nist"'

publications

NAT'L INST. OF STAND S TECH R.IX.

AlllDM b37fiST

NIST TECHNICAL NOTE 1257

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

NBS Reactor:

Summary of Activities

July 1987 Through June 1988

QC

100

U5753

No. 1257

1989

C.2
NATIONAL mSTITTJTE OF STANDARDS &

TECHNOLOGY

Keseardi Mormation Center

Gaithersbtirg, MD 20899
NIST Technical Note 1257 a^^^^

NBS Reacton f/^

Summary of Activities

July 1987 Through

June 1988

Carol O'Connor, Editor

Reactor Radiation Division

Institute for Materials Science and Engineering

National Institute of Standards and Technology

(formerly National Bureau of Standards)

Gaithersburg, MD 20899

January 1989

..<°^^°^.

NOTE: As of 23 August 1988, the National Bureau of

Standards (NBS) became the National Institute of

Standards and Technology (NIST) when President

\ ^^^4=^ ^ Reagan signed into law the Omnibus Trade and

*'"'flrEs o* Competitiveness Act

U.S. Department of Commerce

C. William Verity, Secretary Ernest Ambler, Acting Undersecretary for Technology

National Institute of Standards and Technology

(formerly National Bureau of Standards)

Raymond G. Kammer, Acting Director
National Institute of Standards and Technology Technical Note 1257

Natl. Inst. Stand. Technol. Tech. Note 1257, 227 pages (Jan. 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 Bureau of Standards (NBS)* Reactor serves the needs of

NBS, other government agencies, and outside organizations as a national

center for the application of neutron methods to problems of national

interest. The Reactor Radiation Division operates the reactor and fosters

its scientific and technological use. Toward this end, the Division's small

nucleus of scientists is experienced in the use of reactors for a wide range

of scientific and technical problems. In addition to pursuing their own research and developing sophisticated experimental facilities, they seek out

and encourage collaboration with other scientists engaged in challenging

programs whose work can benefit from use of the reactor, but who do not have

the reactor experience necessary to take full advantage of the facilities

available. The Division also provides irradiation services to a wide

variety of users as well as engineering and other technical services.

The reactor operates at 20 MW and supports 25 experimental facilities

ranging from intense neutron beams to extensive irradiation facilities. A

major expansion of the experimental facilities is currently under way. A

cold neutron source was installed and construction of a large neutron guide

hall is nearing completion. The guide hall will accommodate 15 new instruments served by seven neutron guides from the cold source. This will be a national facility providing state-of-the-art instruments that are currently

unavailable in the United States.

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

NBS work originating outside NBS for which the Division provides reactor

facilities and irradiation services. The remaining sections are selfexplanatory.

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

editing, organization, and preparation of this report; F. Shorten for

generously sharing his expertise in preparing this report; S. Shatzer for

typing manuscripts; and J. Spillman for typing manuscripts and assisting in

the preparation of the final copy.

R_ J. Coc/^d^:^

R. S. Carter, Chief

Reactor Radiation Division

National Institute of Standards

and Technology

*In August 1988, the name of the National Bureau of Standards (NBS) was changed to the National Institute of Standards and Technology (NIST)

.

Since the work described in this report was done prior to the name change,

all references to the Institute read NBS in the body of the text.

IXX
ABSTRACT

This report summarizes all those programs which use the NBS Reactor.

It covers the period for July 1987 through June 1988. 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

In Search of Local Mode Splitting for Hydrogen in Scandium 1 Study of Hydrogen Sites in Amorphous PdgcSi,cH„by Neutron

Vibrational Spectroscopy 4

Neutron Spectroscopy as a Probe of Zeolite Framework Vibrations. . . 5 The Molecular Dynamics and Vibrational Spectroscopy of

Titanyl Phosphates 7 The Dynamics of Molecular Hydrogen Adsorbed in CoNa-A Zeolite. ... 8

Inelastic Neutron Scattering Study of Tetramethyl ammonium

Pillared Montmorillonite 12

SANS Studies of Chromia-Pillared Clays 14

Studies on the Dispersion of Clay Particles in Epoxy by

Small -Angle Neutron Scattering 18

Magneto-Elasticity and Structure of Er/Y Superlattices 21

Field Dependence of the Structure of Er/Y Superlattices 26

Magnetic Structure of Cubic Tb^ ^Yq yAg 29

Magnetic Structure of Yq qj^^q qo 32

Magnetic Rare-Earth Superlattices 34

Anti ferromagnetic Structure and Crystal Field Splittings in

the Cubic Heusler Alloys HoPdpSn and ErPd^Sn 36

Antiferromagnetic Order of the Cu in REa2^^2^6+x ^^ Neutron Diffraction in Co Mg, Solid Solutions 46

P 1-P

Superconductivity in Lanthanum Barium Cuprate Perovskites 50

Crystal Chemistry of Superconductors: A Guide to the

Tailoring of New Compounds 50

Neutron and Electron Diffraction Study of YBa2Cu22Cul jj

^^.23^7.13 ^^ Structure and Crystal Chemistry of La^CaCu^Og and La^SrCu^Og

by Powder Neutron Diffraction 52
CONTENTS

Phase Equilibria in the System Ba-Y-Cu-0-C02 in Air 54

Significance of Plane Versus Chain Sites in 1-2-3 Superconductors. . 55

Inelastic Neutron Scattering Study of H Absorbed in YBapCu^O, . . 57

Theoretical Models for High-Temperature Superconductivity 58

Neutron Powder Diffraction Structure and Electrical Properties

of the Defect Pyrochlores Pb, cMoOg c 62

A Neutron Powder Diffraction Study of Na, Cs Zeolite RHO 63

The Structures of t?-, 7- and ^-Alumina 65

N-Dimensional Crystal lographic Description of the Icosahedral

Phases; the Example of the AKoMn^^Sig Quasiperiodic Structure. 67

A 6-D Structural Model for the Icosahedral (Al , Si)-Mn Quasicrystal

.

68

Neutron Diffraction Studies of the Martensitic Transformation

in Sodium Metal 69

Crystal Structure Study by X-Ray Diffraction 70

Phase Diagram of Alloys in the Ti-Al System 75

Neutron Diffraction Study of Textures of Materials 77

A Maximum-Entropy Density Distribution that Fits an Arbitarily

Large Set of Fourier Amplitudes 82

D-Spacing/Formula Index for Phase Identification by Electron,

Neutron or X-Ray Diffraction 84

Grazing Incidence Neutron Diffraction From Si (110) 88

Surface Ordering and Lamellar Formation in Diblock Copolymers. ... 92

The Significance of Multiple Scattering in the Interpretation

of Small Angle Neutron Scattering Experiments 94

Model Bicontinuous Structure With Fractal Surfaces 97

Phase Shift Dependence of Strong Multiple Scattering 98

Dynamical Theory for the Scattering of Polarized Neutron Beams

From Magnetic Spiral and Related Structures 99

Phase Contrast Matching in Lamellar Structures Composed of

Mixtures of Labeled and Unlabeled Block Copolymer for

Small -Angle Neutron Scattering 101

Temperature, Composition and Molecular Weight Dependence of

Binary Interaction Parameter of Polystyrene/

Poly{vinylmethylether) Blends 105

Characterization of Polyquinol ine Block Copolymer Using

Small Angle Scattering Techniques 110

VI
CONTENTS

Neutron Scattering Studies of Lipid Tubules Formed From a Polymerizable Surfactant 112

Small Angle Neutron Scattering of Poly(vinylalcohol) - Aqueous Solution 116

Small Angle Neutron Scattering Studies of Isolated Neurosecretory Vesicles 117

Densification of Microporous Silica 122

Cold Neutron Project 124

Neutron Reflectometer 125

Neutron Depth Profiling Facility 126

Prompt 7 Activation Analysis Facility 126

High Resolution Small Angle Scattering Spectrometer 127

Design of a High Resolution Time-of-Flight Spectrometer 128

Workshop on Microstructure and Macromolecular Research With

Cold Neutrons 129

NBSR Cold Neutron Source 131

Small Angle Neutron Scattering Facility 133

Cold Source Spectrum and Flux Measurements 134

Supermirror Development 137

Neutron Reflection Studies of Surfaces and Interfaces 139

Simulation of the Phase Space Transformation of Neutrons by

Bragg Reflection From Moving Mosaic Crystals 141

Spin Polarized Inelastic Neutron Scattering Spectrometer (SPINS) . .145

On the Use of Multiple-Slot Multiple Disk Chopper Assemblies

to Pulse Thermal Neutron Beams 146

Calculations of the Performance of Neutron Guides 151

The Smithsonian - NBS Program on the Studying of Art Objects

by Neutron Methods 152

NON-RRD PROGRAMS 157

Neutron Interactions and Dosimetry Group 157

Dosimetry for Material Performance Assessment 157

Personnel Dosimetry 159

Research and Technology Assistance 161

Irradiation and Calibration Facilities 163

Nuclear Methods Group: Overview 164

Vll
CONTENTS

Measurement of Superconductor Stoichiometry by Neutron Activation. .167

Determination of AS, CD, CR, and MO in the NBS Bovine Serum

Standard Reference Material at the PPB Level 169

Measurement of Chromium in Human Blood and Blood Fractions at

Natural (SUB-PPB) Levels 171

Neutron Activation Analysis of Major, Minor, and Trace

Elements in Marine Sediments 174

Determination of Trace Elements in U.S. Diets 179

Atmospheric and Environmental Studies by Instrumental and

Neutron-Capture Prompt r-Ray Activation Analysis 181

Stable Isotope Tracing of Zinc in Infants 187

Neutron Filters for Cold Neutron Beams 188

C. REACTOR OPERATIONS AND SERVICES 191

Reactor Operations and Services 191

Engineering Services 193

Neutron Activation Analysis at the Food and Drug Administration. . .195

Use of NAA in Criminal Investigations 196

D. PERSONNEL ROSTER 197

E. PUBLICATIONS 205

Vlll
A. REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

IN SEARCH OF LOCAL MODE SPLITTING FOR HYDROGEN IN SCANDIUM

T. J. Udovic and J. J. Rush

and

I. S. Anderson

(Paul Scherrer Institute, Villigen, Switzerland)

Recently, incoherent inelastic neutron scattering (IINS) measurements of

the hydrogen local mode frequencies in single-crystal samples of a-YH(D)Q ,g

demonstrated a highly unusual potential which was much softer and anharmonic

along the c-axis than in the basal plane [1]. Despite nearly cubic local

symmetry for the T sites (i.e., a c/a ratio that is only 3% less than the

ideal value), the vibrational mode along the c-axis exhibited a frequency that

was 25% lower than the frequency of the doubly degenerate vibrations in the

basal plane. In addition, the c-axis mode possessed a novel splitting which

was attributed to concentration- and temperature-dependent H pairing along the

c-axis on either side of an yttrium atom [21.

In order to compare the yttrium results to those for scandium, an analogous rare-earth metal which also retains H in solid solution (a-phase),

we have measured preliminary IINS spectra for single-crystal o-ScHq ,^7 using

the BT-4 triple-axis spectrometer. Figure 1 illustrates the IINS spectrum for

q-ScHq j^^ using the Be filter (aE = 5-9 meV FWHM in the range 80-160 meV)

with the Q-vector directed ca. 45° from the c-axis. In this scattering

geometry, all H local mode vibrations are present; i.e., the vibrational mode

along the c-axis at ca. 103 meV and the vibrational modes in the basal plane

at ca. 149 meV. Again, similar to a-YH , the vibrational mode along the c- axis is both substantially lower (>30%) in frequency and intrinsically broader

than the basal-plane modes. A higher-resolution IINS spectrum of the c-axis

mode using the Be/graphite composite filter (aE ~ 2.5 meV FWHM at 100 meV) is

illustrated in figure 2. Despite the broadness of the feature, no splitting

is observed within the resolution of the measurement. Hence, if splitting is

present, it is less than 2.5 meV in contrast to the 3.5-4 meV splitting

observed for a-YH^ ,o- The nature of the potential along the c-axis will be further explored in

the near future. In particular, experiments are in progress for determining
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the frequency of the corresponding second-excited state as well as the effects

of deuterium isotope dilution, hydrogen concentration, and temperature on the

a-phase H spectrum.

C!ou

a

o

*->

(U

1 1 1

^>-ScHoi5, (9K)

1 1 1 1 1

*

•••

• • •

•

• ••••

1 1 1 1 1 1 1 1 80 100 120 140

Energy Loss (meV)

160

Figure 1. IINS spectrum for single-crystal a-ScHg jcy at 9 K using the BT-4

Be-graphite-Be analyzer with the Q-vector directed 45° from the c- axis.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

oo

o

>->

1 I rAI I I

a-ScHo_i57 (9K)

i+ +*

i+ ******* /

J L J L 85 95 105 115

Energy Loss (meV)

125

Figure 2. IINS spectrum for the q-ScHq -.cj c-axis mode at 9 K using the BT-4

Be-graphite-Be analyzer.

References

[1] I. S. Anderson, J. J. Rush, T. J. Udovic, and J. M. Rowe, Phys. Rev.

Lett. 5Z, 2822 (1986).

[2] I. S. Anderson, N. F. Berk, J. J. Rush, and T. J. Udovic, Phys. Rev. B 37, 4358 (1988).
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STUDY OF HYDROGEN SITES IN AMORPHOUS Pdgs^^s^x

By NEUTRON VIBRATIONAL SPECTROSCOPY

J. J. Rush and T. J. Udovic

R. Hempelmann

(Los Alamos National Laboratory, Los Alamos, NM)

D. Richter

(Institut Laue-Langevin, Grenoble, France)

and

G. Driesen

(Institut fOr Festkttrperforschung, JUlich, West Germany)

Pd, Si /H is the most intensively investigated amorphous metal/hydrogen

system and in some sense can now be considered as a prototype, as Pd/H is for

binary crystalline metal/hydrogen systems. The thermodynamics of hydrogen

absorption in Pd, Si H were studied by electrochemical methods by Kirchheim

et al . The temperature and H concentration dependence of the resulting

chemical potential was interpreted in terms of a Gaussian distribution of site

energies. The temperature and H concentration dependence of the electrochemically determined H diffusion coefficient was also explained with the same

set of microscopic parameters. Further support for the Gaussian model was obtained from high-pressure gas volumetric measurements. The applicability of

a Gaussian model is somewhat surprising because such a model neglects H-H

interactions which without doubt considerably contribute to the chemical

potential at high hydrogen concentration. Recent quasielastic neutron

scattering results (Richter et al.) were not consistent with a Gaussian model,

but were interpreted in terms of a bimodal distribution of hydrogen sites.

These results, however, could not provide information on what kind of sites

are involved.

In view of this we have performed a series of neutron vibrational spectra

measurements on the high sensitivity Be-filter spectrometer arrangement on the

BT-4 instrument to provide an independent probe of the H-bonding states in

amorphous P^qb^Mb^x' ^^^^ ^^° orders of magnitude in H concentration

(X = .0013 to .08). The results show the existence of two bands H vibrations,

roughly around 60 meV and in the 90-130 meV range. From experience with many

other metal/hydrogen systems, the former is attributed to octahedral -type

sites (Pdg) and the latter to tetrahedral -types sites (perhaps Pd^Si). There
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

is also a tendency of the higher energy scattering intensity to increase with

increasing H concentration. Thus at least two different types of H-bonding

sites appear to be occupied, with some evidence that the octahedral sites are preferentially filled at lower H concentrations. While the data show that

there is a broad and overlapping distribution of site energies, the results

are not consistent with the assumption of a Gaussian distribution of hydrogen

site energies which has been the basis of interpretation for most of the

earlier electrochemical and thermodynamic data on these and similar glasses.

NEUTRON SPECTROSCOPY AS A PROBE OF ZEOLITE FRAMEWORK VIBRATIONS

T. J. Udovic, R. R. Cavanagh, and J. J. Rush

and

J. M. Nicol

(University of Maryland and the National Bureau of Standards)

Incoherent inelastic neutron scattering (IINS) is a particularly useful

spectroscopic probe of molecular vibrations involving hydrogen motions in the

regime below 250 meV. Indeed, zeolite framework vibrational modes are in an energy regime easily accessible to neutron spectroscopy, yet the low

scattering cross sections for framework atoms (e.g., Al , Si, and 0) result in

low-intensity framework features. The scattering intensity associated with

these framework modes can be enhanced dramatically by the presence of

framework-coupled hydrogenous counter-cations such as protons or ammonium

ions. Such modes can then be more sensitively probed by following the

hydrogen motions of these species rigidly attached to the framework lattice.

Currently we are interested in using this enhancement technique for investigating the framework vibrations of various zeolites.

As demonstrated by the infrared spectroscopic work of Flanigen et al

[1], zeolites possess two classes of vibrations: (i) structure-insensitive

internal vibrations of the framework TO. tetrahedra, the primary building

units in all zeolite frameworks, and (ii) structure-sensitive vibrations

arising from the external linkages between tetrahedra, which are related to

secondary building units and building block polyhedra such as double rings and

large pore openings. This is exemplified in figure 1 by the IINS spectra of
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the protonated forms of Y and rho zeolites. In particular, both zeolite

spectra are similar above 70 meV but differ considerably below 70 meV. Forcefield analyses of several models of the proton-containing group in H-rho have

led to the assignment of the structure-insensitive features at 143 and 131 meV

to in-plane and out-of-plane T-O-H bending modes, respectively, and that at 93

meV to a symmetric T-OH stretching mode [2]. Below 70 meV, H-rho exhibits a large-intensity feature at 45 meV in contrast to the narrower and somewhat

smaller-intensity feature at 52 meV for H-Y. These structure-sensitive

features are attributed to proton-coupled pore-opening modes of the two

zeolite frameworks, which contain different external linkages. Recently, it was shown that NH.-rho possessed, similar to the proton-coupled feature for Hrho, an ammonium-coupled pore-opening feature which was approximately four

times as intense due to the presence of four hydrogens instead of one hydrogen

per site [3]. In contrast to these hydrogen-containing zeolites, the

relatively featureless scattering spectrum of Na-Y, also depicted in figure 1,

illustrates the lack of scattering sensitivity in the absence of hydrogenous

counter-cations.

-| 1 1 1 1 ; 1 1 1 r

Zeolite Spectra (80K)

'+1 A

v.Vv

rtt H-rho

V'-'v.-s*.,

Na-Y

'«V*

60

V^^^^vV'^'^'^+V^^^/

I I I I I I I I 90 120 150 Energy Loss (meV)

180

Figure 1. IINS spectra for Na-Y, H-Y, and H-rho zeolites at 80 K,
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Work is in progress to investigate other zeolites and counter-cations in

order to correlate specific structure-sensitive features to framework

geometry.

References

[1] E. M. Flanigen, H. Khatami, and H. A. Szymanski, ACS Adv. Chem. Ser. 101 . 201 (1971).

[2] M. J. Wax, R. R. Cavanagh, J. J. Rush, G. D. Stucky, L. Abrams, and D. R. Corbin, J. Phys. Chem. 90, 532 (1985).

[3] T. J. Udovic, R. R. Cavanagh, J. J. Rush, M. J. Wax, G. D. Stucky, 6. A.

Jones, and D. R. Corbin, J. Phys. Chem. 9i, 5968 (1987).

THE MOLECULAR DYNAMICS AND VIBRATIONAL SPECTROSCOPY OF TITANYL PHOSPHATES

J. M. Nicol

(University of Maryland and National Bureau of Standards)

J. J. Rush

and

G. D. Stucky and T. G. Gier

(University of California, Santa Barbara, CA)

Potassium titanyl phosphate (kTiPOr, KTP) is a relatively new nonlinear

optical material which because of its high nonlinear optical coefficient, high

optical damage threshold, low phase matching temperature sensitivity, and

chemical and mechanical stability, is finding increasing application. The

structure of KTP is composed of chains of TiOg octahedra linked at the corners

by long and short bonds. It is these short TiO bonds that appear to be

partially responsible for the nonlinear optical properties of KTP. The chains

are in turn linked via phosphate bridges to form an open framework structure,

in which the charge balancing cations are incorporated within the channels.

The K cations may be substituted during synthesis for other cations, which

leads to the possibility of modification of the nonlinear optical properties

by modification of the internal structure characteristics.

Neutron scattering techniques are being applied to the study of the

ammonium analogues of KTP, NH^TiPO^ (NTP) and X^INH^)

j_

JiPO^ (NKTP), as well

as NH.H(TiP0r)2 formed by the selective deammoniation of NTP. The molecular
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

dynamics of the ammonium ions are being probed by quasielastic scattering

using TOP methods, while the vibrational spectroscopy is being investigated by

inelastic neutron scattering using the Be-graphite-Be analyzer on BT-4. In addition it is hoped that information will be obtained on hydronium ions

(H-O''") that are formed during synthesis of titanyl phosphates by hydrothermal

techniques, by comparing the results with materials synthesized by flux

methods.

THE DYNAMICS OF MOLECULAR HYDROGEN ADSORBED IN CoNa-A ZEOLITE

J. M. Nicol

(University of Maryland and National Bureau of Standards)

J. Eckert

(Los Alamos National Laboratory, Los Alamos, NM)

and

J. Howard

(Imperial Chemical Industries, Wilton, England)

Detailed knowledge of the dynamics and interaction of adsorbate molecules

in the cavities of zeolites is crucial for a better understanding of the

catalytic properties of these materials. Although a considerable amount of

information has been obtained on the interaction of small molecules, such as ethyne, ethene, carbon monoxide etc., with the exchangeable cations in

zeolites, only limited information is available on the interaction of

molecular hydrogen with the cations. Detailed knowledge of the adsorption

properties of H^ would be of enormous interest because of the simplicity and

prototypical nature of this system, as far as the catalytic activity of

zeolites is concerned. We are undertaking a program to study molecular

hydrogen adsorption in a series of transition metal exchanged zeolites by

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

rotational and vibrational transitions involving H2, as well as the ability of

neutrons to induce transitions within the librational ground state by nuclear

spin flips, that are generally not allowed in optical spectroscopies, makes

IINS a particularly useful probe of bound hydrogen.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Neutron scattering spectra of H^ adsorbed in Co. ,Na^ g-A (CoNa-A) have

been obtained in the energy range 1-40 meV using the time-of-flight (TOP,

incident energy 14.8 meV: 1-13 meV) and BT-4 (Be/graphite filter configuration: 12-40 meV) spectrometers. Hydrogen was adsorbed to a coverage of 0.5

molecules per supercage in the fully dehydrated zeolite at 50 K. The sample

was cooled to 12 K for data collection.

The IINS spectra of molecular H^ adsorbed in CoNa-A zeolite are depicted

in figures la and lb. In both cases the "background" measurement of the

dehydrated zeolite before H^ adsorption was subtracted using a scale factor

determined by the relative monitor counts of the respective data sets. While

in the energy range of the TOP data the dehydrated zeolite background was featureless, an intense band at 21 meV was observed in the BT-4 data (fig.

Ic). The difference spectrum (fig. lb) therefore contains a few data points

in the region of 21 meV which are believed to be the result of the incomplete

subtraction of this "background" feature. The origin of this peak in the

dehydrated zeolite spectrum may be accounted for by the presence of Al(OH)-

complexes in the /3-cages. These species have been identified in diffraction

studies of CoNa-A [1]. The high intensity and low energy of the mode suggests

that it is due to a torsional mode of the complex.

In figures la and lb the low energy excitation at 3.8 meV, which occurs

with nearly equal intensity in both neutron energy gain and loss, a rather

sharp peak at 15.3 meV and the broad, structured band at 27.5 meV are due to

molecular H^ adsorbed within the CoNa-A framework. Annealing the sample at room temperature and subsequent recooling to 12 K did not reveal any

noticeable change in the IINS spectrum, indicating that even at room temperature little if any dissociation of Hp occurs. By considering the

predictions of a variety of models for adsorbed diatomic molecules, the

observed peaks can be assigned to the rotational and vibrational excitations

of Hp molecules that are weakly bound, presumably to the Co transition metal

cations [2]. A two-fold cosine potential with 2° of rotational freedom in

which the H^ is bound end-on to the Co cations best accounted for the observed

features [3-5]. Within this model the assignment of the peak at 3.8 meV

(0.5 B, where B is the rotational constant) to rotational transition (or

librational ground state splitting) of the H^ molecule, implies a barrier

height of about 1.4 Kcal/mol (7.4-9.2 B). Two transitions to the excited

rotational states are then predicted at 4.2 B and 3.7 B (31.9 and 28.1 meV),
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

in good agreement with the broad band observed at about 27.5 meV in figure

lb. The potential energy level diagram for this model, with the rotational

transitions to the excited states indicated is shown in figure 2. The

remaining peak at 15.3 meV would then be assigned to a vibrational excitation

within this model

.

Following the success of the assignment of the spectrum of molecular H

in CoNa-A, we are now investigating the interaction of H^ with other

transition metal ion-exchanged zeolites by IINS.

1 I

1

1 r

(b) CoNa-A + Hg

i

I,

-6 Energy (meV)

J 1 1 L

1 1 I —

1

1

(c) CoNa-A

*

*

s

s

*

# ^

gz

•

• •

• • •

*****

1 1 1 1 r

Figure 1

10 20 30 40 Energy Loss (meV)

10 20 30 40

Energy Loss (tneV)

The IINS spectra of 0.5 molecules of H^^ per supercage adsorbed in

CoNa-A zeolite at 12 K. (a) TOF spectrum of adsorbed H^;

(b) BT-4 spectrum of adsorbed H2; (c) BT-4 spectrum of the

dehydrated zeolite background.

10
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

10 20

Barrier Height V (B)

Figure 2. The energy levels of a two-dimensional hindered rotor in a double

minimum potential [3]. The observed transitions for H^ adsorbed in

CoNa-A are indicated by arrows. The energy levels and rotational

barriers are given in terms of the rotational constant B.

References

[1] J. M. Adams and D. A. Haselden, J. Solid State Chem. 55, 209 (1984).

[2] J. M. Nicol, J. Eckert, and J. Howard, J. Phys. Chem. (in press).

[3] R. F. Curl, H. P. Hopkins, Jr., and K. S. Pitzer, J. Chem. Phys. 48, 4064,

(1968).

[4] D. White and E. N. Lassettre, J. Chem. Phys. 32, 72 (1960).

[5] A. A. Evett, J. Chem. Phys. 33, 789 (1960).

11
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

INELASTIC NEUTRON SCAHERING STUDY OF

TETRAMETHYLAMMONIUM PILLARED MONTHORILLONITE

D. A. Neumann and J. J. Rush

J. M. Nicol

(University of Maryland and the National Bureau of Standards)

and

N. Wada

(Schlumberger-Doll Research, Ridgefield, CT)

Montmorillonite is a member of a naturally occurring class of expandable

layered silicates known as smectite clays in which the two-dimensional

oxyanions are separated by layers of intercalated cations. Permanent

porosity, such as is present in zeolites, can be induced in these minerals by

exchanging large cations; e.g., tetramethyl ammonium, for the naturally occurring ones. The resulting material is known as a "pillared clay" and the large

cations which prop the host layers apart are referred to as "pillars".

Despite the obvious utility of such structures as catalysts or catalyst

supports, relatively little information is available concerning the details of

the pillar-host interaction. We have therefore undertaken an inelastic

neutron scattering study of the low energy internal modes of tetramethyl

ammonium pillars in montmorillonite. This energy range includes the torsional

excitations of the methyl groups which have recently been shown to be quite

sensitive to the nature of their environment [1] and which are Raman and

infrared inactive.

The experiment was performed at the BT 4 spectrometer using the Begraphite-Be analyzer, currently the most sensitive instrument of its kind in

the world. Two different configurations were used for the primary

spectrometer. The first employed a Cu(220) monochromator with collimations of

60' -40' before and after the monochromator which yielded an energy resolution

of roughly 2-5 meV over the energy range of 35-90 meV. For the lower energy

portion of the spectra, a graphite (002) monochromator was used with a collimation of 40'-20', which gave a resolution of about 1.8-2.8 meV over the

energy range of 20-40 meV. Data collection time was about 6 hours.

Four internal modes of the (CH2)4N''" ion are observed in the data (fig.

1). These are the singly-degenerate, symmetric, torsional mode which belongs

to the Ap symmetry group; the triply-degenerate, antisymmetric torsional

12
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

excitation possessing F, symmetry; and two C-N bending excitations of symmetry

E (doubly-degenerate) and F^ (triply-degenerate) which are observed because

the H atoms ride along on these modes. In addition, a broad feature is

observed at about 60 meV. While several modes of the montmorillonite host

probably contribute to this scattering, the most important is almost certainly

the libration of the hydroxyl groups. The energies of the torsional modes,

27.4 and 38.0 meV, are intermediate to the values obtained for tetramethylammonium ions occluded in the sodalite cage of the zeolite ZK-4 (30.4 and 40.3

meV) [1] and in the gmelinite cage of zeolite omega (25.9 and 36.3 meV) [1].

400

Tetramethylammonium

.

Montmorillonite

Figure 1

40 60

Energy (meV)

Inelastic neutron scattering spectra of montmorillonite pillared

with tetramethylammonium ions taken at 80 K. The solid line

represents a fit which includes five Gaussians and a constant

background. None of the peaks are resolution limited.

This result indicates that the (CH2)4N''^ ion interacts more strongly with

its environment in montmorillonite than in gmelinite cages but more weakly

than in the slightly smaller sodalite cages. In addition, the widths of all

of the observed excitations (after correcting for instrumental resolution) for

tetramethylammonium ions in montmorillonite are quite similar to those

measured by Brun et al . [11 for these ions occluded in gmelinite cages. A

13
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

more quantitative analysis of the data awaits further theoretical work on the

relationship between these modes and the local environment of the

(CH3)4N'^ ion.

References

[1] T. 0. Brun, L. A. Curtiss, L. E. Iton, R. Kleb, J. M. Newsam, R. A.

Beyerlein, and D. E. W. Vaughn, J. Am. Chem. Soc. 109, 4118 (1987).

SANS STUDIES OF CHROMIA- PILLARED CLAYS

A. Moini, T. D. Brewer, and T. J. Pinnavaia

(Michigan State University, East Lansing, MI)

and

D. A. Neumann

Pillared clays are a recently discovered class of microporous materials

with interesting catalytic and adsorption properties. They are typically

prepared by the insertion of thermally stable cations into the galleries of

smectite clays. The intercalated ions function as molecular pillars between

the host layers. Upon removal of the co-intercalated solvent, a twodimensional permanently porous network is formed. The most interesting

pillaring agents studied so far are the polyoxocations which are prepared via

hydrolysis reactions. Upon dehydration, the intercalated polyoxocations are converted to small clusters of metal oxide units which act as pillars [1,2].

The goal of this present small angle neutron scattering (SANS) study was

to learn more about the structural characteristics of chromia-pillared clays

[3]. The synthesis of these materials involved the addition of anhydrous

sodium carbonate to a solution of chromium nitrate followed by aging for 36

hours at 95 °C. A suspension of clay (montmorillonite or fluorhectorite) was

then added dropwise, and the mixture was aged for 1.5 hours. The resulting

products were washed free of excess salt, air-dried, and then calcined at 350

"C.

The SANS curve for a calcined chromia-pillared clay is shown in figure 1. The log-log plot of these data appears in figure 2. There is clearly a powerlaw behavior in the Q-range 0.013-0.031 A" with a slope of -3.45. This

relatively high slope is consistent with the formation of a network of face to

face layers crossl inked by the pillaring chromia aggregates. Particles with

14
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

more two-dimensional or exfoliated structures should exhibit much lower powerlaw slopes.

1 OOOn '

1

'

\

'

\

'

\

'

1

' r

800-

O

600-

400-

200-

0.16

Figure 1. SANS data for chromia-pillared montmorillonite.

The peaks in the high-Q region (Q > 0.08 A' ) are probably due to

scattering from the pillars. The two peaks corresponding to 70 and 51 A are most likely indicative of the lateral interpillar distances taken from the

center of the particles. Adsorption studies on this complex have revealed the

presence of pores between 10 and 15 A in diameter. If this free space is

taken into account, the width of the pillars would be between 45 and 55 A.

Considering the vertical dimension of the particle, as determined from the

interlayer distance (~ 12 A), these pillars may be described as highly

anisotropic clusters.

15
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

O

Figure 2. Log-log plot of the SANS data for chromia-pillared montmorillonite.

The scattering curve for chromia-pillared fluorhectorite is shown in

figure 3. The power-law behavior for this clay is observed in the Q-range

0.015 - 0.036 A' with a slope of -3.73. The scattering in the high Q region

differs from the behavior observed for chromia-montmorillonite. This is an indication that the structure of the pillars could vary to a great extent

depending on the charge density of the clay. In the case of fluorhectorite,

it is possible that much larger particles are formed and that the structure is

not as uniform as chromia-montmorillonite. Further studies are needed to

elucidate the relationships between pillar distribution and the charge density

of the host clay.

16
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

o

1 1

9- \

-

- \ -^-73

-

7- \ -

5-

f

m

m

m -

3- '

1 1

, ^^

-4.5 -3.5 -2.5 -1.5

LN(Q)

Figure 3. Log-log plot of the SANS data for chromia-pillared fluorhectorite.

References

[1] T. J. Pinnavaia, Science 220, 365 (1983).

[2] R. M. Barrer, Zeolites and Clay Minerals as Sorbents and Molecular

Sieves, Academic Press, New York (1973).

[3] T. J. Pinnavaia, M.-S. Tzou, S. D. Landau, J. Am. Chem. Soc. 107,

4783 (1985).

17
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STUDIES ON THE DISPERSION OF CLAY PARTICLES IN EPOXY

BY SMALL-ANGLE NEUTRON SCATTERING

A. Moini, M. S. Wang, and T. J. Pinnavaia

(Michigan State University, East Lansing, MI)

and

D. A. Neumann

The rational design of advanced organic composite materials with improved

performance characteristics has been of growing interest in recent years.

Typical approaches to preparing such materials have included the embedding of

chemically modified inorganic particles with plate-like geometry. We have

been studying the interaction of clay minerals with epoxy to form new types of

composite materials with improved mechanical properties.

A series of commercially available natural clays and modified organoclays

were mixed with epoxy resin (DER 331 or EPON 828) at 50 °C. This step was followed by the addition of melted metaphenylenediamine (MPDA) which served as the curing agent. The final mixture was cured in a vacuum oven at 75 °C.

One of the features of interest in the formation of these clay-epoxy

composites is the degree of clay dispersion in the polymeric medium. Previous

investigations [1,2] have suggested that the clay layer stacking/aggregation

in aqueous suspensions can be studied by small -angle neutron scattering. The

slopes obtained from the log-log plots of SANS data appear to be closely

related to the dimensionality of the particles. For stacked clay layers,

these slopes usually approach the limiting value of -4.0, indicating the

presence of smooth three-dimensional particles. On the other hand, when the

layers are separated from one another upon dispersion in a swelling liquid,

the increased anisotropy lowers the absolute values of the observed slopes.

In the present project, we have investigated the SANS properties of clay

dispersions in epoxy matrices.

The six types of commercial clays studied were HPM-20, Microfine,

Bentonite, Mica 4, Claytone 40 (CT 40), and Claytone PS (CT PS). The first

three have similar general compositions (Na"*"^ 33(^^1 gy'^^O 33^^^4*^10^^^^2^

Mica 4 is a muscovite with the general formula HpK(AlSiO.)^, and the Claytones

are organoclays prepared from montmorillonite. SANS data were collected on a series of clay-epoxy composites prepared from these clays. The results,

18
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

obtained on composites were compared with the data on the pure clays and their

aqueous/organic suspensions . The data for HPM-20 and HPM-20/epoxy composites can be used as a representative example. The log-log plot of the SANS data for the pure clay

(fig. 1) showed a power-law behavior with a slope of -3.70 between Q = 0.015

and 0.0509 A' . This value agrees with the expected results for particles

which are close to three-dimensional as a result of stacked clay layers.

A log-log plot of the SANS data for a 16% HPM-20/epoxy composite is shown

in figure 2. A slope of -3.29 was obtained in the region from Q = 0.014 to

Q = 0.030 A' . A similar decrease in the slope also was observed for clayepoxy phases containing lower concentrations of HPM-20, as shown in table 1. This change in power-law dependence suggests the presence of more anisotropic

particles at lower concentrations. As a reference, a 5% suspension of HPM-20,

in D,0 was studied which gave a slope of -2.12 in the region from Q = 0.015 to

0.030 A . This value may be compared with that obtained for a 7% composite

(-2.69 for Q = 0.015 to 0.028 A"^).

The same type behavior, decreasing power-law slope with decreasing

concentration of clay, was observed for all of the other systems, as shown in

table 1. It is obvious that, at low concentrations, all clay types show some degree of dispersion in the epoxy. Indeed, all of the data collected on composites with very low clay contents {< 5%) gave very similar low slopes.

This feature, in addition to the low scattering power at these low clay

contents, prompted us to concentrate more closely on the products with higher

clay contents.

The most promising clays showed reasonable dispersion even at very high

concentrations. An example of such behavior was a 30% Microfine/epoxy

composite which had a slope of -2.83 in the Q-range from 0.015 to 0.041 A' . The slopes obtained for the pure organoclays were lower than those

obtained for the nonfunctional ized clays. This feature is probably due to a more limited face-to-face stacking of the clay layers in the presence of the

organic phase. The epoxy composites prepared using these organoclays showed

lower power-law slopes compared to the other clays. Comparison of the results

for the 7% composites prepared from HPM-20, Mica 4, and Claytone PS clearly

demonstrates this point. The degree of dispersion of organoclays in epoxy was comparable to or better than that observed for suspensions of these clays in

ethanol/water mixtures.

19
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The above results suggest that SANS studies on clay-epoxy composites

reveal the degree of platelet interaction and anisotropy within the individual

clay particles. This must be distinguished from dispersion which takes place

on a more macroscopic level. It may be possible to couple this technique with

other measurements; e.g., SEM and mechanical strength, to reach a better

understanding of the formation of clay-epoxy composites.

9-

-4.5 -4.0

Figure 1 LN(Q)

Log-log plot of SANS data for HPM-20 clay powder.

O

-4.0

LN(Q)

Figure 2. Log-log plot of SANS data for 16% HPM-20/epoxy composite.

20
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Slopes (and the Q-ranges, A' ) obtained from the log-log plots of

SANS data for clay-epoxy composites

clay conciwt. %\ HPM-20 MICA 4 MICROFINE BENTONITE CT40 CT PS

100% -3.70 -4.20 -3.41 (0.015-0.059) (0.015-0.044) (0.012-0.033)

30 % -2.83 (0.015-0.041)

25 % -3.26 (0.015-0.026) 16% -3.29 -2-58 (0.015-0.030) (0.012-0.022) 7% -2.69 -2.39 -1-58 (0.015-0.028) (0.015-0.022) (0.015-0.025) 5% -2.12a -2.84b

(0.015-0.033) (0.015-0.028)

a clay suspension in 50 % D2O/H2O

b clay suspension in 50 % D20/EtOH

References

[1] D. J. Cebula, R. K. Thomas, and J. W. White, J. C.S.Faraday I 76, 314

(1980).

[2] T. J. Pinnavaia, V. Rainey, M.-S. Tzou, and J. W. White, J. Mol . Catal

.

27, 213 (1984).

MAGNETO-ELASTICITY AND STRUCTURE OF Er|Y SUPERLATTICES

R. W. Erwin and J. J. Rhyne

and

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

(University of Illinois, Urbana, IL)

In the rare-earth superlattices which have been extensively studied,

[Dy^lY ] [1] and [Gd |Y ] [2], the magnetic order can be described in terms of

X y X y

the conventional indirect exchange coupling as applied to the heavy rare-earth

elements [3], and the range and strength of the interactions through the Y layers find a reasonable interpretation in the context of a conduction-band

spin-density-wave. By studying [Er |Y ] superlattices, we move to a system

X y

where the exchange is considerably weaker compared to magneto-elastic

21
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

energies, which have already been shown to be significantly perturbed in the

[Dy |Y 1 superlattices [1]. This enhances the possibility of controlling the

X y

magnetic structure, and further understanding the details of the magnetoelasticity of Er.

The samples for this study were grown at the University of Illinois [1],

2 by depositing 120 - 200 alternating layers of Er and then Y onto 1.6 cm

(1120) sapphire following buffer layers of approximately 1000 A of Nb and

300 A Y, so that the hep c-axis of the superlattice is perpendicular to the

growth plane. They have been shown to be good single crystals (mosaic ~ 30')

with sharp interfaces (only several atomic planes wide) between the layers.

The neutron diffraction measurements employed 13.5 meV neutrons with

resolution of 0.021 A' along Q and 0.008 A" transverse to Q when Q is near

2.0 A'^

Neutron diffraction scans along c* are shown in figure 1 for [Er^p|Yp,].

Since the neutron cross-section selects only magnetic scattering from moments

perpendicular to Q, the scans through (002) measure only the basal -plane

components, while the scans marked (101) select predominantly the c-axis

components.

The fact that no additional magnetic intensity appears on the (101) down

to 5 K, indicates that the ferromagnetic phase transition found in bulk Er at

18 K is suppressed. This same effect was found in the Dy-Y superlattices, and

here is the first hint that the magneto-elastic energy is significantly

different than in bulk Er.

The appearance of magnetic sidebands of the (101) indicates linear-spindensity-wave ordering (LSDW) of the c-axis components at Tj^ = 78 ± 1 K. This

7% reduction from the 84 K value of bulk Er is typical of superlattices [1,2],

and may be due to interfacial alloying and/or other finite size effects. That

the difference is not great indicates that the exchange interactions are very near bulk values. This is also confirmed by our determination of the turn

angle between successive Er basal planes.

Also below 35 K, magnetic intensity appears about the 002 Bragg peaks,

as the basal -plane components of the moments order. These ordering

temperatures are almost a factor of two lower than in bulk Er, and so must be

strongly influenced by magneto-elastic energetics. In fact, the basal-plane

ordering in bulk Er is near the 54 K lock-in transition to the w = 27r/7 state,

where the temperature derivative of w first changes sign. The low temperature

22
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

saturation moment in all three superlattices is about 8.5 ^g, suggesting some residual disorder of the spins. This is consistent with a shorter coherence

length for the basal -plane components than the c-axis components.

100

CMO1-1CO

l->o

o

80-

60-

40-

20-

[Erggr^aJ

C—axis

lor 101

lor

002

0.4

Qz-Tz (A-')

Figure I. Neutron diffraction scans along

(002) for [Er^^lY^j] show the d

32 wave state with

upon lowering the

higher order ha

components is est

plane components

This ordering has

and a different t

moments along

temperature

rmonics). Th

imated as 3 bi

order, as i a shorter coh

urn angle than

the c* direction, through (101) and

evelopment of a 1 inear-spin-densitythe c-axis, which then "squares-up"

(indicated by the appearance of

e coherence length for the c-axis

layers. Below about 30 K the basal

ndicated by the satellites of (002). erence range (about 1.5 bi layers)

the c-axis components.

23
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

We have fit our diffraction data to obtain u> in the separate Er and Y layers. These values are plotted in figure 2 along with w for bulk Er [4].

The magneto-elastic terms in the Hamiltonian favor smaller w, and are responsible in bulk Er for the turn down below 54 K, as well as the ferromagnetic

phase transition below 18 K. None of these features are present in the

superlattices, which all show w clamped at its high temperature value, with

only a slight decrease (about 1°) from 50 K to 5 K. Rough calculation of the

driving energy for ferromagnetism shows that it is reduced from 2.2 K/atom for

bulk Er to about 1.4 K/atom in the superlattices. One difficulty with these

calculations, not heretofore addressed, is the contribution of the c-axis

modulated magneto-elastic waves observed by Gibbs et al . [4]. It would be

interesting to see if such waves exist in the superlattices.

The (J) in the Y layers as given in figure 2 are seen to be the approximate

50" found in the other superlattices and dilute Y alloys [1,2]. In fact, the

data suggest that the Zn/7 lock-in state is stable over an extended temperature range. In addition, our fits give total phase shifts across the Y layers

which cannot be explained as simple multiples of n. As in the Dy-Y

superlattices, the coupling across the Y is not scalar.

Finally it is obvious from examining the raw data that the basal -plane

and c-axis w are not equivalent at low temperatures in the superlattices,

since the centroids of the magnetic scattering are at different Q values.

This is born out by our data analysis. We again invoke the strength of the

magneto-elastic energies compared to the exchange as an explanation for this

effect. It can be argued that exchange alone would tend to produce the same w

for basal-plane and c-axis components. In the superlattice the c-axis w may

be more strongly clamped than the basal -plane w.

24
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

60

J150H

40-

C—axis basal

321^ 2lJ O • -p-p

[Ersah^ig]

[Ei-i3h'26] layers

Y layers

-55

40

T(K)

80

45

Figure 2. The turn angles in the Er and Y layers are shown and compared to

bulk Er. In the Er layers w is "clamped" near the high-temperature

lock-in value of bulk Er (27r/7), although it is difficult to

ascertain if a lock-in occurs in the superlattices. The low

plane w appears to be less "clamped" than the cin the Y layers is near the 50° found in other

dilute Y alloys. The total phase shift across

temperature basal

axis u>. The w superlattices and

the Y layers is not a simple multiple of n.

References

[1] J. J. Rhyne, R. W. Erwin, J. Borchers, Shantnau Sinha, M. B. Salamon, R. Du, and C. P. Flynn, J. Appl . Phys. 61, 4043 (1987); R. W. Erwin, J. J. Rhyne, M. B. Salamon, J. Borchers, Shantnau Sinha, R. Du, J. E. Cunningham, and C. P. Flynn, Phys. Rev. B35, 6808 (1987).

[2] J. Kwo, E. M. Gyorgy, D. B. McWhan, M. Hong, F. J. DiSalvo, C. Vettier,

and J. E. Bower, Phys. Rev. Lett. 55, 1402 (1985); C. F. Majkrzak, J. W. Cable, J. Kwo, M. Hong, D. B. McWhan, Y. Yafet, J. V. Waszczak, and C. Vettier, Phys. Rev. Lett. 56, 2700 (1986).

[3] A. J. Freeman, in Magnetic Properties of Rare-Earth Metals, edited by R. J. Elliot, Plenum, New York, (1972), p. 314, and ref. therein.

[4] D. Gibbs, J. Bohr, J. D. Axe, D. E. Moncton, and K. L. D'Amico, Phys. Rev.

B34 , 8182 (1986).

25
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

FIELD DEPENDENCE OF THE STRUCTURE OF Er|Y SUPERLATTICES

R. W. Erwin and J. J. Rhyne

and

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

(University of Illinois, Urbana, IL)

We have previously obtained the structure in zero field of Er|Y single

crystal superlattices grown by molecular-beam-epitaxy techniques [1].

Sapphire substrates were used with buffer layers of approximately 1000 A of Nb

and 300 A of Y, so that the hep c-axis of the superlattice is perpendicular to

the growth planes. We found long-range order of the c-axis Ising-like Er

moments extending through the "magnetically dead" Y layers as was found for

the X-Y superlattices Dy|Y [2]. The Er layer turn angles for the linear-spindensity-wave are nearly temperature independent at w = 27r/7, the high

temperature commensurate lock-in value in bulk Er [3], although we could not

claim with certainty that the lock-in state is stabilized. The ferromagnetic

transition is completely suppressed, because the magneto-elastic energy

density is considerably reduced in the superlattice compared to the bulk.

We have now studied the magnetic structure of these materials in an applied field along the c-axis by neutron diffraction and SQUID magnetometry.

The bulk magnetization is plotted vs. internal field for two of the

superlattices in figure I. The low-field {< 15 kOe) low-temperature {< 35 K)

states have a magnetization of = 1/7 of the saturation value. The [Ei^i3|Y2g]

superlattice shows evidence of an intermediate fan state.

In figure 2 we show neutron diffraction data for [Er,2|Y25]- The overlap

of superlattice peaks results from the poor resolution for scans directed out

of the scattering plane. At T = 10 K (fig. 2a) the application of a 10 kOe

field (7 kOe internal) slightly shifts the centroid of the scattering for the

magnetic superlattice peaks on each side of r = (110). This indicates that

the Er layer turn angle increases. Our data analysis shows that the fieldinduced state has the commensurate value w = 27r/7 (51.4°), which is shifted

from the zero-field value (50.3° in agreement with our previous analysis).

The original analysis [1] of the zero-field low-temperature data suggested

that w = 27r/7 is the stable value of the turn angle. The absence of any shift

in q at 10 kOe (a slight broadening is evident) confirms this as the stable

state.

26
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

At 40 K (fig. 2b), the zero-field w has the stable value 1-^/1 and is not

shifted by a 10 kOe field. Higher fields strongly shift the magnetic

scattering to smaller q, indicating the development of the linear fan state.

The average turn angle for the Er layers in this state is ~ 35°, which is much

lower than found in any bulk Er state. Of the superlattices we have studied

this is the one with the smallest ratio of Er to Y, and thus has the least

magneto-elastic energy density. This is consistent with the theories of fan

states where large anisotropy or magneto-elastic energies favor a direct

transition from the modulated to ferromagnetic states [4]. These theories do

not yet take into account the perturbation of the turn angle by magnetoelastic effects in the fan state.

Finally, the zero-field remanence state returns to the zero-field-cooled

value of w, but with a reduced coherence length.

27
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1 "T

lOK

20K

30K-I

40K

120

80

40

600

480-

360

m

a

o

C240

120-

20 40

Internal Field (kOe)

: 50.3° zero I kOe/ \

H h

T = 40K

[2^13^26]

zero kOe remanence

-8

Figure 1 Magnetization

and (b) vs

[Er,

internal field along the c-axis for the

The low-field

(left)

(a) [Er.^lYpg] and (b) [Erp^lYjg] superlattices

low-temperature states have a magnetization of approximately 1/7 of

the saturation value corresponding to the net c-axis moment of the

2n/7 lock-in state. The [Er,5|Ypg] superlattice shows evidence of

an intermediate fan state.

Figure 2. (right) (a) Neutron diffraction scans along (lU) for [Ern^lYpcl

at T = 10 K with the applied field along the c-axis. The

calculated Er turn angle shifts from 50.3° to the commensurate

value, 27r/7 = 51.4°, with little or no loss of coherence when the

field is raised from zero to 10 kOe (7 kOe internal), (b) At T = 40 K there is no shift in the Er layer turn angle as the field is

raised, indicating that w = 27r/7 is the zero-field state. The

sharply reduced q of the peaks (w ~ 35°) at 23 and 27 kOe internal

field indicates the development of fan states corresponding to the

magnetization plateaus in figure la.

28
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[1] R. W. Erwin, J. J. Rhyne, J. Borchers, M. B. Salamon, R. Du, and C. P. Flynn, J. Appl . Phys. 63 3461 (1988); J. Borchers, M. B. Salamon, R. Du,

C. P. Flynn, J. J. Rhyne, and R. W. Erwin, ibid, page 3458.

[2] R. W. Erwin, J. J. Rhyne, M. B. Salamon, J. Borchers, Shantanu Sinha,

R. Du, J. E. Cunningham and C. P. Flynn, Phys. Rev. B35 6808 (1987).

[3] D. Gibbs, J. Bohr, J. D. Axe, D. E. Moncton, and K. L. D'Amico, Phys.

Rev. BM 8182 (1986).

[4] Y. Kitano and T. Nagamiya, Progress Theoret. Phys. 3i> 1 (1964).

MAGNETIC STRUCTURE OF CUBIC Tb^ 3YQ ^Ag

J. A. Gotaas

M. R. Said and J. S. Kouvel

(University of Illinois, Chicago, IL)

and

T. 0. Brun

(Argonne National Laboratory, Argonnne, IL)

The CsCl-type compounds RAg (R = rare earth) exhibit a fine balance

between ferromagnetism and antiferromagnetism of various forms. The dilution

of the rare earth by the chemically similar nonmagnetic yttrium should

certainly lead to reductions in ordering temperatures, perhaps to

modifications in the magnetic structures, and ultimately to spin-glass

behavior. Magnetization studies of the series Tb Y, Ag and Gd Y, Ag [1] AA~A AJ.~A

have shown that for x < .5, thermoremanences appear along with associated time

dependences which are indicative of spin-glass behavior. We have carried out

neutron diffraction measurements to clarify the nature of the magnetic state

in these systems, starting with a polycrystall ine sample of Tb^ ^Yq yAg, which

exhibited the largest remanence effects.

The neutron diffraction was performed on BT-6 and BT-9, using a pyrolytic

graphite (PG) monochromator at 2.46 A and a PG analyzer and filter to improve

the signal to noise ratio of the data. A diffraction pattern taken at 4 K showed a set of additional peaks appearing at distinct positions from the

nuclear peaks observed at 60 K. These could be associated with the set of

indices (h + 1/2, k + 1/2, i). This type of antiferromagnetic structure has

29
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

been observed in other RAg compounds, including TbAg. The (ttttO) structure

consists of moments ferromagnetically aligned in [110] planes, with

neighboring planes antiferromagnetically coupled; the resulting magnetic

lattice has tetragonal symmetry with a doubling of the cell axes in two

directions. The structure observed here is a more complex variant of the

{ttttO) structure. Figure 1 shows the first peak in the diffraction pattern, in

which two reasonably sharp peaks are superimposed on a broad peak, approximately centered on the (1/2, 1/2, 0) position. The broad central peak

corresponds to the (ttttO) spin structure and the pair of satellites represent

an incommensurate modulation of the basic antiferromagnetic structure. Such a modulated structure has been observed in HoAg, TmAg, ErAg and DyAg.

600

400

o

o

200

0.3 ^ 0.7'

T = 4.5 K

Resolution ->

y^n*?^

20 25 30 35

26

Figure 1. Multiple peak structure observed at (1/2, 1/2, 0) position at

T = 4.5 K. Instrumental resolution is indicated.

The magnetic peaks are not resolution limited, indicating that the

correlation lengths are finite even at 4 K. The central (ttttO) peak is very

broad, indicating a correlation range of only ~ 42 A, which is approximately

12 chemical unit cells. The satellite peaks, while considerably sharper,

still possess an intrinsic width corresponding to a correlation length of

~ 290 A. Assuming that the structures are similar to those found in the

related RAg compounds, the diffraction pattern is consistent with the

30
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

coexistence of a short-range ordered {7r7r0)-type structure and an incommensurate modulated structure of the type found in HoAg. In this structure, the

individual moments are parallel to the unique c-axis; the propagation vector

for the modulated state is directed along the cube edges, allowing for a set

of domains (h ± 6, k, i), (h, k ± 5, £), etc. The separation of the satellites from the (1/2, 1/2, 0) position indicates that modulation wave vector

has a magnitude of 0.059(27r/a), corresponding to about 17 chemical unit cells.

Figure 2 shows the temperature dependence of the integrated intensity of

the central peak as well as the sum of the integrated intensities of the

satellites. As indicated in the figure, there is still measurable intensity

at 37.5 K, persisting above the nominal transition derived from magnetization

measurements. As the peaks have broadened still further, it is difficult to

distinguish the satellite positions and the integrated intensities; some scattering remains up to 45 K. Clearly most of the magnetic order develops

below approximately ~ 36 K, in agreement with the bulk measurements. Although

the breadth of the peaks makes the precise determination of the peak positions

difficult, the data are consistent with a temperature dependent modulation

wavelength, as is found in HoAg and TmAg.

120

.(-4

CD +J

X3

0)

4-1

80

40

O (1/2 1/2 0) _

Satellites

V T^ (Magn)

Tbo^Yo^^Ag

20 40 60

T (K)

Figure 2. Temperature dependence of the integrated intensities of the central

(1/2, 1/2, 0) peak and the sum of the satellite peaks.

References

[1] M. R. Said, J. S. Kouvel , and T. 0. Brun, J. Appl . Phys. 63, 4340 (1988).

31
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC STRUCTURE OF Yq g^Er^

^3

J. A. Gotaas and J. J. Rhyne

L. E. Wenger

(Wayne State University, Detroit, MI)

and

J. A. Mydosh

(Rijks-Universiteit Leiden, 2300 RA Leiden, The Netherlands)

The nature of the magnetic state in dilute alloys remains a problem of

considerable interest, with the rare-earth elements substituted into yttrium

forming an interesting series of systems with varying exchange interactions

and single-ion anisotropies. It has been shown that long range order persists

down to rare-earth concentrations less than 2-5%, depending on the particular

element. We have continued a systematic study of these systems by investigating Yq gyEi^Q Qo- Measurements were performed on a single-crystal sample

oriented with the a- and c-axes in the scattering plane, using BT-6 and BT-9.

3

The sample was mounted in a pumped He cryostat which could be cooled to a minimum temperature of 0.3 K. The crystal field anisotropies in both bulk erbium and the dilute yttrium

alloys are such that the erbium moments lie predominantly along the c-axis.

The spin orientation factor in the neutron scattering cross-section then

implies that the satellites resulting from an incommensurate modulated

structure will occur only around the allowed nuclear peaks in the basal plane

[e.g. (110)], displaced along the c* reciprocal axis by {2-n/c)s, where s is

the modulation wave vector of the ordered phase. Such magnetic peaks were observed displaced from the (110) nuclear peaks, with s = 0.275. The

scattering at the satellite position displayed two components: a sharp

component that appeared at 3.25 K and was resolution-limited in width,

implying true long range order, and a secondary weaker component (approximately 5% of the main peak at 0.3 K) which persisted to temperatures up to -10

K, with a diffraction width corresponding to a finite correlation length of

only about 80 A. The presence of precursor critical scattering is typical,

but the persistence of the scattering down to 0.3 K is rather unusual. The

net magnetic intensity, which is proportional to the square of the magnetic

order parameter, is displayed in figure 1, where it is denoted by (1, 1,

0.275). No differences were observed in the magnetic intensities on cooling

32
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

and warming. The intensity shown contains the contribution of both components

of the scattering, since it is experimentally difficult to uniquely separate

them.

1 1 1 1 1 1 •l-H CO 5 1.0 _ ^0.97'^^0.03

fl

-^^^•^-^^^jv^ h—

1

^-Q>

^ <%. o ( 1. 1. 0.275)

c6 ^

CD

N• 1—

1

^0

o ( 0. 0, 0.275)

( Int X 100) -

^ %

<^\\ D ( 1, 1, 0.825) _ *>*..

( Int X 100)

O^ 0.0 —m—1-^}!^L-^y-x:^^ -J —6

T (K)

6

Figure 1. Normalized magnetic peak intensity versus temperature for (110 ) [0], (000"^) [ ] and (110^^) [n] satellites. Note that the latter

two intensities are scaled up by a factor of 100.

A careful search for c-axis satellites revealed the presence of an (000 )

peak with an intensity only 0.6% of the main (110 ) satellite, indicating the

existence of a small basal-plane component in the ordered state. This

component shows the same temperature dependence (displayed as (0, 0, 0.275) in

fig. 1) as the main c-axis structure and represents only about 0.1 /in. The

absence of significant basal-plane anisotropy suggests that this basal plane

moment forms a helical component, which would make the structure similar to

that observed in pure erbium between 20 and 52 K. A careful search for higher harmonics of the c-axis structure was carried

out, since general thermodynamic arguments predict that the disorder in the

moment at every site must vanish as T - 0. A peak corresponding to a thirdharmonic component was found to develop at temperatures below approximately

2 K, with an intensity at 0.3 K of only 0.15% of the primary satellite,

indicating that the sinusoidal structure begins to square up. The intensity

of this peak is shown in figure 1 as (1, 1, 0.825).

33
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC RARE- EARTH SUPERLATTICES

C. F. Majkrzak

D. Gibbs, P. B6ni, and A. I. Goldman

(Brookhaven National Laboratory, Upton, NY)

J. Kwo, M. Hong, T. C. Hsieh, R. M. Fleming, D. B. McWhan, and Y. Yafet

(AT&T Bell Laboratories, Murray Hill, NJ)

J. W. Cable

(Oak Ridge National Laboratory, Oak Ridge, TN)

J. Bohr

(Ris(j» National Laboratory, Denmark)

H. Grimm

(IFF, Kernforschungsanlage, JUlich, West Germany)

and

C. L. Chien

(Johns Hopkins University, Baltimore, MD)

Recent advances in molecular-beam epitaxy (MBE) techniques have made it

possible to grow single-crystal, rare-earth (RE) superlattices with a high

degree of perfection and limited interdiffusion [1-3]. Magnetic layers

consisting of a discrete number of atomic planes can be deposited alternately

with nonmagnetic or other magnetic layers of a given thickness. The effects

of reduced dimensionality on the magnetic ground state and corresponding

critical behavior can be investigated. Because the magnetic RE moments

interact through long-range, indirect exchange, a modulation of the magnetic

properties in certain synthetically layered RE structures might also be

expected. Furthermore, since the detailed, microscopic magnetic structures of

the RE metals result from the competition between the isotopic indirectexchange and the anisotropic crystal -field and magnetoelastic interactions,

the study of synthetic RE superlattices with a tailored composition and/or

strain profile can, in principle, give valuable information about such

phenomena as the lock-in transitions from incommensurate to commensurate

phases recently described by a spin-slip model [4-6].

The periodicity of the multilayer structure makes it possible to study

its magnetic state by diffraction and polarized neutrons are especially useful

in determining the more-complicated, noncollinear magnetic structures which

can occur in some of the RE superlattices. The magnetic structures of several

34
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

single-crystal, magnetic RE superlattice systems grown by MBE are currently

being studied by neutron diffraction. In particular, investigations of longrange magnetic order and interlayer interactions in Gd-Y, Dy-Y, and Ho-Y

periodic superlattices have already shown that the magnetic structure is

propagated coherently across the intervening non-magnetic Y layers [7]. In the Gd-Y system, an antiphase domain structure develops for certain Y layer

spacings, whereas modified helical moment configurations are found to occur in

the other systems. In Gd-Dy superlattices, a number of different magnetic

structures are observed, some of which are commensurate and others which are incommensurate with the chemical superlattice wavelength. Theoretical

interaction mechanisms have recently been proposed to account for the magnetic

states of these novel materials [8].

Interlayer interaction studies of the Gd-Y superlattice system involving

more-exotic layered structures, specifically arrangements where two different

Y layer thicknesses corresponding to ferromagnetic and anti ferromagnetic

interactions between Gd layers are propagated in a Fibonacci sequence, are also in progress. The expectation is that something can be learned about the

long-range order, or the lack thereof, in such a quasiperiodic heterostructure

with competing interactions.

An attempt to measure the magnetization profile as a function of

temperature in a ferromagnetic [^^jQ-Ypn] jqq sample by neutron diffraction has

also been made in order to study the effect of reduced dimensionality and

interface anisotropy on the magnetic critical behavior. However, it turns out

that it is necessary to determine the chemical compositional and strain

modulation profiles yery accurately. In this particular case the problem is

complicated by a strongly temperature-dependent strain profile and more- comprehensive measurements must be performed before any conclusions can be

made regarding critical point exponents.

These RE superlattice studies have only just begun and much work remains

to be done. Nevertheless, new and interesting results have already been

obtained [9].

References

[1] J. Kwo, D. B. McWhan, M. Hong, E. M. Gyorgy, L. C. Feldman, and J. E. Cunningham, in Layered Structures, Epitaxy and Interfaces, Matls. Res.

Soc. Symp. Proc. No. 37, p. 509, edited by J. H. Gibson and L. R. Dawson,

Materials Research Society, Pittsburgh, PA (1985).

35
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

[2] S. Sinha, J. E. Cunningham, R. Du, M. B. Salamon, and C. P. Flynn, in

Proceedings of the International Conference on Magnetism, edited by J. J. Rhyne, B. R. Cooper, D. L. Huber, N. C. Koon, and R. C. O'Handley, NorthHolland, Amsterdam (1985).

[3] J. Kwo, E. M. Gyorgy, D. B. McWhan, M. Hong, F. J. DiSalvo, C. Vettier,

and J. E. Bower, Phys. Rev. Lett. 55, 1402 (1985).

[41 D. Gibbs, D. E. Moncton, K. L. D'Amico, J. Bohr, and B. H. Grier, Phys.

Rev. Lett. 55, 234 (1985).

[5] J. Bohr, D. Gibbs, D. E. Moncton, and K. L. D'Amico, Physica 140A , 349

(1986).

[6] D. Gibbs, J. Bohr, J. D. Axe, D. E. Moncton, and K. L. D'Amico, Phys. Rev.

B34, 8182 (1986).

[7] See, for example, the review article by C. F. Majkrzak, D. Gibbs, P. BOni,

A. I. Goldman, J. Kwo, M. Hong, T. C.Hsieh, R. M. Fleming, D. B. McWhan,

Y. Yafet, J. W. Cable, J. Bohr, H. Grimm, and C. L. Chien, J. Appl . Phys.

63, 3447 (1988) and relevant references therein.

[8] See, for example, the review article by Y. Yafet, J. Kwo, M. Hong, C. F. Majkrzak, and T. O'Brien, J. Appl. Phys. 63, 3453 (1988).

[9] C. F. Majkrzak, J. W. Cable, J. Kwo, M. Hong, D. B. McWhan, Y. Yafet, J. V. Waszczak, H. Grimm, and C. Vettier, J. Appl. Phys. 61, 4055 (1987).

ANTIFERROMAGNETIC STRUCTURE AND CRYSTAL FIELD SPLITTINGS IN

THE CUBIC HEUSLER ALLOYS HoPd2Sn AND ErPd^Sn

W.-H. Li, J. W. Lynn, and H. B. Stanley

(University of Maryland and the National Bureau of Standards)

T. J. Udovic

and

R. N. Shelton and P. Klavins

(University of California, Davis, CA)

The Heusler alloy series of general composition RPd^Sn, with R = Sc, Y,

and the heavier rare earths from Tb to Lu, crystallize into the cubic CUpMnAltype structure (Fm3m), with the rare-earth ions occupying sites of cubic point

symmetry. In particular, the coexistence of anti ferromagnetic order and

superconductivity has been reported for both YbPd^Sn [1] and ErPd^Sn [2].

This new class of systems possesses two features which make them particularly

interesting candidates for study. First, they contain a substantially higher

36
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

percentage of magnetic ions in comparison to the RRh.B. [3] and RMOgSg [4]

materials. Second, there is no clear isolation of the magnetic and

superconducting sublattices. The nearest-neighbor distance between magnetic

ions, for example, is substantially smaller than for the RRh.B. and RMOgSg

systems, which leads to a larger exchange interaction between rare-earth ions

themselves, and the rare-earth ions and conduction (4d) electron spins. In the present paper we report diffraction and inelastic neutron scattering

measurements which have been used to determine the magnetic structure and the

crystal-field splittings.

Measurements were carried out on the BT-9 triple-axis spectrometer as well as time-of-fl ight (TOP) spectrometer. Powder diffraction patterns were

taken with a neutron incident energy fixed at 14.8 meV (a = 2.351 A) using

pyrolytic graphite (002) as monochromator, and no analyzer. A pyrolytic

graphite filter was used to reduce higher order wavelength contaminations.

Horizontal collimations of 40', 25', and 25' (FWHM) before and after the

monochromator, and after the sample, were employed. In the study of the

crystal field excitations, on the other hand, the TOP technique is ideally

suited since the excitations are dispersionless. The data collected for many

detectors may be summed to improve the statistical accuracy, while the

momentum dependence of the intensities may also be readily extracted from the

experimental data. The 64 detectors of the TOP machine were placed to cover scattering angles over a range from 6.3 - 114.5°. Neutrons with an incident

energy of E. = 13.8 meV (a = 2.435 A) were used for these measurements.

To study the nature of the long-range magnetic order which developed at

low temperatures, sets of complete diffraction pattern were taken at various

temperatures. To extract the magnetic component, we employed the subtraction

technique [5], where data at high temperatures are subtracted point by point

from the data in the ordered phase. The magnetic diffraction pattern thus

obtained is shown in figure 1 for HoPd^Sn. Pour magnetic Bragg peaks are evident, and may be indexed as (1/2,1/2,1/2), (1/2,1/2,3/2), (1/2,3/2,3/2),

and (1/2,1/2,5/2) + (3/2,3/2,3/2) reflections of an fee type-II

antiferromagnet. This sequence of half-integral reflections shows that the

magnetic unit cell doubles along all three directions with respect to the

chemical unit cell. The basic is the same as that for ErPd^Sn [6].

The temperature dependence of the (1/2,1/2,1/2) peak intensity is shown

in figure 2, where a Neel temperature of T», ~ 5 K is indicated for this

37
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

system. Comparing the integrated intensity of the {1/2,1/2,1/2} reflection

with the {004} nuclear peak yields an ordered magnetic moment of 5.81(8) n^ at

D T = 0.34 K. However, note that there is substantial smearing of the

transition. In addition, the widths of the Bragg peaks are significantly

larger than instrumental resolution at all temperatures, which we interpret as indicating substantial intrinsic disorder. The nuclear peaks, in contrast,

are resolution limited in width.

4000

3000 -

I

2000

oO

c5 z

1000 -

-

-500

1 1 1

J- HoPcl2Sn A = 2.35A

40'-25'-25' —

'! T = 0.44K-T = 6.0K

• -^^

I

,

CM ^^ —

• ^

I

• S

CM ^V

« ?5 + ~ ^ CM f

^ w ^ ~

, ^'^ CO CM I

;. ^ ft

:"5 7

V»

/ • f

: I

» — jt '. * v. > -v ./ V.

-

yV,'^'''

1 1 1 H.V

1

..^

10 20 30 40

Scattering Angle 26 (degrees)

50 60

Figure 1. Magnetic powder diffraction pattern for HoPd^Sn, obtained by subtracting the data measured at T = 6 K from the data at T = 0.44 K.

38
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

T— I-|-1—r—I—1—r- {1/2,1/2,1/2} : 6000

°°N,

-

d ^ \ . "E ^

'

"Z 4000 \

- a>

' a.

' ^

• \X • (0 • \. . - o c V 3

' 6^\

' o

• ^ • O 2000

^"^

) 1 2 3 4 5 6

Temperature (K)

Figure 2. Temperature dependence of the {1/2,1/2,1/2} antiferromagnetic peak

intensity. The rounding of the transition at Tj^ = 5 K is due to

either critical critical fluctuations fluctuations or a distribution distribution of Tm's.j,'s The solid curve is a guide to the eye.

Measurements of the crystal field excitations on the HoPd^Sn powder

sample were taken at six different temperatures in the range from 0.44 to 40 K

using the TOP spectrometer. The scattering spectra that were obtained by

summing over data acquired by 60 detectors at T = 0.44, 10.0, 23.0, and 40.0 K are shown in figure 3. At low temperatures, where the thermal energy is small

in comparison with the excitation energies (e.g., T = 0.44 and 10.0 K), two

dispersionless excitations are clearly observed, with energies of 3.52(1) and

6.65(1) meV at T = 10 K, and correspond to transitions out of the ground

state. At elevated temperatures, when the higher energy crystal field levels

become thermally populated (e.g., T = 23.0 and 40.0 K), one additional

transition on the neutron energy gain side (E < 0) is also evident. This

energy was determined to be -3.5(2) meV at T = 40.0 K. We noted that the

intensities of the transitions at both 3.52 and 6.65 meV decreased with

increasing temperature, as expected due to the depopulation of the crystal

field ground state.

39
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS —I

6001-

500

400

T T T I

HoPdgSn

Ei=l3.8meV J

-LO L5 4.0

ENERGY (meV)

Figure 3. Elastic and inelastic scattering observed on powder HoPd^Sn with

the time-of-flight technique. To improve the statistics, spectra

shown were obtained by summing over data acquired on 60 detectors

spanning a Q range from 0.48 to 3.85 A . At T = 23.0 and 40.0 K,

transitions from higher energy levels to low energy levels are also

evident in neutron energy gain side (E < 0).

To determine the Lea, Leask, and Wolf [71 (LLW) crystal field

parameters W and x, we start with the data obtained at T = 10 K. Utilizing

the energies of the transitions from the ground state, there are nine sets of

40
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

data which are consistent with the experimental data. However, only one set

yields the correct observed transition probabilities, and gave W = 0.0287(2)

meV and x = 0.3248(8). These LLW parameters give a crystalline electric field

(CEF) energy level sequence r^^ ^ - r^' ^ - r,' ^ - r^'^ - r, - r.^^ -

r,^ ', with an overall energy splitting of 17.56 meV at T = 10 K, and the

11) magnetic triplet Tr^ ' (Bethe's notation [8]) as the ground state. The

temperature dependent data are completely consistent with this set of

parameters. Similar measurements were also taken on the ErPd^Sn powder

sample. Following the same analysis procedure as for the Ho systems, the

crystal field parameters for this system were determined to be W = -0.0450(4)

meV and x = 0.3022(6). These LLW parameters give a CEF energy level sequence

Tg^ ^ - Tg - Tg^ ^ - Tg^ ^ - Tj with an overall energy splitting of 20.32 meV

(2)

at T = 10 K, and the magnetic Tg^ ' as the ground state.

Reference

[1] H. A. Kierstead, B. D. Dunlap, S. K. Malik, A. M. Umarji, and G. K. Shenoy, Phys. Rev. B32, 135 (1985).

[2] R. N. Shelton, L. S. Hausermann-Berg, M. J. Johnson, P. Klavins, and

H. D. Yang, Phys. Rev. .gM, 199 (1986).

[31 W. A. Fertig, D. C. Johnson, L. E. DeLong, R. W. McCallum, M. B. Maple,

and B. T. Matthias, Phys. Rev. Lett. 38, 987 (1977).

[41 M. Ishikawa and 0. Fischer, Solid State Commun. 23, 37 (1977).

[5] J. W. Lynn, J. A. Gotaas, R. N. Shelton, H. E. Horng, and C. J. Glinka,

Phys. Rev. g31, 5756 (1985).

[6] H. R. Stanley, J. W. Lynn, R. N. Shelton, and P. Klavins, J. Appl . Phys.

61, 3371 (1987).

[7] K. R. Lea, M. J. M. Leask, and W. P. Wolf, J. Phys. Chem. Solids 23, 1381

(1962).

[8] H. Bethe, Ann. Phys, Opz. 3, 133 (1929).

41
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

ANTI FERROMAGNETIC ORDER OF THE Cu IN RBa2Cu30g^^

J. W. Lynn and W.-H. Li

(University of Maryland and National Bureau of Standards)

H. A. Mook and B. C. Sales

(Oak Ridge National Laboratory)

and

Z. Fisk

(Los Alamos National Laboratory)

The magnetic properties of the oxide superconductors have been of

particular interest due to the intrinsic interest in magnetism as well as because of the possibility that the magnetic fluctuations are responsible for

the superconducting pairing [1]. The ^^^2^^2^6+x ^^ ^ ^^^^ earth) system

orders antiferromagnetically [2-4] for small x (x < 0.4), where the system is

tetragonal and nonsuperconducting. The magnetic structure consists [3,4] of a simple antiparallel arrangement of Cu spins both within the Cu-O planes as well as along the tetragonal c-axis, while the oxygen deficient Cu planes

possess no ordered moment. The three-dimensional ordering can be quite high

(TmiCx == 0) ~ 450 K), indicating that the magnetic interaction energies are large. The 3-d transition temperature is also very sensitive [2] to the

oxygen concentration x, decreasing rapidly with increasing x and approaching

zero for x ~ 0.4.

A second magnetic phase transition has recently been observed [5,6], in

which the oxygen-deficient Cu "chain" layers also order magnetically. We have

been investigating the nature of this ordering and the effect of oxygen

concentration on T|^2 ^^^ ^^^^e now obtained results on a number of single

crystal specimens of NdBa^Cu^Og . We find that at small x and low T the

basic magnetic structure consists of a simple antiferromagnetic arrangement of

spins both within the planes as well as along the c-axis. In particular, we find an unexpectedly large magnetic moment on the Cu chain sites. At

intermediate temperatures the spin arrangement is a superposition of the high

T and low T configurations, and is noncollinear in nature. We also find that

both transition temperatures decrease with increasing x, with the lower

transition l^,^ being much more sensitive to x than the higher transition Tj^,.

The neutron measurements were carried out at the National Bureau of

Standards Research Reactor using standard triple-axis instruments.

42
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Unpolarized diffraction data were collected with an incident energy of either

14.8 or 13.7 meV using a pyrolytic graphite PG(002) monochromator. Polarized

neutron measurements were then taken to establish that the new peaks are magnetic in origin, and this procedure has been described previously [4]. The

Bragg peak corresponding to the (1/2,1/2,3/2) reflection is shown in figure 1. Even though the Cu moments are quite small, the crystal is sufficiently large

{- 50 mg) to obtain an excellent signal-to-noise ratio. Polarized neutron

measurements were employed to establish that the observed half-integral peaks

are wholly magnetic in origin. The half-integral value for the third index

demonstrates that the magnetic structure is doubled along all three

crystallographic directions in comparison to the chemical unit cell. This

contrasts with the spin configuration observed [3,4] in the higher temperature

magnetic phase, where the i index is integral and the magnetic and chemical

unit cells are the same size along the tetragonal c-axis.

8000

6000

+2

c

oO

4000-

2000-

0<ii o o o o 9

0.49 0.50

Sample Rotation

0.51

Figure 1. Observed magnetic Bragg peak for the (1/2,1/2,3/2) peak at low

temperatures.

The temperature dependence of the (1/2,1/2,3/2) peak is shown in the

bottom portion of figure 2. For this value of oxygen concentration (x ~ 0.1)

43
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the lower phase transition occurs at Tj^^ ~ 80 K. The top portion of the

figure compares the intensity of the whole-integral peaks such as (1/2,1/2,2),

which are associated with the higher temperature phase transition; for the

present sample T^,, = 430 K. There is a dramatic downturn in the intensity of

the whole-integral reflections at low temperatures which is associated with

the development of the intensities of the half-integral peaks. It is clear

that the half-integral peaks dominant at low T, and hence they correspond to

the ground state spin configuration of the system. The T = structure

consists of a simple collinear arrangement of spins, with the spin direction

in the tetragonal plane. The nearest-neighbor spins within the Cu-0 planes

(designated Mp, for planes) are aligned antiparallel as they are in the high T

phase. However, along the c-axis the oxygen-deficient Cu moment (designated

Mp, for chains) is nonzero, and aligned antiparallel to the spins in the Cu-0

layers. The doubling of the unit cell along the c-axis direction results

because the sense of the spins is reversed in going from one chemical unit

cell to another.

The values of the ordered moments we obtain at low temperatures are Mp

= 0.97 ± 0.09/ip for the Cu-0 planes (assumed equal), and Mp = 0.46 ± 0.06^0-

This compares with Mp ~0.6/in for the maximum moment found [4] above Tj^^- The

essential difference between the two structures is of course the moment Mp.

We remark that the conventional viewpoint for the RB^2^^3^6+x ^^^^^ °^ materials is that the Cu valence in the Cu-O, planes is 2+, with an associated

1+ magnetic moment, while the Cu "chain" layers contain Cu which is non- magnetic. The unexpectedly large ordered moment 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. It is reasonable to assume that the chain-layer moment is a result

of strong hybridization of the (band) electronic wave functions within this

(as well as the Cu-0) Cu plane, rather than as a result of a perturbation

caused by the remnant oxygen in the layer as has been suggested [6]. Further

work on the magnetic properties of these systems as a function of concentration, magnetic field, and pressure is underway.

44
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2000

1000

c

o

I

8000

CD g 6000

4000

2000

.08

fi ''h''^h,%,^%J^

(1/2,1/2,2)

bkg

^°Oo (1/2,1/2,3/2)

o

o

o o

o

o

o

o

o

o°Oo

OO o Oooooooo<

100 200

Temperature (K)

Figure 2. Magnetic intensities for the NdBapCUo0<- , crystal. The downturn of

the intensity of the (1/2,1/2,2) peak coincides with the development of half-integral peaks such as the (1/2,1/2,3/2) peak shown

the in bottom portion of the figure.

References

[1] See, for example, P. W. Anderson, Science 235, 1196 (1987). P. W. Anderson, G. Baskaran, Z. Zou, and T. Hsu, Phys. Rev. Lett. 58, 2790

(1987). V. J. Emery, Phys. Rev. Lett. 58, 2794 (1987). R. H. Parmenter,

Phys. Rev. Lett. 59, 923 (1987). J. E. Hirsch, Phys. Rev. B35, 8726

(1987); Phys. Rev. Lett. 59, 228 (1987). J. R. Schrieffer, X.-G. Wen, and

S.-C. Zhang, Phys. Rev. Lett. 60, 944 (1988).

[2] D. C. Johnston, S. K. Sinha, A. J. Jacobson and J. M. Newsam, Physica B (to be published, Interlaken Conference), and references therein. See

also J. H. Brewer et al . Phys. Rev. Lett. 60, 1073 (1988).

[3] J. M. Tranquada, D. E. Cox, W. Kunnmann, H. Moudden, G. Shirane, M. Suenaga, P. Zolliker, D. Vaknin, S. K. Sinha, M. S. Alverez, A. J. Jacobson, and D. C. Johnston, Phys. Rev. Lett. 60, 156 (1988).

[41 W.-H. Li, J. W. Lynn, H. A. Mook and B. C. Sales, Bull. Am. Phys. Soc. 33,

(1988). W.-H. Li, J. W. Lynn, H. A. Mook, B. C. Sales and Z. Fisk, Phys.

Rev. B37, 9844 (1988).

45
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

[5] J. W. Lynn, W.-H. Li, H. A. Mook, B. C. Sales, and Z. Fisk (to be

published)

[6] H. Kadowaki, M. Nishi, Y. Yamada, H. Takeya, H. Takei, S. Shapiro, and G. Shirane, Phys. Rev. B37, 7932 (1988).

NEUTRON DIFFRACTION IN Co Hg^ SOLID SOLUTIONS

T. M. Giebultowicz

(University of Notre Dame, Notre Dame, IN)

J. J. Rhyne

and

M. S. Seehra and R. Kannan

(West Virginia University, Morgantown, WV)

Co Mg, offers an excellent prototypical example for the study of

percolation effects in diluted antiferromagnets. The system retains the

original structure of CoO (NaCl-type) in the entire < p < 1 composition

range [1]. The magnetic Co ions form a randomly diluted fee lattice with

predominantly next-nearest neighbor (NNN) AF coupling due to the mediating

role of the oxygen anions.

Recent studies [1] of DC magnetic susceptibility x(T) carried out for

Co Mg, with 0.10 < p < 1 in a broad T range indicate that the percolation

threshold for this system is p ~ 0.13, in agreement with the theoretical

value of p = 0.136 for a fee lattice with NN and NNN interaction. The

'^c variation of the reduced N6el temperature r = T|g(p)/Tjg(p = 1) with p also

reveals a crossover effect at p = 0.45. It is of interest that the system

shows a remarkable similarity [2] to Eu Sr, Te [3], which suggests that such

a crossover behavior is universal for diluted Type II antiferromagnets.

However, the mechanism of this phenomenon, as well as the nature of the

magnetic state in CoO below p (superparamagnetic particles, or a spin glass?)

is not yet fully understood, and neutron scattering measurements are necessary

to obtain more insight into these issues.

We have carried out neutron diffraction measurements on several Co^Mg, „0

P 1-P

powder specimens with various Co concentrations (p = 0.25, 0.37, 0.42, 0.47,

0.54, 0.60, and 0.90). At low temperatures, the systems exhibited the

expected pattern of superstructure peaks corresponding to the Type II AF

structure. Examples of the composition dependence of the (111)m magnetic

46
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

peaks are displayed in figure 1 for the range 0.37 < p < 0.54. For

p = 0.90 - 0.54 the reflections showed no detectable broadening beyond the

instrumental resolution, confirming the existence of a LRO AF phase in this

concentration region. In contrast, the peaks observed for p < 0.47 are broadened and are of Lorentzian shape, indicating a transition to a SRO state.

The inverse correlation length {«;) data plotted in figure 2 clearly suggest

that the LRO->^SRO transition in the system has a sharp composition dependence,

and that the critical concentration for this process is slightly higher than

p = 0.47. The sharp nature of this transition is also indicated by the

behavior of the integrated intensity of the (HI),,, reflection vs. p, which is

plotted in figure 2 normalized by the intensity of the nuclear reflection

(200)|^. The results clearly show a sharp discontinuity in the magnetic

scattering intensity at p . The results of our neutron diffraction studies of Co Mg, „0 demonstrate

P 1-P

that the previously reported crossover behavior in the magnetic susceptibility

at p = 0.45 really reflects the breakdown of the LRO magnetic phase in the

system. Since it is believed that a similar type of transition (LRO -+ spin

glass) occurs in Eu Sr, Te for p < 0.50 [3], these results also indicate why

the magnetic characteristics of the two systems are similar at higher p values.

47
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COjM9f-pO, (1 1 1)y peak. 9 K

0.70 0.75 0.80 0.85 0.90 Q-VECTOR LENGTH (2-n/a) 0.95 1.00

Figure 1. The {111)m magnetic peaks in Co Mg, for several different Co

concentrations. Solid lines are the results of fitting Lorentzian

lineshapes folded with the Gaussian instrumental resolution

function to the experimental points (for p = 0.54 only a Gaussian

line has been fitted).

48
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

C\2

C\2o

T—

I

X

8

Co Mgi_ — T=9 K

0.2

CV2 o

o

02

C\3 O

o

0.6 1.0

Composition p

Figure 2. Left plot: the dependence of the inverse correlation length k on concentration p in the SRO phase in ^On'^^^l-n^* RiQht plot:

relative intensity of the (111)m reflection as a function of p (see

text). The lines plotted in both graphs are guides for the eye.

References

[1] R. Kannan and M. S. Seehra, Phys. Rev. B35, 6847 (1987).

[2] M. S. Seehra, J. C. Dean, and R. Kannan, ibid . B37, 5864 (1988).

[3] F. J. Borgermann, H. Maletta, and W. Zinn, ibid . B35 , 8454 (1987).

49
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SUPERCONDUCTIVITY IN LANTHANUM BARIUM CUPRATE PEROVSKITES

S. Miraglia, A. Santoro, and F. Beech

and

S. A. Sunshine, L. F. Schneemeyer, J. V. Waszczak, and D. W. Murphy

(AT&T Bell Laboratories)

Samples in the system Ba« „La, .^Cu^O, AO.O < x < 0.5; < 5 < 0.25) have

t ~ X l+X o I ~ been prepared and characterized by x-ray powder diffraction, magnetic

susceptibility, electrical resistivity, and for x = 0.5, powder neutron

diffraction. This neutron diffraction study on Ba, nLai s^u^O, 25''"dicates

that the structure is similar to the 92 K superconductor Ba^YCu^Oy with two

exceptions. First, the "Ba site" contains 75% Ba and 25% La and second, the

symmetry is tetragonal. At x = 0.5 the material is a semiconductor, but as x decreases, metallic behavior and superconductivity are observed. Compositions

with X < 0.2 contain traces of BaCu02, but exhibit 7^"^*=^;=, 90 K and R = near

80 K. For X = 0.2 - 0.3, t°"^^^ == 60 K and R = near 50 K are observed. For

c

X < 0.1 orthorhombic symmetry is observed. These results provide further

evidence that oxygen stoichiometry and details of the oxygen ordering are important to superconductivity.

CRYSTAL CHEMISTRY OF SUPERCONDUCTORS:

A GUIDE TO THE TAILORING OF NEW COMPOUNDS

A. Santoro and F. Beech

and

M. Marezio and R. J. Cava

(AT&T Bell Laboratories, Murray Hill, NJ)

The crystal structures of the known superconducting copper oxides can be

described in terms of two basic structural types. The series LaCa ,Cu Op o' (Tl, Bi)2(Ba,

^'^)2^^n-l^^n^2n+4 ^"^ ^^^''2^''n-l^"n^2n+3 ^^" ^^ viewed as made

of alternating slices having the rock salt and perovskite structure. The

compounds Ba^YCu-Og and Ba.YpCu^O,. , on the other hand, comprise perovskite

blocks alternating with blocks in which a crystallographic shear is present.

The effect of this shear is that of forming double chains of edge sharing

squares with oxygen atoms at the corners and copper atoms at the center. The

50
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

superconductor BapYCu^O, can be described in terms of both structural types

and may be considered as an intermediate type between the other two. The

basic building blocks of these superconducting materials can be further broken

down into constituent nets (or meshes). This description allows one to

envisage new structures built from these meshes containing the key structural

elements present in the currently known superconductors. As such, the

structural schemes used in this description may be used as a guide in the

preparation of new materials with interesting electronic properties.

NEUTRON AND ELECTRON DIFFRACTION STUDY OF YBa2Cu22Cul ^^Fe 23O7

^3

P. Bordet, J. L. Hodeau, P. Strobel , and M. Marezio

1 (Laboratoire de Cristallographie, C.N.R.S.)

(also at AT&T Bell Laboratories, Murray Hill, NJ)

and

A. Santoro

The compound of formula YBa2Cu2 j^Qq oO^ ,- has been analyzed by neutron

and electron diffraction techniques. The material is tetragonal with lattice

parameters a = b = 3.8674(1), c = 11.6687(2) A and space group P4/mmm. The Fe

cations substitute only the Cu cations located on the basal plane of the

structure and can adopt three different types of coordination (tetrahedral

,

pyramidal and octahedral) depending upon the content and distribution of the

extra oxygen atoms on the plane. Calculations of the effective valence of

iron cations seem to indicate the Fe

"*" is present in tetrahedral coordination

4+ 2 2+

and Fe in pyramidal and octahedral coordination, while values of Cu * and

2 47+

Cu ' were found for the copper cations located at (OOz) and (000),

respectively. The electron diffraction experiments show diffuse scattering

planes parallel to (110) and (ITO). Crosses of strong intensity are visible

at reciprocal nodes located between the lattice layers. This diffuse

scattering is interpreted in terms of linear clusters of iron cations

extending along the [110] and [lIO] directions having a width of a few

cations. The clusters are separated by domains of orthorhombic YBapCu^Og

having the same orientation or rotated of 90° one with respect to the other.

51
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STRUCTURE AND CRYSTAL CHEMISTRY OF LagCaCUgOg AND La2SrCu20g

BY POWDER NEUTRON DIFFRACTION

R. J. Cava

(AT&T Bell Laboratories, Murray Hill, NJ)

and

A. Santoro and F. Beech

The structures of La^CaCUoOc and LaoSrCUoOc were refined with the

2 2 6 2 2 6

Rietveld method using neutron powder diffraction data collected with the highresolution five-counter diffractometer at the NBS Reactor. The initial model

of the structure was build in both cases by substituting the layers of

-(CuO^) -^ ' in the structure of La^CuO. with blocks of three layers having

composition and sequence -(CuO«) -(M/La) ^-{CuOp) , where M is either a Ca or a Sr atom and M/La indicates that the site may be occupied by M and/or

La atoms.

The refinements show that although the general structural configuration

of La2CaCUp0g and La^SrCu^Og is the same, the distribution of the atoms in the

crystallographic sites is quite different in two cases. We may point out

these differences by representing the two structures as sequences of layers

with the following scheme:

[-(Cu02)Q-(Ca)^-(Cu02)Q-(LaO)^-{LaO)Q-

(Cu02)^-(Ca)^-{Cu02)^-{LaO)^-(LaO)^-](Cu02)o-..

and

[-(Cu02)Q-(La)^-(Cu02)Q-{M0)^-(M0)^-

(Cu02)^-(La)^-{Cu02)^-{M0)^-(M0)^-](Cu02)Q-...

where M = 70% La + 30% Sr and where the content of a unit cell of the

structure is included in the square brackets. From these schemes we see that

the (CuOp) layers are separated by (Ca) layers in La2SrCu20g and by (La)

layers in La^SrCu^Og. This different distribution of atoms may be understood

by considering that the ionic radius of Sr (IX) is larger than that of

La (IX) (1.31 A versus 1.22 A) and for this reason the strontium atoms will

prefer sites with nine-fold coordination and will displace La into the

eight-fold coordinated sites located between the (CUO2) layers of La^SrCUpOg.

52
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Both the calcium and strontium compounds analyzed in this study are terms

of the homologous series La^M ,Cu 0^ 2

^''^'^ n = 2. This series may be

considered as a particular case of a more general class of compounds having

formula

(AO)^ (A'O)y (M)^_j (CuO^)^

and belonging to a structural type in which blocks (AO) (A'O) with rock-salt

X y

structure alternate with blocks (M) iC^^Op^n '^='^''"9 ^ defective ' perovskite

distribution. The condition of equality between cation and anion valences

requires that

2(2n + X + y) = px + qy + s(n-l) + mn, (1)

where p, q, s, and m are the valences of A, A', M, and Cu, respectively. If m 2+ 2+

= s = 2 (case of Ca and Cu ) we have from (1):

x(p-2) + y{q-2) = 2 (2)

and, for y = and p = 3 (case of La ) we obtain

(A0)2 (M)^_j (Cu02)^

i.e.,

^2 %-r"n ^2n+2

2 which is the homologous series of the title compounds .

In this work, the composition of a layer is specified by the chemical symbol,

and the location of the atoms in the unit mesh of the layer is indicated by

the subscripts (cation at the origin of the mesh) and c (cation at the

center of the mesh). Thus, the symbol (CuO^) , for example, indicates that

the copper atom is at the origin of the mesh°and the oxygen atoms at the midpoints of each side, and (LaO) indicates that the lanthamum atom is at the

center and the oxygen atom at the origin of the mesh.

2 Note that for q = 2, y may assume any value. For y = 2 we obtain

(A0)2) (A'0)2 (M)^_j (Cu02)n

which is the homologous series of the well-known compounds

Bi2S^2^%.lCu,02^^4 and Tl2Ba2Ca^_jCu^02^^4

Attempts to prepare other terms of this series, as well as some of the

many other possible compounds derivable with the above formulas, are underway

at the present time.

53
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PHASE EQUILIBRIA IN THE SYSTEM Ba-Y-Cu-0-C02 IN AIR

F. Beech

and

R. S. Roth, C. J. Rawn, J. D. Whittler, and J. 0. Anderson

(Ceramics Division)

Work has continued on this important phase diagram and its current status

is shown in figure 1.

BaO(BaC03)

Ba4Y207

BqzYzOs

BajY^Og

BaY204 2:1:3

20 40 Y2CU2O5 60

1/2(Y203) Mol %

Figure 1. Phase Diagram for Ba-Y-Cu-0-C02 at 950 °C.

Features worthy of note are that the phase previously described as 3:1:2

with the "ordered" perovskite-1 ike lattice a = 72 a', c = 2a' has been shown

to be a solid solution series containing CO^ as an integral part of the

structure. This solid solution region which encompasses the formula

^^^3 2^0 8^"2-x^6 4+x * (^^^2^ strongly influences the melting relations of the

compositions around the Ba^YCu^Og superconducting phase. The superconductor phase melts through a four-phase region, tetragonal ^a^YCu^Og , BaY^CuOg, BaCu02 and liquid from about 950°C to 1002 + 2 °C in air. This

four-phase region is apparently due to the presence of a fourth component,

COp, acting as an integral part of one or more of these phases, probably

mainly in the liquid. The presence of CO^ in one or more of the crystalline

54
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

phases, including the superconductor, is inferred. The tetragonal -» orthorhombic transition occurring upon oxidation of ^^pYCu^Og is concluded

to be metastable. No large primary phase field consisting of only Ba^YCu^Og

plus liquid has been identified in the melting relations of the Ba-Y-Cu-0

system in air.

SIGNIFICANCE OF PLANE VERSUS CHAIN SITES IN 1-2-3 SUPERCONDUCTORS

J. J. Rhyne, J. K. Stalick, and J. A. Gotaas

and

C. L. Chien, G. Xiao, M. Z. Cieplak, D. Musser, A. Gavrin, and F. H. Streitz

(The John Hopkins University, Baltimore, MD)

Atomic site substitution is one of the effective experimental means of

studying the mechanism behind the high T superconductivity in the new perovskite superconductors. For example, it has been shown for YBa^Cu^O, that

substitution of the Y atom by one of the heavy rare earths (e.g., Gd) which

possesses a large magnetic moment does not degrade the superconducting

transition temperature. This suggests that the Y site is well shielded from

the superconducting electrons, and the imposition of a large local moment at

this site does not produce pair breaking. These materials do show magnetic

order for T < 4K due to dipole-dipole coupling.

One of the outstanding questions in high T YBa^Cu^Oy superconductors is

the relative importance of the Cu-O^ planes {Cu(2)-site) and the Cu-0 chains

{Cu{l)-site) . We have used Zn, Ga, Fe, Co, Ni, and Al to selectively

substitute the Cu(2) and Cu(l) sites while maintaining the oxygen content near

7 as determined using neutron diffraction. Bulk results show that Zn strongly

suppresses the T of the material even for concentrations as low as 6%, T =

40 K. The other elements also depress T to some degree but in general remain

in the range 80 K and above for substitutions in the 6% range, except for Co

in which the local magnetic moment of Co is presumed to have an adverse effect

on the electron pairing mechanism.

The neutron diffraction studies have shown that the substituted ions do

not stoichiometrically populate the Cu(l) and Cu(2) sites. Rather the 3+ ions

(Ga and Al ) and the ions for which the 3+ oxidation state is possible (Fe and

Co) substitute for Cu primarily on the Cu{l) site, and in consequence destroy

55
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the integrity of the chain site Cu-O ordering. In addition the orthorhombic

symmetry distortion is gradually eliminated with increasing concentration of

the substituted ion and the material becomes tetragonal. However, the

materials remain high T superconductors in the tetragonal state.

In contrast to the 3+ ions substitutions, Zn(2+), for which the 3+

oxidation state is unknown, is found to largely substitute for the Cu(2) ion

in the plane site and the orthorhombic symmetry is preserved. The resulting

disorder ^in the Cu-O planes, however, severely degrades the superconductivity.

The results for Ni ion substitution are intermediate between those for

the 2+ and 3+ ions. At the 3% substitution level the material remains

orthorhombic, with Ni probably occupying both the Cu(l) and Cu(2) sites.

Attempts to prepare materials with a higher concentration of Ni have not

resulted in single-phase samples. However, Ni appears to have a larger

negative effect on T than do the 3+ ions.

The neutron diffraction results have also shown that all the materials

exhibit total oxygen concentrations near seven, which means that incomplete

oxidation is not the origin of the depressed T in Zn. The Co and Fe

materials actually show oxygen levels above 7 resulting from the increase in

average valence on the Cu(l) site due to the partial substitution of the 3+

ion for the lower valency Cu.

In summary, the neutron results for the site occupancies of the atoms

substituted for Cu, combined with bulk data, have demonstrated that the

integrity of the planes is much more important than that of the chains in

sustaining high T superconductivity. The results also show that the

orthorhombic cell distortion is not critical for high transition temperatures.

56
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

INELASTIC NEUTRON SCATTERING STUDY OF H ABSORBED IN YBagCUjO^^

D. A. Neumann

and

P. F. Miceli, J. M. Tarascon, P. Barboux, and L. H. Greene

(Bell Communications Research, Red Bank, NJ)

An inelastic neutron scattering study of hydrogen absorbed in the high

temperature superconductor, YBa2Cu20y , has been initiated using the Be

filter analyzer at BT4. Preliminary results obtained for two concentrations,

0.4 and 4.0 H atoms per Y, are shown in figure 1, along with the generalized

density of states of the pure material [11. For x = 4.0, scattering due to H modes is observed over nearly the entire energy range of 40-220 meV which

indicates that many different H sites are populated in this material or that

there is a great deal of interaction between the H atoms or both. There are,

however, two principal peaks which occur at about 78 meV and 100 meV and two

Figure 1.

120 200

Energy (meV)

Generalized density of states for H absorbed in YBa^Cu^O,

scattering is dominated by the modes involving the H atoms.'

The

57
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

shoulders at energies of roughly 150 and 175 meV. The 78 meV peak is probably

due to H atoms riding along on the Cu-0 stretching excitations, while the 100

meV peak may be a Cu-H bond-bending mode. The shoulders could then be

stretching excitations involving the H atoms since they have smaller

displacements and would therefore be less intense than the bending modes.

Similar features are observed for the x = 0.4 sample, however better counting

statistics are required before a reliable comparison can be made.

References

[1] J. J. Rhyne, D. A. Neumann, J. A. Gotaas, F. Beech, L. Toth, S. Lawrence,

S. Wolf, M. Osofsky, and D. U. Gubser, Phys. Rev. B36, 2294 (1987).

THEORETICAL MODELS FOR HIGH-TEMPERATURE SUPERCONDUCTIVITY

R. C. Casella

I have carried out an analysis of the effects of certain electronic

energy-band features on gap ratios 2A/kT for high-T superconductors, including the possibility of multigap systems. In addition to phonons, other

intermediate bosons (IB) mediating the superconducting interaction have been

considered (in a quite general way). Interesting results are obtained when

one includes the possibility of an IB with energy w exceeding the width(s) of one or more narrow peak(s) in the density-of-states associated with distinct

sub-bands, each presumably associated (in the tight-binding sense) with

distinct substructures, such as the multi-stacked copper-oxide planes.

Because of the complex nature of the known high-T materials, one feature

which might distinguish this class is the possibility of two sets of carriers

in distinct substructures (e.g., different Cu-0 planes) such that the

amplitude for an electronic transition between them is small, but such that

the carriers of each substructure can nonetheless interact with those of

another via the exchange of the IB between them. I have considered

theoretical models which represent extreme examples of this general class;

namely models in which superconductivity results solely from the exchange of

the IB between the carriers in distinct substructures. That is, taken

separately, each substructure is assumed to be nonsuperconducting (or at best

the intraband IB exchange would lead to low-T superconductivity and is

ignored in the analysis). The fermionic operators c and d for carriers in

58
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

each group create normal -state excitations in sub-bands C and D, respectively,

and enter in a BCS-like generalized Hamiltonian H of the type invoked some years ago by Suhl et al . [1] to describe the interplay between s and d

electrons. The equations of motion in the Heisenberg picture are {^ = 1),

-i C^^ = - e^{t) C^^ +.A(.(1C) C t^^

(1)

-i \, = - ep(lc) d^^ + Ap it) d\^^

_

Where, e.g., ^r(^) is normal -state excitation relative to the ground state in

sub-band C and where, in general,

A^dc) = - ^, V^^CIc -t') < c_^,^ (0) c^,^ (0) >

t

(2)

, y^^it - t') < d_^,^ (0) d^,^ (0) > .

Here

< c_^^ (0) c^^ (0) > = (A(./2E^) tanh (^8 E^/2), (3)

wh

2 2 1/2 ere Ep = (e^ + a ) ' and /3 = 1/kT. Let Br denote the widths of the subbands for I = C, D. For the conventional wide-band class (w « BJ, in weak

2 coupling (g = x^r. Xr.^ « 1 and kT = 1.13 w exp{-l/g)), and assuming App =

Aj, = 2w a

"-^/^ exp(-l/g) , ,Ap = 2w J^^ exp(-l/g),

(4)

^Wc = 3.5 a"^/^ 2Ap/kgT^ = 3.5 a^/2.

Here, J = N(,(0)/Np{0).

In contrast, when w exceeds the width of one or more peak in the sub-band

density-of-states (as shown in fig. 1), a Taylor series expansion about the

density-of-states at the Fermi surface, Np (e) = Np (0) + ..., is no longer

valid and the excitations within the narrower band C extend throughout the

peak. That is, in the presence of IB exchange, the peak consists of a foam of

elementary excitations. For the band structure characterized in figure 1 and

neglecting interband carrier mixing, I find

59
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A(. = B a"^/^ exp{-l/g), Aj3 = B a^/^ exp(-l/g),

2Wc = 3.5 a

^/^ exp (A/g),

(5)

where

g InR 2 ,/.

A = [1 + (-2- ) ] ^ - 1>

a^ = < N^ >/ Np(0), (6)

B = (2c.B^)^/^, R = (2aj/B^).

<Np> denotes the mean density-of-states, averaged over the narrow band C (c.f., fig. 1). This work was motivated in part by early reports of various

values of 2A/kT differing from the classic BCS value 3.5, as determined via

several different types of experiments (tunneling, infrared absorbtion,

nuclear-spin relaxation) in the La-Sr-Cu-0 and Ba-Y-Cu-0 high-T systems. A

scenario such as that illustrated in figure 1 readily accommodates the precise

spin-relaxation data obtained for the Ba^ Y Cu-O^ system [2]. I find g -

0.24 and an IB energy w > 1 eV, suggesting that the IB is not a phonon.

However, the two gap interpretation [2a] of the spin relaxation data is not

unique [2b]. A more complete description of my analysis has been submitted

for publication [3]

.

60
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. Density-of-states and assumed electronic occupancy in the absence

of the intermediate boson (IB) exchange leading to pair

condensates. w is the IB energy, which for the case illustrated,

satisfies, Bp < 2 w « Br^. Br denotes the width of the Ith subband {I = C^D). ^ ^

References

[1] H. Suhl, B. T. Mathias, and R. L. Walker, Phys. Rev. Lett. 3, 552 (1959).

[2] (a) W. W. Warren Jr., R. E. Walstedt, G. F. Brennert, G. P. Espinoza, and

J. P. Remeika, Phys. Rev. Lett. 59, 1860 (1987),

(b) R. E. Walstedt, Bui. Am. Phys. Soc. II, 33, 337 (1988).

[3] R. C. Casella, Nuovo Cimento D (in press).

61
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON POWDER DIFFRACTION STRUCTURE AND ELECTRICAL PROPERTIES

OF THE DEFECT PYROCHLORES Pb, cHoOfi r (M = Nb, Ta) ^'^ ^ ^'^

F. Beech and A. Santoro

W. M. Jordan and C. R. A. Catlow

(University College, London, UK)

and

B. C. H. Steele

(Imperial College, London, UK)

Powder neutron diffraction and Rietveld analysis have been used to

investigate the crystal structures of the defective pyrochlores Pb, cNbpOg ^ and Pb, cTapOg c- Both materials crystallize with the symmetry of space group

Fd3m, with lattice parameters a = 10.5647(2) and a = 10.5558(2) A,

respectively. No evidence has been observed of oxygen or lead vacancy

ordering in these compounds. This result is interpreted in terms of a model

in which all lead present in the structure has seven-fold pyramidal

coordination and forms domains separated by regions of lead vacancies with

hexagonal or bipyramidal configurations of the oxygen atoms. This model,

built on the assumption that the driving force in the formation of this type

of defect pyrochlores is the coordination of lead, leads us to conclude that

the system ^^\a.J^2^6+x ^^ ^ ^^' ^^^ ^^^ exist over a range of compositions

with 0.33 < X < 0.6, and may also explain results obtained in other studies of

related materials. The electric measurements show that both compounds are predominantly electronic conductors and that the ionic contribution to the

total conductivity is \jery small even at the highest temperatures used in the

study.

62
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A NEUTRON POWDER DIFFRACTION STUDY OF Na,Cs ZEOLITE RHO

W. H. Baur and A. Bieniok

(Johann Wolfgang Goethe University, Frankfurt an Main, West Germany)

R. D. Shannon

(Du Pont Company, Wilmington, DE)

and

E. Prince

Several studies [1,2] have shown a simple relation between the lattice

constant of zeolite rho and the degree of elliptical distortion, and therefore

the pore size, of the "double eight ring" that is the basic structural

element. A previous study [3] of a rho sample containing sodium and cesium,

however, was clearly discordant with the general trend. Because of this a neutron powder diffraction study of a rho sample with a similar composition

was undertaken to determine whether the discrepancy was due to a real

exception to the rule or to an insufficiently precise structure determination.

A set of neutron powder diffraction data was collected at 373 K from a sample of zeolite rho with the approximate composition

Na-T cCSo oSi-jc yiAln ^Onc • SDoD. The structure was refined by the Rietveld

7.6 3.2 35.4 11.6 96 2

•' method to R = 8.01%, giving the parameter values shown in table 1. If the

eight ring is undistorted, the x parameters of 0(2) and 0(3) are equal. The

ratio of these parameters is a measure of the elliptical distortion. In an extensive set of structures this ratio is related to the lattice constant, to

a good approximation, by EL = 13.866 - 0.839a. In this structure a = 14.66A,

giving EL = 1.566, in good agreement with the observed value, 1.569. The

structure of Na,Cs rho is not, therefore, an exception to this rule. Figure 1 shows the observed ellipticity parameter, and the pore size derived from it,

plotted against the lattice constant for a variety of samples of zeolite rho.

63
Table 1.

REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Structural parameters for Na,Cs zeolite rho: C is the number

of atoms per unit cell. Cell constant, a = 14.6566(4) A

atom X y z B C Wyckoff

position

site

symmetry

Si/AI .2692(7) .1207(10) .4200(7) 1.0(2) 48 48(h) 1 0(1) .0294(5) .2099(6) .3864(8) 2.0(2) 48 48(h) 1 0(2) .2092(6) .2092(6) .3949(10) 2.1(3) 24 24(g) m

0(3) .1333(6) .1333(6) .6232(9) 1.6(2) 24 24(g) m

Cs .00 .00 .50 2.9(13) 3.2 6(b) 42m

Na(l) .305(7) .305(7) .305(7) 3.0 2.0(5) 8(c) 3m

Na(2) .040(8) .040(8) .504(9) 3.0 4.2(7) 24(g) m 0W(1) .218(8) .218(8) .120(15) 3.0 2.1(5) 24(g) m 0W(2) .169(10) .040(8) .040(8) 3.0 2.2(4) 24(g) m

0W(3) .432(11) .432(11) .282(15) 3.0 1.9(5) 24(g) m

EL

14.0 14.1 14.2 14.3 14.4 14.5 14.6 14.7 14.8 14.9 15.0 a [A]

Figure 1. Variation of the ellipticity parameter EL (left axis, circles), and

pore size, PS (right axis, crosses), with cell constant, a, in a variety of samples of zeolite rho.

64
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[1] J. B. Parise, L. Abrams, T. E. Gier, D. R. Corbin, J. D. Jorgenson, and E. Prince, J. Phys. Chem. 88, 2303 (1984).

[2] W. H. Baur, R. X. Fischer, and R. D. Shannon, Proc. Int. Symp. Innovation

in Zeolite Materials Science, Amsterdam, Elsevier 281-292 (1988).

[3] L. B. McCusker and C. Baerlocker, Proceedings of the 6th International

Zeolite Conference, 812. Guildford: Butterworth (1984).

THE STRUCTURES OF i,-, 7- AND e-ALUMINA

R. S. Zhou and R. L. Snyder

(Alfred University, Alfred, NY)

and

E. Prince

When aluminum hydroxide, which exists as A^OH), (bayerite) and as AlOOH

(boehmite), is heated, water is driven off. The ultimate end product is

corundum, a-Al^O^, but, before corundum is formed, other phases appear that

are very reactive, catalytic materials. Bayerite transforms to a cubic phase

designated T?-alumina. Boehmite transforms to a slightly different, cubic

phase designated 7-alumina. On further heating, both of these phases

transform to a monoclinic phase, designated e-alumina, before recrystalizing

as corundum. Because neither the starting materials, bayerite and boehmite, nor the final product, corundum, is catalytically active, there has been

considerable interest in the structures of the "transitional" phases in

attempts to understand their properties.

Neutron powder diffraction patterns were collected from samples of ri- alumina, 7-alumina and e-alumina on the five detector powder diffractometer.

Particle sizes for all three samples were wery small, so that the diffraction

peaks were much broader than typical ones produced by well crystallized

materials on that instrument. It proved to be possible, nevertheless, to

perform Rietveld-method structure refinements with the data and to extract

useful, structural information from them. All three structures are spinel

like, with oxygen atoms arranged in approximate cubic close packing and

aluminum atoms occupying tetrahedral and octahedral interstices, r; and 7 are both cubic, with very similar cell constants, but the intensity distributions

65
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

in their diffraction patterns are clearly distinct. The hypothesis that these

phases are hydrogen spinels, with the composition DAlgOg, is ruled out; there

is no ordered hydrogen in the structure. In r/ and 7 some of the octahedral

aluminum, roughly the right proportion to be considered to be on the surfaces

of very fine particles, is considerably displaced along a threefold axis from

the center of the octahedron. In r? the displacement is sufficient to make the

coordination be effectively three. The proportion of aluminum found in this

distorted environment was 13% in r? and 25% in 7.

e-alumina is an apparently well-ordered structure, with 50% of the

aluminum in each of tetrahedral and octahedral interstices. It is formed by a displacive transformation from r/ or 7, but is apparently metastable with

respect to corundum, to which it transforms by recrystall ization on further

heating.

Figure 1 shows the configuration of oxygen atoms in four successive (111)

layers in cubic close packing, with the positions of the tetrahedral and

octahedral interstices and the additional sites occupied in r? and 7.

A B

[111]

4: 4-coordinated Al (8a)

3: 3-coordinated Al (32e)

6: Octahedral site (16c)

6": Distorted 6-coorclinated Al(32e)

Figure 1. A cluster of oxygen atoms in cubic close packing, showing the

tetrahedral and octahedral interstices.. The 3-coordinated position

is occupied in r/-alumina, and the G position is occupied in 7-

alumina.

66
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

N-DIMENSIONAL CRYSTALLOGRAPH I C DESCRIPTION OF THE ICOSAHEDRAL PHASES; THE

EXAMPLE OF THE Al^jMPgjSig QUASIPERIODIC STRUCTURE

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

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

and

J. W. Cahn and B. Mozer

Icosahedral phases in aluminum based alloys have been extensively studied

by means of x-ray, neutron and electron diffraction [1]. Many spectra have

been collected, but no fully satisfying crystal lographic model that matches

properly the observed diffracted intensities has been proposed. The

structural characterization of quasiperiodic phases is a formidable task owing

to the numerous parameters which have to be determined in addition to those of

standard 3-D crystallography [2].

The present paper reports experiments carried out on a reproducibly

created and well characterized icosahedral AK^Mn^jSig ternary alloy which has

been investigated by x-ray [3] and neutron diffraction [4]. The

crystallographic analysis is based on the following heuristic hypotheses:

i. Nonredundant indexing requires only six-indices; the 6-D space

description has therefore been used. (This, however, does not necessarily

imply that the actual structure in 6-D would fit with atomic 3-D surfaces

depending only on the perpendicular space variable, Xi.);

ii. The powder diffraction patterns have been indexed using the scheme

proposed by Cahn, Shechtman, and Gratias [5] assuming a primitive 6-D

hypercubic lattice; actually, two other equivalent lattices with same multiplicity could have been considered as well: the Dg+ and Dg- (dual to each

other) lattices defined by,

Dg(±) = F(2A) + (1/2,1/2,1/2,1/2,1/2, ± 1/2)F(2A),

where F(2A) designates the face-centered hypercubic 6-D lattice with parameter

2A, are consistent with both the icosahedral symmetry and the extinction rules

observed in single domain electron diffraction. These lattices lead to

projected quasilattices t times smaller (for Dg+) or larger (for Dg-) than the one obtained for the primitive 6-D lattice.

iii. The 6-D point group of the structure has been assumed to be m35.

It is obvious, even from powder diffraction patterns, that the 6-D point group

is m35 and not a supergroup of m35 (intensities of equivalent reflections in

67
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the Bg holohedral point group are clearly different). Although the hemihedral

noncentrosymmetric 235 group could have been chosen as well, convergent beam

electron diffraction [6] and recent neutron contrast experiments [7] have

shown that the motif is most likely to be centrosymmetric.

References

[1] International Workshop on Aperiodic Crystals, J. de Physique Tj. Colloquium

3 (1986).

[2] P. Bak Phys. Rev. Lett 54 1517 (1985); Phys Rev. B32 5764 (1985); Phys.

Rev. Lett 56, 861 (1986); J. de Physique Z, Colloqium 3 136 (1986).

[3] M. Bessiere et al . (in preparation).

[4] R. Bellissent et al . (in preparation).

[5] J. W. Cahn, D. Shechtman, and D. Gratias, J. Mat. Res. 1, 13 (1986).

[6] L. Bendersky and M. J. Kaufman, Phil. Mag. B53, L75 (1986).

A 6-D STRUCTURAL MODEL FOR THE ICOSAHEDRAL (Al,Si)-Mn QUASICRYSTAL

J. W. Cahn

(Institute for Materials Science and Engineering)

D. Gratias

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

and

B. Mozer

A 6-dimensional (6-D) periodic model is proposed for the Al-Mn-Si

icosahedral quasiperiodic crystal. The model results from an embedding of the

periodic cubic a structure in 6-D. In the Janner-Janssen-Bak description, it

consists of three concentric spherical shells of respectively Mn, Al and Al

aligned in perpendicular space around the lattice nodes and two additional

shells of Al around the body centers. This model is shown to match the x-ray

powder diffraction data with a satisfactory residual R-factor of 0.128.

68
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON DIFFRACTION STUDIES OF THE NARTENSITIC

TRANSFORMATION IN SODIUM METAL

R. Berliner

(University of Missouri, Columbia, MO)

H. G. Smith

(Oak Ridge National Laboratory, Oak Ridge, TN)

J. R. D. Copley

{University of Maryland and the Reactor Radiation Division)

and

J. Trivisonno

(John Carroll University, Cleveland, OH)

Neutron powder diffraction experiments on polycrystalline sodium metal

have shown that it undergoes a martensitic phase transformation at about 35 K from the bcc structure to a new hexagonal form [1,2]. The structure of the new phase, as given by the powder diffraction patterns, appears to be the same

as the structure adopted by lithium metal at low temperature; i.e., the 9R

Samarium type structure [3]. Recent reports [4] and theoretical work [5] have

claimed that this structural transformation in sodium is partly the result of

softening of the S- phonon branch along the [110] symmetry direction.

We have measured the phonon dispersion curve for the n. branch as a function of temperature, and the structure of the transformed phase at 30 K,

using the triple axis spectrometer BT9. No substantial softening of the

phonon branch was observed. The crystallography of the transformed phase is

somewhat different to the one observed earlier in lithium metal [6]. About

each bcc [110] direction, diffracted intensity corresponding to four trigonal

variants of the new phase can be observed. Studies of the (lOi) reflections

showed that the new phase contains both a 9R (Samarium type) structure and a substantial fraction of an hep phase. Preliminary investigations of both

phases show that they evidence the same kind of shifting and broadening that was observed in lithium. Careful monitoring of the diffraction pattern as the

crystal warmed showed that there was a substantial temperature range, starting

at 55 K, over which the 9R phase transformed to bcc leaving the hep phase

intact. Upon further warming the hep phase also reverted to bcc, and the

system remained a single crystal in its original orientation up to a

69
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

temperature in the range from 250 K and 300 K, where it broke into several

pieces, probably due to too fast a warming rate in this latter region.

References

[1] C. S. Barrett and 0. R. Trautz, Trans. Am. Inst. Min. Metall. Pet. Engr.

175 , 579 (1948).

[2] R. Berliner, 0. Fajen, H. G. Smith, and R. J. Hitterman, Bull. Am. Phys.

Soc. 33, 615 (1988).

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

[4] 0. Blaschko and G. Krexner, Phys. Rev. B30, 1667 (1984).

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

[6] H. G. Smith, Phys. Rev. Lett. 58, 1228 (1987).

CRYSTAL STRUCTURE STUDY BY X-RAY DIFFRACTION.

H. L. Ammon

(University of Maryland, College Park, MD)

and

C. S. Choi

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

There is considerable interest in the synthesis and chemistry of cubane

derivatives within the explosives community which is searching for new types

of energetic materials based on high-density and highly-strained molecules.

During the reporting period, we have studied the crystal structures of four

newly synthesized compounds. Due to the unexpectedly long delay of the restoration of the NBS x-ray single crystal diffractometer, the experiments were conducted at the x-ray Laboratory of the Department of Chemistry, University

of Maryland. The data collections were done by using Mo radiation with an incident beam monochromator and an Enraf-Nonius CAD-4 diffractometer

throughout.

1. Crystal Structure of 1,4-diiodocubane

The crystal, CgHgl^, crystallizes in monoclinic, P2,/c, with the cell

dimensions, a = 7.137(1), b = 7.269(2), c = 8.991(2)a, ^ = 111.69(2), V = 3 433.4(3)a ,with two molecules per unit cell. The calculated density was D

70
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

_3

2.73gcni . The structure was solved with Patterson methods. Final R = 0.036

and wR = 0.053 for 714 reflections with I > 3a(I). The molecular structure is

shown in figure 1. The molecule possesses a center of symmetry, with the two

I atoms positioned on opposite corners of the cube.

Figure 1. ORTEP drawing of 1,4-diiodocubane molecule.

2. Crystal Structure of l,4-diammoniumcubane-(Bis-trinitromethide)

The compound, ^io^i2'^8^12' crystallizes in monoclinic, C2/m, with cell

dimensions, a = 14.298(2), b = 8.408(1), c = 7.354(2) A, V = 859.9(5) A^, with

_3

two molecules per unit cell. The calculated density is, D = 1.68gcm . The

structure was solved with MITHRILL direct methods. Final R = 0.039 and wR = 0.054 for 672 reflections with I > 3a(I). ORTEP drawing of the molecole is

given in figure 2. The diammoniumcubane cation possesses 2/m symmetry and the

trinitromethide anion mirror symmetry. The cation is linked to six

trinitromethide anions, three at each end, by three different N-H««»0 hydrogen

bonds for each anion, as shown in figure 2. The diammoniumcubane moiety

undergoes intense libration motions about the long N1«»»N1 molecular axis (the

axis with the smallest moment of inertia), with r.m.s. amplitude of 17°.

71
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 2. ORTEP drawings of diammoniumcubane cations and trinitromethide

anion, viewed along the long axis direction of the cation

(N1«»«N1). The cation possesses 2/m symmetry (H3,N1,C1,C3 on the

mirror plane), and linked to six anions by strong H-bonds. The Hbondings at one end of the cation are shown here. The cation

possesses a pseudo-threefold symmetry, and undergoes an intense

libration motion (r.m.s. amplitude of 17°) about the axis as demonstrated by the elongated thermal ellepsoids (isotropic H atoms).

3. Structure of l,4-di(N,N-diisopropylaminomethyl)-2,7-diphenyl-cubane

The compound, Cg^H-gN^, cp'stallizes in monoclinic, P2,/n, a = 9.641(2),

b = 15.900(5), c = 10.864(2) A, ^8 = 117.92(1), V = 1472(1)a^, with two

.3

molecules per unit cell. The calculated density is D = 1.09gcm . The

structure was solved with MITHRIL direct methods. Final R = 0.054 and wR = 0.060 for 1348 reflections with I > Zo{l). ORTEP drawing of the molecule is

shown in figure 3. The molecule possesses a center of symmetry, with the two

phenyl groups and the two isopropyl groups positioned on opposite corners of

the cube, respectively.

72
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

^^^^'===^»^

Figures. ORTEP drawing of 1,4-di (N,N-diisopropylaminomethyl)-2,7-diphenylcubane.

4. Structure of 1- adamant any! ammonium trinitromethide

The compound, ^iiHioN^Og, crystallizes in orthorhombic, Pnma, a = 23.802(9), b = 8.431(3), c = 7.166(2)A, V = 1438.0(8) A^, with four molecules

_3

per unit cell. The measured and calculated densities are, D = 1.37(5)gcm ,

<j m

D = 1.396gcm' , respectively. The structure was solved with MITHRIL direct

A methods. Final R = 0.048 and wR = 0.061 for 860 reflections with I > 3a(I).

ORTEP drawing of the molecule is given in figure 4. Both the adamantanylammonium cation and trinitromethide anion possess mirror symmetry. The cation

is linked to three trinitromethide anions by six N-H»»«0 hydrogen bonds

through the three ammonium hydrogens.

73
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

h"- Q

;^s«e"

Figure 4. ORTEP drawing of adaman t any 1 ammonium cation, and two out of the

three nearest trinitromethide anions linked by N-H««'0 hydrogen

bonds. A third anion is related by mirror symmetry to the HIA1 inked anion; it is not shown here for clarity.

74
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PHASE DIAGRAM OF ALLOYS IN THE Ti-Al SYSTEM

R. M. Waterstrat

(American Dental Association Health Foundation Research Unit)

and

E. Prince

There has been widespread interest in the effects of impurities,

particularly oxygen, on the phase diagram of alloys in the titanium-aluminum

system. To study impurity effects, it is obviously necessary to have a good

knowledge of the properties of the pure, binary system, but most previous

studies have been on quenched samples, which are subject to ambiguous

interpretations. Because of the high penetrating power of the neutron,

neutron powder diffraction is a useful tool for studying materials at high

temperatures, and, because of the negative scattering length of titanium, it

is particularly sensitive to the presence of ordered phases in this system.

We have performed two types of high-temperature, neutron diffraction

experiments on alloys in the system Ti, Al with x in the range from 0.14 to

0.45. Full diffraction patterns at 900 °C and 1000 °C were taken on samples

that had previously been equilibrated at those temperatures for up to 2 weeks,

in order to determine the composition range within which the ordered,

hexagonal, a« phase was present. For some compositions, the strongest peaks

characteristic of the a^ phase, the disordered, hexagonal, a phase, and the

disordered, body centered-cubic, ^ phase were observed as the temperature was raised in order to verify the approximate transition temperatures and the

identities of the phases on either side of the boundary. Figure 1 shows the

Ti-Al phase diagram given recently by Murray [1], modified to be compatible

with our observations and with our data points shown. For the most part

previous observations are confirmed, but there are two features of particular

interest. First, for x = 0.16 at 900 °C and for x = 0.16 and x = 0.18 at

1000 °C the OLy phase is not observed, but the background in the diffraction

pattern was abnormally high, and the a phase peaks were very weak. This may

be attributed to displacement effects due to short range order. Second, when

the sample with x = 0.40 was heated up, the p phase was not found. A full

diffraction pattern at 1200 °C had only one peak. That peak is compatible

with a disordered, hexagonal structure, as in the a phase, but not with the ^ phase. Because the scattering lengths of Al and Ti are nearly equal in

75
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

magnitude, but opposite in sign, a disordered alloy with x = 0.50 would be a "null matrix", which would give no neutron diffraction pattern at all.

X = 0.40 is close enough to this so that the weakness of the diffraction

pattern is not surprising.

Weight Percent Aluminum

80 90 100

660°C

30 40 50 60 70

Atomic Percent Aluminum

Figure 1. Ti-Al phase diagram with neutron diffraction observations shown.

Solid black dots indicate the region of apparent short range order.

References

[11 J. L. Murray, Calculation of the Titanium-Aluminum Phase Diagram, Met.

Trans. 19A, 243 (1988).

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON DIFFRACTION STUDY OF TEXTURES OF MATERIALS

C. S. Choi and H. J. Prask

(U.S. Army, ARDEC, Dover, NJ and Reactor Radiation Division)

We have studied textures of three different type of materials: coldworked depleted uranium (DU) alloys, a magnetically oriented high T

superconductor, and the standard sample prepared by the international pole

figure standard project committee. The diffraction patterns and pole figure

data were measured with 1.275 A neutrons using the four-circle single crystal

neutron diffractometer. The background was determined from the off-Bragg

intensities of the powder pattern. The random-distribution intensity, R, was determined from the observed pole figure data, F((^,x), by:

R = {sR(x)cos{x)+R{90)/n)/(En.cosx+l),

A. r\.

where R{x) = SF(<^,x) and n = 360/a.^.

The pole density was expressed in terms of the m.r.d. (multiples of a random distribution) unit (which was calculated by F(^,x)/R), and was presented by the equal -area projection type pole figures.

1. Textures of the cold-worked DU alloys

U-0.75 wt% Ti is an important material in the military armament area because of its high density and mechanical strength. Previously, we studied

the textures of small experimental samples as a function of heat-treatment and

cold-work. During this reporting period, we studied the textures of fullscale samples: a standard induction sample, two cold-worked samples, and two

phase III samples. Among them the measurements of the two cold-worked samples were completed. The pole figures, as given in figure 1, showed clear fibertexture with the slip system similar to small-scale, 70% swaged samples

studied previously. Assuming that the orientation distributions are ideal

fiber-textures, the two-dimensional pole-figures were converted to a one- dimensional x-angular distribution by circular averaging of the intensities

at each x-angle. There are two important parameters in the texture analysis:

a slip system (fiber-axes here) and a degree of texture. The degree of

texture may be expressed by the weighted sum of the pole-density variation

77
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

from the complete random density. For fiber texture, it can be calculated

from x-angular distribution:

degree of texture = [AgQ+2(72cos(xjA.))/(l+s{72cos(xJ]

where, a. refers to the deviation at x^> the number 72 corresponds to the

number of (^-angles in each x-angle. The degree of texture as defined above

depends heavily on the number of peaks and the peak positions in the the chiangular distribution function. Therefore, its usage should be limited to

comparison between the same (hkl) poles. The degree of texture obtained for

the full-size samples were compared with those of the small-scale laboratory

samples in table 1. The (111) pole distribution is least sensitive to the

degree of texture because of the evenly spaced peak positions. The degree of

texture of the others in the table shows a close correlation with the degree

of cold-work of the sample.

2. Texture of a magnetically oriented HoBa^CUgOy superconductor

Several rare earth-Ba-CuO high temperature superconductor materials were

made by Claudia Orstertag in the Ceramic Division, by applying high magnetic

field. The orientation distribution of one of the samples, Ho-Ba-CuO, was determined by interpretation of neutron diffraction patterns and pole figures.

Two diffraction patterns, one with the scattering vector parallel and the

other perpendicular to the direction of the applied magnetic field, were

measured. It was clear from the diffraction profiles that the sample was heavily textured with the crystal! ographic c-axis parallel to the applied

field direction. The details of the orientation distributions were attained

by the pole figure measurements as shown in figure 2. Since the diffraction

peaks of (003), (100), and (010) are overlapping, the 003 pole figure contains

100 and 010 distributions. The figure shows that 001 poles have a one- dimensional distribution (along the north-south direction in the figure) and

100 and 010 poles have a two-dimensional distribution (in the plane perpendicular to the N-S direction). The pole density distributions along the

equator could be described reasonably well with a Lorentzian function (FWHM = 33(1)°), as shown in figure 3.

78
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

DU879(020)

DU879(111)

DU8?9(112) DU879(131)

Figure 1. The pole figures of one of the two full scale DU samples. The

contour levels equal or higher than 1 m.r.d. (multiples of a random

distribution) are given by solid and lower than 1 by dotted lines.

The contour intervals are 0.4 m.r.d. for 020 pole figure, and 0.2

m.r.d. for all the others.

79
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. The Degree of Texture

Sample (010) (111) (112) (131)

30A .59 .18 .22 .21

40A .72 .18 .28 .29

60A .67 .25 .35 .39

60B .77 .24 .33 .42

60D .86 .25 .36 .42

60E .71 .28 .37 .40

60F .88 .26 .37 .46

60G .71 .26 .35 .40

60H .76 .29 .36 .39

70A .98 .29 .43 .57

708 1.03 .27 .39 .60

879D .93 .32 .39 .56

892A .96 .37 .38 .58

HOBACUO

Figure 2. 003 pole figure (containing 100 and 010) of the magnetically

oriented sample with 0.1 m.r.d. contour interval.

3. Pole Figure Standard Project

The purpose of the pole figure standard project is to determine the

limitations of various experimental methods. A fine-grained limestone, CaCO-, was chosen as a standard sample since its diffraction pattern includes many

closely spaced peaks and weak peaks. The sample was experimentally deformed

in pure shear at T = 400 »C , P = 100 MPa, k = 3.6x10 s, to a strain

€j = 35%, eg = -3%, €3 = -36%. Crystal data are, trigonal R32/m, a = 4.989 A,

c = 17.061 A. The 012, 104, 006, 110, 113, 202, 108 and 116 pole figures were

measured. Among them, 108 and 116 diffraction peaks overlapped because of

instrumental resolution and occurred as a distorted peak in the diffraction

pattern. A visual inspection of all the pole figures showed excellent

80
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

agreement with those of other laboratories: ILL, JUlich and Geesthacht. The

two pole-figures, 108 and 116, are shown in figure 4.

3000

2500 -

2000

1500

1000

500 -

-200 200

PHI -ANGLE

Figure 3. The equatorial distribution of 003 and 100/010 pole density of the

magnetically oriented sample with 0.001 m.r.d. unit.

CACO3<108) CAC03(1 16)

Figure 4. 108 and 116 pole figure of the standard sample (CaCO^), with 0.1

m.r.d. contour interval.

81
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A MAXIMUM- ENTROPY DENSITY DISTRIBUTION THAT FITS

AN ARBITRARILY LARGE SET OF FOURIER AMPLITUDES

E. Prince

D. M. Collins

(Laboratory for the Structure of Matter, Naval Research Laboratory)

and

L. SjOlin

(Chalmers University of Technology, GSteborg, Sweden)

In crystallography, as in a number of branches of physics, the observable

quantities are related to the Fourier transform of some density distribution,

and the problem is to infer what that distribution looks like. Because the

Fourier transform can only be measured in a finite region of reciprocal space,

the data are inherently incomplete, and the problem is underdetermined. If

the density distribution is everywhere nonnegative, the principle of maximum

entropy provides a powerful criterion for deciding which of the possibly

infinite set of distributions that satisfy the observations is, in some sense,

the best one. Although the solution is conceptually simple, application of

the principle to practical problems has come slowly because the process of

finding the maximum entropy distribution for a large object with a large data

set appeared to be formidable. We have developed a procedure for finding the

maximum entropy distribution that is applicable to macromolecular structures

with modest computing resources and reasonable times.

Consider a unit cell divided into n pixels, and let the mean density in

the kth pixel be p^. We wish to maximize

S(p) = - I pJnp. , (1)

k=l - ^

subject to

n

Ifmafil = (VD)I^X^.^^xp(2.1h..V| = |F^(h.)| (2)

for a set of m reflections. This is a constrained optimization problem in n dimensions, and, for a macromolecular structure, n can be a \iQry large number.

It can be shown, however, that the constrained maximum of S(p) is equal to the

unconstrained minimum of

82
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

*(x) = -^Ij^OOln.iCx) . .IJ|F^(h^)| - |F^(h^)|]. (3)

where

ID pj^(x) = exp[ X x^cos{27rh^.r|^ - <f>rj]

which is the value of p. for which

(4)

-^klnp^ "^ X

x^cos(27rh^.r|^ - <f>^) (5)

is maximum for a given x. Here 4>. is the best previously available estimate

hi. of the phase of F(h.). Finding the minimum of $(x) is an unconstrained

optimization in m dimensions, where m is, in general, very much less than n. The phase ^ of F ^(h.) becomes a better estimate of 6-.

ma£^ J' ^j

Because the Fourier transform of p(r) is a linear function of p{r), $(x) can be shown to be everywhere convex, and it must have a unique minimum. Many

of the modern techniques for nonlinear optimization are applicable.

Preliminary studies using a quasi-Newton type algorithm on a problem with

560000 pixels and 21 reflections gave an estimate of running time, on a Microvax computer, of 3 minutes per 100000 pixels per reflection. Obvious

modifications to the code should reduce that time by at least a factor of ten

and possibly as much as a hundred. It remains to be determined how large an initial set of phases, <^., must be for phases to be extended by maximum

J. entropy to an acceptable structure.

83
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

D-SPACING/FORMULA INDEX FOR PHASE IDENTIFICATION

BY ELECTRON, NEUTRON OR X-RAY DIFFRACTION

V. L. Himes, A. D. Mighell, and J. K. Stalick

The NBS/Sandia/ICDD Electron Diffraction Database is a new computerized

Standard Reference Database designed for phase characterization by electron,

neutron or x-ray diffraction methods. The Database and associated software

[1] permit highly selective identification procedures for microscopic as well

as macroscopic crystalline materials. The Database and software are available

to the scientific community on magnetic tape. A subset of the data will be

made available as a printed D-Spacing/Formula INDEX. Work on the INDEX was carried out in collaboration with the Sandia National Laboratories and the

International Centre for Diffraction Data.

The Electron Diffraction Database, containing approximately 71,000

entries, was derived from two well-known Databases -- NBS CRYSTAL DATA [2] and

the PDF-2 [3]. The database contains chemical, physical and crystallographic

information on a wide variety of materials including minerals, metals,

intermetallics and general inorganic compounds. It is comprehensive as numeric and factual data have been taken from over 1200 journals. All of the

data have been critically evaluated and transformed to standard forms with

NBS*AIDS83 [4] which is a database building and evaluation program. In addition, essential derivative data have been calculated.

The Electron Diffraction Database has been designed to include all the

data required to identify materials using computerized d-spacing/formula

matching techniques. The data for each entry include: the conventional cell,

reduced cell, lattice type, space group, calculated or observed d-spacings,

chemical name, chemical and empirical formulas, materials class indicators,

references and other parameters. To permit selective d-spacing/formula

matching procedures, all the required d-spacings for each material are explicitly stored in the Database. Thus in each entry, there are up to 60

interplanar spacings including all the largest d-spacings (low two theta) that

are most diagnostic for identification purposes. The d-spacings are either

calculated (approximately 86%) or observed. For those cases in which the cell

is known, the d-spacings were systematically calculated starting with the

largest d-values and ending at the cutoff value of 0.83 A. Known space group

and centering data were used to eliminate d-spacings corresponding to

84
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

geometrically extinct reflections. For those cases in which the cell is

unknown, observed d-spacings were used.

The printed INDEX was derived from the comprehensive Database. It contains a critical subset of the data necessary for identification and is

designed to be used independently of or in conjunction with the computer

database. For each compound, the INDEX contains one line of data which

includes: up to four "high Z" elements (Z > 10) in alphabetical order; up to

two "low Z" elements (Z < 11) in alphabetical order; the first ten low-angle

d-spacings rounded to three significant figures; the chemical formula; the

first two symbols of Pearson's code; the first Crystal Data Determinative

Ratio; the unique PDF and CD numbers. These unique pointers permit the

experimentalist to obtain additional information for a compound in NBS CRYSTAL

DATA and in the Powder Diffraction File which are available on magnetic tape

and on CD-ROM. A more detailed description of the data is given in

"NBS*AIDS83: A Manual Describing the Data Formats used in NBS*AIDS83" [5].

The total number of entries in the INDEX is less than the computer version of

the Electron Diffraction Database. The latter permits multiple entries with

the same chemical and d-spacing information but different in other respects

such as the reference to the original literature. To save space, only the

entry with the latest reference is kept in the printed INDEX.

The INDEX is arranged so that the experimentalist can readily identify a material with the chemical and diffraction data routinely collected in the

analytical laboratory. The INDEX is organized as follows: 1) the primary

sort is an alphabetical sort on the "high Z" elements that are present in the

chemical formula; 2) the secondary sort is on ascending magnitude of the dspacings; and 3) compounds without any "high Z" elements are at the end of the

INDEX and are sorted only on ascending magnitude of the d-spacings. The "high

Z" elements in the INDEX correspond to those that can routinely be observed in

x-ray Energy Dispersive Spectra (EDS) commonly taken in the analytical

laboratory. To prepare the primary sort key, the "high Z" elements were extracted from the chemical formula and alphabetized. If there were greater

than four different elements of this type in the formula, only the first four

in ascending order were included in the sort key.

The D-Spacing/Formula INDEX will prove a practical tool for electron

diffractionists because the experimental data obtainable from the analytical

electron microscope (AEM) is precisely that required to reliably identify and

85
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

characterize unknown phases. Extensive experience with online searching of

NBS CRYSTAL DATA [6] and the results of an EMSA-JCPDS Electron Diffraction

Practices Questionnaire [7] show that search/match procedures based on chemistry and calculated d-spacings (fig. 1) are extremely reliable. A

knowledge of elements present and absent in an unknown is usually sufficient

to give a limited set of potential candidates when searching the entire

database. (For example, if it is known from qualitative EDS chemistry that an unknown contains the elements Cr, Fe, and Ni only those elements, then a search of the database yields only three potential compounds.) Likewise

experience has shown that a knowledge of low-angle d-spacings is highly

diagnostic. Matching these d-spacings of an unknown against the Database also

yields a limited answer set. Consequently, when these two sets (D-spacings

and formulas) are intersected, the experimentalist usually obtains a relatively short, but complete, list of all compounds that could cause the

observed experimental data. Due to the quantity and quality of the reference

data available in the INDEX, the d-spacings/formula method can routinely be

used for compound identification in the analytical laboratory.

D-SPACING/FORMULA

^

SEARCHING

A ' B 1

' C V

SET 1: D-SPACINGS SET 2: FORMULAS SET 3: D-SPACINGS/FORMULAS

SET 1

AND SET 1, SET 2- m^

SET 2

A. SET 1 = The set of compounds resulting from the d-spacing search.

B. SET 2 = The set of compounds resulting from the formula search.

C. SET 3 = AND SET 1, SET 2 = the compounds in the Electron Diffraction

Database that have the same or related d-spacings/formulas as the unknown

Figure 1. Identification by d-spacing/formula matching.

86
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[1] M. J. Carr, W. F. Chambers, D. K. Melgaard, V. L. Himes, J. K. Stalick,

and A. D. Mighell, NBS/Sandia/ICDD Electron Diffraction Database (1987);

Sandia Report, SAND87-1992, UC-13, Sandia National Laboratories,

Albuquerque, NM 87185.

[2] NBS CRYSTAL DATA (1987). A magnetic tape of chemical, physical and

crystal lographic data compiled and evaluated by the NBS Crystal Data

Center, National Bureau of Standards, Gaithersburg, MD 20899.

[3] PDF-2. A magnetic tape of chemical, crystallographic and x-ray powder

data compiled and evaluated by the JCPDS-- International Centre for

Diffraction Data, Swarthmore, PA 19081.

[4] NBS*AIDS80: A FORTRAN Program for Crystallographic Data Evaluation. A.

D. Mighell, C. R. Hubbard, and J. K. Stalick, Natl. Bur. Stand. (U.S.).

Tech. Note 1141 (1981); NBS*AIDS83 is an expanded version of NBS*AIDS80.

A copy of the program for research applications may be obtained by writing

the NBS Crystal Data Center.

[5] NBS*AIDS83: A manual describing the data formats used in NBS*AIDS83.

This manual (1987) contains a detailed description of the data items in

the Powder Diffraction File and in NBS Crystal DATA. It may be obtained

from the JCPDS--International Centre for Powder Diffraction Data or from

the NBS Crystal Data Center.

[6] CRYSTDAT (1987). An online search, retrieval and analysis system for NBS

CRYSTAL DATA developed jointly by the National Research Council of Canada

and the National Bureau of Standards.

[7] A Max-D Alphabetic Index to the JCPDS Database. R. Anderson and

G. G. Johnson, Jr., EMSA Bull. 8, No. 1 (1979); and the Proceedings of the

1979 EMSA Meeting.

87
GRAZING INCIDENCE NEUTRON DIFFRACTION FROM SI (110)

J. F. Ankner and H. Zabel

(University of Illinois, Urbana, IL)

and

D. A. Neumann and C. F. Majkrzak

During the past decade, there has been a great deal of interest in the

properties of surfaces and a corresponding development of surface-sensitive

experimental techniques. Of these techniques, surface x-ray diffraction using

glancing incidence has proven to be particularly useful because of two

important facts. For one, the interaction of x-rays with matter is weak,

allowing comparatively simple structure factor calculations. Secondly,

grazing incidence x-ray diffraction is the only probe providing surface as well as substrate information within the same experimental setting: the depth

of penetration of the x-rays into the surface can be controlled by varying the

incident grazing angle <f> below the critical angle for total external

reflection ^ . Neutrons possess both of these virtues and their sensitivity

to light adsorbates and magnetic structures qualifies them as an ideal

complement to x-rays. Unfortunately, neutron fluxes are considerably smaller

than the x-ray fluxes available at synchrotrons, which has prevented a parallel development of neutron and x-ray grazing-incidence diffraction

techniques. However neutron fluxes are large enough to observe surface

diffracted beams. To demonstrate this fact, we have performed the first

surface neutron diffraction experiment using grazing incidence.

The geometry for grazing incidence diffraction is shown in figure 1. A

beam of neutrons of wave-vector t strikes the (110) surface of a perfect Si

crystal at a glancing angle 4 and undergoes specular reflection (^^) • The

sample is oriented such that Ic satisfies the transmission diffraction

condition for the (111) reflection in the plane of the surface. The

diffracted beam then reflects from the crystal surface with wave- vector Tcg and

angle ^g. Under glancing incident angle conditions, the transmitted beam

intensities decay exponentially into the bulk, so only the topmost layers of

the crystal interact with the neutrons.

The experimental arrangement is shown in figure 2. A 4.43 A beam of

neutrons (aa/a = 0.008), collimated to 0.3 mrad by a pair of Cd slits, struck

the (110) face of a Si crystal at glancing angle <t>. This wavelength was

88
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. Grazing incidence diffraction geometry. t, t , and t^ are the

initial, reflected and reflected-diffracted wave-vectors,

respectively.

Defector #2

(^He) [

R.

K

Grophite

Monochromator

Cd Slits ( Perfect Si Crysfol

Sample

Detector # I (^He)

Reactor

Collimotor Be (60')

Filter

Figure 2. Experimental arrangement. The beam was collimated to 1' by the Cd

slits.

89
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

chosen for two reasons. The first was that a long wavelength produces a large

critical angle (3.6 mrad for Si at 4.43 A), which allows one to relax the

collimation for the glancing angle <f) and thereby increase the intensity.

Secondly, A = 4.43 A is the wavelength for which the Bragg angle of the

Si (111) diffracted beam is 45°, which is convenient because the diffracted

beam detector could then be mounted directly above the sample. The specularly

reflected incident beam intensity was recorded by the conventional triple-axis

detector (detector #1) simultaneously with that of the reflected-diffracted

beam (detector #2). The sample was a perfect Si crystal of dimensions 2.75" x

2.8" X 0.5" with a syton polished (110) face.

The data shown in figure 3 were obtained by scanning the incident angle <i> through the critical angle ^ with angles d and x set to satisfy the

diffraction condition. Since the beam was broad by dynamical diffraction

standards, only a small fraction of the incident intensity was diffracted and

therefore the specularly reflected beam intensity may be treated as a simple

specular reflection (the one beam approximation). The specularly reflected

beam intensity (plotted as squares in figure 3) has therefore been fit with a modified Fresnel function [1]. The reflected-diffracted beam for the same scan is shown as the open circles in figure 3. Detector #2 was left wide open

and so performed an integration of the intensity distribution over the

diffracted beam exit angle <f>r. The reflected-diffracted intensity rises to a maximum near <f> as the evanescent wave penetrates into the sample and then

dies out above the critical angle as the intensity is transmitted to the

transmitted-diffracted beam. The reflected diffracted beam was fit using the

two-beam approximation of dynamical diffraction theory and the result is shown

as a solid line. The good correspondence conclusively demonstrates the

existence of a Si (111) reflected-diffracted beam excited under grazing

incidence conditions.

The development of grazing-incidence neutron diffraction techniques opens

up a wide variety of experimental studies in surface and interface physics

which are difficult or impossible to perform using other methods. In particular, neutron studies of surface magnetic structures, magnetic thin

films and interfaces, and low atomic number adsorbates and films promise to be

very fruitful lines of future research due to the insensitivity of x-rays to

these systems and the difficulty of quantitative analysis and lack of depthspecific information of electron and ion diffraction techniques. The present

90
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

work has resulted in the first observation of a reflected-diffracted neutron

beam under grazing-incidence conditions and demonstrates the feasibility of

this technique to these and other surface and interface problems.

xIO'

tn ^ 6 c

ZJo

o

<DO

o

Reflected

» Diffracted

xlO"

cnc

10 oO

-a

<DO

D

Q

(f> (mrad)

Figure 3. Data fit using the dynamical theory of neutron diffraction. The

specularly reflected beam is shown as squares, while the reflected

diffracted beam is indicated by circles. This result conclusively

demonstrates the existence of a reflected-diffracted beam.

References

[1] M. Born and E. Wolf, Principles of Optics, 6th ed., Pergamon Press,

Oxford (1970).

91
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SURFACE ORDERING AND LAMELLAR FORMATION IN DIBLOCK COPOLYMERS

S. H. Anastasiadis and T. P. Russell

(IBM Alamaden Research Center, San Jose, CA)

and

S. K. Satija and C. F. Majkrzak

Block copolymers are one of the most interesting classes of synthetic

high-polymer materials which have great potential for speciality and hightechnology applications [1]. For example, block copolymers are increasingly

being used in applications such as thin films, adhesives and surfactants. A

fundamental understanding of their surface phenomena is therefore essential.

The technique of neutron reflectometry is ideally suited for the study of

polymer surfaces where one can utilize selective deuterium labelling to

highlight scattering from specific parts of the polymer. In this report we give results of recent neutron reflectivity measurements from thin films of

diblock copolymer of hydrogenated polystyrene (PSH) and deuterated

polymethylmethacrylate (DPMMA).

The diblock copolymer with a molecular weight M|, = 30,000 (15 for PSH and

15 K for DPMMA) was dissolved in toluene (~ 3g/100cc). The polymer solution

was spin coated onto a highly polished fused silica block (3" x 1" x 1/2").

The specimen was then placed in vacuum to remove any residual solvent in the

polymer film.

Figure 1 shows the neutron reflectivity measured from the sample. The

filled diamonds is the data from the as cast film. This profile can be well

represented by a calculated profile from a smooth homogeneous 1150 A film of

the block copolymer. The open diamonds are the data after the sample was annealed at 178 °C for 16 hours. The dramatic change in the reflectivity

profile is due to reorientation of lamellar morphology parallel to the film

surface [2,3]. The peak in reflectivity at Q = .04 A' can be thought of as a Bragg peak from the highly ordered lamellae with a repeat distance of 175 A.

Preliminary fits to the data show that the reflectivity profile of the

annealed sample can be fit to a periodic varying density profile throughout

the thickness of the film, starting with PSH at the top of the film. A more stringent fit to the data will help in better determining the interfacial

thickness and interfacial profiles between A and B blocks of the copolymer.

92
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The oscillatory composition profiles in diblock copolymers near the free

surface have been recently predicted [3]. These interesting profiles occur

due to the connectivity of blocks and because the surface modifies the Flory

interaction parameter and the chemical potential in the adjacent copolymer

layer. More detailed studies of dependence of lamellae formation on molecular

weight and temperature are being conducted presently.

r I >I—I -2-^ O

ft;

o

^l^ 1 1 1 1 1 1 1 1 o

oo^ o«>o —

- V ' - y ^o

Si^

>ooo o oo

-

1 1 1 1 1

1 1 1 1

.

—

-4-

-6

0.000 0.032 0.064 0.096

Q(A-^)

0.128 0.160

Figure 1. The filled diamonds are the neutron reflectivity from as cast film

of PSH-DPMMA. The open diamonds represent the reflectivity from

the same sample after annealing at 178 °C for 18 hours.

References

[1] Processing, Structure and Properties of Block Copolymers; M. J. Folkes,

Ed.; Elsevier, New York, (1985)

.

[2] H. Hasegawa and T. Hashimoto, Macromolecules 18, 589 (1985).

[3] G. H. Fredrickson, Macromolecules 20, 2535 (1987).

93
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE SIGNIFICANCE OF MULTIPLE SCATTERING IN THE INTERPRETATION OF SMALL ANGLE

NEUTRON SCATTERING EXPERIMENTS

J. R. D. Copley

(University of Maryland and the National Bureau of Standards)

The multiple scattering of neutrons in small angle neutron scattering

experiments has been studied using the technique of Monte Carlo simulation

[1]. This technique is in general more versatile than analytic techniques,

in that there is (at least in principle) virtually no limit to the complexity

of the sample geometry and/or the sample's differential scattering cross

section. Complications such as inelastic scattering, the scattering from a container, and effects due to instrumental resolution, may also be included.

On the other hand analytic calculations are essentially exact and they proceed

much faster, but in general a new computer program must be written for each

problem.

As a test (and demonstration) of the Monte Carlo approach we have

calculated single and multiple scattering intensities for strongly scattering

samples of a system of monodisperse spheres in vacuo : our results are in

excellent agreement with the semi-analytic calculations of Schelten and

Schmatz [2] over a wide range of values of the dimensionless parameter app^,z,

where op is the total scattering cross section per particle, p^, is the number

density of particles, and z is the sample thickness.

The scattering by systems of monodisperse spheres embedded in a medium

has also been studied: the scattering cross section and number density of the

medium were chosen to represent light water. Simulations were run for 1 mm thick samples with volume fractions f in the range from 0.01 to 0.20, and an "empty" run on the pure medium was also performed. The standard procedure for

subtraction of the scattering by the medium, which involves normalization of

the "empty" run using the factor (l-f)T^/T|^, where T^ and T^. are the

transmissions of the sample and the medium respectively, slightly over- subtracts the multiple scattering due to the medium alone, since this

scattering scales with a higher power of (1-f) than the single scattering.

This is shown in figure 1, which also illustrates the magnitude of the

multiple scattering correction remaining after subtraction of the scattering

by the medium.

In view of its importance as a normalization standard which is frequently

used in small angle scattering experiments, we have attempted to calculate

94
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

single and multiple scattering intensities in experiments on 1 mm thick

samples of light water . The Egelstaff-Schofield kernel [3] was used to

describe the double differential scattering cross section, using appropriately

chosen parameters. We have computed the forward direction enhancement factor

g{A), introduced by Jacrot [4] (p 937), and it is compared with experimental

measurements [5,6] in figure 2. The lack of good agreement at the longer

wavelengths is very possibly due to inadequacies in the model scattering

function. The problem of determining (and understanding) the behavior of g{A)

(as well as the angular dependence of the scattering at small angles) is

widely recognized, and it is to be hoped that additional calculations and

measurements will be undertaken in the future.

CO

IO

O

30

1 1 1

(

1 1 1 1 1 1

('Standard' Procedure)

o Single

20

:

4 Multiple

. Total - Ideal'

10 - -

'- """--^ '^ ^^^ ^r'.4....,,,,,,,,,rs...,g;f!ni!!:!

-10 1 1 1 11 1 1 1 1 4 6 8

Reduced Wave Vector QR

10

Figure 1. Corrected single, multiple, and total scattered intensities for a system of particles immersed in a medium, with a volume fraction of

10%. The "ideal" intensity (i.e., the normalized intensity of

scattering by an infinitely thin sample) is shown as a solid line.

The normalization of the intensities is such that the "ideal"

intensity is unity at QR = 0.

95
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2-

1 1 1 1 1 -Jacrot (1976)

-\ o Jacrot and Zaccai (1981) + May et al (1982) — \V A This Work

—

+ o

® —

1

1 1 1 1

—

1-

8 12

X (A)

Figure 2. Calculated and measured values of the forward scattering

enhancement factor, g(A). The solid line is the function

[1 - exp(-0.6yA)]' suggested by Jacrot (1976). The results of May

et al . (1982) were normalized to unity at a = 10 A.

References

[1] J. R. D. Copley, J. Appl . Cryst. (in press).

[2] J. Schelten and W. Schmatz, J. Appl. Cryst. 13, 385-390 (1980).

[3] P. A. Egelstaff and P. Schofield, Nucl . Sci. Eng. 12, 260-270 (1962).

[4] B. Jacrot, Rep. Prog. Phys. 39, 911-953 (1976).

[5] B. Jacrot and G. Zaccai, Biopolymers 20, 2413-2426 (1981).

[6] R. P. May, K. Ibel , and J. Haas, J. Appl. Cryst. 15, 15-19 (1982).

96
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MODEL BICONTINUOUS STRUCTURE WITH FRACTAL SURFACES

N. F. Berk

We have shown previously [1] that an algorithm originally invented by

Cahn [2] to simulate morphology influenced by spinodal decomposition in

isotropic two-phase systems can be adapted to the description of the

scattering properties of microdispersed and microporous systems distinguished

by a morphology with a well defined length scale, including microemulsions,

controlled pore glasses, and polymer mixtures. Our generalization of Cahn's

scheme associates an interface between two material phases of uniform

densities with a level -set (contour) of a random standing wave, Sjg(r),

composed of N sinusoids having isotropic random wavevectors, Ic, with

wavenumbers distributed according to density P{k), and with uniformly

distributed phase constants, 4> :

1 N

Sfi(r) = 2 A cos{kk • r+^ ), (1)

^ N<A2> n=l " " "

where A are random amplitudes. The continuously connected space between

level sets a and ^ is then given uniform density p(r) = e ^[Sj.(r)], where

e (x) = 1 for xe{a,^), zero otherwise.

If the wavenumber distribution P{k) has finite second moment, then it can

be shown rigorously that the interfaces generated by the model are smooth and

4

lead to classical Porod law scattering: I{q) = 1/q as scattering wavenumber

q

-> 00. However, if P(k) behaves asymptotically as

lim P(k) = 1/k^"^^", < H < 1, (2)

k-+00

(so that P(k) is normal izable but has no second moment) then it can be shown

that the scattering intensity behaves asymptotically as

lim I(q) = l/q^+", (3)

corresponding to a surface with fractal (self affine) dimension D = 3-H, with

2 < D < 3. It is interesting that P(k) with property (2) is the power

spectrum of a 1-dimensional Brownian process, Bm(z). Numerical simulations

97
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(H = 1/2, D = 5/2) of the interfaces reveal fractal -like visualizations

consistent with this mathematical description.

References

[1] N. F. Berk, Phys. Rev. Lett., 58, 2718 (1987); see also R. W. Hopper,

J. Non-Crystalline Solids 49, 263 (1982).

[2] J. W. Cahn, J. Chem. Phys. 42, 93 (1965).

PHASE SHIFT DEPENDENCE OF STRONG MULTIPLE SCATTERING

N. F. Berk

We have developed a new formulation [1] of the phase shift dependence of

incoherent multiple scattering that extends our earlier work [2]. We find in

the limit z » 1, where z is the sample thickness divided by the scattering

mean free path, that the width, a, of the multiple scattering intensity

satisfies the scaling relation,

A^(Z^) = ^(t.)Aj(Z^), (1)

where

and

Z^ = Zj//3^.), (2)

Zj = ^z^p^^R. (3)

In (3), z is the thickness, 4> is the scattering volume fraction, p is the

scattering length density, a is the incident beam wavelength, and R is the

1/2 spherical particle radius. The function /3(i^) in (2) is i//[2a(i/)] '

, where

q(2x) = 2-4(i.sin(,^)+cos(u)-l)/i/^, (4)

and v is the single particle scattering phase shift. If a, is proportional to

1/2

(z,) '

, as in naive treatments of multiple scattering, then (1 and 2)

indicate that the width of multiple scattering is independent of the phase

shift, i.e., independent of the diffractive {u « 1) or refractive (i^ >> 1)

nature of the underlying single particle scattering. In fact, a, contains

98
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

logarithmic corrections to the naive result stemming from the Porod law

behavior of the single particle scattering, and it is these, alone, which

effectively distinguish between the different phase shift regimes [1]. Thus,

incoherent multiple scattering from thick samples tends to be insensitive to

the cross-over from diffractive to refractive behavior.

References

[1] N. F. Berk and K. A. Hardman-Rhyne, J. Appl . Cryst. (1988) in press .

[2] N. F. Berk and K. A. Hardman-Rhyne, J. Appl. Cryst. 18, 467 (1985),

Physica 136B, 218 (1986).

DYNAMICAL THEORY FOR THE SCATTERING OF POLARIZED NEUTRON BEAMS

FROM MAGNETIC SPIRAL AND RELATED STRUCTURES

N. F. Berk and C. F. Majkrzak

We are involved in the study of polarized neutron scattering from

magnetic spiral and multilayered structures using dynamical scattering theory.

The investigation is motivated by increasing interest in a wide variety of

possible applications of polarized beams to the study of magnetic systems and

to the use of magnetic components in neutron scattering instrumentation. The

neutron magnetic interaction with spiral structures depends on the chirality

(handedness) of the spiral. Thus, while a spiral has no net magnetization, it can distinguish between up and down neutron spin states in an incident beam

and scatter them differently. Spiral magnetic structures occur frequently in rare earth materials but usually without net chirality. However, MnSi, which

has a noncentrosymmetric unit cell, is known to form domains favoring a single

chirality. Alternatively, magnetic spirals can be synthesized as multilayers

in which the magnetization, uniform over a single layer, rotates between

successive layers. Such piecewise spirals also present the possibility of

alternating the nonmagnetic nuclear interaction from layer to layer, so that

interference between the chiral nuclear interaction and the spatially varying

magnetic interaction may bias the conversion of one spin state into another.

Both continuous and multilayer magnetic spirals require solution of the

coupled one-dimensional Schroedinger equations of the form.

99
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

V.;'{z) + (n/2)\{z) - pe-'^^^+^^Vjz) =

V:'{z) + (0/2) V(z) - pe'^^^^^^^^^Cz) = 0, (1)

where V'+{z) represent the components of the neutron spinor wave function. The

magnetic interaction with the spiral is given by the exponential terms, where

p is the scattering length density of the magnetization, which lies in the x-y

plane at angle (f) from the x-axis, and G is the wavevector of the spiral along

2 the z-axis. Also in (1), Q = y(Q - 167rb), where b is the uniform nuclear

interaction, and Q = 2ksin(5) is the neutron scattering vector for a beam of

momentum k, incident at glancing angle e. The essential physical assumption

in (1) is that G is small compared to crystalline reciprocal lattice vectors,

so that b and p represent cell averages; then (1) is valid for values of Q

satisfying the same criterion as G. From the formal solutions of (1) it is

possible to construct a 4X4 transfer matrix A(z,,Zq) that connects the spinor

and its first derivative at the incident surface, z = Zq, to its values at the

exit surface, z = z,:

tt{Zj) = A(Zj,Zq) f(ZQ ), (2)

where \t is a four component column matrix. At z = Zq, * defines the

amplitudes for the incident and reflected spinor beams, while at z = z-,, it

defines the amplitude of the transmitted spinor. For the multilayer spiral,

(1) is solved for G = 0, corresponding to a uniform magnetic slab between z, and Zp- In that case A(Zp,z,) depends only on z^ - z,, and the solution for

the multilayer of thickness T, composed of N slabs of thicknesses T , is

represented by

^(T) = A^{T^)...Aj(Tj)lr(0). (3)

We have solved (1) analytically for arbitrary G and have obtained the

transfer matrix. Analytical results for the reflection and transmission

coefficients have been obtained for the continuous spiral, while a computer

program to calculate (3) and its consequences has been developed for the

multilayer. The dependence of the reflection and transmission properties of

such model systems on interaction parameters and on the direction of the

laboratory guide field (quantization axis) for various incident polarization

states is being determined.

100
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PHASE CONTRAST MATCHING IN LAMELLAR STRUCTURES COMPOSED OF MIXTURES OF

LABELED AND UNLABELED BLOCK COPOLYMER FOR SMALL-ANGLE NEUTRON SCATTERING

Y. Matsushita, Y. Nakao, R. Saguchi, K. Mori,

H. Choshi, Y. Muroga, I. Noda, and M. Nagasawa

(Nagoya University, Nagoya, Japan)

and

T. Chang, C. J. Glinka, and C. C. Han

The conformation of a single polymer chain in bulk can be determined by

measuring small -angle neutron scattering (SANS) from a random mixture of

deuterium-labeled and unlabeled polymers with the same chain length at any

mixing ratio. The same method is applicable for determining the conformation

of a block chain of diblock copolymer even in a micro-domain structure if

strong diffraction intensities from the micro-domain structure can be

eliminated. Three methods were employed to eliminate the diffraction. In the

first method a single-chain scattering function is obtained as the difference

between the coherent scattering from a blend of labeled and unlabeled block

copolymers and its corresponding unlabeled block copolymer. This method is

straightforward, but it is difficult to obtain reliable data for a singlechain conformation [1] because the diffraction intensity due to the domain

structure is much more intense than the single-chain scattering and also

because identical domain structures are required for both specimens in order

to compensate for the scattering due to the domain structure.

The second method utilizes the anisotropy of oriented micro-domain

structures. Single-chain scattering from labeled and unlabeled blocks can be

observed with minimum interference when the incident neutron beam is

perpendicular to the lamellar surface because the diffraction from the

lamellae is suppressed in this orientation. Hadziioannou et al . [2] and

Hasegawa et al . [3] used this approach to investigate conformations of

polystyrene block in a lamellar structure of styrene-isoprene copolymers.

Since the orientation of lamellae was never perfect in any experiment, results

of accurate block chain dimensions are also difficult to obtain.

In the third method, the diffraction is eliminated by matching the

average scattering lengths between the two phases ("phase contrast matching")

using random mixtures of labeled and unlabeled block chains. This method was first proposed for polymer blends by Jahshan and Summerfield [4] and

subsequently extended to block copolymers by Koberstein [5]. In principle.

101
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

this is the best method, one should observe the single-chain scattering in a microdomain structure only if one can match the scattering length of A and B phases. However, this requires that jS.n < ^r < ^aq (where ^.„, /9n and /g.p are scattering length of hydrogenated A chain, B chain and deuterated A chain

respectively) and also a uniform distribution of deuterated block chain in the

A phase.

Diblock copolymers of styrene and 2-vinylpyridine with narrow molecular

weight distributions were used in this study to investigate the applicability

of this method. Three labeled diblock copolymers with different molecular

weights, two triblock copolymers with partially labeled styrene blocks, and

their corresponding unlabeled copolymers used as partners in blends were

employed as shown in table 1. Phase contrast ratio for 3 diblock copolymer

samples are shown in figure 1 and for 2 triblock copolymer samples are shown

in figure 2 together with theoretical predictions.

It is clear from figures 1 and 2 that phase contrast matching is success4

ful for the samples with the low molecular weights (3.4 x 10 for the labeled

portions) but not for the samples with the higher molecular weights {9.2 and

4

16.2 X 10 ) and the samples with partially deuterated blocks. We conclude

that the mismatching is caused not only by non-uniform distribution of

deuterated species along the direction perpendicular to the lamellae due to

difference in positions and lengths of the labeled and unlabeled blocks but

also by concentration fluctuations in mixtures of hydrogenated and deuterated

polystyrenes in domains.

102
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Molecular characteristics of samples

Sample

Code

Mn . Uio'^)Mw/Mn

(GPC)

Cs^)

(wt%)

Cd'') (%)

I

DP-33 0.34 0.661.07 1.0449 100

SP-33 0.37

0.63

1.10

1.03

50

II

DP-77 0.92

1.67 1.021.09 48 100

SP-77 0.77

1.49

1.02

1.02

51

III

DP-15 1.62 2.801.05

1.10

47 100

SP-15 1.19

2.43

1.01 1.0648

IV

SPD-4

1.52

1.97

4.01

1.03 1.06

1.08

50 19.1

SP-12 2.11 3.881.04

1.03

50

V

DSP-1

0.31

1.37 2.34

1.01 1.05

1.04

48 22.7

SP-15 1.19 2.43

1.01 1.0648

a) Cs are the total polystyrene content in the sample. Values for DP-33

and SP-33 are determined by pyrolysis gas chromatography, others are determined by elemental analysis.

b) Cd are the styrene-d8 content in the total polystyrene part.

103
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

X

Figure 1. Variation of contrast factor R as a function of X, the volume

fraction of deuterated polystyrene, on semilogarithmic scale.

Solid line is the theoretical prediction. Open Circles - DP-33/SP33, Open triangles - DP-77/SP-77, Open squares - DP-15/SP-15.

2

q: 1 enO

•

••• •

-1

-2

X^^^^

. \f

-3

1 -4

• 1 0.1 0.2

X

Figure 2. Variation of contrast factor R as a function of X on semilogarithmic scale. Solid Circles - SDP-4/SP-12, Solid squares

- DSP-l/SP-15 and the solid line is the theoretical prediction.

104
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[1] R. W. Richards and J. L. Thomason, Polym. 22, 581 (1981).

[2] G. Hadziiannou and A. Skoulios, Macromol . 15, 267 (1982).

[3] H. Hasegawa, T. Hashimoto, H. Kawai, T. P. Lodge, E. J. Amis, C. J,

Glinka, and C. C. Han, Macromol. 18, 67 (1985).

[4] S. N. Jahshan and G. C. J. Summerfield, Polym. Sci .

, Polym. Phys. Ed.

18, 1859 (1980).

[5] J. T. J. Koberstein, Polym. Sci. I., Polym. Phys. Ed. 20, 593 (1982).

TEMPERATURE, COMPOSITION AND MOLECULAR WEIGHT DEPENDENCE

OF BINARY INTERACTION PARAMETER OF POLYSTYRENE/POLY(VINYLMETHYLETHER) BLENDS

C. C. Han, B. J. Bauer, and J. C. Clark

(Polymers Division)

Y. Muroga and Y. Matsushita

(Nagoya University, Nagoya, Japan)

M. Okala

(Tokyo Institute of Technology, Tokyo, Japan)

Q. Tran-Cong

(Kyoto Institute of Technology, Kyoto, Japan)

and

T. Chang

(Korean Research Institute for Chemical Technology, Chungnam, Korea)

The technical importance of polymer blends has been well recognized in

recent years [1]. Making polymers miscible through chemical structure

modification is a yery important topic, but miscibility may not be the

ultimate characteristic one is looking for. This is because synergistic

effects which enhance the property of a phase separated material mainly come

from molecular alignment, reinforcement, phase domain size and morphology.

In order to understand and possibly control the domain sizes and

morphology due to phase decomposition, one has to understand thermodynamics

(statics) as well as phase separation kinetics (dynamics). We understand that

statics and dynamics are inseparable subjects if we wish to talk about phase

behavior of even a simple binary system. The most important quantity needed

in both static and dynamic characterization is the free energy (of mixing) of

105
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the system as a function of temperature and composition. For the case of

polymer systems, we also need to know the molecular weight dependence of the

free energy function.

Small angle neutron scattering (SANS) has been used [2-4] to measure

the effective or scattering binary interaction parameter, X^rr, (for

convenience, we will drop the subscript "effective" or "scattering" throughout

this paper and define X^r. = X .. = X) for a deuterated

polystyrene/poly(vinyl- methylether) (PSD/PVME) system. This technique offers

a rather simple, fast and accurate method of obtaining the X parameter.

Therefore, a systematic study of this X parameter as a function of composition

(<^), temperature (T) and molecular weight (MW) is possible.

The extraction of the X parameter from SANS measurements depends on the mean-field nature of the polymer system and the random phase approximation

(RPA) calculation [5,6]. Nevertheless, within our measurement error, we have

found this procedure quite satisfactory. Furthermore, we should point out

that the parameter extracted from this procedure is different from the Xpparameter in the Flory-Huggins free energy function as long as the Xpparameter is allowed to be compositionally dependent. The exact origin of

this compositional dependence of Xp is not certain, it could be caused by

residual entropic effects of monomer size difference between the two

components; by the local packing orientations; by the chain end effect; etc.

[7-10]. We have allowed the Xp to be compositionally dependent which is

different from the original definition of the Flory-Huggins X-parameter. But,

as long as the interaction between the two types of monomer can be described

by a single q-independent potential function U(<^, T) at a given (f> and T, the

RPA calculation will provide a general scattering structure factor S(q), which

allows the extraction of the effective interaction parameter, X, from the

scattering experiment.

In this paper, we present a systematic study of the effective X parameter as a function of c^, T and MW for high molecular weight and narrow molecular weight distribution deuterated polystyrene/poly(vinylmethylether)

systems by the SANS technique.

In figure 1, X/V values are plotted against 1/T for a typical high

molecular weight series sample at various compositions as indicated in the

figure. At any given composition, the X/V values follow the 1/T dependence

as is clearly indicated by the straight lines in this figure. This is a

106
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

necessary condition if a polymer system does follow the mean-field behavior.

Then, through the compositional dependence of X, the free energy function can

be constructed following the calculation by Sanchez [11].

The calculated free energy curves at several temperatures for the H series are shown in figure 2 together with the corresponding spinodal curve

and measured spinodal temperatures.

It is clear that the binary interaction parameter, Xp, can be obtained

according to Sanchez theory and free energy function can be generated with an empirical functional form of the measured X/V . Spinodal temperatures and

cloud point curves have been generated and compared with experimental values

successfully.

S -6 o

>

22.0 23.0 24.0 1/T no"^ (1/°K)

25.0 26.0

Figure 1. Reciprocal temperature dependence of X/V for various composition

of the H-series sample (MW of PSD = 593x10^ and PVME = 1.1x10^)

is displayed.

107
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

0.08

0.04 -

I I I I I I H - SERIES

Figure 2. Free energy of mixing obtained for the H-series at 152 °C, 148 °C

and 135 °C below (critical temperature) are plotted against 4> , in

the upper part of the figure. Spinodal temperature line together

with experimental data points (in open circle and square) are displayed in the lower part. The calculated spinodal points at

152 °C and 148 °C are also shown in filled circles.

108
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[I] (a) D. R. Paul and S. Newman, eds., Polymer Blends, Volume I and II,

Academic Press, New York (1978). (b) 0. Olabishi, L. M. Robeson, and

M. T. Shaw, "Polymer-Polymer Miscibil ity, " Academic Press, New York

(1979).

[2] C. Herkt-Maetzky and J. Schelton, Phys. Rev. Lett. 51, 896 (1983).

[3] H. Yang, M. Shibayama, R. S. Stein, and C. C. Han, Polym. Bull. 12, 7 (1984).

[4] M. Shibayama, H. Yang, R. S. Stein, and C. C. Han, Macromol . 18, 2179

(1985).

[5] (a) P. G. de Gennes, J. de Physique 31, 235 (1970). (b) P. G. de Gennes,

Scaling Concepts in Polymer Physics, Cornell University Press, New York

(1979).

[6] K. Binder, J. Chem. Phys. 79, 6387 (1983).

[7] D. Patterson, S. N. Bhattacharyya, and P. Picker, Trans. Faraday Soc. 64»

648 (1968).

[8] (a) I. G. Sanchez and R. H. LaCombe, J. Phys. Chem. 80, 2352 (1976).

(b) R. H. LaCombe and I. C. Sanchez, J. Phys. Chem. 80, 2568j (1976).

[9] (a) R. Koningsveld, L. A. Kleintjens and H. M. Schoffleers, Pure Appl

.

Chem. 39, 1 (1974). (b) K. Koningsveld, Advan. Colloid., Interface Sci.

2, 151 (1968).

[10] M. Muthukumar, J. Chem. Phys. 85, 4722 (1986).

[II] I. Sanchez, private communication.

109
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CHARACTERIZATION OF POLYQUINOLINE BLOCK COPOLYMER

USING SMALL ANGLE SCATTERING TECHNIQUES

W.-L. Wu

(Polymers Division)

and

J. K. Stille, J. W. Tsang, and A. J. Parker

(Colorado State University)

Polyquinoline is a major candidate for molecular composites. In a molecular composite, rigid rod molecules are dispersed in a matrix of flexible

polymer. The molecular rods act as the reinforcing fiber. Molecular

composites offer processing advantages while retaining excellent performance

properties at high temperature. In the ultimate molecular composite each

molecular rod should be completely surrounded by flexible polymer molecules to

separate on a larger scale, which must be overcome by modification of chemical

compositions.

This work is aimed at demonstrating that small angle scattering (SAS) is

a viable technique for the structure determination of rigid rod polymers in

solid state. The presence of microvoids in this type of material has hampered

the use of SAS in rigid rod polymers and their blends as a quantitative

measurement technique. To circumvent this difficulty, both small angle

neutron and x-ray measurements were carried out on the same specimen. Due to

the difference in the scattering contrast factors of the voids between x-ray

and neutron scattering the void contribution to the scattering intensity can then be removed. A block copolymer of alternating rigid rod and flexible

polyquinoline was studied using the above scheme to determine the

compatibility between the rigid and the soft components. The average

molecular weight for each block was about 17,000. The SANS and SAXS results,

both in an absolute intensity scale, are given in figures 1 and 2, respectively. The calculated molecular structure factor and the void scattering are given in figure 3. Based on the peak height of the molecular structure

factor, it is concluded that the block copolymer was not phase segregated;

however, a strong intermolecular correlation was observed within the same component.

110
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PQDDP30.AVE

I

>H 20Q

I—

t

iz;

O 100

1 I

1 1 1 r

m

o

o O

°ooO°°°Oo

J I I l_

oo

^foooc^oooopooo^PQ QJi.

0.0 0.1 0.2 0.3

Q (10"^ A"^)

0.4 0.5

Figure 1. SANS result of polyquinoline multi -block copolymer. The soft block

is partially deuterated. The intensity is in absolute scale.

SAXDDP30.AVE

120

t^ 80

m

iz;

g 40

o Oo o oo.

Co OoOq

00( •ooo OnOOO,

U>ooo<i.o I \ I \ \ I -p"o°opoOoopoooo

0.1 0.2 0.3

Q (IQ-^ A~^)

0.4 0.5

Figure 2. SAXS result of the sample of figure 2. The intensity is in

absolute scale.

Ill
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

600

O

g 400

K 200

Q Q^ -Molecular

•o o

D Void

'OOO

a Dq °°°oO°o.

a °°°°oOoo,

I I

I \ I °°T°°°°9°°°°t^nnnnAnnnn ^ nnnfti

0.0 0.1 0.2 0.3

Q

(10"^ A"^)

0.4 0.5

Figure 3. The calculated structure factors of the voids and the multi -block

copolymer.

NEUTRON SCATTERING STUDIES OF LIPID TUBULES FORMED

FROM A POLYNERIZABLE SURFACTANT

C. Han and S. Krueger

(Polymers Division)

and

P. E. Schoen and R. Treanor

(Naval Research Laboratory, Washington, DC)

Small angle neutron scattering (SANS) and wide angle neutron

diffraction studies have been initiated to determine the structure of tubules

formed by the polymerizable lipid, l,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-

phosphocholine. A conversion from spherical liposomes to hollow, thin-walled,

cylinders (tubules) occurs as the lipid is slowly cooled through its chain

melting phase transition temperature [1]. The tubules typically have

diameters between 0.3 and 1 yum and lengths ranging from a few to several

hundred micrometers and can be irreversibly polymerized by irradiation with

254 nm light. Lipids cooled too rapidly tend to form small planar shards,

rather than tubules.

112
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Preliminary SANS and wide angle measurements have been made on suspensions of tubules and shards in D^O. The SANS measurements are useful

for determining the bilayer spacing. As shown in figure 1, a pronounced peak

can be observed at q„ == 0.095 A' for tubules in D^O with concentration C = 30

^m 2 mg/ml . This corresponds to a bilayer spacing d = 27r/q = 66 A. In figure 2,

a similar experiment has been carried out, but on a suspension with less

tubule conversion. It is clear that the peak at q = 0.095 A is much

weaker. Yet, the position is unchanged. This confirms the idea that the

bilayer thickness is being measured, while the intensity of the peak is

related to the concentration of the tubules. No obvious diffraction signal

has been detected from the wide angle measurements conducted on the same material. This supports the notion that, due to the tight crystal -like

packing of the lipid chains, water is completely excluded from the hydrophilic

region. Therefore, there is no scattering contrast between the lipid chains

to give any neutron diffraction signal.

SANS measurements have also been initiated on partially deuterated lipid

chains in tubule form. Figure 3 displays the SANS data obtained from a suspension of tubules in which the lower half of both lipid chains are deuterated. Again, the tubules are in 0,0 and the concentration is 30 mg/ml.

-1

A more pronounced peak is observed at q = 0.1 A and a secondary structure

may also exist. SANS measurements in an extended q range are planned in order

to further study this sample. In addition, use of the contrast variation

[2,3] technique should allow the mapping of a more detailed bilayer structure.

Eventually, the data will be compared with model calculations of the

scattering function S(q) determined for various packing arrangements of the

hydrocarbon chains. The locations of the atoms determined from the data taken

on the planar shards will be used as initial positions in a computer modeling

of the equilibrium placement of the molecules in the cylindrical tubules.

This should provide some insight into the cause of the bending of the sheets

into tubules.

113
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Q (A-')

Figure 1. SANS data from lipid tubules in D^O with C = 30 mg/ml

Q (A-')

Figure 2. SANS data from lipid tubules in D^O with C = 30 mg/ml, but with

incomplete conversion from liposomes to tubules.

114
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

/ —

6 -

5 -

4 -

"o 3 - \

2 - \\°0

1 - \CO -

1 - °a^°^

/ 1 1 1 1 1

I

1 1 1 1 1 1 ., , 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

Q (A-')

Figure 3. SANS data from partially deuterated lipid tubules in D,0 with

C = 30 mg/ml

References

[1] P. Yager, P. E. Schoen, C. Davies, R. Price, and A. Singh, Biophys

48, 899 (1985).

[2] B. Jacrot, Rep. Prog. Phys. 39, 911 (1976).

[3] H. B. Stuhrmann and A. Miller, J. Appl . Cryst. 11, 325 (1978).

115
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SMALL ANGLE NEUTRON SCATTERING OF POLY(VINYLALCOHOL) - AQUEOUS SOLUTION

M. Shibayama, H. Kurokawa, and S. Nomura

(Kyoto Institute of Technology)

S. Roy and R. S. Stein

(University of Massachusetts)

and

L. D. Coyne and W. Wu

(Polymers Division)

Two kinds of poly(vinylalcohol) PVA aqueous gels; i.e., hydrogels (PVA

aqueous solution) and alkaline gels (PVA aqueous solution containing borate

ions), were investigated using small angle neutron scattering as a function of

temperature and concentration. For both gels the scattered intensity, I(q),

rises anomalously as q approaches when the system was in gel state, where q is the magnitude of the scattering vector. When the system is in sol state,

the correlation length can be obtained, which is a few times greater than the

radius of gyration of the PVA molecules, indicating the existence of PVA

clusters even in sol state. The scattering exponent, fx in I(q) - q'^, was evaluated to be around 1.6 to 2.0 for the gels. Its value decreases abruptly

around the gel-to-sol transition temperature. This scattering exponent

observed is in accordance with the value of theoretically predicted values

based on fractals [1,2].

References

[1] D. Stauffer, Phys. Rep. 54, 1 (1979).

[2] L. Leibler and F. Schoesseler, Phys Rev. Lett. 55, 1110 (1985).

116
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SMALL ANGLE NEUTRON SCATTERING STUDIES OF ISOLATED NEUROSECRETORY VESICLES

S. Krueger

(Polymers Division)

and

R. Nossal

(National Institutes of Health, Bethesda, MD)

Small angle neutron scattering (SANS) was used to study the state of

the dense cores within intact neurosecretory vesicles (NSV). These vesicles

transport the neurophysin proteins (NP), along with their associated

hormones, oxytocin (OT) or vasopressin (VP), from the posterior pituitary

gland to the bloodstream, where the entire vesicle contents are released.

Knowledge of the vesicle core structure is important in developing an understanding of this release mechanism. Since the core constituents exist in

a dense state at concentrations which cannot be reproduced (in solution) in

the laboratory, a method was developed to determine the core structure from

SANS experiments performed on intact neurosecretory vesicles.

The H^O/DpO ratio in the solvent can be adjusted, using the method of

contrast variation [1,2] such that the scattering due to the vesicle membranes

is minimized, thus emphasizing the scattering originating from the cores. The

applicability of this method for examining the interior of biological vesicles

was tested by performing an initial study [3] on human red blood cells (RBCs),

which are similar in structure to other biological vesicles. Changes in

intermolecular hemoglobin interactions, occurring when the ionic strength of

the solvent was varied or when the cells were deoxygenated, were examined.

The results agreed with those expected for dense protein solutions,

[4] indicating that the method developed was suitable for the study of

hemoglobin within the cells. Similar SANS studies were then performed on intact NSV.

A contrast variation series was performed on NSV membrane suspensions in

H^O as well as in 10, 20, 40 and 70% D^O buffers. The results, shown in

figure 1, suggest that the scattering from the NSV membranes is minimized when

the solvent contains between 10 and 20% D^O. The data, fit using the flat

sheet approximation [5], yielded a, membrane match point of 18 ± 2% D^O.

Initial data (see fig. 2) taken on intact NSV in 21% D^O, covering a range of Q values such that 0.015 < Q < 0.28 A , showed no evidence of

117
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

scattering beyond the small angle peak. In order to determine the extent of

the core contribution to the scattering at small angles, the scattering from

the NSV membranes alone was subtracted from that due to the intact NSV.

Suspensions of intact NSV as well as NSV membranes were measured in 20% and

40% DpO buffers. Then, a subtracted scattering curve, I-j.u(Q) = I„(Q) " C'I^(Q), where I^(Q) is due to the intact NSV and 1^{Q) is due to the NSV

membranes, was obtained for the samples in each solvent. The constant, C, is

the factor which normalizes L(Q) to I (Q). As the vesicle core contains

mostly protein, its match point is assumed to be approximately that of a typical protein, i.e., around 40% D^O. Since the only contribution to I (Q)

is due to the vesicle membrane, the scattering curves in 40% D^O were used to

find the normalization factor, C. As a check on this procedure, C was also

verified independently through biochemical means [6].

In 20% DpO, the contribution to the scattering intensity due to the

vesicle membranes is small. Therefore, after subtracting the normalized

membrane scattering, Icmk^Q) ^^ approximately equal to I(.(Q)» the scattering

due to the protein core. Figure 3 illustrates L^kCQ) as obtained from the

measured scattering intensities of both intact NSV and NSV membranes in 20%

D2O.

A Guinier fit [1] (see fig. 4) in the Q range 0.010 < Q < 0.020 A"-^ yielded a radius of gyration, R =- 183 ± 7 A. Since the core is dense, it is

probable that this represents the size of the spaces between the proteins

2 rather than the particles themselves. The curvature in the -^"[1.(0)] vs Q

plot suggests that a distribution of sizes of particles (or spaces) is present

in the NSV cores. The "openness" of the NSV core structure was tested by fitting a straight

line to the linear region occurring at small Q values in a log-log plot of

I . (Q) versus Q in order to find its fractal dimension [7]. As illustrated

in figure 5, an average fractal dimension of D = 2.8 ± 0.2, based on several

fits made in the range 0.010 < Q < 0.06 A' , was obtained, thus confirming

the dense nature of the NSV core. The SANS data, along with accompanying biochemical analysis, suggest that

the NSV core constituents form long, flexible aggregates which fold to form a compact, but not solid, structure. Additional data obtained at smaller

angles, made possible by the recent installation of a cold source at the NBS

Reactor, should provide a more complete picture of the NSV core structure.

118
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1.75

1.25 -

o 0.75

0.25 -

-0.25

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00

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\

^

\

'

I

'

\

' \ '

I

<

\ r- 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 Q (A-')

Figure la. Contrast variation series for NSV membranes. Plot of I(Q) vs Q

for NSV membranes in 70% and 40% DpO.

0.25

0.2 -

0.15

0.1

0.05 -

-0.05

HjG

20% D2O (SQUARE)

10% D2O (CIRCLE)

D00

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-n

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,

^

,

\

,

\

,

^

,

I r- 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Q (A-')

Figure lb. Contrast variation series for NSV membranes. Plot of I(Q) vs Q

for NSV membranes in 20% and 10% D2O as well as in H^O.

119
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1

-

1

to 2

tfi

** 3

° oV 00. =

* »» ° 00° „ • » "

° °0 ° 00 ° 00 »o °o

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' 0.05 0.1 0.15 0.2

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Figure 2. in(I(Q)) vs Q plot of intact NSV in 21% D2O covering the range of Q

values from 0.015 < Q < 0.28 A"-^.

0.8

1 'I

'

1

'

I

'

\ 'I

'

I

'

I ^ 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

Q (A-')

Figure 3. Scattering due to the NSV core protein, Is^ib^^^' ^" ^°"''" ^^2^' obtained by subtracting the (normalized) NSV membrane scattering

from the intact NSV scattering.

120
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2

1

'—I

'—I ''

\

' r 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014

Figure 4. Guinier fit to the NSV core protein scattering in 20% DpO. A

radius of gyration, R == 183 ± 7 A, was obtained in the region fit.

2 The smooth curvature of the -^"(IsmkCQ)) vs Q plot suggests a distribution of sizes can be found over the Q range plotted.

1

o

o

-

-1 -

-2 -

-3

-4

D ~ 2.!

-2.1 •2 -1.9 1.8 -1.7 1.6 -1.5

1 '\ ^

1.4 -1.3 -1.2

LOG(Q)

Figure 5. Log-log plot of I^yuCQ) vs Q for the NSV core protein scattering in

20% D2O. The line is a representative fit, made in the range 0.013

< Q < 0.05 a"-^. The calculated fractal dimension, D = 2.8 ± 0.2,

is an average of several fitted values obtained using slightly

different Q ranges.

121
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[1] B, Jacrot, Rep. Prog. Phys. 39, 911 (1976).

[2] H. B. Stuhrmann and A. Miller, J. Appl . Cryst. U, 325 (1978).

[3] S. Krueger and R. Nossal , Biophys. J. 53, 97, (1988)

[4] R. Nossal, C. J. Glinka, and S.-H. Chen, Biopolm. 25, 1157 (1986).

[5] G. Porod in Small Angle X-Ray Scattering, 0. Glatter and 0. Kratky, eds.,

Academic Press, New York, 17 (1982).

[6] S. Krueger and J. T. Russell, unpublished results.

[7] T. A. Witten and L. M. Sander, Phys. Rev. B2Z(9), 5686 (1983).

DENSIFICATION OF MICROPOROUS SILICA

G. G. Long

(Ceramics Division)

and

S. T. Krueger

(Polymers Division)

The sol -gel technique can be used to prepare novel glasses, fibers,

thin and thick films with chemical homogeneity and unique structural and

electrical properties. High purity, crack-free silica bodies with "made-toorder" narrow pore-size distributions have been formed as model systems for

the investigation of the relationships between the physical properties of this

class of material and the amount and character of porosity. The present

research focuses on the characterization of such porous bodies by small angle

neutron scattering (SANS) and multiple small angle neutron scattering (MSANS)

since it has been demonstrated that thermal processing and the resultant

microstructure bear a strong influence on the dielectric and other properties

of the product material.

Samples were prepared [1] by the Shoup [2] technique from 85 wt.%

potassium silicate and 15 wt.% colloidal silica. The porosity of the

precursor body was between 81 and 86%. The average pore radius in the

precursor body was 0.10 ^m as measured by Hg porosimetry. Since the

calculated density was within 2% of that derived from simple geometric

measurements, the pores must be mostly open. Each of the samples measured in

122
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

this study was subjected to a firing temperature above the onset of sintering

which occurs at 1150-1200 °C depending on the average pore size of the dried

precursors. The porosities of the SANS samples were 40, 35, 30, 5, and 2%,

and for several of these both thin samples for diffraction measurements and

thick samples for multiple scattering measurements were available.

MSANS [3,4] was used to measure the average pore sizes present during

the intermediate stages of thermal processing, where the radii could be

expected to be in the 0.08-10 ^m range. Total surfaces areas were estimated

from the single scattering Porod curves. Pore populations were studied in the

late stages of processing by means of diffraction measurements with 14 A

incident neutrons. The results are shown in table 1.

Table 1. Pore radii and surface scattering areas for the microporous

silica samples

2 Sample No. Density Pore Radius ium) Total surface area (cm )

1 0.60 0.185 5.89 x 10*

2 0.65 0.243 8923

4 0.70 0.224

6 0.95 <0.08 1198

9 0.98 <0.08 127

These results indicate that densification during the intermediate

stages is accompanied by pore coarsening. Although pore coarsening had

previously been observed in the earlier stages of thermal processing, this

result was unexpected since the pores are generally expected to undergo

shrinkage in order for the body to densify. The observed pore coarsening

eventually levels off and by the time the material is 95% dense, one cannot

detect any pores with radii greater than 0.08 ^^m. SANS measurements on the

95% dense sample using 14 A incident neutrons reveal the presence of

populations of pores with radii 330 A and less.

References

[1] We are grateful to R. A. Gerhardt, Center for Ceramics Research,

Rutgers University for providing the samples used in this study.

[2] R. D. Shoup, Colloid and Interface Sci. 3, 63 (1976).

[3] N. F. Berk and K. A. Hardman-Rhyne, J. Appl . Crystallogr. 18, 467 (1985).

[4] K. A. Hardman-Rhyne and N. F. Berk, J. Appl. Crystallogr. 18, 473 (1985).

123
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. Majkzrak, C. O'Connor, D. Pierce, 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 fall of 1987. The bids received indicated that the

design package was good, and the successful bidder has proved to be responsible and reliable. Construction began in November, 1987 and at present is

2/3 complete. The contract requires completion of the building before

January, 1989, and actual completion and beneficial occupancy should occur substantially before this date. No major problems have arisen in this phase

of the project.

The neutron guide tubes have been ordered from Cilas-Alcatel in France.

Actual fabrication of components has begun, and the first delivery of neutron

guides will occur in the spring of 1989, with installation beginning immediately. Concurrently, the detailed design of the in-reactor components of the

guide support systems and reactor penetrations is essentially complete, with

fabrication to begin in September. In the first stage of the neutron guide

installation, 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. The design of the first complement of instruments as shown in figure 1 is

underway, with different instruments at quite different stages. Two of the

instruments shown, the short small angle neutron scattering facility (SANS)

and the time-of-flight (TOP) spectrometer already exist inside the reactor

building, and will be moved, with some improvements and modifications, to the

guide hall immediately. As the new instruments come on line, these two will

be replaced, but in the development stage, they will be available to carry on currently ongoing research. When the first guides are installed, the port

currently allocated to the TOP machine will be modified to become the neutron

depth profiling station. The Exxon/NBS high resolution SANS will be ready for

installation when the guides are installed, as will the first experiment to be

124
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

performed at the fundamental neutron physics station. The other instruments

shown will be ready for installation in stages during the following year. A

brief description of some of the instruments is given below.

r///////////////////////////////////////////////////;V/y//////////////////////777///////////////////ffl

NG-1 NG-2

NG-3 NG-4

NG-5

NG-6

NG-7

/////////h'///n////N^H^n^H-HnHn/n/-H-H-H-H-/n///mH/////hwm/////Ji' ///h'h'/i/^hh'NH//////f/?w/

NG-7 NG-6 1.REFLECT0METER 4.T0F 2.INTERFER0METER 5.8 METER SANS

3.30 METER SANS

NG-5

6.TRIPLE-AXIS SPECTROMETER

/.PROMPT GAMMA SPECTROMETER

8. NEUTRON LIFETIME EXPERIMENT

200FT.

Figure 1. Cold Neutron Research Facility layout showing initial

instrumentation complex.

NEUTRON REFLECTOMETER

S. Satija

In the past 10 years there has been growing interest in a variety of

surface sensitive techniques including, most recently, neutron reflection from

surfaces. Current measurements show this to be a powerful probe of surface

properties; e.g., the study of density profiles as functions of depth and

surface roughness. One unique advantage of neutrons is the ability to use deuterium labelling to highlight scattering from selected components in a film. We have initiated a program in neutron reflectivity measurements on a variety of surfaces and interfaces using a modified triple axis spectrometer

in order to develop methods and techniques to be used in a new reflectometer

now being designed for installation in the guide hall. The design goal for

this new instrument is the ability to do measurements of reflectivities of

125
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

order 10" . The spectrometer will use a pyrolytic graphite crystal to both

monochromate and vertically deflect the neutron beam onto a horizontal sample.

This configuration will allow the measurement of reflectivities of liquid

surfaces. The instrument will have two detectors--one at small angles to measure specular reflectivities, and another capable of scanning a large

angular range in order to perform surface diffraction measurements.

Independent movement of both sample and detector will be provided to allow

measurement of off-specular scattering. The resolution will be variable by means of automated slits adjustments within a range of aQ/Q of 0.05-0.15.

NEUTRON DEPTH PROFILING FACILITY

R. G. Downing and B. Grazman

Construction of a neutron depth profiling facility for installation at

the cold source has begun. In order to provide the maximum flexibility in the

final configuration of the presample section of the instrument, the in-pile

plug has been designed to allow easy replacement of the initial collimator

with a converging neutron guide or other optical devices. After extensive

research into the properties of various single crystal filters for removal of

fast neutrons from the beam, a filter of 13 inches of sapphire has been chosen

as the optimum configuration for this application. The detailed design of the

in-reactor components, collimators and shielding is now underway, with

fabrication scheduled for the fall of 1988. At the same time, several new techniques for the actual profiling are under study, including a cooperative

NBS/Texas A&M collaboration on time-of-flight techniques. The final facility

will be ready for installation when the neutron guides are installed in 1989.

PROMPT 7 ACTIVATION ANALYSIS FACILITY

R. M. Lindstrom and C. A. Stone

Preliminary design of this facility has focussed on two topics. The

first has been the high count rates expected from typical samples (in excess

of 50 K counts per second). At this count rate, we have already achieved a resolution of better than 1.9 keV at 1332 keV. These count rates also allow

us to consider more advanced counting techniques, which are currently under

study. The second has been the possibility of using 7-7 and 7-conversion

126
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

electron coincidence counting in analytical measurements. Experiments

performed this past year at the Brookhaven HFBR using a four-detector

coincidence system showed that the intensity of several weak 7-ray peaks could

be determined to within 3%. Standard counting techniques give uncertainties

of 200% for the same counting time. The design of this facility will be

complete within 3 months, and construction will be completed in time for

installation in the guide hall in 1989.

HIGH RESOLUTION SMALL ANGLE SCATTERING SPECTROMETER

C. J. Glinka

and

S. K. Sinha

(Exxon Engineering and Research Company)

Much of the detailed mechanical design of the vacuum flight path for the

30 m long, high resolution SANS spectrometer, being built jointly by NBS and

the Exxon Research and Engineering Co., has been completed and fabrication is

well underway. Within this flight path, the effective source-to-sample

distance can be varied in steps from 5-15 m, through the insertion of neutron

guide tube sections, and the sample-to-detector distance varied continuously

from 2-15 m. A motorized carriage for positioning a large two-dimensional

position-sensitive detector inside the post-sample flight path has been built

and is currently being instrumented. The remaining mechanical design work

should be completed by the end of 1988 with fabrication of components

continuing until mid-1989. Delivery of many of the major commercial

components of the instrument, including two advanced type velocity selectors

and the guide tube sections for the incident flight path, is also expected

during this period.

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

127
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1700 m arc to achieve focusing in the horizontal plane. Calculations indicate

that this arrangement of bent cylindrical mirrors will give about 95% of the

flux gain that an ideally figured toroidal mirror would provide for a small

fraction of the cost of a single mirror of the required length, shape and

surface finish.

The SANS flight path has been designed to accommodate either conventional

pinhole collimation or a focusing mirror. Actual performance tests will

dictate the final choice of beam collimation.

DESIGN OF A HIGH RESOLUTION TIME-OF-FLIGHT SPECTROMETER

J. R. D. Copley

The high resolution time-of-flight spectrometer, primarily designed to

provide an energy resolution of 10-15 /xeV using an incident wavelength of 6 A,

is intended to be highly versatile so that rapid measurements with relatively

poor resolution can be performed prior to the more definitive high resolution

studies. The instrument will use at least six high speed disk choppers, each

fitted with several widely separated neutron windows, in order to achieve this

purpose. We also hope to include an option to use a multiple-slot system (see

"On the Use of Multiple-Slot Multiple Disk Chopper Assemblies to Pulse Thermal

Neutron Beams," by J.R.D. Copley, elsewhere in this report) to achieve high

resolution with additional intensity. The choppers will run on magnetic

bearings, and recent tests of the extent of jitter in such systems suggest

that the multiple-slot concept will work. If the full width of the neutron

guide (6 cm) is to be used, a converging guide will be required, since the

sample size can only be of order 1-2 cm in order to achieve the desired

resolution. Studies of converging guides have been performed, but no definite

decision has as yet been made.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

WORKSHOP ON NICROSTRUCTURE AND NACRONOLECULAR RESEARCH WITH COLD NEUTRONS

C. J. Glinka, J. A. Gotaas, and C. O'Connor

On April 21-22, 1988, over 160 scientists, including 25 from industry, 70

from universities and 30 from Government laboratories and agencies (not

including NBS), gathered at NBS, Gaithersburg, for a Workshop on Microstructure and Macromolecular Research With Cold Neutrons. This workshop was

one of a series, each devoted to a major area of research with cold neutrons,

that are being held in conjunction with the development of the Cold Neutron

Research Facility (CNRF) at the NBS 20 MW research reactor as a National,

user-oriented research facility. The dual aims of this workshop were to

highlight research opportunities in the application of cold neutron techniques

to the study of submicron structure in materials and macromolecular systems,

and to inform and involve the scientific community in the planning for

instrumentation for the CNRF.

The workshop's goal of highlighting research opportunities with cold

neutrons was addressed in two sessions in which invited speakers reviewed

current work in a variety of disciplines and discussed future extensions

utilizing cold neutrons. Talks by T. Russell (IBM Almaden Research Center),

J. Hayter (Oak Ridge National Laboratory), G. Zaccai (Institut Laue-Langevin),

and R. Page (Southwest Research Institute) covered applications in Polymer

Science, Chemistry, Biology and Ceramics, respectively. Metallurgical

applications, with an emphasis on time-resolved studies, were described by

B. Gaul in (Oak Ridge National Laboratory) while S. Sinha (Exxon Research and

Engineering Co.) presented a general formalism for using scattering measurements to characterize fractal behavior in materials. In addition, the use of

cold neutrons to study the structure of surfaces and interfaces was the

subject of talks be R. Thomas (Oxford University) and H. Zabel (University of

Illinois) who discussed the relatively new techniques of neutron reflectometry

and grazing incidence diffraction.

One session of the workshop was devoted entirely to reviewing the current

status and future plans for the NBS CNRF. NBS Deputy Director Ray Kammer

opened the session by outlining the overall scope of the CNRF as a National user facility open to all qualified researchers on the basis of scientific

merit. Kammer's policy overview was followed by a technical overview by J. M. Rowe who described the architectural design of the experimental hall and

129
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

office wing (scheduled for completion in early 1989) associated with the CNRF,

and the network of totally reflecting guide tubes that will transport neutrons

from the reactor cold source to the CNRF. He also presented data on the

performance of the DpO-ice cold source now in operation in the reactor and

gave a timetable for projected instrument development. The remaining four

talks in this session each focused on a specific cold neutron technique and

presented design concepts for its implementation in the CNRF. Described were

a novel SANS instrument that would utilize a doubly curved mirror to focus a beam onto a detector, the current state of development of neutron supermirrors

and their use both to enhance flux and to produce polarized neutron beams, a neutron reflectometer suitable for measurements on both solid and liquid

surfaces, and an improved facility for Neutron Depth Profiling which would

utilize a converging neutron guide to increase the sensitivity of this

technique by more than one order of magnitude over what is now possible using

thermal neutrons.

The last session of the workshop consisted of three discussion sessions

which provided participants with the opportunity to comment upon or inquiry

further about any aspect of the CNRF. The discussions were wide-ranging and

touched upon the need for advanced cold neutron instrumentation for inelastic

scattering, recent progress in neutron optical devices and the practical needs

of potential users of the CNRF.

One clear impression that emerged from the workshop is that there is a strong and growing interest in the scientific potential of the relatively new techniques of neutron reflectometry and grazing incidence diffraction for the

study of near surface and interface structure. As a result of this expressed

interest, the development of a state-of-the-art neutron reflectometer for the

CNRF will be given increased priority. This instrument, along with a 30 m SANS

machine, are expected to be the first instruments to go into operation when

the CNRF guide hall is completed.

Copies of the workshop program containing the abstracts of the invited

talks, and a 12-page booklet describing the CNRF may be obtained by contacting

Carol O'Connor, National Bureau of Standards, Bldg. 235 Rm. A-106,

Gaithersburg, MD 20899 (phone: 301-975-6240).

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NBSR COLD NEUTRON SOURCE

R. S. Carter, P. Kopetka, J. M. Rowe, J. J. Rush, D. Fravel , and J. A. Gotaas

The NBSR cold source was installed in August 1987 and became operational

in October 1987. The source is a 16 L block of DpO ice maintained at 35 K

with a large (8" diam.) reentrant hole. In anticipation that its performance

could be improved by the addition of some H^O, a series of tests were performed over a period of several months with different H^O concentrations.

The optimum H2O concentration was found to be 7 1/2%. (See "Cold Source

Spectrum and Flux Measurements" elsewhere in this report.)

The gain in cold neutron intensity (a> 4 A) achieved by the cold source

was determined in several ways. These included the gain relative to the best

intensity that could be obtained from the best beam hole available without a cold source; the gain versus the cold source empty; and the gain versus the

cold source full, but warm. The gains were 3, 5, and 10 respectively. (For more detail see "Cold Source Spectrum and Flux Measurements" elsewhere in this

report.)

Radiation damage studies were performed by measuring the release of H^,

O2, and the production of H^Op as a function of radiation exposure. After a specified number of megawatt-hours of operation, the reactor was shutdown and

the system allowed to warm up gradually. As the system warmed, the release of

Dp and 0^ was measured. The rate of gas release as a function of ice

temperature typically showed two peaks, one at ~ 200 K and the other near the

melting point. In general most of the release was deuterium with very little

oxygen. Analysis of the water after melting showed that most of the oxygen

could be accounted for by the formation of D2O2 found in the water. As

expected, based on earlier results in the literature, the D2 released tended

towards a saturation value as shown in figure 1. The D2 releases are well

within those anticipated and do not present any safety threat to the integrity

of the cold source. From the figure, it is concluded that extended periods of

operation pose no safety concerns. In fact, the exposure limit of the ice is

set by the tritium level generated in the D2O ice by neutron capture rather

than the buildup of radiolytic products. After about 12 weeks of irradiation

at 20 MW reactor power (three reactor operating cycles), the tritium level in

the cold source ice begins to exceed that in the reactor (D2O moderated and

131
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

reflected) primary cooling system. Therefore, it is deemed prudent to melt

the ice after three reactor cycles and replace it with fresh material.

100 150

Irradiation Time-Hours

200 250

Figure 1. Total Dp release vs. irradiation time at 20 MW.

A phenomena that was not anticipated and that further limits the long

term buildup of radiolytic products was the occurrence of spontaneous

recombination of these products even when the ice is cold. This may be due to

local hot spots that allow some recombination and energy release. This

process or "burp" causes a significant fraction of the accumulated radiolytic

products to recombine releasing enough energy to cause the ice temperature to

rise to 80 to 90 K. Although this energy is easily absorbed in the ice, the

rapid temperature rise perturbs the refrigerator which cools the ice, and may

cause it to shutdown if unattended. This "burp" phenomena appears to occur

about every 3 days or so at full reactor power. Therefore, every 2 days the

ice temperature is intentionally raised by decreasing the refrigerator cooling

to initiate a "burp" in a controlled fashion.

This procedure, which warms up the ice for about 1 hour every 48 hours,

permits long term continuous operation without uncontrolled perturbation of

the refrigerator cooling system.

Thus, the length of time that ice may be maintained in the cold source is

not limited by the buildup of radiolytic products, but by the operational

132
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

desire to limit the buildup of tritium to a readily manageable level. This

requires the melting and replacement of the ice only four times a year. To assure that the ice can be maintained frozen for such long periods of time, a simple, backup refrigerator capable of maintaining the ice below freezing

temperature is available on standby if the main refrigerator should fail.

SMALL ANGLE NEUTRON SCATTERING FACILITY

J. A. Gotaas and C. J. Glinka

The installation in the fall of 1987 of a 20-liter , D^O-ice cold source

in the reactor has resulted in a flux increase at the 8 meter SANS spectrometer that ranges from 2.75 at 5 A to nearly 4 at about 15 A. The beam

current at the sample is now 1 x 10 n/sec, for a minimum accessible Q-value of

-1 4 -1

0.015 A , and is 2 x 10 n/sec, for a minimum Q of 0.004 A , for example.

For strong scatterers, the low Q limit of the instrument is less than

0.003 A" . This is illustrated in figure 1 which shows a SANS pattern for a highly porous glass where the first data point outside the beamstop is at

Q = 0.0024 A'-^ ^4U 1 1 n m — CD

1 1 1 1 1

o

o

160

m

0.0024 A"' _ i ^

mm

m

m WAVELENGTH = 14 A

m

o

u

ra CONVERGING PINHOLE

80

COLLIMATION

m

m —

n 1

m

m

m —

\ 1 1 °°°°P°c)DDQDt](itDmnmQ[

0.0 0.1 0.2 0.3

Scattering Vector Q(10~^ A~^)

0.4

Figure 1. Small angle scattering from a porous silica glass measured using

converging pinhole collimation and 14 A neutrons from the cold

source. The first data point lying wholly outside the instrument's

beamstop is a Q = 0.0024 A .

133
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COLD SOURCE SPECTRUM AND FLUX MEASUREMENTS

C. J. Glinka, T. J. Udovic, J. M. Rowe, and J. J. Rush

and

D. M. Gilliam and G. P. Lamaze

(Center for Radiation Research)

Summarized below are the results of a series of measurements made between

October 1987 and April 1988 to characterize both the spectral shape and the

absolute flux of neutrons from the 16 liter D20-ice cold source installed in

the fall of 1987. The measurements were of three types: 1) time-of-flight

measurements of the spectral shape, 2) absolute measurements with a double

fission chamber of the total cold neutron flux (wavelengths above 4A), and 3)

beam monitor count rates to estimate the gain as a function of wavelength.

1) Spectrum Shape

Time-of-flight measurements of the wavelength distribution of neutrons

from the cold source were made at the SANS beam port (CTE) soon after the

installation of the source and prior to reinstalling the SANS and TOP

instruments. For these measurements a Fermi chopper was set up at the SANS

velocity selector position and was followed by a 3.5 m evacuated flight path

with fission monitors at both ends. Attempts to measure the total, unfiltered

spectrum from the cold source failed because the chopper in its closed

position was not sufficiently opaque to the epithermal and fast neutrons in

the beam. Consequently, most of the measurements ere made with 9 inches of

liquid-nitrogen-cooled, single-crystal quartz in the beam immediately

preceding the chopper. The data were subsequently corrected for background , chopper transmission, the 1/v dependence of the beam monitor efficiency, and

the tabulated transmission of quartz at 77 K. A typical corrected wavelength spectrum with the cold source at 30 K is

shown in figure 1. Although the complete spectrum is not Maxwell ian in shape,

a single Maxwell ian curve with a temperature of 65 K gives a reasonably good

fit to the data from 3 to 9 A (solid curve in fig. 1).

134
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(DO

S5cd

CD

I—

o

Source Temperature 30K

4 6

WAVELENGTH (A)

8

Figure 1. A typical corrected wavelength distribution, measured by time-offlight, with the cold source operating at 30 K with 7.5% H^O

homogeneously mixed in the D^O. The solid curve is a Maxwellian

spectrum at a temperature of 65 K that gave the best fit to the

data from 3 to 9 A.

2) Absolute Flux Measurements

An absolute value for the neutron flux from the cold source was derived

from fission rates measured with a double fission chamber placed at the

entrance to the SANS instrument's pre-sample flight path for direct comparison

with similar measurements made in 1981 when the SANS instrument was first

installed. For this measurement the liquid-nitrogen-cooled SANS filter,

consisting of 8 inches of single-crystal bismuth and 8 inches of polycrystalline beryllium, was in place, but the velocity selector was removed. Thus the

measured fission rates represent an integration over all wavelengths greater

than 3.95 A, the Bragg cutoff for beryllium, weighted by the 1/v cross section

of the fission foils.

The flux inferred from measurements with three fission foils of known

mass, including one foil that was used for the 1981 flux measurement, was

7 2 4.94 X 10 n/cm -sec (assuming a Maxwellian spectrum for wavelengths greater

than 4 A with a characteristic temperature of 65 K) with an uncertainty of

about 7%. This is an increase in cold neutron flux (a > 3.95A) of 2.5 + .2

135
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

over the value measured in 1981 (scaled to 20 MW) which was based on a Maxwellian temperature of 350 K.

3) Flux Gains Versus Wavelength

After reinstalling and calibrating the SANS velocity selector, beam

monitor count rates were measured versus wavelength under various cold source operating conditions. The ratios of count rates measured with the cold source temperature at 30 K (with 7.5% H^O in the DJQ ice) and with the source empty

are plotted in figure 2. The measured gains under this condition increase

from about 4.5 to 5.5 over the wavelength range from 5 to 12 A

SANS beam monitor count rates were also used to assess the effect of

substituting a small percentage of H^O for D^O in the cold source in an effort

to optimize the moderating and transmission characteristics of the source. The best results were obtained with a homogeneous mixture containing about

7.5% H2O which gave about a 20% increase in flux compared to having pure D^O

in the source.

Figure 2,

4 8 12

WAVELENGTH (A)

Data points are ratios of beam monitor count rates measured at the

SANS instrument with the cold source at a temperature of 30 K (with

7.5% HpO in the D^O ice) to those measured with the source empty.

136
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SUPERHIRROR DEVELOPMENT

C. F. Majkrzak and D. A. Neumann

J. R. D. Copley

(University of Maryland and National Bureau of Standards)

and

R. P. DiNardo

(Brookhaven National Laboratory, Upton, NY)

Polarized neutrons play an important role in scattering studies of

condensed matter [1]. Consequently, an efficient means of polarizing a neutron beam is very valuable. In addition to conventional, bulk singlecrystal polarizers such as the Heusler alloy Cu^MnAl , polarizing mirrors are often used for this purpose. This is possible because for most materials the

refractive index for neutrons is less than unity so that external reflection

occurs from flat surfaces in air or vacuum at glancing angles up to a critical

angle of the order of 0.1 deg/A neutron wavelength. Furthermore, because the

neutron possesses a magnetic dipole moment, its propagation through

ferromagnetic materials is determined by a birefringent refractive index.

Thus for a ferromagnetic material which is magnetized parallel to its

reflecting surface, the critical angle depends on the neutron spin state so that only one spin state is effectively reflected between two distinct

critical angles. For many applications it is advantageous to reflect one spin over as wide a range of angles as possible with a high efficiency. To this

end polarizing supermirrors, first suggested by Mezei [2] and Turchin [3]

have been developed in recent years [4,5] which in effect extend the critical

angle of reflection for one spin state by constructive interference of the

neutron wave in a thin-film, multi-layered structure consisting of a ferromagnetic and nonmagnetic material. Reviews of these devices and their

applications are given in references [6-8]. Nevertheless, it has not yet been

possible to produce polarizing supermirrors with high reflectivity beyond

about twice the critical angle of ordinary Ni (0.1 deg/A). Current efforts

are focussed primarily on: 1) extending the critical angle of both polarizing

and non-polarizing supermirrors out to a critical angle equal to three times

that of ordinary Ni; and 2) obtaining, simultaneously, a uniform reflectivity

approaching unity. Recently, direct evidence has been obtained by electron

microscopy performed at ORNL [9] which suggests that the primary reason for

137
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

reduced reflectivity in supermirrors is a progressive roughening of the

layers, presumably due to lattice mismatch, thermally induced strain, or microcrystallite size and orientation. Deposition conditions favoring

amorphous growth and reduced stress are therefore being sought.

Work on Fe-Si [10] and Fe-W [11] polarizing multilayers and supermirrors

deposited by sputtering techniques at Brookhaven National Laboratory is in

progress. Non-polarizing supermirrors, which have a potentially important

application as guide tube coatings to improve beam transport properties, are being developed in collaboration with two commercial film coaters, the Ovonics

Co., Troy, MI, and the Opto-Line Co., Andover, MA. In particular, Ni-Ti, CAl , and C-V systems are being investigated.

In addition, measurements of the flux enhancement gained with converging

guide segments constructed of both ordinary mirrors and supermirrors have been

performed. The measured gains are in good agreement with the predicted values

as shown in figure 1 [12].

ANALYTIC -

Glass

Nickel

Supermirror

MONTE CARLO (SM)

O 100%

100/73% -

0.0 0.2 0.4 0.6 0.8 1.0 2a/2W

Figure 1. Measured and calculated gains, plotted as a function of the exit

window width 2a to the entrance window width 2 W, for converging guide

systems. The experimental measurements and the analytic calculations

are shown as closed symbols and lines respectively. The hatched areas represent the uncertainties in the calculated gains due to the

uncertainties in the critical angle ratios m. The error bars on the

experimental results are due to uncertainties in the widths 2a. The

open symbols represent Monte Carlo calculations, assuming 100%

reflectivity to Q = 0.043 A

-1

(circles), and 100% reflectivity to

0.020 A"-^, 73% reflectivity from 0.020 to 0.043 A"-^ (squares)

138
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[1] R. M. Moon, T. Riste, and W. C. Koehler, Phys. Rev. 181, 920 (1969).

[2] F. Mezei, Comm. Phys. 1, 81 (1976).

[3] V. F. Turchin, Deposited Paper, At. Energy 22, No. 2 (1957).

[4] 0. Scharpf, AIP Conf. Proc. 89, 182 (1981).

[5] T. Ebisawa, N. Achiwa, S. Yamada, T. Akiyoshi, and S. Okamoto, J. Nucl

.

Sci. Tech. 16, 647 (1979).

[6] R. Pynn, Rev. Sci. Instrm. 55, 837 (1984).

[7] C. F. Majkrzak, Applied Optics 23, 3524 (1984).

[8] C. F. Majkrzak et al . Physica B, to be published.

[9] H. Mook and J. Bradshaw, private communication.

[10] R. P. DiNardo, C. F. Majkrzak, and D. A. Neumann, Fabrication of Neutron

Polarizing Multilayers by Sputtering, Proc. of the 32nd Annual Int'l.

Tech. Symposium on Optical and Optoelectronic Applied Science and

Engineering, SPIE, August, 1988, San Diego, CA to be published.

[11] C. F. Majkrzak, D. A. Neumann, J. R. D. Copley, and R. P. DiNardo, Fe-W

Supermirrors for Polarizing Neutrons, Proc. of the 1987 Fall Meeting of

the Materials Research Society, in press.

[12] J. R. D. Copley and C. F. Majkrzak, Converging Neutron Guides, Proc. of

the 32nd Annual Int'l. Tech. Symposium on Optical and Optoelectronic

Applied Science and Engineering, SPIE, August, 1988, San Diego, CA, to be

publ ished.

NEUTRON REFLECTION STUDIES OF SURFACES AND INTERFACES

S. K. Satija and C. F. Majkrzak

In the past ten years there has been growing interest in a variety of

surface sensitive techniques including more recently, neutron reflection from

surfaces. Current developments show this to be a powerful probe of surface

properties; e.g., density profile with depth and surface roughness etc. One

unique advantage of neutrons is that selective deuterium labelling can be used

to highlight scattering from selected components in a film. At the NBS

research reactor we have initiated a comprehensive program in neutron

reflectivity measurements from a variety of surfaces and interfaces in

anticipation for an expanded capability in the cold neutron guide hall.

139
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In order to differentiate between various models of surfaces, it is

crucial to measure reflectivities to very low levels. Recently we have

demonstrated the ability to measure reflectivities down to - 1x10' . An

example of such a measurement is shown in figure 1. The points in figure 1 show the measured neutron reflectivity from a highly polished single x-tal of

quartz. The line shows calculated reflectivity from quartz surface assuming a root mean square surface roughness of 5 A. With the completion of a new dedicated instrument in the cold neutron guide hall we will be able to measure

neutron reflectivities in 1x10" range. This would be better than any instrument currently available in the world.

u A

1 1 1 1 1

t*—{ \^^ ^ -2 - \ -

E-H ^k

O ^L

W ^^^w - H ^^^ K ^^

2-4

^

Ste^ -

&0 ^^[^

o ^K^j^^

r—

(

^^^•^>-* ^^-^• •

--•-^ -6 1 1 1 1 1 1 1 0.00 0.04 0.08 0.12

Q(A-^)

0.16 0.20

Figure 1. Neutron reflectivity from a highly polished quartz single x-tal.

The data has been corrected for background and contribution due to

off specular scattering. The solid line is the calculated reflectivity for quartz surface with an RMS surface roughness of 5 A.

140
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SIMULATION OF THE PHASE SPACE TRANSFORMATION OF NEUTRONS BY

BRAGG REFLECTION FROM MOVING MOSAIC CRYSTALS

D. A. Neumann

Backscattering has proven to be an extremely valuable tool for the study

of single particle motions in condensed matter, primarily due to the excellent

energy resolution {< 1 neM) of these instruments. The principal limitation of

4

this technique has been the rather small flux on the sample {- 10 neutrons/

2 cm /sec at both the Institut Laue-Langevin and Jiilich) partially linked to the

extremely good energy resolution. There is also, however, a substantial

mismatch of the angular resolution of the primary and secondary sides of all

cold neutron backscattering instruments currently in operation because the

divergence of the incident beam is limited by the neutron guide on which the

instrument is installed, while the angular resolution of the secondary

spectrometer is quite low due to the large area analyzing crystals and the

detector geometry. Therefore it is possible to increase the flux at the

sample position without degrading the energy resolution by increasing the

angular divergence of the incident beam. This has in fact been done to some extent at Jiilich through the use of a converging supermirror guide placed

immediately before the sample. However it seems impossible to match the (\ resolution of the primary spectrometer to that of the secondary spectrometer

with current supermirror technology. To overcome this difficulty Schelten and

Alefeld have proposed a novel neutron phase space transformation which uses moving mosaic crystals to change a well-coll imated, white ileutron beam into a divergent, nearly monochromatic one [1]. Physically, this occurs because the

slower moving neutrons are diffracted at higher angles and therefore get a "push" from the moving crystal, while the Bragg condition is satisfied at

smaller angles for the faster neutrons causing diffraction to occur from

crystallites moving away from the incident neutrons thereby reducing their

speed. In order to assess the possible gains for a backscattering spectrometer built at the Cold Neutron Research Facility, a simulation of this type

of transform has been performed incorporating parameters relevant to the NBSR.

CO

A backscattering spectrometer built at the NBS would be located on a Ni

2 guide of dimension 6 x 15 cm . Therefore the beam must be compressed in order

2 to achieve a reasonable sample size of 3 x 3 cm . It is envisaged that this

would be accomplished with a converging supermirror nose with a critical angle

of about twice that of Ni . Simulations of this element indicate that the beam

141
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

divergence r? after such a compression would be approximately twice the

critical angle of Ni in the horizontal plane {r?. = 2e ) and about three times

e in the vertical direction (»? = 3^ ). For the purposes of this

simulation, the phase space crystal was chosen to be pyrolytic graphite

(d = 3.354 A and e = 69.181°) with a thickness of 5 mm. The incident

distribution of neutrons was taken to be a 65 K Maxwell -Boltzmann distribution

(in accord with measurements of the flux from the NBS cold source) truncated

at 4 A to simulate a Be filter in the incident beam and at 10 A because

wavelengths longer than this have essentially no probability of being

diffracted by the moving crystal. This distribution was then multiplied by

the square of the incident wavelength in order to account for the fact that e is proportional to the wavelength. The horizontal and vertical mosaics and

the velocity of the graphite crystal were included as input parameters. The

reflectivity of graphite was accounted for with the Bacon-Lowde equation for

diffraction from ideally imperfect crystals [3]. This will overestimate the

reflectivity of the deflector crystal resulting in the simulated gains being

somewhat larger than what one would actually observe. (Note that the

reflectivity is a function of the crystal speed. This has been included.)

All of these simulations have been performed using the assumption that Si

(111) crystals will be used as the monochromator (a ~ 6.27 A).

Two-dimensional projections of simulated Bragg reflections from a crystal

having an isotropic 10° mosaic are shown in figure 1 for three different

crystal speeds. Here the incident and final k and k values of the

X y

diffracted neutrons are represented by individual dots and the reference

values are indicated by the solid lines. Two effects are evident. The first

is that the phase space volume increases as the crystal velocity increases.

This is because the Bragg reflection takes place at a lower angle in the

Doppler frame. The second effect is that the diffracted beam tilts in phase

space as the crystal velocity is changed. This tilt can be optimized so that

the maximum number of neutrons have the correct energy to be backscattered

from a Si (111) crystal. Note that this does not violate Liouville's theorem

because the orientation, not the volume, of the final phase space element has

been changed.

The most important information from the standpoint of increasing the flux

of backscattering instruments is displayed in figure 2. Here the peak

intensity (relative to that obtained for a crystal velocity of zero) is shown

142
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

as a function of speed for mosaics of 1°, 3°, 5", 10°, and 20°. For mosaics

of 3° or larger, the relative intensity increases from about 1 to a broad

maximum, before decreasing again. For the parameters chosen here, the maximum

gain is about 6 which occurs for a crystal with a 10° mosaic moving at about

300 m/s. The results for a 20° crystal show a smaller gain due to the

decrease in the reflectivity. The results for a crystal having a mosaic of 1°

appear somewhat unique. Here the intensity increases linearly with the

crystal speed and has a relative value of only about 1/2 for a speed of 0.

This is a result of the fact that a 1° mosaic is too small when compared to

the divergence of the incident beam.

1.0

I

^ 0.5-

0.0

1.0

I<^

>. ^ 0.5

0.0

1.0

I

^ 0.5

0.0

(a)

(b)

(c)

250 m/s

500 m/s

-1.0 -0.5 0.0 0.5 1.0

Figure 1. (a) Projection of a 3-dimensional simulation of Bragg diffraction

from a stationary crystal with a mosaic of 10°. The dots represent

the initial and final wave vectors of the diffracted neutrons, (b)

Same view for a crystal speed of 250 m/s. Note that the initial

phase space volume has expanded and the final volume has been

"tilted" compared to the results obtained for the stationary

crystal, (c) Crystal speed = 500 m/s.

143
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1 1 1 1 1 r

a 4

\ mosaac

/

^fi

OL L

.a-oxy- O'O^ ^-o--

.^-o

10°

5°

20°

3°

200 400 600

Crystal speed (m/s)

800

Figure 2. Peak intensity relative to that obtained for a stationary crystal.

For a mosaic of 10°, the phase space transform leads to a gain of 6

for a crystal speed of 300 m/s. The dashed lines are guides to the

eye.

The resulting gain factor of 6 would not be appreciably altered if

supermirrors were developed to the point were it would be possible to

fabricate guides with a critical angle twice that of Ni. However, if supermirrors suitable for focusing noses having even larger critical angles also

became available the gain from the phase space transform would be reduced.

For example, if the incident divergences were doubled (which would require a nose section having a critical angle of four times that of Ni) one would only

attain a gain of 2-3 via the phase space transform instead of the value of 6

reported here. In addition, these simulations have shown that it is essential

that the phase space crystal have an anisotropic mosaic to limit the vertical

divergence and that the phase space transform technique may not be particularly useful as the sole monochromating device in an instrument because the

final energy distribution is somewhat skewed to higher energies.

144
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

References

[1] J. Schelten and B. Alefeld, in Proc. Workshop on Neutron Scattering

Instrumentation for SNQ, Maria Laach, 3-5 Sept. 1984, R. Scherm and H. H. Stiller, eds., report Jai-1954 (1984).

[2] The simulation of the converging guides was done using a program written

by J. R. D. Copley.

[3] G. E. Bacon and R. D. Lowde, Acta Cryst. 1, 303 (1948).

SPIN POLARIZED INELASTIC NEUTRON SCATTERING SPECTROMETER (SPINS)

C. F. Majkrzak

Conceptual design work on an inelastic neutron scattering spectrometer to

be situated on a neutron guide in the new NBS cold neutron facility is now in

progress. The proposed machine is an innovative modification of a standard

triple axis spectrometer with the capability of measuring spin-dependent cross

sections. The use of state-of-the-art supermirror polarizers and a novel

energy-dependent flipper will make it possible to obtain an energy resolution

as good as about 10 /zeV without prohibitive restriction of beam divergence.

Although the four spin-dependent neutron cross sections can be measured, it

will also be possible to use unpolarized beams when desired. The spectrometer

will be capable of covering a range of incident neutron energies from 15 meV

to 2 meV with resolutions from 1 meV down to about 10 /xeV and with tunable

instrumental resolution. In order to decouple the dependence of the energy

resolution on the angular divergence of the beam, the proposed spectrometer

will utilize a novel energy-dependent spin flipping device in conjunction with

a pair of polarizing supermirrors as an energy analyser and/or monochromator

preceding the sample as desired. The energy-dependent flipper is of the type

first proposed by G. M. Drabkin [1]. Using this monochromating device, a very

high energy resolution can be obtained even for a considerably divergent beam

with a corresponding gain in intensity. The resolution function of the

spectrometer can therefore be tuned for a particular experiment.

It should be emphasized that the proposed spectrometer is designed for

both polarized and unpolarized beam experiments. The energy-dependent

analyser device utilizes the neutron spin but does not require that the sample

have a scattering cross section that is spin-dependent. Furthermore, the

spectrometer will be designed to be completely flexible in choice of either PG

145
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

or energy-dependent flipper and pair of supermirrors at both the tnonochromator

and analyser positions. This spectrometer should find wide application to

problems in condensed matter physics and chemistry. For more details, see reference [2].

References

[1] G. M. Drabkin, Sov. Phys. JETP 43, 1107 (1962).

[2] C. F. Majkrzak, C. J. Glinka, and S. K. Satija, SPIE Conf. Proc. No. 983,

to be published.

ON THE USE OF MULTIPLE-SLOT MULTIPLE DISK

CHOPPER ASSEMBLIES TO PULSE THERMAL NEUTRON BEAMS

J. R. D. Copley

(University of Maryland and the National Bureau of Standards)

Single-slot disk choppers, illustrated in figure 1, are commonly used to

pulse thermal neutron beams, but their use in high resolution applications is

limited because the maximum transmitted beam intensity, given that the chopper

is rotating at its maximum possible speed, is proportional to the square of

the burst time of the chopper, which is proportional to the width of the

incident beam. This means that in order to obtain high resolution using

single-slot disk choppers it may be necessary to use an incident beam which is narrower than the available beam width, severely reducing the intensity at the

sample position.

The transmitted intensity can be doubled, with no associated increase in

the burst time, by doubling the beam width and using counter-rotating choppers

[1] to double the effective chopping speed (fig. 2). In order to increase the

intensity still further, without degrading the resolution, we propose [2] the use of multiply-slotted choppers in combination with a multiply-slotted beam

mask. The first (and most practical) example of this concept requires two

slots in each of two counter-rotating choppers and a mask (fig. 3), giving a transmitted beam intensity which is four times that of the single-slot single

chopper arrangement, with no change in burst time. A further doubling may be

achieved, with no change in the burst time, if three choppers (with relative

angular frequencies w, -w, and w/2) and a mask, each fitted with four slots, are employed. The purpose of the mask and the additional choppers in these

systems is to suppress the early and late "satellite" bursts which would

otherwise be permitted to occur.

146
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(a)

(b)

Figure 1. The single-slot single chopper assembly, (a) A schematic view of

the setup. For clarity the width of the neutron guide is

exaggerated. The width of the slots in the chopper and the mask is

b and the chopper rotational frequency is w. The burst time aT is

b/v where v = wR. The system is shown at the start of a burst,

t = -AT. (b) The corresponding y-t diagram. The unhatched area represents the transmitted neutrons. The arrow to the left of the

y-t diagram indicates the time associated with the schematic view

of the assembly. Plots of intensity as functions of y and t also shown.

are

147
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(a)

(b)

Figure 2. The single-slot double chopper assembly, (a) A schematic view of

the setup. The width of the slots is 2b and the chopper rotational

frequencies are w and -w. The burst time is again b/v, and the

system is shown at the time t = aT/2: the choppers have passed the

fully open position, and the transmitted intensity is one-half its

maximum value, (b) The corresponding y-t diagram. See the caption

to figure 1 (b).

148
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(a)

(b)

Figure 3. The double-slot double chopper assembly, (a) A schematic view of

the setup. The width of the slots is 2b, the separation of their

centres is 4b, and the chopper rotational frequencies are w and -w. The burst time is again b/v, and the system is shown at the time

t = 2 aT: the slots in the choppers are aligned, but the mask stops

the unwanted satellite burst, (b) The corresponding y-t diagram.

See the caption to figure 1 (b).

149
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The effects of relative phasing errors in multiple chopper systems have

been studied in considerable detail. The first effect is that the intensity

of the principal burst is reduced, and to an extent this effect can be

tolerated. The second and potentially much more damaging effect is that the

satellite bursts are not necessarily completely suppressed. For example, if

the width of a slot is 2b, the centre-to-centre adjacent slot separation is

2B, and the distance of the slots from the chopper axis is R, then relative

phase angle deviations |5^| > {B-2b)/R in a two-slot two chopper arrangement

result in nonzero satellite burst intensity. To obviate this problem B/2b

should be somewhat greater than unity, and the data acquisition system should

be gated off whenever an unacceptable pulse (as defined above) occurs. Our calculations, combined with information regarding achievable phase

stability in actual disk chopper systems, have persuaded us to consider very

seriously the idea of including the option of multiple chopper assemblies in

the new high resolution time-of-flight instrument which is to be installed in

the neutron guide hall. There are however certain other matters which must be

considered, including the effects of nonzero radial extent of the slots in the

choppers, nonzero separation between the choppers in a chopper assembly, and

the spatial distribution of neutrons leaving a multiple-slot assembly.

References

[1] P. A. Egelstaff, Proc. of the First International Conference on the

Peaceful Uses of Atomic Energy, Geneva, 1955 (United Nations, New York,

Vol. 4, p. 70 (1956).

[2] J. R. D. Copley, Nucl . Instr. Meth.,(in press).

150
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CALCULATIONS OF THE PERFORMANCE OF NEUTRON GUIDES

J. R. D. Copley

(University of Maryland and the National Bureau of Standards)

We have written a number of computer programs to investigate the behavior

of parallel and converging neutron guides. The calculations are for the most

part performed analytically in the case of straight-sided guides, whereas a Monte Carlo ray tracing technique is employed with curved guides and complex

guide systems. The Monte Carlo calculations also serve as a check on the

analytic calculations. Acceptance diagrams at the entrance, at the exit, and

at points beyond the exit, are readily computed and plotted. 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 p measures

the angle between the neutron direction and the guide direction. Guide gains

and spatial and angular distributions may be computed using these acceptance

diagrams. Most of the programs handle only one lateral guide dimension, but

there is also a program which can be used to calculate the performance of a guide system with two lateral dimensions. Most of our effort has been devoted

to calculations for straight-sided converging guides and for curved converging

guides with the profile of a logarithmic spiral. We have also investigated

the idea of placing additional blades within a straight-sided converging

guide, blades which transmit the neutrons incident at angles higher than the

critical angle for reflection by the guide.

The major conclusions from this work may be summarized as follows:

(i) Current density gains of order two or three are relatively easy to

achieve using guides which converge in one lateral dimension, as long

as the taper angle is correctly chosen and the converging section has

a significantly higher critical angle (by a factor of order two) than

the parallel section which precedes it: gains of order four or more appear to be extremely difficult to achieve,

(ii) The angular distribution of the neutrons exiting a converging guide is

in general broad and highly non-uniform. The sample position should be

close to the exit of a converging guide in order to reap as much

benefit as possible from the increased current density at the exit.

151
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(iii) Since the performance of a converging guide depends on the wavelength

of the neutrons, the benefits of this type of device are most easily

realized when it is designed to be used exclusively with a single

choice of neutron wavelength.

Measurements of the performance of a converging guide system, described

under "Supermirror Development" by C. F. Majkrzak et al . in this report, are

in very good agreement with calculation. This gives us considerable

confidence to use the results of calculations in the design of instruments.

THE SMITHSONIAN - NBS PROGRAM ON THE STUDYING OF ART OBJECTS

BY NEUTRON METHODS.

Y. T. Cheng, M. J. Blackman, and J. S. 01 in

(Smithsonian Institution and the National Bureau of Standards)

and

M. Ganoczy

1. The Application of Neutron Radiography and Activation Analysis to the

Study of Ancient Bronzes

It is often desirable to have both the structural and compositional

information available in addition to stylistic consideration in the study of

ancient metal objects. X-ray radiography is utilized most commonly in

structural analysis. The technique is useful except in cases where the object

contains some high density materials such as lead and where organic substances

and other low density contents inside the metal object are of interest. The

compositional information generally is provided by detailed quantitative

analysis of small samples taken from various inconspicuous places in the metal

objects. The pitfalls for such a method are the common sampling difficulties:

that the samples taken may not be true representations of the whole object and

that the method is destructive. In this study, a neutron technique that

combines neutron radiography and whole object neutron activation analysis was used to compliment the conventional approaches in providing structural and

compositional information of a metal object.

The neutron radiography extends the ability to image the structure and

the interior of a metal object beyond what can be accomplished with x-ray

radiation, and the whole object neutron activation analysis (NAA) can give an

152
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

average composition of the major components in the object studied. The

collection of 20 Tibet an Lo-Han figures from the National Museum of Natural

History (fig. 1) was studied by the neutron technique. Five of the 20

religious figures still have their bottom seals in place, the rest have their

seals and contents removed. High resolution neutron radiography was developed

and applied to the five sealed figures to obtain clear images of the contents

inside. The whole object NAA was carried out for the 15 opened figures. The

whole object NAA differs from normal NAA in that: 1) it activates the entire

object thus only a fraction of the neutron fluence needed for NAA study is

required, 2) it uses a highly uniform neutron field to activate the test

object so a proper averaging can be obtained. In addition, in whole NAA, the

wall thickness of the test object, and to a lesser degree, the shape of the

object and its alloying type all need to be considered and calibrated. The

radiation released by the test object is yery closely related to the thickness

of the material being activated. This is because a truly uniform activation

is difficult to achieve as neutrons are being attenuated more when they

penetrate deeper into the material. The outer material can also shield the

gamma radiation inside from being fully counted. A test calibration using

copper cylinders with various wall thicknesses was conducted. The test shows

that the detected radiation level per unit copper mass is an exponentially

decreasing function of the cylinder wall thickness. A slight modification of

the calibration was necessary to account for the fact that the shapes of these

Tibetan figures were not cylindrical. Neutron radiographs of the 15 opened

figures were digitized and evaluated by comparing with standards in deriving

an average wall thickness for each figure. Each derived average wall

thickness was then used to check against the calibration to obtain a corrected

copper radiation level for that particular figure. Our initial result on the

study of the Lo-Han figures indicates that they are in general alloys of

copper and lead with small amounts of arsenic and indium. Gamma ray induced

lead x-ray fluorescence was detected in the energy spectrum. Some figures

also contain tin or low levels of antimony and zinc. The copper contents

range from about 70% to 95% (see fig. 2).

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. The Tibetan bronze statues collection at the National Museum of

Natural History.

154
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

100

1 [ -i 1 1 1 1 1i r

787 790 797 794 784 785 792 781 788 791 782 796 790A 799 789 STD

STATUE ID.

Figure 2. Percent weight content of copper in Tibetan bronze statues.

2. Neutron Activation Autoradiography

The study of works by Thomas W. Dewing using neutron activation autoradiography techniques continued with the paintings "Alma Thayer", "Lady

Listening", "Lady in White #1", "Lady in White #2", and "Spinet". All were

from the National Museum of American Art (NMAA). A Scholarly Studies proposal was submitted to the Office of Fellowships and Grants of the Smithsonian

Institution and funding was granted to support art historian Dr. Susan Hobbs

for collaboration in this continuing study. Meantime, the collaboration with

NMAA has developed further. A new project, studying another prominent

American artist Albert Pinkman Ryder has been initiated. His works are highly

imaginative and "picture the inner reality of the mind and present to us the

purest poetic imagery in the century." Four of the Ryder paintings from NMAA

"Lord Ullin's Daughter", "Christ Appearing to Mary", "Pastoral Scene" and

"Jonah" have been studied by autoradiography to date. Table 1 shows the

neutron activation analysis result of the four paintings studied so far.

155
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Amount per unit area (mg/cni**2) in paintings by Albert P. Ryder

ELEMENT LORD ULLIN'S CHRIST APPEARING PASTORAL JONAH

DAUGHTER TO MARY STUDY

NA SODIUM 0.486 1.101 1.470 1.018

MG MAGNESIUM * * * * AL ALUMINIUM 0.930 2.055 1.667 1.788

CL CHLORINE 0.298 0.508 1.757 0.494

K POTASSIUM 0.106 0.150 0.111 0.505

CA CALCIUM 18.660 5.330 14.805 15.946

SC SCANDIUM TRACE TRACE TRACE TRACE

TI TITANIUM * * * *

V VANADIUM * 0.002 0.003 * CR CHROMINIUM 0.138 0.385 1.296 0.562

MN MANGANESE 0.179 0.108 0.139 0.100

FE IRON 1.257 6.487 6.316 4.722

CO COBALT 0.001 * 0.059 0.125

CU COPPER * 0.089 * * ZN ZINC 2.147 0.824 18.716 12.751

AS ARSENIC 0.006 0.012 0.080 0.028

SE SELENIUM * * 2.159 0.003

BR BROMINE 0.011 0.009 0.025 0.005

SR STRONTIUM 0.030 1.206 1.293 1.214

AG SILVER * * * * CD CADMIUM * * 0.322 0.012

IN INDIUM * TRACE TRACE TRACE

SN TIN * 0.432 0.001 0.001

SB ANTIMONY 0.121 0.012 0.396 0.036

BA BARIUM 0.161 53.538 10.295 8.777

SM SAMARIUM TRACE TRACE TRACE TRACE

AU GOLD 0.001 0.002 0.001 TRACE

HG MERCURY 0.250 0.417 0.254 0.821

U URANIUM * * * *

Elements with "*" are not detected.

We wish to thank Dr. Paul Taylor, Department of Anthropology, National Museum

of Natural History and Dr. Elizabeth Broun, Acting Director, National Museum

of American Art. We also wish to acknowledge Fred Shorten's assistance in

providing the photograph used for figure 1.

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B. NON-RRD PROGRAMS

NEUTRON INTERACTIONS AND DOSIMETRY GROUP

J. A. Grundl

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. Strong 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 88, with emphasis on NBS reactor

related activities, are outlined below in titled paragraphs. Projects that

define the group's activities and major participants are included.

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 including substantial European

participation are an important feature of this project.

1. Neutron Fluence Standards

These unique artifact standards are neutron sensors (activation foils

generally) in which a radioactive species relevant for dosimetry is induced by

irradiation in a standard neutron field. NBS maintains a variety of standard

neutron fields to supply such neutron fluence standards to customers under NBS

Spec. Publ . 250 Calibration Services and to the Nuclear Regulatory Commission

(NRC) under a general consultation contract. These fluence standards provide

benchmark referencing for dosimetry measurement methods used in the nuclear

industry.

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NON-RRD PROGRAMS

137 Of particular interest is the production of 30-year Cs in

238 237 fin fissionable foils of U and Np, and the production of 5.7-year Co in

235

copper by 30-day irradiations in the NBS U Cavity Fission Source at the NBS

reactor. Although long half-lives make these radioactive species difficult to

produce in standard neutron fields, irradiations are carried out at some expense because long half-lives are especially appropriate for long-term

neutron fluence monitoring in power reactors.

2. NBS-Westinghouse Cooperative Agreement

In a move to improve Quality Assurance (QA) methods associated with

dosimetry procedures at commercial power reactors, NBS and Westinghouse have

begun negotiating a cooperative agreement. Under this agreement, NBS will

review the measurement techniques for reactor neutron dosimetry at

Westinghouse to insure that direct measurement links exist with standard

neutron fields at NBS. Westinghouse and NBS personnel have met and agreed

upon important elements of a written agreement. Efforts are already underway

to investigate some measurement discrepancies in power reactor data obtained

with paired uranium detectors (PUD) neutron fluence detectors furnished by

NBS.

3. Dosimetry Benchmarking for the HSST-Program

NBS is helping the NRC benchmark fast neutron dosimetry for an HSST

steel testing program carried out by the Materials Engineering Associates

(MEA) Corporation at the University of Buffalo's Pulstar Reactor. The focus

of this activity is radioactive counting procedures at the Idaho Nuclear

Engineering Laboratory (INEL) where analysis of all dosimetry involved in the

MEA tests are performed. Comparisons of experimental dosimetry with neutron

transport calculations were presented by NBS at the I4th ASTM- ElO Radiation

Effects on Materials Symposium, in Andover, MA in June 1988.

93 93m

4. Fission Spectrum Cross Section of Nb{n,n') Nb

Because of its long half-life (16 years) and a low energy threshold

(1 MeV), the Nb{n,n') reaction is a candidate for long term neutron fluencemonitoring. One drawback has been the lack of adequate cross-section

information. Now, in cooperation with the universities of Illinois and

Arkansas, the spectrum averaged cross sections of the niobium reaction have

158
NON-RRD PROGRAMS

235 252

been measured in the U and Cf standard fission neutron fields at NBS.

Free-field neutron fluences at both irradiation facilities were established by

neutron source emission-rate calibrations at the NBS MnSO. Bath Facility.

5. Benchmark Measurements in Commercial Power Reactors

Efforts continue to benchmark reference neutron dosimetry associated

with fast neutron exposures of critical structures at nuclear power plants.

The benchmark work focuses on both measurement of neutron exposures that cause embrittlement of steel and on the characterization of test reactor neutron

environments used to study embrittlement models.

NBS is assisting the Babcock and Wilcox (B&W) Owner's Group conduct a full power cycle benchmark designed to check a variety of dosimetry methods,

e.g., conventional foil activation versus solid-state track fission-event

recorders. PUDs and lithium fluoride chips gamma sensors, both developed at

NBS, are also included in this comprehensive dosimetry technique comparison.

PERSONNEL DOSIMETRY

R. Schwartz, C. Eisenhauer, J. Coyne, and E. Boswell

Standard neutron fields are developed and applied for calibration of

radiation protection instrumentation and for the investigation and testing of new types of dose measuring techniques. Substantial responsibilities in

national and international dosimetry methods research focuses on tissue dose

modeling and tissue equivalent proportional counter measurements.

1. Calibration Service

Approximately 40 neutron radiation protection instruments were calibrated this year, the majority of them for nuclear power plants. The

remotely operated detector positioner continues to operate well, minimizing

exposure to personnel, speeding up data taking, and improving accuracy.

2. Performance Tests of Radiation Protection Instrumentation

In a joint project involving Harwell and the National Physical

Laboratory in England, and the Naval Surface Warfare Center and Naval Research

Laboratory in the United States, the properties of the new Chalk River "Bubble

159
NON-RRD PROGRAMS

Damage Detector" were investigated. The results of this work were sufficiently promising that this collaboration will continue under the auspices of the

Naval Medical Command.

In an effort to understand the cause of the persistent slow drift in

the 9" remmeters commonly used for neutron radiation protection measurements,

a detailed study was made of the behavior of the 3BF proportional counters

used as neutron detectors in these instruments. It was discovered that the

drift is caused by an unfortunate combination of the somewhat unstable

electronics in the remmeter instrument package, and the abysmal performance of

the proportional counter. A' good counter (readily available from other

manufacturers) would eliminate the problem.

3. Tissue Equivalent Proportional Counter (TEPC) Studies

In a joint program with PTB and the University of Saarlands, a detailed

study was made of the behavior of various configurations of TEPC's in the NBS

filtered neutron beams. The purpose of this investigation was to learn how to

improve the response of TEPC-based remmeters in the keV-to-100 keV neutron

energy range. These types of remmeters are under active development at

several laboratories in the United States and in Europe. It is recognized,

however, that their performance needs to be improved in the energy region made

accessible by our filtered beams. An immediate result of this study showed

that the neutron dose due to contaminants in the beams as measured by the TEPC

3 was in agreement with the predictions based on NBS He and proton recoil

spectroscopy. This work also demonstrated that the NBS filtered beams are, by

a yery significant margin, purer and of higher intensity than those available

elsewhere.

4. International Standards Writing

The ISO Draft Standard Proposal, "Procedures for Calibrating and

Determining the Energy Response of Neutron Measuring Devices Used for

Radiation Protection," has been completely rewritten although further changes

will have to be made. A draft of the chapter on calibrations, for the

forthcoming ICRU publication "Determining of Dose Equivalents from External

Radiation Sources - Part 3," has also been completed.

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NON-RRD PROGRAMS

5. Data Acquisition Systems

The three Datacraft computers used for data acquisition at the linac

and the 3-MV positive-ion accelerator for the past 13 years have been

replaced. The new system consists of a Charles River Data System UV2403FT

computer, MIZAR MZ9400 computer, and AST Research Inc. Premium/286 computer

connected by a high speed local area network. The system is operational but

will require some additional programming efforts.

RESEARCH AND TECHNOLOGY ASSISTANCE

all group members

Research activities and technology assistance are strongly coupled

especially in neutron dosimetry. A multiplicity of institutional involvements, drawn to the group by unique irradiation facilities and measurement

capabilities, encourages a variety of attractive projects and unavoidable

responsibilities.

1. Neutron Lifetime Measurement

In collaboration with scientists of the Quantum Metrology Division, the

University of Sussex, and the Central Bureau for Nuclear Measurements, an ambitious experimental program has been undertaken to improve previous

measurements of the free neutron lifetime. The half-life for this most

fundamental example of nuclidic disintegration is known to an accuracy of only

± 2.5%, while the half-lives of less stable particles such as the pion and the muon are known as much as 1400 times more accurately. The first lifetime data

from this collaboration are expected between late August and early December

1988 from measurements at the Institut Laue-Langevin cold neutron guidehall in

Grenoble, France. The experiment will next move to the new cold neutron

guidehall at NBS for more exhaustive measurements. The group so far has

carried out the absolute efficiency calibration of the B neutron density

monitor and will improve this calibration by means of a total absorption

detector and an alpha-gamma coincidence calibration scheme. Group personnel

also have participated in the Grenoble measurements.

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NON-RRD PROGRAMS

2. Capture Cross-Section Measurement in ISNF

Spectrum-averaged cross sections for six reactions of interest in

reactor physics have been measured in the Intermediate Energy Standard Neutron

Field (ISNF). The ISNF neutron energy spectrum resembles a fast reactor

spectrum, but with much less complexity. The ISNF neutron fluence is

252 determined by fluence transfer from a calibrated Cf fission source. The

following spectrum-averaged cross sections were reported this year:

^^Na(n,7) = 1.57 ± ,10 mb, ^^Sc{n,7) = 24.4 ± 0.8 mb, ^^Co(n,7) = 36.3 ± 1.5

mb, ^°^Ag(n,7) = 23.8 ± 0.9 mb, ^^^In(n,n') = 97.0 ± 2.5 mb, and ^^^Au{n,7) =

11 mb.

3. Fission Chamber Monitors at AFRRI

Neutron dosimetry at the Armed Forces Radiobiological Research

Institute's reactor exposure room was put on a more ;table basis by the

installation and testing of two fission chamber monitors. The AFRRI staff has

learned to operate these monitors confidently and have found them useful in

resolving conflicting readings among other dosimetry systems. Linearity tests

of reactor instrumentation, vs. NBS absolute fission chambers and tissueequivalent ionization chambers were carried out over the full range of reactor

power for the three most commonly used irradiation configurations.

4. Reactor Beam Calibrations

Absolute fission chambers and fissionable isotope mass standards were employed to determine absolute neutron fluence rates and improvement in the

"capture flux" resulting from installation of the Cold Source at the NBS

Research Reactor. These results influenced plans for further upgrading of the

Cold Source.

5. Mass Assay of Ultra-Light Fissionable Deposits

Westinghouse Research Center, Pittsburgh is working cooperatively with

NBS to establish mass scales for ultra-light fissionable deposits. These

deposits, with masses in the picogram or sub-picogram range, are used with

mica Solid Track Recorders (SSTR's) and represent a significant new dosimetry

measurement technique. Currently achieved accuracy is better than 5%, the

goal is 3% or better.

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NON-RRD PROGRAMS

6. Paired Uranium Detectors (PUDs)

In 1984, PUDs were provided to Westinghouse Nuclear Technology Systems

Division as backup dosimetry for ultra-lightweight SSTR neutron dosimeters.

These dosimeters have been recovered and analyzed after an 18-month exposure

in the Diablo Canyon power reactor. The results show a presently unexplained

15% discrepancy between the PUDs and SSTRs. NBS will now re- irradiate several

235

of the PUD/SSTR pairs in a carefully controlled experiment in the NBS U standard neutron field in an attempt to resolve the discrepancy.

7. LiF Chip Development and Application

A lithium fluoride crystal dosimeter package was returned to NBS after

irradiation through a full fuel cycle in the cavity surrounding the reactor

vessel at the Oconee 2 nuclear power plant. The sample retained virtually

perfect optical quality, despite the heat and humidity of the environment.

The gamma dose recorded was comfortably within the accurately readable range.

This gamma dose data will be employed by the operating utility to confirm

calculations of gamma and neutron dose as they affect the reactor vessel

embrittlement and safe operating lifetime.

IRRADIATION AND CALIBRATION FACILITIES

E. D. McGarry, J. Grundl , C. Eisenhauer, and E. Boswell

Well -characterized neutron fields are built and maintained as permanent

irradiation facilities providing certified fluences of pure fission neutrons,

sub-MeV distributions, monoenergetic keV beams, and thermal neutrons. Passive

and active detectors of all kinds are exposed in these neutron fields for

response calibrations, for cross-section measurements, and for the investigation of new measurement techniques. A high intensity, neutron-driven gamma

field operates for special purpose measurements.

A multi-purpose fission rate measurement capability is centered around

the NBS "go anywhere" double fission chambers and the NBS 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 NBS

are derived from source strength calibrations at this facility.

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NON-RRD PROGRAMS

1. Cavity Fission Source Operations

Efforts to improve cavity fission source operations and calibration

base documentation are continuing. A new general purpose shield cave for high

and intermediate level radioactive components has been designed and shopwork

on the shield walls has begun. When complete, this shield cave will greatly

simplify irradiation operations at the reactor thermal column. New documentation describing the complicated path by which absolute fission neutron fluence

rates are established are in final draft stage.

2. Scattering Corrections in the Cavity Fission Source

Corrections for neutron scattering in the hardware and irradiation

samples of the cavity fission source are under review. Existing corrections

are based on Monte Carlo calculations made by Los Alamos National Laboratory

(LANL) for an earlier configuration of the cavity fission source with a different Cd box and Al enclosure. Furthermore, recent calibrations of solid

state track recorders (SSTR's) involve a significantly different irradiation

sample assembly. Recalculation of neutron scattering with the MCNP Monte

Carlo code has yielded corrections for scattering in SSTR's that differ from

the one calculated by LANL. We, therefore, recalculated scattering corrections with the MCNP Monte Carlo code. Corrections for scattering for SSTR's

235

vary from - .006 for Ni reactors to + .018 for U fissionable deposits.

NUCLEAR HETHODS GROUP: OVERVIEW

R. F. Fleming

(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

reactor-based activation analysis, which includes instrumental and radiochemical neutron activation analysis (INAA and RNAA) , as well as fast neutron

activation analysis (FNAA). In addition, the group has a unique capability in

neutron beam analysis with both prompt gamma activation analysis (PGAA) and

neutron depth profiling (NOP). The NOP technique utilizes prompt charged

particle emission to determine elemental distributions within the first few

micrometers 'Of a surface while the PGAA technique utilizes prompt gamma-ray

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NON-RRD PROGRAMS

emission to measure the total amount of an element in a sample, regardless of

its distribution. These techniques provide an arsenal of tools to address a wide variety of analytical problems in science and technology.

The activities of the past year have been highlighted by the initiation

of the National Facility for Cold Neutron Research to be established at NBS

during FY 89. The Group's involvement includes the design and construction of

second generation instruments for PGAA and NOP. In addition, a facility is

envisioned at which we will study the techniques for focusing neutron beams to

increase the neutron intensity on a point. The combination of intense

focussed beams applied to the existing analytical methods could result in

greatly enhanced measurement capability. During FY 88 the cold source itself

was installed and became operational, and construction of the guide hall will

be completed during the the first quarter of FY 89. The Group's efforts have

been aided substantially by its ability to use the existing cold neutron beams

at the KFA JUlich facility. Plans are underway to include both the PGAA and

NDP experimental systems in the first phase of implementation. A major grant

from the Eastman Kodak Company is contributing to the timely development of

NDP using cold neutrons.

The Group's contribution to the certification of Standard Reference

Materials is illustrated by the multi -element measurements done on the SRM

Bovine Serum, Buffalo River Sediment, and glass-film XRF standards. Work has

been initiated on the new Orchard Leaves, Total Diet, Oyster Tissue, and a carbonaceous marine sediment, with Group members serving as the Technical

Champion on each of these new SRM's. A new ability to quantify nitrogen in

biological samples will result from this year's research to develop an NAAliquid scintillation beta counting method exploiting the thermal neutron

reaction 14N(n,p)14C and measuring the radioactive COp. This project is being

done in collaboration with the University of Illinois.

The Group has taken an active role in the Bureau's program on hightemperature superconductivity, both in the measurement of impurities in

starting materials and in final products, and in the determination of the

actual stoichiometry of the metallic constituents. The effort this year has

been in the development of accurate, rapid measurements of these materials by

both NAA and PGAA.

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NON-RRD PROGRAMS

The Biomonitoring Specimen Bank Research Project continued its support for

other agencies' monitoring programs. These included the EPA human liver

project, the NOAA National Status and Trends program, the NCI Micronutrient

program, the lAEA/NBS/FDA/USDA Total Diet Study, and most recently, the NOAA

Alaska Marine Mammal Project. Research has centered on banking protocols and

improved analytical methodology. Our participation in intercalibration

exercises with the project participants and the development of marine QA

materials helped enhance the quality of the analytical results used in the

assessment of the Nation's environmental health. Of major importance this

year has been the completion of the reanalysis of 30 livers each from the 1982

and 1984 collections to quantify the stability of key elements under the

carefully controlled storage conditions.

Bioanalytical research focused on the determination of metal species in

various materials. Elements at trace and ultratrace levels have been

determined in separated proteins and other macromolecules. The use of

autoradiography to determine selenium has been added to the INAA and RNAA

techniques. The occurrence of inorganic and organic compounds of tin in

marine tissues is also being studied.

The strong interaction with industrial scientists using neutron depth

profiling, prompt gamma activation analysis, and neutron activation analysis

has continued with a growing number of guest workers, research associates, and

joint publications. An important development this year has been the demonstration of two-parameter, coincidence spectroscopy for thin samples in

collaboration with the group under Professor W.-K. Chu at the University of

North Carolina and with Eastman Kodak. For appropriate samples this technique

will increase the measurement sensitivity equivalent to a ten-fold increase in

reactor neutron flux. The measurement of distributions of lithium and boron

in metals, glasses, and polymers continues to produce important results.

The joint NBS/FDA/USDA study of trace elements in human diet, sponsored

by the International Atomic Energy Agency, has completed its fourth year. A

total of 40 minor and trace elements have been measured on the U.S. total diet

material collected from several regions. In addition, measurements have been

carried out on selected elements in diets recei^ved from countries participating in this global study. A candidate total diet material prepared in

cooperation with OSRM is being evaluated as an elemental standard.

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NON-RRD PROGRAMS

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 the various sources of

random and systematic errors in analysis by nuclear methods.

Particular attention will be paid to count rate dependent effects, gamma

ray self-absorption, detector efficiency calibration, and monitor activation

analysis. Maintaining full accuracy at high count rates using current

generation data aquisition 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.

MEASUREMENT OF SUPERCONDUCTOR STOICHIOMETRY BY NEUTRON ACTIVATION

R. M. Lindstrom and R. F. Fleming

(Inorganic Analytical Research Division)

Prompt and delayed neutron activation analysis have been applied to the

nondestructive measurement of the major metals in small samples of YBa2Cu20y

superconductors, starting materials, and intermediate products. The small

activation cross section and low gamma ray energies of Y-90m make the determination of yttrium imprecise in the presence of the large quantities of Cu-64

radioactivity. The physical parameters for neutron-capture prompt gamma-ray

activation analysis (PGAA) are more attractive than delayed counting for

stoichiometry measurements. The PGAA spectra of Y, Ba, and Cu show three,

four, and six analytically useful gamma ray lines respectively, with nicely

balanced intensities for the composition range of interest. A 100-mg sample

gives a Poisson precision for yttrium (the weakest element) of 2% after only a 2-hour irradiation. Since the concentrations and atom ratios Y/Cu and Ba/Cu

may be calculated immediately after the irradiation ends, the results can be

returned within a day.

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Atom Ratios in Superconductors and Unfired Precursors

Sample Y/Cu Ba/Cu Sum

Superconductors

S3C 0.360 ± 0.007 0.711 ± 0.007 1.071 ± 0.031

(2.7%) (1.0%) (2.9%)

S4C 0.346 ± 0.007 0.826 ± 0.014 1.172 ± 0.031

(2.0%) (1.7%) (2.6%)

B7C 0.331 ± 0.006 0.705 ± 0.014 1.036 ± 0.015

(1.9%) (2.0%) (1.5%)

Precursors

P3C 0.367 ± 0.011 0.737 ± 0.015 1.104 ± 0.019

(3.1%) (2.1%) (1.7%)

P4D 0.334 ± 0.006 0.777 ± 0.012 1.111 ± 0.012

(1.7%) (1.6%) (1.3%)

Compositional measurements of substituted superconductors have been

made in collaboration with the neutron scattering group. In these materials

nominally 3-8% of the Cu had been substituted by Al , Fe, Ni, Zn, or 6a.

Classical delayed activation analysis was used to measure the substituent and

copper. An example is Fe-substituted 1:2:3 ^^^2^^"l-v'^^v^3^7-x' ^^^^^ nominally y = 0.08. The sample was analyzed for three elements:

Element g/g sample

Cu 0.238 ± 0.012

Ba 0.414 ± 0.024

Fe 0.0285 ± 0.0005

From the chemical formula,

atoms Fe / atoms Ba = 0.169 ± 0.010 = 3y / 2 atoms Fe / atoms Cu = 0.136 ± 0.007 = y / (1-y)

from which we have two measurements of the value of y:

y(Fe/Ba) = 0.115 ± 0.007

y(Fe/Cu) = 0.120 ± 0.007, which agree within errors

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In other samples the M/Cu ratios were not always found to be as expected:

"8% Al": Al/Cu = 0.0872 ± 0.0025

"8% Ni": Ni/Cu = 0.0880 ± 0.0018

"3% Ni": Ni/Cu = 0.0308 ± 0.0012

"6% Zn": Zn/Cu = 0.0654 ± 0.0015

"8% Ga": Ga/Cu = 0.00024 ± 0.00002

Al/Cu = 0.0872 ± 0.0014

DETERMINATION OF AS, CD, CR AND NO IN THE NBS BOVINE

SERUM STANDARD REFERENCE MATERIAL AT THE PPB LEVEL

R. R. Greenberg, R. Zeisler, and T. M. Sullivan

(Center for Analytical Chemistry)

As bioanalytical methods for trace element determinations have become

more sensitive, biological and medical trace element research has included

studies of many of the "difficult" elements such as Al , As, Cd, Cr, Mo, Mn, Sb

and V. These elements are currently of interest, for example, in human blood- serum where they typically occur at the low ng/g level or below. The accurate

determination of trace elements at these levels usually requires certified

reference materials for method evaluation, and for quality assurance purposes.

This need for low-level reference materials for accurate analyses of humanblood serum and related materials has been well documented. To help meet this

need the National Bureau of Standards and the Department of Agriculture have

cooperated in the production and certification of a frozen. Bovine Serum

Standard Reference Material (SRM) with uncontaminated, or nearly

uncontaminated levels of a wide variety of trace elements.

The certification of trace elements in this Bovine Serum (SRM 1598) was particularly difficult due to the very low levels on many of the elements of

interest. A variety of analytical techniques has been used at NBS for the

Bovine Serum certification. For several of these techniques, an extension of

procedures beyond previously demonstrated measurement competence has been

required. One of these analytical techniques, neutron activation analysis

(NAA), was able to determine the concentrations of most of the elements

desired for certification. In addition to the instrumental measurements made,

a number of the difficult, low-level elements have been determined with appropriate pre- or post-irradiation chemical separations.

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Two radiochemical separations have been used to reduce interferences from

matrix activities such as from Na, Br and P, or in some cases to totally

isolate the element of interest from essentially all other radionuclides.

Post-irradiation separations are particularly useful for low-level determinations since no reagent blank has to be considered. Arsenic, along with

Mo, has been determined using the inorganic ion exchanger HMD, and Cd along

with Cu, have been determined in the eluent from the same samples using

sequential extractions into solutions of bismuth and zinc

diethyldithicarbamates in chloroform. This previously-developed procedure has

been modified to include a predigestion step using a microwave oven. Dissolution was then completed with nitric and perchloric acids in a conventional manner (on a hot plate). The predigestion step allowed complete

sample decomposition in two to three hours instead of the two days previously

required to insure complete destruction of the organic sample matrix. This

reduction in sample decay time improved the signal (number of counts) for As

and Cd by factors of four and two respectively, and resulted in a comparable

improvement in the detection limits. Arsenic and Cd were observed in the

Bovine Serum at 0.15 and 0.093 ng/g respectively, while Mo was present at 11

ng/g.

Chromium has been also determined in an the Bovine Serum SRM following a post-irradiation extraction of Cr (VI) into a solution of tribenzylamine in

chloroform. This newly developed procedure has also been applied to human

blood and blood fractions, and is described elsewhere in this report. The Cr

concentration in the Bovine Serum was 0.18 ng/g.

In addition to the elements determined after a radiochemical separation,

three other biologically-important elements, Al , Mn and V, which are present

at ng/g and sub-ng/g levels, have been determined previously in this material

utilizing NAA combined with a pre-irradiation, chemical separation. These

results, when combined with the results from other analytical techniques, will

allow the certification of many of these difficult elements in a natural

matrix material. The new Bovine Serum SRM should be of great value for method

development, and for quality assurance purposes, when researchers analyze

blood-serum or related materials.

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MEASUREMENT OF CHROMIUM IN HUMAN BLOOD AND BLOOD FRACTIONS AT

NATURAL (SUB-PPB) LEVELS

R. R. Greenberg and R. Zeisler

(Center for Analytical Chemistry)

Chromium was recognized as one of the elements essential for humans more

than twenty-five years ago. However, at elevated concentrations, some forms

of Cr are toxic and possibly even carcinogenic. In recent years, several

analytical techniques have demonstrated the capability to accurately determine

chromium at the naturally-occurring, ultratrace-levels normally found in

uncontaminated samples of human serum. A variety of problems, however, have

limited the determination of Cr to this single fraction of human blood. In view of the importance of this element, more detailed investigations of its occurrence and role at natural levels are needed, requiring even more sensitive analytical methods.

A reliable radiochemical procedure for Cr has been developed based upon

neutron activation followed by a radiochemical separation. The separation

procedure involves the liquid/liquid extraction of Cr(VI) into a 5% solution

of tri benzyl ami ne/chloroform, back-extraction into an aqueous solution (2

mol/L) of sodium hydroxide and precipitation as barium chromate.

Radiochemical neutron activation analysis (RNAA) is one of the best analytical

techniques currently available for trace and ultratrace level determination of

Cr in biological materials. It possesses the sensitivity required to

determine sub-manogram amounts of Cr, and the nearly blank-free nature of the

technique allows chemical dissolution and separation of Cr from the sample

matrix (after irradiation) without regard to reagent blank. In addition, NAA

is free from chemical interferences, and most types of matrix effects which

can interfere with other, non-nuclear, analytical techniques. However, the

nuclear interference from the fast neutron reaction Fe-54(n, alpha)Cr-51, can

be significant. This interference can be minimized, however, by using a highly thermal ized facility such as the RT-4 facility of the NBS Research

Reactor. In this facility, the measured Fe interference is 0.087 /zg of Cr per

gram of Fe, or approximately two orders of magnitude lower than at a typical

light water reactor. The RT-4 interference is equivalent to a Cr blank of

0.039 ng of Cr per gram of whole blood for men, and 0.035 ng/g for women. Chromium concentrations have been determined in whole-blood samples from

nine individuals, and are listed in table 1. The Cr concentrations for eight

171
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of these people were between 0.04 and 0.3 ng/g on a fresh weight basis. The

ninth individual had a considerably higher level of Cr, and this is discussed

below. Serum samples have been analyzed from seven of these individuals, and

packed cells for two. Duplicate samples from a single collection have been run for the whole blood from one person and for the serum from a second. Both

duplicate values are consistent with the observed counting statistics. In addition, blood from these two individuals has been sampled on two occasions

more than one year apart. No differences in the Cr concentrations, above the

analytical uncertainties, can be seen for subject B2 with time. A small, but

real, increase in both the whole blood and serum Cr levels from 81 was observed. It should be noted that between the 1986 and 1987 sample

collections, individual Bl was taking a daily dietary-supplement containing

200 fig of Cr in the form of an amino-acid chelate, while no supplement was taken prior to the 1986 collection. This factor of five increase in Cr

intake, compared to the average American dietary intake of approximately 40%

in the blood, and 90% in the serum. Since serum accounts for approximately

50% by weight, of whole blood in men, there appears to be no change in the Cr

concentration in the packed cells of this individual. Thus the large increase

in dietary Cr had only a relatively small effect, elevating the serum level

for Bl from the second lowest concentration observed in this study, to the

median value. Thus, at least for this individual, Cr levels in the blood may

be under some type of bioregulatory mechanism.

An interesting observation can be made concerning individual T2. This

person had concentrations of Cr in both whole blood and serum which were elevated by factors of 5-10 compared to the other individuals studied.

Subsequent questioning revealed that this person has been diagnosed as a borderline diabetic, and has a family history of diabetes (mother). In view

of the possible link between Cr and glucose metabolism, further studies of the

Cr concentrations in whole blood and blood fractions from diabetics may be

indicated. However, in view of the difficulty of accurate Cr determinations,

at the naturally occurring levels in these materials, carefully validated

analytical methods, and rigorous quality assurance procedures should be used

for these studies.

172
Bl Male 3/86 159 ± 0.023

Bl Male 3/86 160 ± 0.016

Bl Male 9/87 226 ± 0.027

NON-RRD PROGRAMS

Table 1. Chromium concentrations (ng/g) determined in human whole-blood,

blood-serum, and packed cells (corrected for Fe interference)

Sample

Subject Date Whole Blood Blood Serum Packed Cells

. 102 ± 0.012

0. 193 ± 0.021

B2 Female 3/86 0.273 ±0.019 0.378 ±0.024

B2 Female 3/86 0.445 ±0.044

B2 Female 9/87 0.292 ±0.043 0.454 ±0.044

Ml Female 3/86 0.148 ±0.019 0.117 ±0.015

Tl Male 3/86 0.340 ±0.018

Dl Male 3/86 0.150 ±0.016 0.182 ±0.027

Wl Male 3/86 0.119 ±0.025

Jl Male 9/87 0.280 ±0.036 0.258 ±0.038 0.185 ±0.027

Rl Male 9/87 0.038 ±0.014 0.077 ±0.010

T2 Female 9/87 1.286 ±0.048 1.743 ±0.042 0.765 ±0.058

Notes : 1. Concentrations are in ng/g, on a fresh weight basis.

2. Uncertainties are 1 sigma counting statistics.

3. Fe interferences applied for Cr:

Whole blood (men) - 0.039 ng/g

Whole blood (women) - 0.035 ng/g

Packed cells (both) - 0.082 ng/g

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NEUTRON ACTIVATION ANALYSIS OF MAJOR, MINOR, AND TRACE ELEMENTS

IN MARINE SEDIMENTS

S. F. Stone, R. Zeisler, and B. J. Koster

(Center for Analytical Chemistry)

Neutron Activation Analysis (NAA) techniques are well established in

the multi -element assay of geological materials. Similarly, applications of

NAA to the analysis of marine sediments have been described. However, the

different emphasis on elemental composition in studying and monitoring the

health of the environment presents a new challenge to the analyst. To

investigate as many elements as possible, previous multi-element procedures

need to be re-evaluated and modified. In this work, we have utilized the NAA

steps of a recently developed sequential analysis procedure [1] that obtained

concentration for 45 biological and pollutant elements in marine bivalves.

This procedure, with modification, was applied to samples or marine sediments

collected for the National Oceanic and Atmospheric Administration (NOAA)

National Status and Trends (NS&T) specimen banking program [2].

Duplicate samples of bottom sediments from more than 80 sites were collected and banked as part of the NS&T program during 1985-1987. Each

sample consisted of a combination of aliquots from three stations per site.

Each sample was obtained from a box core or grab sampler using a cylindrical

Teflon corer. The top 3 cm of each core (approximately 50 g) were combined in

a clean Teflon bag, or in later samples, in a clean Teflon jar. Two replicate

station aliquots were taken to obtain two similar site samples of about 150 g each. The samples were sealed and stored in liquid nitrogen vapor freezers.

Samples selected for analysis were removed from cryogenic storage,

thawed, and thoroughly mixed in their Teflon containers. After mixing, the

samples were freeze-dried at -10 °C. The samples were ground/mixed using

Teflon balls in Teflon jars and a Spex Mixer/Mill. Pellets were prepared for

analysis with a Perkin-Elmer pellet press from the dry, homogenized material.

Neutron activation techniques were applied in sequence in order to

obtain as much information as possible on the elemental composition of each

sample. The samples were analyzed by either epithermal neutron activation

analysis followed by thermal neutron activation analysis (NAA) or prompt gamma

activation analysis (PGAA) followed by thermal NAA. The epithermal NAA

irradiations were done at the University of Maryland reactor in College Park.

Samples were irradiated inside boron nitride capsules at a fluence rate of

174
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16 -? -

1

2.1 • 10 n • m' • s" for 120 seconds. The National Bureau of Standards

Research Reactor was used for the PGAA and thermal NAA irradiations, at

12 -2 -1

fluence rates of 3.5 • 10 n • m • s for several hours and

17 -2 -1

2.8 • 10 n • m • s for 60 seconds and 8 hours, respectively.

Eighteen selected samples from 3 years of collection, 1985-1987, were

analyzed. These samples represent both "clean" reference and presumed

"contaminated" sites. A concentration profile from one site, MW2S138, Marina

del Rey, CA, is shown in figure 1. Concentrations for 43 elements over nine

orders of magnitude were obtained by PGAA and thermal NAA. A comparison of

the concentrations of two pollutant elements for all investigated sites is

given in figure 2. In addition, the Certified Reference Material (CRM)

Sediment SD-N-1/2 from the International Atomic Energy Agency was analyzed

using the combination of PGAA and thermal NAA. The results are shown in

table 1. Good agreement with certified values can be seen for most elements,

with the differences between the techniques dependent on counting statistics.

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Concentration in mg/kg

s

B

3

H

BNa

Mg

Al

SIS

CIK

Ca

Sc

Tl

V

Cr

Mn

Fe

Co

Cu

Zn As

Se

Rb

Sr

(Mo)

Ag

Cd

(Sn)

Sb

I Cs

Ba

LaCe

Sm

EuGd

Tb

Hf

Ta

Au

Hg

Th

(U)

^^^^^^^^^^^^^^^^^^^^^^^^^^^^

P^^K^J^^SJS^^^S^^V.^^-? "\Vn\v~'

• ^^^^^^^^'^^^^s^

Figure 1. Concentration profile for MW2S138, Marina del Rey, California,

Concentrations in mg/Kg, dry weight; (parentheses) indicates limitof-detection.

176
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Concentration in nig/kg

o

Elliott Bay

Nisqually Reach

Marina Del Rey

Newport Bay

Dana Point

Imperial Beach

Corpus Christi

Matagorda Bay

Galveston Bay

Mobile Bay

Mississippi River Delta

Pascagoula Bay

Charleston Harbor

Baltimore Harbor

Chesapeal(e Bay

Delaware Bay

Dorchester Bay

HIngham Bay

-1 o

1 1 c> «

n

n"1

hs^^j5jj^^j5?5j^<^^

-1 !

1 1

J i

1J i

J 3

1

1

1

J !

1

J i

1 1

J i \^$$$$$$$^^^i$$^$$$$^$^^m^a^ J ". h$$$^^^$^^$$S$$f$$^:^^^^^^BH

J- \

1 1

J - i

J\^^^^^$$^^^^^^m 3

$$$$:^$$$^S$$$$J$$??^^

>

J ! i — 1 1

^J^j^?$^?$?$?$§$SS$§$$^^

J 1 ' 1

J ?

J

... ^ l^:§$$$S$^$$$^HHBHH^H^H

Figure 2. Comparison of Cr and As concentrations for 18 selected sediment

samples. Concentrations in mg/Kg, dry weight.

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Table 1. Results for IAEA/SEDIMENT SD-N-1/2

PGAA INAA Certified (information*)

H % 1.257 ± 0.050

B 87.7±1 .5 N % 2.3 ± 1.3 Na % 0.62 ± 0.25 1.105 ± 0.010 1.04 (1.03 - 1.07)*

Mg % 0.86 ± 0.19 0.76 (0.74 - 0.79)*

Al % 2.52 ± 0.28 3.69 ± 0.03 3.75 (3.58 3.85)*

Si % 27.22 ± 0.93 28.05 (26.10 - 29.23)*

S 4100 ± 1200

CI 9290 ± 140 9840 ± 530 9040 (9040 - 9600)*

K % 1.522 i: 0.058 1.47 ± 0.16 1.54 (1.46 - 1.66)*

Ca % 5.03 ± 0.50 5.98 ± 0.19 5.32 (5.12 - 5.60)*

' Sc 6.87 ± 0.06 7.10 (6.90 - 7.21)

Ti % 0.272 i: 0.002 0.293 ± 0.003 0.27 (0.24 - 0.31)*

V 77 ± 3 77.7 (65.0 80.7)

Cr 145 ± 16 149 (125 - 161)

Mn 850 ± 260 850 ± 13 777 (728 - 801)

Fe % 3.32 ± 0.20 3.69 ± 0.31 3.64 (3.53 - 3.78)*

Co 11.55±0.05 12.1 (11.2 12.7)

Cu < 100 72.7 (68.1 - 75.2)

Zn 443 ± 6 439 (423 - 452)

As 56.3 ±0.4 50.0 (42.4 - 60.0)

Se 1.40 ± 0.25 2.90 (2.30 - 3.78)*

Rb 69.7 ±2.2 74.2 (68.6 - 77.0)

Sr 303 ±6 291 (277 - 303)

Mo <5.6 1.49 (1.30 - 2.60)*

Ag 1.80 ± 0.15 2.3 (2.0 3.2)

Cd 12.3 ± 0.49 8.11 ± 1.3 11.0 (10.0 - 12.0)

Sn <60

Sb

1 3.79 ± 0.0422 ± 5

3.62 (3.20 - 3.95)

20.5 (20.5 - 22.1)*

Cs 4.15 ± 0.06 4.9 (4.1 - 5.4)

Ba 292 ± 5 289 (276 - 310)

La 29.9 ±0.3 31.9 (30.0 - 35.5)

Ce 54.4 ± 0.6 60.3 (58.2 - 65.0)

Sm 5.52 ± 0.33 5.72 ± 0.12 5.58 (5.40 - 6.35)

Eu 1.132 ± 0.012 1.16 (1.12 - 1.30)

Gd 5.90 ± 0.45

Tb 0.681 ± 0.021 0.86 (0.80 - 0.92)

Hf 8.61 ± 0.07 8.40 (7.45 - 8.77)*

Ta 1.03 ± 0.03 1.10 (0.83 - 1.20)*

Au 0.0307 ± 0.0012 0.04 (0.03 - 0.04)*

Hg 3.50 ± 0.18 1.46 (0.06 - 1.72)*

Th 6.47 ± 0.06 7.04 (6.85 7.20)

U <1.0 2.41 (2.29 - 2.53)

Concentrations in mg/kg unless otherwise noted

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References

[1] R. Zeisler, S. F. Stone, and R. W. Sanders, Anal. Chem. (submitted).

[2] G. G. Lauenstein, M. M. Schantz, S. A. Wise, and R. Zeisler, "Specimen

Banking in the National Status and Trends Program: Development of

Protocols and First Year Results," Oceans '86 Conference Record, IEEE, New

York, N.Y., 586 (1986).

This work was supported in part by the Oceans Assessment Division, National

Oceanic and Atmospheric Administration. The authors wish to acknowledge the

assistance of Donald A. Becker and Manoranjani P. M. Tillekeratne in the

epi thermal NAA.

DETERMINATION OF TRACE ELEMENTS IN U.S. DIETS

V. Iyengar

(Center for Analytical Chemistry)

An international project sponsored by the International Atomic Energy

Agency (IAEA), and supported by the National Bureau of Standards (NBS), the

U.S. Food and Drug Administration (FDA) and the U.S. Department of Agriculture

(USDA) is in progress. This study is designed to assess the daily dietary

intake of certain dietary components by selected target populations in several

countries. The countries involved are Australia, Brazil, China, Iran, Italy,

Spain, Sudan, Sweden, Thailand, Turkey and the United States. Mixed total

diets from these countries are being analyzed for caloric energy, phytate and

fiber content, and minor and trace elements. Analysis for these constituents

are being carried out in selected reference laboratories identified by the

IAEA. The NBS is one such reference center to determine a select group of

inorganic elements.

The U.S. efforts involve both as a collection center and as a reference

laboratory. A part of the study was concerned with evaluating analytical

approaches. Mainly neutron activation analysis was used in both the

instrumental and radiochemical modes. Guidelines were developed for the

preparation of mixed diet reference standards for quality control, and one material (Mixed Diet SRM 1548) is currently being characterized for

certification. Simultaneously, collection of U.S. mixed diets based on the

FDA Total Diet Study scheme was initiated. Until now six such collections

have been completed from the following regions: Southeast (GA, TX, WV), North

Central (lA, KS, OH), Northeast (NY, PA, RI), South (AL, LA, TX), West (AZ,

CA, OR) and Central (IL, IN, WI). One portion of mixed diet from each of the

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six collections has been stored in the Specimen Bank. Studies are also in

progress to assess long-term stability of organic nutrients in mixed diets

under different storage conditions [1-61.

Five of these diets have already been analyzed for vitamins, fiber,

phytate and several minor and trace elements. Neutron activation analysis

(instrumental and radiochemical) has been extensively used as a multielement

analysis tool. The results obtained for several elements show remarkable

agreement with the daily intake data calculated from the individual food

analysis results of FDA-TDS study, confirming the validity of the mixed diet

approach for monitoring the daily intake of minor and trace elements. The

results did not indicate any significant inter-regional variations in the

overall daily intake. This is attributable to the fact that these U.S.

collections represent national diets due to standardized collection procedures

of the TDS scheme. In the present study, analytical results obtained for over

30 elements for the mixed diet samples provide a basis for establishing

baseline values for the daily dietary intake of a number of elements that are not covered by the FDA-TDS scheme.

References

[11 G. V. Iyengar, Trans Am. Nucl . Soc. 56» 233-34 (1988).

[2] G. V. Iyengar, J. T. Tanner, W. R. Wolf, and R. Zeisler, J. Res. Natl.

Bur. Stand. (U.S.) 93, 360-362 (1988).

[3] G. V. Iyengar, Clin. Nutr. 6, 105-117 (1987).

[41 G. V. Iyengar, Clin. Nutr. 6, 143-153 (1987).

[5] G. V. Iyengar, Clin. Nutr. 6, 156-158 (1987).

[6] G. V. Iyengar, J. Jones, K. Cook, J. Tanner, and W. Wolf, Trans. Am.

Nucl. Soc. 55, 177-178 (1987).

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ATTfOSPHERIC AND ENVIRONMENTAL STUDIES BY INSTRUMENTAL AND

NEUTRON-CAPTURE PROMPT r-RAY ACTIVATION ANALYSIS

G. E. Gordon and J. M. Ondov

(Department of Chemistry and Biochemistry, University of Maryland,)

We continue to make extensive use of instrumental neutron activation

analysis (INAA) and neutron-capture prompt r-ray activation analysis (PGAA)

for continued 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." Examples of these studies are briefly discussed in the

following sections.

1. Mauna Loa Observatory Studies

Since 1979, our group has collected airborne particle samples at Mauna

Loa Observatory (MLO) on the island of Hawaii, as a part of the research

program on remote area aerosols initiated by Prof. W. H. Zoller, now at the

University of Washington. The MLO samples from February 1979 through January

1983 were collected and analyzed by J. R. Parrington [1]. Diane Hermann took over the project at that point and recently reported results through May 1985

in her thesis. There are several differences between her results and those of

Parrington. First, she mainly analyzed only samples collected under

conditions of downslope (DS) winds, which occur at night and bring down air

from above Mauna Loa. These are good samples in which to observe very low

concentrations of elements transported from long distances. Parrington also

analyzed samples collected under unslope (US) wind conditions, which are less

desirable because of their heavier loadings of marine aerosol, crustal

material from the island and human activities on the island. The second major

differences is that, starting in January 1983 Kilauea volcano has erupted

every few weeks, and during May 1984, Mauna Loa volcano erupted for several

weeks. The volcanoes presented an opportunity to observe their emissions in

various phases of their eruptive cycles, but they created problems of

interference with the observation of remote area aerosol compositions.

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Table 1. Geometric means and standard deviations of elemental concentrations

observed at Mauna Loa Observatory, February 1979 - May 1985

CI ean seasons Dust seasons

Ele- Unit Cone

.

Geom. No. Cone

.

Geom. No. ment a Spls. a Spls.

Na ng/m3 8.5 2.4 168 24 2.3 124 Mg ng/m;? 3.5 2 124 24 2.9 111 Al ng/m^ 6.1 2.1 170 52 3.3 124 CI ng/m;^ 6.3 3.3 136 6.8 2.7 101 K ng/iD-^ 3.2 2 146 27 2.5 120

Ca ng/m^ 4.6 2.3 156 55 3.6 122 Sc Pg/m^ l.A 2.2 166 13 3.1 124 Ti ng/m^ 0.87 1.9 117 4.5 2.7 108 V pg/m;: 14 2 170 95 2.9 124 Cr ng/m^ 1.6 3.7 135 1.6 3.7 95

Mn Pg/m^ 87 2.1 170 760 3.2 124

Fe ng/m;^ 5.8 2 162 41 2.9 124 Co pg/ni;: 3.7 2.5 162 20 2.6 123 Zn ng/m^ 0.11 3.6 150 0.35 2.6 120 Ga Pg/m^ 23 3.6 65

As Pg/m^ 14 2.5 118 61 3.6 110

Se ng/m^ 0.013 2.2 165 0.025 2.5 124 Br ng/TD^ 3 2.3 166 2.4 2.1 107 Rb PgA^ 24 2 52 140 2.8 112 Ag Pg/m^ 2.3 2.3 81 2.8 2 46

In pg/m3 0.36 2.5 21 0.67 2.6 27 Sb pg/m^ 1.8 2.9 155 7 2.6 117

I ng/m^ 1.7 1.7 169 1.3 1.7 119

Cs pg/m^ 1.1 2.6 137 11 3.3 120 La pg/m^ 3.2 2.9 155 42 3.7 121

Ce Pg/m^ 7.5 2.7 142 73 3.2 123 Sm Pg/Di;: 0.57 3 131 6.4 3.1 112 Eu pg/m;: 0.21 2.4 143 1.3 2.9 116 Tb Pg/m^ 0.19 2.4 56 0.97 2.5 87 Yb Pg/m 0.85 2.7 67 2.5 3.2 101

Lu Pg/m^ 0.41 2.8 34 0.57 2.7 81 Hf pg/m;: 0.52 2.2 137 3.3 3 119 Ta vgM: 0.3 1.9 80 1.1 2.5 92 W Pg/m^ 3.2 3.4 63 6.2 3 52 Au Pg/n> 0.17 2.8 103 0.23 3.6 79

Th Pg/m^ 1.1 2.6 125 12 3.2 120 SO4 ng/m-^ 130 3 169 220 2.4 101

The major feature of the MLO data is the observation of large amounts of

crustal dust from Asia every Spring, from February through June, the result of

vast dust storms in loess regions of China. Table 1 shows the concentrations

of elements observed during the dust and nondust seasons. Note the much

greater concentrations of most elements, especially crustal elements, during

the dust season. The data were treated by various receptor-modeling methods to determine

the sources of mass and of various elements. Evidence for the following

182
NON-RRD PROGRAMS

components was obtained: "normal" Asian dust, Asian anthropogenic materials,

and Se-SO- component, marine aerosol, Hawaiian basalt and volatile volcanic

emissions. Asian dust is not pure soil, but is soil contaminated by emissions

from coal combustion in China. The Asian anthropogenic component is more highly enriched material from coal combustion. Note that during the clean

seasons, wind trajectories suggest that both crustal and anthropogenic

material come from North and Central America much of the time, but concen- trations of most species are so low that we can't distinguish them chemically

from the Asian sources. The Se-SO- component results from biological

processes in the oceans, which release dimethyl sulfide, which is slowly

converted to SO^ gas and then to sulfate particles. The associated Se appears

to arise from similar processes. Hawaiian basalt is a good representation of

ash from the volcanoes. Table 2 shows the mass concentrations from the

various sources during the dust and non-dust seasons.

Table 2. Source contributions {%) to total suspended particulate load at

Mauna Loa Observatory during clean and dust seasons

Component Clean season Dust season

Se-S04 62.4 10.9 Continental dust 21.7 79.5 Marine aerosol 6.4 2.8 Anthropogenic 4.3 3.2 Basalt 2.7 1.9 Volcanic volcano 2.4 1.7

Mass cone, (ng/m-^) 600 2800

2. Deep Creek Lake Samples

In August/September 1983, various groups collected samples at a site near Deep Creek Lake, MD, an area strongly affected by emissions from distant coalfired power plants in the Ohio River Valley and from nearby plants in WV, OH

and PA. Ambient particulate samples were collected every 12 hrs with a dichotomous sampler, which sorted the particles every 12 hrs (diam < 2.5 urn)

and a coarse fraction (2.5-10 nm) . The particulate samples were analyzed by

x-ray fluorescence (XRF) for about 17 elements. Our group then obtained fine

fraction samples for all sampling periods and 22 coarse-fraction samples for

further analysis by INAA for about 35 elements, including many that were also

observed by XRF. A paper on the combined fine-fraction analyses has been

183
NON-RRD PROGRAMS

submitted to Atmos. Environ [2]. Results of the analyses are listed in

table 3 along with INAA results for the 22 coarse-fraction samples. This

paper mainly serves to introduce the data set to the atmospheric community,

with rather little interpretation. We are now performing various receptormodel treatments of the data.

Table 3. Concentrations of elements observed at Deep Creek Lake (ng/m^)

Fine Fraction Coarse Fraction

Average Sig. No . pts Average Sig. No. pts

Na 32.3 + 25.4 117 22.08 + 20.72 22 Mg 119 + 86 14 Al 55.6 + 42.5 104 402 + 527 22 Si 150.6 + 83.3 120

s 6754 + 4252 120 1418 + 1443 12

CI 20.6 + 30.3 104 14.61 + 11.71 22 K 42.5 + 21.2 120 150 + 164 22 Ca A6.5 ± 31.9 120 705 + 771 21 Sc 0.012 + 0.011 116 0.09 + 0.11 21 Ti 30 + 43 22 V 0.862 + 1.273 104 0.75 + 0.74 22 Cr 0.86 + 0.81 116 1.04 + 1.80 20 Mn 3.07 + 1.94 104 7.41 + 8.40 22 Fe 58.84 + 45.04 120 295 + 332 22 Co 0.035 ± 0.033 116 0.11 + 0.11 21

2n 12.1 ± 9.1 116 3.06 + 4.89 21 Ni 0.65 ± 1.16 106

Ga 0.066 ± 0.131 111 0.11 + 0.13 22 As 0.741 ± 0.627 111 0.20 J C.15 22 Se 2.40 ± 1.35 116 0.07 + 0.12 21

Br 5.10 ± 2.46 120 2.01 + 1.19 22 Rb 1.33 + 1.48 15 Mo - 0.31 + 0.23 15 Cd 0.63 ± 0.87 111 In 0.005 + 0.008 18

Sb 0.64 ± 0.99 116 0.136 + 0.354 22 I 0.56 ± 0.34 104

Cs 0.030 ± 0.045 116 0.041 + 0.047 22 Ba 4.85 + 3.40 20 La 0.090 ± 0.129 111 0.257 + 0.276 22

Ce 0.195 ± 0.182 116 0.647 + 0.749 21 Sm 0.018 ± 0.048 111 0.048 + 0.056 22 Eu 0.0027 ±C).0062 116 0.009 + 0.010 19 Tb 0.004 + 0.005 14 Yb 0.0230 ±C).0263 116 0.017 + 0.020 22

Lu 0.004 + 0.004 16 Hf 0.0024 ±c).0092 116 0.026 + 0.033 20 W 0.088 + 0.142 111 0.040 + 0.036 22 Pb 46.59 + 19.3 120

184
NON-RRD PROGRAMS

To determine compositions of particles emitted from coal -fired power

plants near the DCL site, researchers from NEA, Inc. collected particulate

samples from three large, nearby plants, the Ft. Martin, Harrison, and

Pleasant plants. The samples were analyzed by XRF and, then, selected fine

fraction samples were sent to our group for analysis by INAA. Both our results and those from XRF for elements that are marginal or impossible by

INAA are listed in table 4. Because of the differing sizes of the plants, we have expressed the emissions in terms of the mass of each species (in pg) per

unit energy produced (in J). Janet Joseph is attempting to interpret the

results in her M.S. thesis. We had a priori hoped that emissions from the

plants would be sufficiently distinctive as to allow us to identify them

separately at the DCL site. Indeed, the data of table 4 reveal quite

significant differences among the three plants. However, the area is so strongly influenced by emissions from more distant plants in the Ohio River

Valley that it has so far not been possible to distinguish particles from the

local plants from those of the more distant ones. We also collected several sets of samples in the DCL area with a microorifice impactor, which separates particles of diam below about 2.5 nm into

eight size fractions. These sample sets have also been analyzed by INAA for

about 30 elements to provide detailed size distributions of very fine

particles bearing the different elements. We see peaks in the size spectra at

different diameters for different elements, suggesting that they were produced

by different processes, or that some had been airborne for longer times than

others, allowing for more coalescence or growth. Jeff Dodd is attempting to

interpret the results in his M.S. thesis.

185
NON-RRD PROGRAMS

Table 4. Normalized emission factors of elements (pg/J) in fine particles

Ft.. Martin Harrlson Pleasants

Vs 15.4 27. 1 23.0

As A0.3 57. 2 29.2

E (MWe)« A70 820 540

Na 3.9 + 2.5 57 ± 16 4.4 + 1.1

Al 46 + 31 940 ± 440 160 + 140

Si (XRF) 240 + 115 320 ± 130 320 ± 140

S (XRF) 1570 + 790 4260 ± 1450 2760 + 1270 K 6.8 + 4.1 82 ± 19 12 + 6

Ca 8.6 + 3.3 600 + 160 120 + 49

Sc 0.011 + 10.009 0.26 ± 0.07 0.030 ± 0.012 Ti 2.0 ± 0.8 61 ± 19 8.6 + 3.8

•V 0.20 + 0.08 6.5 ± 1.7 1.3 + 0.6

Cr 0.31 + 0.27 3.4 ± 1.0 1.3 + 1.1

Mn 0.074 + 0.035 3.9 ± 0.9 0.43 + 0.19

Fe 23 + 15 845 ± 201 122 ± 49

Co 0.042 + 0.032 0.34 ± 0.09 0.037 ± 0.015

Hi (XRF) 1.4 + 0.9 1.2 ± 0.3 0.33 + 0.18

Cu ND ND ND

Zn 0.57 + 0.57 7.4 ± 3.0 2.4 + 0.9

Ga 0.068 ± 0.038 1.4 + 0.3 0.25 + 0.11

As 0.42 + 0.62 10 + 2 5.4 ± 2.5 Se 65 + 29 27 + 7 23 + 5 Br (XRF) 3.6 + 0.9 2.4 + 0.6 0.92 + 0.39

Kb m> 0.81 ± 0.20 0.12 + 0.08 Sr HD 28 ± 7 1.6 + 1.3 Mo ND 1.9 + 0.7 0.45 + 0.30 Ag ND 0.15 + 0.18 ND

Cd ND NE1 ND

In 0.0010 ± .0011 0.011 + 0.003 0.0020 ± .0009 Sb 0.10 ± 0.10 0.45 ± 0.19 0.27 + 0.14

Cs ND 0.11 ± 0.03 0.0095 ± .0052 Ba 0.79 + 0.77 26 + 6 7.8 + 3.6 La 0.026 ± 0.020 0.45 ± 0.13 0.037 ± 0.014

Ce ND 1.4 ± 0.4 0.17 ± 0.07 »d ND 0.63 ± 0.31 ND

Sm 0.017 + 0.025 0.11 ± 0.03 0.025 + 0.030 Eu 0.0014 + .0009 0.024 + 0.006 0.0035 ± 1.0023 Gd ND 0.16 ± 0.16 ND Tb ND D.OIB ± 0.005 ND Xb ND 0.036 ± O.O09 ND iM 0.0016 ± .0015 0.011 ± 0.005 0.0013 ± Ci.0008 Hf 0.0030 ± .0043 0.043 ± 0.018 0.0055 ± C .0027 V ND 0.22 ± 0.05 0.055 + 0.032

Pb (XRF) 28 ± 10 9.2 ± 7.3 6.6 + 1.7 Th 0.0092 ± .0057 0.17 ± 0.03 0.020 + 0.006 V 0.016 + 0.015 0.30 + 0.07 0.075 + 0.051 All data were normalized to gross electrical generating load. ND - not detected in greater than half of the samples.

Vg - stack gas velocity (Stevens, 1984).

As ~ stack cross sectional area (U.S. DOE, 1983). E - gross electrical generating load (Stevens, 1984).

References

[1] J. R. Parrington, Ph.D. Dissertation, Dept. of Chemistry, University of

Maryland, College Park, MD (1983).

[21 T. L. Vossler, C. W. Lewis, R. K. Stevens, T. G. Dzubay, G. E. Gordon,

S. G. Tuncel, G. M. Russwurm, and G. J. Keeler, submitted to Atmos.

Environ. (1988).

186 (
NON-RRD PROGRAMS

STABLE ISOTOPE TRACING OF ZINC IN INFANTS

G. E. Gordon and S. H. Harrison

(Department of Chemistry and Biochemistry, University of Maryland)

In cooperation with Dr. K. Sivasubramanian and coworkers of Georgetown

University Medical Center, we are testing the use of enriched stable Zn to

trace the behavior of Zn in infants, especially preterm infants, who are often

at considerable risk of Zn deficiency. The tracer consists of Zn enriched to

80% or more in Zn (vs. its normal isotopic abundance of 0.6%) and is

administered to the infant, usually in their infant formula. Samples of

blood, urine and feces are collected as available for several days and the Zn

is separated prior to irradiation in the NISI Reactor. The latter produces

245-day Zn, 14-hr Zn and 4-hr Zn, whose activities are proportional to

64 68 70

the masses of stable Zn, Zn and Zn, respectively, in the samples. From

the Zn/ Zn and Zn/ Zn ratios in the samples along with knowledge of the mass and Zn abundance in the administered tracer, we can calculate the

fraction of tracer that appears in the various body-pool samples. To date,

six infants have been studied. Because of the smaller samples available from

infants and less control of the sampling regime, they are much more difficult

to study than the adult volunteers with whom the procedures were verified.

However, preliminary results indicate that the procedure can be done, but with

somewhat lower precision.

187
NON-RRD PROGRAMS

NEUTRON FILTERS FOR COLD NEUTRON BEAMS

C. A. Stone

(Center for Analytical Chemistry)

Single crystals have long been used to filter out the fast neutron

component of a neutron beam while allowing thermal neutrons to pass through

with little attenuation. Detailed comparisons of the performance of neutron

filters have not been accomplished, primarily because of the limited data on the total neutron cross section for most materials. Freund [1] presented a semi -empirical method to determine the total neutron cross section of single

crystals. This approach is simple and reproduces experimentally observed

cross sections.

Extensive calculations have been carried out, following the method

presented by Freund, to determine the optimum filters for cold neutron beams.

Figure 1 shows the components to the total neutron cross section for sapphire.

The component labeled SPH represents the single phonon scattering cross section and that labeled MPH represents the multiple phonon scattering cross

section.

10

c

u

e

Vi

ViO

uU

X.

CSKgSgfW*^^ JH Y

>7

-a Absorption -^ SPH

-fl MPH

» Total

.01

.0001 .001 .01 .1 1 Neutron Energy (eV)

Figure 1. Neutron cross section for single crystal sapphire.

188
NON-RRD PROGRAMS

For several in-beam experiments, the relevant comparison between neutron

filter choices is not necessarily the total transmission of neutrons through

the crystal. Rather, it is the total neutron transmission versus a defined

fast neutron transmission. In order to make this comparison, a set of

"equivalent lengths" for filters was determined. The length of a given filter

was defined as that which will attenuate the fast neutrons to a specified

value. Table 1 shows the equivalent lengths for several filters. Each column

is labeled with the fast neutron transmission in percent. Fast neutron cross

sections, which were used to calculate the attenuation coefficients, were

taken from reference [2]. The neutron transmission is shown in figure 2 for

several filters with a fast neutron of transmission of 0.0001%.

3

C3e

^o

se

uH

s

o

u

s

a>

0.0

.0001 .001 .01

Energy (eV)

Beryllium

Bismuth

Graphite

Quartz

Silicon Sapphire

Figure 2. Neutron transmission for a 99.999% fast neutron attenuation

189
NON-RRD PROGRAMS

Table 1. Lengths of various neutron filters which give equivalent fast

neutron attenuation

Fast Neutron

Scattering Attenuation Filter Length for Fast

Cross Section Density

(g/cm^)

Coefficient Nwtrpn Att?n\iatipn (pm)

Filter (bams) (cm-i) 99.9% 99.99%

Beryllium 6.151 1.85 0.760 9.1 12.1

Bismuth 9.300 9.8 0.26 26.3 35.1

Graphite 4.730 2.25 0.535 12.9 17.2

Quartz 9.5657 2.202 0.2111 32.7 43.6

Sapphire 13.1098 3.98 0.332 20.8 27.8

Silicon 2.0437 3.329 0.1021 67.7 90.2

Figure 3 shows the total neutron transmission for a series of filters as

a function of the fast neutron transmission. A 77-K Maxwell ian probability

distribution was taken for the neutron spectrum shape and the crystal

temperature was taken as 296 K. This figure clearly shows sapphire as the

optimum choice for a cold neutron filter.

1.0

CAE

CAc

uH

e

o

us

Z.

"3©

Q— Beryllium

o

Graphite e

Quartz

Sapphire

r, SiUcon

.0001 .001 .01 .1 Fast Neutron Transmission (%)

Figure 3. Total neutron transmission for 296 K neutron filters and 77 K (Maxwell ian) neutrons.

References

[1] A. K. Freund, Nucl . Instr. Meth. 2i3, 495 (1983).

[21 S. F. Mughabghab, Neutron Cross Sections, Academic Press, Orlando, FL

(1984).

190
C. REACTOR OPERATIONS AND SERVICES

REACTOR OPERATIONS AND SERVICES

T. Raby, J. Torrence, J. Ring, and N. Bickford

There were numerous activities this year that required extended reactor

shutdown or operation at reduced power. Included among these are the

installation of the cold neutron source, the beginning of construction of the new guide hall and confinement building annex, replacement of the shim arms,

overhaul of the fuel transfer system and shipment of spent fuel. Two major

problems were also encountered during this period, the failure of one of the

main heat exchanger and the progressive leaks in the thermal shield cooling

system. As a result, the reactor was on-line about 50% of the time at various

power levels which is equivalent to about 35% had the reactor been operating

at the full power level of 20 MW throughout.

Installation and testing of the cold source was a difficult and lengthy

operation. The entire core was unloaded and the systems drained. The

operation required almost 3 months. Construction of the new cold neutron

facility complex was begun and is in progress. Shutdowns between operating

cycles were extended to permit the contractor to do work near the confinement

building. Application for license changes and associated safety analyses, to

incorporate the new cold neutron guide tubes into the NBSR Technical

Specifications was made to the Nuclear Regulatory Commission.

The shutdown period was used to perform major maintenance operations.

The fuel transfer system was overhauled. The shim arms were replaced for the

second time after 7 years of operation. The replacement took less than a month compared to nearly 6 months the previous time. Shipment of all spent

fuel was completed. In all nine shipments were made involving 180 elements

which is equal to all the previous shipments since the NBSR began operation.

For years, the thermal shield cooling system has been developing leaks.

By 1988, approximately 70 out of 190 cooling tubes had to be isolated as leakers, or suspected leakers. The situation was close to becoming

intolerable because of the significantly decreased cooling capacity. Recently

a new method developed by National Nuclear Corporation of England was shown to

be effective in sealing small leaks in inaccessible areas and in a hostile,

highly radioactive environment. The treatment was applied to all proven

leakers of the thermal shield over a 2-week period with \/ery encouraging

191
REACTOR OPERATIONS AND SERVICES

initial results. The repaired system will be tested over the next several

months under actual reactor operating conditions.

The main heat exchanger had developed several leaks in the past, one of

which was so small that it could not be found from among 1200 U-tubes. The

shutdown period was used to attempt to locate this small leak. Several

suspect tubes were plugged following which the heat exchanger tested leak

tight. Shortly thereafter, when the flow systems were refilled and returned

to normal, major leaks developed suddenly, resulting in the loss of 400

gallons of heavy water. The leaks were traced to this same heat exchanger.

Sixteen tubes were confirmed leakers and were plugged. The heat exchanger is

being monitored until replacement heat exchangers can be obtained. This will

take several years.

The operating staff now numbers 16, 15 of whom are licensed senior

operators, and one in training for licensure. The staff is considerably

smaller than that of comparable reactors. This requires each member of the

staff to carry out duties and responsibilities significantly beyond that of

routine shift operation of the reactor.

A summary of the operating statistics for the past year is presented in

the following table. Fuel utilization continues to be the best in the

country.

No. of equivalent days at 20 MW 126

Equivalent on-line time at 20 MW 35%

Average U-235 burnup 66%

No. of irradiations 675

Hours of irradiations 1850

Hours per irradiation 2.7

The same program of reactor irradiations continued. Irradiation services were provided to many organizations from within and outside NBS covering wide

areas of research, applications, and standards.

192
REACTOR OPERATIONS AND SERVICES

ENGINEERING SERVICES

J. H. Nicklas and R. S. Conway

In addition to normal engineering and design services provided to

reactor operations, experimenters and users, the engineering staff was involved in a continuing effort to upgrade the reactor systems, components

and instrumentation. Among the major projects undertaken are: New fuel elements have been qualified and are currently in production.

These more heavily loaded elements will increase reactor core lifetime and

will result in considerable cost savings throughout the fuel cycle, fewer

shutdowns, and less handling for refueling.

For the first time, replacement shim arms were assembled with completely

new mounting components. In the past, the old mounts which were highly

radioactive had to be used. This required the entire assembly operation to be

done remotely under water which required two months to complete. During this

previous replacement, the old mounts were carefully inspected and the precise

measurements needed to make new mounts were determined. The use of the new mounts eliminated the lengthy time required previously to disassemble the used

shim arms from their mounts and reduced the shim-arm replacement time to less

than two weeks. Because of the success of this procedure, another set of

mounts was immediately fabricated for future use. For years, the fuel transfer system has been causing problems because of

the sticking transfer arms due to worn out bearings that we have not been able

to replace because of their location. A unique tool has now been designed and

fabricated to remove and replace some of the bearings. The first attempt to remove the bearings with the new tool will be made in the near future.

A long standing problem that has been getting progessively worse has been

leaks in the thermal shield cooling tubes. These tubes are buried inside the

biological shield and are not accessible. The system consists of many

redundant individual tubes with separate valves enabling leaking tubes to be

isolated. At the beginning of this year, more than 50 of the cooling tubes were isolated as known or suspected leakers. To address this problem we finally located a firm that has developed a method for sealing such leaks in

highly radioactive environments. They were successful in sealing all but two

or three of the leaks. A few have reopened during successive operating

cycles, but, on the whole the results have been quite satisfactory. We

193
REACTOR OPERATIONS AND SERVICES

anticipate that periodic treatment will continue to be required, but it

appears that sound and reliable operation of the thermal shield system can be

maintained at reasonable cost.

The design drawings and specifications for the replacement of the main

heat exchangers are in the final stages of completion. The existing heat

exchangers have been the source of numerous problems resulting in significant

loss of operating time and some loss of valuable heavy water. The new heat

exchanger design will utilize advanced fabrication methods, testing procedures

and new stainless steel alloys that are resistant to stress corrosion. This

will assure their long life and reliable operation. A survey is being made to

evaluate tube and heat exchanger manufacturers. Technical visits have already

been made to several leading manufacturers across the country.

The cryogenic bismuth tip instrumentation project was completed. This

instrumentation system monitors the temperature and rate of the D^O and H^O

cooling water flow through the bismuth tip. This project involved installing

stainless steel piping, tubing, venturi flow elements, transducers, alarm

units, thermocouples, analog, and digital readout meters. The entire system

including safety functions and alarms, was interfaced with the reactor console

control room. This allows the operator to monitor performance and take

corrective action as required. The final checkout and energizing of the

bismuth tip instrumentation readout panels and alarms were completed on schedule.

194
REACTOR OPERATIONS AND SERVICES

NEUTRON ACTIVATION ANALYSIS AT THE FOOD AND DRUG ADMINISTRATION

W. C. Cunningham and D. L. Anderson

(Food and Drug Administration, Washington, DC)

The Food and Drug Administration (FDA) maintains a neutron activation

analysis (NAA) facility in the reactor building of the National Bureau of

Standards (NBS). Although this facility is directed by FDA's Center for Food

Safety and Applied Nutrition, it provides agency-wide analytical support for

special investigations and applications research. NAA complements other

analytical techniques used at FDA and serves as a reference technique and

confirmatory quality assurance (QA) tool.

During the past year, this facility provided support in all of the areas noted above. Radiochemical and instrumental NAA procedures (RNAA and INAA,

respectively) continue as the prime analytical tools; however, during this

year extensive efforts were directed to applying neutron-capture prompt gammaray activation analysis (PGAA) to FDA needs. PGAA provides a cross-check for some elements but is also sensitive for B, Cd, H and S and increases the

capabilities of the FDA NAA facility. The combination of several nuclear

techniques enables diverse multi-element information to be obtained for foods

and related materials. This methods development and applications research was part of the ongoing FDA effort to improve overall analytical capabilities.

Research efforts continued this past year to accumulate general analytical

information on food supplements. PGAA work was primarily to determine element

concentrations and detection limits for these materials. INAA work focused on

an examination of interferences and matrix effects. These materials are particularly interesting because many of them have both biological and mineral

components in the same supplement. As a result, analytical approaches must be

able to simultaneously handle problems associated with both. To date, more

than 40 different product types have been analyzed by the nuclear techniques.

Preliminary work shows that PGAA was able to provide element

concentrations for H, B, and CI in virtually all supplements. Levels of C, N,

Na, Si, S, K, and Ca were below detection limits in some materials but above

in most. Levels of Al , Ti , Mn, Fe, Cu, Zn, Cd, Sm and Gd were above detection

limits in only a few materials, predominantly the high-mineral supplements.

Besides providing a general QA benefit for several elements, PGAA provides

FDA's Element Research Section with specific added capabilities: It can be

used to obtain element concentrations for H, C, N, Si and S and it serves as

195
REACTOR OPERATIONS AND SERVICES

an alternative technique to obtain element concentrations for B, Cd, CI and K. Moreover, PGAA is an instrumental technique, it requires minimal test sample

preparation, and it has a relatively short analysis time.

USE OF NAA IN CRIMINAL INVESTIGATIONS

Neutron Activation Analysis Unit

(Federal Bureau of Investigation, Washington, DC)

The Federal Bureau of Investigation (FBI) continues to utilize the NBSR

for Neutron Activation Analysis (NAA) of various materials collected for their

investigation of a wide range of criminal cases. Much of their investigation

involves trace element comparisons of bullet leads and analysis of trace

elements when the use of a handgun is suspected.

One case which utilized NAA involved a double homicide of a husband and

wife. Fragments of bullets were removed from the husband's head. The trace

elements in those fragments matched exactly with the trace elements in the

unfired bullets found in the suspect's handgun and those still in the box at

the suspect's residence. This match of trace elements provided a valuable

clue in solving the crime.

Since NAA is sensitive and non-destructive, analysis of wery small

samples of evidence is possible with the added advantage of retaining the

material for introduction during a trial.

196
D. PERSONNEL ROSTER

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V)

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j«: re o E

0) Q oE^ r^ r— U

re Ol O S_

tj -1- s- re t— S- J= c D1 => +-> re 13 +-> 3

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-(-> re V)

+-> 3 O) re c >>

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+J (_> V)

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i. UJ u O) re <: O) :3 a. 3 Q o )c + -X =tfc •X

197
PERSONNEL ROSTER

NON-RRD NBS STAFF LOCATED AT REACTOR

OccuDational Health

and Safety Division (354)

D. Brown

C. Campbell

I. Jensen

F. Moore

D. Nelson

J. Shubiak

L. SI aback

Ionizing Radiation

Division (536)

E. Boswell

C. Eisenhauer

D. Gilliam

J. Grundl

G. Lamaze

E. McGarry

R. Schwartz

J. Coyne

Inorganic Analytical

Research Division (551)

D. Becker

S. Carpenter

G. Downing

K. Fitzpatrick

R. Fleming

B. Grazman

R. Greenberg

G. Iyengar

J. Langland

R. Lindstrom

J. Maki

B. Norman

S. Stone

R. Zeisler

GUEST WORKERS AND COLLABORATORS

INSTITUTE FOR MATERIALS

SCIENCE AND ENGINEERING (400)

J. Cahn

Ceramics Division (420)

J. Blendell

E. Fuller

G. Long

C. Ostertag

R. Roth

W. Haller

Polymers Division (440)

B. Bauer

R. Briber

F. Brinkman

T. Chang

C. Chiang

J. Clark

L. Coyne

T. Davis

C. Han

S. Krueger

G. 01 sen

R. Waterstrat

W. Wu

Metallurgy Division (450)

R. Fields

R. Reno

R. Shaefer

R. Shull

Center of Basic Standards (520)

M. Arif

S. Dewey

G. Greene

Surface Science Division (541)

R. Cavanagh

T. Madey

Organic Analytical

Division (552)

B. Koster

L. Sander

S. Wise

Gas and Particulate

Science Division (553)

C. Poston

H. Rook

J. Small

C. Stone

198
PERSONNEL ROSTER

Semiconductor Electronics Naval Research Laboratory

Division (727) D. Gubser

J. Ehrstein P. S. Keath

J. Marshall S. Lawrence

J. Suehle M. Osofsky

C. Roland

ThermoDhvsics Division (774) P. Schoen

H. Hanley L. Toth

J. Straty C. Trask

R. Treanor

Armed Forces Institute of Pathol oqv S. Wolf

D. Nagarajan

Naval Surface Weaoons Center

Army Armament Research, Development G. Riel

and Enqineerinq Center M. Spano

C. Choi

H. Prask Smithsonian Institution

S. Trevino R. Bishop

M. Blackman

Department of Aqri culture T. Chase

G. Iyengar Y. Cheng

R. Cunningham

Federal Bureau of Investiqation J. Mishara

R. Bilko E. Myers

R. Halberst J. Olin

R. Hargadon

J. Haverkost Arqonne National Laboratory

K. Lundy T. Brun

C. Peters P. Thiyagarajan

J. Riley

D. Thompson Battel le Pacific Northwest

Laboratories

Food and Druq Administration L. Brackenbush

D. Anderson F. Brauer

W. Cunningham G. Endres

A. Kyah M. Failey

J. Tanner R. Sanders

National Institutes of Health Brookhaven National Laboratory

J. Bennett P. Boni

M. Channing D. Cox

W. Eckel man D. Gibbs

M. Geller A. Goldman

R. Finn

R. Frank C.N.R.S. Grenoble, France

A. Katki B. Barbara

R. Nossal M. Marezio

S. Miraglia

National Oceanic and D. Tran Qui

Atmospheric Administration

G. Lauenstein ETH. Zurich, Switzerland

I. Anderson

199
PERSONNEL ROSTER

Energy Research Foundation

(The Netherlands)

J. Woittiez

Hahn-Meitner Institute

(Berlin)

D. Behne

Institut Laue-Lanqevin

Grenoble. France

A. Magerl

D. Richter

J. Soubeyroux

KFA Jijlich, Germany

H. Grimm

R. Hempelmann

M. Steepler

Los Alamos National Laboratory

T. Bowles

J. Eckert

R. Hjelm

R. Robinson

J. Wilkerson

M. Yethridge

Oak Ridge National Laboratory

J. Cable

J. Fernandez-Baca

J. Hayter

F. Kam

H. Mook

R. Nicklow

B. Sales

H. Smith

Risci National Laboratory

J. Bohr

Sandia National Laboratory

Z. Fisk

Colorado State University

A. Parker

J. Stille

J. Tsang

College of William and Mary

E. Schoe

R. Wright

Goethe University

W. Bauer

A. Bienok

Iowa State University

A.

R. GoldmanBarnes

John Carroll University

J. Trivisonno

Johns Hopkins University

C. L. Chien

M. Creplak

A. Ganrin

D. Musser

F. Streitz

G. Xiao

Kyoto Institute of Technology

Q. Tran-Cong

Kyoto University (Japan)

H. Hasegawa

T. Hashimoto

Q. Trancong

S. Sakurai

Y. Shibayama

M.I.T.

J. Didiskein

M. Green

B. Wuensch

Alfred University

R. Snyder

R. Zhow

McMaster University

W. Clarke

R. Barr

Auburn University

B. Taterchuck

Chalmers University of Technology

L. Sjolin

R. Alenljung

Miami University (Ohio)

J. Cantrell

200
PERSONNEL ROSTER

Michigan State University

T. D. Brewer

Y. Fan

A. Moini

T. Pinnavaia

S. Sol in

M. S. Wang

Naqova University

H. Choshi

Y. Matsushita

K. Mori

Y. Muroga

Y. Nahao

I. Nodo

R. Saguchi

Northwestern University

C. Sellers

J. Weertman

Ohio University

R. Cappelltetti

Oregon State Graduate School

P. Davis

Penn State University

L. Pilione

J. Yehoda

Purdue University

A. Overhauser

Rutgers University

R. Gerhardt

San Jose State University

P. Englert

A. Ling

Southwest Research Institute

R. Page

Temple University

J. Crow

Texas A&M University

E. Schweikert

Tokyo Institute of Technology

M. Okala

University of Antwerp (Belgium)

K. Michel

University of California (Davis)

P. Klavins

R. Shelton

University of California (Irvine)

V. Guinn

University of California

(Santa Barbara)

M. Eddy

J. Pint

D. Klingensmith

C. Levi

R. Odette

G. Stucky

University of California (San Diego)

J. Arnold

K. Nishiizumi

University of Cincinnati

H. Jackson

P. Boulchand

University of Exeter (U.K.)

R. Slade

University of Houston

P. Chu

University of Illinois

J. Anker

J. Borchers

B. Boyle

R. Du

C. Flynn

M. Salamon

H. Zabel

University of Illinois (Chicago)

M. Said

J. Kowel

University of London

C. Catlow

W. Jordon

B. Steele

University of Annecv (France)

J. Bouillot

201
PERSONNEL ROSTER

University of Maryland

H. Ammon

A. Andrews

T. Clinton

J. Copley

J. Dodd

G. Gordon

M. Han

S. Harrison

D. Herman

J. Hoff

W. Li

J. Lynn

L. Mackie

J. Nicol

J. Ondov

A. Sheffield

S. Skanthakumar

J. Valette-Silver

W. Walters

H. Zhang

University of Massachusetts

5. Roy

R. Stein

University of Milan (Italy)

M. Zocchi

University of Michigan

D. Vincent

University of Missouri

R. Berliner

W. Ching

6. Hammouda

P. Schmidt

S. Werner

D. Worcester

University of Muenster

F. Kemper

University of Nancy (France)

P. Mangin

University of Nebraska

D. Sellmyer

University of North Carolina

W-K Chu

E. Frye

N. Parikh

M. Swanson

University of Notre Dame

J. Furdyna

T. Giebultowicz

P. Klosowski

University of Odense

E. Anderson

University of Pennsylvania

P. Davis

University of Peruglia

G. Albert

University of Vermont

T. Flanagan

University of Virginia

T. Williamson

University of Washington

K. Mottet

W. Zoller

University of West Virginia

R. Kannan

M. Seehra

University of Wisconsin

D. Huber

Utah State University

T. Isenhour

Yale Univeristv

J. Flanagan

AT&T Bell Laboratories

F. Bates

R. Cava

H. Chen

D. Johnson

J. Mitchell

D. Murphy

J. Remeika

W. Rhodes

J. Riley

J. Rosedale

L. Scheemeyer

S. Sunshine

J. Waszazak

S. Yognasubiamian

202
PERSONNEL ROSTER

Aerospace Corporation

R. Bowman

J. Knudsen

Allied Corporation

G. Fish

A. Maeland

J. LaSalle

Atomic Energy of Canada, LTD

W. Lennard

Bell Communications Research

Laboratories

P. Barboux

L. Greene

P. Miceli

J. Tarascon

Charles Evans & Assoc.

R. Fleming

CIDTECH

D. Carta

GTE Laboratories

G. Hamill

W. R. Grace

M. Wax

R. Wormsbecker

Hughes, Malibu

R. Wilson

IBM (San Jose)

G. Hadziioannou

T. Russel

S. Anastasiadis

Imperial Chemical Industries

J. Howard

H. Stanley

Intel Corporation

N. Cox

Lockheed EMSCO

D. Lindstrom

Directed Technologies, Inc.

N. Chesser

E. I. DuPont de Nemours Co,

D. Corbin

G. Jones

R. Shannon

F. Tebbe

C. Torardi

Research Triangle

N. Wadlen

Schumberger-Doll Research

N. Wada

Westinghouse-Hanford Corp.

W. McElroy

Eastman Kodak

T. Hossain

M. Landry

J. O'Reilly

C. Swanson

J. Tritten

H. Yang

Exxon

R. Busch

J. Huang

M. Kim

D. Lohse

R. Overfield

S. Sinha

G. E. Microelectronics Center

C. Tino

203

E. PUBLICATIONS

Abeles, B.; Yang, L.; and Majkrzak, C. F.; "Plasma Enhanced Exchange of H and D During Growth of Amorphous Semiconductor Superlattices," Proc. of

the Materials Research Society Symposium on Surfaces, Superlattices and

Thin Films, Boston, MA (1986).

Abeles, B.; Yang, L.; Leta, D. L.; and Majkrzak, C. F.; "Fast Diffusion of

Interstital D in Amorphous Si,: J. of Non-Crystalline Solids 97 and 98 . 353 (1987).

Ammon, H. L.; Choi, C. S.; and Reddy, S.; "Crystal Structure of 1, 4-

Diidocubane," Acta Cryst. (in press).

Anderson, I. S.; Berk, N. F.; Rush, J. J.; and Udovic, T. J.; "Concentration

and Temperature Dependence of Hydrogen Vibrations Along the C Axis for

Hydrogen in Yttrium: Evidence of Dynamically Coupled Hydrogen Pairs,"

Phys Rev. B, 37, 4358 (1988).

Baur, W. H.; Bieniok, A.; Shannon, R. D.; Prince, E.; "Neutron Powder

Diffraction Study and Thermogravimetry of Sodium Cesium Zeolite Rho,"

J. of Solid State Chem. (submitted for publication).

Berk, N. F.; Hardman-Rhyne, K. A.; "Analysis of SAS Data Dominated by

Incoherent Multiple Scattering," J. Appl . Cryst. 21 (1988).

Bohr, J.; Gibbs, D.; Moncton, D. E.; D'Amico, K. L.; Majkrzak, C. F.; and

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, II, Physica B, (to be

publ ished)

.

Borchers, J. A.; Salamon, M. B.; Du, R. ; Flynn, C. P.; Erwin, R. W.; and

Rhyne J. J.; "Magnetic Characterization of Er Y Superlattices," J. Appl. Phys. 63, 3458 (1988).

Bowman, R. C, Jr.; Cantrell, J. S.; Samwer, K.; Tebbe, J.; Rush, J. J.;

"Properties of Amorphous Zr RhH Prepared From Glassy and Crystalline

Alloys," Phys. Rev., B3Z, 8575 (1988).

Bowman, R. C, Jr.; Torgeson, D. R.; Barnes, R. G.; Maeland, A. J.; and

Rush, J. J.; "Relationship of Hydrogen Site Occupancy to Diffusion

Behavior in Crystalline and Amorphous Zr^PdH , Z. Physik. Chem., (in

press)

.

Bowman, R. C, Jr.; Maeland, A. J.; Venturini, E. L.; Rush, J. J.; and

Cantrell, J. S.; "Studies of the Structure and Properties, of Amorphous

a-ZrygFe^^H , " Z. Physik Chem., (in press).

Buchenau, U.; Monkenbusch, M.; Stamm, M.; Majkrzak, C. F.; and Nucker, N.;

"Neutron Scattering Study of Relaxations and Vibrations in Molten

Polyethylene," Proc. of the Workshop on Polymer Motion in Dense

Systems, September 1987 (in press).

205
PUBLICATIONS

Cahn, J. W.; Gratias, D.; Mozer, B.; "Patterson-Fourier Analysis of the

Icosahedral (Al,Si)-Mu Alloy." Phys. Rev. B (in press).

Cahn, J. W.; Gratias, D.; Mozer, B.; "A 6-D Structural Model for the

Icosahedral (Al,Si)-Mu Quasicrystal ," J. of Phy. Paris, France (in

press).

Carr, M. J.; Chambers, W. F.; Melgaard, D. K.; Himes, V. L.; Stalick, J. K.;

and Mighell, A. D.; "NBS/Sandia/ICDD Electron Diffraction Database,"

T.R. SAND87-1992, NTIS, 5285 Port Royal Road, Springfield, VA 22161.

Casella, R. C; "Theoretical Models For High-Temperature Superconductivity,"

Nuovo Cimento D (in press).

Choi, C. S.; Prask, H. J.; "Orientation Distribution of Fiber-axes and

Neutron Powder Diffraction Profiles." ICOTOM-8 Conference Proceedings

by the Metallurgical Society of AIME (in press).

Copley, J.R.D.; "The Significance of Multiple Scattering in the Interpretation of Small Angle Neutron Scattering Experiments," J. of Applied

Cryst. (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 Physics Research A. (in press).

Copley, J.R.D. and Majkrzak, C. F.; "Converging Neutron Guides," Proc. of

the 32nd Annual Int'l. Tech. Symposium on Optical and Optoelectronic

Applied Science and Engineering, SPIE, August 1988, San Diego, CA (to

be published).

DiNardo, R. P.; Majkrzak, C. F.; Neumann, D. A.; "Fabrication of Neutron

Polarizing Multilayers by Sputtering," Proc. of the 32nd Annual Int'l.

Tech. Symposium on Optical and Optoelectronic Applied Science and

Engineering, SPIE, August 1988, San Diego (to be published).

Endoh, Y. and Majkrzak, C. F.; "Polarized Neutron Diffraction Studies of

Magnetic Multilayer Structures," Chapter in a book on metallic

superlattices, edited by T. Shinjo and T. Takada, Elsevier Science

Publications (in press).

Erwin, R. W.; Rhyne, J. J.; Borchers, J.; Salamon, M. B.; Du, R.; and Flynn,

C. P.; "Magneto-Elasticity and Structure of Er Y Superlattices," J. Appl. Phys. 63, 3461 (1988).

Fan, Y. B. ; Solin, S. A.; Neumann, D. A.; Zabel , H.; and Rush, J. J.;

"Elastic Neutron Scattering Studies of the Structure of Graphite

Intercalated with Potassium and Ammonia," Phys. Rev., B36, 3386(1987).

Fernandez-Baca, J. A.; Lynn, J. W.; Rhyne, J. J.; and Fish, G. E.; "Low

Temperature Spin Waves in Amorphous '^^gn-x^^^'^iO'" *^* ^PP^ • ^^^^ ^'

3749 (1988).

206
PUBLICATIONS

Fernandez-Baca, J. A.; Lynn, J. W.; Rhyne, J. J.; Fish, G. E.; "Study of the

Long-wavelength Spin-wave Energies and Linewidths of the Amorphous

Invar Alloy FSj^^B^," Phys. Rev. B 36, 8497-8511 (in press).

Fowler, H. A.; Mozer, B.; and Sims, J.; "Triple Shell Symmetry in

oc-(Al,Si)-Mn," Phys. Rev. B37, 3906-3913 (1988).

Giebultowicz, T. M.; Rhyne, J. J.; Ching, W. Y.; Huber, D. L.; and Furdyna,

J. K.; "Spin Dynamics in Znj_^MnJe," J. Appl . Phys. 63, 3297 (1988).

Gotaas, J. A.; Lynn, J. W.; Shelton, R. N.; Klavins, P.; and Braun, H. F.;

"Suppression of Superconductivity by Antiferromagnetism in Tm^Fe^Sic,"

Phys. Rev. B 36, 7277-80 (1987).

Gotaas, J. A.; Rhyne, J. J.; Wenger, L. E.; and Mydosh, J. A.; "Magnetic

Phase Transition in Yq gyDyQ Q3," J. Appl. Phys. 63, 3577-9 (1988).

Gotaas, J. A.; Rhyne, J. J.; Wenger, L. E.; Mydosh, J. A.; "Magnetic

Structure of Yq gyErQ q-'" ^0 ^^ published in Proc. of the

International Conference on Magnetism 1988.

Gotaas, J. A.; Said, M. R.; Kouvel , J. S,; Brun, T. 0.; "Magnetic Structure

of Cubic TbQ q-Yq yAg," to be published in Proc. of the International

Conference on Magnetism 1988.

Gratias, D.; Cahn, J.W.; Mozer, B.; "Six-dimensional Fourier Analysis of

Icosahedral Aly2Mn2jS0g Alloy," Phys. Rev. B. (in press).

Gratias, D.; Cahn, J. W.; Bessiere, M.; Calvayrac, Y.; Lefebre, S.; Quivy,

A.; Mozer, B.; "N-dimensional Crystal lographic Description of the

Icosahedral Phases; The Example of the AK^Mn^iSig Quasiperiodic

Structure," Proc. of the NATO Conference, Acquafredda, Plenum (in

press)

Grimm, H.; Stiller, H.; Majkrzak, C. F.; Rupprecht, A.; and Dahlborg, U.;

"Observation of Acoustic Umklapp-Phonons in Water-Stabilized DNA by

Neutron Scattering," Phys. Rev. Letts. 59, 1780 (1987).

Grimm, H.; Stiller, H.; Majkrzak, C. F.; and Rupprecht, A.; "Neutron

Scattering Study of the Hydration Hull of DNA by H2O/D2O Exchange,"

Proc. of the Int'l. Conf. on Neutron Scattering, Grenoble, France, July

1988, Physica B (to be published).

Hanley, H.J.M.; Straty, G. C; Glinka, C. J.; and Hayter, J. B.; "Low-Q

Neutron Diffraction from Supercooled D-Glycerol," Molecular Physics,

62, 1165-1174 (1987).

207
PUBLICATIONS

Heise, W. H.; Lu, K.; Kuo, Y-J; Tatarchuk, B. J.; Udovic, T. J.; and Rush,

J. J.; "Neutron Scattering Study of Hydrogen on Ruthenium Sulfide," J. Phys. Chem. (1988) (in press).

Himes, V. L.; and Mighell, A. D., "NBS*SEARCH: A Program to Search the

Database," Data Commission of the Interntl Union of Crys., Chester, UK,

Chap. 3.1, 144-155 (1987)

Himes, V. L.; Mighell, A. D.; Stalick, J. K.; Young, S. L.; Carr, M. J.;

Anderson, R.; Holomany, M. A.; Jenkins, R.; Lyman, C. E.; "MAX-D Index

for Phase Identification by Electron or X-ray Diffraction," U.S.

Department of Commerce and the JCPDS- International Centre for

Diffraction Data, Swarthmore, PA. 1988 (in press).

Himes, V. L. and Mighell, A.D.; "NBS Crystal Data: Compound Identification

and Characterization Using Lattice-Formula Matching Techniques,"

Computerized Metallurgical Databases, published by The Metallurgical

Society, 1988 (in press).

Hong, M.; Fleming, R. M.; Kwo, J.; Waszczak, J. V.; Mannaerts, J. P.; and

Majkrzak, C. F.; "Magnetic Rare Earth Dy-Y Superlattices," J. Appl

.

Phys. 61, 4052 (1987).

Horton, J. C; Squires, G. L.; Boothroyd, A. T.; Fetters, L. J.; Rennie, A. R.; Glinka, C. J.; and Robinson, R. A.; "Small-Angle Neutron Scattering

from Star-Branched Polymers in the Molten State," Macromolecules

(submitted for publication).

Krueger, S. and Nossal , R.; "SANS Studies of Interacting Hemoglobin in

Intact Erythrocytes," Biophys. J. 53, 97 (1988).

Kwo, J.; Hong, M.; DiSalvo, F. J.; Waszczak, J. V.; and Majkrzak, C. F.;

"Modulated Magnetic Properties of Synthetic Rare Earth Gd-Y

Superlattices," Phys. Rev. B35, 7295 (1987).

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.; and Grimm, H.; "Rare-Earth Magnetic Superlattices," Int'l

Conf. on Magn., Paris, France, July, 1988, J. dePhysique (to be

published)

.

Li, W-H.; Lynn, J. W.; Mook, H. A.; Sales, B. C; and Fisk, Z.; "Long Range

Anti ferromagnetic Order of the Cu in Oxygen Deficient RB^2^^3^f6+x'"

Phys. Rev. B37, 9844 (1988) (Rapid Communications).

Li, W-H; Lynn, J. W.; Stanley, H. B.; Udovic, T. J.; Shelton, R. N.; and

Klavins, P.; "Anti ferromagnetic Structure and Crystal Field Splittings

in the Cubic Heusler Alloys HoPd2Sn and ErP^Sn," J. de Physique (1988)

(submitted for publication).

Li, W-H; Lynn, J. W.; Stanley, H. B.; Udovic, T. J.; Shelton, R. N.; and

Klavins, P.; "Crystal -Field Splittings in the Cubic Heusler Alloys

HoPd2Sn," (1988) (submitted for publication)

208
PUBLICATIONS

Loidl, A.; Knorr, K. ; Rowe, J. M. ; Mclntyre, G. J.; "Glass and Phase

Transitions in (KBr)j_^(KCN)^," Phys. Rev. B 3Z, 389-398 (1988).

Lynn, J. W.; Li, W-H.; and Li, q.; "Two-dimensional Character of the

Magnetic Order in ErBa2Cu20^," Solid State Science, Vol. 1, 357-361

(1987).

Lynn, J. W.; Li, W-H.; Li, Q.; Ku, H. C; Yang, H. D.; and Shelton, R. N.;

"Magnetic Fluctuations and Two-Dimensional Ordering in ErBa«Cu«0,,"

Phys. Rev. B 36, 2374-2377 (1987).

Lynn, J. W.; Li, W-H.; "Anti ferromagnetic Order of the Cu in RBa^Cu^Og ,

J. de Physique, (to be published).

Lynn, J. W.; and Li, W-H.; "Magnetic Order in

^^2^^2'^6+x'" l^^gnetism

Conference, Vancouver, Canada, J. Appl . Phys. (to be published).

Lynn, J. W.; Li, W-H.; Mook, H. A.; Sales, B. C; Fisk, Z.; "Nature of the

Magnetic Order of Cu in Oxygen Deficient NdBa^Cu^Og , " Phys. Rev.

Lett. 60, 2781 (1988).

Lynn, J. W. and Rhyne, J. J.; "Spin Dynamics of Amorphous Magnets," in Chap.

14 in Spin Waves and Magnetic Excitations , edited by A. S. BorovikRomanov and S. K. Sinha, North Holland Physics Publishers, Amsterdam,

177 (1988).

Majkrzak, C. F.; Cable, J. W.; Kwo, J.; Hong, M.; McWhan, D. B.; Yafet, Y.;

Waszczzak, J. V.; Grim, H.; and Vettier, C; "Polarized Neutron

Diffraction Studies of Gd-Y Synthetic Superlattices," J. Appl. Phys.

61, 4055 (1987).

Majkrzak, C. F.; Gibbs, D.; Boni, P.; Goldman, A. I.; Kow, J.; Hong, M.;

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

Bohr, J.; Grimm, H.; and Chien, C. L.; "Magnetic Superlattices," J. Appl. Phys., 63, 3447 (1988).

Majkrzak, C. F.; "Polarized Neutron Diffraction Studies of Synthetic

Superlattices," Metallic Multilayers and Epitaxy, (The Metallurgical

Society, Pittsburgh, PA (1988).

Majkrzak, C. F.; Neumann, D. F.; Copley, J.R.D.; and DiNardo, R. P.; "Fe-W

Supermirrors for Polarizing Neutrons," Proc. of the 1987 Fall Meeting

of the Materials Research Society (in press).

Majkrzak, C. F.; "Polarized Neutron Scattering: Some Current Methods and

Applications," Proc. of the Int'l Conf. on Neutron Scattering,

Grenoble, France, July 1988, Physica B (to be published).

Majkrzak, C. F.; "Applications of Supermirrors and Multilayers at the NBS

Cold Neutron Research Facility," Proceedings of the 32nd Annual Int'l

Tech. Symposium on Optical and Optoelectronic Applied Science and

Engineering, SPIE, August 1988, San Diego, CA (to be published).

209
PUBLICATIONS

Majkrzak, C. F.; "Supermirrors," Proc. of the Workshop on X-ray and Neutron

Scattering from Magnetic Matls, Nov. 1987, Argonne, IL, Physica B (to

be published)

.

Majkrzak, C. F.; Cox, D. E.; and Lehmann, M. S.; "Neutron Diffraction," to

appear as a chapter in Physical Methods of Chemistry , edited by

Rossiter and Hamilton, John Wiley and Sons, Inc. (to be published).

Matsushita, Y.; Nakao, Y.; Saguchi, R.; Mori, K.; Choshi, H.; Muroga, Y.;

Noda, I.; Nagasawa, K. ; Chang, T.; Glinka, C. J.; and Han, C. C;

"Phase Contrast Matching in Lamellar Structures Composed of Mixtures of

Labeled and Unlabeled Block Copolymers for Small -Angle Neutron

Scattering," Macromol . (in press).

Mighell, A. D.; Stalick, J. K.; and Himes, V. L.; "NBS Crystal Data:

Database Description and Applications," Crystallographic Databases:

Information Content, Software Systems, Scientific Applications. Data

Commission of the International Union of Crystallography, 134-143

(1987).

Neumann, D. A.; Zabel , H.; Rush, J. J.; Fan, Y. B.; Solin, S. A.;

"Quasielastic Neutron Scattering Study of Rotations and Diffusion in Kc

(NH)," J. of Phys. C. 20, L761 (1987).

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. B3Z, 8424 (1988).

Neumann, D. A.; Zabel, H.; and Morkoc, H.; "Terracing in Strained-layer

Superlattices," J. Appl . Phys. (in press).

Nicol, J. M.; Rush, J. J.; Kelley, R. D.; "Neutron Spectroscopic Evidence

for Subsurface Hydrogen in Palladium," Phys. Rev. B36, 9315-17 (1987).

Nicol, J. M.; Udovic, T. J.; Rush, J. J.; and Kelley, R. D.; "Isotope

Dilution Neutron Sectroscopy: A Vibrational Probe of

Hydrogen/Deuterium Adsorbate Interactions on Palladium Black,"

Langmuir, 4, 294 (1988).

Nicol, J.M.; Rush, J. J.; and Kelley, R. D.; "Inelastic Neutron Scattering

Studies of the Interaction of Hydrogen with Palladium Black," Surf.

Sci. 197, 67-80 (1988).

Nicol, J. M.; Eckert, J.; Howard, J.; "The Dynamics of Molecular Hydrogen

Adsorbed in CoNa-A Zeolite," J. Phys. Chem. (in press).

Osofsky, M.; Toth, L. E.; Lawrence, S.; Qadri, S. B.; Shih, A.; Mueller, D. Hein, R. A.; Fuller, W. W.; Rachford, F. J.; Skelton, E. F.; Elam, T. Gubser, D. U.; Wolf, S. A.; Gotaas, J. A.; Rhyne, J. J.; Kurtz, R. Stockbauer, R.; "Experimental Program on High Temperature Oxide

Superconductors at the Naval Research Laboratory," (to be published).

Parise, J. B.; McCarron, E. M.; Sleight, A. W.; Prince, E.; "Refinement of

the Structure of /S'-MoO-," Maters. Sci, Forum (in press).

210
PUBLICATIONS

Prask, H. J.; Choi, C. S.; Chesser, N. J.; Rosasco, G. J.; "Ammonium

Perchl orate Structure and Dynamics at Low Temperatures," J. Chem.

Phys. 88, 5106-5122 (1988).

Prince, E.; "The Maximum Entropy Distribution Consistent with Observed

Structure Amplitudes," Acta. Cryst. A. (submitted for publication).

Prince, E.; "An Alternative Approach to the Hauptman-Karle Determinantal

Inequalities," Acta. Cryst. A. (in press).

Rhyne, J. J.; "Neutron Scattering in Intermetallics," Invited Paper, Intn'l

Symposium on Magnetism of Intermetallic Compounds, Kyoto, Japan, J. Mag. and Mag. Matls. 70, 88 (1987).

Rhyne, J. J.; Erwin, R. W.; Borchers, J.; Salamon, M. B.; Du, R.; and Flynn,

C. P.; "Magnetic Ordering in Rare-Earth Multilayers Studied by Neutron

Diffraction," Invited Paper, 1987 Metallurgical Society Annual Meeting,

Trans. Metallurgical Soc. (to be published in 1988).

Rhyne, J. J.; Erwin, R. W.; Fernandez-Baca, J. A.; and Fish, G. E.;

"Magnetic Correlations in Amorphous Fe-Zr Alloys," J. Appl . Phys. 63,

4080 (1988).

Rush, J. J.; Berk, N. F.; Magerl , A.; Rowe, J. M.; and Provo, J. L.;

"Anomalous Vibrations of Hydrogen Isotopes in /3-phase Vanadium

Hydride," Phys. Rev. B., Rapid Comm. 37, (1988).

Rush, J. J.; Udovic, T. J.; Hempelmann, R.; Richter, D.; and Driesen, G.;

"Hydrogen Sites in Amorphous PdgrSi,nJ Probed by Neutron Vibrational

Spectroscopy," J. Phys. F (1988), in press.

Rush, J. J., "Research Opportunities and Planned Facilities at the Advanced

Neutron Source," A.N.S. Trans., in press.

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," Acta. Crys. A. (submitted for

publication)

Shelton, R. N.; McCallum, R. W.; Damento, M. A.; Gschneider, K. A.; Ku, H. C; Yang, H. D.; Lynn, J. W.; "Effects of Crystal Anisotropy on Magnetization and Magnetic Order in Superconducting RBaCuO ?," Physica

148B, 285 (1987).

Slade, R. C; Ramanan, A.; Nicol, J.; Rittar, C; "Synthesis, "Characterization and Inelastic Neutron Scattering Spectra of Hydrogen Insertion

Compounds of the Mixed V/Mo Oxide VgMOgO^Q, Mater. Res. Bull. 23, 647-

651 (1988)

Spano, M. L. and Rhyne, J. J.; "Small Angle Neutron Scattering From

Amorphous ErFe2 and HoFe2 Alloys, J, Appl. Phys. 63, 3752 (1988).

211
PUBLICATIONS

Spano, M. L.; Gotaas, J, A.; Rhyne, J. J.; "Neutron Scattering Study of

Magnetic Order in a Tbp rDyQ ^Single Crystal," to be published in Proc.

of the International Conference on Magnetism 1988.

Stamm, M. and Majkrzak, C. F.; "Investigation of Polymeric Thin Films by

Total Reflection of Neutrons," American Chemical Society Preprints

(1987).

Stanley, H. B. and Lynn, J. W.; "Anti ferromagnetic Structure of the Cubic

Superconductor ErPd2Sn," J. Appl . Phys. 61, 3371-3373 (1987).

Torardi, C. C; Reiff, W. M.; and Prince, E.; "Topochemical Li -ion Insertion

into FeClMoO and Fe(MoO): Structure and Magnetism of LiFeClMoO and

LiFe(MoO)," Mater. Sci. Forum (in press).

Tran Qui, D.; Handoune, S.; Soubeyeoux, J. L.; and Prince, E.; "Neutron

Powder Diffraction Study of Solid Solution Li, Tip, Ih P^Oj^," J. of

Solid State Chem. 72, 309-315 (1988).

Udovic, T. J.; Cavanagh, R. R.; Rush, J. J.; Wax, M. J.; Stucky, 6. D.;

Jones, G. A.; and Corbin D. R.; "Neutron Scattering Study of NH-"^

Dynamics During the Deammoniation of NH.-rho Zeolite," J. Phys. Chem.

91, 5968 (1987).

Udovic, T. J.; Cavanagh, R. R.; and Rush, J. J.; "Neutron Spectroscopic

Evidence for Adsorbed Hydroxyl Species on Platinum Black," J. Am.

Chem. Soc, 5590 (1988).

Wong-Ng, W.; Hubbard, C. R.; Stalick, J. K.; and Evans, E. H.;

"Computerization of the ICDD Powder Diffraction Database. Critical

Review of Sets 1 to 32," Powder Diffraction, 3, 12 (1988).

Xiao, G.; Cieplak, M. Z.; Musser, D.; Gavrin, A.; Streitz, F. H.; Chien, C.

L.; Rhyne, J. J.; and Gotaas, J. A.; "Significance of Plane versus

Chain Sites in High-Temperature Oxide Superconductors," Nature 332 , 238-40 (1988).

Yu, H.; Kitano, T.; Kim, C.Y.; Amis, E. J.; Chang, T.; Landry, M. R.;

Wesson, J. A.; Han, C. C; Lodge, T. P.;and Glinka, C. J.; "Study of

the Uniaxial Deformation of Rubber Network Chains by Small Angle

Neutron Scattering," Advances in Elastomers and Rubber Elasticity,

edited by J. Lai and J. E. Mark, Plenum Publishing Corp., 407-420

(1987).

Yu, S. C. and Lynn, J. W.; "X-ray Diffraction Studies of Amorphous

B C

Nigp 2A^^A'^^ 3.20

Q Qg," (submitted for publication).

Yu, S. C; Lynn, J. W.; Rhyne, J. J.; Fish, G. E.; "Spin Wave Excitations in

Amorphouse Fe^gBj^Sig," J. Appl. Phys. 63, 4083 (1988).

212
PUBLICATIONS

Zabel , H.; and Neumann, D.; "Neutron Scattering Studies of Potassium-Ammonia

Layers in Graphite," Can. J. Chem 66. 666 (1988).

INDEPENDENT PROGRAMS

Bauer, B. J.; Briber, R. M.; and Han, C. C; "Small Angle Neutron Scattering

Studies of Single Phase Interpenetrating Polymer Networks," Polymer

Preprints (ACS), 28(2), 169 (1987).

Becker, D. A.; "Quality Assurance Techniques for Zinc Analysis by Neutron

Activation," Trans. Am. Nucl . Soc. 55, 174 (1987).

Becker, D. A.; "Fast-Neutron INAA: Nickel Sensitivites and Fluence at Three

Reactors," Trans. Am. Nucl. Soc. 56 , 193 (1988).

Bowman, R. C, Jr.; Downing, R. G.; and Knudsen, J. P.; "NDP Evaluations for

Boron Implanted Compound Semiconductors," Trans. Am. Nucl. Soc. 55, 212

(1987).

Bowman, R. C, Jr.; Marks, J.; Downing, R. G.; Knudsen, J. F.; and To, G.A.;

"Effects of Boron Implantation of Silicon Dioxide Passivated HgCdTe,"

Proc. Mater. Res. Soc. Sym. 90, 279, (1987).

Clark, W. B.; Koekebakker, M.; Barr, R.D.; Downing, R. G.; and Fleming, R. F.; "Analysis of Ultratrace Lithium and Boron by Neutron Activation and

3 4 Mass-Spectrometric Measurement if He and He," Inter. J. of Appl

.

Radiation and Isotopes 38(9) , 735-743 (1987).

Cox, J. N.; Hsu, R. ; McGregor, P. J.; and Downing, R. G.; "NDP and FTIR

Studies of Borophosphosilicate CVD Thin -Film Glasses," Trans. Am. Nucl.

Soc. 55, 207 (1987).

Dzubay, T. G.; Stevens, R. K,; Gordon, G. E.; Olmez, I.; Sheffield, A. E.;

and Courntey, W. J.; "A Composite Receptor Method Applied to

Philadelphia Aerosol", Environ. Sci . Technol . 22, 46-52 (1988).

Dzubay, T. G.; Stevens, R. K.; Gordon, G. E.; Olmez, I.; Sheffield, A. E.;

and Courtney, W. J.; "A Composite Receptor Method Applied to

Philadelphia Aerosol", in Measurement of Toxic and Related Air

Pollutants, S. Hochheiser and R. K. M. Jananty, eds. Air Pollution

Control Assn., Pittsburgh, PA, 502-507 (1987).

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; German i, M.; Gordon, G.; Hanamura, S.; Kellogg, R. B.; Rhodes, J.

R.; and Schindler, J. S.; "Polymer Film Standards for X-ray Fluorescence

Spectrometers", J. Trace and Microprobe Tech. 5, 327-341 (1988)

Eisenhauer, C. M.; Schwartz, R. B.; and McCall, R. C; "Effect of Air

Scatter on Calibration of Instruments for Detecting Neutrons, Radiation

Protection Dosimetry 19, 2 . 77-84 (1987).

213
PUBLICATIONS

Fleming, R. F. and Lindstrom, R. M.; "Precise Determination of Aluminum by

Instrumental Neutron Activation," J. Radioanal. Nucl . Chem. 113, 35-42

(1987).

Gokmen, I.; Gordon, G. E.; and Aras, N. K.; "Application ofDifferent

Activation Analysis Techniques for Determination of Trace Elements in

Human Blood", J. Radioanal Nucl. Chem. 113, 453-459 (1987).

Greenberg, R. R. and Zeisler, R. L.; "A Radiochemical Procedure for the

Determination of Chromium in Biological Materials," J. Radioanal. Nuc.

Chem. (1987) (in press).

Greenberg, R. R.; Zeisler, R. L.; and Malozowski, S.; "Investigation of

Natural Chromium Levels in Human Blood," J. Trace Elem. Electrolytes

Health Dis., (1988) (in press).

Greenberg, R. R.; "Evaluation of Precision and Accuracy of Selenium

Measurements in Biological Materials Using Neutron Activation Analysis,"

Trans, the Am. Nucl. Soc. 56, 148-9 (1988).

Greenberg, R. R.; Zeisler, R. L.; and Malozowski, S.; "Investigation of

Natural Chromium Levels in Human Blood," to be submitted to Proc. Fifth

Int'l Workshop on Trace Element Analytical Chemistry in Medicine and

Biology.

Greenberg, R. R.; Zeisler, R. L.; Kingston, H. M.; and Sullivan, T. M.;

"Neutron Activation Analysis of the NBS Bovine Serum Standard Reference

Material Using Chemical Separations," to be submitted to Fresenius A. Anal . Chem.

Greenberg, R. R.; "Analysis of Atmospheric Particulate Samples Via

Instrumental Neutron Activation Analysis," to be submitted Proc. of

Conf. on Recent Developments in Monitoring Methods for Toxics in the

Atmosphere.

Greenberg, R. R. and Zeisler, R. L.; "A Radiochemical Procedure for the

Determination of Chromium in Biological Materials," J. Radioanal. Nucl.

Chem. (1987) (in press).

Hadziioannou, G.; Cotts, P.; ten Brinke, G.; Han, C. C; Lutz, P.;

Strazielle, C.; Rempp, P.; and Kovacs, A.; "Thermodynamic and

Hydrodynamic Properties of Dilute Solutions of Cyclic Polystyrenes,"

Macromol. 20, 493 (1987).

Han, C. C; Sato, T.; Okada, M.; and Wu, C; "Polymer Diffusion in an Interacting System," Polymer Preprints, ACS 28, 358(1987).

Han, C. C; Okada, M.; Muroga, Y.; Tran-Cong, Q.; and McCrackin, F. L.;

"Temperature, Composition and Molecule Weight Dependence of Binary

Interaction Parameter for PS/PVME Blends," Polymer (in press).

Hasegawa, H.; Tanaka, T.; Hashimoto, T.; and Han, C. C; "SANS and SAXS

Studies on Molecular Conformation of a Block Polymer in Microphase

Space. II. Contrast Matching Technique," Macromol. 20, 2120 (1987).

214
PUBLICATIONS

Han, C. C; "Dynamics of Phase Separation in Binary Polymer Mixtures,"

Proceedings for the First Toyota Conference on "Molecular Conformation

and Dynamics of Macromolecules in Condensed Systems," Inuyama, Japan,

Sept. 29-Oct. 1, 1987.

Iyengar, G. V.; "Dietary Intake Studies of Nutrient and Selected Toxic

Elements in Human Subjects: Analytical Approaches," Clin. Nutr. 6, 105-

117 (1987).

Iyengar, G. V.; "Dietary Collection Procedures, " Clin. Nutr. 6, 143-153

(1987).

Iyengar, G. V.; "Practical Constraints in Monitoring Micronutrient Intake,"

Clin. Nutr. 6, 156-158 (1987).

Iyengar, G. V.; Jones, J.; Cook, K.; Tanner, J. T.; and Wolf, W. R.;

"Comparison of Zinc Determination in Foods by Different Analytical

Techniques," Trans. Am. Nucl . Soc. 55, 177-178 (1987).

Iyengar, G. V.; Stoeppler, M.; Thomassen, Y.; and Weiz, B.; "Quality

Control," in Trace Elements in Health and Disease ^ Symposium Report,

Environmental Health Series, World Health Organization, Regional Office,

Copenhagen, Denmark, 26, 33-36 (1987).

Iyengar, G. V.; Tanner, J. T.; Wolf, W. R.; and Zeisler, R. L.; "Development

of Multi -Purpose Reference Materials," J. Res. Natl. Bur. Stand. (U.S.)

93, 1-2 (1988).

Iyengar, G. V.; "The Role of Neutron Activation Analysis in Nutritional

Biomonitoring Programs," Trans. Am. Nucl. Soc. 56, 233-234. (1988).

Iyengar, G. V.; "Biological Trace Element Research: A Multidisciplinary

Science," Sci . Total Environ. 71, 1-5 (1988).

Iyengar, G. V. and Behne, D.; "Appropriate Reference Parameters for the

Evaluation of Elemental Analysis Data From Biomedical Specimens," J. Res. Natl. Bur. Stands., (U.S.) 93, 326-328 (1988).

Iyengar, G. V. and Gopal-Ayengar, A. R.; Human Health and Trace E Elements

Including Effects on High Altitude Populations, Ambio, XVII, 31-35

(1988).

Iyengar, G. V. and 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.; Tanner, J. T.; Wolf, W. R.; Zeisler, R. L.; "Development of

Multi-Purpose Biological Reference Materials," J. Res. Natl. Bur.

Stands. (U.S.) 93, 360-362 (1988).

Iyengar, G. V.; Tanner, J. T.; Wolf, W. R.; and Zeisler, R. L.; "Development

of Multi-Purpose Reference Materials," J. Res. Natl. Bur. Stand. (U.S.)

93, 1-2 (1988).

215
PUBLICATIONS

Jamieson, D.. N.; Bowman, R. C; Adams, P. M.; Knudsen, J. F.; and Downing,

R. G.; "Study of Boron Implantation in CdTe," in Fundamentals of BeamSolid Interactions and Transient Thermal Processing , M. JU. Aziz, L. E. Rehn, and B. Stritzker, eds. 101, 299-304 (1988).

Knudsen, J. F.; Downing, R. G.; and Simons, D. S.; "NDP, SIMS, and Modeling

of Boron Implantation Profiles in Silicon," Trans. Am. Nucl . Soc. 55,

210 (1987).

Lamaze, G. P.; Gilliam, D. M.; Willliams, A. P.; "Prompt Gamma as a Fluence

Rate Monitor in Neutron Beam Experiments," J. of Radioanal. and Nucl.

Chem. 123(2) (1988).

Lamaze, G. P. and Grundl , J. A.; "NBS Measurement Services: Activation Foil

Irradiation With Californium Fission Sources, NBS Spec. Publ . 250-13

(1988).

Lamaze, G. P. and Grundl, J. A.; "NBS Measurement Services: Activation Foil

Irradiation by Reactor Cavity Fission Sources, NBS Spec. Publ. 250-14

(1988).

Lauenstein, G. G.; Wise, S. A.; Zeisler, R. L.; Koster, B. J.; Schantz, M. M.; and Golembiewska, S. L.; National Status and Trends Program for

Marine Environmental Quality Specimen Bank Project: Field Manual, NOAA

Technical Memorandum NOS OMA 37, Rockville, MD, December 1987.

Lindstrom, R. M.; Zeisler, R. L.; and Rossbach, M.; "Activation Analysis

Opportunities Using Cold Neutron Beams," J. Radioanal. Nucl. Chem. 112 , 321-330 (1987).

Lindstrom, R. M.; Nuclear Analytical Methods in Standards Certification, in

H. H. Ross, ed., "Comparison of Nuclear Analytical Methods With

Competive Methods," (IAEA-TECDOC-435), International Atomic Energy

Agency, Vienna, Austria 187-193 (1987).

Lindstrom, R. M.; "Measurement of Superconductor Stoichiometry by Prompt and

Delayed Neutron Activation," Trans. Am. Nucl. Soc. 56, 231 (1988).

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), International Atomic Energy Agency, Vienna, Austria (1988)

(in press).

Lindstrom, R. M.; Fleming, R. F.; and Rook, H. L.; "Neutron Microprobe:

Prospects and Potential Applications, Microbeam Analysis 1988," Proc.

22nd Ann. Conf. Microbeam Analysis Soc. (1988).

Lindstrom, R. M.; Neutron Activation Analysis in Electronic Technology,

(submitted for publication to the Electrochemical Society) (1988).

216
PUBLICATIONS

Matsushita, Y.; Nakao, Y.; Saguchi, R. ; Mori, K.; Choshi, H.; Noda, I.;

Nagasawa, N.; Chang, T.; Glinka, C. J.; and Han, C. C; "Phase Contrast

Matching in Lamellar Structures Composed of Mixtures of Labeled and

Unlabeled Block Copolymer for Small Angle Neutron Scattering," Macromol

.

21, 1802 (1988).

McGarry, E. D. and Boswell, E.; "Neutron Source Strength Calibrations," NBS

Spec. Publ. 250-18 (1988).

Moody, J. R.; Greenberg, R. R. ; Pratt, K.W.; and Rains, T. C; "Recommended

Inorganic Chemicals for Use as Calibrants," (submitted to Anal. Chem.).

Okada, M.; Sato, T.; and Han, C. C; "Dynamics of Concentration Fluctuation

on Both Sides of Phase Boundary," Proceedings for the International

Meeting on Dynamics of Ordering Processes in Condensed Matter, Kyoto,

Japan, August 27-30, 1987.

Olmez, I.; Gulovali, M. C; Gordon, G. E.; and Henkin, R. I.; "Trace

Elements in Human Parotid Saliva", Biol. Trace Elem, Res. (in press).

Riley, J. E., Jr. and Downing, R. G.; "Quantitative Determination of Boron

in Semiconductors Using Neutron Depth Profiling," Trans. Am. Nucl . Soc.

55, 207 (1987).

Riley, J. E., Jr.; Downing, R. G.; and Fleming, R. F.; "Neutron Depth

Profiling of Lithium in Lithium Niobate," Trans. Am. Nucl. Soc. 55, 214

(1987).

Riley, J. E., Jr. and Lindstrom R. M.; Determination of Boron in

Borosilicate Glasses by Neutron Capture Prompt Gamma-Ray Activation

Analysis," J. Radioanal. Nucl. Chem. 109, 109-115 (1987).

Rossbach, M.; SchSrpf, 0.; Kaiser, W.; Graf, W.; Schirmer, A.; Faber, W.;

Duppich, J.; and Zeisler, R. L.; "The Use of Focusing Supermirror

Neutron Guides to Enhance Cold Neutron Fluence Rates," Nucl. Instrum.

Meth., (submitted for publication).

Rossbach, M.; Zeisler, R.; and Lindstrom, R. M.; PGNAA with Cold Neutrons - A Challenge for Chemical Analysis, Proc. International Symposium on the

Utilization of Multi -Purpose Research Reactors, Grenoble, France, 19-23

October 1987: IAEA-SM-300-016, (1988) (in press).

Stone, S. F.; Zeisler, R. L.; and Gordon, G. E.; "Quantitative Determination of Proteins Using Polyacryl amide Gel Electrophoresis and Neutron

Activation," J. Trace Elem. Electrolytes Health Dis. (1988) in press.

Stone, S. F.; Becker, D. A.; Koster, B. J.; Pella, P. A.; Sleater, G. A.;

Tillekeratne, M. P. M.; Zeisler, R. L.; and Sanders, R. W.; "Inorganic

Methods and Results for Marine Bivalves and Sediments," in Progress in

Environmental Specimen Banking, NBS Spec. Publ. 740, 62-73 (1988).

Stone, S. F.; Zeisler, R.; and Koster, B. J.; "Neutron Activation Analysis of

Major, Minor, and Trace Elements in Marine Sediments", Trans. Am. Nucl.

Soc. 56, 228-229 (1988).

217
PUBLICATIONS

Stone, S. F.; Becker, D. A.; Koster, B. J.; Pella, P. A.; Sleater, G. A.;

Tillekeratne, M.P.M.; and Zeisler, R. L.; Inorganic Analytical Methods

and Results for Marine Bivalves and Sediments, in Progress in

Environmental Specimen Banking, NBS Spec. Publ . 740, U.S. Government

Printing Office, Washington, DC, 62-73 (1988).

Tuncel, S. G.; Gordon, G. E.; Olmez. I.; Parrington, J. R.; Shaw, R. W.,

Jr.; and Paur, R. J.; "Trace Element Concentrations on Fine Particles in

the Ohio River Valley" in The Chemistry of Acid Rain I: Sources and

Atmospheric Processes, R.W. Johnson and G. E. Gordon, eds., ACS Symp.

Series No. 349, American Chemical Society, Washington, DC, 66-81 (1987).

Tuncel, G. and Zoller, W. H.; "Iridium in the South Pole Atmosphere:

Estimation of a Meteoritic Component", Nature 329, 703-705 (1987).

Vossler, T. L.; Lewis, C. W.; Stevens, R. K.; Dzubay, T. G.; Gordon, G. E.;

Tuncel, S. G.; Russwurm, G. M.; and Keeler, G. J.; "Composition and

Origin of Summertime Air Pollutants at Deep Creek Lake, MD", (submitted

to Atmos Environ.).

Williamson, T. G. and Lamaze, G. P.; "Niobium as a Neutron Dosimeter,"

Trans. Am. Nucl . Soc. 55, 553 (1987).

Williamson, T. G.; Lamaze, G. P.; Gilliam, D. M.; and Eisenhauer, C. M.;

"Iron and Cadmium Capture Gamma Ray Photofission Measurements,

Proceedings of Meeting on Theory and Practices in Radiation Protection

and Shielding, Knoxville, TN.

Wise, S.A.; Zeisler, R. L.; and Goldstein, G. M.; eds.. Progress in

Environmental Specimen Banking, NBS Spec. Publ. 740, U.S. Government

Printing Office, Washington, DC, 217 (1988).

Wise, S. A.; Koster, B. J.; and Zeisler, R. L.; Status of Specimen Banking

Activities at the National Bureau of Standards, in Progress in

Environmental Specimen Banking, NBS Spec. Publ. 740, U.S. Government

Office, Washington, DC, 10-18 (1988).

Wu, W. and Gilmer, J. W.; "Molecular Weight Measured by Scattering

Techniques in Random Block Copolymers," Poly. Comm. 28, 202 (1987).

Wu, W.; Hunston, D. L.; Yang, H.; and Stein, R. S.; "Epoxy Network Structure

(IV) - A Neutron Scattering Study of Epoxies Swollen in A Deuterated

Solvent," Macromol. 21(3) , 756 (1988).

Wu, W. and Bauer, B. J.; "Network Structure in Epoxies (V) - Deformation

Mechanism in Epoxies," Macromol. 21(2) , 756 (1988).

Wu, W.; Bauer, B. J.; and Su, W.; "Network Structure in Epoxies (VI) - The

Growth Process Investigated by Neutron Scattering," (submitted for

publication).

Zeisler, R. L. and Becker, D. A.; "Determination of Zinc in a Monel Alloy by

Compton Suppression Spectrometry," Trans. Am. Nucl. Soc. 55, 175

(1987).

218
PUBLICATIONS

Zeisler, R. L.; Stone, S. F.; and Sanders, R. W.; "Sequential Determination

of Biological and Pollutant Elements in Marine Bivalves," Anal. Chem.

(submitted for publication).

Zeisler, R. L.; Greenberg, R. R.; and Stone, S. F.; "Radiochemical and

Instrumental Neutron Activation Analysis Procedures for the

Determination of Low Level Trace Elements in Human Livers," J.

Radioanal. Nucl . Chem. (1987) (in press).

Zeisler, R. L.; Greenberg, R. R.; Stone, S.F.; and Sullivan, T. M.;

"Selenium Determinations for the Assessment of Sample Stability in

Specimen Banking," Trans. Am. Nucl. Chem. (1987) (in press).

Zeisler, R. L. and Greenberg, R. R. ; "Determination of Baseline Platinum

Levels in Biological Materials," J. Trace Elem. Electrolytes Health Dis.

(1988) (in press).

Zeisler, R. L.; Greenberg, R. R.; and Stone, S. F.; The Determination of

Trace Elements in Human Livers, in Progress in Environmental Specimen

Banking, NBS Spec. Publ . 740, U.S. Government Printing Office,

Washington, DC, 82-90 (1988).

219
NBS-114A (REV. 2-ec) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NIST/TN-1257

2. Performing Organ. Report No, 3. Publication Date

January 1989

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities July 1987 Through June 1988,

5. AUTHOR(S)

Carol O'Connor, Editor

6. PERFORMING ORGANIZATION (If 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 20689

7. Contract/Grant No.

8. Type of Report & Period Covered

July 1987 through

June 1988.

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State, ZIP)

Same as item #6 above.

10. SUPPLEMENTARY NOTES

QJ Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual sumrr)ary of ntost significant infornnation. If document includes a significant

bibliography or literature survey, mention it here)

This report summarizes all those programs which use the NBS Reactor . It covers

the period for July 1987 through June 1988. 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.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

activation analysis; cold neutrons; crystal structure; diffraction; isotopes;

molecular dynamics; neutron; neutron radiography; nondestructive evaluation;

nuclear reactor; radiation.

13. AVAILABILITY

[y~| Unlimited

I I For Official Distribution. Do Not Release to NTIS

l~~\ Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

[X] Order From National Technical Information Service (NTIS), Springfield, VA, 22161

14. NO. OF

PRINTED PAGES

227

15. Price

USCOMM-DC 6043-P80

'U.b.COtftfiNOIElNT PRINTING OfF ICE :1989-242-31 1 :92623
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