jet milling and air-classification to obtain very small

particle size, to allow evaluation of homogeneity at smaller sample sizes; a detailed moisture content and moisture uptake evaluation, along with weight

loss measurements during drying; and, a dissolution study to help establish

both the "insolubles" content of the leaves, if any, plus evaluate the

ability of different dissolution techniques to totally solubilize the leaf

materials. The space available here is not sufficient to present all of the

information; however, the instrumental neutron activation analysis (INAA)

homogeneity data are presented in tables 1 and 2, and fluence monitor data

documenting the constant fluence rates in the RT-4 pneumatic tube facility

are presented in figure 1.

Since these leaf materials were ground to extremely fine particle sizes

through use of a jet-mill, it was expected that a very high degree of

homogeneity would be obtained. The homogeneity study was thus designed to

establish whether smaller than the usual 250 mg sample size could be

specified while still maintaining appropriate certification uncertainties.

The homogeneity study was made by INAA, with a sample size of 100 mg.

Experimental conditions are as follows: short half-life isotopes were

13 -2 -1

measured after a 60 second irradiation at 2 x 10 n«cm s fluence rate

(RT-4 at 15 MW power level), with four counts usually at 2, 9, 22, and 60

minutes decay. Counting geometries were always at or greater than 10 cm for

these counts, and data were corrected for differences in irradiation time

(using copper foil fluence monitors), decay time before counting, live time

of count, decay during counting period, pulse pileup, and for weight losses

during drying. For these preliminary results, the elements determined under

these conditions were aluminum, calcium, manganese, potassium, sodium, and

chlorine.

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Activation products with half-lives of one day or more were determined

after a second irradiation on these same samples, this time for four hours at

13 -2 -1 a fluence rate of 6 x 10 n«cm s (RT-1 at 15 MW power level). Samples were counted twice, after approximately 6 days and 30 days. These 4 hours

irradiations were actually two 2-hour irradiations. After the first

irradiation, each rabbit was immediately flipped end-for-end, and irradiated

for an additional 2 hours. With the specific configuration of the NIST

reactor pneumatic tubes, this exactly corrects for the linear fluence dropoff

in these tubes, providing all samples with exactly the same neutron exposure

(within measurement uncertainties of ± 0.25%). For these preliminary

results, the elements lanthanum, scandium, cobalt, iron, chromium, samarium

(apple leaves only) and bromine (peach leaves only) were measured under these

conditions.

In addition to those corrections specified above, conditions were monitored as closely as possible to eliminate or minimize all sources of

error in these analyses.

The results for SRM 1515, Apple Leaves are contained in table 1, and

results for SRM 1547 are contained in table 2. The measured homogeneity of

both these materials is very good, with "Additional Variance" requirements of

up to about 2% for most elements measured. It should be noted that the

"Additional Variance" value includes all experimental uncertainties in the

entire measurement process (preparation, irradiation, counting, and data

reduction) except for the counting statistics (a).

In order to evaluate the effect of the copper foil fluence monitor

correction on the short half-life measurements, potassium values shown in

table 1 for Apple Leaves were recalculated without using the fluence monitor

correction factor. The copper foil data had an experimentally observed

standard deviation of 1.014% (Is) for 42 irradiations (n = 42) over a 56 day

period, while the counting statistics for this data (a) averaged 0.11%

(fig. 1). Without the copper foil fluence correction factor, the Apple Leaf

potassium values had s = 1.07%, a = 0.56% (since counting statistics are the

same), and an "Additional Variance" of 1.00%. Since use of the fluence

normalization factors reduced the experimentally observed variability (s)

from 1.07 to 0.55%, this demonstrates the need for such fluence monitoring

when high precision data is required, and when irradiations are performed

over a relatively long period of time. Further, the above data was

240
NON-RRD PROGRAMS

calculated with only 13 data points for the non-fluence corrected potassium

values because one irradiation was known to be about 12% longer than the

others due to operator error. However, when the fluence monitor correction

was applied this value was indistinguishable from the other 13 values, and

thus was included in the fluence corrected data in table 1.

In conclusion, the data in tables 1 and 2 indicate that these two new

SRMs are homogeneous at the 100 mg sample size to better than ±1.5% at the

Is confidence level for at least six elements, plus better than + 3.0% for at

least three addi tonal elements.

Table 1. Homogeneity results for SRM 1515, Apple Leaves . Excess Variance Additional

Element n14^S^ 0^ Observed?

No

Variance

Potassium 0.55% 0.56% 0.0%

Manganese 14 0.63% 0.16% Yes 0.62%

Aluminum 15 0.72% 0.61% No 0.42%

Calcium 13^ 0.92% 0.91% No 0.30%

Lanthanum 15 1.07% 0.26% Yes 1.07%

Samarium 14 1.33% 0.10% Yes 1.37%

Sodium 14 5.41% 1.90% Yes 5.20%

Chlorine 14 1.44% 0.68% Yes 1.30%

Scandium 15 1.91% 0.81% Yes 1.72%

Cobalt 14 2.95% 1.68% Yes 2.31%

Iron 15 5.58% 2.74% Yes 4.46%

Chromium 15 12.82%

mean (in /

... 1 1 „.

9.61%

'o relative).

No 5.00%

^ s about

b „ „„.._„.. unweighted

/ w.»i .-•- : ..»\

Determination of excess variance based upon agreement between s and a

(i.e., whether s fell between 5-95% probability for a normal population).

Additional variance required to bring "probability of exceeding" to 50 ± 2%

for a normal population. For the elements scandium, cobalt, iron, and

chromium, this "Additional Variance" must include an estimated 2% random

uncertainty due to the very close counting geometry. All other analytical

uncertainties including any inhomogeneity are also located in the

"Additional Variance" column as well.

One homogeneity sample was lost for all determinations except aluminum,

lanthanum, scandium, iron, and chromium.

A second sample was counted at a different geometry, thus could not be

directly compared to the others.

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Table 2. Homogeneity results for SRM 1547, Peach Leaves

Excess Variance Additional

Element n

15

s^ a^ Observed? Variance

Potassium 1.03% 0.45% Yes 0.95%

Manganese 15 0.74% 0.10% Yes 0.76%

Aluminum 15 1.44% 0.61% Yes 1.35%

Calcium 15 0.89% 0.91% No 0.0%

Lanthanum 15 0.79% 0.17% Yes 0.74%

Bromine 15 0.90% 0.39% Yes 0.84%

Sodium 15 3.34% 2.35% Yes 2.43%

Chlorine 15 1.83% 1.04% Yes 1.59%

Scandium 15 2.62% 0.64% Yes 2.58%

Cobalt 15 2.43% 1.13% Yes 2.11%

Iron 15 2.87% 1.08% Yes 2.69%

Chromium 15 5.56% 4.09% Yes 2.92%

s about unweighted mean (in % relative).

A priori uncertainty based only on counting statistics (in % relative).

^ Determination of excess variance based upon agreement between s and a

(i.e., whether s fell between 5-95% probability for a normal population).

Additional variance required to bring "probability of exceeding" to 50 ± 2%

for a normal population. For the elements scandium, cobalt, iron, and

chromium, this "Additional Variance" must include an estimated 2% random

uncertainty due to the very close counting geometry. All other analytical

uncertainties including any inhomogeneity are also located in the

"Additional Variance" column as well.

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+3%

+2% -

+1% -

Mean

Conditions

60 second irradiations

RT-4 pneumatic tube n = 42

Time period = 56 days

I

I

i i' j L

i

•1% -

-2% -

-3% L

u

I i

I

J

S about weighted mean = 1.014%

Observed s.d. of mean =0.156%

A priori s.d. of mean =0.016%

Figure 1. Copper foil fluence monitor data,

References

[1] Bowen, H. J. M.; Cawse, P. A. Production of a homogeneous biological

material for intercomparison of elementary analyses by different

laboratories in Activation analysis: principles and applications,

Lenihan, J. M. and Thompson, S. J., eds. Academic Press (1965).

[2] Smith, G. W.; Becker, D. A. Preparation of an NBS biological SRM for

trace elemental analysis, in Nuclear activation techniques in the life

sciences. IAEA, Vienna (1967).

[3] Gladney, E. S. et al . Compilation of elemental concentration data for

NBS clinical, biological, geological, and environmental SRMs, Natl. Bur.

Stand. (U.S.) Tech. Note 260, 1987. Ill p.

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PROMPT GAMMA ACTIVATION ANALYSIS OF GASEOUS SAMPLES

R. Zeisler, C. A. Stone, W. D. Dorko

(Center for Analytical Chemistry)

and

M. Rossbach

(Nuclear Research Center (KFA), Julich, FRG)

Neutron-capture prompt gamma-ray activation analysis (PGAA) is an instrumental multielemental technique that has been successfully applied to

the analysis of a wide variety of sample types. Environmental, geological

and biological samples are routinely analyzed at thermal neutron PGAA

facilities. An advantage of the PGAA technique is that there is in principle

no limit to the sample size or type and its physical form. The PGAA

technique has been applied primarily to the analysis of small solid samples,

but in only a few instances has it been applied to the analysis of liquid

samples. It appears that PGAA has not been applied to the analysis of

gaseous samples. Although modern analytical chemistry of gases utilizes very

sensitive methods such as gas chromatography and mass spectrometry, a nuclear

technique based on PGAA will establish an independent analytical method for

reference materials certification. In addition, the technique may be

sufficiently sensitive to determine lower concentrations of certain elements

than is nowadays possible. In this contribution we present results from the

analysis of chlorine in nitrogen using the thermal neutron facility at NIST.

This work has been expanded to include measurements with a high flux, large

diameter guided beams of cold neutrons at the ELLA Cold Neutron Research

Facility of the Nuclear Research Center (KFA), Julich. The prospect of

performing analyses using cold neutrons dramatically increases the

applicability of this novel technique. Briefly, the NIST PGAA instrument

8 2 [1] has a thermal neutron beam (2.5 cm diam, 3.5 x 10 neutrons/cm s flux)

which strikes a sample approximately 50 cm from a collimated Ge spectrometer.

The ELLA PGAA instrument [2] is located at the end of a cold neutron guide

8 2 (5 X 10 cm area, 2.6 x 10 neutrons/cm s flux) with the sample position 20 cm away from the detector. The gas samples used in these analyses were contained

in a specially designed thin-walled Teflon sample cell which had a volume of

3 2000 cm . Measurements were performed by placing this cell in the neutron

beams. Since the cell was larger than the two neutron beams, the neutron

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NON-RRD PROGRAMS

beam and the viewing angle of the detectors defined the sample volume. The

3 3 effective sample size was approximately 24 cm at NIST and 190 cm at ELLA.

A section of a typical prompt gamma spectrum of nitrogen containing a chlorine compound is shown in figure 1.

Studies at NIST involved determining the count rate of chlorine lines

for dilute samples of vinylchloride in nitrogen. Figure 2 shows the measured

count rates for a series of dilutions between 100 and 5000 (volume) ppm.

These results show good reproducibility at each dilution and an excellent

correlation of the count rate with dilution. Background measurements

included gas samples of pure nitrogen, helium, argon, and ambient air; there

was no detectable blank contribution to the data. Other gases measured

included hydrogen (as methane) in helium and in argon. Initial measurements

at ELLA have focused on determining concentration of hydrogen as methane in

nitrogen gas. Background measurements included pure nitrogen, helium and

ambient air samples. Although the hydrogen background at the ELLA facility

is much lower than at the NIST (thermal) facility, it was significant enough

to limit measurements to the 1000 ppm level. Painted lead bricks and

boroplastic shielding materials were identified as major sources of the

hydrogen background. Changes are currently under way to eliminate the

1000

800

S 600 U

a,

12 400

B

aoU

200

. . r— ,,...,.... 1 . , H

CI J

- \ ""' (II) - -\. (H)

XI C\

-

1

^PlHitiUiMj... 1

•

0.6

500 1000 1500 2000

nnergy (keV) 2500

^ 0.1 u

I

I I .... I .... I

:000 2000 3000 4000

Chlorine Concentraiion ippm)

5000

Figure 1. (left) Prompt gamma spectrum of nitrogen containing 5000 ppm

vinylchloride from 500 to 2500 keV. The gas sample was counted 1 hour at the NIST instrument. The hydrogen peak is a background

contribution to the spectra.

Figure 2. (right) Count rate of chlorine (as vinylchloride) in nitrogen at

various concentrations. The correlation between count rate and

concentration is excellent (R = 0.99973).

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NON-RRD PROGRAMS

hydrogen background. Experiments will also be performed to determine

chlorine in nitrogen to directly compare results from both facilities. There

are several attractive features about using PGAA as a gas analysis technique.

It is a relatively simple technique requiring no sample preparation. Since

the samples are much less dense than either the solid or liquid samples, self

shielding and self absorption effects are insignificant. There are few

physical parameters in the PGAA analysis and these are well -determined, which

lends it to absolute determinations. This application of PGAA is suitable to

in situ analysis of gas reactions, process control monitoring as well as for

basic studies of neutron capture gamma-ray emission rates.

References

[1] Failey, M. P.; Anderson, D. L.; Zoller, W. H.; Gordon, G. E.; Lindstrom,

R. M. Anal. Chem. 51 2209-2220 (1979).

[2] Lindstrom, R. M.; Zeisler, R.; Rossbach, M. J. Radioanal. Nucl . Chem.

112, 321-330. (1987).

INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS OF MARINE SAMPLES

S. F. Stone, B. J. Koster, and R. Zeisler

(Center for Analytical Chemistry)

The National Biomonitoring Specimen Bank (NBSB) at NIST has been

involved in the National Statue and Trends program since 1985. Each year,

samples are collected and banked from approximately 20% of the sites from

both the Mussel Watch and Benthic Surveillance programs. In this way, a complete archive of the sites will be created by 1991. Precise sampling

protocols have been developed to ensure that the samples are not contaminated

during collection and processing [1]. "B" sections of a small number of the

samples were used for the determination of inorganic and organic real-time

and trend monitoring data. For analysis, the samples were cryogenically

homogenized. The respective "A" sections were banked undisturbed.

Analytical procedures focus on instrumental nuclear methods. A sequential

analysis approach has been developed, that allows the same 200 mg sub-sample

of the homogenized specimen to be taken through a number of procedures.

246
NON-RRD PROGRAMS

These procedures include x-ray fluorescence (XRF-BFP), prompt gamma

activation analysis (PGAA), and instrumental neutron activation analysis

(INAA) [2] for the bivalve samples, PGAA and INAA for the sediment samples

[3], and INAA alone for the fish tissue samples.

During the 3 years of collection, analysis has been completed on sediment, fish muscle, and fish liver samples from 12 sites in the Benthic

Surveillance project; and, sediment and bivalves from 18 sites in the Mussel

Watch project. All sample types have been a challenge to the applied

procedures due to the greatly varying concentrations of trace elements among

the sites. Nevertheless, the applied nuclear methods have shown their

flexibility in providing accurate measurements for elements that may vary two

to three orders of magnitude among the samples. An extension of this work

was the determination of over 30 elements in Standard Reference Material

(SRM) 1941, "Organics in Marine Sediment". The results for the SRM are given

in table 1. Concentrations for these elements will be included for in

formation on the SRM certificate.

The composition of this material appears unusual in many respects,

containing high levels of many of the elements, including S, Fe, Ti, Sc, many

of the rare earths, and U. This unusual composition, in addition to the

normal complexity of a sediment spectra, meant that great care was necessary

during the analysis, and when considering interferences. However, these

interferences must always be considered in similar materials, such as those

analyzed in the NS&T program.

References

[1] Lauenstein, G. G.; Calder, J. A. Progress in environmental specimen

banking. Wise, S. A.; Zeisler, R. and Goldstein, G. M., eds. Natl. Bur.

Stand. Spec. Publ . 740, 1988, pp. 19-30.

[2] Zeisler, R.; Stone, S. F.; Sanders, R. W. Anal. Chem, 60» 2760-2765

(1988).

[3] Stone, S. F.; Koster, B. J.; Zeisler, R. Biol. Trace Element Res. (in

press)

.

247
NON-RRD PROGRAMS

Table 1. Instrumental neutron activatiion analysis resijlts. Element

concentrat ions in mg/kg, dry weight basis

Element Gamma Energy SRM 1941 lAEA-SCl-N-1/2

Used Mean Uncertainty Value Uncertainty

b1 477 75.5 1.7 87.7 1.5

Na 1368, 2754 12910 290 10740 120

Al 1778 64800 2400 37290 650

Sil 3539, 4933 222000 8000 272000 11000

si 841 16410 840 3000 1000

CI 1642, 2167 16400 400 9460 120

K^ 770 15800 120 15200 580

Sc 889 34.34 0.42 6.913 0.060

Ti 320 17220 310 2812 93

V 1434 812 31 79.0 1.3

Cr 320 634.5 9.7 150.8 2.4

Mn 846 787.8 9.5 856.1 5.7

Fe 1099, 1292 105400 1000 36230 380

Co 1173, 1332 27.48 0.14 11.455 0.074

Zn 1115 1012 43^ 437.6 6.5

As 559 75.4 4.0 56.30 0.44

Se 264 10.11 0.50 1.76 0.27

Rb 1076 92.1 1.3 69.6 2.2

Ag 657 1.24 0.47 1.54 0.25

Sb 1691 15.20 0.42 3.55 0.061

Cdl 558 2.32 0.29 12.30 0.52

Cs 795 4.78 0.13 4.36 0.10

La 1596 359 12 29.11 0.29

Ce 145 271.8 3.6 54.77 0.77

Sm^ 333 25.69 0.40 5.52 0.20

Eu 778 2.184 0.060 1.065 0.042

Tb 298 2.19 0.40 0.669 0.0010

Gd^ 182 15.16 0.37 5.43 0.35

Hf 482 22.43 0.29 8.48 0.12

Ta 1221 16.43 0.45 0.990 0.12

Th 311 25.63 0.25 6.73 0.10

U (1596) (22) <6.6

1 PGAA

ts/yn for P = 0.05

1 s counting statistics

includes an allowance for uncertainties in peak integration

248
NON-RRD PROGRAMS

DETERMINATION OF B AND Li IN DIETARY SAMPLES USING NA-MS

G. V. Iyengar and R. G. Downing

(Center for Analytical Chemistry)

W. B. Clarke

(McMaster University, Hamilton, Canada)

and

J. T. Tanner

(Food and Drug Administration, Washington DC)

An international human nutrition project sponsored by the International Atomic Energy Agency in Vienna, and jointly supported by the

National Institute of Standards and Technology, the U.S. Food and Drug

Administration, and the U.S. Department of Agriculture is in its fifth year.

Under this program, diets from different countries including the United

States are being analyzed for a number of minor and trace elements. In view

of the emerging interest on the role of lithium and boron in animal and human

nutrition, analytical work on the diets was extended to include Li and B. As

a first step, diets from the United States were selected for preliminary

studies. A combination of neutron activation (NA) and mass spectrometry (MS) was used for the simultaneous determinations of B and Li. This technique

developed by Clarke et al . [1] has the required detection limit (< 10 ng/g)

to measure the natural levels of these two elements in biomaterials. The

method has been successfully used to quantify B and Li in several biological

and dietary reference materials. This report deals with the application of

NA-MS to determine B and Li in mixed total human diets prepared as described

earlier [2]. These food composites represent the U.S. diet based on the Food

and Drug Administration's Total Diet Study, and reflect the daily consumption

of foods by 25-30 year old adult males. Until now, five collections

belonging to Southeast (Georgia, Texas, West Virginia), North Central (Ohio,

Iowa, Kansas), Northeast (New York, Pennsylvania, Rhode Island), South

(Alabama, Louisiana, Texas), and West (Arizona, California, Oregon) have been

analyzed. The concentrations (dry weight basis) in these collections range

from 50 ± 0.6 to 124.3 ± 1.2 /zg/kg for Li, and 2.5 ± 0.2 to 3.6 + 0.3 mg/kg

for B. Based on initial estimates, the average intake amounts to 1.5 ± 0.25

(range 1.3 - 1.8) mg of B, and 37.35 ± 14.61 (range 25 - 62) /xg of Li. Since

the weights of the 201 individual components remain the same in all

249
NON-RRD PROGRAMS

composites, the changes observed in the composition may be linked to changes

within a food item; e.g., fat content in meat and factors susceptible to

geographical variations. Movement of foods across the country is a factor

that needs to be considered in interpreting these findings. Analysis of

future collections and more background information on the origin of foods

should clarify this situation. The daily intake of Li calculated from the

present study is the lowest in comparison with earlier published results

[3,4], and is comparable with the recent findings reported for Canada [5].

For B, the intake is in the same range as observed in Canada [5] and Finland

[6], and lower than that reported from the United Kingdom [4].

References

[1] Clarke, W. B.; Koekebakker, M.; Barr, R. D.; Downing, R. G.; Fleming, R.

F. Appl. Radiat. Isot. 38, 735 1987.

[2] Iyengar, G. V.; Tanner, J. T.; Wolf, W. R.; Zeisler, R. Sci . Total

Environ. 61, 235 (1987).

[3] Reference Man. ICRP-23, Pergamon Press, New York, (1975).

[4] Hamilton, E. I. The chemical elements and man. Wiley, NY (1979).

[5] Clarke, W. B.; Gibson, R. S. J. Food Comp. Analysis (in press).

[6] Acta Agriculturae Scandinavica. Supplement 22, (1980).

EXHUMATION CONFIRMS LEAD ANALYSES RESULTS

Neutron Activation Analysis Unit

(Federal Bureau of Investigation, Washington, DC)

Investigation of a drug-related double murder in the Northeast section

of Washington, DC, produced no suspects after 2 years until an acquaintance

of the perpetrators came forward with information which implicated three of

the areas most notorious hoodlums. Investigators set out to gather the

corroborative evidence necessary for prosecution.

A search of the suspects residence revealed a spent bullet in the

basement which appeared to be the same caliber as the three bullets removed

from one of the victims. Neutron activation analyses of these bullets and an additional fragment of lead removed from the victim revealed that the lead

250
NON-RRD PROGRAMS

fragment was slightly different in elemental composition from the bullets,

thereby indicating that the victim had been shot four times. To make the

matter more interesting, this fragment was the only specimen from the victim

with exactly the same elemental composition as the bullet found in the

suspect's basement.

After convincing prosecutors of the probable fourth bullet, the body was exhumed and reautopsied. A fourth bullet was recovered from the jawbone.

Neutron activation analysis was used to show that the composition of this

bullet was identical to the composition of the bullet from the suspects

basement. This dramatic evidence was critical in establishing the

credibility of the prosecution's case. The accused were found guilty of murder.

INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS OF MICROSCOPIC SAMPLES

R. M. Lindstrom

(Inorganic Analytical Research Division)

and

D. J. Lindstrom

(NASA Johnson Space Center, Houston, TX)

The high intrinsic sensitivity of neutron activation analysis has been

widely employed for the determination of low concentrations in centigramsized samples. By extending the standard measurement conditions to intense

neutron irradiation and low-background, high-efficiency gamma ray counting,

three orders of magnitude improvement in efficiency can be gained, and

compositional measurements can be obtained in submicrogram samples.

Under a microscope, samples ranging from 0.2 to 1000 ng were picked with

a tungsten probe and heat sealed separately in high-purity quartz tubes

0.1-0.2 mm in diam and 5-10 mm long. Sets of samples and standards were

sealed in an outer envelope and irradiated with a thermal neutron fluence

of 2x10^° n/cm^.

The sample vials were cleaned in nitric acid and the induced radioactivity was assayed with high-efficiency solid and well -type Ge detectors

with very low background. Detectors were operated in a counting room 20 m underground (Johnson Space Center) or a dedicated low-background laboratory

251
NON-RRD PROGRAMS

(NIST). An optimized thickness of low-background lead was used for detector

shielding.

In the analysis of such small quantities of material, measuring sample

weights and assuring homogeneous standards are major sources of analytical

uncertainty. For the smallest samples, too small to weigh accurately,

normalization to a major element like iron provides accurate concentration

ratios. Well -prepared synthetic silicate glasses have proven to be homogeneous at 10 /ig sample size. Since the size of these samples is smaller than or comparable to the 10 /xm range of recoil fission fragments, large errors can

be incurred in determining uranium-235 unless the sample is counted inside an irradiation container which is thick-walled enough to retain the fission

products.

Detection limits for many elements are well below picogram levels and some approach femtograms. Because the method is nondestructive (though some sample handling is required), the samples are available with little

compromise for further characterization by microprobe or other techniques

after instrumental neutron activation analysis is completed.

LOW-BACKGROUND GAMMA RAY ASSAY LABORATORY FOR ACTIVATION ANALYSIS

R. M. Lindstrom and J. K. Langland

(Inorganic Analytical Research Division)

In activation analysis, as in environmental monitoring and measuring

of cosmic-ray activation products, there is at times a need to reduce the

background of a germanium gamma-ray detector as low as possible, for example

instrumental neutron activation analysis (INAA) of wery pure materials such

as semiconductor silicon, INAA of very small samples such as individual

grains of cosmic dust, and radiochemical activation analysis of ultratrace

concentrations. Although it is not easy to achieve truly low backgrounds at

a laboratory in close proximity to a reactor or laboratories in which

millicurie quantities of radioactivity are handled, with care the background

achievable can be remarkably good.

Many sources of gamma-ray background need to be guarded against. In

most counting rooms on most days the dominant radioactivity is environmental

potassium, uranium, thorium, and their daughters in concrete and other

materials of construction of the building. Radioactivity may be present in

252
NON-RRD PROGRAMS

the detector itself or its shield. Radiochemical laboratories may be sources

of detectable radioactivity at levels far below health physics significance.

At a research reactor, the atmosphere inside the counting room may contain

41

Ar from irradiated air. Cosmic rays set the ultimate limit to the background unless the counting room is moved deep underground.

The chances for contamination were lessened by installing the

detectors in a dedicated room, as far away from radiochemical work,

irradiation facilities, and sample changers as practicable. We used a prefabricated environmental chamber 2.74 m x 4.57 m inside, installed in a high-bay area with only a 10 cm concrete roof overhead. A wall -mounted air

conditioner removes the heat of the counting equipment and keeps a slight

positive pressure in the room. Traffic is discouraged by keeping the air

temperature cooler than most people find comfortable. A sticky floor mat at

the entrance keeps shoe-borne dirt out. The smoke detector in the room is

the optical type instead of ionizing, since the latter may contain 1 to as much as 100 /iCi of ^^^Am or ^^^Ra.

Two detectors are used for low-background measurements, a Ge well

detector in a cylindrical shield and a large solid detector in a shield made

of stacked lead bricks. The specifications of the two detectors are as

fol 1 ows

Detector identification Ty Anne

EG&G Ortec model no. GEM-40195 GWL-180210-S

Crystal geometry cylinder closed-end well

Ge type p n Cryostat upright dipstick upright dipstick

Low-bkg modifications yes no Crystal size, dia x length 60 x 79 mm 60 x 74 mm

Well dimensions (room T) none 10 dia x 51 mm deep

Standard efficiency 25 cm 45% 30%

Resolution 01333 keV 1.76 kev 2.01 kev

The well detector, named Anne, is housed in a cylindrical shield,

built twenty years ago to house a scintillation coincidence gamma

spectrometer at the Naval Radiological Defense Laboratory [1] and subsequently transferred to NIST. The walls and roof of this shield are 10 cm of

selected lead, clad in stainless steel. The dimensions are large enough to

253
NON-RRD PROGRAMS

house the detector in its Dewar with 25 cm of clearance above the crystal

can. The Dewar rests on a disk of lead 5 cm thick, which in turn rests clear

of the walls on rubber blocks. The shield thus provides excellent vibration

damping, an especially important consideration for a well detector with large

microphonic sensitivity.

The solid detector "Ty" incorporated the manufacturer's low-background

modifications: a magnesium end cap, charcoal cryosorber, and 3 cm of old

lead between the crystal and the preamplifier. This detector was housed in a shield made of new 2" x 4" x 8" bricks of low-activity lead [2] from an ore

206

body with a low radiogenic Pb component and hence a low content of other

radium daughters. By neutron activation analysis we have found lead from

this source to be unusually low in trace impurities. Except for degreasing

with ethanol , the bricks were not specially cleaned before use. The shield

arrangement is shown in figure 1. The supporting structure is made of welded

fiO aluminum to avoid the possibility of Co contamination in steel. Beneath

the table is a 10 cm shadow shield of nonselected lead to absorb radiation

from the concrete floor.

The optimum thickness of the shield was determined by experiment,

balancing background against bulk and expense. Once the decay gamma rays

4

from natural radioactivity are reduced (by a factor 10 in 15 cm), increasing

thickness gives an increasing background from the buildup of tertiary cosmic

ray particles. As figure 2 shows, the positron annihilation peak increases

slowly with increasing thickness of the lead roof. The final dimensions were

6" (15 cm) walls and a 4" (10 cm) roof. To ensure a tight fit, the lead

bricks were stacked snugly together with the aid of a mallet and the outer

wall courses were offset from the inner by 6 mm. The lead shield was lined with material of lower atomic number to

absorb the Pb fluorescent x-rays. A commonly used lining is 1 mm Cd with 0.1 mm Cu inside. While Cd is an excellent absorber for lead K x-rays, its large

cross section for radiative neutron capture is undesirable when neutrons are

an important contributor to the background. When the solid detector was experimentally surrounded by Cd sheet inside the shield, the count rate of

the 559 keV capture line was 0.003 c/s. At NIST it has been the practice to

replace Cd with 6 mm or more of copper, which absorbs the x-rays equally

well, reacts less with neutrons, cost less, is nontoxic, and can also be used

structurally. The present shield was accordingly lined with 12 mm of OFHC

254
NON-RRD PROGRAMS

copper, whereupon the continuum background increased by a third over that in

the unlined lead, and new peaks appeared in the spectrum from decay of the

levels of the copper-63 and -65, excited by inelastic scattering of highenergy cosmic ray neutrons. In the near future, the copper will be removed

and replaced by thin tin.

Background lines from excited Cu

Enerqv c/s Isotooe

669.6 0.0017 63

770.6 0.0004 65

962.1 0.0024 63

1115.5 0.0008 65

1327.0 0.0006 63

1412.0 0.0002 63

1481.8 0.0003 65

"ix:

Szd m

r

P

u

Effect of Roof Thickness for 8" Walls

1 a

B . n

-1 -J

-

.1 ^

• « *

.01

"

001 -

1

k

t

1

r i

•

4 6 8

Inches Pb in roof

10

Integral 100- 1100 keV

5 1 1 keV positron

K -10

Figure 1. (left) Low-background shield for Ty detector.

Figure 2. (right) Background vs. roof thickness for 8" thick walls. The

cosmic-ray positron peak at 511 keV and the integral background

increase with increasing thickness beyond 4".

It was originally intended to install a thick inner lining of low-Z

plastic material to reduce low-energy x-rays still further and inhibit

bremsstrahlung from charged particles. Experiment showed that this was not

desirable. To test the effect of adding large quantities of hydrogen, the

detector was surrounded by 12 L of water in 2-L polyethylene bottles. The

255
NON-RRD PROGRAMS

effect of the hydrogen in moderating high-energy cosmic-ray neutrons was dramatic. The hydrogen capture line at 2223 keV appeared at 0.020 c/s (count

per second), and on prolonged counting the characteristic lines at 596.4 and

868.4 keV from capture of the thermal ized neutrons in the germanium detector

itself were visible at 0.005 and 0.002 c/s, respectively. With a 1-L

Marinelli beaker the hydrogen capture line was 0.003 c/s, whether or not the

detector and Marinelli were surrounded by Cd sheet either outside or inside

the lead. From the measured counting efficiency in the Marinelli geometry

2

the thermal neutron flux is estimated to be 0.02 n/cm s. The shield will

finally be lined with thin sheets of acrylic, whose only purpose is to

provide an easily cleanable or replaceable hedge against contamination.

In the unlined lead shield, the background shows only 511-keV positron

annihilation radiation, products of cosmic-ray neutron interactions with the

germanium of the detector itself [3,4], excitation lines of ' Pb, radon

daughters, K, and Co, in that order of importance (table 1). Only the

60

annihilation line is higher than 5 c/hr. Except for a trace of Co, no lines are detected which can be attributed with certainty to long-lived

radioactivity in the materials of which the detector or the shield are constructed. The remaining radon activity will be reduced by flushing the

shield continuously with nitrogen boiling off from the Dewar.

The background spectrum of the detector in the unlined lead shield is

shown in figure 3. The conspicuous broad peaks extending upward from 596 and

74

693 keV result from inelastic scattering of fast cosmic-ray neutrons on 6e

72

and 6e, respectively [3]; an enlarged view of this portion of the spectrum

can be seen in the accompanying section of this report concerned with cold

fusion. From the 693-keV line, produced with an 80 mb cross section, the

2

fast neutron flux is estimated to be 0.02 n/cm s and the energy about 1 MeV

[5]. The integral background from 100 to 2400 keV is 1.54 c/s.

The influence of the NIST reactor (located 60 m from the shields) was insignificant. No difference in either continuum or peaked background was

41 visible whether or not the reactor was operating. In particular, Ar from

irradiated air, small amounts of which are easily measurable in a laboratory

adjacent to the pneumatic tubes, is rarely detectable. The air from the

reactor confinement building and radiochemistry laboratories is discharged

from a 30-m stack 70 m from the counting room; under most weather conditions

256
NON-RRD PROGRAMS

the air inlet for the building is well away from where the plume reaches

ground level

.

Having shown that the main source of residual background in these

detectors is cosmic radiation, we conclude that the greatest additional

improvements to background will require either deep burial of the counting

room or active (anticoincidence) shielding.

Table 1. Gamma rays in residual background

Energy

fkeV)

Nuclide Count rate, c/s

Tv Anne

53.5 73mg^ 0.0005

66.6 73\e 0.003 0.001

72.8 Pb Ka2 (0.003)

75.0 Pb Kal 0.015

84.4 Pb m' (0.0004) 0.009

87.3 Pb W

139.9 75mg^ 0.002 0.001

159.7 77mgg 0.001

197.9 71mgg 0.002 0.002

238.6 ^^^Pb(Th) 0.0005 0.017

295.2 ^^^Pb(U) 0.0002 0.002

511.0

569.6

583.1

annihilation

208,,

0.03

0.0003

0.025

0.006

596.1 '^Ge(n,n') 0.010 0.03

693.4 '^Ge(n,n') 0.009 0.02

609.3 ^•*B1 0.002 0.003

803.3 206*pb 0.001 0.001

1173.2 60co 0.0003 0.001

1332.5 eOco 0.0002 0.001

1460.8 «K 0.0004 0.002

257
NON-RRD PROGRAMS

leee

lee - - - -

leee isee Energy <keU> 2000

Figure 3. Background spectrum (140 h counting time) of the Ty detector in

the unlined low-background shield. Except for Pb x-rays, the 511-

keV annihilation line, and inelastic scattering of fast neutrons

from germanium and lead, the background spectrum is nearly

featureless.

References

[1] Euler, B. A.; Covell, D. F.; Yamamoto, S. Nucl . Instr. Meth. 72,

143 (1969).

[2] Doe Run lead. Division Lead Co., Summit, IL.

[3] Chasman, C; Jones, K. W.; Ristinen, R. A. Nucl. Instr. Meth. 37, 1 (1965).

[4] Roy, J.-C; Cote, J.-E.; Durham, R. W.; Joshi, S. R. J. Radioanal.

Nucl. Chem. 130, 221 (1989).

[5] Chasman, C; Jones, K. W.; Ristinen, R. A. Phys. Rev. Lett. 15, 245

(1965).

INVESTIGATION OF REPORTED COLD NUCLEAR FUSION

R. M. Lindstrom

(Inorganic Analytical Research Division)

To sustain the thesis of Fleischmann and Pons's (University of Utah)

and Jones et al . (Brigham Young University (BYU)) that nuclear fusion has

been induced by electrochemical methods [1,2], the observation of neutrons is

a necessary confirmation. Four signatures of the fusion process are measurable: tritium generation, helium-3 generation, neutron generation, and

energy generation. Neither paper claims to have measured an increase in

3 tritium or He, although the Utah group has made tritium measurements in the

258
NON-RRD PROGRAMS

electrolyte and has collected gas samples. Only the Utah group reports the

generation of heat. The well-known thermodynamics of the d-d reaction (2 x

12

10 neutrons/s per watt) make the heat generated inconsistent, by a factor

g of 10 , with the neutron intensity observed. The only unambiguous diagnostic

marker of the fusion process reported is therefore the generation of 2.5 MeV

neutrons.

Mere qualitative observation of neutrons is not sufficient to confirm

fusion. Only a quantitative measurement statistically and temporally above

background can establish that fact. Th>re is quantitative evidence, on the

contrary, that the reported observations can be explained simply by cosmic

rays and other sources of background. The Utah group detected neutrons by

observing the characteristic prompt gamma rays emitted on neutron capture in

hydrogen, while the BYU group detected the energetic neutrons directly.

To test the claims of the Utah group, a large (31.4% efficiency

relative to 3" x 3" Nal) high-resolution germanium gamma-ray detector was set

up at NIST without shielding adjacent to a 70-L cylindrical tank of water.

The gamma-ray spectrum (fig. 1) clearly showed the characteristic neutron

capture line of hydrogen-1 at 2223.3 keV at 0.0015 ± 0.0002 counts per second

(s.d.). This peak, clearly visible after only ten hours counting, was adjacent to a background line at 2204.1 keV at 0.0143 ± 0.0004 c/s from

214 238

Bi, a daughter of U through radon.

Judging from a published photograph [3], the geometry of this

experiment is comparable to that of the Utah measurement, and differs chiefly

in the absence of Utah's electrochemical cell. Figure lA of the Utah paper

[2] is a gamma-ray spectrum showing this region of the spectrum. Their

spectrum was obtained with a sodium iodide scintillation spectrometer with a resolution of 50 keV fwhm (measured from the figure): this is very good for

Nal, perhaps a record, but still twenty times worse than the NIST Ge detector

214

and insufficient to resolve the hydrogen capture line from Bi . The count

rate is 0.017 c/s, coincidentally the same as the background observed at NIST

for the sum of the two lines. The caption to this figure states that the

background is featureless in this region; on the other hand it also appears

to say that the background is four times higher than the signal. Internal

inconsistencies aside, it appears that it is not necessary to invoke nuclear

fusion to explain the "neutron" signal in the Utah paper.

259
NON-RRD PROGRAMS

Recent NIST measurements with a low-background gamma detector

described elsewhere in this report allow an estimation of the cosmic-ray

neutron intensity and energy. From the counting rate of Ge(n,n') inelastic

scattering lines [4] in the background (fig. 2), the neutron flux was found

2

to be 0.02 n/cm s; from the width of these peaks [5] the energy is estimated

to be about 2 MeV, just the value of the neutrons produced by the d,d

reaction. These fast cosmic-ray neutrons become thermal ized and captured in

a modest amount of water; the effective thermal flux in a 1-L Marinelli

2 beaker on the detector is 0.02 n/cm s, as measured by the intensity of the

2223 keV capture line.

gee

see

7ee

eee

see

4ee

see

2eQ ''k:^*^.^Mft^A ^WA^''^*^"''|1'^

H capture

VlVvAi<H*MWl*if«

2iee 2150 22ee Energy (keU)

ese Energy CkeU) Figure 1.

Figure 2,

(left) Background spectrum (109 h counting time) of an unshielded

high-resolution gamma detector adjacent to a 70-liter tank of tap

water. The 2223-keV line from the capture of cosmic- ray neutrons

is visible next to the much more intense 2204-keV line from the

radon daughter Bi-214.

(right) Broad peaks in the background of a well -shielded gamma-ray

detector, caused by inelastic scattering of cosmic-ray neutrons.

The width of the peaks gives information on the neutron energy.

The BYU group reports a measured neutron counting rate (their run 6,

_3

assuming 0.5 neutrons/fusion) of 4 x 10 /s (this number is 100 times larger

in the published paper than in the widely circulated preprint version).

2 Their detector has a 150 cm cross section, so the integral cosmic background

at Provo should be greater than 3 c/s. They report a background in the 2 MeV

_3

region of 10 c/s, implying excellent energy discrimination. The net signal

is thus only twice background. The cosmic-ray neutron flux is highly

variable [6]. The neutron flux in Colorado has been observed to rise 500%

above normal following a large solar flare. Since we are now beginning a period of high solar activity, one may conclude by Occam's principle that the

most likely interpretation of the BYU measurement as well is variability in

the neutron detector background, not nuclear fusion.

260
NON-RRD PROGRAMS

References

[1] Jones, S. E.; Palmer, E. P.; Czirr, J. B.; Decker, D. L.; Jensen, G. L.;

Thorne, J. M.; Taylor, S. F.; Rafelski, J. Nature 338, 737 (1989).

[2] Fleischmann, M.; Pons, S. J. Electroanal. Chem. 261, 310 (1989).

[3] Pool, R. Science 243, 1661 (1989).

[4] Chasman, C; Jones, K. W.; Ristinen, R. A. Nucl . Inst. Meth. 3Z, 1 (1965).

[5] Chasman, C; Jones, K. W.; Ristinen, R. A. Phys. Rev. Lett. 15, 245

(1965).

[6] Forbush, S. E. Handbuch der Physik, Springer-Verlag, Berlin 1966,

V. XLIX/1, p. 159.

FACILITIES FOR ACTIVATION ANALYSIS

R. M. Lindstrom and J. K. Langland

(Inorganic Analytical Research Division)

Beginning in 1977, the group has implemented a flexible network of

computers to acquire and process data from 21 gamma-ray and charged particle

spectrometers (see fig. 1). The system is now in its third generation of

multiuser computers, centered on a VAX 11/730 file and peripheral server with

a network linking it with two more microVAXs in the group, three additional

computer-based multichannel analyzers, nine stand-alone analyzers, and 11

personal computers, with each unit in the system used for the part of the

analytical process for which it is best suited. Data are acquired and

partially processed on the computer-based analyzers and the VAX, and the data

transferred to microcomputers for further statistical interpretation,

graphics, and report writing. The group's network is part of a building-wide

Ethernet system with seven more minicomputers (operated by the Reactor

Radiation Division) and which in turn is linked to the NIST-wide fiber optic

data trunk. Two of the group's multichannel analyzers are directly connected

to the Ethernet. Progressive growth of the computer capabilities over the

past decade has occurred without ever experiencing a break in the group's

ability to acquire and process data, and without forcing users to new technology before they are ready to do so.

261
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-*a^

Figure 1. Schematic diagram of the data acquisition and processing network

used by the Nuclear Methods Group.

ATNOSPHERIC, ENVIRONMENTAL BIOLOGICAL STUDIES BY INSTRUMENTAL AND

NEUTRON-CAPTURE PROMPT 7-RAY ACTIVATION ANALYSIS

G. E. Gordon and J. M. Ondov

(University of Maryland, College Park, MD)

We continue to make considerable use of instrumental neutron activation

analysis (INAA) and neutron-capture prompt 7-ray activation anaysis (PGAA)

for development and testing of the methods themselves and to determine

concentrations of about 40 elements in particles, gases, rain, and fog from

the atmosphere, in related source materials such as crustal dust and coal fly

ash, and in standards appropriate for use in this field. By measuring

concentrations of such a large number of species, we are able to identify

contributions from certain types of air-pollution sources to the atmospheric

burden at ambient sampling sites, a technique now known as "receptor

modeling." Also, we are beginning to use neutron activation analysis to

observe several isotopes of Zn to determine the presence of a stable isotope

tracer in samples from humans. Examples of these studies are briefly

discussed in the following sections.

Our activities at the reactor have not been as extensive this year as in

the past for two major reasons: (1) the reduced operating schedule of the

reactor in connection with installation of the cold neutron facility, and (2)

262
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the fact that an unusually large number of our students had either recently

graduated or were writing theses. Over the past 2-1/2 years, nine students

have written theses (5 Ph.D. and 4 M.S.). All but one of these students made

much use of the reactor during their time in our department, so the reactor

has served a vital role in our graduate research program. We are pleased to

report that a new group of students is about to begin heavy use of the

reactor when the present shutdown ends.

EFFECTS OF NEUTRON SCATTERING BY HYDROGEN ON NEUTRON-CAPTURE

PROMPT 7-RAY ACTIVATION ANALYSIS (PGAA)

E. Mackey and G. E. Gordon

(University of Maryland, College Park, MD)

In a continuing effort to improve accuracy in PGAA, we are investigating

the effects of neutron scattering by H on PGAA elemental sensitivities.

Previous work by Anderson and Cunningham [1] and by Kitto [2] performed at

the NIST/University of Maryland PGAA facility [3] has shown increasing

elemental sensitivities with increasing H content. Kitto's results indicated

that each element is affected differently, with sensitivity enhancements

ranging from 1.8 to 4.3% enhancement per wt. % H. The first phase of the

present work was designed to measure sensitivity enhancements as a function

of H content. The second phase was designed to measure elemental

sensitivities in hydrogenous samples as a function of sample size or,

equivalently, as a function of the absolute amount of scatterer. The third

phase, now in progress, is designed to measure sensitivity vs. sample shape.

Sensitivities for 11 elements were measured over a broad range of H concentrations. For each element, an aqueous and a D^O standard solution were prepared from a salt of the element. A series of samples ranging in H

concentration from to 11% H (i.e., 100% 0^0 to 100% H2O) were prepared by

mixing appropriate amounts of the two stock solutions. Sample volume and

shape were constant (400 /iL in a 1.5- x 1.5-cm Teflon bag). Gamma rays

emitted by the samples were collected during irradiations of up to 3 hrs.

The results, shown in table 1, indicate that most elements studied undergo

about the same amount of enhancement. The most notable exception is Sm, for

which the enhancement is only about one-fourth that of the other elements

studied. If neutron scattering results in a slight shift of the energy

263
B 1.90 + 0.15 Ag

Na l.kl + 0.29 Cd

CI 1.73 ± 0.20 I

K 2.13 ± 0.13 Sm

Mn 2.90 + 0.26 Gd

Br 2.18 + 0.20

NON-RRD PROGRAMS

distribution towards lower energy, the effective absorption cross section for

Sm would be decreased due to the broad absorption resonance at 0.09 eV in

149

Sm. This provides a possible explanation for the anomalous enhancement

behavior of Sm, although further investigation is needed.

Table 1. Enhancement of elemental sensitivities in PGAA with increasing

hydrogen concentration

Element % Enhancement/wt. %H Element % Enhancement/wt. %H

1.65 ± 0.20

1.43 ± 0.17

1.90 ± 0.18

0.54 ± 0.074

1.57 ± 0.14

In the second phase of study, a series of disk-shaped pellets of 1.27-cm

diam and varying thickness were prepared from each of several hydrogenous

Standard Reference Materials (SRM 1571 Orchard Leaves, SRM 912 Urea, SRM 922

Tris-hydroxymethylaminomethane) . Thicknesses ranged from 0.5 to 10 mm. Spectra of these samples were collected during irradiations of up to 6 h.

Results from these experiments indicate that sensitivities increase with

decreasing sample thickness as shown, for example, for B in SRM 1571 in

figure 1. Similar behavior is observed for K and H in SRM 1571, and for H in

both SRM 912 and 922. These findings are consistent with the theoretical

work of Copley and Stone [4]. By use of Monte Carlo calculations, they show

that, in a scattering matrix, the mean path length of the neutron is

increased relative to the path length in a non-scattering matrix.

Preliminary work in the third phase of this study has indicated that the use of spherical samples may eliminate scattering-induced sensitivity

enhancement. A comparison was made between sensitivities obtained for CI in

spherical and in disk-shaped samples of the same material. Sensitivities

decrease with increasing sample size for the disk-shaped samples of constant

diameter and ranging in thickness from approximately 0.1 to 1 cm. However,

sensitivity is constant within ± 2% for spherical samples ranging in mass

from 0.25 to 1.6 g (or, in diam, from 0.8 to 1.4 cm). Further work in this area is in progress.

264
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»/U —' r-—r —

' T

'

1

Q Q B

Q

'

1

770 - B

-

i

PQ

t:nf\ 1 L 1 .

Q

1 2 4 6 8

Sample thickness (mm)

10

Figure 1. Boron sensitivity in SRM 1571 Orchard Leaves as a function of

sample thickness.

References

[1] Anderson, D. L.; Cunningham, W. C. Presented at the International Conf.

on Nuclear Analytical Methods in the Life Sciences, Natl. Inst. Stand.

Technol., Paper A47, April 1989. Biol. Trace Elem. Res. (submitted for

publication)

[2] Kitto, M. E., Ph.D. thesis, Department of Chemistry and Biochemistry,

University of Maryland, College Park, 1987.

[3] Anderson, D.L.; Failey, M. P.; Zoller, W. H.; Walters, W. B.; Gordon, G.

E.; Lindstrom, R. M. J. Radioanal. Chem. 63> 97-119 (1981).

[4] Copley, J.; Stone, C. Nucl . Instrum. Meth (submitted for publication).

SUBNICROMETER SIZE DISTRIBUTIONS OF AIRBORNE PARTICLES

BEARING VARIOUS TRACE ELEMENTS

J. M. Ondov, J. A. Dodd, and G. Tuncel

(University of Maryland, College Park, MD)

Knowledge of the composition and size distributions of atmospheric fine

particles is important because these parameters govern respirability,

deposition, nucleation of water vapor, and light scattering. Submicrometer

particles are of special interest, as they are respirable, have long atmospheric residence times, and are frequently enriched in potentially toxic

species. Trace elements borne by these particles are also useful for

apportioning sources and tracking air masses over long distances.

265
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Despite the importance of this information, reliable measurements of the

distributions of major, minor, and trace constituents of the submicrometer

aerosol have been limited. Most ambient sampling is done with either "whole"

filter samples or with dichotomous samplers, which fractionate particles into

"fine" and "coarse" particles (typically, < 2.5- and 2.5- to lO-fim diam

groups, respectively [1]). Chemical characterization of size-segregated

submicrometer particles has been limited to measurements of sulfate, carbon,

major ions such as sulfate and ammonium, and a few elements that can be

observed with x-ray fluorescence (XRF).

The lack of high quality elemental composition data for size-classified

submicrometer aerosol has been due in part to the lack of reliable samplers

capable of providing sufficient quantities of size-segregated particles in

this range for detailed analysis. Fractionation into several size groups is

usually done with cascade impactors. For some time, they were limited to

sizing particles above about 0.4-/xm in diam. This limit was extended to

-0.05 urn by operation at greatly reduced pressures, but at the expense of

high (near sonic) jet velocities conducive to particle bounce [2-4]. Despite

this advance, applications have been limited because of impractical pumping

requirements, low flow rate, and particle-bounce problems.

In 1981 Kuhlmey et al . developed an impactor capable of sizing

submicrometer particles at modest pressure drops (i.e., about 250 Torr for

0.06-^m minimum size cut) and modest jet velocities (127 m/s for 0.09-/xm cut)

using micro-orifice technology [5]. The impactor's low-pressure drop and

28-L/min flow rate permit collection of samples suitable for trace analysis

with a standard air-sampling pump.

We have tested the micro-orifice impactor (MOI) by field collections of

particles at a rural site in Western Maryland near Deep Creek Lake, as part

of a larger study of air pollution during the summer of 1983 [6]. Most

samples were collected between August 1-31, 1983, with sampling periods

ranging from 6 to 24 h. The MOI was horizontally configured and equipped

with a cyclone pre-col lector and an external 37-mm after-filter as described

by Kulmey et al . [5]. Cutoff diameters for the stages ranged from about 1.0

to 0.08 /im and the cyclone removed particles down to 3-iLim diameter.

Impactor collection surfaces and the after-filters from seven out of the

60 sample sets were analyzed by INAA at the NBS reactor using a combination

of 10-min followed by 3-h irradiations, each followed by taking of two 7-ray

266
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spectra of samples and appropriate flux monitors and standards irradiated

along with the samples using Ge detectors [7].

Concentrations of a minimum of 26 elements, including Al , As, Br, Ca,

Ce, CI, Co, Cr, Fe, K, La, Mg, Mn, Na, Se, Sb, V, Ti, and Zn could be

detected on at least three of five submicrometer impactions stages, i.e.,

enough data to estimate the mean diameters and standard deviations of the

size distributions of particles bearing those elements. Examples of the

"raw" size distributions for Al and V resulting from six experiments are shown in figure 2. There are clear differences in these distributions, as expected, since Al mostly arises from crustal sources, whereas V often has

additional high temperature such as oil-fired power plants and steel plants.

Only because of the high sensitivity of instrumental neutron activation

analysis (INAA) with the large flux of the NIST reactor was it possible to

observe so many elements with a total fine particle loading of only 180 fig.

Detection on more stages was generally achieved with loadings of 240 to 400

Hg. However, evidence for particle bounce was observed when loadings were

> 1 mg. Despite the use of thin, high purity Teflon impaction surfaces,

detection of Ag, Cu, Gd, Hf, I, In, Nd, Sc, Sm, Ta, Th, W, and Yb was frequently limited by their concentrations in substrate blanks in

polyethylene packaging materials used in the analyses. Bromine loss during

sample storage and extended neutron irradiation is also evident. The results

of these analyses demonstrate the feasibility of determining sizedistribution functions for many important minor and trace elements present in

ambient aerosol. We anticipate that similar or better results will be

achievable in more polluted urban areas with shorter sampling times.

A manuscript describing the experimental work has been submitted for

publication [8]. We are now applying deconvolution procedures to the raw size spectra to remove the effects of the nonsharp collection-efficiency

curves to obtain the inherent size distributions, which will be published

later.

267
NON-RRD PROGRAMS

0.01

0.01

n

E

0.01

Fifty percent cutoff diometer, /wn

Figure 2. Size-distribution functions for Al and V obtained by irradiation

of collection surfaces and after-filter from micro-orifice

impactor experiments.

References

[1] Dzubay, T. G; Stevens, R. K.; Gordon, G. E.; Olmez, I.; Sheffield, A.

E.; Courtney, W. J. Environ. Sci . Technol . 22, 46-52 (1988).

[2] McFarland, A. R; Nye, H. S.; Erikson, C. H. Development of a low

pressure impactor. U.S. Environmental Protection Agency Report No. EPA650/2-74-014.

[3] Pilat, M. J.; Powell, E. B.; Carr, R. C. APCA J. 4, 35 (1977).

[4] Hering, S. V.; Flagan, R. C; Friedlander, S. K. Environ. Sci. Technol.

12, 667 (1978).

[5] Kuhlmey, G. A.; Liu, B. Y. H.; Marple, V. A. Amer. Indust. Hyg. Assn.

J. 42, 790 (1981).

[61 Vossler, T. L.; Lewis, C. W.; Stevens, R. K.; Dzubay. T. G.; Gordon, G.

E.; Tuncel , S. G.; Russwurm. G. M.; Keeler, G. J. Atmos. Environ. 23,

1535 (1989).

[7] Germani, M. S.; GOkmen, I.; Sigleo, A. C; Kowalczyk, G. S.; Olmez, I.;

Small, A.; Anderson, D. L.; Failey, M. P.; Gulovali, M. C; Choquette,

C. E.; Lepel, E. A.; Gordon, G. E.; Zoller, W. H. Anal. Chem. 52, 240-

245 (1980).

[8] Ondov, J. M.; Dodd, J. A.; Tuncel, G. Nuclear analyses of trace

elements in size-classified submicrometer aerosol particles from a rural

airshed. Aerosol Sci. Technol. (submitted for publication).

268
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CALIFORNIA AIR RESOURCES BOARD AIR-FILTER SAMPLES

M. Han, A. Mizohata, and G. E. Gordon

(University of Maryland, College Park, MD)

To test the quality of our analyses, we occasionally participate in

"blind, round-robin" analyses of new standards or particular kinds of

samples. Recently we analyzed six air filters containing atmospheric

particles collected in California and three blank filters. This study was done for the California Air Resources Board (CARB) to check on laboratories

that were doing x-ray fluorescence (XRF) analyses of large numbers of samples

collected as part of a major study of air pollution in the Los Angeles

airshed. Four laboratories had analyzed most of the same samples by XRF

before we received them, but we did not receive their results until we reported our values. We were the only group to do instrumental neutron

activation analysis (INAA).

Table 2 shows a representative comparison of four sets of results for a sample containing particles with diam < 10 /zm, i.e., fine and coarse

particles. Most XRF analysts do not report data for elements as light as Na

and Mg because corrections for self-absorption of their very soft x-rays are large and uncertain; thus, the agreement for those reported is surprisingly

good. Corrections even for Al are large and only the EPA/NSI XRF result

agrees with our INAA value, which should be quite accurate. We don't measure

S well, as indicated by the large assigned error. There was considerable

spread in the CI values, possibly because of variable losses of volatile CI

species. Our Ca value is not \/ery precise and appears to be lower than the

XRF values.

Iron and K should be measurable with comparable reliability by both INAA

and XRF. Except for the EPA/NSI data, the XRF values are greater than ours outside of the quoted errors. This may reflect a concern that was a major

reason for having us perform INAA: the dichotomous sampler, with which these

samples were collected, produces a nonuniform deposit with greater deposition

in the center of the filter. Furthermore, some XRF instruments have a greater x-ray intensity in the center of the irradiating beam. The

combination of nonuniform deposits and beams would yield greater apparent

masses of elements on the filters. The fact that Fe and K XRF values are greater than ours suggests that this was a problem, as INAA is a bulk

measurement, not dependent on the uniformity of the deposit.

269
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Table 2. Comparison of CARB INAA and XRF results for filter MK-948

Element This Work EPA/NSI

(ng/filter)

NEA DRI ARB-NEA-STI

Na 10000 + 500 No 7215 + 914

Mg 2950 + 1250 Errors 2597 + 179

Al 6800 + 700 9600 + 1450 18201 + 5349 5262 + 298

S 66000 + 23000 14100 + 900 13670 + 73 13872 13824 ± 702

CI 1500 + 250 2230 + 200 1501 ± 433 952 1376 + 82

K 3000 + 400 4900 + 260 4464 + 866 3810 3473 ± 178

Ca 5900 + 1000 11800 + 600 11217 + 1799 8571 9658 + 507

Ti 1000 + 165 2200 + 115 1539 + 77 1520 1635 + 105

V 31.7 + 2.0 73 + 25 81 + 107 96 <90

Cr 85 + 6 160 ± 15 140 + 10 115 910 ± 57

Mn 210 + 12 330 ± 23 304 ± 13 250 <250

Fe 8700 + 600 14000 + 730 11063 + 42 11121 10967 + 693

Cu 380 + 80 425 + 25 345 + 7 241 321 ± 106

Zn 400 + 90 980 ± 50 788 + 9 683 772 + 139

As 8.5 ± 0.7 <70 <200 330 + 150

Se 20 ± 4 24 + 6 18 + 5 29 <1600

Br 140 ± 15 245 + 15 200 + 7 144 <430

Sb 19.6 ± 1.1 <230 <185 <6600

INAA values for Ti , V, and Cr were lower than the XRF values in most

samples. We would be most surprised if we were wrong on these elements,

expecially V and Cr. In previous comparisons we have made with XRF on the same samples [1-3], we have often found that XRF yields higher apparent

values than INAA for trace elements whose x-rays fall among those of minor

and major elements, here K, Ca, and Fe. Perhaps software used to extract net

peak areas does not completely remove tails of the large peaks. In addition,

there are specific interferences between elements, e.g., L lines of Br, Ba,

and Pb fall under the K lines of Al , V, and As, respectively. There is

usually enough Pb in atmospheric samples that one cannot measure As reliably.

The problem of Ba interference with V is subtle in that the interference can

be significant even when the Ba K line cannot be measured reliably.

Although the agreement for Mn is not outstanding for the example in

table 2, it is surprisingly good for most samples. Some of the As, Se, and

Sb XRF values also agree reasonably well with INAA, despite their low

concentrations. As in previous comparisons, [1-3] our INAA values for Br are lower than those from XRF, which are usually reliable. We have previously

speculated that there are slow losses of volatile Br species to the gas

phase. Since we are always the last group to analyze the samples, if this

270
NON-RRD PROGRAMS

hypothesis is correct, the samples contain less Br by the time we get them.

However, it is also possible that we lose Br during irradiations.

This exercise strengthens our belief that one should occasionally

participate in blind, round-robin comparisons. As the present exercise did

not include other INAA studies, we were unable to check the masses of many

additional elements for which XRF provided no values. Furthermore, when

there were disagreements, it wasn't always clear which group(s) were wrong.

The exercise should have been more valuable to the XRF groups. Not only did

they often disagree with our values, but they often have disagreements with

each other well outside of their stated errors . In the past, they have often

done intercomparisons using standards that are ideal for XRF, e.g., very

thin, uniform films with only one or two elements per standard [4], for which

various XRF analysts obtain much better results than for the "real world"

samples analyzed here.

References

[1] Dzubay, T. G.; Stevens, R. K.; Gordon, G. E.; Olmez, I.; Sheffield, A.

E.; Courtney, W. J. Environ. Sci. Technol . 22, 46-52 (1988).

[2] Tuncel , S. G.; Olmez, I.; Parrington, J. R.; Gordon, G. E.; Stevens, R. K. Environ. Sci. Technol. 19, 529-537 (1985).

[3] Hermann, D.; Ph.D. thesis. Department of Chemistry and Biochemistry,

University of Maryland, College Park, 1988.

[4] Dzubay, T. G.; Morosoff, H.; Whitaker, G. L.; Yasuda. H.; Bazan, F.;

Bennett, R. L.; Cooper, J.; Courtney, W. J.; Frazier, C. A.; Gatti, R. C; Germani, M.; Gordon, G.; Hanamura, S.; Kellogg, R. B.; Rhodes, J.

R.; Schindler, J. S. J. Trace and Microprobe Tech. 5, 327-341 (1988).

STABLE ISOTOPE TRACING OF ZINC IN INFANTS

S. H. Harrison, 0. J. Chitale, T. Quinn, and G. E. Gordon

(University of Maryland, College Park, MD)

Much has been learned about the absorption and subsequent behavior of

trace elements in human beings by administration of radioactive tracers,

which can be observed both in vivo and in samples collected from the body,

e.g., feces, urine, and blood. However, because of the radiation exposure,

these convenient, definitive tracers cannot be used for' study of some of the

most important population groups at risk of trace element deficiencies:

pregnant women and infants. For this reason, enriched stable isotope tracers

271
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have come into wide use during the past decade. One administers a sample of

the element in which a minor isotope has been enriched to nearly 100%. The

appearance of the tracer is observed by an increase of the abundance ratio of

the tracer isotope relative to another stable isotope. Isotopic ratios are normally measured by mass spectrometry, but in favorable cases one can observe two or more isotopes via their neutron irradiation products. We have

been doing tracer studies of Zn using stable Zn, whose natural abundance is

about 0.6%, for which enrichments up to about 80% are used as the tracer.

Three stable Zn isotopes have observable neutron irradiation products: 244-d

^^Zn, 14-h ^^""Zn, and 4-h ^^""Zn from stable ^^Zn, ^^Zn, and ^°Zn,

respectively. In earlier work involving the NIST reactor, we verified the

use of stable Zn tracer by simultaneously using it with radioactive Zn in

vivo tracer in adult volunteers. This work has been submitted for

publication [1,2].

Over the past 2 years, we have been using the method to study Zn

nutrition in various classes of newborn infants: pre-term, normal, and low

birth-weight full -term. This study is being conducted in cooperation with

Drs. K. Sivasubramanian and M. Wastney of Georgetown University Medical

Center, using subjects from Georgetown's neonatal unit. Depending on how the

infant is being fed, the Zn is administered orally or intravenously.

Samples of urine, feces, red bood cells (RBC), and plasma are collected at

various times after administration. Because of the enormous activities of

irradiation products of Na, K, CI, and Br that would be formed by irradiation

of the raw samples, we must perform extensive pre-irradiation chemistry to

produce reasonably pure Zn samples in which 7 rays of 14-h Zn and 4-h

71m

Zn can be observed soon after irradiations.

Studies of infants are much more difficult than those of adults.

Although the amounts of feces available are usually adequate, very small

quantities of the others, especially RBC and plasma, are available.

Typically 1 mL of blood is taken per sample vs. 10 mL from adults. Careful

attention by nurses is needed to prevent mixing of urine and feces. Usually

samples can be collected only as long as the infant remains in the neonatal

unit (typically 1 week), whereas adult volunteers can be asked to provide

samples for as long as the experiment requires.

Despite these difficulties, we have begun to obtain results. Tracer

experiments have been conducted with seven infants, of which final results

272
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are available for two infants. Results obtained from the feces samples from

two cases are shown in figure 3. The fraction of tracer appearing versus the

days following administration are shown. For the first case, the only

significant amount outside of errors appears on Day 5, about 1.5% of the

tracer, at which time the experiment was terminated when the infant was released. Results for Case 2 were much better, as several samples contained

significant amounts of tracer, the maximum being 10% in one sample from the

second day. Many additional samples have been separated and are awaiting

start-up of the reactor for irradiation. Dr. Wastney is subjecting the

results to kinetic analyses as they are obtained.

Fraction of Zn-70 Stiihle Tracer appearing in Feces Samples

g

Case 1 (R) 1 .9

D a '

1

1 ' 1

!

1

1 I T

1

1 1

[

^

J 1

1 '

J

12

lU

8 ^ 6 e 4

2

l-O-l Case 2 (M)

B

a

o m ° QEQ D D

1 1 1 1 1

—

1 T T

' 1 3 4 Time (days)

Figure 3. Fraction of stable ^^Zn tracer appearing in feces from two infants

vs. day.

References

[1] Gfikmen, I. G.; Aras, N. K.; Gordon, G. E.; Wastney, M. E.; Henkin, R. I. Anal . Chem. (in press).

[2] Wastney, M. E.; GOkmen, I. G.; Aamodt, R. L.; Rumble, W. F.; Henkin, R. I.; Gordon, G. E. Am. J. Physiol, (submitted for publication).

273
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INVESTIGATION OF THE GAMMA-RAY SPECTRUM FOR THE

^^^e(n,g) and ^^°Te(n,g) REACTIONS

C. Ford, P. F. Mantica, Jr., B. E. Zimmerman, and W. B. Walters

(University of Maryland, College Park, MD)

and

C. A. Stone

(Center for Analytical Chemistry)

We have made an initial attempt to determine the spectrum of gamma rays

Ic 130.

128 following neutron capture on the two heavy stable Te nuclides, Te and

Te. Te is an element whose isotopes do not have large cross sections for

neutron capture and is not generally observed in trace element analysis. The

129 131

structure of the daughter nuclides Te and Te has been studied in

numerous radioactive decay investigations and in a variety of transfer

reaction measurements, but still has not been fully accounted for in

theoretical models. Literature concerning the spectrum of capture-gamma rays

is also sparse and quite incomplete. At low energies, both nuclides have

1/2"*" levels that are populated rather strongly in (n,7) reactions by cascades

through levels in the 2 to 3 MeV range. Consequently, these nuclides are important candidates for determination in prompt gamma ray activation

analysis (PGAA) using coincidence techniques.

The use of coincidence techniques for determining additional elements in

PGAA would be important for elements that are not now regularly determined by

singles counting. For the technique to be suitable, the element under study

should have one or two major cascades of two or three gamma rays from the

capture state to the ground. Important factors in determining the sensitivity of the method will be the detection efficiencies and gamma-ray

intensities. Because these nuclides have both high and low energy gamma rays

that appear to carry significant portions of the decay, these measurements to

make a better accounting for the capture-gamma-ray spectrum itself are a first step in developing possible coincidence methods for their determination

by coincidence counting in PGAA.

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FUNDAMENTAL PHYSICS

Dr. Geoffrey Greene

(Center for Atomic, Molecular, and Optical Physics)

The Fundamental Neutron Physics Program at the NIST Cold Neutron

Research Facility includes research in particle physics, basic nuclear

physics, and neutron interferometry. It is a collaborative effort involving

personnel from the Reactor Radiation Division, as well as from other

organizational units within the National Measurement Laboratory, including

the Quantum Metrology Division, Center for Atomic, Molecular, and Optical

Physics; and the Neutron Interactions and Dosimetry Group, Center for

Radiation Research. This work has a strong collaborative character with

contributions from other institutions including the University of Missouri,

Los Alamos National Laboratory, the University of Sussex (U.K.), and Harvard

University. In addition, this work receives support from the Department of

Energy and NATO.

This year considerable effort has gone into the design and initial

construction of the Neutron Interferometry Position at the Cold Neutron

Facility. This work has included detailed analysis of the vibration

isolation system as well as the completion of the design for the first stage

of seismic isolation.

In the area of nuclear and particle physics, significant work has gone

into an experimental effort to determine the half-life of the neutron. Very

successful preliminary runs were carried out at the Institut Laue Langevin in

Grenoble, France. This experiment will be installed on guide #6 at the NIST

facility as the initial instrument on the fundamental physics end position.

NEUTRON ACTIVATION ANALYSIS AT THE FOOD AND DRUG ADMINISTRATION

D. L. Anderson, W. C. Cunningham, and E. A. Mackey

(U.S. Food and Drug Administration, Washington, DC)

The Food and Drug Administration (FDA) maintains a neutron activation

analysis (NAA) facility in the reactor building of NIST. This facility is

directed by FDA's Center for Food Safety and Applied Nutrition and provides

agency-wide analytical support for special investigations and applications

research. NAA complements other analytical techniques used at FDA and serves

275
NON-RRD PROGRAMS

as a reference technique and confirmatory quality assurance (QA) tool.

Instrumental, neutron-capture prompt-7, and radiochemical NAA procedures

(INAA, PGAA, and RNAA, respectively) continue as the prime analytical

approaches. This combination of nuclear techniques enables diverse

multielement information to be obtained for foods and related materials.

Methods development and applications research is a continuing FDA effort

to improve overall analytical capabilities. During this past year

approximately 30 food and biological standards were analyzed to continue

accumulation of general analytical information on foods and related

materials. The standards were from NIST, Japanese National Institute for

Environmental Studies (NIES), International Atomic Energy Agency (IAEA), and

U.S. Department of Agriculture (USDA). Related work included efforts to

promote the generation of biological reference material. FDA's NAA facility

participated in certification of 13 food reference materials in collaboration

with USDA, Agriculture Canada, and NIST. Matrices included a mixed diet and

12 individual biological materials. In a cooperative effort between FDA, the

University of Maryland, and NIST, several PGAA experiments have been designed

to characterize matrix effects due primarily to the presence of hydrogen.

During the past year, the relationship between boron sensitivity and hydrogen

content was measured for several matrices. As shown in figure 1, B

sensitivity (i.e., c/s-mg) increases with increasing weight percent H for

both solid and liquid prepared standards.

Other matrix-effect studies using standard H^O/D^O solutions were carried out to show the sensitivity behavior of H, CI, K, Na, I, Br, Mn, Ag,

Cd, Sm, and Gd as a function of hydrogen content. Enhancements are also

observed for these elements, but the degree of enhancement (for a given H

concentration) varies significantly.

PGAA and INAA freeze-drying loss studies on mixed food composite

materials were initiated during the past year. These composites are mixtures

of a large number of foods and beverages derived from either the FDA Total

Diet Study or the USDA Mixed Diet Study. Two of the composite materials

studied are also being issued by NIST in dried form as reference materials.

These are RM 8431a Mixed Diet from the USDA Mixed Diet Study and SRM 1548

Total Diet from the FDA Total Diet Study. The possibility of element loss

during the freeze-drying of these previously dried materials was studied here

relative to the QA value of these matrices. Because the neutron flux used

276
NON-RRD PROGRAMS

for PGAA is very low, radiation damage is negligible and the technique is

essentially non-destructive. Analytical portions can be analyzed, freezedried, and then re-analyzed to monitor for element losses. In work done so far, no freeze-drying losses are observed for B, C, N, Na, S, CI, and K in

either RM 8431a or SRM 1548. Preliminary measurements for wet diet

composites, however, indicate that approximately 30% of the boron is lost

during the freeze-drying process. Thus, it appears that none of these

elements are lost after the initial freeze-drying; i.e., with subsequent

freeze-drying of previously dried material. On the other hand, the initial

freeze-drying operation appears to result in potential boron loss. Because

freeze-drying may be widely employed, it is important to understand such

losses in order to accurately reflect the elemental content of original wetweight samples. NAA and additional PGAA are under way to explain these

findings and to look for other element losses.

% Increase in B sensitivity vs. %H

1/1

v\

V

I/I a

Vu

w

H3B03inH20/D20

B4C in graphite/mannitol

%H

Figure 1. Effect of hydrogen content on Boron sensitivity,

277
NON-RRD PROGRAMS

GERMANIUM DETECTOR OPTIMIZATION OF MDA

FOR EFFICIENCY VS. LOW INTRINSIC BACKGROUND[1]

D. R. Brown and L. A. Slaback

(Occupational Health and Safety Division)

The efficiency and minimum detectability characteristics of four

intrinsic germanium (InGe) detectors were evaluated as a function of sample

type; e.g., small point, a 200 ml cylindrical container, and two marinelli

geometries (1 liter and 3.5 liter). Of particular interest is the

performance of these detectors in determining reactor activation and fission

products in environmental samples. The detectors and shields used are shown

in tables 1 and 2.

Table 1. Detector characteristics

Detector

Parameters HPl HP2 Tv* HP3

Nominal Efficiency 21% 45% 45% 30%

Ge Crystal Diam (mm) 56 68 59 54

Ge Crystal Length (mm) 41 61 79 70

Ge Dead Layer (mm) 1 .6 .7 .7

End Cap Material Al Al Mg Al

End Cap Thickness (mm) 0.5 1 1 1 End Cap - Crystal (mm) 5 5 3 3

End Cap Diam (mm) 75.0 86.5 86.5 75.0

Low Bkg Construction No No Yes No

Shield Used A B C B

*has added background reducing design features

Table 2. Shield parameters

Lead

Shield Sides Too Liner Desiqn

A 6" 6" .06" Cu cube, cast lead,

B 4" 4" .06" Cd, .06" Cu cylindrical , cast lead

C 6" 4" .5" Cu stacked lead bricks

278
NON-RRD PROGRAMS

The efficiency was determined and the minimum detectable activity (MDA) was calculated for all geometries and over a range of energies from 80 keV to

1.6 MeV. For bulk environmental samples, e.g., the Marinelli geometries, the

MDA results were notable for their similarity. Most important is the need to

optimize the sample geometry for the particular detector being used. A

properly sized sample container of the 20% detector out-performed the 45%

detectors.

Reference:

[1] Brown, D. R.; Slaback, L. A. Germanium detector optimization of MDA for

efficiency vs. low intrinsic background. Proceedings of Topical Meeting

on Instrumentation, 4-8 December, 1988, Health Phys. Soc. pp. 46-52.

279
C. REACTOR OPERATIONS AND ENGINEERING SERVICES

REACTOR OPERATIONS AND SERVICES

T. Raby, J. Torrence, J. Ring, and N. Bickford

Construction of the new Cold Neutron Research Facility continues to

require significant reactor shutdowns that will extend into the coming years.

Accordingly, this year the reactor was on-line 56% of the time equivalent to

48% full power operation which comprised essentially all available operating

time. Operations were the smoothest of any year with no unscheduled

shutdowns of any significance.

The repair of the thermal shield cooling system using a new leak sealing

method developed by the National Nuclear Corporation of England was partially

successful. The method requires repeated applications of the sealant, on the

average of twice a year, for the sealant to hold in a high radiation

environment and to withstand temperature fluctuations. All past repairs were scheduled so as not to interfere with reactor operation.

The existing main heat exchangers continue to require extreme care and

careful maintenance. As yet, a wery small leak, on the order of a few drops

a minute, could not be found. New, more reliable heat exchangers are in the

procurement stage and are not expected to be ready before the end of 1990.

Extensive negotiations with the Department of Energy (DOE) were undertaken to assure future supplies of both nuclear fuel and heavy water.

Nuclear fuel is now on an accelerated fabrication schedule that will

guarantee a current reserve of at least 5 years. Immediate heavy water needs

will be met by DOE. However, future supplies will have to await further

negotiations with DOE and the Canadian Government since heavy water is in

critically short supply.

The small operating staff continues to perform double duties, operation

and engineering. The latter includes design, installation, quality control,

testing, repair, and maintenance. Of the total 16 operators at the beginning

of the year, 15 held senior operator licenses, and one trainee also qualified

and obtained a senior license making the NIST reactor the only reactor in its

class with all operators holding a senior level license. More recently one senior operator transferred to the Health Physics Group but will continue to

maintain his license. A new trainee was just hired to replace him.

280

i
REACTOR OPERATIONS AND ENGINEERING SERVICES

A summary of the operating statistics for the past year follows. Fuel

utilization continues to be the best in the country.

No. of equivalent days at 20 MW 175

Equivalent on-line time at 20 MW 48%

Average U-235 burnup 66%

No. of irradiations 1160

Hours of irradiations 4900

Hours per irradiation 4.2

The same program of reactor irradiations continued. Irradiation

services were provided to many organizations from within and outside NIST

covering wide areas of research, applications, and standards.

REACTOR OPERATIONS AND ENGINEERING

J. H. Nicklas and R. S. Conway

Design and engineering services were provided, on a regular basis, to

reactor operations and the research groups throughout the year. They

included successful resolution of several complex problems that occurred

which otherwise would have resulted in lengthy delays. An example of this was the timely determination of the cause of malfunction during testing of

control rod drive No. 2 which was extremely hard to locate or even duplicate.

The corrective steps taken assured reliable operation and permitted the

reactor to start-up on schedule.

There were nine major projects that were undertaken in addition to

regular engineering services. These include:

Specifications for Replacement Heat Exchangers . The specifications for more reliable heat exchangers for the primary and auxiliary systems were computed using the latest in design materials, fabrication, testing and

quality assurance innovations and techniques. The new design will assure a close to zero leakage as possible over the lifetime of the units.

Procurement will begin later this year.

281
REACTOR OPERATIONS AND ENGINEERING SERVICES

Nuclear Fuel Fabrication . The first group of advanced heavier loaded

fuel elements were qualified and accepted. Accordingly, all future elements

will further improve fuel utilization by at least 10% and as much as 20% a significant cost saving in addition to reducing the number of refueling

outages.

Control Rod Fabrications . The NBSR control rods are the only ones of

their kind in the United States with a very unusual design. The original

components were hand-crafted at Argonne National Laboratory. Since the

shutdown of CP-5 a decade ago, the only expertise left resides with the

current engineering staff at the reactor. As a consequence, an ambitious

program was undertaken to have enough complete control rod assemblies, ready

for installaton, to last for the term of the current license or until 2004.

This program will be completed over the next 2-3 years prior to the expected

retirement of the principals involved. Less experienced engineers are also

being trained to assume this responsibility in the future.

Thermal Shield Cooling System . Together with Reactor Operations,

extensive maintenance and repair were carried out on this system. Initially

40 of 200 tubes suspected of leaks were treated using the special method

developed by the National Nuclear Corporation of England. The treatment was repeated on 25 tubes and will be repeated again several times in the future.

Experience has shown that several applications are needed to fully seal the

leaks, however, improvements were noted with each application.

Secondary Auxiliary and Experimental Cooling System . A complete

redesign of this system to provide for significantly increased cooling

capacity was completed. The current capacity is inadequate because of the

increased number of components served by the system. The new design

separates this system from the main cooling system, thereby improving the

main system's cooling capacity as well.

Monitors . Back-ups to two existing crucial monitors were designed and are in the process of being installed. A second N-16 monitor was incorporated into a complete redesign of the secondary coolant monitoring

system. The new design will return possibly contaminated water back to the

system rather than discharging it to the environment and will provide

redundancy in the early detection of heat exchanger leaks during reactor

operation. A second extended range stack effluent radiation monitor was designed and installed. The new monitor will not only serve as a back-up to

282
REACTOR OPERATIONS AND ENGINEERING SERVICES

the existing stack monitor, but would also, because of its extended range, be

the principal instrument used for emergency action in the case of a radiation

emergency.

Automatic Control System . The current automatic control system for the

reactor is one of a kind and 25 years old, and can no longer be easily

maintained or repaired. The system was completely redesigned employing the

latest advances in technology. A mockup of the system was tested in the

laboratory for several months and was found superior in reliability and

performance. The new system will be installed next year after further

testing.

Reactor Control Room . A comprehensive study of control room instrumentation and controls was made over the last year by a visiting

engineering specialist and members of the instrumentation group. A detailed

plan was developed for future upgrade and modernization of the system using

up-to-date design features and equipment. Although many components were upgraded whenever possible over the years, the bulk of the system remains as originally installed at the time of construction of the reactor more than 25

years ago.

Emergency Power SupdIv System . Design and specifications for a back-up

emergency power supply system were completed. The system will be installed

next year. The new system will guard against unnecessary reactor shutdowns

since the reactor cannot be operated without a source of emergency power

available at all times.

283
oCO

NEUTRON

CONDENSED

MATTER

SCIENCE

J.

J.

Rush,

Leader

J.

K.

Spillman,

Sec'y

L.

K.

Clutter,

Sec'y

REACTOR

RADIATION

DIVISION

J.

M.

Rowe,

Chief

T.

M.

Raby,

Deputy

H.

J.

Prask,

Sci.

Ass't

E.C.

Maxwell,

Admin.

Officer

S.

L.

Neal,

Admin.

Asst.

E.

S.

Altman,

Sec'y

COLD

NEUTRON

PROJECT

J.

M.

Rowe,

Manager

1.

G.

Schroder,

Tech.

Leader

C.

L

O'Connor,

User

Coord.

N.

P.

Repetti,

Sec'y

REACTOR

OPERATIONS

&

ENGINEERING

T.

M.

Raby,

Chief

J.

F.

Torrence,

Deputy

J.

H.

Nicklas,

Chief

Eng.

G.

C.

Harrison,

Sec'y

C.

M.

Sweeney,

Sec'y

284
PERSONNEL ROSTER

Research and Engineering Staff

N. F. Berk

R. C. Casella

R. Conway

J. R. D. Copley

R. W. Erwin

C. J. Glinka

J. Gotaas

G. Greene

V. Himes

P. A. Kopetka

S. Krueger

J. LaRock

H. Layer

Condensed matter theory

SANS theory for microstructure analysis

Computer software for graphics and data analysis

Theory of neutron scattering from light-atom

defects in metals

Group theory analyses of neutron scattering

from condensed matter

Elementary particle theory, especially as related to reactor generated experiments

Electronic engineering

Nuclear instrumentation

Time-of-flight spectrometer development

Neutron instrumentation conceptual design

Solid state physics

Magnetic materials

Phase transformations

Spin echo techniques

Cryogenics

SANS microstructure of metals and porous media

Magnetic materials

Cold neutron instrument development

Low temperature phase transformation

SANS microstructure studies

Magnetism

Develops system and user software for cold

neutron instrumentation

Interfaces spectrometers with data acquisition

systems

Crystal database development

X-ray crystallography

Mechanical engineering

Cold Source design

Electro-mechanical systems

Small angle neutron scattering instrumentation

Microstructure of materials

Biological problems

Mechanical engineering

Neutron instrumentation design

Electronics and data processing

Advanced instrumentation

Fundamental physics

285
PERSONNEL ROSTER

C. F. Majkrzak

A. Mighell

B. Mozer

D. Neumann

J. H. Nicklas

D. Pierce

H. J. Prask

E. Prince

T. M. Raby

J. J. Rhyne

J. M. Rowe

J. J. Rush

A. Santoro

Condensed matter physics

Polarized neutron scattering

Polarizing and monochromating devices

Crystal lographic database development

Single crystal diffraction

Theory of crystal lattices

Structure and microstructure of metallic glasses

Dynamics of liquids

NDE of alloys

Two-dimensional materials

Solid state physics

Neutron and x-ray scattering instrumentation

Mechanical engineering

Reactor fuel design

Reactor engineering support

Mechanical engineering

Neutron instrumentation design

Residual stress measurement

Neutron NDE of hardware

Neutron NDE instrumentation

Structural properties of alloys, catalysts, and

minerals

Advanced crystal lographic refinement methods

Software for materials structure analyses

Reactor operations

Nuclear engineering

Reactor standards

Properties and transformations of high

technology magnetic materials

Structure of amorphous solids

Data acquisition and analysis system

Orientationally disordered solids

Hydrogen in metals

Cold neutron research and instrumentation

Catalysts and molecular materials

Hydrogen in metals

Two-dimensional systems

Inelastic scattering methods

Structure of electronic and structured ceramics

Theory of crystal lattices

Powder diffraction methods

286
PERSONNEL ROSTER

s. Satija Low-dimensional molecular systems

Fractal aspects of microporous media

Neutron reflectometry

I. G. Schrflder Cold neutron instrumentation development

Nuclear and engineering physics

Optical devices for neutron transport

F. Shorten Physical measurement

Safety

J. Stalick Neutron and x-ray diffraction

Inorganic chemistry

Crystal database development

J. Sturrock Design engineering

Nuclear systems and components

M. Suthar Design engineering

Nuclear systems and components

J. F. Torrence Reactor supervision

Reactor maintenance

Nuclear engineering

T. J. Udovic Neutron time-of-flight instrumentation

Properties of catalysts

Spectroscopy of surfaces

Technical Staff

Reactor Ooerations Neutron Research

Richard D . Beas ley George M. Baltic

Myron H. Bell Donald H.Fravel

Nathan A. Bickford Wayne C. Knill

Mark G. Cassell s Hugh L. McConaghy

Forest C. Clark Michael J. Rinehart

Howard W. Dilks William H. Rymes

Daniel J. Flynn Thuan Thai

Larry T. Lindstirom Robert H. Williams

Michael J . McDonald

William W . MueVler

Thomas J. Myers Reactor Enqineerinq

John H. R ing

Ricky P. Sprow James A. Beatty

Robert F. Stiber Richard P. Hayes

Attila L. Toth

Daniel P. Wilkison

287
PERSONNEL ROSTER

NON-RRD NBS STAFF LOCATED AT REACTOR

Occupational Health

and Safety Division

D. Brown

C. Campbell

J. Clark

I. Jensen

F. Moore

D. Nelson

J. Shubiak

L. SI aback

Ionizing Radiation

Division (536)

13541

E.C.

D.

J.

E.

R.J.

Boswell

Eisenhauer

Gilliam

Grundl

McGarry

Schwartz

Coyne

Inorqanic Analytical

Research Division (551)

D. Becker

G. Downing

K. Fitzpatrick

B. Grazman

R. Greenberg

G. Iyengar

G. Lamaze

J. Langland

R. Lindstrom

J. Maki

D. Mildner

B. Norman

C. Stone

S. Stone

R. Zeisler

INSTITUTE FOR MATERIALS

SCIENCE AND ENGINEERING (400)

J. Cahn

Ceramics Division (420)

E. Fuller

R. Krause

G. Long

S. Malghan

C. Ostertag

W. Haller

Polymers Division (440)

B. Bauer

R. Briber

F. Brinkman

T. Chang

J. Clark

L. Coyne

T. Davis

C. Han

S. Krueger

A. Nakatani

G. 01 sen

W. Wu

GUEST WORKERS AND COLLABORATORS

Metallurgy Division

F. Biancaniello

R. Fields

F. Gayle

C. Johnson

D. Lashmore

R. Shaefer

(450)

Surface Science Division (541)

R. Cavanagh

Organic Analytical

Division (552)

B. Koster

L. Sander

S. Wise

Gas and Particulate

Science Division (553)

W. Dorko

C. Poston

J. Small

Center for Atomic, Molecular

and Optical Physics (570)

M. Arif

R. Deslattes

S. Dewey

G. Greene

288
PERSONNEL ROSTER

Semiconductor Electronics

Division (727)

J. Ehrstein

J. Marshall

J. Suehle

Thermophvsics Division (774)

H. Hanley

J. Straty

Armed Forces Institute of Pathology

D. Nagarajan

Army Armament Research. Develooment

and Engineering Center

C. Choi

S. Trevino

Army Ballistics Research Lab

D.-R. Chang

B. Rice

L. Vandekieft

Federal Bureau of Investigation

R. Bilko

R. Halberstam

K. Hargadon

J. Havekost

J. Inga

K. Lundy

R. Rebbert

J. Riley

P. Sanderson

Food and Drug Administration

D. Anderson

W. Cunningham

J. Tanner

Geological Survey

M. Mrose

NASA

D. Lindstrom

National Institutes of Health

R. Finn

R. Nossal

National Oceanic and

Atmospheric Administration

G. Lauenstein

Naval Research Laboratory

D. Collins

K. Grabowski

P. Skeath

C. Roland

C. Trask

Naval Surface Weapons Center

G. Riel

M. Spano

Smithsonian Institution

R. Bishop

M. Blackman

Y. Cheng

R. Cunningham

E. Myers

J. Olin

Argonne National Laboratory

T. Brun

J. Jorgensen

J. Liu

P. Thiyagarajan

K. Vandervoort

Battelle Pacific Northwest

Laboratories

F. Brauer

G. Dudder

G. Endres

M. Failey

Boris Kidric Ins t.,

Belgrade, Yugosl.avia

M. Davidovic

D. Djordjevic

Brookhaven National Laboratory

R. DiNardo

L. Passell

C.E. C.M./C.N.R.S . Grenoble, France

M. Bessiere

Y. Calvayrac

M. Cornier-Qui(quandon

D. Gratias

S. Lefebvre

M. Marezio

S. Miraglia

A. Quivy

C.E. N. Saclay, 1France

R. Bellissent

289
PERSONNEL ROSTER

Paul Scherrer Inst. Oak Ridqe National Laboratory

Villiaen, Switzerland J. Cable

I. Anderson J. Fernandez-Baca

J. Hayter

Enerqv Research Foundat ion G. Ludtka

(The Netherlands) H. Mook

J. Woittiez R. Nicklow

B. Sales

Hahn-Meitner Institute H. Smith

(Berlin)

D. Behne Risd National Laboratory

J. Bohr

Institut Laue-Lanaevin

Grenoble, France Alfred University

A. Magerl R. Snyder

D. Richter R. Zhow

C. Vettier

Auburn University

Instituto se Pesouisas B. Taterchuck

Enerqeticas Nucleares, Sao Paulo, Brazil

M. Saiki Chalmers University of Technoloqy

L. Sjolin

KFA JUlich, Germanv

H. Grimm Colleqe of William and Mary

R. Hempelmann E. Schoe

M. Rossbach R. Wright

M. Stoepler

Colorado School of Mines

Korean Inst, of Sci. & Tech. N. Wada

H. Kim

Florida International U.

Lawrence Berkeley Lab. W. Jones

D. Morris

R. Sid Goethe University

W. Bauer

Los Alamos National Laboratory A. Bienok

T. Bowles

S. W. Cheong Harvard University

J. Eckert T. Chupp

Z. Fisk J. Richardson

H. Robertson E. Wasserman

R. Robinson

T. Sosnick Iowa State University

J. Trewhella A. Goldman

J. Wilkerson R. Barnes

J. Yethiraj

John Carroll University

J. Trivisonno

290
PERSONNEL ROSTER

Johns Hopkins University

C,

M.

A.

D.

F.G.

L. Chien

Creplak

Ganrin

Musser

Streitz

Xiao

Kyoto Institute of Technology

H. Kurokawa

S. Nomura

M. Shibayama

Q. Tran-Cong

Kyoto University fJaoan)

H. Hasegawa

T. Hashimoto

H. Jinnai

S. Sakurai

Lehigh University

A. Klein

L. Sperling

S. Yang

J. Yoo

M.I.T.

J.

M.

M.

S.

J.

B.

Didiskein

Dresselhaus

Green

Haile

Speck

Wuensch

McMaster University

W. Clarke

R. Barr

Miami University (Ohio)

J. Cantrell

Michigan State University

T. D. Brewer

Y. Fan

H. Kim

A. Moini

T. Pinnavaia

S. Sol in

M. S. Wang

Naqoya University

H. Choshi

Y. Matsushita

Y. Mogi

K. Mori

Y. Muroga

M. Nagasawa

I. Nodo

R. Saguchi

Y. Takahashi

Northwestern University

A. Allen

J. Barker

J. Weertman

Oregon State Graduate School

P. Davis

Penn State University

L. Pilione

J. Yehoda

Purdue University

A. Overhauser

Rutgers University

R. Gerhardt

T. Madey

San Jose State University

P. Englert

A. Ling

Scottish Universities Research Reactors

R. Scott

Temple University

J. Crow

C.-S. Jee

A. Kebede

T. Mihalisin

Texas A&M University

E. Schweikert

University of Annecy (France)

J. Bouillot

University of Antwerp (Belgium)

K. Michel

University of

P. Klavins

R. Shelton

California (Davis)

291
PERSONNEL ROSTER

University of CaVifornia (Irvine) University of Maryland

V. Guinn H.

0.

Ammon

Chitale

University of CaVifornia T. Clinton

(Santa Barbara) F. Divita

S. Cox J. Dodd

J. Pint C. Ford

D. Klingensmith G. Gordon

C. Levi M. Han

R. Odette W. Li

G. Stucky Z.

J.

Lin

Lynn

University of CaVifornia (San Dieqo) E. Mackey

J. Arnold F. Mantica

J. Ferreira A. Mizohata

B. Lee J. Nicol

B. Maple J. Ondov

J. Neumeier C. Purdy

K. Nishiizumi T. Quinn

K. Yang S.

S.

Regdos

Skanthakumar

University of Deliiware G. Tuncel

J. Beamish J. Valette-Silver

W. Dubner W.

S.

Walters

Wight

University of Exeter (U.K.) Z. Wu

R. Slade H. Zhang

B. Zimmerman i

University of Florida

S. Nagler University of Massachusetts

A. Hanyu

University of Houston L. Jong i

W.-K. Chu R. Stein

D. Gray

University of Milan (Italy) i

University of 111 inois M. Zocchi

J. Ankner

J. Borchers University of Michigan

B. Boyle D. Vincent

R. Du R. Fleming

J. Dura

C. Flynn University of Missouri

J. Kordas R. Berliner

A. Matheny W. Ching

G. Moore B. Hammouda

M. Salamon H. Kaiser

F. Tsui S. Werner

H. Zabel D. Worcester

University of 111 inois (Chicago) University of Nancy (France)

M. Said C. Dutour

J. Kouvel P. Mangin

G. Marchal

M. Verghat

292
PERSONNEL ROSTER

University of New Hampshire

N. Blakemore

R. Blakemore

Y. Gorby

University of North Carolina

E. Frye

N. Parikh

M. Swanson

University of Notre Dame

J. Furdyna

T. Giebultowicz

P. Klosowski

H. Luo

N. Samarth

U niversity of Pennsylvania

P. Davis

University of Pittsburg

W. Goldberg

University of Sussex, U.K.

J. Byrne

P. Dawber

J. Spain

University of Vermont

T. Flanagan

University of Virginia

T. Williamson

University of Washington

J. Billman

B. Meckel

E. Kaler

E. Mader

K. Mottet

W. Zoller

University of West Virginia

R. Kannan

M. Seehra

University of Wisconsin

D. Huber

Utah State University

T. Isenhour

Yale University

J. Flanagan

AT&T Bell Laboratories

F. Bates

R. Cava

G. Fredrickson

J. Mitchell

D. Murphy

W. Rhodes

J. Riley

J. Rosedale

L. Schneemeyer

S. Sunshine

J. Waszazak

S. Yegnasubramanian

Aero space Corporation

R. Bowman

J. Knudsen

Alliied Signal Corporation

T. Barden

G. Fish

A. Maeland

C. Parker

Atom ic Energy of Canada, LTD

W. Lennard

Bell Communications Research

Laboratories

P. Barboux

M. Giroud

L. Greene

G. Hull

P. Miceli

J. Tarascon

CARB

A. Svensson

Charles Evans & Assoc.

R. Fleming

CIDTECH

J. Carbone

M. Wadsworth

Directed Technologies, Inc.

N. Chesser

E. I . DuPont de Nemours Co.

J. Parise

M. Subramanian

293
PERSONNEL ROSTER

Eastman Kodak

T. Hossain

M. Landry

J. Levine

J. O'Reilly

C. Swanson

J. Tritten

H. Yang

Exxon

B. Abies

R. Busch

L. Fetters

J. Huang

J. Hughes

M. Kim

K. Liang

M. Lin

D. Lohse

R. Overfield

E. Sheu

S. Sinha

E. Sirota

GEN Corp.

I. Hargis

S. Aggarwal

GTE Laboratories

G. Hamill

W. R. Grace

R. Wormsbecker

Hughes, Malibu

R. Wilson

IBM (San Jose)

G. Hadziioannou

T. P. Russell

S. H. Anastasiadis

Imperial Chemical Industries

J. Howard

H. Stanley

Intel Corporation

N. Cox

Lockheed EMSCO

D. Lindstrom

Optoline Corp.

J. Bradshaw

Polaroid Corp.

S. Roy

Research Triangle

N. Wadlen

Southwest Research Inst . R. Page

SRL Inc.

S. Johnson

Westinghouse-Hanford Corp,

W. McElroy

294
E. PUBLICATIONS

Abies, B.; Yang, L.; Leta, D.; Majkrzak, C. F. "Fast Diffusion of

Interstitial Deuterium in Amorphous Silicon," Proceedings of the 12th

Int'l. Conf. on Amorphous and Liquid Semiconductors, Prague, 24-28 August

1987.

Ammon, H. L.; Choi, C. S.; Reddy, S. "Crystal Structure of 1,4-

diiodocubane," Acta Cryst. C44, 1671-1672 (1988).

Ammon, H. L.; Choi, C. S.; Bashir-Hashemi, B.; Moriarty, R. M.; Khosrowshahi,

S. J. "Structure of 1 - adamant anyl ammonium Trinitromethide," Acta Cryst.

C45, 319-321 (1989).

Ammon, H. L.; Choi, C. S.; Damvarapu, R. S.; Iyer, S.; Alster, J. "Crystal

Structure of Cubane-l,4-diammonium Bis-(trinitromethide)," Acta Cryst.,

in press.

Anastasiadis, S. H.; Russell, T. P.; Satija, S. K.; Majkrzak, C. F. "Neutron

Reflectivity Studies of the Surface Induced Ordering of Diblock

Copolymer Films," Phys. Rev. Lett. 62, 1852 (1989).

Anastasiadis, S. H.; Russell, T. P.; Satija, S. K.; Majkrzak, C. F. "Neutron

Reflectivity Studies of Thin Diblock Copolymer Films," Proceedings of

the National Meeting of the American Chemical Society, Dallas, Texas,

April 1989, p. 14.

Anastasiadis, S. H.; Russell, T. P.; Satija, S. K.; Majkrzak, C. F. "A

Neutron Reflectivity Study of the Order-Disorder Transition in Thin Film

Diblock Copolymer Films," Proceedings of the MRS Symposium on Neutron

Scattering for Materials Science, Boston, MA, 1989 (to be published).

Anastasiadis, S. H.; Russell, T. P.; Satija, S. K.; Majkrzak, C. F. "The

Morphology of Symmetric Diblock Copolymers as Revealed by Neutron

Reflectivity," J. Chem. Phys. (to be published).

Ankner, J. F.; Zabel , H.; Neumann, D. A.; Majkrzak, C. F. "Grazing-Incidence

Neutron Diffraction from Si (110)," Phys. Rev. B, in press.

Ankner, J. F.; Zabel, H.; Neumann, D. A.; Majkrzak, C. F. "Grazing-Angle

Neutron Diffraction," Phys. Rev. B40, 792 (1989).

Ankner, J. F.; Zabel, H.; Neumann, D. A.; Majkrzak, C. F.; Dura, J. A.;

Flynn, C. P. "Grazing-Angle Neutron Diffraction," Les Editions de

Physique (in press)

Ankner, J. F.; Zabel, H.; Neumann, D. A.; Majkrzak, C. F.; Matheny, A.;

Dura, J. A.; Flynn, C. P. "Neutron Reflectivity Study of Gd-Y

Interface," Proceedings of the MRS Symposium on Neutron Scattering for

Materials Science, Boston, MA, 1989 (to be published).

Bates, F. S.; Rosedale, J. H.; Fredrickson, G. H.; Glinka, C. J.

"Fluctuation-Induced First-Order Transition of an Isotropic System to a Periodic State," Phys. Rev. Lett. 61, 2229-2232 (1988).

295
PUBLICATIONS

Bauer, B. J.; Briber, R. M.; Han, C. C. Macromol . 22(2) , 940, (1989).

Bauer, W. H.; Bieniok, A.; Shannon, R. D.; Prince, E. "Neutron Powder

Diffraction Study and Thermogravimetry of Sodium Cesium Zeolite Rho,"

J. Solid State Chem. (in press).

Berk, N. F.; Hardman-Rhyne, K. A.; "Analysis of SAS Data Dominated by

Incoherent Multiple Scattering," J. Appl . Cryst. 21 645-651 (1988).

Bohr, J.; Gibbs, J.; Moncton, D. E.; D'Amico, K. L.; Majkrzak, C. F.;

Mohanty, K. "Synchrotron X-Ray Scattering Studies of Rare-Earth

Metals", Proc. of the Workshop on X-Ray and Neutron Scattering from

Magnetic Materials, November 1987, Argonne, IL, Physica B 159, 93

(1989).

Borchers, J. A.; Nieuwenhuys, G. J.; Salamon, M. B.; Flynn, C. P.; Du, R.;

Erwin, R. W.; Rhyne, J. J. "Magnetic Structure and Magnetostriction of

Epitaxial Er Films," J. Phys. Colloque C8, Suppl . #12, 49, 1685 (1988).

Borchers, J.; Salamon, M. B.; Du, R.; Flynn, C. P.; Erwin, R. W.; Rhyne, J.

J. "Characterization of Structural and Magnetic Order of Er/Y

Superlattices," Superlattices and Microstructures Vol. 4/5, Academic

Press, 1988, pp. 439-442.

Boumazouza, D., Mangin, P.; George, B.; Louis, P.; Brand, R. A.; Rhyne, J.

J.; Erwin, R. W. "Comment on the Paper 'Magnetism in Aug2 5^617 c'*"

Phys. Rev. 39, 749 (1989).

Briber, R. M.; Bauer, B. J. Macromol. 21(11) , 3296, (1988).

Buchenau, U.; Monkenbusch, M.; Stamm, M.; Majkrzak, C. F.; Nucker, N. "Neutron Scattering Study of Relaxations and Vibrations in Molten

Polyethylene," Proc. of the Workshop on Polymer Motion in Dense Systems,

1988.

Cahn, J. W.; Gratias, D.; Mozer, B. "A 6-D Structural Model for the

Icosahedral (AljSi)-Mu Quasicrystal ," J. Phys. (France) 49, 1225

(1988).

Cahn, J. W.; Gratias, D.; Mozer, B. "Patterson-Fourier Analysis of the

Icosahedral (AljSi)-Mu Alloy." Phys. Rev. B38, 1638 (1988).

Carr, M. J., Chambers, W. F., Melgaard, D., Himes, V. L., Stalick, J. K.;

Mighell, A. D. "NIST/Sandia/ICDD Electron Diffraction Database: A

Database for Phase Identification by Electron Diffraction." J. Res.

Natl. Inst. Stand. Technol . 94, 15-20 (1989).

Casella, R. C. "Comparison of Interplanar-Boson-Exchange Models of HighTemperature Superconductivity-'Possible Experimental Tests", Appl. Phys.

Lett, (in press)

.

296
PUBLICATIONS

Case! la, R. C. "Dependence of T on the Number of CuO^ Planes per Cluster in

Interplanar-Boson-Exchange Models of High-T Superconductivity", Solid

State Commun. 70, 75-77 (1989).

Casella, R. C. "Theoretical Models For High-Temperature Superconductivity,"

Nuovo Cimento DIO, 1439-1448 (1988).

Cava, R. J.; Marezio, M.; Krajewski, J. J.; Peck, W. F., Jr.; Santoro, A.;

Beech, F. "Neutron Powder Diffraction Study of Pb2Sr2YCu30g, the

Prototype of a New Family of Superconductors," Physica C, 157, 272-278

(1989)

Chien, C. L.; Xiao, G.; Cieplaak, M. Z.; Musser, D.; Rhyne, J. J.; Gotaas, J.

A. "Superconductivity in Orthorhombic and Tetragonal YBa^jCu, A )-j0

Systems (A = Zn, Ga, Al , and Co)," Superconductivity and Its

Applications, Kwok, H. S.; Shaw, D. T., eds., Elsevier Publishing, 1988,

pp 110.

Choi, C. S.; Prask, H. J. "Orientation Distribution of Fiber-Axes and

Neutron Powder Diffraction Profiles." Eighth International Conference on Texture of Materials, Kallend, J. S.; Gottstein, G., eds. The

Metallugical Society, Inc., Publications, 215-221 (1988).

Choi, C. S.; Prask, H. J.; Ostertag, C. P. "Texture Study of Magnetically

Aligned YBa^Cu^Oy-type Materials by Neutron Diffraction." J. Appl

.

Cryst. (in press)

.

Copley, J. R. D. "An Analytical Method to Characterize the Performance of

Multiple Section Straight-Sided Neutron Guide Systems," Nuclear

Instrument Methods in Phys. Res. A (submitted).

Copley, J. R. D. "On the Use of Acceptance Diagrams to Calculate the

Performance of Multiple Section Straight-Sided Neutron Guide Systems,"

Advanced Neutron Sources , Physics Conference Series vol. 97, Institute

of Physics Publishing, London, 1989 (in press).

Copley, J. R. D. "On the Use of Multiple Slot Multiple Disk Chopper

Assemblies to Pulse Thermal Neutron Beams," Nuclear Instruments and

Methods in Phys. Res. A2Z3, 67-76 (1988).

Copley, J. R. D. "The Effect of Chopper Jitter on the Time-Dependent

Intensity Transmitted by Multiple-Slot Disk Chopper Systems," in

Advanced Neutron Sources , Physics Conference Series Vol. 97, Institute

of Physics Publishing, London, 1989 (in press).

Copley, J. R. D. "The Significance of Multiple Scattering in the Interpretation of Small Angle Neutron Scattering Experiments," J. Appl. Cryst.

21, 639-644 (1988).

297
PUBLICATIONS

Copley, J. R. D.; Majkrzak, C. F. "Calculations and Measurement of the

Performance of Converging Neutron Guides," in Thin-Film Optical Devices:

Mirrors, Supermirrors, Multilayer Monochromators, Polarizers and Beam

Guides , Majkrzak, C. F., ed. Proc. SPIE 983, 93-104 (1989).

Copley, J. R. D.; Stone, C. A. "Neutron Scattering and Its Effect on Reaction Rates in Neutron Absorption Experiments," Nuclear Instruments

and Methods in Phys. Res. A281, 593 (1989).

DiNardo, R. P.; Majkrzak, C. F.; Neumann, D. A. "Fabrication of Neutron

Polarizing Multilayers by Sputtering," SPIE Proceedings Vol. 983, ed.

C. F. Majkrzak, SPIE, Bellingham, WA, 149 (1989).

DiNardo, R. P.; Majkrzak, C. F.; Neumann, D. A. "Fabrication of Neutron

Polarizing Fe-Si Multilayers by Sputtering," in Thin Film Neutron

Optical Devices: Mirrors, Supermirrors, Multilayer Monochromators,

Polarizers, and Beam Guides , ed. C. F. Majkrzak, SPIE, Bellingham, WA,

149 (1988).

DiNardo, R. P.; Takacs, P. Z.; Majkrzak, C. F.; Stefan, P. M. "Sputter

Deposition System for Controlled Fabrication of Multilayer Mirrors,"

Proc. of the 29th SPIE Int'l. Tech. Symposium, August 1985, San Diego,

CA. Vol. 563, p. 30.

Endoh, Y.; Majkrzak, C. F. "Polarized Neutron Diffraction Studies of

Magnetic Multilayer Structures," Chapter in a book on metallic

superlattices, Shinjo, T.; Takada, T., eds. Elsevier Science

Publications (1989).

Erwin, R. W.; Rhyne, J. J.; Borchers, J.; Du, R.; Salamon, M. B.; Flynn, C.

P. "Magnetoelasticity in Rare-Earth Superlattices and Films," Physica B (to be published)

.

Erwin, R. W.; Rhyne, J. J.; Borchers, J.; Salamon, M. B.; Du, R.; Flynn, C.

P. "Structure of Er|Y Superlattices," J. de Phys. Colloque C8, Suppl

.

#12, 1631 (1988).

Fan, Y. B.; Solin, S. A.; Neumann, D. A.; Sabel , H.; Rush, J. J. "Elastic

Neutron Scattering Studies of the Structure of Graphite Intercalated

With Potassium and Ammonia," Phys. Rev. B36, 3386 (1989).

Fernandez-Baca, J. A., Rhyne, J. J.; Erwin, R. W.; Fish, G. E. "Neutron

Scattering Study of the Magnetic Correlations of Iron-Rich Fe-Ni-Zr

Glasses," J. Phys. Colloque C8, Suppl. #12, 1207 (1988).

Fernandez-Baca, J. A.; Lynn, J. W.; Rhyne, J. J.; Fish, G. E. "Low

temperature Spin Waves in Amorphous '^^gn-x'^^^^lO' " '^' ^PP^ • P^^^s. 63,

3749 (1988).

Fischer, R.; Baur, W.; Shannon, R.; Parise, J.; Faber, J.; Prince, E. "New,

Different Forms of Ammonium Loaded, and Partly Deammoniated Zeolite Rho

Studied by Neutron Powder Diffraction," Acta Crystallogr. Sect. C.

(1988) in press.

298
PUBLICATIONS

Flynn, C. P.; Borchers, J. A.; Demers, R. T.; Du, R.-R.; Dura, J. A.; Klein,

M. v.; Kong, S. H.; Salamon, M. B.; Tsui, T.-F.; Yadavalli, S.; Zhu, X.;

Zabel, H.; Cunningham, J. E.; Erwin, R. W.; Rhyne, J. J. "Growth and

Properties of Superlattices with Ant i ferromagnetic Rare Earths," (to be

published)

.

Flynn, C. P.; Tsui, F.; Salamon, M. B.; Erwin, R. W.; Rhyne, J. J.

"Dependence of Magnetic Coupling on Growth Direction in Epitaxial Dy-Y

Superlattices," Phys. Lett. F (submitted for publication).

Flynn, C. P.; Tsui, F.; Salamon, M. B.; Erwin, R. W.; Rhyne, J. J.

"Anisotropic Response of Rare Earths in Superlattices," (to be

published).

Forano, C; Slade, R. C. T.; Andersen, E. K.; Andersen, I. G. K.; Prince, E. "Neutron Diffraction Determination of Full Structures of Anhydrous Li-X

and Li-Y Zeolytes," J. Solid State Chem. (in press).

Giebultowicz, T M.; Rhyne, J. J.; Ching, W. Y.; Huber, D. L; Furdyna, J. K.;

Lebech, B.; Galazka, R. R. "Harmonic Magnons in Zn, Mn Te and

Cdjj^MnJe," Phys. Rev. B39, 6857 (1989).

Giebultowicz, T. M.; Holden, T. M. "Neutron Scattering Studies of Magnetic

Ordering and Magnetic Dynamics of Diluted Magnetic Semiconductors," in

Diluted Magnetic Semiconductors , Furdyna, J. K.; Kossut, J., eds., in

the series Semiconductors and Semimetals , Vol. 25, p. 120, Academic

Press, Boston, MA 1988.

Giebultowicz, T. M.; Klosowski, P.; Rhyne, J. J.; Udovic, T. J.; Furdyna, J.

K.; Giriat, W. "Magnetic Exchange Interactions in Co-based II-VI

Diluted Magnetic Semiconductors: Zn, Co S," Phys. Rev. B (in press).

Giebultowicz, T. M.; Rhyne, J. J.; Seehra, M. S.; Kannan, R. "Neutron

Diffraction in COoMg, Solid Solutions," J. Phys. Colloque C8, 49,

1105 (1988).

Giebultowicz, T. M.; Rhyne, J. J.; Furdyna, J. K.; Galazka, R. R. "Neutron

Diffraction Studies of Cd, Mn Te and Zn, Mn Te Single Crystals," J.

Phys. Colloque C8, 49, 1199 (1988).

Glinka, C. J. "Workshop on Microstructure and Macromolecular Research with

Cold Neutrons," J. A. Gotaas and C. O'Connor, J. Res. Natl. Inst. Stand.

Technol. 93(6) , 667-669 (1988).

Goldman, A.; Gao, Y.; Ting, S-T.; Crow, J. E.; Li, W.-H.; Lynn, J. W.

"Crystal Electric Fields in Rare Earth-Ba-Cu-Oxide Superconductors," J.

Mag. Mag. Mater. 76-77 , 607 (1988).

Gotaas, J. A.; Rhyne, J. J.; Wenger, L. E.; Mydosh, J. A. "Magnetic

Structure of Yq g^ErQ Q3," J. Phys. (Paris) 49, C8-365-366 (1988).

299
PUBLICATIONS

Gotaas, J. A.; Said, M. R.; Kouve! , J. S.; Brun, T. 0. "Magnetic Structure

of Cubic TbQ 3YQ ^Ag", J. Phys. (Paris) 49, C8-345-346 (1988).

Gratias, D.; Cahn, J. W.; Bessiere, M.; Calvayrac, Y.; Lefebre, S.; Quivy,

A.; Mozer, B. "N-dimensional Crystallographic Description of the

Icosahedral Phases; The Example of the AU-Mn^iSig Quasiperiodic

Structure," Proc. of the NATO Conference, Acquafredda, Plenum (1988).

Gratias, D.; Cahn, J. W.; Mozer, B. "Six-Dimensional Fourier Analysis of

Icosahedral A1^3Mn2jSOg Alloy," Phys. Rev. B38, 1643 (1988).

Grimm, H.; Stiller, H.; Majkrzak, C. F.; Ruppoecht, A. "Neutron Scattering

Study of the Hydration Hull of DNA by HpO/D^O Exchange," Proceedings of

the Int'l. Conf. on Neutron Scattering, Grenoble, France, July 1988,

Physica B 156 and 157 , 464 (1989).

Grimm, H.; Stiller, H.; Majkrzak, C. F.; Rupprecht, A.; Dahlborg, U. "Observation of Acoustic Umklapp Phonons in Water-Stabilized DNA by

Neutron Scattering," Phys. Rev. Lett. 59, 1780 (1987).

Heise, W. H.; Lu, K.; Kuo, Y-J; Tatarchuk, B. J.; Udovic, T. J.; Rush, J. J.

"Neutron Scattering Study of Hydrogen on Ruthenium Sulfide," J. Phys.

Chem. 92, 5184 (1988).

Himes V. L.; Mighell, A. D.; Stalick, J. K.; Young, S.; Carr, M.; Anderson,

R.; Holomany, M.; Jenkins, R.; Lyman, C. "Elemental and Interplanar

Spacing Index for Phase Identification by Electron and X-Ray

Diffraction," published jointly by NIST and the International Centre for

Diffraction Data (1989).

Himes, V. L.; Mighell, A. D. "NBS Crystal Data: Compound Identification and

Characterization Using Lattice-Formula Matching Techniques,"

Metallurgical Society (publisher), Chapter in Computerized Metallurgical

Databases, pp. 153-168 (1988).

Horton, J. C; Squires, G. L.; Boothroyd, A. T.; Fetters, L. J.; Rennie, A.

R.; Glinka, C. J.; Robinson, R. A. "Small Angle Neutron Scattering From

Star-Branched Polymers in the Molten State," Macromol . 22, 681-686

(1989).

Krueger, S.; Zaccai, G.; Wlodawer, A.; Langowski, J.; O'Dea, M.; Maxwell, A.;

Gellert M. "Neutron and Light Scattering Studies of DNA Gyrase and Its

Complex With DNA," (1989) (submitted for publication).

Krueger, S.; Lynn, J. W.; Russell, J. T.; Nossal , R. "Small Angle Neutron

Scattering Method for in situ Studies of the Dense Cores of Biological

Cells and Vesicles: Application to Isolated Neurosecretory Vesicles,"

J. Appl . Crystallogr. (to be published).

Krueger, S.; Olson, G. J.; Rhyne, J. J.; Blakemore, R. P.; Gorby, Y. A.;

Blakemore, N. "Small Angle Neutron and X-Ray Scattering From Magnetite

Crystals in Magnetotactic Bacteria," J. Mag. Mag. Mater, (to be

published).

300
PUBLICATIONS

Kwo, J.; Hong, M.; Hsieh, T. C; Fleming, R. M. ; McWhan, D. B.; Yafet, Y.;

Majkrzak, C. F.; Gibbs, D.; Boni, P.; Goldman, A. I.; Cable, J. W.;

Bohr, J.; Grimm, H. "Rare-Earth Magnetic Superlattices," International

Conference on Magnetism, Paris, France, July 1988, J. Phys. Colloque C8,

49, 1651 (1988).

Lee, E.; Elminger, M.; Passell, L.; Majkrzak, C. F. "The Brookhaven Neutron

Reflection Spectrometer," (to be published).

Li, W.-H.; Lynn, J. W.; Mook, H. A.; Sales, B. C; Fisk, Z. "Long Range

Antiferromagnetic Order of the Cu in Oxygen-Deficient, /?BapCu^Og ",

Rhys. Rev. B3Z [Rapid Communications), 9844 (1988).

Li, W.-H.; Lynn, J. W.; Stanley, H. B.; Udovic, T. J.; Shelton, R. N.;

Klavins, P. "Antiferromagnetic Structure and Crystal Field Splittings

in the Cubic Heusler Alloys HoPd2Sn and ErP2Sn," J. Phys. (Suppl.) 49,

C8-373 (1988).

Li, W.-H; Lynn, J. W.; Stanley, H. B.; Udovic, T. J.; Shelton, R. N.;

Klavins, P. "Crystal-Field Splittings in the Cubic Heusler Alloys

HoPd2Sn," Phys. Rev. B39, 4119 (1989).

Long, C. G.; Krueger, S. "Multiple Small Angle Neutron Scattering

Characterization of the Densification of Ceramics: Application to

Microporous Silica," J. Appl . Crystallogr. (in press).

Long, C. G.; Krueger, S.; Gerhardt, R. A. "Small Angle Neutron Scattering

Characterization of Microporous Silica," Proc. Symp. on Adv.

Characterization Tech. for Ceramics, 24-26 October 1988.

Lynn, J. W.; Li, W.-H. "Magnetic Order in /?Ba2Cu30g^^," J. Appl. Phys. 64,

6065 (1988).

Lynn, J. W.; Li, W.-H.; Mook, A; Sales, B. C; Fisk, Z. "Nature of the

Magnetic Order of Cu in Oxygen Deficient /^Ba^Cu^Og , " Phys. Rev. Lett.

60, 2781 (1988).

Lynn, J. W.; Li, W.-H.; Mook, H. A.; Sales, B. C; Fisk, Z. "Antiferromagnetic Order of the Cu in f^^^2^^2^6+x'" '^' ^^^^' —' ^^'^' ^^^^

(1988).

Lynn, J. W.; Li, W.-H.; Trevino, S. F.; Fisk, Z. "Pressure Dependence of the

the Cu Magnetic Order in NdBa2Cu20g^^," Phys. Rev. B460 , (1989) (to be

published.

Lynn, J. W.; Skanthakumar, S.; Clinton, T. W.; Kebede, A.; Jee, C.-S.; Crow,

J. E.; Mihalisin, T. Phys. Rev. B40 [Rapid Communications) , (1989) (to

be published) .

301
PUBLICATIONS

Majkrazak, C. F.; Neumann, D. A.; Copley, J. R. D.; DiNardo, R. P. "Fe-W

Supermirrors for Polarizing Neutrons," Proc. MRS Fall 1988 Symposium D,

103 , 115 (1988).

Majkrzak, C. F. "Multilayer and Supermirror Polarizers for Neutrons,"

Proceedings of the Workshop on X-Ray and Neutron Scattering From

Magnetic Materials, ANL, November 1987, Physica B 159, 143 (1989).

Majkrzak, C. F. "Polarized Neutron Diffraction Studies of Synthetic

Superlattices," Metallic Multilayers and Epitaxy, Hong, M.; Wolf, S.;

Gubser, D. C, eds. The Metallurgical Society, Pittsburgh, PA; 1988.

Majkrzak, C. F. "Polarized Neutron Scattering: Methods and Studies

Involving Artificial Superlattices," Proc. of the Int'l Conf. on Neutron

Scattering, Grenoble, France, July 1988, Physica B, 156-157 , 619 (1989).

Majkrzak, C. F. "Summary of the Recent Conference on Thin-Film Neutron

Optical Devices," Proc. of ICANS-X, Los Alamos, NM, October 3-7, 1988

(in press).

Majkrzak, C. F.; Berk, N. F. "Neutron Flux Enhancement Using Spin-Dependent

Interaction Potentials," Phys. Rev. B40, 371 (1989).

Majkrzak, C. F.; Cox, D. E.; Lehmann, M. S. "Neutron Diffraction," to appear

as a chapter in Physical Methods of Chemistry , Rossiter and Hamilton,

eds. John Wiley and Sons, Inc. (to be published).

Majkrzak, C. F.; Gibbs, D.; Kwo, J.; Hong, M.; Yafet, Y.; Bohr, J.; Chien, C.

L. "Magnetic Rare Earth Superlattices," Adv. Phys. (to be published).

Majkrzak, C. F.; Gibbs, D.; Kwo, J.; Hong, M.; Yafet, Y.; Bohr, J.; Chien, C.

L. "Magnetic Rare Earth Superlattices," Adv. Phys. (to be published).

Majkrzak, C. F.; Glinka, C. J.; Satija, S. K. "Applications of Mirrors,

Supermirrors, and Multilayers at the NBS Cold Neutron Research

Facility," SPIE Proc. Vol. 983, Majkrzak, C. F., ed. SPIE, Bellingham,

WA, 1989 p. 129.

Majkrzak, C. F.; Neumann, D. A.; Copley, J. R. D.; DiNardo, R. P. "Fe-W

Supermirrors for Polarizing Neutrons," Proc. of the 1987 Fall Meeting of

the Mater. Res. Soc, Vol. 103, p. 115.

Majkrzak, C. F.; Satija, S. K.; Neumann, D. A.; Rush, J. J.; Lashmore, D.;

Johnson, C; Bradshaw, J.; Passell, L.; DiNardo, R. "Determination of

Hydrogen Density Profiles in Thin Films and Multilayers by Neutron

Reflection," Proc. of the MRS Symposium on Neutron Scattering for

Materials Science, Boston, MA, 1989 (to be published).

Mangin, P.; Boumazouza, D.; George, B.; Rhyne, J. J.; Erwin, R. W. "Static

and Dynamic Properties of the (^^^ Cr, )yrPjrC,Q Reentrant Spin Glass

Amorphous Alloy," Phys. Rev. B (to be published).

302
PUBLICATIONS

Matsushita, Y.; Nakao; Saguchi, R.; Mori, K.; Chosi, H.; Muroga, Y.; Noda,

I.; Nagasawa, K.; Chang, T.; Glinka, C. J.; Han, C. C. "Phase Contrast

Matching in Lamellar Structures Composed of Mixtures of Labeled and

Unlabeled Block Copolymers for Small Angle Neutron Scattering,"

Macromol. 21, 1802-1806 (1988).

Miceli, P. F.; Tarascon, J. M.; Bagley, B. G.; Greene, L. H.; Barboux, P.;

Hull, G. W.; Giroud, M.; Rhyne, J. J.; Neumann, D. A. " Magnetic

Properties of Some High T Compounds," in the Proc. of the 10th Winter

Meeting on Low Temperature Physics of High Temperature

Superconductivity, World Scientific Publishing, (in press).

Miceli, P. F.; Tarascon, J. M.; Barboux, R.; Greene, L. H.; Bagley, B. G.;

Hull, G. W.; Giroud, M.; Rhyne, J. J.; Neumann, D. A. "Magnetic

Transitions in the System YBa2Cu2 qCOq o^e+v'" ^^^^' ^^^ ' ^^' ^^^'^^ (1989).

Miceli, P. F.; Tarascon, J. M.; Greene, L. H.; Barboux, P.; Giroud, M.;

Neumann, D. A.; Rhyne, J. J.; Schneemeyer, L. F.; Waszczak, J. V. "Antiferromagnetic Order in Yba^Cu^ Co Og^ , " Phys. Rev. B38, 9209

(1988).

Miceli, P. F.; Tarascon, J. M.; Greene, L. H.; Barboux, P.; Jorgensen, J. D.;

Rhyne, J. J.; Neumann, D. A. "Charge Transfer and Bond Lengths in

YBa^jCu, ^M^Occj" Proc. Mater. Res. Soc. (in press).

2 3-x X 5+5 ^ ^ '

Mighell, A. D.; Himes, V. L. "A New Method for Phase Identification for

Electron Microscopists, " J. Elect. Micros. Techn. (submitted for

publ ication)

Minor, W.; Giebultowicz, T. M. "Studies of fee Heisenberg Antiferromagnets

by Monte Carlo Simulations on Large Spin Arrays," J. Phys. Colloque C8,

49, 1551 (1988).

Neumann, D. A.; Zabel , H.; Morkoc, H, "Terracing in Strained-Layer

Superlattices," J. Appl . Phys. 64, 3024 (1988).

Neumann, D. A.; Zabel, H.; Fan, Y. B.; Solin, S. A.; Rush, J. J. "Neutron

Scattering Study of Phonon-Libron Coupling in Potassium-Ammonia

Intercalated Graphite," Phys. Rev. B37, 8424 (1988).

Neumann, D. A.; Zabel, H.; Magerl , A.; Fan, Y. B.; Solin, S. A. "Neutron

Spectroscopy of Rotational Tunneling of NH^ in Graphite," in Graphite

Intercalation Compounds: Science and Applications , Endo, M.;

Dresselhaus, M. S.; Dresselhaus, G., eds. Mater. Res. Soc. 9 (1988).

Nicol, J. M.; Eckert, J.; Howard, J. "The Dynamics of Molecular Hydrogen

Adsorbed in CoNa-A Zeolite," J. Phys. Chem. 92, 7117 (1988).

Nicol, J. M.; Rush, J. J.; Kelley, R. D. "Inelastic Neutron Scattering

Studies of the Interaction of Hydrogen With Palladium Black," Surface

Sci. 197, 67 (1988).

303
PUBLICATIONS

Parise, J. B.; McCarron, E. M.; Sleight, A. W.; Prince, E. "Refinement of

the Structure of ^'-Mo03," Matls. Sci. Forum 27/28 , 85-88 (1988).

Parise, J. B.; Torardi, C. C; Subramanian, M. A.; Gopalakrishnan, J.;

Sleight, A. W.; Prince, E. "Superconducting TK n^'^? 0^"^6+5* ^

High Rsolution Neutron Powder and Single Crystal X Ray Diffraction

Investigation," Phys. 059, 239-244 (1989).

Prince, E. "Principles of Rietveld Refinement," Proc. of the International

Workshop on the Rietveld Method, Petten, The Netherlands, (in press,

1989)

Prince, E. "The Crystal Structure of Ammonium Paradodecatunstate

Tetrahydrate by Neutron Diffraction," Howard T. Evans, Acta Cryst. Sect.

C. (in press, 1989)

Prince, E. "The Maximum Extropy Distribution Consistent with Observed

Structure Amplitudes," Acta Crystallogr. Sect. A. A45, 200-203 (1988).

Prince, E. "Phase Extension by Combined Entropy Maximization and Solvent

Flattening", Acta Crystallogr. A4i, 216-222 (1988).

Prince, E. "An Alternative Approach to the Hauptman-Karle Determinantal

Inequalities," Acta Crystallogr. Sect. A. A45, 144 (1988).

Prince, E.; Slade, R. C. T.; Ramanan, A.; West, B. C. "The Structure of

VgMOgO-Q Determined by Powder Neutron Diffraction," J. of Solid State

Chemistry (in press)

.

Rhyne, J. J. "Highlights from the Exotic Phenomena of Lanthanide Magnetism,"

Chapter 76, Handbook on the Physics and Chemistry of Rare Earths, Vol.

11, Gschneidner, K. A.; Eyring, L., eds. North Holland Publishing,

Amsterdam, 1988, pp. 293-322.

Rhyne, J. J.; Erwin, R. W.; Borchers, J.; Salamon, M. B.; Du, R.; Flynn, C.

P. "Exchange and Magnetostrictive Effects in Rare Earth Superlattices,"

J. Less Com. Metals 148, 17 (1989).

Rhyne, J. J.; Erwin, R. W.; Borchers, J.; Salamon, M. B.; Du, R.; Flynn, C.

P. "Magnetic Multilayers," Physica Scripta (to be published).

Rhyne, J. J.; Erwin, R. W.; Borchers, J.; Salamon, M. B.; Du, R.; Flynn, C.

P. "Magnetic Ordering in Rare Earth Multilayers Studied by Neutron

Diffraction," Metallic Multilayers and Epitaxy, Hong, M.; Wolf, S.;

Gubser, D. C, eds. Metallurgical Soc. Inc., Warrendale, PA, 1988,

pp. 11-32.

Rhyne, J. J.; Erwin, R. W.; Borchers, J.; Salamon, M. B.; Du, R.; Flynn, C.

P. "Neutron Scattering Studies of Magnetic Multilayers," Physica B159,

111 (1989).

304
PUBLICATIONS

Rodgers, J. R.; Mighell, A. D. "Numeric Databases in Materials and

Biological Sciences," Editors of a Special Issue of the J. Res. Natl.

Inst. Stand. Technol . 94, 1-94 (1989).

Rodgers, J. R.; Mighell, A. D. For a Special Issued (on Numeric Databases in

Materials and Biological Sciences) of the J. Res. Natl. Inst. Stand.

Technolo. 94, 1-94 (1989).

Rush, J. J. "Research Opportunities and Planned Facilities at the Advanced

Neutron Source," A.N.S. Trans. 5Z, 290 (1988).

Rush, J. J.; Flanagan, T. B.; Craft, A. P.; Clewley, J. D.; Sakamoto, Y.

"The Optic Mode Frequencies and Solubilities of Hydrogen in Ordered and

Disordered Rd^Mn," J. Phys, F (in press).

Rush, J. J.; Udovic, T. J.; Hempelmann, R.; Richter, D.; Driesen, G.;

"Hydrogen Sites in Amorphous f'^gB^hB^^x P>^ot)ed by Neutron

VibrationalSpectroscopy," J. Phys.: Condensed Matter 1, 1061-1070

(1989).

Santoro, A. "Crystallography of Superconductors," in High-Temoerature

Superconductivity , J. W. Lynn, ed., Springer-Verlag publishers, (in

press, 1989).

Santoro, A. "Crystal Chemistry of Superconductors and Related Compounds," in

Chemistry of Superconducting Materials , Vanderah, T. A., ed., Noyes

Publications (in press, 1989).

Santoro, A. "Defective Structures of Ba^YCu^O and Ba^YCu^, M

(M = Fe, Co, Co, Al , Ga, ...)," in Chemistry of Superconducting

Materials , Vanderah, T. A., ed., Noyes Publications (in press, 1989).

Santoro, A.; Beech, F.; Marezio, M.; Cava, R. J. "Crystal Chemistry of

Superconductors. A Guide to the Tailoring of New Compounds," Physica

C156, 693-700 (1988).

Satija, S. K.; Majkrzak, C. F.; Anastasiadis, S. H.; Russell, T. P. "The

Morphology of Symmetric Di block Copolymers as Revealed by Neutron

Reflectivity," Proc. of the MRS Symposium on Neutron Scattering for

Materials Science, Boston, MA 1989 (to be published).

Schwarzenbach, D.; Abrahams, S. C; Flack, H. D.; Gonschorek, W.; Hahn, T.;

Marsh, R. E.; Prince, E.; Robertson, B. E.; Rollett, J. S.; Wilson, A.

J. C. "Report of the International Union of Crystallography

Subcommittee on Statistical Descriptors," Crystallogr. Sect. A., A45

63-75 (1989).

Seehra, M. S.; Giebultowicz, T. M. "Magnetic Structures of fee Systems with

Nearest-Neighbor and Next-Nearest Neighbor Exchange Interactions," Phys.

Rev. B38, 11898 (1988).

305
PUBLICATIONS

Sjolin, L.; Svensson, L.; Prince, E.; Sundell , S. "Phase Inprovement in the

Structure Interpretation of Fragment TR^C from Bull Testis Calmodulin

Using Combined Entropy Maximization and Solvent Flattening," Acta

Crystallogr. B (in press).

Skanthakumar, S.; Zhang, H.; Clinton, T. W.; Li, W-H.; Lynn, J. W.; Fisk, Z.;

Cheong, S-W. "Magnetic Phase Transitions and Structural Distortion in

Nd^CuO.," Physica C (to be published).

Spano, M. L., Gotaas, J. A.; Rhyne, J. J. "Neutron Scattering Study of

Magnetic Order in a Tb«^ rDy^s r Single Crystal," J. Phys. Colloque C8,

Suppl. 12, 345 (1988). ^'^ ^'^

Tarascon, J. M.; Miceli, P. F.; Barboux, P.; Hwang, D. M.; Hull, G. W.;

Giroud, M.; Greene, L. H.; Le Page, Y.; McKinnon, W. R.; Tselepis, E.;

Pleizier, G.; Eibschutz, M.; Neumann, D. A.; Rhyne, J. J. "Structure

and Magnetic Properties of Doped Co and Fe-Bi«Sr«Cu, „M Phases,"

Phys. Rev. B39, 11587 (1989). ^ '^ i-x x y

Torardi, C. C; Reiff, W. M.; Prince, E. "Topochemical Li-ion Insertion into

FeClMoO. and Fe2(MoO.)~: Structure and Magnetism of LiFeClMoO, and

Li2Fe2(Mo04)3," Matls. Sci. Forum 27/28, 223-228 (1988).

Tran Qui, D.; Hamdoune, S.; Soubeyroux, J. L.; Prince, E. "Neutron Powder

Diffraction Study of Solid Solution Li, Ti« y^^v'^-^^i?'" *^- Solid State

Chem. 72, 309-315 (1988). ^^^ ^'^ x j i^

Udovic, T. J.; Nicol, J. M.; Cavanagh, R. R.; Rush, J. J. "Hydrogen

Adsorbate-Adsorbate Interactions on Transition Metal Surfaces as Studied

by Incoherent Inelastic Neutron Scattering," 196th National Meeting of

the American Chemical Society, Los Angeles, CA, September 28, 1988.

Udovic, T. J.; Rush, J. J.; Sander, L. C. "Neutron Scattering Study of the

Vibrations and Dynamics of Trimethylsilyl Adsorbates on Silica," 63rd

American Chemical Society Colloid and Surface Science Symposium,

Seattle, WA, June 20, 1989.

Vergnat, M.; Houssaini, S.; DuFour, C; Brunson, A.; Marchal, G.; Mangin,

Ph.; Erwin, R. W.; Rhyne, J. J.; Vettier, C. "Evidence of Hydrogen

Modulation in Si/Si :H Amorphous Multilayers," Phys. Rev. B (to be

published) .

Yafet, Y.; Kwo, J.; Hong, M.; Majkrzak, C. F.; O'Brien, T. "Interlayer

Exchange in Magnetic Superlattices," J. Appl . Phys. 63, 3453 (1988).

Yethiraj, M.; Robinson, R. A.; Rhyne, J. J.; Gotaas, J, A.; Buschow, K. H. J. "Magnetic and Crystal lographic Properties of UNiSn," J. Mag. Mag. Mater.

(to be published) .

306
PUBLICATIONS

Yoo, J. N.; Sperling, L. H.; Glinka, C. J.; Klein, A. "Characterization of

Film Formation from Polystyrene Latex Particles Via SANS," Macromol

(submitted for publication).

Yu, S.C.; Lynn, J.W.; Rhyne, J.J.; Fish, G.E. "Spin Wave Excitations in

Amorphous Fe^gBj^Sig," J. Appl . Phys. 63, 4083 (1988)

Zabel , H.; Neumann, D. A. "Neutron Scattering Studies of Potassium-Ammonia

Layers in Graphite," Can. J. Chem. 66, 666 (1988).

Zabel, H., Neumann, D. A. "Neutron Scattering Studies of Potassium-Ammonia

Layers in Graphite," Can. J. Chem. 66, 666 (1988).

INDEPENDENT PROGRAMS

Banerjee, I.; Frost, M.; Davies, P.; Cox, J. N. and Downing, R. G., "SIMS

and NDP Studies of Si02;Si3N4/Si02/Si Structures," Proc. SIMS VII

Conf., John Wiley and Sons (submitted for publication).

Becker, D. A. "Fast Neutron INAA: Nickel Sensitivities and Fluence

Variations at Three Reactors," Trans. Am. Nucl . Soc. 56> 193 (1988).

Becker, D. A. "Homogeneity and Evaluation of the New NIST Leaf CRMs," J.

Radioanal. Nucl. Chem. (in press).

Becker, P. R.; Koster, B. J.; Wise, S. A. and Zeisler, R., "Alaskan Marine

Mamal Tissue Archival Project," Biol. Trace Elem. Res. (submitted for

publication) .

Blackman, M. J., Ceramic Technology and Problems of Social Evolution in

Southwestern Iran. Proceedings of the Materials Research Society.

Pittsburg, PA, 1988.

Blackman, M. J. Chemical Characterization of Ceramics, Unfired clay

Artifacts, and Source Clays from Tell Leilan, Syria. Ninevite 5 Symposium Volume, ed. Harvey Weiss, Yale University Press, New Haven, CT

(in press)

Blackman, M. J.; Mery, S.; Wright, R. P. Production and Exchange of Ceramics

on the Oman Peninsula from the Perspective of Hili. J. Field

Archaeology (1988).

Burger, G.; Schwartz, R. B. Guidelines on Calibration of Neutron Measuring

Devices. Technical Reports Series No. 285, International Atomic Energy

Agency, Vienna, Austria, 1988.

Carpenter, J. M.; Mildner, D. F. R.; Cudrnak, S. S.; Hilleke, R. 0. "The

Neutron Transmission of Single Crystal MgO Filters," Nucl. Instrum.

Meth. A2Z8, 397-401 (1989).

307
PUBLICATIONS

Caswell, R. S.; Coyne, J. J. "Effects of Track Structure on Neutron

Microdosimetry and Nanodosimetry, Nuclear Tracks and Radiation

Measurements," (in press).

Caswell, R. S.; Coyne, J. J. "Microdosimetry of Radon and Radon Daughters,"

Radiation Protection Dosimetry (submitted for publication).

Coyne, J. J.; Caswell, R. S.; Zoetelief, J. "Calculations of the Relative

Effectiveness of Alanine for Neutrons with Energies up to 17.1 MeV,"

Radiation Protection Dosimetry (submitted for publication).

Coyne, L. D.; Wu., W. "An Examination of Mechanisms Responsible for

Incoherent Scattering of Subthermal Neutrons by Polymers," Polymer Comm.

(in press)

252 Eisenhauer, C. M.; Hunt, J. B. "Anisotropic Neutron Emission from a CF

Source," Radiation Protection Dosimetry 22(4) , 253-258 (1988).

Germani, M. S.; Zoller, W. H. "Vapor-Phase Concentrations of As, Se, Br, I and Hg in the Stack of a Coal -Fired Power Plant," Environ. Sci . Technol

22, 1079-1085 (1988).

Gilliam, D. M.; Greene, G. L.; Lamaze, G. P. "Absolute Neutron Counting

Based on B-10 Alpha-Gamma Coincidence Methods," Nucl . Instru. Methods,

(in press)

Gilliam, D. M.; Hocken, D. G.; Humphreys, J. C; Lamaze, G. P. "Neutron

Sensitivity of LiF Chip Gamma Dosimeters at Megagray Doses," Reactor

Dosimetry, Methods, Applications, and Standards, American Society for

Testing and Materials, Spec. Tech. Publ . STPlOOl , 206 (1989).

Gokmen, I. G.; Aras, N. K.; Gordon, G. E.; Wastney, M. E.; Henkin, R. I. "Radiochemical Neutron Activation Analysis of Zinc Isotopes in Human

Blood, Urine and Feces for In Vivo Tracer Experiments," Anal. Chem.

(submitted for publication).

Grazman, B.; Troutner, D. E. "Rh-105 As a Potential Radiotherapeutic Agent."

Applied Radiation and Isotopes, International J. Radiation Applic.

Instrum. Part A. Applied Radiation and Isotopes 39:257 , (1988).

Greenberg, R. R. "Evaluation of Precision and Accuracy of Selenium

Measurements in Biological Materials Using Neutron Activation Analysis,"

Trans, of the Am. Nucl. Soc. 56, 148-9 (1988).

Greenberg, R. R.; Zeisler, R. "A Radiochemical Procedure for Ultratrace

Determination of Chromium in Biological Materials," J. Radioanal. Nucl.

Chem. 124, 5-20 (1988).

Greenberg, R. R. "Analysis of Atmospheric Particulate Samples Via

Instrumental Neutron Activation Analysis," Proc. of Conf. on Recent

Developments in Monitoring Methods for Toxics in the Atmosphere, (in

press)

308
PUBLICATIONS

Greenberg, R. R.; Fleming, R. F.; Linstrom, R. M. "Elemental

Characterization of Four Coal Standard Reference Materials via

Instrumental Neutron Activation Analysis and Neutron-Capture Prompt

Gamma Activation Analysis," (to be submitted to Anal. Chem.)

Greenberg, R. R.; Kingston, H. M.; Zeisler, R. ; Woittiez, J. R. W. "Neutron

Activation Analysis of Biological Samples with a Pre-Irradiation

Chemical Separation," (to be submitted to Biol. Trace Elem. Res.).

Greenberg, R. R.; Stone, S. F.; Zeisler, R. "The Determination of Trace

Elements in Human Livers," Proc. 10th U.S. -German Seminar of State and

Planning on Environmental Specimen Banking, Virginia Institute of Marine

Sci., Gloucester Point, VA, October 6-8, 1986, NBS Spec. Publ . 740,

82-90 (1988).

Greenberg, R. R.; Zeisler, R.; Malozowski, S. "Investigation of Natural

Chromium Levels in Human Blood," Trace Eelemnt Analytical Chemistry in

Medicine and Biology, 5, Bratter, P.; Schramel , P., eds. 220-228 (1988).

Greenberg, R. R.; Zeisler, R.; Kingston, H. M.; Sullivan T. M. "Neutron

Activation Analysis of the NIST Bovine Serum Standard Reference Material

Using Chemical Separations," Fresenius Z. Anal. Chem. 332, 652-656

(1988).

Hastie, D. R.; Schiff, H. I.; Whelpadale, D. M.; Peterson, R. E.; Zoller, W.

H.; Anderson, D. L. "Nitrogen and Sulphur over the Western Atlantic

Ocean," Atmos. Environ. 22, 2381-2392 (1988).

Hastie, D. R.; Schiff, H. I.; Whelpdale, D. M.; Peterson, R. E.; Zoller, W.

H. Anderson, D. L.; Church, T. M. "Description and Intercomparison of

Techniques to Measure N and S Compounds in the Western Atlantic Ocean

Experiment," Atmos. Environ. 22, 2393-2400 (1988).

Hunt, J. B.; Champlong, P.; Chemtob, M.; Kluge H.; Schwartz, R. B. "International Intercomparison of Neutron Survey Instrument Calibrations,"

Radiation Protection Dosimetry 27, 103-110 (1989).

Iyengar, G. V.; Behne, D. "Appropriate Reference Parameters for the

Evaluation of Elemental Analysis Data from Biomedical Specimens," J.

Res. Natl. Bur. Stand. (US) 93, 326-328 (1988).

Iyengar, G. V.; Gopal-Ayengar, A. R. "Human Health and Trace Elements

Including Effects on High Altitude Populations," Ambio U, 31-35 (1988).

Iyengar, G. V.; Iyengar, V. "Clinical Samples. In, Quantitative Trace

Analysis of Biological Materials," McKenzie, H. A.; Smythe, L. E.,

eds., Elsevier Science Publishers, Amsterdam, 1988, pp. 401-417.

Iyengar, G. V.; Woittiez, J. R. W. "Trace Elements in Human Clinical

Specimens: Evaluation of Literature Data to Identify Reference Values,"

Clin. Chem. 34, 474-481 (1988).

Iyengar, G. V. "Biological Trace Element Research: A Multi-disciplinary

Science," Sci. Total Environ. 71, 1-5 (1988).

309
PUBLICATIONS

Iyengar, G. V. "Elemental Analysis of Biological Systems: Biomedical,

Compositional, Environmental and Methodological Aspects," Vol. I. CRC

Publishers, Boca Raton, PL, 1989.

Iyengar, G. V. "Nutritional Chemistry of Chromium," Sci. Total Environ.

1989, (in press).

Iyengar, G. V. "The Role of Neutron Activation Analysis in Nutritional

Biomonitoring Programs," Trans. Am. Nucl . Soc. 56, 233-234 (1988).

Iyengar, G. V. "Trends in the Daily Intake of Trace Elements by Human

Subjects: An Analytical Appraisal," Proc. of International Conf. of

Biovailabil ity 88, The Royal Society of Chemistry, London, 1989, (in

press)

.

Iyengar, G. V.; Clarke, W. B.; Downing, R. G.; Tanner, J. T. "Boron and

Lithium in Biological Materials," Trace Element Analytical Chemistry in

Medicine and Biology, Vol. 5, Braetter, P.; Schramel , P., eds., Walter

de Gruyter, Berlin, 1988, pp. 267-269.

Iyengar, G. V.; Tanner, J. T.; Tanner, W. R. ; Wolf; Zeisler, R. "Development

of Multi-Purpose Biological Reference and Materials," J. Res. Natl. Bur.

Stand. (US) 93, 360-362 (1988).

Iyengar, G. V.; Wolf, W. R.; Tanner, J. T. "Multipurpose Reference

Materials," Fres. Z. Anal. Chem. 332, 549-551 (1988).

Joel, E. C; Olin, J. S., Blackman, M. J.; Barnes, I. L. "Lead Isotope

Studies of Spanish, Spanish Colonial and Mexican Majolica," Proc. 26th

International Archaeometry Symposium, Toronto, Canada, 1989, pp. 188-195.

Kitto, M. E.; Anderson, D. L. "The Use of Whatman-4I Filters for Particle

Collection," Atmos. Environ. 22, 2629-2630 (1988).

Kitto, M. E.; Anderson, D. L.; Zoller, W. H. "Simultaneous Collection of

Particles and Gases Followed by Multielement Analysis Using Nuclear

Techniques," J. Atmos. Chem. 7, 241-259 (1988).

Lamaze, G. P.; Grundl , J. A. "Activation Foil Irradiation by Reactor Cavity

Fission Sources," NBS Measurement Services, Spec. Publ . 250-14 (1988).

Lamaze, G. P.; Grundl, J. A. "Activation Foil Irradiation with Californium

Fission Sources," NBS Measurement Services, Spec. Publ. 250-14, (1988).

Lamaze, G. P.; Eisenhauer, C. M.; Grundl, J. A.; McGarry, E. D.; Schima, F. J.; Spiegel, V. "Cross-Section Measurements in the Intermediate-Energy

Standard Neutron Field," International Conference on Nuclear Data for

Science and Technology, Mito, Japan, (1988).

Lamaze, G. P.; Eisenhauer, C. M.; Grundl, J. A.; McGarry, E. D.; Schima, F. J.; Spiegel, V. "Cross-Section Measurements in the Intermediate-Energy

Standard Neutron Field," Proc. of the International Conference on Nuclear Data for Science and Technology, Mito, Japan, May 30-June 3,

1988, pp. 1033-1036, 1988 JAERI.

310
PUBLICATIONS

Lamaze, G. P.; Gilliam, D. M.; Williams, A. P. "Prompt Gamma as a Fluence

Rate Monitor in Neutron Beam Experiments," J. of Radioanalytical and

Nuclear Chemistry 123(2) , 551-559 (1988).

Lamaze, G. P.; Schima, F. J.; Eisenhauer, C. M.; Spiegel, V. "SpectrumAveraged Cross-Section Measurement of ^^^Rh {n,n')^°^ Rh in the ^^^Cf

Fission Neutron Spectrum," Nuclear Science and Engineering UOO, 43-47

(1988).

Lindstrom, D. J.; Zolensky, M. E.; Lindstrom, R. M. "Procedures for

Instrumental Neutron Activation Analysis of Individual Cosmic Dust

Particles," Abstr. XXth Lunar and Planet. Sci. Conf., Lunar and Planet.

Inst. Houston, 1989, pp. 574-575.

Lindstrom, R. M. "Analytical Standards in Silicon Analysis," Proc. IAEA

Consultants' Meeting on the Need for Intercomparison and Reference

Materials for Characterization of Silicon, (Gaithersburg, MD, 1987:

lAEA-TECDOC) (to be published by International Atomic Energy Agency,

Vienna, Austria, 1989).

Lindstrom, R. M. "Measurement of Superconductor Stoichiometry by Prompt and

Delayed Neutron Activation," Trans. Am. Nucl . Soc. 56, 231 (1988).

Lindstrom, R. M. "Neutron Activation Analysis in Electronic Technology," T.

J. Shaffner and D. K. Schroder (eds.). Diagnostic Techniques for

Semiconductor Materials and Devices , (PV 88-20), Electrochem. Soc,

Pennington, NJ, 1988, pp 3-14.

Lindstrom, R. M.; Fleming, R. F.; Rook, H. L. "Neutron Microprobe:

Prospects and Potential Applications," Newbury, D. E., ed. Microbeam

Analvsis--1988 , San Francisco Press, 1988, pp. 407-408.

McGarry, E. D. "1988 NIST Annual Report: LWR Pressure Vessel Surveillance

Dosimetry Improvement Program," in Compilation of Contract Research for

the Materials Engineering Branch, Division of Engineering Technology,

Annual Report for FY 88, USNRC Report NUREG-0975, Vol. 7, April 1989.

McGarry, E. D.; Rogers, J.; Prill inger, I. G.; Hawthorne, R. J. "Consideration of Calculated Experimental Neutron Dosimetry for Out-of-Core

Metallurgy Irradiation Experiments at the Buffalo Reactor," Proc. of

14th International Conference on the Effects of Radiation on Materials,

N. Packen Ed. ASTM STP 1014, American Society for Testing and Materials,

Philadelphia, PA (in press).

Moody, J. R.; Greenberg, R. R.; Pratt, K. W.; Rains, T. C. "Recommended

Inorganic Chemicals for Use as Calibrants," Anal. Chem. 60, 1203a-18a,

(1988).

Olin, J. S.; Blackman, M. J. "Compositional Classification of Mexican

Majolica Ceramics of the Spanish Colonial Period," Archaeological

Chemistry IV, Allen, R., ed., American Chemical Society, Washington, DC,

pp. 87-112, 1989.

311
PUBLICATIONS

Olmez, I.; Gulovali, M. C; Gordon, G. E.; Henkin, R. I. "Trace Elements in

Human Parotid Saliva," Trace Elem. Res. 22, 259-270 (1988).

Ondov, J. M.; Choquette, C. E.; Zoller, W. H.; Gordon, G. E.; Biermann, A.H.;

Heft, R. E. "Atmospheric Behavior of Trace Elements Emitted From a Coal -Fired Power Plant," Atmos. Environ, (in press).

Ondov, J. M.; Dodd, J. A.; Tuncel , G. "Nuclear Analyses of Trace Elements in

Size-Classified Submicrometer Aerosol Particles from a Rural Airshed,"

Aerosol Sci. Technol (submitted for publication).

Parikh, N. R.; Frey, E. C; Hofsaass, H. C; Swanson, M. L.; Downing, R. G.;

Hossain, T. Z.; Chu, W-K. "Neutron Depth Profiling by Coincidence

Spectrometry," Nucl . Instr. Methods (submitted for publication).

Perks, C. A.; Devine, R. T.; Harrison, K. G.; Goodenough, R. J.; Hunt, J. B.;

Johnson, T. L.; Riel, G. L.; Schwartz, R. B. "Neutron Dosimetry Studies

Using the New Chalk River Nuclear Laboratories Bubble-Damage Detector,"

Radiation Protection Dosimetry 23, 131-134 (1988).

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Rossbach, M.; Scharpf, 0., Kaiser, W.; Graf, W.; Schirmer, A.; Faber, W.;

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Rossbach, M.; Zeisler, R.; Lindstrom, R. M. "PGNAA With Cold Neutrons--A

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312
PUBLICATIONS

Shibayama, M.; Roy, S.; Wu, W.; Kurokawa, H.; Nomura, S.; Stein, R. S.

Macromol . (in press)

SkOld, K.; Price, D. L.; Mildner, D. F. R. (Book Review), "Neutron

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Stone, C. A. guest editorialist. Scientific Computing and Automation,

February, 1989.

Stone, S. F.; Becker, D. A.; Koster, B. J.; Pella, P. A.; Sleater, G.;

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Stone, S. F.; Zeisler, R.; Gorden, G. E. "Quantitative Determination of

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Biology, Vol. 5, Bratter, P., Schramel , P., eds., Walter de Gruyter,

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Stone, S. F.; Zeisler, R.; Koster, B. J. "Neutron Activation Analysis of

Major, Minor and Trace Elements in Marine Sediments," Trans. Am. Nucl.

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Tuncel , G.; Zoller, W. H. "Iridium in the South Pole Atmosphere: Estimation

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Wastney, M, E.; Gokmen, I. G.; Aamodt, R. L.; Rumble, W. F.; Henkin, R. I.;

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Williamson, T. G.; Lamaze, G. P.; Gilliam, D. M.; Eisenhauer, C. M., NIST,

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313
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Williamson, T. G.; Lamaze, G. P.; Gilliam, D. M.; Eisenhauer, C. M. "Iron

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314
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Level Trace Elements in Human Livers," J. Radioanal. Nucl . Chem. 124 , 47-63 (1988).

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315 ^ U.S. GOVERNMENT PRINTING OFFICE 1990 — 261 "913 05127
NBS-114A (REV. 2-8C) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NIST/TN-1272

2. Performing Organ. Report No. 3. Publication Date

December 1989

4. TITLE AND SUBTITLE

NIST Reactor: Summary of Activities July 1988 Through June 1989,

5. AUTHOR(S)

Carol O'Connor, Editor

6, PERFORMING ORGANIZATION f(f joint or other thon NBS. see instructions)

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

(formerly NATIONAL BUREAU OF STANDARDS)

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

July 1988 through

June 1989

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State. ZIP)

Same as item #6 above.

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This report summarizes all those programs which use the NIST reactor. It covers

the period for July 1988 through June 1989. The programs range from the use of

neutron beams to study the structure and dynamics of materials through nuclear

physics and neutron standards to sample irradiations for activation analysis,

isotope production, neutron radiography, and nondestructive evaluation.

Ive entries: alphabetical order; capitalize only proper names; and separate key words by semicolons)

sis; cold neutrons; crystal structure; diffraction; isotopes;

12. KEY WORDS (Six to twel\

activation analys: ^ ^ ^ ^ molecular dynamics; neutron; neutron radiography; nondestructive evaluation;

nuclear reactor; radiation.

13. AVAILABILITY

rxl Unlimited

I I For Official Distribution. Do Not Release to NTIS

rX] Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

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14. NO. OF

PRINTED PAGES

324

15. Price

USCOMM-DC 6043-P80
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