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

NBS

PUBLICATIONS

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a NBS TECHNICAL NOTE 1 240

^CAU O*

U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards

NBS Reactor:

Summary of Activities

July 1986 Through

June 1987
Tm he National Bureau of Standards 1 was established by an act of Congress on March 3, 1901. The Bureau's overall ^L. goal i s t0 strengthen and advance the nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research to assure international competitiveness and leadership of U.S.

industry, science arid technology. NBS work involves development and transfer of measurements, standards and related science and technology, in support of continually improving U.S. productivity, product quality and reliability, innovation

and underlying science and engineering. The Bureau's technical work is performed by the National Measurement

Laboratory, the National Engineering Laboratory, the Institute for Computer Sciences and Technology, and the Institute for Materials Science and Engineering.

The National Measurement Laboratory

Provides the national system of physical and chemical measurement;

coordinates the system with measurement systems of other nations and

furnishes essential services leading to accurate and uniform physical and

chemical measurement throughout the Nation's scientific community,

industry, and commerce; provides advisory and research services to other Government agencies; conducts physical and chemical research; develops,

produces, and distributes Standard Reference Materials; provides

calibration services; and manages the National Standard Reference Data

System. The Laboratory consists of the following centers:

• Basic Standards2 • Radiation Research

• Chemical Physics

• Analytical Chemistry

The National Engineering Laboratory

Provides technology and technical services to the public and private sectors

to address national needs and to solve national problems; conducts research

in engineering and applied science in support of these efforts; builds and

maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement

capabilities; provides engineering measurement traceability services; develops test methods and proposes engineering standards and code

changes; develops and proposes new engineering practices; and develops

and improves mechanisms to transfer results of its research to the ultimate

user. The Laboratory consists of the following centers:

Applied Mathematics

Electronics and Electrical Engineering2 Manufacturing Engineering

Building Technology

Fire Research

Chemical Engineering3

The Institute for Computer Sciences and Technology

Conducts research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of

computer technology to improve effectiveness and economy in Government

operations in accordance with Public Law 89-306 (40 U.S.C. 759),

relevant Executive Orders, and other directives; carries out this mission by

managing the Federal Information Processing Standards Program,

developing Federal ADP standards guidelines, and managing Federal

participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government. The Institute consists of the following divisions:

Information Systems Engineering

Systems and Software

Technology

Computer Security

System and Network

Architecture

Advanced Systems

The Institute for Materials Science and Engineering

Conducts research and provides measurements, data, standards, reference

materials, quantitative understanding and other technical information

fundamental to the processing, structure, properties and performance of

materials; addresses the scientific basis for new advanced materials

technologies; plans research around cross-cutting scientific themes such as nondestructive evaluation and phase diagram development; oversees Bureau-wide technical programs in nuclear reactor radiation research and

nondestructive evaluation; and broadly disseminates generic technical information resulting from its programs. The Institute consists of the following Divisions:

Ceramics

Fracture and Deformation3 Polymers

Metallurgy Reactor Radiation

i Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address

Gatthersburg, MD 20899.

2 Some divisions within the center are located at Boulder, CO 80303.

'Located at Boulder, CO, with some elements at Gaithersburg, MD
Research Information Center

National Bureau of Standards

*.r^ -r- • . i. u* ** Gaithersburg, Maryland 20899

NBS Technical Note 1240

,6^53

NBS Reactor: /^/

Summary of Activities

July 1 986 Through

June 1987

Frederick J. Shorten, Editor

Reactor Radiation Division

Institute for Materials Science and Engineering

National Bureau of Standards

Gaithersburg, MD 20899

November 1987

U.S. Department of Commerce

C. William Verity, Secretary

National Bureau of Standards

Ernest Ambler, Director
National Bureau of Standards Technical Note 1 240

Natl. Bur. Stand. (U.S.), Tech. Note 1240, 197 pages (Nov. 1987)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1987

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

The National Bureau of Standards Reactor was built not only to serve the needs

of the NBS but also those of 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 was established to operate the reactor and

to foster its scientific and technological use. Toward this end, the Division has a small nucleus of scientists 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 actively seek out and

encourage collaboration with other scientists engaged in challenging programs whose

work can benefit from use of the reactor, but who as yet 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 has

been installed and construction of a large neutron guide hall will start this fall

(November, 1987). The guide hall will accommodate fifteen new instruments served by seven neutron guides from the cold source. This will be a national user facility

providing state-of-the-art instruments that are currently unavailable in the United

States

.

This report attempts to summarize all 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 self-explanatory.

Appreciation is extended to F. J. Shorten of the Reactor Radiation Division for

his extensive contributions to the editing, organization, and preparation of this

report, and K. E. Ferrel for efforts in typing manuscripts.

(R./ <^A^v

R. S. Carter

Chief, Reactor Radiation Division

National Bureau of Standards

iii
ABSTRACT

This report summarizes all those programs which use the NBS reactor. It covers

the period for July 1986 through June 1987. 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; crystal structure; diffraction; isotopes; molecular

dynamics; neutron; cold neutrons; 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 Bureau of Standards, nor does it imply

that the products are necessarily the best available for the purpose.

IV
TABLE OF CONTENTS

FOREWORD iii

ABSTRACT iv

A. REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS 1

Ammonia Adsorption by Zeolite H-Rho 1 Surface Adsorption Sites of Hydrogen on Palladium Black 3 Neuron Scattering Studies of Molecular Hydrogen Adsorption

in CoNa-A Zeolite 6 Isotope Dilution Neutron Spectroscopy: A Vibrational Probe of

Hydrogen/Deuterium Adsorbate Interactions on Palladium Black 8 Neutron Scattering Studies of the Structure and Dynamics of

Potassium-Ammonia Intercalated Graphite 11

Inelastic and Quasielastic Neutron Scattering Studies

of Pellicular Zirconium Hydrogen Phosphate, Zr (HPO, ) _ . H_0 14

Inelastic and Quasilastic Neutron Scattering Studies

of Hydrogen Oxide Bronzes 15

Concentration Dependence of the Local Mode Splitting

for Hydrogen in Yttrium 16

Investigation of Hydrogen Trapping in PdSc_ n9 18

Phonon Density of States of La.. „Sr_ ~Cu0, and La^CuO. 20 1.80.24 24

Phonon Density of States of YBa_Cuo

0_, and YBao Cuo 0, 23

The Floppy to Rigid Transition in Glassy GeSe and SiTe Alloys 26

Magnetic Structure of Dy-Y Superlattices 27

Magnetization Process in Dy Thin Films and Dy-Y Superlattices 30

Spin Dynamics in Dilute Magnetic Semiconductors Cd.. Mn Te and

-L - X. X

Znn Mn Te 34 1-x x Measurements of Phase Transitions with Neutron Spin Rotation 37

Magnetic Field- Induced State in Y Gd 39

Magnetic Phase Transition in Yn ^DY- _- 42

Absolute Measurement of the Ordered Magnetic Moment

in Holmium Rich (Er. Ho )Rh.B. 43 1-x x 4 4

Neutron Scattering Study of the Spin Dynamics of Amorphous

Fe

78

B

13

Si

g Alloy 46

Magnetic Structure of Cubic Tb Y

Q Ag 48

Recent Progress on BT-2 Triple-Axis Polarized Spectrometer 49

X-Ray Diffraction Studies of Amorphous

Ni

71.12

Cr l9.00 S1 7.30B

1.50

C

0.08

A11 °y 5 °

v
TABLE OF CONTENTS

Two -Dimensional Ordering in ErBa^CuuO.- 53

Suppression of Superconductivity by Antiferromagnetism in TnuFe„Si .... 57

Crystal Structure of the High-Temperature Superconductor

Lan oc Sr„ 1c CuO. Above and Below T 59

1 . 85 . 15 4 c The Structure and Properties of Bao YCu„0, 60

z Jo

Synthesis and Structure Refinement in the Non- Stoichiometric

Solid Solutions Ba2Re4 [BaxRe2/3 _ 2/3x l Ti9°27 (^ = Nd ' Sm ) 61

Neutron Powder Diffraction Study of Ba_YCu„0, c 63

I 5 o . _> Structural Distortion in La.. nc Ba. . ,-CuO, 69 1.85 . 15 4

Neutron Study of the Crystal Structure and Vacancy

Distribution of the Superconductor Ba^Y Cu~0-, » 70

2 3 9-6

Neutron and Synchrotron X-ray Powder Studies of a High

Ionic Conductor Solid Solution: Li.. Ti_ In P-0., _ 71 1+x 2-x x 3 12

Neutron Powder Diffraction Study of V_Mo-0. _ 73

9 6 40

Neutron Powder Diffraction Study of Anhydrous Lithium Exchanged

Zeolite X 75

Phase Extension by Maximum Entropy 76

Sub-Surface Residual Stress Measurements by Means of Neutron

Diffraction 79

Residual Stress Characterization of Al^O^/SiC (Whiskers) Using

Neutron Diffraction Techniques 83

Fiber Texture and Neutron Powder Diffraction Pattern 85

Crystal Data Center 88

A Matrix Approach to Symmetry 90

Small Angle Neutron Scattering Research at NBS 97

Curvature Properties of a Model Bicontinuous Structure

with a Well Defined Length Scale 99

Interpretation of Small Angle Neutron Data from

Porous Glass Using Cahn's Morphology 100

Phase Separation of a Binary Fluid in Porous Glass 103

Determination of Bonded Phase Absorbate Thicknesses

by Small Angle Neutron Scattering 105

SANS Study of Organophillic Bentonite Dispersed in Toluene 107

Small Angle Scattering Study of the Superconducting Transition

in ErBa Cu 108

Network Formation of Thermosetting Polymers - A Small

vi
TABLE OF CONTENTS

Angle Neutron Scattering Study of Epoxies 112

SANS Studies of Crosslinked Polymer Blends 114

SANS Studies of Single Phase Interpenetrating Polymer Networks 117

SANS Studies of Interacting Hemoglobin Molecules in Intact

Erythrocytes 121

Cold Neutron Project 126

NBSR Cold Neutron Source 131

Hydrogen in Metals 132

Coherent Neutrino Scattering from Crystals 133

Neutron-Antineutron Oscillations and the Possibility of "Squeezed

States" in Neutron Interferometry 135

Patterson Fourier Analysis of the Icosahedral (Al,Si)-Mn Alloy 135

Six-Dimensional Fourier Analysis of Icosahedral Al_,„Mn. n Si, Alloy 136

73 21 6

J Triple-Shell Symmetry in Alpha (Al.Si)-Mn 136

B. NON-RRD PROGRAMS 137

Neutron Activation Analysis of Microscopic Samples 137

A Radiochemical Procedure for Ultratrace Determination

of Chromium in Biological Materials 139

Determination of Trace Elements in International Diets 143

Status of Specimen Banking Activities at the National

Bureau of Standards 145

ASTM Task Group on Nuclear Methods of Chemical Analysis 155

NDP and FTIR Studies of Borophosphosilicate CVD

Thin Film Glasses 157

Fission Spectrum Averaged Cross Section of the

93 93

Nb(n.n') Nb Reaction 160

A B(n,a,7) Coincidence Technique for Absolute

Neutron Counting 164

Filtered Beams 167

C. REACTOR OPERATIONS AND SERVICES 170

Reactor Operations and Services 170

Engineering Services 171

D. SERVICE PROGRAMS 173

Neutron Activation Analysis at the Food and Drug Administration 173

E. PERSONNEL ROSTER 174

F. PUBLICATIONS 182

vn

A. Reactor Radiation Division and Collaborative Programs

AMMONIA ADSORPTION BY ZEOLITE H-RHO

J. M. Nicol

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

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

and

CD. Stucky

(University of California, Santa Barbara, CA)

Previously, quasielastic (QNS) and incoherent inelastic (IINS) neutron

scattering were used to characterize the deammoniation of zeolite NH, -Rho over the

temperature range 473 - 723 K, as well as the rotational dynamics of bound NH, in

1 4

the cavities of this catalyst. Studies have now been undertaken of the reverse process, the adsorption of ammonia by zeolite H-Rho. Ammonia was adsorbed at 295 K

into the cavities of H-Rho, generated in the previous study, to loadings of 1 , 3, 6 and 11 NH., per unit cell. The addition of NH_ to H-Rho results in the formation of + +

NH, ions by the coordination of the NH„ to the H cations in the zeolite framework.

Figures 1 and 2 depict IINS data collected in the 34 - 190 meV and 5 - 20 meV

regions as a function of NH., loading.

The changes visible in figure 1, namely, the rise in intensity of the peak at

45 meV, the decrease in intensity of the features at ca. 142, 131, and 93 meV and

the peak formed at 180 meV indicate changes in the vibrational density of states

resulting from the formation of NH, cations from NH„ and H . The decrease in

intensity of the proton-related features at 142, 131, and 93 meV as the NH., loading

is increased is a result of a decrease in the number of H cations. The generation

of NH, is seen by the appearance of the ammonium bending mode at 180 meV. The peak

at 45 meV has been shown previously to be associated with adsorbate-coupled

breathing (i.e., pore opening) modes of the zeolite framework. The increase in the

intensity of the 45 meV feature with increasing NH., loading is associated with an increase in the total number of H atoms in the system which are coupled to these

modes. During deammoniation, a shift from 38 to 45 meV was observed. In the case of reammoniation, no corresponding shift (i.e, 45 to 38 mev) is observed.

In the 5-20 meV region, modes due to the hindered rotations of the NH.

cations are observed at ca. 8 and 15 meV . Intensity differences are evident in data

collected at 10 and 80 K. In particular, at the fullest loading of 11 NH . /uc

,

additional baseline intensity is seen below ca. 10 meV at 80 K, which subsequently

disappears on cooling the sample to 10 K. This additional intensity appears to be
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGARMS

a

B

oo

.

/A

t

1 1 1 r H-Rho + NR,

80K

*V* VA

NHa A (f) "

•V. ^W, ^'VlV (d) 3

* ^ A. a. .AA (b)

J L J L

30. 90. .150. 210. Energy Loss (meV)

Figure 1. The IINS spectra at 80 K (except where indicated) for zeolite H-Rho as a function of NH loading per unit cell.

H-Rho + NH3 10K

"1 1 T

NHa

(d) 11

+< u4

^4 v^'*

'**

** + i * i (a)o

J L J L 4.00 9.00 '14.00 19.00 Energy Loss (meV)

4.00 9.00 . -14.00 19.00 Energy Loss (meV)

Figure 2. The low-energy IINS spectra of zeolite H-RHo as a function of NH.

loading per unit cell: (a) data collected at 80 K and (b) dat<

collected at 10 K.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

due to a very broad quasielastic feature. The motion causing this feature is frozen

at 10 K. Quasielastic data (not shown) also indicate such a weakly bound component.

Currently the QES data are being analyzed to identify the mechanism and energetics

of the NH. reorientational motions

4

A comparison of the data of reammoniation to that collected during

deammoniation will be made, in order to identify behavioral differences of the

NH. cations which can be related to the differences in the catalytic properties of

the two materials

1. T. J. Udovic, R. R. Cavanagh, J. J. Rush, M. J. Wax, G. D. Stucky, G. A. Jones

and D. R. Corbin, J. Phys . Chem, in press.

2. M. J. Wax, R. R. Cavanagh, J. J. Rush, G. D. Stucky, L. Abrams , D. R. Corbin, J Phys. Chem. 90, 532, 1986.

SURFACE ADSORPTION SITES OF HYDROGEN ON PALLADIUM BLACK

J.M. Nicol

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. D. Kelley

(Surfaces Science Division)

and

J. J. Rush

The ability of inelastic neutron scattering (IINS) in addressing surface

science problems has previously been demonstrated at NBS in studies of hydrogen and

1 2 hydrocarbons adsorbed on metal powders . This work has shown that results

obtained by IINS on high- surface -area metal powders, which possess a distribution of

particle sizes and are polycrystalline in nature, are generally consistent with

vibrational spectroscopy results found for adsorption on single crystals.

The adsorption sites for hydrogen on the surface of palladium black (a highsurface-area Pd powder) has been investigated by a combination of IINS and normal

coordinate analysis (NCA) . The spectrum of H-activated Pd black is shown in figure

1. Strong scattering features are observed at 468, 760, 819 and 969 cm . As the

sample was activated under conditions where bulk hydride species should not be

present all scattering features are assumed to be due to surface and/or near surface

species. The 468 cm feature has been assigned to the vibrations of subsurface H
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

E (cm 1 ) 250 500 750 1000 1250 1500 1750

100 150 E (meV)

Figure 1. The IINS spectrum at 80K of hydrogen- activated palladium black.

400

Model Pd-H Normal Modes

3 - Fold Symmetric Site

2.2

790+40crrf'

600 800 1000

cm -1

1200 1400

Figure 2. Vibrational modes of hydrogen on a symmetric 3 -fold site as a function of

force constant and Pd-H bond length calculated from normal coordinate

analysis. The shaded region indicates the range of bond lengths and

force constants consistent with the observed frequencies and relative

intensities

.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

3 in octrahedral sites below the top most Pd surface atom plane . Vibrations of H

adsorbed on surface sites are responsible for the remaining feature at 760, 819 and

969 cm . By comparing the experimental results with predicted IINS spectra

obtained from NCA calculations these features were assigned to a specific surface

site.

The NCA calculations employed established methods, which were previously

applied to H adsorbed on Raney nickel . A number of 2, 3 and 4 fold binding sites

found on Pd(100) and Pd(lll) surfaces (the predominant crystal planes expected on small Pd particles) were considered. The number of metal atoms considered was large

enough to define the symmetry of the binding site, second layer atoms being ignored.

A Pd-Pd bond length of 2.75 A (as found in bulk Pd) and a Pd-Pd force constant of

0.35 mdym/A were used. For all binding conditions a range of meaningful Pd-H force

constants and bond lengths were considered, from which the "best fit" to the data was obtained.

While a number of models were compatible with the experimental vibrational

frequencies and relative intensities, only the 3-fold site on Pd(lll) was found to

be physically resonable. The results of the NCA for the 3-fold site on Pd(lll) is

shown in figure 2. For binding in a symmetric 3- fold site one predicts a 2:1

intensity ratio for the observed spectral features, 2 degenerate modes parallel to

the surface and a non- degenerate mode perpendicular to the surface. In fitting the

features at 760, 819 and 969 cm we have assumed that the degerate mode is

represented by the peaks at 769 and 819 cm , as the intensity of these modes when

taken together is twice that of the mode at 969 cm . The best fit to the data is

obtained for a Pd-H bond length of 2.1 ± 0.05 A and the force constant is 0.43 ± 0.03 mdyn/A.

The assignment of our features to a surface 3 -fold site is in good agreement

with HREELS spectra of H adsorbed on Pd(lll) , where a vibrational energy of 759 and

1000 cm was obtained for the degenerate parallel and perpendicular modes

4 respectively . The observed splitting of the degenerate mode can be explained by dispersion of

optical phonon modes. Results of H isotope-dilution experiments confirm this

observation .

1. R.R. Cavanagh, R.D. Kelley and J.J. Rush, J. Chem. Phys . 7_7, 1540 (1982).

2. R.D. Kelley, R.R. Cavanagh, J.J. Rush, Surface Sci. 155, 480 (1985).

3. J.M. Nicol, J.J. Rush and R.D. Kelley, Phys. Rev. B, submitted.

4. H. Conrad, M.E. Kordesch, R. Scala and W. Stenzel, J. Electron Spectrosc. Relat

Phenom. 38, 289 (1986).

5. J.M. Nicol, T.J. Udovic, R.D. Kelley and J.J. Rush, in this report.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SCATTERING STUDIES OF MOLECULAR HYDROGEN ADSORPTION

IN CoNa-A ZEOLITE

J. M. Nicol

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

J . Eckert

(Los Alamos National Laboratory, Los Alamos, NM)

and

J . Howard

(Imperial Chemical Industries, Wilton, England)

Inelastic incoherent neutron scattering (IINS) has been applied to the study of

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

zeolite (Co. ., Na -A). Data have been collected in the energy range 1-40 meV using

the time of flight (TOF) and BT-4 spectrometers (TOF: 1-13 meV and BT-4,

Be/graphite-fliter configuration: 12-40 meV) . Hydrogen was adsorbed to a coverage

of 0.5 molecules per supercage in the fully dehydrated zeolite at 50K.

Subsequently, the sample was cooled to 12K for data collection.

Figure 1 shows the TOF spectrum for H~/CoNa-A at 12K using an incident energy

of 13.8 meV and contains data for both neutron energy loss (positive E) and neutron

energy gain (negative E) . The spectrum has been corrected for the featureless,

dehydrated zeolite background. The data points between ± 1 meV are due to less than

perfect subtraction of the elastic peak. Scattering due to adsorbed hydrogen is

observed at 3.8 meV. Data collected in the energy range 12-40 meV on BT-4 at 12K

(neutron energy loss only) are illustrated in figure 2. The data points in the

difference spectrum near 23 meV may result from incomplete subtraction of the

intense 20.5 meV peak present in the bare zeolite spectrum. This peak is most

likely related to a cation breathing mode coupled to residual hydrogen (probably in

the form of OH groups) . Two new features in the difference spectrum are observed at

15.5 and 28 meV. These features and the 3.8 meV feature in figure 1 are due

hydrogen interacting with the cations (most probably the Co ions) in the zeolite

framework. After annealing the sealed sample to 298K and recooling to 12K, no change was observed in the TOF spectrum. In addition, hydrogen could be reversibly

evacuated from the zeolite with ease at 298K, indicative of weak physisorption

.

This strongly suggests that we are dealing with molecular hydrogen, and that no dissociation is occurring. Spectra collected periodically during the sample warming

exhibited an unusual temperature dependence, in that very little broadening was observed with increasing temperature.

6
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

-2. 2. Energy (meV)

Figure 1. The time of flight spectrum at 1 2K of 0.5 hydrogen molecules per

supercage adsorbed in dehydrated CoNa-A zeolite. The spectrum has been

corrected for the dehydrated zeolite background.

*

1 1 1

• CoNa-A + H2

•

l/l -t-> c

• 3 4

* c (a) o

u

•

• 4

--> 3 ..* 4 •

<u z * X) * 1 N ^ ..

* ** A "3E

**

* V*--. u A o ****» z

to*

+

.

1 1

**4* x2 •V*

1 1 1 10. 20. 30. Energy Loss (meV)

40.

Figure 2. The Be/graphite filter spectrum at 1 2K of 0.5 hydrogen molecules per

supercage adsorbed in dehydrated CoNa-A zeolite: (a) dehydrated zeolite

background, (b) CoNa-A + 0.5 H molecules per supercage and (c)

difference spectrum.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Currently, the spectra are being analysed to establish the origin of the

observed modes in terms of rotational and vibrational transitions of hydrogen

interacting with the cobalt ions in the supercages . A number of potential force

fields of different symmetry are being considered. Consideration of ortho-para

hydrogen conversion at low temperature is also being made to explain the temperature

dependence of the TOF spectra.

ISOTOPE DILUTION NEUTRON SPECTROSCOPY: A VIBRATIONAL PROBE OF

HYDROGEN/DEUTERIUM ADSORBATE INTERACTIONS ON PALLADIUM BLACK

J. M. Nicol

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. D. Kelley

(Surface Science Division)

and

T . J . Udovic and J . J . Rush

In conjunction with deuterium isotope dilution, incoherent inelastic neutron

scattering (IINS) has been used to investigate the existence and degree of H-H

interactions for H adsorbed on Pd black. The presence of H-H interactions can be seen clearly in IINS by the effect of isotope dilution on the vibrational density of

states. Dynamic coupling between hydrogen atoms in an adsorbate layer can result in a significant dispersion of the corresponding hydrogen vibrational modes over

momentum space . Although isotope dilution of H with D leaves the adsorbate layer

electronically and chemically unchanged, it can somewhat change the dynamic coupling

between adsorbate oscillators and, concomitantly, the degree of phonon dispersion.

The isotope dilution results are illustrated by the IINS spectrum in figure 1

The vibrational spectrum of pure H (ca. 0.7 monolayers) on Pd black is depicted for

comparison in figure la. The assignment of the vibrational features for H/Pd black

to subsurface octahedral (58 meV) and surface threefold (94, 101 and 120 meV) sites

1 has been discussed previously. In particular, the existence of H-H interactions is

suggested by the broad, complex nature of the 94 meV feature assigned to the

degenerate parallel stretching mode of surface H.

The spectrum of dilute H in D (ca. 0.7 monolayers, H/D ~ 0.1) on Pd black is

shown in figure lb. In addition to the presence of H scattering features, careful
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

C

oo

a

o

u

<un•t—\ 136

o

(«)

-I r—jp 1—

1* 120

r

+ 4 i 7 ' + 4

V* * i 60 » , +1Tl 70-78 I

, ' H *tlxt«.i.,

123 M%( ,*

^

X10

20. 60. 100.

Energy Loss (meV)

140.

Figure 1. Neutron energy loss spectra of (a) pure H and (b) dilute H in D (0.07 H/

0.65 D) adsorbed on Pd black. (c) Difference spectrum following the

further addition of 0.04 monolayers H to the dilute H in D sample. (The

solid line is intended only as a guide to the eye.)

examination of figure lb indicates additional scattering intensity at ca. 43, 70-76

and 90 meV due to D adsorbed in the same sites occupied by H in pure H/Pd black. A

comparison of figures la and lb indicates that the subsurface/surface H intensity

ratio is markedly higher for dilute H in D than for pure H. This suggests that, for

dilute H in D, the subsurface H/D ratio is larger than the surface H/D ratio (i.e.,

there is preferential adsorption of H in the subsurface sites)

The difference spectrum following the further addition of 0.04 monolayers H to

the dilute H in D sample is shown in figure lc . By creation of a difference
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

spectrum, the scattering contributions due to D are effectively eliminated, leaving

a clearer representation of the scattering features due to the additional dilute H

atoms. The change from a broad complex feature peaked at ca. 94 meV for pure H

(figure la) to a sharper feature centered at ca. 101 meV for dilute H in D (Fig. lc)

corroborates the existence of dynamic H-H interactions within the pure H surface

phase. These interactions cause a dispersion of the phonon optical modes similar to

2 3 that for /3-Pd hydride and H/Pt black. One can rule out mixed-site population and

anharmonicity in explaining the origin of the complex feature for pure H since the

presence of these factors would yield vibrational density-of -states structure that

was independent of isotope dilution. Simple mass-defect theory, which has

2 previously been used to describe the isotope dilution results for /3-Pd hydride and

3 H/Pt black, predicted a value of 101 meV for the H local mode energy of dilute H in

D on Pd black, in good agreement with the observed value.

The overlap of scattering contributions from subsurface H overtone vibrations

in the vicinity of the 120 meV feature (assigned to the perpendicular stretching

mode of surface H) precludes any definite conclusions to be drawn about this dilute

H feature in figure lc. Moreover, except for the small shift to higher energy, there

appears to be little effect of isotope dilution on the density of states assigned to

subsurface H at 58 meV. This is consistent with the lower total concentration (ca.

0.1 ML as suggested by the relative scattering intensities) and degree of H dilution

(H/D —0.4) in the subsurface phase compared to the surface phase.

The present results again illustrate the potential of isotope dilution neutron

spectroscopy for probing the interactions of hydrogenous adsorbates in

polycrystalline materials such as catalysts. Future experiments are planned to more quantitatively investigate the effects of isotope dilution on the phonon density of

states for surface H on Pd black.

1. J.M. Nicol, J.J. Rush and R.D. Kelley, in this publication.

2. J.J. Rush, J.M. Rowe and D.Richter, Phys . Rev. B 31, 6102 (1985).

3. J.J. Rush, R.R. Cavanagh, R.D. Kelley and J.M. Rowe, J. Chem. Phys. 83, 5 33 9 (1985).

10
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SCATTERING STUDIES OF THE STRUCTURE AND DYNAMICS

OF POTASSIUM-AMMONIA INTERCALATED GRAPHITE

D . A . Neumann and J . J . Rush

and

H. Zabel

(University of Illinois, Urbana, IL)

and

Y. B. Fan and S. A. Solin

(Michigan State University, East Lansing, MI)

Potassium-ammonia intercalated graphite is an ideal system for the study of the

structure and dynamics of a simple two-dimensional (2D) molecular liquid. In

1 addition, the intercalant layer forms a 2D analog of the widely studied metalammonia solutions. We have therefore performed extensive elastic, quasielastic , and

inelastic neutron scattering studies which probe the structure and dynamics of these

compounds

.

The elastic scattering results have shown that the intercalant layer in the

stage 1 system, KC9/ (ND„) . „, does indeed form a two-dimensional liquid at room

temperature. It has also been shown that the data can be best described using a

25

20

> 15

0)E*»*_*>%o>

i_<u 10

i

1

1 -r KC24 (ND33'4.3 ),

0V- 1 L_ I | 0.1 0.2 0.3 0.4 0.5 q

Figure 1. [001] L phonon dispersion of stage 1 KC (ND ) at room temperature

24 v 3'4.3

11
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

T = 300K

Q,,= I.IOA

r, = 0.79 meV

rresl r 92 meV

r2

= l.l7meV r

dJf

= 0.22meV.

20^eV

-0.8 -0.4 0.0 0.4 ENERGY (meV)

0.8

Figure 2. a) Quasielastic spectrum at 78 K. The open circles are the

experimentally measured points, the solid line is a fit to a 6-function

plus a Lorentzian, both convoluted with the Gaussian instrumental

resolution, and the solid squares represent the Lorentzian contribution

to the scattering. A scattering function of this type is indicative of

a rotational motion of the ammonia molecules, b) Quasielastic spectrum

at 150 K. This shows the broadening of the Lorentzian component of the

scattering function. The activation energy of this motion is estimated

to be 3 - 5 meV. c) Quasielastic spectrum at 200 K (above the

intercalant melting transition). Here the previously observed

Lorentzian has broadened into a flat background. However the peak still

includes both a 6-function and a Lorentzian component due to the

appearance of a different reorientational motion. d) Qualielastic

spectrum at room temperature. The elastic component has also been

broadened due to translational motion of the ammonia molecules.

12
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

model in which four ammonia molecules are clustered about a single K ion. It was

not found necessary to include in the model any modulation of the liquid imposed by

the graphite bounding layers. Scans along the c -axis have shown that adjacent

intercalant layers are uncorrelated and that the graphite layers stack in an eclipsed configuration. It was also discovered that upon cooling the K- ammonia

layer freezes into a solid phase at a temperature of about 185 K. The structure of

this phase has not yet been determined, but it is currently believed to be

discommensurate and based on a 3 x 3 commensurate structure.

The measured c-axis phonon dispersion of this compound is shown in figure 1.

The most striking feature is the existence of three modes due to the splitting of

the acoustic branch by an additional excitation having an energy of 6.7 meV . The

solid line represents the results of a model calculation in which the phonon

dispersion of the stage 1 compound is described by a ID Born-von Karmen model

consisting of a single force constant and two masses, one for the carbon sheet and

the other for the K-ammonia layer. The additional mode is then included as an Einstein oscillator and the hybridization follows from a coupling term. Similar

results have also been observed for the stage 1 compound KC_

9 (ND„) although the

value of the coupling constant is reduced by an amount consistent with the reduction

in the ammonia concentration. The physical motion corresponding to the additional

excitation is however, still not clear. Models which describe it as a libration of

a single molecule all suffer from the fact that the potential barrier required for a

7 meV excitation is so small that at room temperature, the splitting should be

completely destroyed by anharmonicity . It is therefore probable that this motion

corresponds to a collective excitation of the molecules associated with a single K

ion.

The quasielastic scattering results, shown In figure 2, were performed on samples made with hydrogenated ammonia in order to increase the incoherent

scattering cross section. Below the intercalant melting transition these results

display a two-component peak, one component of which is resolution limited. This

lineshape is typical of a single rotational motion, which in this case has been

identified as spinning of the ammonia molecule about its three-fold symmetry axis.

Above the melting transition, two other motions are observed. The first corresponds

to reorientations of the molecular complexes about the graphite c-axis while the

second is due to translation motions of the ammonia molecules

.

J. C. Thompson, Electrons in Liquid Ammonia , (Clarendon, Oxford, 1976)

13
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

INELASTIC AND QUASIELASTIC NEUTRON SCATTERING STUDIES OF

PELLICULAR ZIRCONIUM HYDROGEN PHOSPHATE, Zr(HPO ) H

R.C.T. Slade

(University of Exeter, England)

and

(National Bureau of Standards, Gaithersburg, MD)

and

G. Albert!

(University of Perugia, Italy)

and

J.M. Nicol

Zirconium hydrogen phosphate (ZRP) is of interest as an inorganic ion-exchanger

and also as a protonic solid electrolyte. Pellicular ZRP (sheets made up of

platelets all with their c-axes nearly normal to the sheets) is of contemporary

interest and was first synthesised in Perugia. The Exeter Solid State Chemistry

Group has an on-going collaborative research programme probing structure and

dynamics in protonic electrolytes.

The incoherent inelastic neutron scattering spectrum of pellicular ZRP

confirmed that it is correctly chemically formulated , the P-O-H bending mode being

observed at ca. 1100 cm together with librational modes of H_0 at lower

frequencies

.

Investigation of the incoherent quasielastic neutron scattering spectrum of ZRP on the time -of- flight spectrometer (incident wavelength 5 A) revealed broadening at

90 C with a width (FWHM) for the Lorentzian component of 390 /zeV. Examination of

ZRP at 70 C on the triple-axis spectrometer showed Q- independent broadening

(measurements at Q/A " =1.34 and 2.00 avoiding Bragg scattering) with a width for

the Lorentzian component of 150 /xeV. The Q- independence of the broadening

characterises the motion reponsible as a reorientation (of FLO)

.

14
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

INELASTIC AND QUASIELASTIC NEUTRON SCATTERING STUDIES OF

HYDROGEN OXIDE BRONZES

R.C.T. Slade

(University of Exeter, England)

and

(National Bureau of Standards, Gaithersburg, MD)

and

H.A. Pressman and A. Ramanan

(University of Exeter, England)

and

J.M. Nicol

Hydrogen oxide bronzes , H MO , are nonstoichiometric insertion compounds of

transition metal oxides MO and of interest in catalysis and as mixed

n

J (electronic/protonic) conductors. In such systems H is believed to be attached to

( as -OH and, sometimes, as -0H~ coordinated to M) and rapid hydrogen self -diffusion

may be observed. The Exeter group has an ongoing collaborative programme

investigating hydrogen oxide bronzes.

The inelastic neutron scattering scattering spectrum of the compound

H.. _VQMo ,0. _ was recorded, completing the vibrational spectroscopy of the optically

dark phases H V Q Mo^0, n (x = 8 , 18). The presence of hydroxyl was confirmed by the

observation of the M-O-H deformation at 1040 cm (and no peak at ca . 1600 cm characteristic of -OH-). In the higher x value phase a broad band at lower energies

-1

(centered at 640 cm ) is attributed to H being carried by oxygen in the breathing

modes of the MO, octrahedra.

D The single phase H~

nMoO„ was studied on the time-of -flight spectrometer at A o = 5 A. At 60 C Q- dependent broadening of the spectrum was observed. Grouping

detectors known from the diffraction pattern to be free of Bragg contamination, the

el • -1

width (FWHM) of the Lorentzian component was 150 ± 7 /ieV at Q = 1.3 A and 250 ±

., ,. mean

el • -

1

22 peV at Q = 2.0 A . The Q-dependence of the broadening confirms a diffusive

motion of H is being observed. The percentage of the total proton population

undergoing diffusion is, as would be anticipated, Q- independent at 42 ± 2 %.

15
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CONCENTRATION DEPENDENCE OF THE LOCAL MODE SPLITTING

FOR HYDROGEN IN YTTRIUM

T. J. Udovic, J. J. Rush, J. M. Rowe , N. F. Berk

and

I . S . Anderson

(Swiss Institute for Nuclear Research, Villigen, Switzerland)

Recently, incoherent inelastic neutron scattering measurements of the local

mode frequencies in single - crystal samples of YH(D)_ .._ demonstrated a highly

unusual potential which is much softer and anharmonic along the c axis than in the

basal plane. The observation of a vibrational frequency which is reduced by ca. 25

% along the c axis is surprising since the T sites have nearly cubic local symmetry

with a c/a ratio that is only 3 % less than the ideal value. Low temperature

results with improved energy resolution showed a novel splitting of the c axis mode

which was interpreted in terms of the known H pairing in this system.

We have performed high resolution measurements of the local mode frequencies of

hydrogen in yttrium as a function of concentration and isotopic dilution in order to

wa

O

o

Isotope

i i Dilution @8K

**A

" YH .i8

/*v

7 V

~~ ^0.17^0.019

/ \

*

/ \

*

/ ' ' \

/ \ * */ \ * * / \

/

•

1

85. 95. 105.

Energy Loss (meV)

115.

Figure 1 . Comparison of the vibrational features for the H local mode polarized

along the c direction in single-crystal NH „ and YD H _ „ at 8 K.

16
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

T I I 1 1 1 YHj @80K

c

O

o

4 4*

4

. +++ %* x=0.18

'. 4 x=0.10

+++

+ +++

x=0.05

++

t +

x=0.03

+

J I J L 85. 95. 105. 115.

Energy Loss (meV)

Figure 2. Concentration dependence of the vibrational features for the H local

mode polarized along the c direction in polycrystaline YH at 80 K.

separate the effect of interactions between H atoms at higher concentrations from

the metal -hydrogen interactions.

Figure 1 shows the spectrum taken from the single crystal of YH„ .. at 8 K,

together with the data taken from the same crystal with composition YDn n Hn mn . u . l / u . u i y The spectrum for YH_ 10 shows two distinct peaks of roughly equal intensity centered

U . lo

at 9 9 and 103 meV, respectively. This observation of a splitting in the local mode

frequency polarized along the c direction for hydrogen parallels the earlier

measurements of a similar splitting for YDA 10 . However, the spectrum taken from

U . lo

the isotopically diluted hydrogen shows a single peak, centered at 100 meV , whose

full width (6 meV) is considerably narrower than the full width (-11 meV) of the

doublet measured for the pure hydrogen sample. This observation clearly favors a model of dynamical coupling as an explanation of local mode splitting.

A simple phenomenological model based on an elementary pair of coupled harmonic

oscillators relates the peaks at 99 and 103 meV to local "acoustic" and "optic"

vibrational modes of hydrogen pairs. Such a model also predicts a single peak for

the isotope diluted case, with a small upward shift in energy compared to the

17
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

nominal isotopic fundamentals, in good agreement with the experimental observations.

The concentration dependence of the local mode frequencies from a polycrystalline sample is shown in figure 2. The essential features are an overall

shift of the spectrum to lower energy as the concentration is decreased, together

with a broadening and collapse of the high-energy peak. In terms of the above

model, these observations may be explained by a relaxation of long-range, straininduced ordering present at high concentrations. This relaxation would result in a distribution of coupling constants, responsible for the behavior of the high-energy

peak. At the same time, the loss of long-range order would allow metal atom

displacements, otherwise hindered at high concentration due to the ordering of H

atom pairs , which give rise to an overall shift of the local mode spectrum to lower

energy.

1. I. S. Anderson, J. J. Rush, T. J. Udovic and J. M. Rowe , Phys . Rev. Lett. 57

(1986) 2822.

INVESTIGATION OF HYDROGEN TRAPPING IN PdSc

T. J. Udovic and J. J. Rush

and

I . S . Anderson

(Swiss Institute for Nuclear Research, Villigen, Switzerland)

and

H. Schone

(College of William and Mary, Williamsburg, VA)

Preliminary incoherent inelastic neutron scattering (I INS) experiments were

performed using the BT-4 triple-axis spectrometer to investigate the effect of Sc

impurity atoms on the vibrational density of states of H absorbed in Pd . Figure 1 shows the H vibrational spectrum of PdSc

Q 02

H

Q as a function of temperature after

subtraction of the PdSc

Q Q2 background spectrum using the Be-filter detector (with a resolution of ca. 6 meV below 100 meV) . Normally, the local modes of a- and /3-phase

Pd-H occur at 69 and 58 meV , respectively. Indeed, the spectrum at 295 K shows a broad local mode distribution peaking at 69 meV, suggesting the presence of a-phase

H. However, upon cooling to 80 K, a marked change in the spectrum is seen, with a broad feature peaking at ca. 60 meV and a shoulder at ca. 80 meV. Although it

appears that some a-phase H is still present at 80 K, the vibrational distribution

indicates that the Sc atoms perturb the main fraction H atoms that would otherwise

18
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

70. 90. 110. Energy Loss (meV)

150.

Figure 1 . Temperature dependence of the H vibrational spectrum for PdSc n? H

(minus the PdSc __ background spectrum) using the BT-4 triple-axis

spectrometer in the Be-filter detector configuration.

i i i

PdScoQgHx @80K

x=0.02

x=0.01

30. 50. 70. 90. Energy Loss (meV)

110.

Figure 2. Hydrogen concentration dependence of the H vibrational spectrum for

PdSc^ „„H (minus the PdSc^dSc, „„ background spectrum) using the BT-4

si configuration,

triple-axis spectrometer in the composite Be/graphite-filter detector

19
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

populate the /3-phase within the pure Pd matrix. The 2 meV shift from the expected

/3-phase position suggests that the Sc atoms actually trap at least some of the H

atoms, resulting in a perturbed site location compared to a- or /3-phase H. The

spectra can be explained by an ad-mixture of /3-phase and trapped H.

A higher-resolution configuration (i.e., the composite Be/graphite filter

detector with a resolution ranging from 2 to 5 meV over the energy regime scanned)

was used to explore r the 80 K spectrum r of PdSc_ ^^H as a function of H

. 02 x concentration. Figure 2 illustrates the results for x = 0.01 and 0.02. The

spectrum for PdScn ..H. n9 is similar to that in Fig. 1, and no features have been

more clearlyJ resolved. The spectrum for PdSc_ „„H_ -.. illustrates a more unusual

. 02 . 01

vibrational distribution with little evidence for /3-phase H. This suggests that,

for lower H concentrations, all the H is, indeed, trapped by the Sc atoms, yielding

significant vibrational contributions centered at higher energy.

Future experiments will focus on investigating this trapping phenomenon more thoroughly as function of temperature and H concentration.

PHONON DENSITY OF STATES OF La- Sr„ o Cu0, AND Lao Cu0, l.o U.z 4 z 4

J. J. Rhyne and J. A. Gotaas

and

L. Toth and S. Lawrence

(Ceramics Branch, Naval Research Laboratory, Washington, DC)

and

S. Wolf, M. Osofsky, and D. U. Gubser

(Metal Physics Branch, Naval Research Laboratory, Washington, DC)

The system La~ Sr CuO was the first of the new "high-T " superconductors, with

transition temperatures in the range of 30-40K, and it is believed that the

superconductivity in this system may still be of the BCS type, and hence mediated by

phonons . Detailed knowledge of the phonon dispersion would require single crystals

of sufficient size to perform inelastic scattering experiments on, but useful

information can be garnered by measuring the phonon density of states, which requires

only powdered samples. We have used BT-4 in both triple-axis and Be filter modes to

measure inelastic scattering in the superconductor La Sr n o Cu0 / and the non1 . o 0.2 4

superconducting end compound La CuO in an effort to identify key features in the

phonon spectrum. To obtain the density of states from the inelastic scattering, we have used the incoherent approximation, which has been shown to be reasonably

20
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2 accurate even for predominantly coherent scatterers. This yields the neutronweighted density of states, since the scattering from any mode depends on the atoms

participating in it according to the ratio of the total scattering amplitude over the

atomic mass. This will tend to weight modes involving oxygen atoms more heavily than

the other atoms, but that will be the same for both systems studied, and furthermore

it is believed that the oxygen atoms are crucial to the superconductivity in these

compounds

In order to cover the energy range from 5 to 95 meV, data were taken in three

overlapping modes, which were then scaled to form a single density of states, after

correcting the data for background and other energy factors that convert the measured

scattering to the double differential cross section. The resulting density of states was normalized so that the integrated intensity was unity, to make comparison between

the two samples easier.

Figure 1 displays the neutron weighted density of states (DOS), g(w), for

La.. SrA o Cu0. at T = 10K. The line through the data is simply a guide to the eye.

There is a typical u> dependence to the DOS at low energies, followed by a peak (or

shoulder) in the vicinity of 12 meV, increasing to the largest feature in the

scattering, a peak at approximately 20 meV. There is a slight drop to form a valley,

then an increase to a second peak at about 30 meV. There is a deeper valley in the

scattering at 35 meV , followed by another peak at 40 meV, another at 55-60 meV, then

*m

oQ

CDN• i—

"3

u

o

o

O

1 1 1 1 1 1

J- La

l.8

Sr0.2 Cu04_

f\ +

+ T=10K

— +f* \

—

—

pf>

\ —

—

1

1 1

i i K

0. 30. 60.

E (meV)

90.

Figure 1. Neutron-weighted phonon density of states for La- o Srn «CuO, at 10K.

21
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

O

C\2

*

CO

oQ

<DN• i—

<

13

o

55

La2Cu04

T=10K

30. 60.

E (meV)

Figure 2. Density of states for non- superconducting La-CuO, at 10K. Scattering

above 45 meV is shifted upward by approximately 5 meV with respect to the

spectrum seen in Fig. 1.

a sharp drop before a broad collection of peaks between 65 and 85 meV. The intensity

then drops to zero in the vicinity of 90 meV.

Figure 2 shows the same data range for the non- superconducting compound La9 CuO.

.

The general features of the DOS are clearly similar, with the differences that the

shoulder at 12 meV is less pronounced, and the valley between the peaks at 20 and 30

meV is deeper. Otherwise, the most significant change is that the intensity at

energies between 45 and 90 meV has shifted substantially upward in the nonsuperconductor, as though the entire scattering pattern had been shifted toward

higher energies by approximately 5 meV.

The comparison between the two DOS spectra suggests a general softening of the

phonon spectrum for the superconducting compound, but it is difficult to single out a given feature that may be closely coupled to the superconducting mechanism. Further

interpretation requires some sort of detailed lattice dynamical model to fit the

observed DOS.

1. J. G. Bednorz and K. A. Muller, Z. Phys . B64, 189 (1986).

2. P. F. Miceli, S. E. Youngquist, D. A. Neumann, H. Zabel, J. J. Rush and J. M. Rowe, Phys. Rev. B34, 8977 (1986).

22
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PHONON DENSITY OF STATES OF YBa-Cu.O^ Ail AND YBa_Cu„Ot Z D o

J. J. Rhyne , D. A. Neumann, J. A. Gotaas , and F. Beech

and

L. Toth and S. Lawrence

(Ceramics Branch, Naval Research Laboratory, Washington, DC)

and

S. Wolf, M. Osofsky, and D. U. Gubser

(Metal Physics Branch, Naval Research Laboratory, Washington, DC)

We have used inelastic neutron scattering to probe the vibrational modes in the

high temperature superconductor YBa 9 Cu„0 and in the non- superconducting but

crys tallographically equivalent compound YBa_Cu„0, _,., to examine possible phonon

effects contributing to the superconducting mechanism in these compounds. The

vibrational density of states (DOS) was obtained from the inelastic neutron

2 scattering data using the incoherent approximation. The measurements yield the

neutron-weighted phonon DOS, since the scattering from different species is weighted

by the values of the total scattering cross section divided by the mass. For 0, Cu

,

Ba , and Y these values are 0.26, 0.12, 0.043, and 0.08 (barns/amu) respectively.

Thus —80% of the observed scattering will be due to vibrations of the oxygen atoms.

The data were collected on BT-4; low energy data ( u> < 25 meV ) were taken In

the constant-Q mode (E_=13.8 meV) at several values of the scattering vector between

. -1

3.3 and 5.0 A and averaged to improve the incoherent approximation. Higher energy

data (> 20 meV) were taken using the Be -graphite -Be filter analyzer. After making

all background corrections and converting the measured intensities to g(w) , we used

the overlapping energy regions to scale the DOS obtained in the three different

energy ranges to obtain a single DOS, which was then normalized so that the

2 integrated DOS was unity. Previous studies of the DOS of coherent scatterers

suggest that any effects due to coherent scattering will only be manifested in the

relative intensities of the various features and will be of the order of the size of

the error bars in our case. The neutron-weighted phonon DOS of YBa^Cu at 120 K is shown in figure 1. Below

9 meV , the DOS displays the u> -dependence typical of three dimensional systems. The

small shoulder at about 12 meV is probably due to a zone boundary interlayer shear

mode. The DOS then increases, reaching a large maximum at 19-20 meV, followed by

another maximum at roughly 25 meV before dropping sharply to a minimum at 28-30 meV

.

There is a broad feature centered at about 34 meV , followed by a narrower, less

intense maximum at about 44 meV . Above 50 meV, the DOS increases to a shoulder at

23
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

30. 60.

E (meV)

Figure 1 . Vibrational density of states as measured by inelastic neutron scattering

scattering at 120 K. The largest spectral weight is contained in peaks

involving oxygen vibrations (see text)

.

+->

• i—i 2

0)

oQ

30. 60.

E (meV)

Figure 2. Vibrational density of states for the non- superconducting control compound

YBa Cu 0, measured at 78 K. The scattering above about 45 meV is

essentially unchanged from the superconducting material, while that at

lower energies shows significant changes in relative weights of the peaks.

24
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

about 60 meV and then a peak at 70 meV before dropping to zero at about 90 meV. The

rather unusual relative intensities of the low- and high-energy DOS peaks is due to

the degree of atom participation in the modes in these energy regions.

We have also measured the DOS in the superconducting state at T=12K. The only

clearly discernible difference was a slight shift of (^"l meV) in the energy range of

10-20 meV, which can be explained by typical anharmonic effects.

The DOS of the non- superconducting (semiconducting) YBa_Cu„0, compound is

significantly different, particularly in the relative weights of the peaks in the

energy range below about 45 meV . As observed in figure 2, the feature at ~ 70 meV is

essentially the same for the non- superconducting compound as for the YBa 9 Cu_0 7

, and

thus probably represents vibrational states associated with the planar and

tetrahedral oxygen sites (0(1), 0(2), and 0(3)) which have not changed their

occupancy. The double peak structure at 19-25 meV is dramatically different in the non- superconducting material, for which the relative height of the DOS feature at 19

meV has been strongly reduced compared to that at 25 meV. The scattering minimum

near 30 meV is common to both materials, however the broad relatively weaker feature

around 34 meV in the superconductor has become a dominant peak in the nonsuperconductor with a shoulder extending out to include the peak near 44 meV

.

Another minimum occurs around 47 meV in both materials. It is thus suggestive that

the scattering between about 25 meV and 45 meV reflects optic modes involving the

copper and oxygen atoms with polarization vectors in the plane, since these would

certainly be affected by the removal of oxygen atoms from the 0(4) site.

In the absence of a complete model calculation, a definitive assignment of

specific vibrational modes to the observed peaks in the DOS cannot be made. However,

as stated above, the overall spectrum is dominated by oxygen atom modes, and those

arising from the 0(4) linear chain site contribute to the lower energy peaks in the

spectrum and do not contribute strongly to the major features above 45 meV, which

remain unaffected by removal of more than 90 per cent of the oxygen from the 0(4)

site

.

1. R. J. Cava, B. Batlogg, R. B. van Dover, D. W. Murphy, S. Sunshine, T. Siegrist,

J. P. Remeika, E. A. Rietman, S. Zuhurah, and G. P. Espinosa, Phys . Rev. Lett. 58,

1676 (1987).

2. P. F. Miceli, S. E. Youngquist, D. A. Neumann, H. Zabel , J. J. Rush, and J. M.

Rowe, Phys. Rev. B 34, 8977 (1986).

25
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE FLOPPY TO RIGID TRANSITION IN GLASSY GeSe AND SiTe ALLOYS

W. A. Kamitakahara

(Ames Laboratory, Ames, IA)

and

R. L. Cappelletti

(Ohio University, Athens, OH)

and

P. Boolchand

(University of Cincinnati, Cincinnati, OH)

and

D . A . Neumann

Some years ago Phillips introduced the notion of overconstrained and

underconstrained glasses. In an underconstrained glass the number of degrees of

freedom per atom, N, (3 in three dimensions) is greater than the number of

mechanical constraints imposed by bond- stretching and bond-bending forces, N , while

in an overconstrained system the opposite is true. More recently, Thorpe has

developed this idea by showing that in an underconstrained glass it is possible to

2 have displacements without the atoms being subjected to a restoring force. These

deformations can then be thought of as zero-energy "excitations" which have been

termed "floppy" modes. (When van der Waals and dihedral angle forces are included

the floppy modes actually occur at non-zero energies as of course they must.) Thus

by adjusting the number of constraints per atom one can observe both floppy and

rigid behavior. In practice this can be achieved by varying the ratio of Se or Te

(N = 2) to Ge or Si (N =4) in a glassy alloy and then looking for an excess of

low energy modes in the vibrational density of states. We have therefore performed

inelastic neutron scattering studies of these systems in an attempt to directly

observe the floppy modes

The results of these measurements do indeed show a large feature in the

vibrational density of states of amorphous Se at an energy of about 4 meV. Upon

alloying with Ge this peak rapidly becomes less prominent, in qualitative agreement

with the concept of a floppy to rigid transition. However the observed

concentration dependence of the integrated intensity does not quantitatively agree

with simple rigidity percolation models. In addition, the temperature dependence of

this feature has been measured for the pure Se sample. These results show only

slight differences from those obtained at room temperature. No unambiguous evidence

for floppy modes was observed for the SiTe samples; however pure glassy Te samples,

26
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

which would have the highest fraction of floppy modes, were not available

1. J. C. Phillips, J. Non-Cryst. Solids 34, 153 (1979); 43, 37 (1981).

2. M. F. Thorpe, J. Non-Cryst. Solids 57, 355 (1983).

MAGNETIC STRUCTURE OF Dy-Y SUPERIATTICES

R. W. Erwin and J. J. Rhyne

and

M. B. Salamon, J. Borchers , S. Sinha, R. Du, J. E. Cunningham and C. P. Flynn

(University of Illinois, Urbana, IL)

Recent advances in the technologies required to manufacture superlattices and

multilayers have not only greatly expanded the control of materials properties, but

just as significantly opened new avenues for the investigation of microscopic

interactions. For many superlattices interdiffusion can now be limited to be

between only two growth planes, so that one has nearly arbitrary control over the

stacking sequence of atoms. These sharp chemical boundaries provide an ideal milieu

for studies of dimensionality and interface effects, and the control of layer

thickness makes it possible to study the details of interactions propagating through

the interlayers . We have been focusing on rare-earth magnetic interactions by

studying single-crystal rare-earth-metal superlattices grown by molecular beam

1 epitaxy.

We have shown by neutron diffraction that it is possible to characterize the

magnetic structures in single-crystal superlattices by means of a simple model for

the superlattice structure factors. In the Dy-Y superlattices investigated here the

measurements show that the magnetic structure is modulated by the separate magnetic

properties of each layer type. This is shown in figure 1 where we plot the turn

angles obtained in the Dy and Y layers for [Dy,

fi |Y„ ] „q , [Dy, ,-|Y, ,]64 and

[Dy-i /- |YQ ] in _. The helimagnetic turn angle in the Y layers is consistent with the

52° value obtained in dilute alloys and other superlattices as well as band3 structure calculations. The turn angle in the Dy layers is qualitatively similar

to that of bulk Dy , with an apparent trend towards larger values as the relative

amount of Y is increased. This may be evidence that magnetoelastic effects are perturbing the Dy turn angle. The most salient difference between the superlattices

4 and bulk Dy is the suppression of the ferromagnetic transition.

In figure 1 is also shown the total magnetic phase shift across the Dy and Y

layers between the nominal interfaces. The phase shift across the Y layers is

27
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

clearly not a multiple of n radians so that the coupling cannot be simply scalar as

2 obtained for Gd-Y superlattices

.

We have also obtained the magnetic coherence length by deconvoluting the

instrumental width and chemical coherence length from the observed magnetic

superlattice linewidths. These results are shown in figures 2 and 3, and it is

6.00

5.50

5.00-

4.50

O

w 4.00 z

| 3.50

3.00

2.50

2.00

-a a 3-

Ylayer [Dy^lYa,] 89

LAYER TOTAL PHASE SHIFT

Dy layers

it , AA ^ A- $-4&-Q> C Ylayer[Dy

16 IY

9 ] 100

40 80 120 160

T(K)

55

50-

45

40

35

30

25

20

15

4 + %«%? 4 ^ps «6 STB

^30°Lock40 80 120 160

T(K)

Figure 1. Left-hand side: Total phase shift of spin-density wave across Y layers

and Dy layers as a function of temperature for [ Dy ^ | Y

2 0-'8Q and for

[Dy

1f;|Yq L nn

. Note the Y phase shift is not a multiple of it. Right-hand side: Temperature dependence of the interplane turn angles

for Y layers and Dy layers in [ DY16l l Y

20 ] E9

[Dy

15

|Y 14^64 and

[Dy |Y ] Note the 30° lock in at low T for the sample with the

small number of Y planes. [Dy

16 | Yg

}

. The turn angle of bulk Dy,

which drops to 0° at the 85 K ferromagnetic transition, is shown for

comparison.

28
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

10 15 20 25

Y THICKNESS(# Y planes)

Figure 2. Magnetic correlation length (in both A and in number of complete

bilayers) obtained from the intrinsic Q width of the magnetic satellite

peaks as function of the Y thickness (number of atomic planes) for the

three samples.

600

500

x 400

O

UJ

200 100

r(A)

50

300

—i r

J Dependence of Coherence length

UJo

z

UJ

orUJx

o

o

200

30 25

2:140 A

single Dy layer

0.00 0.01 0.02 0.03

r"'=(Y THICKNESSr'(A"')

0.04

Figure 3. Magnetic correlation length plotted against the inverse of the Y thickness showing 1 /r dependence.

29
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

found that the coherence length falls off as the inverse of the Y layer thickness.

Note that the coherence falls below two bilayers at about 28 atomic planes of Y. If

the coherence in the chirality of the helical order were lost we would expect the

coherence range to be below two bilayers.

In conclusion, the nature of the magnetic structure in the Dy-Y superlattices

,

including the phase and chirality coherence, suggests that the order is propagated

via a spin-density wave in the Y conduction bands stabilized by the Dy 4f spins.

1. J. Kwo, D. B. McWhan, M. Hong, E. M. Gyorgy, L. C. Feldman and J. E. Cunningham, in Layered Structures, Epitaxy, and Interfaces . Materials Research

Society Symposia Proceedings No. 37, edited by J. H. Gibson and L. R. Dawson

(Materials Research Society, Pittsburgh, 1985), p. 509.

2. 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); L. E. Wenger, G. W. Hunter, J. A. Mydosh, J. S. Gotaas and J. J. Rhyne , Phys. Rev. Lett. 56, 1090

(1986); B. D. Rainford, H. B. Stanley and B. V. B. Sarkissian, Physica 130B , 388

(1985).

3. S. H. Liu, R. P. Gupta and S. K. Sinha, Phys. Rev. B 4, 1100 (1971).

4. R. W. Erwin, J. J. Rhyne, M. B. Salamon, J. Borchers , Shantanu Sinha, R. Du, J. E. Cunningham and C. P. Flynn, Phys. Rev. B 35, 6808 (1987).

HAGNETIZATION PROCESS IN Dy THIN FILMS AND Dy-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)

The epitaxial growth of single crystal rare-earth superlattices by molecular

beam techniques provides a unique method of studying the interactions responsible

for the intricate magnetic structures found in the constituent elements. We have

shown that the helimagnetic phase of Dy remains intact in Dy-Y superlattices (and

thin Dy films) with a coherence of both phase and chirality through the magnetically

'dead' Y interlayers . In this report we describe how the ferromagnetic phase is

suppressed in Dy-Y superlattices and also perturbed in Dy thin films. We will also

discuss the field effects on the coherence of the helimagnetic state in order to

obtain an estimate of the coupling strength across the Y interlayers.

The suppression of ferromagnetism in [ Dy 13 I Y

5Q ] 40 . [ DY15 I Y34 ] 74 - [ DY16 I Y2 o^ 89 ' [Dy

1 - I Y.. , ] , , and [Dy.. , | Yq

]

.. „„ is clearly deduced from the temperature independence

of the nuclear Bragg peaks observed in the neutron diffraction patterns. It is

30
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

evident that this effect is not simply the result of exchange dilution, since the

Neel temperatures of the superlattices are within 5 to 10 percent of the value for

bulk Dy (180 K) . Instead it is predominantly caused by the decreased magnetoelastic energy density when non-moment bearing Y atoms are placed in the lattice.

We can calculate this effect by making the approximation that the basal plane

orthorhombic distortion, the e mode, is completely clamped in the superlattice

.

Experimentally we have shown this to be the case by observing the temperature and

field dependence of basal plane nuclear reflections. The only allowed strains occur along the c-axis so that the magneto-elastic energy density can be expressed as

_ 1 z. z.2

f = o c ( € ) me /

A (cosw) ( e )

where

z a 1 q

C ~ C ll +

3 C22

and A

Z = cJ1

A

1 + yjc^

.

The strains A. and A„ are defined in Ref. 2, c, -, and c„~ are the symmetry elastic

constants and o> is the magnetic helix turn angle. Solving for the equilibrium

80

70

60

50

40

S 30

20

10

H = /

1.5 KOe I W U Vyi

(0002-) / \

25kOe

H reduced to iii

i-......^V H = Warmed to 60 K

[Dy, 5 Y14 ] 6< 130 K Magnetic Satellites (0002 -)

H =

1.5 kOe ^^'"^w;

25kOe

1.8 1.9 2.0 2.1 1.80 1.90 2.00 2.10

Q,(A-')

Figure 1. The field dependence of the magnetic satellites is compared at 1 K and

at 130 K for [Dy |Y J,^. A second order transition to the

ferromagnetic state is observed at low temperature with a considerable

remanence. At high temperature the magnetization process is initiated

by a breakdown of the helimagnetic coherence due to pseudo-random field

effects. This allows an estimate of the coupling strength across the Y layers of 1 K per Dy layer per basal-plane atom.

31
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

strains in the superlattice results in the expression for the magnetoelastic driving

energy for ferromagnetism:

1 2 z 2 z Af = "^"(sin w) (A ) /c me 2

'

At T = 10 K in ferromagnetic bulk Dy A = 0.0009 and A = 0.0049, while the

elastic constants are c. - = 4.2x10 ergs/cm and c„ 9 = 13.1x10 ergs/cm .

' Using u> = 30° we find that Af (10K) = 0.6 K/atom, favoring ferromagnetism.

Therefore, even at low temperatures the magnetoelastic energy is not sufficient to

overcome the exchange -energy barrier of -1.0 K/atom in any Dy thin film elastically

constrained so that the 7-mode is completely clamped.

In a 4000 A thick Dy film grown on the same Nb and sapphire substrate as the

superlattices the temperature of the ferromagnetic transition is reduced to just

below 80 K on cooling, and a 20 K temperature hysteresis is observed. An

orthorhombic distortion is observed in a saturating field along the easy a-axis,

although its value is about 1/4 of the 7-mode strain in bulk Dy. The Nb buffer

layer is found to be unstrained suggesting that the magnetic film can slip on the

substrate when the magnetoelastic energy is sufficient. This would explain the

observed partial suppression of the ferromagnetic phase in the Dy film including the

hysteresis

.

The effect of an applied field on the superlattice helimagnetic state is shown

in figure 1. At low temperature (10 K in the figure) intensity is gradually

transferred from the helimagnetic superlattice peaks to the main Bragg peak (not

shown in the figure). The peak positions and widths are field independent. This

second order transition is, however, irreversible in most of the superlattices

studied, due to the large basal plane anisotropy. These anisotropy barriers can be

reduced and the helimagnetic phase regained upon warming the temperature to about 40

to 60 K, although the degree of coherence is less than in the zero-field-cooled

state

.

At high temperatures the magnetization process is qualitatively different than

at 10 K. Upon applying a magnetic field of 1.5 kOe , the magnetic satellites are observed to broaden. The full width of the most intense magnetic peak has been

plotted for two superlattices in figure 2. This rapid destruction of the coherence

has not been observed in any bulk helimagnets, and must therefore be a consequence

of the weak interlayer coupling of the Dy spins, along with the rapid decrease of

basal -plane anisotropy as the temperature is raised. Our data analysis gives an

32
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

o

-

1

1

I150K

^OK

/lOK

-5* 8~"~ §80K

[Dy

9 l(Dy Y)

g

] 90

i i i 10 5 10 15 H(kOe)

20

Figure 2. The intrinsic width of the magnetic satellites is plotted against the

applied field for several temperatures and for two different

superlattices. This width should increase as a power law of the applied

field when random-field theory applies, as is observed at high

temperatures.

uncompensated magnetic moment per layer of Dy of 5 . 4/x_ at 130 K due to the mismatch

of the helix wavelength with the Dy- layer thickness for the sample shown in

1 figure 1. We suggest that the Zeeman energy of the external magnetic field coupled

to this excess magnetic moment per layer is sufficient to break the weak interlayer

coupling between Dy spins. This is a random- field effect since the net layer

moments are in pseudo- random directions relative to the external field. We can approximate the strength of the interlayer coupling at 130 K as 5 kOe x 5 . 5/i ~ 1 K

per Dy layer per basal-plane atom. This is orders of magnitude larger than

estimates of the exchange coupling in rare-earths at a distance equivalent to the

interlayer spacing, which is additional evidence in support of the formation of an incipient spin density wave in Y in the presence of magnetic moments.

1. J. J. Rhyne, R. W. Erwin, J. Borchers , S. 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, S. Sinha, R. Du, J. E. Cunningham and C. P. Flynn, Phys. Rev. B3J5,

6808 (1987).

2. W. E. Evenson and S. H. Liu, Phys. Rev. 178, 783 (1969).

3. J. J. Rhyne and S. Legvold, Phys. Rev. 138, A507 (1965); F. J. Darnell and E. P. Moore, J. Appl. Phys. 34, 1337 (1963).

4. M. Rosen and H. Klimer, Phys. Rev. Bl, 3748 (1970).

33
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SPIN DYNAMICS IN DILUTE MAGNETIC SEMICONDUCTORS C<L Mn Te AND Zil Mn Te 1-x X 1-X X

T. M. Giebultowicz and J. K. Furdyna

(University of Notre Dame, Notre Dame, Indiana)

and

J . J . Rhyne

and

W. Y. Ching

(University of Missouri, Kansas City, MO)

and

D. L. Huber

(University of Wisconsin, Madison, WI)

The dilute magnetic semiconductors Cd, Mn Te and Zn, Mn Te are often referred

1-x x 1-x x

to as "frustrated" antiferromagnets . This term is supposed to describe a system in

which the energies of all pairs of ant if erromagnet Ically bonded spins cannot be

minimized simultaneously. A prototypical example of a frustrated antiferromagnet is a FCC array of spins , each interacting antiferromagnetically only with its nearest

neighbors. ° In Cd.. Mn Te and Zn, Mn Te the magnetic ions Mn form site-dilute FCC 1-X X 1-X X

° lattices , and the antiferromagnetic interactions between these ions are extremely

short-rangeo (JTM,„ ~ . 1J ._ J . Thus, both these compounds are a very close

nnn NN f j

realization of this idealized model. As follows from many recent theoretical

analyses and model studies , the consequences of the frustration of the spin lattice

are far reaching in the context of the magnetic properties of such systems. For

example, the ground state of the system is highly degenerate, there is no long-range

spin order in three dimensions, and the mechanism of spin excitations becomes very

complex. Frustration may also result in a spin glass behavior of the system in the case of site -diluted lattices. Cd.. Mn Te and Zn.. Mn Te show, indeed, many of the 1-x x 1-x x

J characteristic features of a spin glass at low temperatures. It is not clear,

however, whether these systems belong to the same universality class as, for

example, CuMn or AuFe

.

As with other spin glasses, the characterization of the spin dynamics in

Cd.. Mn Te and Zn, Mn Te at low temperatures and in the vicinity of the spin 1-xx 1-xx » freezing temperature is a problem of considerable importance. Recent model studies

of spin dynamics in dilute FCC Heisenberg ant if erromagnets have indicated that

quas iharmonic magnons may exist in these systems despite the absence of the longrange spin order. In order to verify these findings, we have carried out a series

of inelastic neutron scattering experiments on single crystals of Cd- ^Mn. f.-f^ e anc*

Zn, Mn Te with x = 0.65 and 0.41. The inelastic scattering spectra were compared 1-xx

34
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CduUn.jTe — 4.2 K

12- 15. 10. ENERGY (meV)

Figure 1. Fit of the theoretical lineshapes to the inelastic magnetic neutron

scattering spectra in Cd Mn £ 7 Te measured for several Q-vectors

along the <£,E;,0> direction.

Zn _ ssMn _eS Te

5°

en

I.

cmj - Q=(2*/a)(1.0.1.0,0)

4> - Q=(2n/a)(1

6. 9. 12. ENERGY (meV)

15. 18.

Figure 2. Examples of the same fit as in figure 1 for three different Q-points in

Zn

0.35

Mn

0.65

Te -

35
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Zn 3SMne5 Te - Q=(2ix/a)(1 .5,1 .5,0)

7. 9. 11. ENERGY (meV)

exchange° constants was assumed to be J. T„ T /J- T „TllT NN' NNN

Figure 3. The inelastic magnetic scattering spectra normalized by the detailed

balance factor [1 - exp(-E/kT )] measured in Zn oc Mn

o fi5 Te at Q

=

(2-ir/a) (1 ,1 ,0) for several different temperatures.

-> with the dynamic structure factors S(Q,E) obtained from the model. The calculations

were performed for systems with the same fraction of site occupancy as in the

measured samples, and with Heisenberg NN and NNN interactions. The ratio of the

0.1. Examples of the fits of the

theoretical curves to the experimental data obtained for the samples with high Mn

concentration are shown in figure 1 and 2. The results of this analysis show that

the model provides a very good description of the spin dynamics in the systems

studied for most of the Brillouin zone. Certain discrepancies were found to occur

only for Q-points close to the magnetic reflection center (1,~ 0). This fact may

suggest that there is an additional interaction mechanism in the real systems not

accounted for by the model (e.g. , one such possibility may be the MoriyaDzialoshinsky anisotropy)

.

The variation of spin dynamics with temperature was studied in detail for the

Zn„ „ r Mn_ , r Te sample. As indicated by the static spin-spin inverse correlation (J.JjU.dd

range /c(T) , and by the energy distribution in quasielastic magnetic scattering

measured vs. T, a transition from the low- temperature short-range ordered magnetic

phase to the paramagnetic state occurs in this system at T ~ 43 K. Surprisingly,

36
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

for certain Q-vectors the dynamic structure factor does not exhibit significant

changes up to temperatures as high as 70K (see figure 3) , indicating that magnon

modes occur in the system even in the thermally disordered phase.

1. For review of these works see, e.g., K. Binder and A. P. Young, Rev. of Mod.

Physics 58, 801 (1987)

2. W. Y. Ching, D. L. Huber, Phys . Rev. B25, 5761, and B26, 6164 (1982)

MEASUREMENTS OF PHASE TRANSITIONS WITH NEUTRON SPIN ROTATION

J. W. Lynn, Q. Li, W. -H. Li and S. Sun-Mack

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. W. Erwin

We have been employing a technique of measuring the magnetic properties of

systems by monitoring the change in phase of a neutron caused by changes in the

12 -»-»• magnetization of the sample. ' In essence the phase angle B»dx is measured along

the path of the neutron, and any changes in B as a function of temperature or applied field are then observed. The qualitative behavior of the sample can be

determined directly, and quantitative information can be obtained if the thickness

and shape of the sample are known and care is taken to eliminate return fields from

2 the path of the neutron outside the sample. We have used this technique to make

measurements on ferromagnets such as U~NiSn and Zr<-SboFe, reentrant ferromagnetic

spin r glass & materials such as (Fe Ni n )-,,-P n ,B,A1„ , superconductors such as Nb and x 1-x 75 16 6 3 r YBa^Cu^O-,, and magnetic superconductors such as (Er.. Ho )Rh,B, and TnuFe^Si,.

The measurements were made on the BT-2 triple-axis polarized beam spectrometer.

A monochromatic polarized beam is directed towards the sample, the polarization

state can be manipulated with flat- coil spin rotators placed before and after the

sample, and the final polarization is analyzed with a Heusler alloy analyzer. At

the position of the first flipper the spin of the neutron is rotated by n/2 so that

-» -* B J_ P. The spin then begins to precess with the classic Larmor precessional

frequency as it travels through the sample to the second flipper coil. The total

phase angle along the path is

^l E'dx

37
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

where 7T = 2.916 kHz/0e and v is the velocity. The instrument is set at one particular value for 4> , for example in the paramagnetic state of the sample where

B , is zero, and then changes in B can be readily detected. Figure 1 shows such

samp

11

a measurement for (Fe~ -. cNi^ ~ ) P^^ B,A1„, a sample which is just on the

ferromagnetic side of the paramagnetic-ferromagnetic-spin glass phase diagram. We

observe a change in the phase angle below -50 K as the system enters the

ferromagnetic state, but then the ferromagnetic component is lost at low

Figure 1 . The observed intensity for neutrons which have undergone a spin rotation

of tt. The increase in intensity an cooling signals the onset of

f erromagnetism , while the decrease at low temperature indicates the

destruction of the ferromagnetic state as the spin glass state develops.

38
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

4

temperatures as the spin glass state develops. These measurements were taken in an applied field of ~2 0e . One advantage of this technique is that intensity is no problem since we are observing the transmitted intensity of the primary beam, and

hence measurements can be made on very small samples . The data in figure 1 were taken on a sample weighing -4 mg. Another advantage of the method is that the

measurements can be carried out with the identical sample and under the identical

experimental conditions as conventional neutron measurements , which facilitates

comparison of the measured properties. We have found this quite useful in the case of some of our results on magnetic superconductors since this is the only neutron

technique where the superconducting phase transition can be observed directly.

1. J. W. Lynn, Q. Li, and R. W. Erwin, Bull. Am. Phys . Soc. 32, 922 (1987).

2. N. Stusser, M. Th. Rekveldt, and T. Spruijt, Phys. Rev. B31, 5905 (1985); ibid

31 6423 (1986).

3. See, for example, M. A. Manheimer, S. M. Bhagat and H. S. Chen, J. Magn. Magn.

Mat. 38, 147 (1983).

4. R. W. Erwin, J. W. Lynn, and A. Magerl, J. Magn. Magn. Mat. 54, 101 (1986).

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

Rev. B31, 5756 (1985).

MAGNETIC FIELD-INDUCED STATE IN Y, Gd 1-x x

J. A. Gotaas and J. J. Rhyne

and

L. E. Wenger

(Wayne State University, Detroit, MI)

and

J. A. Mydosh

(Kammerlingh Onnes Lab, Rijksuniversiteit Leiden, The Netherlands)

We have previously studied the magnetic phase transition in single crystals of

1 o Y

l_ xGd

x

in botn zero-field and in magnetic fields up to 7 Tesla. ' A new sample (x = 0.044) has been used to achieve a more favorable scattering geometry which

permitted measurements of the basal plane reflection (100) and its magnetic

satellite, as well as the (002) and its satellite. The modulated magnetic state

produces reflections which are satellites of the allowed nuclear reflections with

indices (h k £±8) , where the modulation wave vector S = 0.28c*. The intensity of the

39
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

observed peaks depends on the structure factor of the nuclear reflection, the

absorption, the magnetic form factor, and a spin structure factor which depends on

3 the relative orientation of the spin directions and scattering vector. If all other

factors affecting the intensity are removed, this spin orientation factor will then

lead to the satellite of the (100) being only half as intense as the satellite of the

(002) in a helical phase.

Figure 1 displays data taken on this sample in a field applied along a basal

plane direction perpendicular to the scattering vector. The zero-field peak

intensities have been normalized to reflect the intensity ratio of 0.51 between the

(100 ) and (002 ) satellites, which facilitates the direct comparison of their field

dependence. The field dependence of the (002 ) satellite intensity is as observed

2 + earlier, with a sharp decrease in intensity at H . In contrast, the (100 ) satellite shows no such drop, but rather a uniform gradual decrease with field. Note

that the (002 ) satellite contains contributions from the full basal plane magnetic

moment, but the (100 ) satellite is only sensitive to the moment components which are transverse to Q, or in this case parallel to the applied magnetic field. These data

therefore suggest that the sudden drop in intensity at H results from a disordering

of the helical moment components perpendicular to the applied field.

The different behavior of the two reflections under the applied field can be

understood more precisely with the help of the spin density wave concept. In

addition to the possibility of helical spin density waves (HSDW) , there can also

1.0

£ 0.8 -

(0E| 0.4

0.2

^0.956 6^0.044 OH

*s (002"

)

-

}

A (100+

)

•^. A A~~ _^_ _ A

A ^5~=: A^^-^^^

A ^—» A ~~~ "

I I I I I 0.0 1.0 2.0 3.0 4.0 H (Tesla)

5.0

Figure 1. Normalized peak intensities of (002") [«] and (100 ) satellites as function of applied field at 4.4 K.

40
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

4 exist linear spin density waves (LSDW). In zero field, the linear state is

energetically unfavorable in the absence of basal plane anisotropy. However, the

application of the magnetic field can serve to destabilize the helical state in favor

of the linear state, where moments lying in the basal plane have their magnitude

modulated along the c axis. This is not a reduction of the actual physical 4f spin

of the magnetic ions, but only a reduced conf igurational average at each of the

appropriate sites. Thus the LSDW represents a state with disordered transverse

components

.

Since the average moment per site in the basal plane (and hence perpendicular to

Q) is smaller in the LSDW state, the scattered intensity will be reduced at the +

(002 ) satellites. We can calculate that the average moment in the LSDW state is

reduced to (1/72) of the moment in the HSDW state. Since the scattering intensity is

proportional to the square of the moment, this leads to a reduction by a factor of

two in the peak intensity at the (002 ) satellite on conversion of the HSDW to a LSDW, precisely as observed in the measurements.

For the (100 ) reflection the LSDW state could have moments either parallel or perpendicular to Q. In the former case, there will be essentially no scattering from

the LSDW state at the (100 ) satellite position, while in the latter case there will

be essentially the same scattering from either a HSDW or a LSDW. The identical

intensities observed for the (100 ) reflection and the collapsed (002 ) peak suggest

that the field- induced transition is from the helical state to a linear state

transverse to Q and hence parallel to the applied field in this geometry.

The neutron diffraction data presented here demonstrate that the field- induced

magnetic transition in these dilute Y(Gd) alloys is a modification of the spin

structure from a simple helical spin density wave to a superposition of a linear spin

density wave and a ferromagnetic component, with the linear state moments parallel to

the applied field but modulated in magnitude along the c axis.

1. J. A. Gotaas, J.J. Rhyne , L.E. Wenger and J. A. Mydosh, J. Magn. and Magn. Mater.

54-57 . 93 (1986).

2. L.E. Wenger, Gary W. Hunter, J. A. Mydosh, J. A. Gotaas and J.J. Rhyne, Phys . Rev.

Lett. 56, 1090 (1986).

3. Stephen W. Lovesey, Theory of Neutron Scattering from Condensed Matter . Vol 2. (Oxford, 1984) Chap. 12.

4. A.W. Overhauser, Phys. Rev. 128, 1437 (1962).

41
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC PHASE TRANSITION IN Y

9?DY

J. A. Gotaas and J. J. Rhyne

and

L. E. Wenger

(Wayne State University, Detroit, MI)

and

J. A. Mydosh

(Kamerlingh Onnes Lab, Rijksuniversteit Leiden, The Netherlands)

As part of a systematic investigation of the magnetic states in dilute alloys of

rare earth ions in yttrium, we have carried out neutron diffraction measurements

on a single crystal of the dilute alloy Y_

Q Dy. ._. We have verified that in zero

applied magnetic field, the system orders into a modulated state at T = 9K. In

these dilute alloys, the propagation vector lies along the c axis and has magnitude S = 0.28c*, with the magnetic moments lying in the basal plane of the hexagonal

lattice. Within experimental error, the full free -ion moment is found for the Dy and

the temperature dependence is consistent with that of the Brillouin function for

J=15/2 . At T = 6K, a magnetic field applied in the basal plane causes no shift in

the value of the modulation wave vector of the magnetic satellite (000 ) and there is no additional broadening of the diffraction peak, similar to the behavior observed in

the Y(Gd) system. As shown in figure 1, when the magnetic field is increased, the

scattered intensity at 0.28c* drops continuously, with the helical phase being

completely suppressed in a field of 3 T. On reducing the field, there is hysteresis

in the peak intensity at 0.28c*, with only 79% of the original intensity being

recovered at H=0 . This residual intensity grows slowly with time, increasing to

approximately 82% of the original value over a period of one hour. This behavior

differs from that of the Y(Gd) system, which shows no hysteresis and displays a sharp transition between helical and sinusoidal phases. The difference presumably is

due to the presence of the crystal field anisotropy in the case of Dy, in contrast to

the S-state Gd ion. Further experiments as a function of both field and Dy

concentration are planned to clarify this.

1. J. A. Gotaas, J. J. Rhyne, L. E. Wenger and J. A. Mydosh, NBS Technical Note

1231 , 33 (1986) .

42
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CO

CDN• i-H la

o

2;

o

CO

1 1 1 \ Y0.97Dy(

1 1 1

3.03

O'

T = 6K

o a Field Increasing

o —

Field Decreasing

o

o

1 1 -J 1 1 0.00 1.00 2.00

H (Tesla)

3.00

Figure 1. Normalized peak intensity of (000 ) magnetic satellite as a function of

applied magnetic field, showing smooth suppression of modulated state

and hysteresis on reducing field at T = 6K.

ABSOLUTE MEASUREMENT OF THE ORDERED MAGNETIC MOMENT

IN HOLMIUM RICH (Ern Ho )Rh,B, 1-x x 4 4

Q. Li, J. W. Lynn and J. A. Gotaas

(University of Maryland, College Park, MD)

and

(National Bureau of Standards , Gaithersburg, MD)

HoRh.B, is an Ising-like ferromagnet (T = 6.5 K) where the ordered magnetic

M

1 2 moment is locked along the tetragonal c-axis. A crystal-field model predicts a ground- state doublet with a saturation magnetic moment of 10.0 \i . However, from

1 B our previous neutron diffraction studies it appeared that the ordered moment was substantially less than the full 10 /x value. A similar discrepancy has also been

B

noted for ErRh.B. . New powder neutron diffraction measurements were performed on

4 4

(Er, Ho )Rh.B. for concentrations x = 1.0, 0.89, 0.84 and 0.75 in order to 1-x x 4 4

investigate the possible origin of these discrepancies.

The usual method to determine the magnetic moment is to place the magnetic

intensities on an absolute basis by comparison with the nuclear intensities.

However, in the case of HoRh.B, the structure factors for the low angle nuclear

4 4

°

43
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

peaks happen to sum to very small values, so that even small uncertainties in the

coherent nuclear scattering amplitudes are greatly amplified in the calculated

nuclear structure factor. At larger angles, on the other hand, one has to rely on calculated free- ion values of the magnetic form factor to extract the moment <// >, which may introduce inaccuracies in the determined value. We therefore decided to

make a determination of the magnetic moment which was independent of the nuclear

scattering intensities of the samples by employing an independent (copper powder)

diffraction standard. We have also measured the magnetic form factor in order to

determine if the observed reduced value of the magnetic scattering might be

attributed to a moment on the rhodium sublattice rather than a reduction of the

holmium moment. The data were taken with a combined sample of 25 % (by weight)

HoRh,B, and 75 % Cu. Use of the mixed sample substantially reduced the error

4 4

introduced by absorption corrections of Cu and HoRh B since the absorption factors

are the same. Thus within experimental error the necessity of an absorption

correction was averted with this method.

The measurements in the ordered state were taken at T = 1.7 K, which was sufficiently low to obtain the full ordered moment. The magnetic component of the

intensity can be obtained by subtracting the scattering observed well above the

ordering temperature from the low temperature data. We have also made a measurement

of the magnetic form factor of HoRh B by measuring the intensities of eight powder

reflections. The results are shown in figure 1. The solid curve is the spherical

component of the free-ion calculation, and it is seen to agree quite closely with

the measurements . Thus we can conclude that there are no anomalies in the form

factor, and there is no obvious Rh contribution to the magnetic scattering

amplitudes. The final value of the magnetic moment was

</z Z > = (8.61 ± 0.06) /i_.

D

Our diffraction results for the other concentrations of (Er. Ho )Rh. B. yield

1-x x 4 4

the same value for the ordered moment of holmium, within experimental error. This

value is significantly reduced from the value of 10 /j. expected from a single- ion

crystal field model, and indicates that a more elaborate calculation is warranted.

44
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

10.0

9.0

t r

HoRh4 B4

Spherical Average

i(r) « 0.4 < j. > O.fe <q.- '^Qj)

5.0

[301} !l23}

{130}

v{222}

• Theory

* Experiment

J_ _L

0.0 0.1 0.2

sine/X(&-')

0.3

Figure 1. Magnetic form factor for HoRh.B,. The observations are in good

agreement with the calculated free-ion spherical form factor for Ho

(solid curve). The theory points include a small aspherical

correction for the holmium form factor. The X's show how the form

factor would appear assuming a substantial rhodium moment. The rhodium

moment is actually determined to be zero within the experimental

uncertainty of 0.07 y D

. B

J. W. Lynn, J. A. Gotaas , R. N. Shelton, H. E. Horng , and C. J. Glinka, Phys . Rev. B3.1, 5756 (1985). Additional experimental details and discussion can be

found here

.

B. D. Dunlap, L. N. Hall, F. Behroozi, G. W. Crabtree , and D. G. Niarchos , Phys.

Rev. B29 . 6244 (1984), and references therein; B. D. Dunlap and J. W. Lynn (to

be published)

.

45
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SCATTERING STUDY OF THE SPIN DYNAMICS

OF AMORPHOUS Fe^-B, _Si_ ALLOY

S. C. Yu, J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

J . J . Rhyne

and

G. E. Fish

(Allied Signal Inc., Morristown, NJ)

In order to obtain a better understanding of the magnetic properties of

amorphous alloys at high temperature, we have started a neutron study of the spin

dynamics of the high transition temperature amorphous ferromagnetic alloy Fe _Bno Si

(Metglas 2605S2) . The amorphous nature of the system required that measurements be

taken near the forward (000) beam position. A fixed incident energy of 13.5 meV was used and a pyrolytic graphite (PG) filter was placed after the PG (002)

monochromator to suppress high order wavelength contaminations. Nominal soller slit

horizontal collimators of 10' -10' -10' -10' were used to produced a FWHM energy

resolution of 0.35 meV at the elastic position. Well defined spin waves were observed over the entire accessible wave vector range of 0.06 A < q < 0.12 A , for temperatures between 473 K (0.67 T ) and 705 K (0.99 T ). At lower temperatures

the spin wave energies were outside the range of accessible (q,E) due to neutron

kinetic restrictions which apply to structurally amorphous materials.

In analyzing the data, the spin-wave energies and linewidths were obtained by

convoluting a theoretical cross -section with the instrumental resolution and leastsquares fitting to the observed spectra, after subtraction of the background

scattering. The spectral weight function used in the convolution was a double

3 Lorentzian.

The spin wave dispersion relation exhibits the conventional quadratic

2 relationship E = D(T) q + A typical of an isotropic ferromagnet, where the small

energy gap A of 0.05 meV is attributed primarily to the dipole-dipole interaction.

The spin-wave stiffness constant D obtained from such data is shown in figure 1 as a

. 2 function of temperature. An estimate of the T = value of D s 156 meV-A was obtained from a plot of D(T) versus T extrapolated to low temperatures, while the

Curie temperature of 710 K was obtained from the extrapolation of D(T) to zero at

46
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

o<

>

E

150

100

473K

800

Figure 1. Temperature dependence of the spin-wave stiffness constant.

high temperatures. At room temperature D has attained 93 % of the saturated lowtemperature value. Thus we do not expect much change in the dynamic susceptibility

in going from room temperature to low temperatures; the primary effect for the

observed scattering will be due to the change in the thermal population of the

magnetic excitations of the system. The temperature range over which the spin waves were accessible was too high for the spin wave renormalization to be proportional to

5/2 4 (T/T ) . Spin wave linewidth data for T/T ~ 0.95 showed the q wave -vector

dependence expected for magnon-magnon interactions.

The overall results indicate that conventional hydrodynamic spin wave theory

provides an appropriate description of the long wavelength magnetic excitations in

2 amorphous Fe „B-„SiQ, with a value of D/T = 0.22 meV-A /K consistent with that

found for other amorphous transition metal ferromagnets

.

1.

2.

3.

J. W. Lynn and J. J. Rhyne , in Spin Waves and Magnetic Excitations , ed. by A. S Borovik Romanov and S. K. Sinha (North Holland, 1988), Chap. 15.

A. K. Bhatnagar and N. Ravi, Phys . Rev. B 28(1) 359 (1983).

R. W. Erwin, J. W. Lynn, J. J. Rhyne and H. S. Chen, J. Appl. Phys.

(1985).

57 3473

47
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC STRUCTURE OF CUBIC Tb Y ^g

J. A. Gotaas

and

M. Said and J. S. Kouvel

(University of Illinois, Chicago, IL)

and

T. 0. Brun

(Argonne National Laboratory, Argonne, IL)

The cubic compound TbAg has an ordered antiferromagnetic state below T = 106K,

with the (nnO) structure. The (nnO) structure is made up of alternating

ferromagnetic (110) planes which are antif erromagnet ically aligned, so that the

basic magnetic unit cell is tetragonal with the basal plane dimensions doubled with

2 respect to the nuclear cell. In the case of TbAg, the moments have been shown to

lie along the c-axis. On diluting the magnetic Tb ions by non-magnetic Y ions, the

transition temperature decreases linearly with decreasing Tb concentration. For

concentrations below 50% Tb , magnetization measurements begin to show typical spin

glass properties, such as a time dependent thermoremanence , which suggests the

coexistence of ant if erromagnetism with a spin-glass state. We have used neutron

diffraction to investigate the nature of this mixed phase in the compound

Tb_ „Y_ -,Ag. For this composition, T„T = 36K as determined by low-field

. 3 . 7 & r N

J magnetization measurements. We have taken complete diffraction patterns at 60K and

4.5K. At 60K, the pattern arises from the crystallographic structure and is of the

CsCl-type, with a lattice parameter of 3.612A. At 4.5K, we have additional peaks

appearing of two types

.

The first type appears at the expected positions for the (nnO) structure, but

is a broadened peak instead of being resolution limited. If we interpret the

broadening as due to a finite correlation range of the (nnO) structure, it yields a value of approximately 20A, or roughly 3 times the expanded magnetic unit cell. The

second type of peak is much narrower, and corresponds to satellites of the (7T7rO) structure. Detailed modeling remains to be done, but the data is qualitatively

consistent with the type of structure observed in HoAg and TmAg , which is a

3 modulated structure based upon the (nnO) antiferromagnetic structure. It can be

described as a structure made up of two sublattices, each of which is modulated in

magnitude along the propagation vector in the lattice. The modulation wave vector

in these compounds is along a cube edge (100) -type direction. If we assume the same type of modulation here, the modulation wavelength would be approximately 60A, or on

48
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the order of nine magnetic unit cells, although the structure is likely

incommensurate

.

Preliminary temperature dependent measurements have been made on these peaks,

showing a similar temperature dependence for both types, with an ordering

temperature apparently between 37 and 40K, with some intensity persisting to above

45K. The apparent discrepancy in ordering temperature may be partially due to

differences in thermometry. Further work is planned, including more detailed

temperature dependences, higher-resolution measurements to study the peak structure

more carefully, field- dependent measurements and the investigation of other

compositions

.

1. J. W. Cable, W. C. Koehler and E. 0. Wollan, Phys . Rev. 136, A240 (1964).

2. H. A. Gersch and W. C. Koehler, Phys. Chem Solids 5, 180 (1958).

3. P. Morin, D. Schmitt and C. Vettier, J. Phys. (Paris) 46, 9 (1985).

RECENT PROGRESS ON BT-2 TRIPLE-AXIS POLARIZED SPECTROMETER

W-H. Li and J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

BT-2 is now operational as a variable incident energy three-axis polarized

neutron spectrometer. The monochromator is composed of five Heusler alloy (Cu9 MnAl)

3 crystals, each of which measures 2.955 x 0.675 x 0.15 inch , and are mounted in

reflection geometry on a vertically curved aluminum frame between two Nd-Fe-B

permanent magnets. The use of Nd-Fe-B magnets instead of SmCo, reduces the

radiation hazard of the magnet assembly. The analyzer is a flat Heusler alloy

assembly in reflection geometry. A pyrolytic graphite filter, or cold beryllium

filter, can be automatically placed in the reactor beam for filtering purposes.

Guide fields of ~ 130 Oe are built into the beam paths before and after the sample.

Flat-coil spin flippers can be used to rotate the polarization before and after

scattering as dictated by experimental requirement. New non-magnetic Soller slit

collimators have been constructed, with a minimum divergence of 5' (FWHM) . Be-Cu

blades coated with Cd are used, and can be removed to coarsen the divergence as required. The collimators were found to function within specifications at 14.8 meV.

49
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Before the shut down of the reactor for installation of the cold source, we have carried out the following experiments to test the operation of the

spectrometer. Spin-flip and non-spin-flip incoherent scattering cross sections

2 from vanadium were measured, spin rotation transmition measurements were conducted on LLNiSn and Zr^Sb-Fe to detect ferromagnetic phase transitions. Clear phase

transitions starting at temperature around 50 K and 270 C for quasi-crystal U«NiSn

3 and ferromagnetic Zr^Sb-Fe, respectively, were observed. Preliminary inelastic

scattering of high-Tc superconductor YBa9 Cu„07 and amorphous metglas Fe,

nNi,r.P1

, B, were also performed. The results show that BT-2 is now capable of carry out

inelastic scattering.

One of the difficulties with using Heusler alloy crystals for polarized beam

research is the very high reflection of these crystals for A/2 sections. We

therefore plan to replace these crystals with pyrolytic graphite monochromator and

2 3 analyzer crystals, and to obtain the polarization by use of multilayer devices. '

We expect to have this upgrade completed within the next year.

1. A. Freund, R. Pynn, W. G. Stirling, and C. M. E. Zeyen, Physica, 120B . 86

(1983).

2. J. W. Lynn, J. K. Kjems, L. Passell, A. M. Saxena, and B. P. Schoenborn, J Appl. Cryst., 9, 454 (1976).

3. C. F. Majkrzak and L. Passell, Acta Cryst., A41, 41 (1985).

X-RAY DIFFRACTION STUDIES OF AMORPHOUS

Ni

71 . 12

Cr

19 . 00

Si

7 . 30

B

1 . 50

C

. 08

ALL0Y

S. C. Yu and J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

The low cost metallic glass brazing foils provide strength and ductility which

are comparable to that obtained using gold-nickel foils. The flexibility of the

ribbon is related to its atomic structure; it is amorphous, or glassy, rather than

crystalline. We have begun an investigation of the Ni rich brazing filler metal

system by probing the atomic structure of the Ni-Cr based amorphous alloy with a conventional reflection type x-ray diffraction technique.

The sample used for this study is a metallic glass alloy with weight percent

composition of Ni _ _Cr n n or.Si ,.B. cn^n no- a commercial product labeled MBF-50A

/ Z . 1Z JL y . UU / . jU 1 . _>U U.Uo

by Allied Signal. The scattered intensity was measured in step- scan mode at

50
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

intervals of 0.05° over an angle range 29 = 12° - 160°. The Mo K (A = 0.7107 A)

radiation was filtered, and the wide-angle vertical scan x-ray diffractometer was equipped with a pyrolytic graphite monochromator . The observed intensity

distributions, 1(29), were converted to scattering intensity distribution, I(K), as a function of scattering wave vector, K = 47rsin 9/\, over the range from 1.85 A to

17.41 A . All data were collected at room temperature.

The basic experimental and analytical techniques used in this study were taken

2 from Cargill. We obtained the total interference function (or structure factor)

I(K) from the resulting normalized coherent scattering intensity. From this total

interference function, the atomic distribution function in real space, W(r) , was

3 obtained by Fourier inversion.

The coordination number (CN) is estimated from the area under the first peak of

the radial distribution function located between r = and the first minimum r . in

r. mm

the radial distribution function (RDF) which is defined by 47rr p(r):

-J?

-::N - l.

mln

47rr 2pdr,

The density of this metallic brazing foil sample, which was required to obtain the

3 4

radial distribution function, was taken to be 7.86 g/cm . The atomic percentage of

the sample (i.e., Ni,. , Cr.

g ? oSi ]3 00

B, _,C_ ,_) is used for the analysis instead

of the weight percentage.

Figure 1. Atomic distribution function of the Ni-Cr based amorphous alloy.

51
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The atomic distribution function W(r) of the amorphous alloy is shown in figure

1. In this distribution, a shoulder is observed in the peak at r = 4.66 A, which is

often the case in amorphous alloys. The spurious ripples present at r values less

than about 2 A are due to the relatively small remaining errors in the determination

of the normalization constant. Such errors, however, do not affect the peak

positions of the distribution function. The first peak occurs at r = 2.47 A which

is followed by a split double peak at 4.18 A and 4.66 A and other smaller peaks at

larger r. For the present alloy, the nearest neighbor distance and the coordination

number were found to be 2.47 A and 12.23, respectively.

If we assume that each of the atoms in the sample is packed with 12 nearest

neighbors (pseudo-dodecahedral- type structure), the nearest neighbor distance should

be the statistical average of the 12 contact distances, which is the sum of the

neighboring atomic radii as given by Teatum et.al. The differences between the

nearest neighbor distance obtained from the first peak position of W(r) and the

calculated nearest neighbor distance (2.51 A) from the atomic radii of each element

for CN =12, using the above model, are only 1.6 %.

1. D. Bose, A. Datta and N. DeCristofaro , Welding Journal 60(10) (1981) 29.

2. G. S. Cargill III, Solid State Physics , vol. 30, eds . F. Seitz, D. Turnbull and

H. Ehrenreich (Academic Press, N.Y. , 1975) p. 227.

3. C. N. J. Wagner, J. Non-Cryst. Solids 31 (1978) 1-40.

4. METGLAS data sheets, Allied Signal Inc.

5. S. Steeb and P. Lamparter, J. Non-Cryst. Solids 61 & 62 (1984) 237.

6. E. Teatum, K. Gschneidner, and J. Waber, 1960, LA- 2345, U.S. Department of

Commerce, Washington, D. C.

52
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

TWO-DIMENSIONAL ORDERING IN ErBa Cu

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

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

H. C. Ku, H. D. Yang, and R. N. Shelton

(Iowa State University, Ames, IA)

The discovery of superconductivity in YBa~Cu„0 has generated unprecedented

excitement in the physics community both because of the possible new fundamental

phenomena this class of systems represents as well as the enormous potential for

applications. The substitution of the heavy rare-earth elements for yttrium has

2 3 little if any detrimental effect on the superconducting transition temperature,

and hence these are ideal materials to investigate the interplay between magnetism

4 and superconductivity. We find that the Er moments exhibit a two-dimensional

ordering (or long range correlations) which is driven by the dipolar coupling of the

moments. The configuration of spins is such that chains form which are aligned

ferromagnetically , but with adjacent chains antiparallel

.

The diffraction data were taken with a wavelength of 2.3509 A and a pyrolytic

graphite monochromator and filter, in a pumped He-3 cryostat. Powder x-ray

diffraction patterns were indexed on an orthorhombic unit cell (Pmmm) , with room temperature lattice parameters of (3.845, 3.884, 11.53) A. A minor amount (< 5 %)

of a secondary ternary oxide phase was barely detectable in the x-ray pattern,

although it was easily detected with neutrons when the impurity ordered magnetically

(T ~ 12 K) . Magnetization measurements showed an onset temperature for

superconductivity of 95 K, with a Meissner exclusion of 75 % at low temperatures.

To isolate the magnetic scattering in ErBa9 Cu„07 we have employed the

subtraction technique. Well above any magnetic ordering temperature the magnetic

moments will be completely uncorrelated, and the diffraction pattern will consist of

coherent nuclear Bragg peaks and "background" . At low temperatures , on the other

hand, magnetic peaks will develop in the scattering due to magnetic order or correlations, which will appear in addition to the nuclear Bragg peaks. A

subtraction of the high temperature data from the data at low T then isolates the

magnetic response. Such a subtraction is shown in the top portion of figure 1. We see a rapid rise in the scattering, with a maximum at an angle of 17.8°, and then a long tail of scattering which extends towards larger angles. The position of the

peak coincides with a {1/2,0,0} type reflection, so that we can determine

53
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

immediately that the scattering is antiferromagnetic in nature. Note also that the

net scattering at the lowest angles is negative, which simply reflects the sum rule on the magnetic response; in some regions of q the magnetic scattering must decrease

in order to produce peaks elsewhere. The pronounced asymmetry of the observed peak

is a classic profile of a two-dimensionally ordered system. To understand the

origin of this behavior we note that there is only one Er ion per unit cell, so that

the Er sublattice is simple orthorhombic . The lattice parameters then show that the

separation of the Er ions along the a and b lattice directions is nearly the same,

while the distance along the c axis is about three times longer. Hence the dipolar

interactions will be very much smaller along this direction, and two dimensional

correlations seems likely. If the spin structure is collinear, then there are only

two possible spin configurations. The first is where the nearest neighbors are antiparallel , while the next nearest neighbors are parallel as shown in the inset to

the figure. The unit cell will be doubled along one direction, and this will give

rise to peaks like {1/2,0}, {1/2,1}, etc., and is consistent with the data in figure

1. Note that the spins form chains along the b axis which are parallel, while

adjacent chains along the a axis are antiparallel. The other possible spin

configuration is obtained by reversing all the next nearest neighbors along the b

direction, so that the unit cell doubles along both directions. The lowest order

peak in this model is the {1/2,1/2} peak, which is inconsistent with the data.

To quantitatively fit these data we have employed a model which assumes that

the scattering originates from a Bragg line. We remark that since the orthorhombic

distortion of this system is small and the scattering profile from a 2-d powder is

quite broad, we cannot unambiguously determine if the peak is a {1/2,0} or {0,1/2}

type reflection. The solid curve in the figure is a least squares fit, assuming

there is no intrinsic width to the Bragg line, and no correlations along the line.

The fit is excellent, and hence we conclude that there are strong correlations in

the a-b plane, while the correlation length along the c-axis is small. Of course for a powder it is difficult to determine whether the system is truly long range

ordered (viz. 2d Ising model), or whether it is simply highly correlated.

Additional measurements at lower temperatures would be useful.

The bottom portion of the figure shows the temperature dependence of the

intensity at the peak position. We see that the scattering is still increasing

rapidly down to 0.3 K, which is the lowest temperature we could achieve. Comparing

the magnetic intensity with the {001} nuclear intensity establishes that the ordered

magnetic moment <fi > is already 2 . 9 /z . We would expect the intensity to continue

54
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1500

1000-

g

E

ro

i

o

o

+-

•500

500-

15.0 20.0 25.0 30.0

Scattering Angle 26 (Degrees)

| 3000

*EO

I

o

o

en -QO

2500

2000

26 = 17.8

_L _L 0.4 0.8T (K)

1.2

Figure 1. a) Magnetic intensity observed at low temperatures. The solid curve is

a least squares fit of the data to the two-dimensional model as described in t^he text. ,The data were taken with an simple collimation

(FWHM) of 40 , and 25 before and after the sample, b) Temperature

dependence of the peak intensity. The solid curve is a guide to the

eye. The inset shows the magnetic configuration of spins.

55
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

to increase until the full ground state moment is obtained, and then become

independent of temperature. At sufficiently low temperatures the peak intensity

would presumably start to increase again as 3-d order eventually sets in, with the

data in figure 1 narrowing into a set of resolution limited Bragg peaks. The only

related system which has been investigated so far is La^CuO, , where the Cu moments

7 exhibit 3-d order (T ~ 220 K) with a similar doubling of the unit cell. In the

present system we would also expect a 3-d type of order if the Cu ions aligned since

nearest neighbor spacings are comparable in all three directions. However, we have no evidence in the present experiments that the Cu ions order.

1. M. K. Wu, J. R. Ashburn, C. J. Torng, P. H. Hor, R. L. Meng, L. Gao , Z. J. Huang, Y. Q. Wang and C. W. Chu, Phys . Rev. Lett. 58, 908 (1987).

2. P. H. Hor, R. L. Meng, Y. Q. Wang, L. Gao, Z. J. Huang, J. Bechtold, K. Forster,

and C. W. Chu, Phys. Rev. Lett. 58, 1891 (1987).

3. Z. Fisk, J. D. Thompson, E. Zirngiebl, J. L. Smith and S-W. Cheong (preprint).

4. For a review see Topics in Current Physics , edited by 0. Fischer and M. B. Maple

(Springer-Verlag, New York, 1983), Vols. 32 and 34.

5. Additional details can be found in J . W. Lynn, J. A. Gotaas , R. N. Shelton, H. E. Horng and C. J. Glinka, Phys. Rev. B31, 5756 (1985).

6. See, for example, J. K. Kjems, L. Passell, H. Taub , J. G. Dash, and A. D. Novaco, Phys. Rev. B13 . 1446 (1976), and references therein.

7. D. Vaknin, S. K. Sinha, D. E. Moncton, D. C. Johnston, J. Newsam, C. R. Safinya,

and H. E. King, Jr. (preprint).

56
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SUPPRESSION OF SUPERCONDUCTIVITY BY ANTIFERROMAGNETISM IN Tm Fe Si

J. A. Gotaas

and

J . W . Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. N. Shelton and P. Klavins

(Iowa State University, Ames, IA)

Tm_Fe„Si is of great interest because It orders antiferromagnetically at

ambient pressure with T = 1.1 K, while the application of pressure drives the

1 Z

system superconducting. The most interesting feature is that the superconducting

phase is suppressed once the antiferromagnetic ordering takes place. If the ordered

magnetic state is purely antiferromagnetic, then this represents a unique

experimental observation of the destruction of superconductivity by

antiferromagnetism in rare earth ternary compounds. We have previously examined

Tm-Fe-Si,. via neutron diffraction under applied pressures up to 5.8 kbar and

3 4

temperatures down to 0.3 K. We have now extended this to a pressure of 8.2 kbar,

at which point the superconducting phase transition occurs at T = 3 K.

The crystallographic structure of Tm9 Fe„Si is primitive tetragonal with space

5 15

group P4/mnc , and remains unchanged under application of pressures up to 8 kbar, as we have determined by high resolution neutron diffraction patterns taken on BT-1 at

room temperature and 78 K. The magnetic pattern at 8.2 kbar is also the same as that found at ambient pressure.

It is essential to determine if there is any ferromagnetic component (at any

pressure) which might be responsible for the destruction of the superconductivity.

As a result of the multi-sublattice magnetic structure there is magnetic intensity

at virtually all the nuclear peak positions, which complicates the detection of a possible ferromagnetic component. Two peaks which have no antiferromagnetic

contribution ({200} and {002}) were examined carefully and found to have no ferromagnetic contribution, but the experimental precision was only 1.5/jl . To

improve the precision of this important result, an additional experiment was carried

out with polarized neutrons at BT-2. If a polarized neutron beam is transmitted

through a sample which orders ferromagnetically , the local magnetization will tend

to rotate the polarization of the beam; the polarized beam transmission measurement

thus serves as a sensitive indicator of any ferromagnetic ordering in a system. No

57
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

change was observed in the beam polarization as a function of temperature in

Tm.Fe„Si,- at 8.2 kbar and we estimate from these data that any ferromagnetic

2 3 5 ° component must be < . 1/z . A careful search for ferromagnetic fluctuations or ~ B

possible oscillatory magnetic states was made around the forward beam and at the

nuclear peaks in the vicinity of the transition, but no evidence was found for such

additional effects which might accompany the destruction of the superconducting

phase

The theories which have been developed for antiferromagnetic superconductors

generally predict that the magnetic and superconducting states will coexist, with

some modifications of the superconducting properties (particularly H _) in the

7 8 8 magnetically ordered state. ' Machida et al . do explicitly consider a choice of

parameters in which the superconducting state is destroyed by the antiferromagnetic

transition, but then the superconducting state would be expected to reemerge at

lower temperatures. We have examined Tm_Fe„Si at 8.2 kbar via ac susceptibility

measurements down to 40 mK, and find no evidence for such an additional transition.

Our neutron diffraction measurements show that there is no ferromagnetic

component in the ordered state, and no change in the nature of the antiferromagnetic

ordering under increased pressure. This is the first direct experimental

observation of the quenching of superconductivity by purely antiferromagnetic order,

and should place strict constraints on the various theories which have been applied

to antiferromagnetic superconductors.

1. C. B. Vining and R. N. Shelton, Phys . Rev. B28, 2732 (1983).

2. C. B. Vining and R. N. Shelton, Solid State Commun. 54, 53 (1985).

3. J. W. Lynn, J. A. Gotaas and R. N. Shelton, NBS Technical Note 1217 . 58 (1985).

4. J. A. Gotaas, J. W. Lynn and R. N. Shelton, NBS Technical Note 1231 . 30 (1986).

5. A. R. Moodenbaugh, D. E. Cox and C. B. Vining, Phys. Rev. B32, 3103 (1985).

6. J. W. Lynn, Q. Li and R. W. Erwin, Bull. Am. Phys. Soc . 32, 922 (1987).

7. A general review of theory is given by P. Fulde and J. Keller, in Topics in

Current Physics , edited by . Fischer and M. B. Maple ( Springer- Verlag , New

York, 1983), Vol 34, Chapter 9.

8. Kazushige Machida, Kazuo Nokura and Takeo Matsubara, Phys. Rev. B22 . 2307

(1980)

58
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CRYSTAL STRUCTURE OF THE HIGH-TEMPERATURE

SUPERCONDUCTOR La.. oc Sr_ , c CuO, ABOVE AND BELOW T

1.85 0.15 4 c

A. Santoro

and

R. J. Cava, D. W. Johnson, Jr., and W. W. Rhodes

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

This material has been shown to support bulk superconductivity at temperatures

on the order of 40 K. They have also been shown to undergo a second-order

structural phase transition from tetragonal to orthorhombic symmetry on cooling.

This transition occurs at approximately 200 K for x = 0.15. The crystal structure

of La.. oc Srn

_ CuO. has been determined at 300, 60, and 10 K by neutron-diffraction

1 . o_> U . 15 4

powder profile analysis.

The ambient temperature crystal structure has tetragonal symmetry, space group

I4/mmm, and is of the undistorted K-NiF, type whereas the crystal structure at 60

and 10 K has orthorhombic symmetry.

The orthorhombic distortion causes a doubling in the volume of the

crystallographic unit cell, with the relation between the orthorhombic (0) and

tetragonal (T) cells given by (a,b,c) = (1,1,0/ - 1,1,0/0,0,1) (a,b,c)

The major change in the structure in the tetragonal to orthorhombic phase

transition involves the buckling of the copper- oxygen bipyramidal planes present in

both phases. The crystal structure of the orthorhombic phase is not significantly

different above and below T . Whilst the copper - oxygen coordination polyhedron

changes shape in a subtle manner at the tetragonal- to -orthorhombic phase transition,

it is unchanged at T .

1. R. J. Cava, R. B. Van Dover, B. Batlogg, and E. A. Rietman, Phys . Rev. Lett. 58,

408 (1987).

59
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE STRUCTURE AND PROPERTIES OF Ba_YCu_0,

L -3d

A. Santoro

and

S. Miraglia

(Laboratoire de Cristallographie , CNRS , Grenoble, France)

and

F. Beech

(Imperial College, University of London, UK)

and

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

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

Recently, there have been several reports of variability in the oxygen

stoichiometry for the material Ba_YCu„0 , with superconductivity being maximized

near x = 7 . Elucidation of the nature of the oxygen nonstoichiometry is crucial to a detailed understanding of the electronic properties, including superconductivity.

Gallagher, et al . showed that the basic perovskite framework of cations is

maintained for 7 . > x > 6 . . A reversible transformation was observed for x ~ 6 .

5

from the orthorhombic symmetry Pmmm observed for values of x close to 7.0 to the

tetragonal symmetry and space group P4/mmm.

The structure of Ba_YCu„0, has been determined by neutron diffraction powder

profile analysis. The cell is tetragonal P4/mmm with a = 3.8570(1)A and c =

11. 8194(3) A. The cations are in a perovskite type arrangement, with Ba and Y

ordered on the A site to give a cell tripled along c. The oxygens occupy only 2/3

of the perovskite anion sites and are ordered such that 1/3 of the Cu is two-fold

coordinated and 2/3 is five-fold coordinated. This configuration can be derived

from that of the superconductor Ba9 YCu_0 by removing the oxygen atoms along the b

axis at the (0,1/2,0) position.

2 This model is consistent with the results of Beech et al . who found that

oxygen vacancies in Ba_YCu„0, „ occur only in the 0(4) sites i.e. , in the chains

extending along the b-axis of the orthorhombic cell.

A pressed pellet of the material exhibited semi -conducting behavior with a band

gap of 0.21 eV from 125 - 300 K. Magnetic measurements suggest that the compound

1+ 2+ can be described as Ba_YCu Cu_ ,

.

I lb

1. P. K. Gallagher, H. M. O'Bryan, S. A. Sunshine, and D. W. Murphy, MRB 22 995

(1987).

2. F. Beech, S. Miraglia, A. Santoro, and R. S. Roth, Phys . Rev. B 8778 (1987).

60
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SYNTHESIS AND STRUCTURE REFINEMENT IN THE NON- STOICHIOMETRIC SOLID SOLUTIONS

Ba

2

Re4

[Ba

x

Re xjTigO^ (RE = Nd, Sm)

F. Beech

(Imperial College, University of London, London, UK)

and

A. Santoro and R. S. Roth

and

P. Davis

(University of Pennsylvania, PA)

and

J. L. Soubeyroux

(ILL, Grenoble, France)

and

M. Zocchi

(University of Milan, Milan, Italy)

The multiphase composition at BaO : Sm_0„ : 5Ti0 9 is important since it finds

application in microwave filter devices due to its high dielectric constant, very

low dielectric loss and zero temperature coefficient of the dielectric constant.

The aim of this project is to isolate the active single phase material and

investigate its structure and inherent electrical properties. The Neodynium

analogues are somewhat lossy compared to the Samarium system however they are more amenable to neutron investigation since Sm has a high neutron absorbance.

A small "single" crystal was obtained from a partially melted specimen of

lOBaO: 15 . 5Nd_0 • 74. 5TiO_ which was investigated by x-ray techniques. The structure

analysis suggested a formulation for the single phase material of

Ba_Nd. [Ba Nd_ ._ _.„x]Ti 0_ 7 with x ~ 0. Solid state synthesis of compositions

containing this formula show that a single phase solid solution exists with x varying from 1.0 to and the composition in equilibrium with Ti0_ contains x slightly greater than 0.25. This composition with a small amount of Rutile (Ti0_)

and Nd.Ti^O^., will always be present in a solid state preparation of the ideal

4 y Z4

composition BaO:Nd : 5TiO

It was discovered in the course of this investigation that conventional ceramic

techniques were applicable only to the synthesis of small (<1 gm) batches of the

single phase material. Due to the low diffusion lengths in this system very high

temperature (>1500° C) processing is required, unfortunately any inevitable

inhomogeneity in the firing mixture results in the low temperature formation of

Nd. Ti n o , which melts at 1350° C.

4 y z4

61
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In order to circumnavigate this problem the molecular level mixing offered by

Sol-Gel techniques has been utilized. Synthetic routes to the single phase

materials have been devised and the x = 0,1 end members of the Nd system and the x = composition in the Sm system have been isolated. Work is in progress on the x = 1 Sm composition.

Powder neutron diffraction data has been taken on BT1 for both the Nd

materials. Analysis of the data using the Rietveld technique for the x = material

has lead to a structure based on corner shared groups of perovskite-like molecules

6 - 9+

of [Nd.Ti Q 9

] containing three kinds of tunnels, pentagonal Ba , diamond shaped

2 + [Ba Nd~ ._ 9 „x] and vacant triangular sites. The analysis of the x = 1 Nd

composition is in progress.

High resolution electron microscopy lattice images taken down the c axis show a "herring bone weave" pattern, with angles near 60° . All postulated structures based on the 1:1:5 compositions show calculated lattice images with 90° angles. However,

calculated images based on the neutron refined structure agree with the observed

pattern.

The current structural thrusts of this project center on the elucidation of the x = 1, Nd compound. We are also investigating the Samarium structure using

synchrotron radiation at the NSLS Brookhaven National Laboratory. Measurements on the inherent electrical characteristics of the single phase materials are in

progress

62
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON POWDER DIFFRACTION STUDY OF BaoYCuo 0. c

S. Miraglia and D. Tran Qui

(Laboratorie de Cristallographic , CNRS , Grenoble, France)

and

F. Beech

(Imperial College, University of London, London, UK)

and

(National Bureau of Standards, Gaithersburg, MD)

and

A. Santoro

1. Introduction

The compound Ba^YCu-O,. has been prepared with oxygen content varying from x - 6.0 to x — 7.0. Within this range of compositions the structure of the material

2 can be described as a three-layered oxygen-deficient perovskite and exhibits a tetragonal (P4/mmm) to orthorhombic (Pmmm) phase transition associated with ordering

of the oxygen atoms. The orthorhombic structure of Ba^YCu-O-, and its relationship

to the atomic arrangement of perovskite are illustrated in figure 1. The phase transition is induced by changes in oxygen stoichiometry which is, in

turn, a function of the temperature and of the oxygen partial pressure in the sample

3 container. The orthorhombic, superconducting phase exists for values of 8 comprised between ~ 6.5 and 7.0, while for S < 6.5 the symmetry of the compound is

tetragonal. The transition occurs for values of 6 of about, or slightly higher

than, 6.5 depending on the temperature of the experiment and the sample

1 ^ - ft preparation. ' The oxygen atoms which are removed from the structure or

7 8 introduced in it are those present in the basal plane of the unit cell ' and they are labeled 0(4) and 0(5) in figure 1.

The variation of oxygen content of Ba-YCu-0.. is directly related with the

existence of the one -dimensional chains of near- squares of CuO^ extending along the

b-axis of the unit cell and considered to be the factor responsible for the enhanced

9 value of T . In fact, the value of T is a function of the oxygen stoichiometry,

the highest value of this temperature corresponding to a value of 5 slightly less

9 than 7.0. It seems important, therefore, to know the structural details of the

material and to determine the subtle structural changes that occur when the oxygen

content is varied. For this reason we have refined the structure of the compound

Ba^YCu-O, s at room temperature with the profile method applied to neutron

diffraction powder data. The results of this study are reported in this paper

63
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

together with a comparison of the structural details obtained for the other

compositions analyzed so far.

2

Experimental

The neutron diffraction measurements were made at room temperature with the

high resolution five counter diffractometer at the National Bureau of Standards

Reactor, using the experimental conditions shown in table 1. The structure was refined using the Rietveld method adapted to the multicounter diffractometer and

modified to include the background parameters. In the final refinement all the

structural, lattice, and profile parameters were varied simultaneously and the

results are given in table 2. In table 3 are shown the relevant bond distances

found for Ba«YCu„0, _ and they are compared with those obtained for other

compositions of the system Ba

9 YCu„Oj. (6 < 8 < 7) .

3. Discussion

One of the important structural features of the system Bao YCu„0 c is that the

2+ li8

coordination of the ions Ba is ten- fold for 5 = 7 and eight- fold for 5=6. This

point can be easily comprehended by reference to figure 2. An analysis of the data

reported in table 3 shows that the distances Ba-O(l) and Ba-0(4) increase with

decreasing oxygen content, while the distances Ba-0(2) and Ba-0(3) decrease. This

2+

means that the Ba ions move away from the plane formed by atoms 0(1), being 0.301

8 A above this plane in Ba^YCu-iO-, and 0.513 A in Ba^YCu^O, nfi

. Correspondingly,

their distance from average plane formed by atoms 0(2) and 0(3) decreases from 2.263

to 2.174 A. In other words, they move towards that part of the original

cuboctahedron of perovskite that is left after the removal of the atoms 0(4)

The coordination of ions Y , on the contrary, does not change with the oxygen

content, and the coordination polyhedron (a near-rectangular prism) does not vary

significantly in going from x = to x = 1

In Ba9 YCu„07 the ions Cu(l) are four-coordinated and they are located at the

center of near rectangles connected by vertices and forming chains along the b-axis.

In Ba 9 YCu„0, these ions are two -coordinated, suggesting for this compound the

formulation Ba^YCu Cu„ 0,, where Cu = Cu(l) and Cu = Cu(2) . The distances

Cu(l) - 0(1) and Cu(l) - 0(4) decrease continuously as the oxygen is removed from

the (0,1/2,0) sites. The description of the Cu(l) coordination for compositions

comprised between these extremes is rather complex. A simple statistical

distribution of the oxygen on the (0,1/2,0) sites would result in three-fold oxygen

64
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

coordination for the copper ion. This coordination for copper has, to our

12

knowledge, never been reported and therefore we must consider the possible

existence of very small domains (of the order of only a few unit cells) , with no long range coherence or order, in each one of which the vacant sites are distributed

so that the coordination of Cu(l) is either four or two. This assumption is

consistent with the rather large temperature factors of Cu(l) and 0(1) that are observed experimentally and with the fact that these temperature factors increase

with decreasing x values.

Also the environment of Cu(2) changes significantly with the oxygen content.

The distance Cu(2) - 0(1) increases continuously (from 2.295 to 2.469 A) in going

from x = to x = 1 and, correspondingly, the distance of Cu(2) from the average

plane of the atoms 0(2) and 0(3) decreases (from 0.269 to 0.217 A). This shift

shows that the coordination of Cu(2) tends to be more and more square -planar with

decreasing oxygen content.

As mentioned previously, the oxygen atoms 0(4) show a large temperature factor.

7 8 This feature has been observed in all compositions analyzed so far ' and has been

13 14 reported by other groups as well. In addition, it has been found that this

factor does not decrease significantly with temperature, thus indicating the

presence of static disorder. This is not surprising considering that this atom is

relatively weakly bonded in the structure. The results given in table 2 show that

0(4) is highly anisotropic in the direction of the a-axis (similar results have been

obtained also for Bao YCuo 0-7 and Ba o YCuo 0, „) . Based on the above observations, an

A 5 1 A 5 b . o attempt has been made to refine the structure with the oxygen atom 0(4) split over

the two positions (+x, 1/2,0) (position 2k of space group Pmmm) instead of the

constrained (0,1/2,0) position. The results of this refinement do not differ

significantly from those reported in table 2, but the value of the atomic coordinate

x (x = -0.053(4)) can be considered to be significantly different from zero. In

addition, with this assignment, the isotropic temperature factor of 0(4) becomes 1.1

• 2 15 A . The statistical test developed by Prince was applied in order to determine if

the model with 0(4) at (±x, 1/2,0) (model 2) gives a better fit to the experimental

data than the model with 0(4) at (0,1/2,0) (model 1). The slope of the regression

line showed that model 2 fits the data significantly better than model 1. With this

configuration of the oxygen atoms 0(4) the near -squares of copper and oxygen forming

the chains along the b-axis become buckled much in the same way observed for the

two-dimensional distributions of Cu-0 atoms extending horizontally at z - 0.36.

However, a definitive answer to the problem of the location of the atoms 0(4) would

65
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Experimental conditions used to collect the intensity data.

Monochromatic beam:

Wavelength:

Horizontal divergences

:

Sample container:

29 angular range

:

reflection 220 of a Cu monochromator

1.548 (1) A

10, 20, 10' of arc for the in-pile, monochromatic

beam, and diffracted beam collimators, respectively

vanadium can of about 10mm diameter

10° - 120°, steps: 0.05°

Measurements made at room temperature

0(5)

Figure 1. (a) Crystal structure of perovskite ABX, Large and small circles

represent the A and B cations, respectively. The circles of intermediate

size are the X anions. Three unit cells of perovskite are stacked

together along the c-axis.

Note that the perovskite oxygen atoms

missing in this compound.

(b) Idealized crystal structure of Ba9 YCu_0

at (0,0,1/2) and (1/2,070) are

66
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 2. Refined structural parameters of Ba^YCUoO, ,.

Space group Pmmm - a = 3.8468(1), b = 3.8747(1), c = 11.7466(5)

Atom Position x y z B n

Ba 2t mm 1/2 1/2 0.1917(2) 0.42(7) 1.0

Y lh mmm 1/2 1/2 1/2 0.65(6) 0.5

Cu(l) la mmm 1.07(7) 0.5

Cu(2) 2q mm 0.3596(2) 0.46(4) 1.0

0(1) 2q mm 0.1528(3) 1.48(7) 1.0

0(2) 2s mm 1/2 0.3788(4) 0.42(7) 1.0

0(3) 2r mm 1/2 0.3767(4) 0.70(7) 1.0

0(4) le mmm 1/2 (*) 0.25

(*) B

11 = 4.7(4), B

22 = 1.7(4), B

33 = 0.3(5)

R

N

= 5.65, R

p = 6.20, R^ = 8.20, R

E = 5.34, X = 1 . 54

Table 3. Relevant bond distances in Bao YCuo 0-, 2 3 7-x

x = 0" ' x = 0.2' ' x = 0.5 V ' x = 0.94 v

Ba - 0(1) x4 2.7408(4) 2.7470(8) 2.7690(8) 2.7751(5)

Ba

Ba

- 0(2)

- 0(3)

x2

x2

2.984(2)

2.960(2)

2.972(3)

2.938(6)

2.930(4)

2.902(4)

2.905(1)

Ba - 0(4) x2 2.896(2) 2.922(4) 2.956(2)

Y

Y

- 0(2)

- 0(3)

x4

x4

2.409(1)

2.386(1)

2.403(3)

2.389(2)

2.404(3)

2.408(3)

2.4004(8)

Cu(l) - 0(1) x2 1.846(2) 1.843(3) 1.795(3) 1.795(2)

Cu(l) - 0(4) x2 1.9429(1) 1.9428(1) 1.9374(1)

Cu(2) - 0(1) xl 2.295(3) 2.323(4) 2.429(4) 2.469(2)

Cu(2)

Cu(2)

- 0(2)

- 0(3)

x2

x2

1.9299(4)

1.9607(4)

1.9305(6)

1.9585(8)

1.9366(6)

1.9478(6)

1.9406(3)

(•k~k~k\

(*) From ref. (7). The distances reported are those obtained for the

samples at room temperature. (**) This work. (***) Ref. (8).

67
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

require the collection of more data at low temperatures and, for this reason, we report as an interim structure the model with the atom 0(4) located at (0,1/2,0).

The background modulation mentioned previously in the angular range of 20

between 10° and 21° can be related to the presence of short range ordering of the

oxygen vacancies along the b-axis. Attempts to detect long range ordering, however,

were unsuccessful. No evidence of super -lattice lines could be found in the powder

pattern of Ba 9 YCu„0, _ , and doubling of the b-axis and ordering of vacancies did not

result in an improvement of the agreement between observed and calculated

intensities

1. P. K. Gallagher, H. M. 0' Bryan, S. A. Sunshine, D. W. Murphy. Mat. Res. Bull.

22, 995 (1987).

2. T. Siegriest, S. Sunshine, D. W. Murphy, R. J. Cava, and S. M. Zahurak. Phys

Rev. B, 35, 7137 (1987).

3. G. S. Grader and P. K. Gallagher. Preprint.

4. J. D. Jorgensen, M. A. Beno , D. G. Hinks , L. Soderholm, K. J. Volin, R. L. Hitterman, J. D. Grace, I. K. Schuller, C. U. Segre, K. Zhang, and M. S. Kleefisch. Preprint.

5. P. K. Gallagher. Preprint.

6. H. M. 0' Bryan and P. K. Gallagher. Preprint.

7. See e.g. F. Beech, S. Miraglia, A. Santoro, and R. S. Roth. Phys. Rev. B, 35,

8778 (1987).

8. A. Santoro, S. Miraglia, F. Beech, S. A. Sunshine, D. W. Murphy, L. F. Schneemeyer, and J . V. Waszczak. Mat. Res. Bull . . 22, 1007 (1987).

9. F. Herman, R. V. Kasowski, and W. Y. Hsu. Preprint.

10. H. M. Rietveld. J. Appl . Crvst . 2, 65 (1969).

11. E. Prince. U.S. Tech. Note 1117 (F. J. Shorten, Ed.) p. 8.

12. R. D. Shannon. Acta Cryst. A32, 751 (1976).

13. W. I. F. David, W. T. A. Harrison, J. M. F. Gunn, 0. Moze , A. K. Soper, P. Day,

J. D. Jorgensen, D. G. Hinks, M. A. Beno, L. Soderholm, D. W. Capone , I. K. Schuller, C. U. Segre, K. Zhang, and J . D. Grace. Nature, 327, 310 (1987).

14. M. A. Beno, L. Soderholm, D. W. Capone, D. G. Hinks, J. D. Jorgensen, and I. K. Schuller. (1987) Appl. Phys. Lett. 51 57 (1987).

15. E. Prince. Acta Cryst. B38, 1099 (1982).

68
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STRUCTURAL DISTORTION IN La

x 85BaQ 15Cu04

F. Beech

(Imperial College, University of London, London, UK)

and

(National Bureau of Standards, Gaithersburg, MD)

and

S. Miraglia

(Laboratoire de Cristallographie , CNRS , Grenoble, France)

and

A. Santoro

The structure of the 33 K superconductor La, R[.Ba

n

, ,-CuO, has been reexamined

at 300 and 10 K. At room temperature the tetragonal I4/mmm structure (similar to

K9 NiF.) is confirmed. However, at low temperature the compound has been found to

exhibit orthorhombic symmetry. The low temperature phase can be described by

adopting space group Cmca and using the orthorhombic cell related to the room temperature tetragonal cell by means of: (abc)„ = (11, -110, 001) (abc) . These

2 results are similar to those found for La.. oc Sr„ n c CuO. . The powder pattern of the 1.85 0.15 4

r material contains two very weak peaks not yet accounted for, and refinements are still in progress in order to characterize the structural details.

1. J. D. Jorgensen et al ., Phys . Rev. Letters 58, 1024 (1987).

2. R. J. Cava, A. Santoro, D W. Johnson, and W. W. Rhodes, Phys. Rev. B35, 6716

(1987).

69
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON STUDY OF THE CRYSTAL STRUCTURE AND VACANCY

DISTRIBUTION OF THE SUPERCONDUCTOR Ba

?

Y Cu-OF. Beech

(Imperial College, University of London, London, UK)

and

(National Bureau of Standards, Gaithersburg, MD)

and

S. Miraglia

(Laboratoire de Cristallographie , CNRS , Grenoble, France)

and

A. Santoro and R. S. Roth

Two samples of the high temperature superconductor Ba Y Cu„0o c with 6 = 2 . and 2.2, have been studied at room temperature and at 10 K, with the neutron powder

diffraction method and profile analysis. The structure of the compound is

orthorhombic.

The oxygen atoms are located on four sets of sites and not on five sets as reported earlier in x-ray diffraction studies. Of the two sets of copper atoms, one

is surrounded by four oxygen atoms at distances 1.9299(4)A and 1.9607(4)A. This

arrangement forms a two-dimensional framework of Cu-0 atoms that extends

indefinitely along the a- and b- axis. A fifth oxygen atom is located at 2.295(3)A

from the copper atom, giving a pyramidal configuration. In the other set, the Cu

atoms are also surrounded by four oxygen atoms, with distances 1.9429(1)A and

1.846 (2 )A. In this case, however, the oxygen atoms form rectangles connected by

vertices, and resulting in chains along the b-axis.

In the compound with 8 = 2.0 all oxygen sites are fully occupied. When 5=2.2

there are oxygen vacancies, but these are confined to one set of positions only,

specifically to the oxygen atoms of the chains, located on the b-axis.

No detectable change of the structure has been observed between room and low

temperature

70
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON AND SYNCHROTRON X-RAY POWDER STUDIES OF A HIGH IONIC CONDUCTOR

SOLID SOLUTION: Lin Ti_ In Po 1 _ 1+x 2-x x 3 12

D. Tran Qui

(Laboratoire de Cristallographie , CNRS , Grenoble -Cedex, France)

and

E. Prince

and

Soubeyroux

(Institut Laue Langevin, Grenoble, France)

and

D. Cox

(Brookhaven National Laboratory, Upton, NY)

Recently (1) it was reported that Li exhibits high mobility in the

Li- Ti 9 In P^O- _ system. On the basis of x-ray powder patterns, it was suggested

that, for moderate substitution of Ti for In (0 < x < 0.4) an R3c , NASICON-type

structure is formed in Li.. Ti~ In P n n _ and further substitution (x>0.4) of In 1+x 2-x x 3 12

induces, similar to the NASICON system, a distortion leading to monoclinic symmetry.

More detailed electrical measurements performed on carefully sintered pellets have

shown that the conductivity curve of this solid solution actually has two maxima,

-2 -1 -3 -1

one, 2.10 (flcm) , at x -0.35, and another, 8.10 (ficm) , at x « 1.8 (1,2).

Structural studies using single crystals of different compositions have

unambiguously shown that insertion of In in the solid solution induces much more complicated structural changes in its framework than previously stated.

Li.. Ti_ In P_0

1 „ compounds adopt , depending on x value, three structure types,

corresponding to three different phases: phase I, < x < . 4 , is rhombohedral (or

may be slightly monoclinic); phase II, 0.4 < x < 1.0 is orthorhombic , Pbca; and

phase III, 1.0 < x < 2.0 is monoclinic P2 1 /n. In contrast with the NASICON system,

the transitions from phase I to phase II and from phase II to phase III correspond

to structural reorganisation in the framework. Only the rhombohedral R3c structure

in phase I is NASICON-type (3,4).

In order to better understand the influence of the framework on the Li mobility in

Li.. Ti_ In P„0nr, solid solutions, two series of structural studies have been

1+x 2-x x 3 12

performed by using the high resolution powder diffractomer at the NBS research

reactor (5,6)

:

a - Distortion of the fTi~ In P„0 n _] framework as a function of x. 2-x x 3 12

71
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Neutron powder refinements of highly conducting, polycrystalline samples with

nominal compositions x = 0.25, 0.40 and 0.45 indicate that lithiums in the large

eight-coordinated sites are in a highly disordered configuration, occuping only 6%

of the site capacity, while the low energy octahedral sites are 95% filled (7) .

b - Thermal expansion of the [Ti_ In P.O.. 9

] framework.

Such a site distribution, which is unfavorable for fast ion diffusion, may change in

the highly conducting state: transfer of Li ions from octahedral sites into the

large cavities is therefore expected at high temperature.

Refinements of the [Ti. In P o 1o ] framework at 40, 200, 600 and 800 K, have fully

2-x x 3 12 J confirmed this expectation, and the observed expansion of this framework is

consistent with the reported electrical conductivity behaviour of this materials

(1).

Neutron studies have in addition suggested the existence of a parasitic phase in the

Li., Ti_ In P.O., _ solid solution. This parasitic phase has been confirmed by a 1+x 2-x x 3 12 J high resolution a synchrotron x-ray diffraction pattern of Li.. -_Ti- 7 ,-In_ _ P.O. 9 which showed 26 extra reflections, well resolved from the expected lines. Rietveld

refinement applied to the x-ray pattern confirms a neutron observation that the

observed Ti/In ratio is substantially lower than it should be according to the

chemical analysis. These extra reflections are indexed, and a space group and a solution of the crystal structure of this unwanted phase is identified as LiInP.07

.

1. S. Hamdoune, D. Tran Qui and E.J.L. Schouler. (1986) Solid State Ionics 19 587-

591.

2. S. Hamdoune, M. Gondrand and D. Tran Qui Mater. Res. in press

3. S. Hamdoune, Relation between structure and Transport Properties in Solid

Solution: Li- .Ti_ In P.O.. . , These, Laboratoire de Cr is tallographie CNRS 1+2 2 -x x 3 12 or

Grenoble July 1986

4. D. Tran Qui, S. Hamdoune Acta. Cryst. C43 397-399.

5. E. Prince and A. Santoro, National Bureau of Standards, U.S. Tech Note No. 1117,

p. 11 (1980) .

6. E. Prince, National Bureau of Standards, U.S. Tech Note 1117, p. 87. D. Tran

Qui, S. Hamdoune, J.L. Soubeyroux and E. Prince, Journal of Solid State

Chemistry in press.

72
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON POWDER DIFFRACTION STUDY OF Vn Mo^Oy _ y 6 40

R.C.T. Slade

(University of Exeter, England)

and

(National Bureau of Standards, Gaithersburg, MD)

and

A . Ramanan

(University of Exeter, England)

and

E. Prince

The phases in the system V^O^-MoO., are being investigated because of their

importance in catalysis. The single phase VqMo,0,

n has a monoclinic unit cell and

systematic absences in x-ray powder diffraction studies consistent with the space

group C2

.

The room temperature powder diffraction pattern was analysed using Rietveld

procedures in the space group C2 . All peaks were accounted for. The final model

shows disorders about special positions for one metal atom and one oxygen atom,

equivalent to those proposed by Eick and Kihlborg [1] for the phase Vo Mo0 o

. All

z o sites are fully occupied. The distribution of V and Mo atoms between metal atom

sites was determined. An alternative model with anisotropic temperature factors for

those atoms on special positions lead to physically unrealistic values for those

parameters. Table 1 presents the final model. The work is being prepared for

publication.

1. H.A. Eick and L. Kihlborg, Acta Chem. Scand. , 20, 1658 (1966)

73
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Refined model for VqMo,0 ,_ in space group C2

Atom Position X N

*+

Ml.

M2

4c

4c

0.0001(8)

0.1856(6)

0.0260(112)

0.0267(165)

0.0901(29)

0.0824(31)

21 75(31)

99(34)

314(7)

286(7)

01 4c 0.0987(2) 0.0261(51) 0.0024(15) 1 22(9) 1 000

02 4c 0.2079(2) 0.5257(53) 0.9992(12) 52(8) 1 000

03 4c 0.1885(2) 0.0329 0.4927(14) 1 10(10) 1 000

04

05+

2b

4c

0.0000

0.9994(7)

0.0697(62)

0.5282(86)

0.5000

0.0685(19)

21

86(25)

23(19)

500

500

R = n

= 9 19 R

P = 6.77 R =8.74

wp

R = 6.09

e a = 19 3611(7 ) A b = 3.6250(1) A, c = 4.1215(2) A

-k*

{3 = 90.617(3)

Mo/V sites.

N(Mo) shown.

Disorder about special (2a) position,

74
REACTOR RADIATION DIVISION AND COILABORATIVE PROGRAMS

NEUTRON POWDER DIFFRACTION STUDY OF ANHYDROUS LITHIUM EXCHANGED ZEOLITE X

R.C.T. Slade

(University of Exeter, England)

and

(National Bureau of Standards, Gaithersburg, MD)

and

E.K. Andersen and I.G. Andersen

(Odense Universitet, Denmark)

and

E. Prince

Zeolite X is a synthetic molecular sieve with an aluminos ilicate framework

isomorphous with the mineral faujasite. In its alkali metal forms, the framework

Si/Al ratio in zeolite X is such that there are more exchangeable cations than

available sites within the sodalite units that link to form the framework. Previous

studies of alkali- exchanged faujasites have identified cation sites within the

sodalite units and the hexagonal prisms linking them. Sites for the excess alkali

metal within the supercages have been suggested, but never definitively located.

Lithium exchanged zeolite X was prepared by potentiometric titration of the

ammonium form with lithium hydroxide. Exchange was > 93%.

The room temperature powder diffraction pattern was analysed using Rietveld

procedures in the space group Fd3m. The final model locates all of the atoms in the

structure. Lithium atoms occupy sites of three types: (1) at the windows linking

sodalite units and hexagonal prisms (Lithium coordinated by three oxygens in a nearly planar configuration), (2) at the windows linking sodalite units and the

supercage (fully occupied, also with 3-coordination) and (3) at sites III' on the

walls of the supercage (above an approximate square of oxygens). The values

obtained are presented in table: 1. The work is being prepared for publication.

Table 1. Refined model for anhydrous lithium zeolite X in space group Fd3m.

Atom Position X Y Z B N

Tet* 192i 0.1242(4) 0.9495(3) 0.0377(4) 0.43(12) 1.000

01 96g 0.1779(3) 0.1779(3) 0.9785(3) 1.83(19) 0.500

02 96g 0.1712(3) 0.1712(3) 0.3235(4) 1.60(21) 0.500

03 96g 0.2506(3) 0.2506(3) 0.1517(4) 2.27(22) 0.500

04 96h 0.1015(3) 0.8985(3) 0.0000 2.97(28) 0.500

Lil 32e 0.0465(11) 0.0465(11) 0.0465(11) 2 . 2±1 .

4

0.138(15)

Li2 32e 0.2220(12) 0.2220(12) 0.2220(12) 4.811.6 0.167(17)

Lilll' 96g 0.0938(22) 0.0938(22) 0.8896(34) . 8±1 .

9

0.115(15)

R = 10.18 R - 7.96 R = 10.16 R = 9.41 a = 24.6715(10) A Si/Al n p wp e

75
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PHASE EXTENSION BY MAXIMUM ENTROPY

E. Prince

and

L. Sjolin and R. Alenljung

(Chalmers University of Technology, Goteborg, Sweden)

The intensities measured in a neutron diffraction experiment depend on the

amplitudes of the Fourier transform of the contents of the unit cell at points of

the reciprocal lattice. The diffraction data contain no phase information, so it is

not, in general, possible to perform the inverse transform to obtain the

distribution of scattering matter in the unit cell. Hauptman and Karle , in the

work for which they were awarded the 1985 Nobel Prize in chemistry, showed how to

make use of the facts that crystals are composed of atoms and that electron density

is everywhere positive to determine the most probable values of the phases of many

reflections given the amplitudes of all reflections and the phases of some of them.

Although the direct methods of Hauptman and Karle are very powerful for determining

crystal structures when these unit cells contain no more than a few hundred atoms,

they have not been particularly successful for biological macromolecules , where the

cell contents may be many thousands of atoms.

2 3 Building on information theory, as developed by Shannon and Jaynes , Gull and

4 Daniell developed a method for extending the inverse Fourier transform that can be

described conceptually as a process of generating, by a random process, enormous numbers of trial density maps and considering the most frequently occurring of those

that are consistent with the data to be the best solution. Their method consists of

dividing the map into a large number of cells, called pixels, and finding the

maximum of a function of the form

s = " I Pk

^

Pk

.

where p, is the mean density in the k th pixel, subject to one or more constraints

that face the Fourier transform of the distribution p(t) to be consistent with the

data. Because of the resemblance of this function to the entropy function of

statistical mechanics, the method has become known as the method of maximum entropy.

A Fourier sum computed with a limited number of amplitudes and previously

determined phases gives a density distribution under the highly unrealistic

assumption that the amplitudes of all terms not included in the sum are exactly

76
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

zero. There is no assurance that this map will not have negative regions and other

physically nonsensical features. A maximum entropy distribution will necessarily be

positive everywhere, and replaces the zero terms by values that are "most likely",

or, perhaps, "least surprising." The maximum entropy distribution has the form

N

pk

= (N/V) F(000) exp(Zkx)/ £ exp (Z x)

,

j=l

where V is the volume of the unit cell, N is the number of pixels, F(000) is the

total number of electrons in the unit cell, and

x = ^n (p

2 /p 1

)

,

where p.. and p 9 are the densities in any two pixels such that p.. ^ p 9• Z, is a function of the densities in the low resolution map:

zk

= (pk

" Pp/ ( P2 " p;) -

where

pk

= I |F| cos (27rh-rk- 5),

and the sum is over the reflections used in the low resolution map. The

distribution access with the data used in the low resolution map if £ Pi_P/. = I

(p' ) , and the sum on the left is a well behaved function of x that can be set equal

to the sum on the right by standard, numerical methods.

Repeated application of maximization entropy at progressively higher

resolution, in each case using the observed amplitudes with calculated phases, will

eventually lead to an everywhere -positive density distribution that is in agreement

with all observed data. There is no assurance, however, that the solution will be

unique. Further control over the nature of the solution can be gained by making use of the fact that a protein crystal is typically divided by a smooth envelope into

two continuous regions, one of which contains the protein molecule, while the other

contains solvent whose density is essentially constant. At each step the solvent is

flattened, while entropy maximization is applied to the protein.

Figure 1 shows portions of three density maps calculated from data taken from

ribonuclease A. Figure la is a map at 2 A resolution with phases taken from the

77
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. Several overlaid sections of Fourier density maps of ribonuclease A: a)

Density map at 2 A resolution with phases from the refined structure; b)

Density map truncated at 5 A resolution; c) Map at 2 A resolution with

phases extend from 5 A to 2 A by the maximum entropy/solvent flattening

procedure.

refined structure. Figure lb is the map with the series truncated at 5 A

resolution. In figure lc the phases of all reflections with resolution higher than

5 A have been treated as unknown, but extended using the maximum entropy and solvent

flattening procedure back to 2 A. The close similarity between a and c indicates

that the refined structure has been very closely reproduced.

1. J. Karle in Structure & Statistics in Crystallography . A. J. C. Wilsen, ed. pp.

7-22 (1985)

2. C. E. Shannon. Bell Svst. Tech. J . 379-423 (1948).

3. E. T. Jaynes , in The Maximum Entropy Formalism . R. D. Levine & M. Tribus, eds . pp. 15-118 (1979).

4. S. F. Gull & G. J. Daniell. Nature (London) 272, 686-690 (1978).

5. B. C. Wang. Methods in Enzymology . 114. Diffraction Methods in Biological

Macromolecules . H. W. Wycoff, C. H. W. Hus & S. N. Timasheff, eds. pp. 114-167

(1985)

6. A. Wlodawer & L. Sjolin. Biochemistry . 22, 2720-2728 (1983).
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SUB- SURFACE RESIDUAL STRESS MEASUREMENTS BY MEANS OF NEUTRON DIFFRACTION

H. J. Prask and C. S. Choi

(ARDEC, Picatinny Arsenal, Dover, NJ)

and

(National Bureau of Standards)

Neutron diffraction is a measurement technique which closely parallels x-ray

diffraction in methodology and analytical formalism. However, in the normal

diffraction wavelength range neutrons are, in general, about a thousand times more penetrating than x-rays. In addition the coherent scattering cross-section for

neutrons varies in a random manner with atomic number in contrast to the essentially

monatonically increasing dependence of x-rays. We have made use of these neutron

properties to nondestructively determine sub-surface residual stress in a variety of

samples, utilizing energy dispersive neutron diffraction (EDND) to improve

resolution and because it appears to reduce anomalous peak shifts in textured

samples. We have examined aluminum and steel calibration samples to test the

technique, and have applied the technique to the characterization of sub- and near- surface residual stresses in two types of armament -system components: U-0.75 wt % Ti

2 cylindrical rods and 7075 -T6 aluminum alloy ogives.

U-0.75wt % Ti ("U-0.75Ti") is an alloy of considerable importance in certain

military applications. In order to improve performance and decrease production

costs, fabrication-process changes are dictated which can affect desired material

properties such as yield strength, ultimate strength, ductility, and susceptibility

to stress-corrosion cracking (SCC) . These properties depend in varying degrees on the residual stress distribution produced by the fabrication method which includes

gamma-phase solutionizing, quenching, aging, and cold work. Two different types of

samples were studied. For convenience, the residual stress determinations were made on 10 cm long pieces cut from the mid-point of 46 cm long, 3.3 cm (starting)

diameter rods. However, with slight modification of the instrument uncut rods could

also be examined. One group was 7-phase solutionized in a vacuum furnace, water

bath quenched, and rotary straightened ("mild" cold work). Of these, some were machined to the final 2.5 cm diameter, and one was moderately cold worked and

machined to the final 2.5 cm diameter. In addition, one sample was solutionized in an induction furnace and water- spray quenched, aged, rotary straightened and

machined to the final diameter. In all cases aging after quenching was 1-2 hours at

400° C or less.

We utilize the overall equilibrium conditions required by elasticity theory to

determine d„. That is, since the body is static with no external force applied.

79
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

residual stresses normal to any plane must balance and at any surface the stress

orthogonal to that surface must vanish. Stresses inferred from measured strains can

2 be adjusted, by adjusting d„ , to fulfill the equilibrium conditions. Employing the

(112) reflection we have determined strains in the mid-point r-0 plane of the 10 cm long DU pieces. Determination of stresses was made using Eqs . 2-4 of ref. 2 and

recently determined values of Poisson's Ratio (0.267) and the elastic modulus

(176600 MPa) for a'-DU. We find that the results for all of the mildly cold-worked

samples, including the induction- furnace solutionized/spray-water quenched sample,

exhibit stress distributions of the type shown in figure la. The moderately coldworked specimen exhibits a stress distribution which is quite different as shown in

Figure lb.

In the past few years several failures have occurred during ballistic

acceptance testing of the 155 mm M483A1 projectile. The purpose of this projectile

is to deliver submunitions . An ogive at the forward end, that contains a small

explosive charge, is threaded to the projectile body and sealed from it by a pusher

plate. The aft end is sealed by a shear plate. At detonation, the pressure

developed in the ogive cavity creates an aft directed force that acts on the pusher

plate transmitting it through the submunitions to the aft-end shear plate. For

effective operation, the force must be sufficient to fracture the shear plate and

accelerate the submunitions, thus scattering the submunitions behind the forward

traveling projectile body. The malfunctions occurred when the ogive body failed

before the aft-end pusher plate.

The ogive is manufactured from 7075-T6 aluminum and is pictured in figure 2. Production ogives are manufactured by two different suppliers, A and B, who use somewhat different manufacturing methods. In full-scale tests the primary failure

mode, exclusive to the B-type ogive, is a circumferential fracture at the first

loaded thread. A single failure of an A-type ogive, by longitudinal fracture in the

conical region, has also been reported. One ogive of type B and one ogive of type A were studied by EDND employing six 4mm x 4mm x 4mm beam spot positions, three at

each end of one diameter in the plane of the potential failure site. Overall

equilibrium was also used to determine d~ . It was assumed that the average of the

0° and 180° data was representative of the full circumference. Theoretical

diffraction elastic constants were used for (200) in the stress/strain calculations.

In figure 3, final absolute residual stress values are shown for both ogive

types for 0° and 180° positions at the first thread position. In contrast to

previous measurements, the nondestructive EDND stress determination indicates very

80
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

T r 400r

200

a. -200

to -400

V)

LU

tr

it—

r

+

+

-flr

+

- r i -|- -r

+

i

f

•<r.

•

i 4

+

f

<r.

+

200

-200

% 4

+

+

+

J I I I L

' i

+

-, , i

-10 10 -10 10 -10 10

POSITION (MM)

Figure 1. EDND determined residual stress distributions for (la) mildly coldworked U-0.75Ti specimens (typical), and (lb) the moderately cold-worked

specimen. The crosses and solid circles correspond to measurements

along the two orthogonal diameters at the mid-plane of 1 cm long by 2.5

cm diameter rods. Representative standard deviations are shown near the

centerline of each stress distribution.

Figure 2. M483A1 ogive with forward end at upper right. Overall length is 19.3

cm, ID at aft end is 4.7 cm. The region of interest is under the most

forward thread shown, 8.6 mm thick.

81
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

i i

* 50

1

v

~f- r

i i j

-50

S. -loo

2

to A

uj -150

or

-

i i \i > 50 -

1

5 n

/ u J

-50

i i i ID 2 4 6 OD ID 2 4

DISTANCE (mm)

Figure 3. a and a residual stress distributions of the A and B type gives as determined by EDND. "OD" corresponds to the thread-root position. The

open and closed circles correspond to measurements made 180° apart.

significant differences in the two ogive types. In the A- type ogives it is found

that Jlust below the thread root ("OD") the a stresses are about -20 MPa

zz (compressive) whereas the B-type show +30 to +70 MPa (tensile) stresses. This is

completely consistent with the principal failure mode differences that have been

observed.

1. H. J. Prask and C. S. Choi, J. Nucl. Matls . 126, 124-131 (1984).

2. H. J. Prask and C. S. Choi, "Residual Stress Measurements in Armament System

Components by Means of Neutron Diffraction", Proceedings of ASM's 1987

Conference on Residual Stress - In Design, Process and Materials Selection,

Cincinnati, Ohio, April 1987, in press.

3. H. J. Prask, C. S. Choi and K. A. Hardman-Rhyne , "Residual Stress

Characterization of Al^0~/SiC (whiskers) Using Neutron Diffraction Techniques",

presented at Amer. Cer. Soc . Conf., Pittsburgh, April 1987.

82
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

RESIDUAL STRESS CHARACTERIZATION OF Al

?0_/SiC (WHISKERS) USING NEUTRON

DIFFRACTION TECHNIQUES

H. J. Prask and C. S. Choi

(ARDEC, Picatinny Arsenal, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

and

K. R. Hardman-Rhyne

(Ceramics Division)

Neutron diffraction is a measurement technique which closely parallels x-ray

diffraction in methodology and analytical formalism. However, in the normal

diffraction wavelength range neutrons are, in general, about a thousand times more penetrating than x-rays. In addition the coherent scattering cross-section for

neutrons varies in a random manner with atomic number in contrast to the essentially

monatomically increasing dependence of x-rays. We have made use of these neutron

properties to nondestructively determine sub -surface residual stress in

metallurgical samples, described in another contribution to this report. We have

also made use of neutron diffraction to partially characterize residual stresses in

each constituent of an Al~0,.-25wt % SiC (whisker) ceramic composite.

The composite was prepared elsewhere by hot-pressing a dried powder mixture of

SiC whiskers (diameters < 1 /xm, lengths < 80 /zm) and alumina into a 13 mm thick

slab. The neutron sample was a cube, 13 mm on a side, cut from the edge of the

slab. Energy dispersive neutron diffraction was used to measure strains along the

fourfold axis perpendicular to the slab -edge surface, as shown in figure 2,

employing a 4mm x 4mm x 4mm beam spot. Details of the technique are given in

reference 1. The pertinent region of the neutron diffraction pattern (A = 1.54A) is

shown in figure 1. The specific peaks examined were Al9 O_(300) and SiC(114), the

latter being the "cleanest" SiC peak of reasonable intensity in the pattern. A

profile for the envelope of intensity around this peak, excluding Al~0., (125) , was obtained from a sample of SiC whiskers.

In these initial measurements several simplifying assumptions were made.

Isotropic bulk values were used to calculate the diffraction elastic constants

(A1

?

• E = 386 GPa, fj, = 0.23; SiC: E = 406 GPa, p = 0.22) and shear stresses were assumed to be zero. The d 's for each component were obtained from measurements on a o block identical to the sample specimen, crushed in a mortar and pestle. The beamspot centers for the measurements are indicated in figure 2, where Y = +6 . 5mm

corresponds to the slab edge and the hot pressing was along the Z-direction.

83
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(300) Al 2 ;

66.0 70.0 74.0

Figure 1. The region of the neutron diffraction pattern of the Al 0~/SiC sample

examined in the residual stress measurements. 2 3'

200

H. P.

\7

A 1

i Z / i, A - , ./ / / /y

A*

t /

5

Y- POSITION (mm)

Figure 2. A schematic of the ceramic block (13 mm on a side) with measurement

points indicated, and the three residual stress components for each

constituent as a function of position along the Y-axis (SiC = open

symbols)

.

84
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Strains were measured in five directions at each point. Under the assumptions

described above, the three stress components obtained at each measurement point are shown in figure 2, for each constituent. Overall, it is clear that the alumina is

either in tension or slightly compressed, while the SiC is in definite compression

for this sample.

1. H. J. Prask and C. S. Choi, J. Nucl . Matls . 126, 124-131 (1984)

FIBER TEXTURE AND NEUTRON POWDER DIFFRACTION PATTERN

C. S.Choi and H. J. Prask

(ARDEC, Picatinny Arsenal, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

In recent years, Rietveld profile refinement of neutron powder diffraction data

has been widely used for the crystallographic study of crystalline powder samples,

but not for polycrystalline solid samples because of the effect of texture. The

Rietveld method determines not only the structural parameters but also the peak

widths, and hence is particularly attractive for the microstructural study of a polycrystalline solid. The purpose of the present study is two-fold:

characterization of the crystallite orientation distribution in fiber- textured

samples by means of a simple distribution function; and its application in Rietveld

profile refinements for the correction of texture effects.

The pole density distributions of fiber textured samples exhibit axial

symmetry, and hence show concentric intensity distributions about the symmetry axis.

For simplicity, we assume that the pole density distribution is Gaussian. In

general, a crystal lattice (except the triclinic case) has multiple equivalent

lattice planes, each with different tilt angles. Then, the observed pole density

distribution as a function of tilt angles, P(p) , can be described by a superposition

of Gaussian peaks centered at respective tilt angle, such that

P(p) = Sv(N

i /Wsinpi )exp-A(p-pi

) 2 /W2 (1)

where, S is the scale factor, N. is the number of superimposed peaks (including the

equivalent reflections) at the tilt angles (p.), and A = 41n2 . For multi-axis fiber

texture, the pole density distribution can be expressed by a superposition of each

fiber texture

.

85
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Summary of the Rietveld profile refinement for 60 % swaged samples, 6E 6G

6H, and 75 % swaged samples 7A and 7B. The calculated profiles were corrected for the duplex fiber texture models. In the Table, Axis refers

to the fiber axis, and width to the FWHM of the fiber axis distributions.

Sample 6E 6G 6H 7A 7B

a 2.8599(1) 2.8607(1) 2.8599(2) 2.8624(2) 2.8618(1)

b 5.8335(4) 5.8325(4) 5.8346(6) 5.8293(6) 5.8345(5)

c 4.9611(2) 4.9618(2) 4.9613(2) 4.9632(2) 4.9623(2)

U 5532(58) 5552(60) 6010(82) 5815(77) 5855(57)

W 1626(16) 1669(16) 1646(23) 1709(24) 1743(18)

Rb 4.96 4.96 6.46 8.09 6.88

Rp 7.44 7.27 8.56 9.11 6.94

Rw 9.64 9.77 11.39 11.73 8.64

Re 6.52 6.40 8.92 9.24 4.58

Axis-1 [252] [252] [252] [252] [252]

Width 31 31 31 22 23

Ratio .45 .44 .44 .40 .37

Axis -2 [041] [041] [041] [051] [051]

Width 29 30 30 23 24

Ratio .55 .56 .56 .60 .63

A generalized crystallite orientation distribution may be obtained by

considering the total number of poles F(p,hkl) for individual lattice points instead

of the pole density P(p) for a group of equivalent reflections as shown in the

eq.(l), and expressing the tilt angle p. with reciprocal lattice vectors. Then eq

.

(1) can be rewritten:

F(p,hkl) = (K/W)exp-A{(p-a)/W) (2)

86
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1

••

t

1 A

ft J?

f*. kh

80 85 90 95 100 105 110 115 120

An(la JLLL /U-jVl.-

75 80 85 90 95 100 105 110 115 120

Injl.

Figure 2. The results of the Rietveld profile refinements of the swaged uranium

alloys (60% area reduction), without texture corrections (top) and with

the corrections (bottom). The observed neutron diffraction data are

indicated by the circles.

where a = acos(br) .b) and b~ and b are the unit reciprocal lattice vectors for the

fiber axis and (hkl) pole, respectively. This function represents both the pole

figure of a given (hkl) reflection (by fixing the hkl) and the crystallite

orientation distribution or inverse pole figure for a given scattering vector (by

fixing the tilt angle). If we know the crystal structure of the sample, the

crystallite orientation distribution can be converted to the powder diffraction

pattern by multiplying F(p,hkl) by the corresponding integrated reflectivity.

Therefore, the crystallite orientation distribution can be used as a correction

factor for the texture effect in the Rietveld refinement, or vice versa. We have

modified our Rietveld program to include a general type of fiber texture and for all

crystal symmetries by adding several subroutines.

The diffraction patterns of four swaged uranium alloys were measured with the

high-resolution powder diffractometer at the NBS reactor with the fiber-axis

direction oriented perpendicular to the diffraction plane. The pole figures of four

reflections, (020) (111) (112) and (131), were measured for each sample, using the

single crystal diffractometer . Duplex fiber texture pole density distribution

functions (eq. 1) with fiber axes [041] and [252] were found from the four observed

87
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

pole density curves. The p(p) , eq . (1), were converted to F(/9,hkl), eq.(2), with

o p=90 in this case. Then, the texture correction factor for the above powder

patterns are given by F(p ,hkl)/sin(p . ) . Since the crystal structure of the samples was well known, only the profile parameters and the texture parameters were refined

by using the modified Rietveld program. The results of the profile refinements were quite satisfactory and are given in table 1. The observed and calculated diffraction

profiles with the texture correction and without the corrections are shown in figure

1.

CRYSTAL DATA CENTER

V. L. Himes, A. D. Mighell, and J. K. Stalick

The NBS Crystal Data Center is concerned with the collection, evaluation and

dissemination of data on solid-state materials. The Data Center maintains a comprehensive database with chemical, physical and crystallographic information on all types of well characterized substances. These materials fall into the following

categories: inorganics, organics , organometallics , metals, intermetallics , and

minerals. During the year, the database and specially designed scientific software

have been made available to the scientific community in three distinct modes: 1)

NBS CRYSTAL DATA Distribution Package (1987); 2) International Online Search System;

3) Specialized Database for Electron Diffractionists

.

1. NBS CRYSTAL DATA Distribution Package (1987)

This product includes NBS CRYSTAL DATA, a FORTRAN program (NBS*SEARCH) , and

accompanying documentation. NBS CRYSTAL DATA contains up-to-date crystallographic

data on more than 115,000 materials. Each entry consists of the reduced cell and

volume, crystal system, space group symbol and number, chemical name, chemical

formula, literature reference and other data. For convenience, NBS CRYSTAL DATA is

provided in both full and abbreviated formats. The Database formats and contents

are described in detail in NBS Technical Notes CRYSTAL DATA: Version 1.0 Database

Specifications (Stalick and Mighell, 1986) and NBS*SEARCH: A Program to Search NBS

CRYSTAL DATA (Himes and Mighell, 1987). NBS*SEARCH software has been designed to be

used in conjunction with the 1-line Search File for the characterization and

identification of crystalline materials. Selected data for each entry from NBS

CRYSTAL DATA have been used to create a 1-line Search File in which each record of

132 characters corresponds to the data for one crystalline compound.

88
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2. Online Dissemination of NBS CRYSTAL DATA

The NBS Crystal Data Center and CISTI's CAN/SND Scientific Numeric Database

Service (Canada) have collaborated to make the data available through CRYSTDAT.

CRYSTDAT is an online, state-of-the-art database search system that can easily be

accessed by scientists worldwide. Within CRYSTDAT, especially designed scientific,

database management and computer systems software have been integrated to form a unified analysis system. During the year the system has been extensively upgraded

with respect to data (-115,000 entries) and software. Currently over 110

institutions, including most major US industrial companies have signed up to use CRYSTDAT. Over the past months, CRYSTDAT has been intensively used in conjunction

with the development of technologically important materials. In the synthesis of

new optical materials, for example, space group and point group frequencies for

special classes of compounds have proved invaluable. In the design of lasers and

superconductors, the database has been systematically searched for candidate

compounds with the appropriate lattice parameters, space group and chemical

composition.

3. Database for Electron Diffractionists

A new product, designed specifically for electron diffractionists , has been

prepared. This product allows the experimentalist to identify materials using such

typical electron diffraction data as elemental information and d-spacings. The

database for electron diffractionists was prepared in three basic steps. First, an augmented NBS CRYSTAL DATA was prepared. To generate this derivative database, dspacings (3.6 million) were calculated for all inorganic compounds in NBS CRYSTAL

DATA using cell and space group information. Second, selected data items for 60,000

entries were extracted from the augmented database. These data were then combined

with similar data on 10,000 entries from the Powder Diffraction File. Third, a streamlined database, formatted for rapid searching, was built with d-spacings and

elemental data for - 70,000 inorganic compounds. Search software has been written

to be used in conjunction with the streamlined database. The product can be

integrated with software associated with commercial electron microscopes or used

independently. Extensive tests using observed electron diffraction data have proved

that the product provides a major new analytical tool for electron diffractionists

.

The generation of this new product was carried out as a collaborative effort between

the NBS Crystal Data Center and Dr. Martin Carr of the Sandia National Laboratories.

89
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A MATRIX APPROACH TO SYMMETRY

V. L. Himes and A. D. Mighell

In the collection of crystallographic diffraction data the initial sequence of

steps is directed towards defining the lattice and the crystal symmetry. In doing

so, the experimentalist traditionally relies on familiar or standard orientations to

guide both the collection and the evaluation of data. On the diffractometer , for

example, a conventional unit cell (as defined by the magnitudes of the cell

parameters) is determined and the assumed Laue symmetry is verified by taking

specially oriented films or by checking the intensities of equivalent (h,k,l)'s

listed for standard orientations. There are many valid reasons for choosing

conventional cells and orientations in the latter stages of experimental work.

However, by choosing specific or familiar orientations in the initial stages,

assumptions are made that influence what data is collected and, consequently,

mistakes are more likely to be made. The lattice and its symmetry need not be

expressed with respect to a standard cell. The properties of the lattice are reflected in any primitive cell because translation of the primitive unit cell

generates the entire lattice. The matrix approach to symmetry represents a powerful new strategy in which the emphasis is shifted from standard cells and

standard orientations to matrices.

In the matrix approach to symmetry, the matrices that transform the lattice

into itself are generated. This group of symmetry matrices defines the holohedry of

the lattice. The metric symmetry (and any pseudosymmetry) of the lattice is

determined simply by counting the number of matrices. However, the experimentalist

need not rely solely on metric information. The group of matrices generated in this

way may be viewed as sets of equivalent (h,k,l)'s represented in matrix form. Thus

the Laue symmetry may be readily analyzed without transformation to standard

familiar orientations. Furthermore, using extremely simple mathematics, the nature

and the direction of each symmetry operation of the lattice may be calculated. This

information may, in turn, be used to obtain a transformation matrix to a conventional or standard cell of the lattice.

By providing the conceptual and practical framework required to perform

experimental procedures in a logical and general manner, the matrix method should

revolutionize the automation of diffractometers . New theory and computer algorithms

have been developed that permit the determination and interpretation of symmetry

using any cell of the lattice. Symmetry can be directly analyzed in the most

general way possible without relying on assumptions, conventions and standard cells.

The method is precisely what the experimentalist needs as it permits the efficient

measurement of exactly the data required to establish the Laue group. In applying

90
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the technique, the experimentalist is always aware of the highest possible symmetry,

all pseudosymme tries and the interaction of experimental error and symmetry. The

symmetry for an unknown crystal is determined through a straightforward sequence of

steps, discussed in the following sections, as soon as a cell defining the lattice

has been determined.

1. Generation of the Symmetry Matrices

The basis of the matrix approach to symmetry is to generate the matrices that

relate any primitive cell of the lattice to itself. Although any method that will

generate the required matrices will suffice, it has been found that the B-matrix

algorithm (Santoro, Mighell & Rodgers , 1980) is efficient and reliable. With the

algorithm, the matrices B in the following equation are determined:

ai = I Bij aj (i,j = 1, 2, 3)

J

where ai and aj define two primitive triplets of noncoplanar translations (a triplet

is called primitive when it defines a primitive cell) . When using the B-matrix

algorithm for the analysis of symmetry, one selects a primitive cell and generates a set (or sets) of symmetry matrices. Only B-matrices with integer elements and a determinant of +1 are considered. The treatment of experimental error using the

matrix method is conceptually very simple. Generated with each symmetry matrix ia a 'tolerance' matrix. The tolerance matrix represents the tolerances in the unit cell

parameters required to transform the cell into itself by the specified matrix.

Suppose Cell 1 is defined by lattice parameters a, b, c, a, /3 , y. If, when applied

to Cell 1, the matrix procedure yields the matrix B with the tolerance matrix

tol a tol b tol c tol a tol (3 tol 7

then the transformation of Cell 1 by the matrix B will give Cell 2 having lattice

parameters

a' = a + tol a b' = b + tol b c' = c + tol c a' = a + tol a f3' = /3 + tol @

7' = 7 + tol 7

Thus , the matrix procedure enables a direct comparison of the calculated errors with

the experimental errors for the refined unit cell. The computer program based on the B-matrix algorithm is very fast even when analyzing highly skewed unit cells.

91
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In addition, the computer time is essentially independent of the magnitudes of the

tolerances specified for the unit cell parameters.

2. Determination of the Metric Lattice Symmetry

By relating the lattice to itself, all the symmetry operations of the lattice

are obtained. The metric lattice symmetry is then determined by counting the number

of matrices. The greater the number of matrices found, the higher the symmetry.

Using the B-matrix algorithm, the numbers of matrices for the seven lattice metric

symmetries are: triclinic, 1; monoclinic, 2; orthorhombic , 4; rhombohedral , 6; tetragonal, 8; hexagonal, 12; and cubic, 24.

An important feature of the matrix approach is that one can determine the

highest possible metric symmetry within any specified tolerance of the unit cell

parameters, and that all possible pseudosymmetries are immediately apparent. By

initially assuming very large experimental errors, a menu of all possible symmetries

is obtained. Thus, to determine metric symmetry using the matrix procedure, one sets large limits for the tolerances (such as 1.0 and 6.0 for the cell edges and

angles, respectively) and analyzes the set(s) of symmetry matrices and tolerance

matrices obtained. Theoretically, it is the nature of the matrices themselves that

defines the sets to be analyzed (i.e., those defining a symmetry group).

Practically, however, the usual result is that the tolerance matrices alone clearly

define the groups and all that is required to determine the metric lattice symmetry

and pseudosymmetry is to count.

*To obtain a complete group of symmetry operations using the B-matrix algorithm,

multiply the matrices by -1 to generate a set twice the size.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

When the symmetry matrices are used to transform an experimentally determined

unit cell, metrically similar unit cells are generated (refer to the definition of

tolerance matrices) . If the lattice symmetry elements correspond to

crystallographic symmetry elements, then these metrically similar cells are symmetrically equivalent and the observed metric differences are due to experimental

errors. The matrix approach to symmetry provides an ideal way to evaluate the

experimental errors by simply averaging the set of tolerance matrices. The

resulting 'error' matrix (= averaged tolerance matrix) may be compared directly to

the e.s.d.'s for the refined unit cell, or it may be applied to the refined cell to

calculate an idealized cell reflecting the exact metric symmetry. In either case,

the extent to which the refined cell parameters deviate from the exact metric

symmetry is easily established.

3. Determination of the Laue Symmetry

The symmetry operations of the lattice may be generated using the B-matrix

algorithm by transforming the lattice into itself. The transformation of Cell 1 to

Cell 2 can be represented by the equation:

a2 al

b2 B bl

c2 cl

where (ai,bi,ci), i=lm2 represents the basis vectors in direct space and

bll bl2 bl3

b21 b22 b23

b31 b32 b33

The same matrix, B, can be used to transform the values of the (h,k,l)'s for the

setting defined by Cell 1 to the setting defined by Cell 2. Thus, the B-matrices

also may be viewed as matrix representations of equivalent (h,k,l)'s. With the

matrix approch to symmetry, the metric symmetry may be determined to within any

specified tolerance of the unit cell parameters, and the same group of B-matrices

may be used to experimentally determine the Laue symmetry. The metric lattice

symmetry, the Laue symmetry and all possible pseudosymmetries can be readily

evaluated without transformation to standard or familiar orientations. In practice,

the Laue symmetry may be determined by evaluating the intensities of equivalent

reflections. A more theoretical proof of the Laue symmetry, as well as an analysis

of all possible subgroups, is obtained by analyzing the B-matrices themselves.

93
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The symmetry operations of the lattice are represented by the B-matrices . The

values of the elements in each matrix depend upon the kind and orientation of the

element with respect to the coordinate system chosen. Because the B-matrix

algorithm generates matrices with a determinant of +1 , the nature of the symmetry

axis is found by calculating the trace of the matrix: tr(B) = bll + b22 + b33. The

trace of the matrix is invariant under similarity transformations; that is, it is

independent of the basis chosen , The symmetry axis is an n-fold rotation axis

where n = 1,2,3,4,6 for tr(B) = 3,-1,0,1,2, respectively. The direction of the axis

is given by the solutions q of a linear algebraic equation of the form (B - l)q = 0,

where 1 is the identity matrix.

4. Practical Symmetry Determination

A primitive unit cell with

a = 13.8102(21) b = 13.8091(22) c = 16.6620(28) A

a = 89.994(13) (3 = 89.993(13) 7 = 89.980(13) °

was determined for the complex C56 H60 Cu5 N22. The group of B-matrices generated

from this unit cell is given in table 1. The metric lattice symmetry is tetragonal

since eight symmetry matrices were found. When evaluating symmetry using the matrix

method, the experimentalist need not rely solely on metric information. The group

of B-matrices may be viewed as sets of equivalent (h,k,l)'s represented in matrix

form. Once a reflection has been found on the diffractometer , the equation

eq

= Bi

may be used to generate sets of reflections that should have equivalent intensities

if the metric and crystal symmetry agree. Substitution of the B-matrices from table

1 into the above equation, where i = 1,...8 for the tetragonal system, .generates the

following set of (h,k,l)'s:

(-h,-k,l) (-h,k,-l) (-k,-h,-l) (-k,h,l)

( k,-h,l) ( k,h,-l) ( h,-k,-l) ( h,k,l)

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

This is the familiar set used for the tetragonal system since the primitive cell

ased to generate the symmetry matrices reflected the conventional metric conditions

consistent with the highest possible symmetry of the lattice (i.e., in the

tetragonal system, a cell with a = b ^ c and a = ft = 7 = 90° as oppposed to a primitive cell with a ^ b f c and a ^ /3 ^ 7 ^ 90°). For sets of general (h,k,l)'s,

it was found that the intensities for all eight reflections in the sets were equivalent, indicating 4/mmm Laue symmetry for the complex. This observation was confirmed by a full structure determination (Himes , Mighell & Siedle, 1981).

Using the matrix approach, the Laue symmetry and any pseudosymmetry , metric or crystal, may be determined from any cell defining the lattice. A second unit cell was determined for the complex C56 H60 Cu5 N22 and refined on a diffractometer

:

a = 19.5263(27) b = 42.4583(59) c = 30.8742(45) A

a = 29.242(13) /3 = 18.442(13) 7 = 23.106(12)°

As expected, the matrix procedure predicted tetragonal symmetry since eight B- matrices were generated (table 2) . The group of matrices used to determine the

metric symmetry also were used to evaluate the Laue symmetry from this skewed unit

cell. For example, when the (5,6,7) reflection was multiplied by each of the B- matrices from table 2, the following set of (h,k,l)'s was predicted and

subsequently found, to have equal intensities:

(-1, -6, -4) (-1, 2, 1) (-5,-14, -7) (-5, -6, -8)

( 5, 14, 8) ( 1, -2, 4) ( 1, 6, -1) ( 5, 6, 7)

Once the symmetry has been evaluated, these same matrices may be used to

obtain a transformation matrix to a conventional or standard cell.

5. Concluding Remarks

The matrix approach to symmetry has been used routinely to determine symmetry

for all types of compounds from small molecules to proteins. This approach, which

deals with symmetry in its most abstract form, provides the conceptual and practical

framework required to perform experimental procedures in the most logical and

general manner possible. Unlike techniques currently in use in modern

diffractometry , automated procedures based on this new method will determine

95
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Symmetry matrices found for C56 H60 Cu5 N22. Program limits of 1.0 and 6.0 were used for the cell edges and angles, respectively.

(1)

(5)

-1 o

1

(2) ( 1 | (".) 0-1

1 o

1

(6) | 1 J (/)

0-1

0-10

1 I (4)

0-1

100-10

0-1

(8)

Table 2. C56 H60 Cu5 N22: Symmetry matrices calculated from a skewed cell.

Program limits of 1.0 and 6.0 were used for the cell edges and angles,

respectively.

(2)

(6)

(4)

(8)

symmetry without risk of error as the technique does not rely on assumptions,

conventions, or standard cells. A FORTRAN program, NBS*LATTICE, has been written to

analyze lattice relationships and is available for distribution. The present

version of NBS*LATTICE performs several functions including the determination of

metric lattice symmetry.

1. Himes, V.L. & Mighell, A.D., Acta Cryst. A43 . 375-384, (1987).

2. Himes, V.L. & Mighell, A.D. & Siedle, A.R. . J. Am. Chem. Soc. 103, 211-212,

(1981) .

3. Santoro, A., Mighell, A.D. & Rodgers , J.R. Acta Cryst. A36, 796-800, (1980).

96
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SMALL ANGLE NEUTRON SCATTERING RESEARCH AT NBS

J. A. Gotaas and C. J. Glinka

Until the reactor shutdown for the installation of the cold source, the SANS

instrument was utilized by experimenters for more than 98% of the available beam

time, including scientists from universities (20), industry (10), government

laboratories (3) and six NBS divisions and NBS-Boulder (16). The areas of

experiments included polymers (44%), chemistry and physics (16%), magnetism (15%),

ceramics (9%), metallurgy (7%) and biology (6%). A brief review of some of this

work follows; much of it is described more completely elsewhere in this report.

As can be seen from the distribution of beam time given above, research in

polymers is one of the most active programs on the SANS, with scientists from the

Polymers Division playing a key role. C. Han (Polymers Division), with a number of

collaborators from university, industry and NBS, has continued detailed studies of

the conformations of a variety of polymer blends, of the critical behavior of low

density polymer materials, and has examined the phase diagram and interaction

parameters of rubber/rubber mixtures. In collaboration with V. Soni (Shell), Han

has also used SANS to characterize the formation of micelles in block copolymers for

emulsion and oil recovery applications. W. Wu and B. Bauer (Polymers Division) have

continued their extensive studies of epoxy networks, determining the fractal

dimension of networks and the intranetwork form factor as a function of molecular

weight, as well as elucidating molecular mechanisms for the growth and deformation

of epoxy networks. B. Bauer and R. Briber (Polymers Division) have studied the

phase diagram of crosslinked polymer blends. Finally, M. Landry (Kodak) has used

SANS to characterize both bulk polystyrene and polystyrene blends in the vicinity of

the glass transition temperature.

The most active research effort from industry has been that of Exxon, which has

involved a number of Exxon scientists along with collaborators from universities and

NBS, and has formed a substantial part of the research in chemistry and physics. S. Sinha and J. Huang (Exxon) with H. Stanley (U. Maryland) have studied the phase

separation of binary fluids, including the effects of adsorption on surfaces, and

have characterized the structure of heavy oils. R. Overfield (Exxon) and H. Stanley

have studied the thermal dissociation of heavy oils. W. Dozier (Exxon) has used

SANS to study the structure of microemuls ions . J. Gregory (Mobil) and C. Glinka

(Reactor Radiation Division) have examined the structure of hydrogen- implanted

silicon, a material useful for solar cells. H. Hanley and G. Straty (NBS-Boulder)

have studied concentrated latex solutions and supercooled glycerol. C. Glinka and

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

L. Sander (Center for Analytical Chemistry) have continued their study of the

structure of bonded phases in porous silica. R. Slade (U. Exeter, England) used

SANS as a tool to study the porosity of clay materials.

SANS has continued to prove a vital tool for probing the microscopic structure

of amorphous magnetic systems. J. Rhyne (Reactor Radiation Division) and M. Spano

(Naval Surface Weapons Center) have studied a wide range of concentrations of

various amorphous rare earth-iron systems, examining the competition between

exchange and anisotropy which leads to the formation of an intriguing low

temperature state, the correlated spin glass. Rhyne and G. Fish (Allied

Corporation) have measured the short correlation ranges in amorphous Fe-Zr resulting

from the competition between ferromagnetic and ant i f er romagne t ic exchange

interactions. In an international collaboration, Rhyne and B. Barbara (CNRS,

France) have probed the critical behavior resulting from the presence of random

exchange and anisotropy fields in amorphous Dy Gd.. Ni_ alloys. In a different

X J_ - X A. area, J. Lynn, W.-H. Li and Q. Li (U. Maryland) have examined the new high

temperature superconductor ErBa9 Cu„07 (T =95K) and found evidence for the screening

of paramagnetic fluctuations by the superconducting electrons, the first such

observation in a superconducting rare earth system.

K. Hardman-Rhyne (Ceramics) continued to take advantage of the non-destructive

interaction of neutrons with samples to evaluate the structures of calcinated Green

State alumina and alumina powder, as well as the porosity of a variety of systems,

including slipcast alumina sheets and, with T. Coyle (Ceramics), sol-gel networks.

Hardman-Rhyne also used SANS to study the effects of stress in causing microcracks

in composites and creep cavitation in siliconized SiC.

SANS has also been of great utility in the characterization of metallurgical

samples, as B. Mozer (Reactor Radiation Division) and R. Shull (Metallurgy) have

compared the microstructures of amorphous metallic alloys prepared by different

techniques. E. Case (Michigan State U.) has examined the microstructure of borondoped Ni_Al as part of an investigation of embri ttlement mechanisms. R. Fields

(Fracture and Deformation Division) and R. Reno (U. Maryland) have also used SANS to

study the precipitation of Cu-rich particles and austenite in aged A710 steel.

Finally, R. Odette, J. Fint and D. Klingensmith (U. California-Santa Barbara) made

strenuous efforts to push the background of the SANS instrument to record- low levels

in their attempt to observe small structural changes corresponding to embrittlement

in irradiated steels.

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Finally, several research groups have taken advantage of SANS to study the

structure of biological systems. D. Engelman and J. Flanagan (Yale U.) examined the

unfolded states of proteins with altered amino acid sequences in order to understand

how one -dimensional amino acid chains fold to produce three-dimensional proteins.

As part of a continuing program, S. Krueger (U. Maryland) and R. Nossal (National

Institutes of Health) have studied neurosectretory vesicle systems in an effort to

understand the role of proteins and protein interactions in their function.

As usual, the demand for beam time on the SANS instrument continued to be

greater than the amount available, leaving a number of experiments for the future.

The increased flux resulting from the new cold source may be expected to ameliorate

this situation somewhat, but will certainly be partially counteracted by the desire

of researchers to perform ever more demanding experiments

.

CURVATURE PROPERTIES OF A MODEL BICONTINUOUS STRUCTURE

WITH A WELL DEFINED LENGTH SCALE

N. F. Berk

We have shown previously 1

, 2 that an algorithm originally invented by Cahn3 to

simulate morphology influenced by spinodal decomposition in isotropic 2-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 and controlled pore glasses.

Cahn's scheme associates an interface between two material phases of uniform

density with a level-set (contour) of a random standing wave, S (r) , composed of N

sinusoids having fixed wavelength . A, but random directions, k , phase constants,

<f> , and amplitudes, A : n

r n

N

S N(r) = "Z= I A cos(kk -r+4 ), (1) N

VN<A2 > n=l

n n n

where k = 27r/A and <A2 > is the mean square sinusoid amplitude. For example, for an

->• isometric partition, a 2-phase interface coincides with the O-set of S (r)--the set

-+ -> {r} on which S (r) = 0--since over a large space (1) is positive as often as it is

negative. Numerical simulations of this process are remarkably evocative of the

morphology of phase separated glasses, as imaged by micrographic techniques; the

model structure is highly interconnected, even well away from volume fraction

isometry

.

• ^ 99
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The character of the morphology is further elucidated by its curvature

properties. 2 If K t and /c 2 are the local principal curvatures 4 on a /3-set, the local

mean curvature, H = (k 1 +k 1 )/2, may be computed from H = V«n/2, where n(r) is the

unit normal vector field generated by S(r) = -S

N

(r) of (1). Then, on a /3-set H(r) =

(k2 /HS' ' (r) )/2S' (r) , where (') denotes the normal derivative. For N = 50, numerical

simulation gives <H> ~ 0.7k/3, where <•> = /•dS/S here denotes the average over the

surface 2, so that <H> = on a 0-set, the surface separating isometric bulk

partitions. For a family of parallel surfaces (constant S'(r)), the local Gauss

curvature, K = « x

/c 2

, satisfies K(r) = 2H(r) 2 -

| H' (r) | . With S'=D, one then has H =

k

2 £/2D and K = k

4

(/3 2 -D 2 /k 2 )/2D 2

; for /3 = , in particular, H = and K = -k2 /2,

independent of D. Such a surface is saddle -like everywhere and satisfies formal

requirements for nonplanar minimum area. The actual /3-sets of (1) are not a parallel family2

, but on average the 0-set has qualities of a minimal surface, with

simulations giving D ~ <S ' > - k/j2 and <H 2 > * 0.04k2

, so that <K> « -k2 /2.

1. N.F. Berk, NBS Technical Note 1231 . ed. F.J. Shorten, National Bureau of

Standards, (Gaithersburg) , p. 77 (1986).

2. N.F. Berk, Phys . Rev. Lett., 58, 2718 (1987).

3. J. W. Cahn, J. Chem. Phys., 42, 93 (1965).

4. T. Y. Thomas, Concepts from Tensor Analysis and Differential Geometry . Academic

Press, (New York) (1961).

INTERPRETATION OF SMALL ANGLE NEUTRON DATA FROM POROUS

GLASS USING CAHN'S MORPHOLOGY

N.F. Berk and C.J. Glinka

and

H.B. Stanley

(University of Maryland, College Park, MD 20742)

and

(National Bureau of Standards, Gaithersburg, MD)

Despite intensive recent experimental investigation in many laboratories , the

detailed internal structure of microporous glass has not yet been theoretically

1 2 understood. We have applied a morphological model ' based on Cahn's theory of

3 spinodal decomposition that appears to describe the bulk pore structure. This

model implicitly assumes that the internal pore surfaces are smooth, although we are investigating methods to incorporate roughening effects. In fact, the nature of the

internal surfaces is still the subject of considerable controversy, with claims both

100
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

for smooth and rough surfaces in nominally similar commercial glasses.

2 The basic model is described elsewhere . The essential idea is that

interfaces for random, interpenetrating structures with a well defined length scale can be modelled mathematically as isometric contours of a stochastic function having

random Fourier components with a common wavenumber k = 2n/X. Scattering from this

morphology is characterized by four distinctive features: (a) a sharp diffraction

line at q = k, where q is the scattering wavevector; (b) a divergent contribution

4 going as 1/q for q->0 ; (c) a sharp step at q = 2k; and (d) Porod law behavior, 1/q , as q

-* <», as required of scattering from smooth bodies. The relative strengths of

the "singular" features, (a) - (c) , depend on composition (the volume fractions of

the spatial partitions generated by the model) and contrast conditions of the

experiment being modelled.

In applying the model to real controlled pore glasses one can expect on physical grounds that the wavenumber, k, of the morphology will be distributed about

a modal value, k~ , with some effective width, Ak, according to a distribution P(k) . 2 Such k dispersion can be incorporated in the model and is found to moderate the

various singular features of the scattering associated with the nondispersed

morphology: the peak at q ~ k_ is broadened, the hyperbolic divergence at q = is

cured, while the step at q ~ 2k _ is rounded off. The relative changes in these

features brought about by dispersion are sensitive to the actual shape of P(k) . For

example, increasing the width of P(k) not only rounds off the shoulder at q = 2k

but it can also cause it to be masked by scattering from the broadened peak at q =

Figure 1. Small angle neutron scattering from dry controlled pore glass.

The solid line is a fit using the model discussed in the text and

incorporating the k dispersion of Eqn. (2). The fit accounts for

instrumental resolution and a beam stop.

101
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

k n. The scattering near q = is also sensitive to the shape of P(k). The

scattering formula for the small q "singular" features for given P(k) is

k ^q^J 4 J |q'-q| q

2 where C-. and C depend on composion and contrast . Thus , the scattering observed

near q = depends not only on the degree to which the 1/q divergence is moderated

in the second term of (1) but also on the behavior of P(k) near k = in the first

term. It particular, the broadened peak will contribute zero intensity at the

3 origin only if P(k) -* faster than k . We have found that our measured scattering from various samples of controlled

pore glasses are well described by the model at small q assuming a P(k) of the

normalized inverse Gaussian (Wald) type,

P(k) = yt,/(27rk3)el/(k ' /i)2/2^ ) (2 )

for k>0 , where v and /z are free parameters, and <k> = p, and <(k - <k> )> = fi /u =

(Ak) . The mode, k , n is given by k =jz{(1 + 9/z /^v j -3/j,/zu). Figure 1 illustrates the scattering from a typical sample of commercially available glass,

which was carefully cleaned and dried, compared to the scattering predicted by the

model. The data show a characteristic peak centered at q n = 0.024 A and a non- Porod power law decay, 1/q , with m ~ 3.5, for q » q_ . The solid line is a model

fit incorporating (1) and terms not shown here and using (2) with kn = 0.025 A (<k>

-1 -1 = 0.033 A ) and Ak = 0.03 A . The effects of instrumental resolution have also

been included. The model fits well in the region of the peak, but fails in the

tail, as it must without incorporating a means of describing the apparent roughness

indicated by the scattering at high q. The choice of distribution (2) is arbitrary,

but it does reflect the apparent need for a P(k) that falls sharply as k -+ 0.

We are investigating the structural implications of the shape of the P(k) that

appears to best fit the data, including a method to produce computer simulations of

the corresponding morphology.

1. N.F. Berk, NBS Technical Note 1231 . ed. F.J. Shorten, National Bureau of

Standards, (Gaithersburg) , p. 77 (1986); See also N.F. Berk elsewhere in this

Summary of Activities

.

2. N.F. Berk, Phys . Rev. Lett., 5_8, 2718 (1987)

3. J. W. Cahn, J. Chem. Phys., 42, 93 (1965).

102
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PHASE SEPARATION OF A BINARY FLUID IN POROUS GLASS

H.B. Stanley

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

S.K. Sinha

(Exxon Research and Engineering Co., Annandale , NJ)

and

S.K. Satija

(University of Delaware, Newark, DE)

and

C.J. Glinka

The critical behavior of a binary fluid mixture confined in a porous medium is

thought to be dramatically different from that in the bulk, especially if one of the

two phases preferentially wets the medium . We have investigated the phase

separation of a critical concentration of 2,6 lutidine and water by means of small

angle scattering at the NBSR and observe for the first time, the development of

critical fluctuations. Data were taken with a neutron wavelength of 8A for momentum

transfers .009 < q < .125 A . The porous glass used (trade -name VYCOR) has an

SANS from porous VYCOR

1 I dft

! i i i

B — B m -dry VYCOR

B CD o- contrast matched

£§

z

m b

B

B with lutidine/water _

at T=10C

p 03 B o _ m b a- contrast matched _

<w> B °n with H20/D20

!z; • ffl B o o B <3, " m

iy^

^fi^

uZk Sl~^

55 _ (tf> ^\i* ^^^^^niiiiiiiiiiiiiiiiiiiiiiiiiiiiii 0oBnm_

f~\ i i i i i i °(100 0.04 0.08 0.12

Q(l/A)

Figure 1. Comparison of the small angle scattering from dry VYCOR porous glass with

that from VYCOR saturated with contrast matching solutions of H 0/D

(lower curve) and lutidine/water (middle curve). Notice the 100-fold

change of scale between the dry and wetted VYCOR scattering curves.

103
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

average pore size of the order of 100A and a well defined inter-pore distance as indicated by the distinctive sharp peak in the scattering cross-section (see figure

1) . The manufacturing process involves quenching a borosilicate glass -forming melt

into a separated mixture of SiO_-rich and B_0„-rich phases. The latter is leached

out, leaving the fully connected internal pore space.

The scattering from the pore structure itself could be reduced by a factor of

about 500 by imbibing a contrast matching solution of H-O/D-O, as shown in figure 1. When imbibed with a contrast matching solution of lutidine plus H9 0/D-0, at the

critical concentration of 28% lutidine, some residual scattering remained (see

figure 1) even well below the bulk phase separation temperature of 31C which is

likely due to preferential wetting of the pore surfaces by one of the components of

the fluid mixture

.

In figure 2 we illustrate the scattering from lutidine/water , at the critical

composition, in VYCOR as a function of temperature. We notice that the scattering

reflects the pore structure of the dry glass, but is not due simply to changing

contrast even at the lowest temperatures measured (5 C) , because the peak shape is

significantly broader (see figure 1) . As the temperature is raised a second

Lutidine/water in VYCOR, T-dependence

o

o

o

E-D

W2

1 1 1 a

1

I I 1 1 1

m T=85C <D

~ ~

m CO - n <

— B B

bulk © m transition "

1 . — © %} d

T=75CX:^^ 6cj

— _ o o o -

1 1 1 1 1 <%, °0. 20. 40. ^V TEMPERATURE (C) _ T=55C

ft* A iiA !*!' "A " J

1 1 1 1 k^ a) warming

0.00 0.02 0.04

Q0/A)

0.06 0.08

1 1 1 1 l l I l

m T=85C

<d n • n

<D H

© ID ®0)

-

_ T=75C^\!b

***** ^bCL " T=60C ^,

b) cooling -

i i i i

I ^^f^aa^EBBspa

—

0.00 0.02 0.04

Q(l/A)

0.06 0.08

Figure 2. a)Temperature dependence of the scattering from VYCOR imbibed with a contrast matching solution of lutidine/water at the critical point

composition. The correlation range derived from the lorentzian tails of

the scattering curves appears to diverge between 50 to 60C, well above

the bulk transition temperature of 31C. b)0nce heated above the phase

separation temperature, the scattering is irreversible on cooling

(compare with a)

.

104
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

component centered at q=0 becomes dominant, and cooling shows the changes to be

largely irreversible (at least on a time scale of several hours) as illustrated by

figure 2b. The scattering for wavevector transfers greater than about .07 A

follows an Ornstein-Zernike form from which estimates of the correlation lengths of

the fluctuations could be made. These are illustrated inset in figure 2a for the

data taken on warming. It can be seen that no anomaly occurs at the bulk

transition temperature (around 31 C) , but that there is a divergence at higher

temperature indicating a phase separation between 50 and 60 C, in agreement with

2 light scattering data . After heating and phase separation we see no time

dependence over a period of an hour, but we do have evidence for changes over a period of weeks, indicating that slow diffusion may be needed to regain the low

temperature homogeneous equilibrium state. Even after several weeks at room temperature, however, the sample did not return to its original state.

A theoretical study of these wetting and phase separation processes in porous

c\

4

3 media is currently in progress, based on the formulation of J.W. Cahn as extended

by N. Berk.

1. M.C. Goh, W.I. Goldburg and CM. Knobler Phys . Rev. Letts. 58 1008 (1987)

2. S.B. Dierker and P. Wiltzius, Phys, Rev. Lets. 58, 1865 (1987).

3. J.W. Cahn, J. Chem Phys. 42, 93 (1965).

4. N.F. Berk, Phys. Rev. Letts. 58, 2718 (1987).

DETERMINATION OF BONDED PHASE ADSORBATE THICKNESSES BY

SMALL ANGLE NEUTRON SCATTERING

C. J. Glinka

and

L. C. Sander

(Center for Analytical Chemistry)

We have been using SANS to characterize the structure of linear hydrocarbon

chains chemically grafted to the internal pore surfaces of microporous silica

particles. The aim of this work has been to relate the structure of the bonded

adsorbate layers to the performance of chemically modified microporous particles

used in chemical separation (e.g. in high performance, reve r s e - phas e liquid

chromatography) and processing.

105
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CO

C\2 o

Io

co

* o

^

cP"

.<*> Dc

f^—A<*pflUt**Stt ** 1 *****

0.00 0.04 0.08 0.12

Q-SQUARED (1/A**2)*10

-1

Figure 1 . IQ versus Q plots of the small angle scattering from a porous silica

gel with C18 alkyl chains grafted to the internal pore surfaces and

imbibed with various mixtures of deuterated and protonated methanol (A

100 % ME0H, + 79 % ME0H, 36 % ME0H and o 18 % ME0H). The slopes of

the linear portions of the curves can be fit tp a model (inset) which

gives the thickness and scattering ensity of the bonded phase layer.

Our most recent measurements have focused on the outer (i.e. larger Q) portion

of the SANS patterns observed from such systems where the distance scale probed is

commensurate with the thickness of the bonded phase layers and where the details of

the pore structure have no effect on the scattering. The only scattering from the

-4

pore structure which is observed at larger Q's is the Q , Porod law, scattering

from the pore -silica interfaces, and this scattering can be suppressed by filling

the pores with a solution (a mixture of protonated and deuterated methanol in our case) which matches the scattering density of silica. By so doing, the signal from

the bonded phase layers is accentuated.

If the thickness of the bonded phase is much smaller than the size of the

-2

pores, then in the pore masked condition the scattering should exhibit the Q

dependence characteristic of thin sheets. This is indeed what is typically observed

as illustrated in figure 1 (squares) which shows the scattering from C18 alkyl

106
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

-2

chains bonded to a large pore (1000 A) silica gel. The intensity of the Q

scattering (the slope of the linear region in figure 1) is proportional to the

square of the product of the thickness and the scattering density of the bonded

layer. Although not separable in a single measurement, both of these quantities can be obtained by carrying out a series of measurements in which the contrast with the

pore filling solution is varied. Figure 1 shows such contrast variation series from

which the average thickness of the C18 layer was determined to be 16 ± 2 A (compared

to a fully extended chain length of 25 A). This represents the first direct

measurement of bonded phase thickness in such materials.

We have carried out similar measurements on bonded phases of alkyl chains

ranging from C4 to C30. The SANS results are being used to develop correlations

between the bonded phase morphology and chromatographic trends observed when these

phases are used to separate solute mixtures of polycyclic aromatic hydrocarbons.

L. C. Sander, C. J. Glinka and S. A. Wise, (submitted to Analytical Chemistry)

SANS STUDY OF ORGANOPHILIC BENTONITE DISPERSED IN TOLUENE

R.C.T. Slade

(University of Exeter, England)

and

(National Bureau of Standards, Gaithersburg, MD)

and

C.J. Glinka

Organophilic bentonites (montmorillonite clays) are additives used in preparing

thixotropic marine paints. The normally organophobic clays are made organophilic by

exchange to incorporate quaternary ammonium cations in the interlayer region.

Studies of aqueous suspensions of alkali - exchanged montmor illonites by SANS

revealed suspended platelets and gave details of the platelet constitution for

various exchange cations. No studies of suspensions of organophilic bentonites in

organic solvents have been made previously.

Organophilic Claytone 40 (English China Clays International) was suspended in

o mixtures of toluene/d -toluene. Sols were prepared with 0.75% and 1.50% clay by mass

.

Small angle scattering of neutrons (A = 5 A) was observed for all samples.

Plots of ln(I) versus ln(Q) were linear in the region 0.015-0.05 A . The gradients

107
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

of such plots were, however, solvent composition dependent, ranging (for 1.5% sols)

Q from -2.3 (100% toluene) to -3.1 (100% d -toluene). The pattern was similar for the

lower concentration (0.75%) sols.

The results of this preliminary study are not consistent with a model of

individual clay sheets or composite platelets in suspension (anticipated gradients

in ln(I) versus ln(Q) plots would be -2). The scattering is more indicative of

globular, composite particles with dimensions far larger than those observed in

aqueous suspensions of alkali -exchanged clays. Further studies will be made at

longer wavelength to probe the observed region of linear dependence of ln(I) on

ln(Q) in detail.

1. D. J. Cebula, R. K. Thomas, and J. W. White, J.C.S. Faraday I, 76., 314-321

(1980).

SMALL ANGLE SCATTERING STUDY OF THE SUPERCONDUCTING TRANSITION IN ErBa Cu

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

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

H. C. Ku, H. D. Yang, and R. N. Shelton

(Iowa State University, Ames, IA)

The discovery of superconductivity above the boiling point of liquid nitrogen

in the oxide compounds such as YBa_Cu„07 has created tremendous excitement not only

because of the possible new fundamental superconducting mechanism in this class of

systems but also because of the enormous potential for applications. The

substitution of the heavy rare-earth elements for yttrium has little if any

2 3 detrimental effect on the superconducting transition temperature, and hence these are ideal materials to investigate the interplay between magnetism and

4 superconductivity. In the low T systems this coupling is thought to be primarily

electromagnetic in origin, but the direct London screening of the long wavelength

magnetic fluctuations by the superconducting electrons has so far eluded detection.

Our present small angle neutron scattering results show that the intensity at small

wave vectors q does in fact decrease when the sample becomes superconducting.

Furthermore, the overall amplitude, temperature dependence, and q-dependent shape of

this change in the scattering is consistent with the expected suppression effect.

108
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

8

4

JCro

i

ifi -4

-t —c

3O -8

O

a> -12

z. -16

-20

t r i r

T = 75K

T = 60K

j i

i i J L 0.015' 0.030 0.045 0.060

Q(A')

Figure 1. Wave vector dependence of the net intensity for two temperatures below

V

However, this interpretation would require a London penetration depth A which is

much smaller than expected, and suggests that either another length scale might be

relevant to describe the magnetic screening, or the observation represents a new aspect common to this class of superconductors.

The SANS data were obtained with a neutron wavelength of 6.0 A using the high

resolution focusing beam configuration. We would expect to observe a paramagnetic

signal, which would be superposed on metallurgical scattering which rises steeply at

very small q. Since the ordering temperature is so low, the magnetic correlations

caused by the Er magnetism will be negligible in the vicinity of the superconducting

transition. Above T the magnetic scattering will then be independent of q, which

means that fluctuations of all wavelengths are equally likely to occur. Below T however, it will cost additional energy to make fluctuations with wavelengths which

are comparable to or larger than the London penetration depth, and hence we would

expect the fluctuations for q < 1/A to be suppressed in amplitude. Subtracting the

data above T from the data below T will then emphasize any changes in the observed

5 scattering, while the metallurgical scattering should cancel. Some difference data

at two temperatures are shown in figure 1. Above T we did not detect any change in

Li scattering, while at 75 K we see a small effect which is statistically significant;

all the data points are below zero or within one standard deviation of zero. Reducing the temperature to 60 K clearly decreases the scattering further, while

109
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

little additional change was found at lower T. We remark that one important check

is to compare the magnitude of the decrease in the scattering at small Q with the

observed intensity of the raw data at large Q where the nuclear scattering is small

and the paramagnetic scattering dominates. For the paramagnetic suppression

interpretation to be valid, we can certainly not reduce the scattering at small q more than the paramagnetic intensity that was originally there, so that the

intensity at large Q places an upper bound on the overall size of the possible

effect. The data of figure 1 are well within this bound.

The results for the temperature dependence of the scattering are shown in the

top portion of figure 2. The data at each Q exhibit the same T dependence, so we have summed the data over a range of wave vectors from 0.023 to 0.037 A to improve

the statistics. The intensity clearly decreases below the superconducting

transition temperature, and exhibits behavior which is quite similar to the behavior

of the magnetization as shown in the bottom portion of the figure. Here the cooling

data were taken in an applied field of 100 Oe , while the warming data were obtained

by cooling in zero field, and then applying a field of 100 Oe

.

Experimentally we have demonstrated that the SANS scattering decreases below

the superconducting transition. If it is correct to interpret this change as due to

magnetic screening, then we can use the data of figure 1 to estimate the magnetic

screening length in this material. The screening in real space should be described

by an exponential, which yields a squared Lorentzian scattering function with A = — 1/2

[J2 - 1] /q, • A fit to this functional form yields A ~ 22 A, which would be a very small London length. We can compare this value to the related oxide

fi 7 superconductor La, nc Sr_ n ,-CuO. , where A T has been measured ' to be 2000 -» 2500 A.

1 . 85 . 15 4 L

This range is typical for a strong type -II superconductor, and suggests that our screening length is not a direct measure of A . Another relevant length scale is of course the superconducting coherence length £_, which is the correct order of

magnitude. A second possibility is that the screening in these magnetic

1/2 superconductors occurs on the length scale of (7A ) , where 7 is the magnetic

4

L

stiffness parameter. This is the quantity which controls the size of the

oscillatory wave vector in the "low T " magnetic superconductors, and is also the

correct order of magnitude. A more interesting possibility, however, is that the

change we observe originates from another property of these oxide superconductors

unrelated to the Er magnetism. It would be very useful to have a direct measurement

of the London penetration depth of this material.

110
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

10

c

_C

"O -10

Oi_

CT> <u _c -20

+_

<D

"Z. -30

E

5 "0.2

20 40 60 80 100 120 140

T(K)

Figure 2. a) Temperature dependence of the scattering, integrated over the Q range

of 0.023 to 0.037 A . b) Temperature dependence of the magnetization.

1. M. K. Wu, J. R. Ashburn, C. J. Torng, P. H. Hor , R. L. Meng, L. Gao , Z. J. Huang, Y. Q. Wang and C. W. Chu, Phys . Rev. Lett. 58, 908 (1987).

2. P. H. Hor, R. L. Meng, Y. Q. Wang, L. Gao, Z. J. Huang, J. Bechtold, K. Forster,

and C. W. Chu, Phys. Rev. Lett. 58, 1891 (1987).

3. Z. Fisk, J. D. Thompson, E. Zirngiebl, J. L. Smith and S-W. Cheong (preprint).

4. For a review see Topics in Current Physics , edited by 0. Fishcer and M. B. Maple

(Springer-Verlag, New York, 1983), Vols. 32 and 34.

5. Additional experimental details are given by J. W. Lynn, Physica 136B . 117

(1986).

6. G. Aeppli, R. J. Cava, E. J. Ansaldo, J. H. Brewer, S. R. Kreitzman, G. M. Luke,

D. R. Noakes, and R. F. Kiefl, Phys. Rev. B35, 7129 (1987).

7. W. J. Kossler, J. R. Kempton, X. H. Yu, H. E. Schone , Y. J. Uemura, A. R. Moodenbaugh, M. Suenaga and C. E. Stronach, Phys. Rev. B35, 7133 (1987).

Ill
NETWORK FORMATION OF THERMOSETTING POLYMERS - A SMALL ANGLE

NEUTRON SCATTERING STUDY OF EPOXIES

W-L. Wu and B. J. Bauer

(Polymers Division)

The crosslink process of long chain molecules in bulk up to its gelation point

has been simulated successfully in the classical theory by Flory & Stockmayer (FS) . Their model is equivalent to a Bethe tree in which no closed loops are allowed. On

the other hand, the results of a percolation model which allows for closed loops

have been applied successfully in the crosslink of many systems e.g. silica gel and

colloidal particles. It is the goal of this work to determine which model does the cure of thermoset follow. Intuitively, one expects that the percolation model will

prevail due to the size of the thermoset monomers. However, there is an obvious

difference between the percolation model and the cure of thermoset; there are two

types of bonds in a cured thermoset, one is the monomer chain by which the reaction

ends are originally connected and the other is that formed between the reacted ends.

These two bonds are different in length for most cases. In the percolation model,

however, only one type of bond is considered. It is, therefore, of interest to

determine whether any of these two models will adequately describe the curing of

thermoset

.

Epoxy was chosen as the model system for thermoset and all the cure was conducted in the bulk state instead of in solution. More specifically, diglycidal

ether of Bisphenol A (DGEBA) was cured with di- and tri amines connected with

polypropylene chain (Jeffamine D-230 & T-403 respectively). All the curing was conducted at 60° C in the early stage and followed by a 23° C cure as the gel point was approached. The reason for lowering the cure temperature in the later stage was to capture samples with a small undercure , e, defined as the distance to reach the

critical degree of cure P . The extent of cure was monitored by both infrared

spectroscopy (IR) and viscosity. As the cure precedes, specimens of different

degree of cure were removed from the reaction bath and dissolved in deuterated THF

.

For each specimen, solutions of 3 to 5 levels of concentration were prepared; the

lowest concentration was in the range of 0.2 % by volume. All these solutions were

kept at -5° C throughout the whole experiment and no further cure was detected in

any of the solutions. Small angle neutron scattering (SANS) results on these

solutions were extrapolated to zero angle and zero polymer concentration to obtain

the values of molecular weight (M ) and radius of gyration (R ) of the crosslinked ° w

°J g

polymer chains at various degrees of cure

.

112
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS'

Since all the scattering measurements were carried out in solution, the

excluded volume effect must be included in the data interpretation. Furthermore, we are dealing with a polydispersed system in terms of the size of the crosslinked

molecules. One should not, therefore, expect to observe a simple fractal type

scattering exemplified by the following relation

I(q) cc q

where q is the magnitude of the scattering vector and D is the mass fractal

dimension by which the value of M and R are related through the simple relation M

D w g

& w

oc R . After taking into account both the polydispers ity and the excluded volume

o effects, the effective value for D is 1.64 for the percolation model and 1.0 for the

F-S model.

The results of the epoxy cured with di-amine yield the value 1.15 for the

exponent D which is close to what is predicted by F-S. This is a rather surprising

result because the monomer sizes of the epoxy as well as the di-amine are far

shorter than a long chain. Furthermore, the crosslink reaction is confined at the

chain ends of the monomers instead of randomly distributed along the chains. A

plausible explanation is that the primary amine reacts much faster than the

secondary one as observed by other investigators, hence, linear chains of

significant length are formed in the beginning of the cure. The later stage of cure

is the crosslink of these linear long chains via the reaction of the secondary

amines along the backbone chains. Such a two-stage reaction is expected to conform

to F-S theory. In order to test the hypothesis mentioned above, tri-amine was included in this study. In this case even though the primary amine reacts much

faster than the secondary one, a three dimensional network will still prevail over a linear chain. The SANS results on T-403 cured epoxy yield a value for the exponent

D of 1.67 which is almost identical to what is predicted by percolation. To further

test the percolation result, a high molecular weight specimen of tri-amine cured

epoxy with a narrow size distribution was prepared through a solution fraction

method. A typical fractal scattering behavior is observed in the SANS result and

the fractal dimension is about 2.1. This value is close to that predicted by the

percolation theory and is called "animal -like" behavior.

In summary, the results indicate that the crosslinking of thermoset in the bulk

state follows the percolation process. However, in certain cases some specific

chemical reaction mechanisms can modify the process towards what is predicted in F-S

theory.

113
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SANS STUDIES OF CROSSLINKED POLYMER BLENDS

B. J. Bauer, R. M. Briber, and C. C. Han

(Polymers Division)

P. G. de Gennes has developed a theory describing the scattering function of

crosslinked polymer blends. He makes an analogy with a dielectric medium. In a dielectric medium the separation of + and - charges is counteracted by an electrostatic force. In a polymer blend separation of the polymers causes chains to

stretch so it is counteracted by elastic forces. He assumes that the blend

components demonstrate "good miscibility" when crosslinked, and that crosslinks are present between the two different polymer types

.

Equation (1) is the scattering function for a blend of equal amounts of two

polymers with n units between crosslinks of step size b, Xn i- s tne spinodal value

of the interaction parameter of the uncrosslinked blend, and x is the interaction

parameter at the temperature of the scattering experiment. C is a coefficient of

-2 -2

internal rigidity which is roughly estimated as C = 36 n b

I"

1 = C/q 2 + (xQ

- X) + b

2 q2 /24 (1)

This predicts that a plot of intensity versus q should have a maximum that

varies as the inverse square root of n. There also should be no zero angle

scattering. As the spinodal is approached, the peak will increase in intensity, but

not change position. The single phase region will be greatly extended compared to

the uncrosslinked blend.

Blends of high molecular weight polystyrene -d8 (PSD) and polyvinylmethyl ether

(PVME) were made and were crosslinked by exposure to gamma irradiation at 45 C. Table 1 gives characterization of the samples studied. Scattering experiments were carried out from 120 C to 180 C.

Figure 1 shows corrected scattering intensity for blend crosslinked with 125

Mrad irradiation. As the temperature is increased a shoulder appears at 0.025 A

The form of the scattering differs from the de Gennes prediction by not going to zero at q = . The problem seems to lie in the assumption that upon crosslinking

2 the polymers have "good miscibility", indicating a flat baseline. Previous studies

have shown that low temperature scattering is weak, but has non zero low angle

scattering.

To account for this non-zero baseline, a scattering experiment was performed at

45 C, the crosslinking temperature. When this is subtracted from the data of figure

114
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

i

20

18

is

14

12

10

el8.

**

Crosslinked Blend D

180°C

170°C

x 160°C

+ 150°C

a 140°C

o 130°C

a 120°

C

00 0.02 0.04 0.06 q(A-1

)

0.08 0.10

Figure 1. I versus q for sample D, 125 Mrad.

10

8

8

7

e

5

4

31"

2

lh

8

ioM

Crosslinked Blend D

45 C Baseline Subtracted

« y^ %

'* xxx . X

x* x - ^r + + * *

AA *.w

180°C

170°C

x 160°C

+ 150°C

a 140°C

o 130°C

o 120°C

0.04 0.06 q(A" 1

)

Figure 2. I versus q for sample D, 125 Mrad minus I versus q for sample A, Mrad,

45 C.

115
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

0.10

0.09

0.08

0.07

0.06

i

g 0.05 J

0.04|-

0.03

0.02

0.01

"I10

a Crosslinked Blend

o Crosslinked Blend C

-1 1 L. 2.20 2.30 2.40 1/T (° K))

2.50 2.60

Figure 3. I versus T~ for samples C and D. max c

Table 1. Crosslinked polymer blends. Starting PVME Mw

PSD Mw = 6.2 x 10 . $

PSD

0.3.

1.7 x 10

mp

A

le Dose (Mrad)

E 5 B 25

C 50

D 125

M -PSD

c N -PSD

c M -PVME

c N -PVME

c

160,000 1450 380,000 6520

32,000 290 76,000 1300

16,000 145 38,000 652

6,500 58 15,000 261

116
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1, figure 2 results. This is qualitatively what is predicted, a prominent peak

increasing with increasing temperature, and intensity dropping to zero as q

-> 0. The peak position changes as the inverse square root of the irradiation time as is

expected, but the coefficient of internal rigidity appears smaller than predicted.

The spinodal temperature is reached when the peak goes to infinity. Figure 3

is a plot of inverse scattering intensity versus inverse temperature for the samples

with 50 and 125 Mrad exposure. There is only a weak dependence on temperature,

extrapolations give spinodal temperatures of 260 C and 423 C, while for the

uncrosslinked blend it is 150 C. Qualitatively, de Gennes' prediction of the scattering from a crosslinked

polymer blend is good when the non-zero baseline is accounted for. The scattering

has prominent peaks that vary in position with the crosslink density and go to zero

as q -* 0. Crosslinking greatly extends the one phase region of the blend.

1. P. G. de Gennes, J. Physique Lett., 40, L-69 (1979).

2. C. C. Han, M. Okada, Y. Muroga, B. J. Bauer, and Q. Tran-Cong, Poly. Eng. Sci.,

26, 3 (1986).

SANS STUDIES OF SINGLE PHASE INTERPENETRATING POLYMER NETWORKS

B. J. Bauer, R. M. Briber, and C. C. Han

(Polymers Division)

Interpenetrating Polymer Networks (IPN's) are systems in which one of the the

polymeric components is polymerized in the presence of the other, with one or both

being crosslinked to itself. In virtually every case phase separation takes place

during the polymerization, giving a two phase morphology. We have succeeded in

polymerizing samples of semi -IPN's where one component is linear (polyvinylmethyl

ether, PVME) and the other is crosslinked (polystyrene-d8 , PSD). IPN's were formed

without phase separation taking place giving single phase samples that can be

2 studied by SANS in a way similar to blends of uncrosslinked linear polymers.

i 3 Binder and Frisch have studied the thermodynamics of weakly crosslinked IPN's.

They add terms to the free energy of the blend due to the elastic contributions of

the network. The second derivative of the free energy with respect to composition

is given in equation (1)

.

3

2 AF/3$2 = (B - l/3)/(n

c* ) + l/n(l - $

Q

)

- 2 (1)

117
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

0.40

1 1 1 1 1

"T - 1 T i - -

0.36 dIPN-1 at 120° C

o IPN-2 at 70°C

-

0.32 aIPN-3 at 120°C > + IPN-4 at 120°C y/O

0.28 -

0.24 /a +/&

7 0.20 °/

0.16

O / •'"Or

'

0.12

0.08 -

0.04

OOO §L 1 L 1- . - .1 1 1 i i i .000 0.001 0.002 0.003 2 /A -2 \ q (a )

0.004 0.005

-1 2 Figure 1. I versus q for samples 1,3, and 4 at 120 C and sample 2 at 75 C

n is the degree of polymerization of the PVME , n is the number of units between

crosslinks in PSD, $> is the volume fraction PSD, and x i- s the interaction

parameter. B is from rubber elasticity theory and can vary from to 1 depending on the particular theory. The last two terms are identical to those of an uncrosslinked polymer blend. If B > 1/3 then the crosslinks should cause enhanced

single phase stability, and B < 1/3 should destabilize the single phase region.

Table 1 gives the parameters of the IPN's in this study. Figure 1 is a plot of

2 inverse scattering intensity versus q . Samples 1, 3, and 4 are linear as is true

for an uncrosslinked blend. Sample 2, however, has a large amount of excess low

angle scattering, indicating phase separation. In the process of polymerizing, the

most densely crosslinked sample phase separated while the lower crosslink density

ones did not.

Figure 2 is a plot of inverse zero angle scattering intensity versus inverse

temperature. In uncrosslinked blends this gives a linear relationship and

extrapolation to zero gives the spinodal. Samples 1 and 4 fit this well giving

spinodals of 151 C and 146 C. Sample 2 has a pronounced curvature, indicating a different exponent.

118
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

8.0

7.2

6.4

5.0

MO

4.0

«HX

^^ 4.0 o

GQ 3.2

2.4

1.0 h

0.8

-O.i

oIPN-1 0.0 % DVB

oIPN-4 0.1 % DVB

a IPN-3 0.3 % DVB

.30 2.40 2.60 2.00 1/T X 10

3

(° K)

2.70

-1 -1

Figure 2. S(0) versus T for samples 1, 3, and 4

2.80

16

13

12

10-

wO 9

X~ 7

o

^0

4

3

IfI

Stretched IPN-3

oL/Io = 1.0 oL/Lq m 2.5

30 2.36 2.40 2.46 1A X 10

3

(° K)

2.60 2.66

Figure 3. S(0) " versus T " for deformed sample 3 parallel and perpendicular to the

deformation direction.

119
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. IPN's of PSD/PVME. Linear PVME Mw = 633,000.

Sample M n

c c

IPN-1 0.57

IPN-2 0.49 17,000 150

IPN-3 0.56 56,000 500

IPN-4 0.45 190,000 1700

At temperatures close to 70 C, the polymerization temperature, the sample with

no crosslinking is furthest from the spinodal. As crosslink density increases, one

gets closer to the spinodal until at the highest crosslink density, phase separation

has occurred. As the temperature is increased, however, the lines cross over, with

sample 3 having a higher crosslink density being further from the spinodal.

Sample 3 was also studied in a deformed state. The sample was placed in a holder with a groove cut into it. When compressed, the sample deformed in one direction only, the dimension perpendicular to it remained constant. The sample was stretched a factor of 2.5 in one direction and 1.0 in the other. The scattering

pattern was asymmetric and averages were made of 15° sectors along the stretch and

perpendicular to it. Zero angle scattering intensities from lorentzian plots are shown in figure 3. The two plots extrapolate to zero at different temperatures,

indicating that the blend is destabilized along the direction of deformation.

Because of the narrow sector, the statistics are poor and the exact shape of the

curves cannot be determined. For the three highest temperatures, inverse intensity

2 versus q gave good fits perpendicular to the direction of deformation, but along

the direction of deformation, the plots gave negative intercepts.

In conclusion, at the temperature of synthesis, the presence of crosslinker

decreases the single phase stability, causing phase separation at the highest

concentration. As the temperature is increased, however, the crosslinks inhibit

phase separation. Upon deformation the sample is destabilized along the direction

of deformation, causing different spinodal temperatures along the two directions.

1. L. H. Sperling, "Interpenetrating Polymer Networks and Related Materials,"

Plenum Press, New York, 1981.

2. C. C. Han, M. Okada, Y. Muroga, B. J. Bauer, and Q. Tran-Cong, Poly. Eng . Sci.,

26, 3 (1986).

3. K. Binder and H. L. Frisch, J. Chem. Phys ., 81, 2126 (1984).

120
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SANS STUDIES OF INTERACTING HEMOGLOBIN MOLECULES IN INTACT ERYTHROCYTES

S . Krueger

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. Nossal

(National Institutes of Health, Bethesda, MD)

Small angle neutron scattering (SANS) was used to investigate interaction

forces between hemoglobin (Hb) molecules contained within human red cells. The

scattering separately attributable to cell membranes and intracellular Hb was identified, and a series of D-O-H-0 contrast variation measurements were made in

order to establish conditions for which scattering from the cell membrane is

minimized (ca. 15% D_0)

In figure 1, the scattering profile from a normal RBC sample is compared with

that from a preparation of RBC membrane fragments. These samples were washed and

suspended in 100 % D_0, conditions where incoherent scattering from hydrogen atoms

in the solvent should be minimized. The data indicate that membrane scattering is

negligible for Q > 0.06 A . Scattering cross sections obtained during contrast

variation measurements on RBC's are shown in figure 2.

The average intracellular concentration of Hb in RBCs is about 330 mg/ml , so interference scattering must be taken into account in the data analysis. To a first

approximation, the differential cross-section per unit volume for protein scattering

may be written as (1,2)

I(Q) = K N

p

(Ap)

2 V2 P(Q) S'(Q) (1)

where N is the number of protein molecules per unit volume in the solution, V is

P P

the volume occupied by a single protein molecule and Ap = \ p - p \ , the "contrast",

p s is the difference between the average scattering density of the protein and that of

the solvent. K is the fraction of the solution actually occupied by the protein

cores of the cells. P(Q) is the "particle structure factor" representing the

scattering from a single core particle averaged over all orientations and normalized

such that P(0) = 1, and S'(Q) is the "averaged interparticle structure factor" which

accounts for the interference scattering between particles

Since hemoglobin is a spherical molecule, P(Q) is easily calculated. S'(Q) can be computed by solving the Orns tein- Zernicke equation in a mean spherical

121
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

approximation (MSA) when the interparticle potential consists of a hard core and a Yukawa potential tail. An analytic solution for this case, which is based on the

DLVO theory of interacting colloidal particles, has been provided by Hayter and

Penfold (3) and their FORTRAN subroutine has been incorporated into a program which

fits the data to the theoretical I(Q) given by Eq . 1.

In order to calculate the protein and membrane match points, MSA fits were made

to the large Q (i.e. Q > 0.06 A" ) regions of the curves for RBCs in , 10, 20, 50,

70 and 100 % D_0. Because protein scattering cross sections are small compared with

membrane scattering in 50, 70 and 100 % D_0, the MSA fits were somewhat uncertain

for those conditions. However, the fitted MSA amplitudes, Amp, are relatively

insensitive to slight variations in the shape of the scattering cross sections. A

1/2 plot of (Amp) vs % D_0 (see figure 3) places the Hb match point at approximately

39 % D_0, in good agreement with results of earlier studies on Hb . Model

calculations of the entire scattering cross section for the protein, I (Q) , were

made for each solution condition by using the parameters of the best fit to the

corresponding "large Q" data. The calculated I (Q) then was subtracted from I(Q) in

each case, yielding the scattering cross -sections I (Q) for the membranes alone. m

40

30

P. 20

10

100% D2

cells membranes

.03 .06 .09

Q (A" 1 )

120

Figure 1. Comparison between scattering from intact RBCs and membranes, showing

that the scattering from the Hb within the cells can be distinguished.

122
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2.0 r

O 1.0

(0) — o

o

o

(10)

°

c D

to

(20) v

I

>-cr~ltHi*>TRfc^*i*tr-t^'-,-- ^v od

i i i i \^r^s~±£3t> i .03 .06 .09 120

Q (A" 1 )

o

4.0 r

3.0 -

2.0

1.0 -

. (100)

Q (A" 1 )

Figure 2. Contrast variation data, taken to establish optimal conditions for

observing Hb interactions. a), b) Scattering cross-sections for

differing D.O percentages (in parentheses), plotted on an absolute scale.

123
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

100

Figure 3. Amplitudes of separate scattering components (normalized to -1.0 at 100

% D_0 concentration) , illustrating the approximate membrane and protein

match points

.

0.4 r

0.3

P, 0.2 -

0.1

g 15% D2

o

( 15°) o °

„ — o tv - " m D V — " jPcPc}^

45 r^ ^fe. _

°

q

a tuP°a

„ (30PWT

rOs*

° \f\

tfC d ckS^'^ W_i

t^^^ *tte V~~^ *\

(600)

^^^^

* T&&. S& I I I I I I I I j^t;

.03 .06 .09 .120

o _ v Q (A" 1 )

.150

Figure 4. RBCs in 15 % DO buffer (pH 7.4) of differing osmolarity (mOsm, in

parentheses) . The lines represent calculated Hb scattering cross- sections based on the parameters of best fit to the data for Q > 0.06

A" .

124
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Red Blood Cells Under Varying Salt Conditions

15 % DO Buffer pH 7 .

4

High Salt .286 20 26.8

(600 mOsm)

Normal Salt .223 12 27.8

(300 mOsm)

Low Salt .166 4 28.4

(150 mOsm)

N = number of cells per unit volume remained constant as the salt conditions were

varied.

I m

(Q) is fit by using a flat sheet approximation (4) whereby the membrane is

represented by a flat sheet with constant thickness, t, and two other, much larger,

dimensions. The scattering intensity I (Q) can be separated into a factor

proportional to Q and a second "thickness factor" such that

Im

(Q) - ^

e'^t (2)

1/2 A plot of normalized values of (I

q

) ' vs % D

2 0, (see figure 3) shows that the

membrane "match point" lies between 14 % and 18 % DO.

All further experiments were performed with RBCs in 15 % DO where the

contribution of the membrane to the total scattering is minimized. For

illustration, figure 4 shows the scattering profiles for RBCs in normal buffer (300

mOsm) as well as in "low salt" buffer (150 mOsm) and "high salt" buffer (600 mOsm) . When the ionic strength of the solution is increased from that of the normal buffer,

the cells shrink. Conversely, a decrease in ionic strength causes the cells to

swell. In both cases, the concentration of Hb inside the cells changes, producing a corresponding change in the Hb volume fraction r\ . The volume fraction rj , as well as effective Hb radius R and surface charge Z, were determined from the data fitting

and are given in table 1.

In addition, oxygenation studies on normal cells were performed, and results

contrasted with those of similar studies of erythrocytes obtained from sickle cell

disease patients (5)

.

125
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. D. Bendedouch and S.-H. Chen., J. Phys . Chem. 87:1473-1477, (1983).

2. R. Nossal, C. J. Glinka, and S.-H. Chen, Biopolymers 25:1157-1175, (1986).

3. J. B. Hayter and J . Penfold, Mol. Physics 42:109-118, (1981).

4. G. Porod, In: Small Angle X-ray Scattering. Academic Press, New York, (1982)

pp. 18-50.

5. R. Nossal and S. Krueger, Biophys. J. 51, 295a (1987).

COLD NEUTRON PROJECT

J. R. D. Copley, C. J. Glinka, J. Gotaas , G. Greene, M. Kahn,

W. Knill, J. LaRock, C. Majkzrak, C. O'Connor, D. Pierce,

J.M. Rowe, I.G. Schroder, T. Udovic, and R. Williams

1 . Cold Neutron Research Facility

The final design for the construction of the Cold Neutron Research Facility,

figure 1, has been completed by the Architect/Engineering firm of Burns and Roe. A

design package of 150 drawings and 1000 pages of specifications has been produced

and will be included in the final solicitation for fixed price construction bids.

This solicitation will be issued at the end of July, and bids will be due in late

October, with a construction start scheduled for late in 1987. The estimated

construction period is 14 months.

The final design incorporates a neutron guide hall of 100 x 200' , and an associated office/laboratory addition of 12,000 square feet. The guide hall will be

equipped with a full span travelling crane of 20 ton capacity, with a crane hook

clearance of 25'. The walls and crane are supported on augured cast-in-place

concrete piles, and completely decoupled from the guide hall floor. The floor is

slab on grade, supported by 95 percent compacted fill to provide a 2000 lb/sq. ft.

floor loading capacity. Services are provided by means of floor trenches, and the

floor is effectively decoupled into independent sections by these trenches to

minimize vibration transmission. A recessed pit for future installation of a very

stable vibration isolation system is provided. Additional independent reinforced

concrete beams (7) supported by concrete pilings and decoupled from the rest of the

floor are provided for support of the neutron guide tubes and mounting fixtures.

The entire building is air-conditioned for temperature and humidity control. The

design provides large window areas for maximum natural light. The office and

laboratory area is an addition to the existing building which will provide an additional 35 offices, 12 laboratories, a conference room, a terminal room, space

for all mechanical equipment (HVAC, etc.), and additional storage space.

126
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2

.

Neutron Devices

Extensive effort has gone into the development of computer simulation codes to

evaluate the performance of devices such as elliptical mirrors, toroidal mirrors,

converging guide systems, logarithmic spirals and other neutron focussing systems.

The effects of various sources of non-optimum performance such as aberrations have

been studied, and configurations to minimize such problems have been developed and

studied. The use of computer ray tracing allows easy introduction of realistic

estimates of component performance, including surface irregularities, actual

reflectivity of mirrors, and misalignment. There are many areas of cold neutron

research in which these devices can provide important increases in neutron

intensity, and we are currently evaluating alternative configurations for such use.

3

.

Instrument Improvements

a. Small Angle Neutron Scattering (SANS)

In order to make efficient use of the cold source flux, several upgrades to the

current 8m SANS instrument have been implemented during the recent shutdown to

install the cold source. The instrument's former 16 -bit, 1/4 megabyte data

acquisition computer has been replaced with a 32 -bit, 6 megabyte machine using a CAMAC interface, paralleling the data acquisition architecture developed for the

time-of -flight spectrometer. This new system includes high speed, CAMAC-based

histogramming memory that allows rapid acquisition of data in separate memory areas that can be moved into the computer while a new area is being filled, thus enabling

real time experiments. The external histogramming memory also frees the computer's

cpu to carry out data analysis tasks, such as imaging and circularly averaging the

256 x 256 element data arrays associated with each data set, on-line while the data

collection is in progress. The data acquisition software for the new system is

based on a suite of programs developed, and proven reliable, for the time-of -flight

spectrometer.

Other upgrades include additional shielding added to the detector flight path,

2 the purchase of a second, 64 x64 cm area detector and the implementation of a computer programable circulating bath and resistance heater system to provide

improved variability and control of sample temperatures.

b. Time-of-Flight (TOF)

The neutron time-of -flight (TOF) spectrometer became operational during the

previous year. The first materials investigated included zeolites, ionic

conductors, intercalates, organic compounds, metal hydrides, and high- technology

alloys and magnetic materials. Modifications planned for the coming year include

(i) vertically curving (i.e., focussing) the second monochromator crystal to

127
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

" V^HSN^SSi^W^^'H-f't'

i H

Figure 1. Plan view of Cold Neutron Research Facility. Existing structures are indicated by shading.

substantially increase the neutron flux on the sample; (ii) altering the

chopper/sample area shielding design to decrease the sample -monochromator distance

thereby increase the neutron flux, the sample -chopper distance to increase the

resolution, and the neutron background reaching the detectors; (iii) installing an

128
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

oscillating radial collimator between the sample and detectors to eliminate

parasitic background scattering from the cryostat or furnace walls surrounding the

sample; (iv) ganging detectors in pairs to allow utilization of all detectors with

the present TOF interface unit during experiments; (v) altering the Be -filter

elevator to permanently accommodate the pyrolytic graphite filter as a secondary

filter option for incident energies above 5 meV; and (vi) improving the biological

shielding from BT-6 to decrease the fast neutron and gamma radiation background

levels in the vicinity of the TOF spectrometer.

4. Instrument Design

Several instrument designs are now underway, primarily at a conceptual stage.

Design criteria are being developed and estimates of performance based on realistic

assumptions are in progress.

a. High Resolution Time-of -Flight Spectrometer

This instrument is being designed to provide approximately 10-15 microvolt

energy resolution with an incident wavelength of 6 Angstroms using multiple phased

choppers and a sample-detector distance of 4 m. Such an instrument will offer a relatively wide range of wave vectors for quasielastic scattering studies at good

resolution. A secondary design goal is the capability for rapid and routine

decrease of energy resolution at fixed incident energy, with commensurate increase

of intensity to allow for more rapid exploratory studies at the beginning of

experiments. Our current estimates indicate that these criteria can be met with

satisfactory intensity in a technically achievable design. This instrument will

incorporate some of the neutron devices discussed above.

5 b. High Resolution Small Angle Neutron Scattering Spectrometer

Design of new 30m SANS instrument. Design work is underway for a new high

resolution SANS instrument to be built jointly by NBS and the Exxon Research and

Engineering Co. for the Cold Neutron Research Facility. With the space available in

the CNRF guide hall, an instrument approximately 30m long can be built to resolve

small angle scattering at Q-values as low as 0.0005 A with a beam current at the

4 sample of at least 10 n/sec. This represents an order of magnitude improvement in

Q- resolution over the present 8m SANS instrument. The new instrument would also

have a wider Q-range as a result of using two large area detectors, one which can be

remotely positioning within an evacuated flight path at distances from 2.5 to 15m

from the sample, with the second offset from the beam direction at a fixed distance

of 1.5m from the sample to extend the Q-range to nearly 1 A . In addition,

129
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

provisions are being made, through the specification of non-magnetic construction

materials and the incorporation of neutron guide fields within the incident beam

flight path, to have the option of using a polarized beam.

The principal monochromator for the instrument will be an improved type of

mechanical velocity selector recently developed at the Central Institute for Physics

in Hungary. This type of selector has been designed to provide not only continuous

tunability of the wavelength of the beam over a wide range, but also continuous

adjustment of the wavelength spread, A7/7, from about 0.05 to 0.25, FWHM. For

polarized beam measurements, the velocity selector will either be followed by a polarizing filter or replaced by a double monochromator of multilayer polaring

crystals

.

We are exploring the feasibility of using ellipically curved, grazing incidence

mirrors to collimate and focus the incident beam. Preliminary calculations indicate

that substantial gains in beam current at the sample, over what is possible with any

type of pinhole collimation, can be achieved if suitable mirrors can be fabricated.

We are currently exploring possible sources for such mirrors.

c. Depth Profiling Facility

The neutron depth profiling (NDP) instrument is being designed to take

advantage of the two or more orders -of -magnitude increase in signal intensity

expected over the existing facility. Drawing from five years of experience at the

BT-3 instrument and in collaboration with academic and industrial users of the

facility, the new instrument will be constructed at the short cold-neutron guide

(NG-0) contained within the reactor confinement building. New features to be

incorporated will include: automated sample handling, near real-time spectral

^processing, goniometer positioning of the sample and detectors, and temperature

control of sample. More sophisticated improvements being considered include; in

situ ion milling of the sample, medium resolution optical imaging, laser alignment

for off -angle positions, and ultimately, focused neutrons for added intensity and

spatial specificity. The use of multiple charged particle and/or time-of -flight

detectors will improve depth resolution. The increase in signal intensity will

permit multidimensional imaging of elemental distributions and routine profiling of

nuclides with absorption cross sections for charged particle emission of less than 1 barn.

d. Prompt Gamma Analysis Facility

The neutron capture prompt gamma instrument is expected to show an order of

magnitude better sensitivity than existing thermal-beam installations, primarily

130
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

because of the absence of fast neutrons and gamma rays from the beam. Particular

care is being given in the design to the elimination of background lines from H, B,

C, and N. The system will allow samples to be irradiated in vacuum or a controlled

atmosphere under remote control. The computer based counting system is being

designed for high resolution gamma ray spectroscopy at high counting rates. In

order to resolve cascade transitions in complex spectra, we intend that two or more high efficiency Comp ton- suppressed detectors will be operable as a gamma- gamma

coincidence spectrometer or as separate single-parameter detectors.

5 . Microstructure and Macromolecular Research with Cold Neutrons Workshop

On December 8-9, 1987, NBS will sponsor a workshop on MICROSTRUCTURE AND

MACROMOLECULAR RESEARCH WITH COLD NEUTRONS, one of a series of workshops which will

focus on the scientific opportunities arising from the cold neutron capabilities of

the CNRF. Invited technical talks will cover current areas of research on submicron

structures in materials, including macromolecular structures in polymers and

biomaterials , and discuss new frontiers which will benefit significantly from the

availability of cold neutrons. An important goal of the workshop is to introduce

the potential user community to the instruments and techniques planned for the

facility, and to provide an opportunity for early input which may guide the ultimate

development of the CNRF. For technical information, contact Charles J. Glinka

(Reactor Radiation Division, 301-975-6242), James A. Gotaas (RRD, 301-975-6243) or Charles C. Han (Polymer Division, 301-975-6771). For general information about the

workshop, please contact Mrs. Kathy Stang, A345 Physics Building, National Bureau of

Standards, Gaithersburg, MD 20899.

NBSR COLD NEUTRON SOURCE

R. S. Carter and P. A. Kopetka

The required modifications to the cold source cryostat that were indicated by

the tests described in the previous report have been completed and the cryostat has

successfully passed a complete series of tests including a one week run at low

temperature while hooked up to the refrigerator external to the reactor.

The insertion of the cold source including its outer shield of bismuth and lead was completed July 17, 1987. The various tubing and instrumentation connections

will be made during July, and initial tests are expected to start in August.

131
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

HYDROGEN IN METALS

R. C. Casella

I have carried out an analysis using a two-well potential for the a-phase

motion of hydrogen in yttrium (without pairing) , which analysis results in a prediction for the hydrogen/deuterium isotope shift that runs counter to

experiment. This result is interpreted as lending further credence to the pairing

interpretation of Anderson et al ., since it tends to require an explanation of the

neutron scattering data which lies outside the simple picture of an isolated

hydrogen atom moving in a potential determined solely by its interaction with the

metallic host atoms. This (indirect) inference is further limited by the

specificity of the potential employed and the approximate nature of the solutions

obtained. The assumed potential is of the form

-* 2 2 2 2 2 2 V(r) = A (x - aV + (mwf/2) (y + z

Z

) . (1)

[Eq. (1) is essentially equivalent to the quartic form employed earlier by N. Berk,

2 J. Rush, J. M. Rowe and collaborators for the motion of hydrogen in the /3-phase of

V^X, X = H,D,T.] I have obtained variational solutions for the motion along x (x | | c-axis) , employing linear combinations of trial wave functions centered at x = ± a, which are of the form of ground-state and first-excited-state oscillator functions,

but with the coefficient in the exponent of the gaussian treated as a variational

parameter in each case. Initially, analytic solutions were found via perturbative

2 2 1/2 expansion in a parameter e = (e n/w), where e~ = (1/ma ) and u> = (8Aa /m) . w is

the local oscillator energy for motion along x about (x = ± a, y = 0, z = 0) . (h =

1.) For hydrogen in yttrium, setting a = 0.65 angstrom, one finds e_ = 9.8 meV.

1 From the inelastic neutron data, A=E1 (||) -E_(||)= 100.1 meV. If one ignores

the small splitting of each level and assumes u> - A, then e — (1/10). Within this

small-overlap hypothesis (SOH) , I find

A = w + 3e

Q/8 = w(l + 3e/8). (2)

Thus, the parameter A in the potential is determined by the hydrogen data. Holding

A fixed, one can then predict the corresponding excitation A(D) for inelastic

neutron scattering from deuterium in yttrium. I find A(D) = 70.0 meV, to be

compared with the experimental result, A(D) =75.8 meV. That is, under SOH the

132
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

anharmonic correction leads to a predicted ratio A(H)/A(D) = 1.430, which is larger

than the harmonic ratio 1.414, whereas the experimental ratio, 1.321, is smaller.

A somewhat more general analysis, in which the SOH was not made, but still

employing variational trial functions of the same analytic form as before, was also

carried out using numerical techniques. Of the many solutions obtained of this

class, when compared with experiment, the physically allowed solutions reduced to

essentially those obtained under SOH, evidencing small splittings about the SOH

values

.

Short of obtaining agreement with the experimental ratio for a single fixed

value of A, any conclusion will be limited by the analytic form of the assumed

potential. It is perhaps worth recalling that the theoretical predictions I derived

3 some time ago for the ratio of various cross sections for neutron scattering apply

to the general two -well problem, although they remain somewhat difficult to

implement experimentally.

1. I. S. Anderson, J. J. Rush, T. Udovic , and J. M. Rowe , Phys . Rev. Letters, 57 , 2822 (1986).

2. N. F. Berk, A. Magerl , J. J. Rush, J. M. Rowe, and J. L. Provo (unpublished).

3. R. C. Casella, Phys. Rev. B 24, 2913 (1981).

COHERENT NEUTRINO SCATTERING FROM CRYSTALS

R. C. Casella

I have previously demonstrated that for reactor antineutr inos of wavelengths

less than or of order crystal lattice constants (E > 10 keV) , the net force exerted

by the antineutrino "wind" on a crystal is linear in the number N of nuclei in the

target crystal, rather than quadratic in N as postulated in reference 2 in order to

explain an observed force ~ 10 dyne on a crystal in the neighborhood of a reactor,

2 as reported therein. I have subsequently investigated the force exerted by

ultralow-energy ant ineutr inos with wavelengths large compared with the crystal

dimension, say, > 1 cm (i.e., E < 10 MeV) . Based upon standard nuclear physics,

-2 -1 -1 one expects the current density J [cm s Mev ] of such antineutrinos emanating

3 from a fission reactor to be negligible because of phase-space considerations.

2 1 Nonetheless, since N enhancements can occur at such ultralow energies, I have

estimated an upper bound on the force exerted by the reactor antineutrino wind on

133
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

such a crystal by ignoring the phase-space fall-off at ultralow E, approximating the

3 Avignone -Greenwood spectrum by a simple exponentially falling one of the form, J =

J exp(- E/En

) , with E « 1-2 MeV and normalizing the integrated spectrum dE J(E)

to that expected several meters from the core of a 20 megawatt reactor of the NBS

type. If one assumes zero-mass neutrinos, then the low energy cross section, as calculated within the standard Glashow-Weinberg- Salam electroweak theory, is

2 proportional to E . Moreover, in computing the momentum transfer, an additional

factor of E enters. Therefore, extrapolating from the MeV region where typically

the cross section for coherent scattering from the nucleons in each nucleus leads to

-42 2 2 nuclear cross sections -10 cm , I find that, even with an N enhancement, the net

force is entirely negligible. I have also considered the effect of possible massive

neutrinos, assuming an electron- type neutrino mass of order 10 eV, the upper bound

determined from tritium end-point laboratory experiments and as estimated from the

timing of the neutrino burst from Supernova 1987A (as observed in the Kamiokande and

1MB underground detectors). Again, although considerably larger, the estimated

4 force is entirely negligible. Aharonov et al . have subsequently provided

additional arguments supporting my original conclusions.

1. R. C. Casella, Nuovo Cimento 94A , 42 (1986); R. C. Casella, in Intersections

Between Particle and Nuclear Physics -- 1986 , ed. D. F. Geesman, AIP Conf. Proc

.

No. 150, p. 1040, American Institute of Physics, New York (1986).

2. J. Weber, Phys . Rev. C 31, 1468 (1985).

3. F. T. Avignone III and Z. D. Greenwood, Phys. Rev. C 22, 594 (1980) and F. T.

Avignone III, private communication.

4. Y. Aharonov, F. T. Avignone III, A. Casher, and S. Nussinov, Phys. Rev. Letters

58, 1173 (1987).

134
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON-ANTINEUTRON OSCILLATIONS AND THE POSSIBILITY

OF "SQUEEZED STATES" IN NEUTRON INTERFEROMETRY

R. C. Casella

Recently, Yurke has concluded that by employing the output of one interferometer as the input to a second interferometer, the analogue of a "squeezed

photon" state can be achieved for the neutrons, despite their fermionic nature,

leading to a coherent state for which 6(f) ~ 1/N rather than 1/./N , 8$ is the

precision with which the interferometric phase shift <f> can, in principle, be

measured. If the construction of squeezed neutron states is indeed possible, then

despite formidable practical problems associated with "regeneration" upon

interaction of the mixed state |a n + b n > with the interferometer "mirrors", the

possibility of employing neutron interferometry to detect neutron- ant ineutron (nn)

2 oscillations, which I have discussed earlier, is reopened, at least in principle.

Motivated by conversations with S. A. Werner, I have begun an investigation of the

possibility of constructing such squeezed neutron (or other fermionic)

states as well as the general concept of squeezed states.

1. B. Yurke, Phys . Rev. Letters 56, 1515 (1986).

2. R. C. Casella, Phys. Rev. Letters 53, 1033 (1984).

PATTERSON FOURIER ANALYSIS OF THE ICOSAHEDRAL (Al.Si)-Mn ALLOY

J. W. Cahn

(Institute for Material Science)

and

D. Gratias

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

and

B. Mozer

X-ray and neutron diffraction data obtained from single phase icosahedral

powder Al

7 ~Mn91 Si, are analyzed using a generalized Patterson auto correlation

function in 3 dimensions. The icosahedral pattern is quasiperiodic . The local

atomic arrangements match those encountered in the prototypic crystalline a phase.

Extra peaks in the local icosahedral pattern match those of an icosahedrally rotated

a

.

135
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SIX- DIMENSIONAL FOURIER ANALYSIS OF ICOSAHEDRAL Al^Mn^Sig ALLOY

D. Gratias

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

and

J. W. Cahn

(Institute for Materials Science)

and

B. Mozer

Fourier analysis of X-ray and neutron diffraction data of an icosahedral alloy are displayed both as a 3D quasiperiodic function and as a 6-D periodic function.

The 6-D analysis leads to a simpler description that contains the same information

as the 3D analysis: The 6-D function has only two elongated peaks in the unit cell,

but each peak contains much chemical detail.

TRIPLE-SHELL SYMMETRY IN ALPHA (Al,Si)-Mn

H.A. Fowler and J. Sims

(Center for Applied Mathematics)

and

B. Mozer

We describe 3-D graphics modeling experiments executed on a calligraphic

system. Utilizing precise data from neutron diffraction, a triple icosahedral shell

has been identified in the alpha (Al,Si)-Mn phase. These triple shells are centered

in the unit cell; the Pm3 structure is completed by double shells on the cube corners. The triple shell can also be viewed as a composite of twelve coordination

icosahedra around the manganese sites on the second (Mackay) shell.

136
B. Non-RRD Programs

NEUTRON ACTIVATION ANALYSIS OF MICROSCOPIC SAMPLES

R. M. Lindstrom

(Center for Analytical Chemistry)

and

D. J. Lindstrom

(Lockheed EMSCO, Johnson Space Center, Houston, Texas)

An experiment was undertaken to determine the feasibility of neutron activation

analysis of very small samples. Johnson Space Center (JSC) is interested in the

compositional analysis of individual grains of cosmic dust, with dimensions of 10

micrometers and below, collected in high altitude aircraft flights. The test

consisted of a sustained irradiation at high neutron flux in the NBS Reactor,

followed by radioassay using a low-background NBS gamma-ray detector (EG&G Ortec,

model GEM-40195) installed in the underground Radiation Counting Laboratory at JSC.

Neutron activation analysis of such small samples has been reported only once before, in a short article with little experimental detail (reference below).

Samples were individually packaged in quartz tubes. NBS samples were 8 6g of

SRM 1633 Fly Ash (melted to glass on a Pt foil), 15 6g of K-411 Mineral Glass (SRM

470), and 11 6g of K-412. JCL samples were Murchison chondrite and Washington

University standard glass. The package was irradiated in the G2 tube at a nominal

flux of 3 . 0E14 n/cmos for 102 hours. The calculated fluence is thus 1 . 1E20 n/crao

.

A sevenfold increase in sensitivity is possible in future measurements by

irradiating for a full fuel cycle. After cooling for four days in the water-filled

thimble, the activity was low enough to ship to JSC without special precautions.

The low- level Ty detector was set up in a 4" lead shield in the RCL, 60 feet

beneath ground level. The counting room is constructed of welded, selected steel

plate surrounded by 3 feet of dunite gravel, a mineral low in K, U, and Th . A

cryogenic system that can remove radon from the air supplied to the counting room

was not in operation for these preliminary measurements because of high operating

expense

.

Quartz can be handled without hazard after a week's irradiation, and its

transparency is unimpaired by radiation damage. All quartz was somewhat active.

NBS quartz contains Sb , and Suprasil cut at JSC with a file contained activities

from Cr, Fe , Sc , Co, and Ba. Samples needed to be transferred before counting. The

quartz tubes were readily opened by scoring and snapping. Subsamples of as little

as 10 ng (determined by the activity ratio from weighable larger pieces) were

137
NON-RRD PROGRAMS

readily picked from a crushed larger sample using only a sharp pick and a stereo

microscope

.

The gamma background in the underground shield contains no more than the

following components

1. Pb x-rays, since the shield is not lined with low-Z material.

2. Continuum, peaking around 200 keV with centroid about 350, which is

presumably due to the interaction of high energy cosmic rays with the lead

shield around the detector.

3. The 511-keV positron annihilation line, from cosmic-ray activation

products

.

4. Decay products (Pb-214, Bi-214) of 3 . 8 - day Rn-222 . This component was reduced by a factor of five by flushing the shield continuously with

nitrogen boiling off from the Dewar.

5. A small amount (0.0003 ct/sec) of K-40, not detectable with certainty in an overnight count. The ratio of the counting rate inside the shield to that

outside suggests that most of this comes through the the hole in the shield

through which the detector is inserted.

None of these components of the background signal is clearly assignable to the

detector or Dewar.

The integral background from 100 to 1100 keV for several detectors in several

shields is as follows:

-Det Rel eff Location Background Figures of merit

name E (%) B (ct/s) E/B E**2/B

Ty 44.7 JSC RCL Pb 0.43

Ty 44.7 RCL room 1.29

Fran 47.4 NBS B119 1.79

Ty 44.7 NBS B119 3.77

Abby 34.8 NBS B119 1.70

Sarah 26.3 NBS B119 1.30

AMD 18.4 Compt sup 1.45

AMD 18.4 Unsupp 1.52

104 4600

35 1550

26 1271

12 530

21 710

20 530

13 230

12 220

138
NON-RRD PROGRAMS

Clearly, the combination of the large, low-background Ty detector in the clean

lead shield installed in the underground counting room at the RCL is greatly

superior to any other combination.

In agreement with calculations, usable, signals for several elements were recorded with sample sizes down to 10 ng. In the gamma-ray spectra of the Murchison

samples, the major peaks observed are from Fe , Cr, Co, and Sc. Masses of these

elements can be determined with impressive sensitivies. For example, amounts of Sc

and Co of about 10

A -12 grams can be analyzed with an accuracy of better than 5%.

With optimized experimental design and long counting times, several additional

elements should be analyzable with reasonable precision by INAA in particles of

chondritic composition. These include Ir, Zn, Ni , and Se.

Primarily because of shipping delays, we were unable to count the samples until

12-20 days after irradiation. Several elements (Na, Br, La, Sm) could probably have

been easily detected if we had been able to count the samples earlier.

Many other elements might be detected if present in higher abundance than in

chondritic materials. These include K, Ca, Hf, Zr, As, Sb , Rb , Cs , Sr, Ba, Ta , U,

Th, Ag, Au, and the additional rare earths Ce , Nd, Eu, Tb , Yb , and Lu.

A RADIOCHEMICAL PROCEDURE FOR ULTRATRACE DETERMINATION OF CHROMIUM

IN BIOLOGICAL MATERIALS

R. R. Greenberg and R. Zeisler

Chromium was recognized as one of the elements essential for optimum human

nutrition more than twenty five years ago. However, at elevated levels, some forms

2 3 of Cr are toxic and possible even carcenogenic . Unfortunately, the accurate

determination of Cr in biological materials continues to be one of the more

difficult problems in analytical chemistry. In particular, the determination of

this element at naturally occurring ultratrace levels in biological fluids such as blood, blood serum, and milk or milk powder frequently leads to erroneous results.

4

The results of an interlaboratory comparison of trace element concentrations in

milk powder, conducted by the International Atomic Energy Agency (IAEA), included Cr

concentrations reported by 13 different laboratories. These results ranged over

five orders of magnitude, and only one laboratory reported Cr concentrations which

were within 50 % of the current, best estimate of the actual Cr concentration.

Neutron activation analysis (NAA) is one of the best analytical techniques

currently available for trace and ultra-trace level determination of Cr in

139
NON-RRD PROGRAMS

Table 1. Preliminary Chromium Concentrations Determined in Human Whole-Blood

Samples

Individual Cr Conce

BG 0.157 ± 0.023

BK 0.267 ± 0.019

M 0.142 ± 0.019

T 0.338 ± 0.018

D 0.148 ± 0.016

W 0.117 ± 0.025

0.158 ± 0.016

2

Fresh weight basis. Uncertainties are 1 sigma counting statistics

2 Complete analysis of a duplicate sample.

Table 2. Chromium Concentrations (ng/g) Determined in NBS Standard Reference

Materials

Material This Work Certified

Bovine Liver 80 ± 2 88 ± 12

(SRM 1577)

Milk Powder 2.65 ±0.17 2.6±0.7

(SRM 1549)

Uncertainties are 2s//n

140
NON-RRD PROGRAMS

biological materials. It possesses the sensitivity required to determine sub-ng

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, is significant and must be considered when Fe is present in the

sample. The interference may be considerable depending on the fast flux of the

irradiation facility, and upon the relative amounts of Cr and Fe in the material.

The interference from the fast neutron reaction can be minimized, however, by using

a highly thermalized facility such as the RT-4 facility of the NBS Research

Reactor. Even in matrices with Fe concentrations more than 100,000 times greater

than that of Cr, such as whole blood, the interference in RT-4 is smaller than the

directly produced Cr-51 activity, and can be accurately subtracted.

To achieve the ultimate sensitivity of NAA, often the most effective approach

is to perform a radiochemical separation to isolate the element(s) of interest from

other elements which can interfere directly via gamma-ray overlap, or indirectly by

elevating the background level of radiation under the peak of interest via Compton

events and/or bremss trahlung . Chromium is particularly susceptible to the latter

type of interference in view of the relatively low energy of its 320 keV gamma -ray.

A variety of s ingle- element , radiochemical procedures have been developed previously

(8-10) to separate Cr from an irradiated biological matrix. These have

predominantly been based upon the distillation of chromyl chloride, or upon the

liquid/liquid extraction of Cr(VI) into a solution of tribenzylamine (TBA) in

Q chloroform. Separations based upon the former can suffer from low yields unless a

9 relatively complex distillation apparatus is used. However, use of such a piece of

apparatus is at least inconvenient, and also provides the potential for cross- contamination of samples, in view of the relatively long half-life of Cr-51.

Liquid/liquid extractions of the Cr(VI)/TBA complex are more convenient and use a

Q much simpler apparatus, however, low yields, and/or other problems have resulted in

- .8,10 the determination or incorrect Cr concentrations m some matrices

.

In view of the relative ease of liquid/liquid extraction procedures,

investigations have focused on identifying and eliminating earlier problems, and

developing a reliable, radiochemical separation procedure, based on extraction with

TBA, to determine Cr in biological materials at the ppb and sub-ppb levels. Such a procedure has been developed and includes a two-stage dissolution procedure to

minimize the possibility of losses of volatile Cr compounds, the addition of

141
NON-RRD PROGRAMS

potassium permanganate to oxidize and maintain Cr in the +6 state, two extractions

with 5 % TBA in chloroform to quantitatively extract Cr(VI) , and a back- extraction

into an aqueous solution of sodium hydroxide to provide a stable environment for

Cr(VI). The Cr can also be precipitated as barium chromate to improve the counting

geometry for samples containing very low levels of Cr i.e., <1 ng.

This procedure has been used to determine the Cr concentrations in whole-blood

samples collected, under clean conditions, from six individuals. The results

obtained are listed in table 1. Duplicate samples have been run for one person and

both values are listed. The apparent Cr produced by the interference from Fe has

been determined and subtracted. The uncertainties listed in table 1 represent 1 sigma counting statistics and are typically about 10 % of the Cr concentration.

These relatively high uncertainties are not truly representative of the quality of

the separation since these samples were processed after decay periods to 2-3 halflives of Cr-51. This was to allow instrumental measurements using an anti-compton

system to be made. In addition, relatively mild irradiation conditions were used:

2 16 hours at a fluence rate of 2.7 E 13 n/cm -s. Since the background radiation

under the Cr peak was due to natural sources outside of the sample, and therefore

constant, increasing the irradiation time by a factor of two, and reducing the decay

time to one half life of Cr-51, should reduce the uncertainty due to counting

statistics to a few percent.

Four samples of the Milk Powder, and three samples of the original NBS Bovine

Liver (SRM 157 7) were analyzed as an additional check of the analytical procedures

developed in this work. The results obtained are compared with the certified values

in table 2. The values found in this work are within the concentration range

certified by NBS.

1. W. Mertz, Physiol. Rev. 49 (1969) 163-167.

2. U. S. EPA, Quality Criteria for Water, Washington D. C. (1976).

3. J. C. Arcos, Amer. Laboratory 10 (1978) 29-41.

4. R. Dybczynski, A. Veglia, and 0. Suschny, "Report on the Intercomparison Run A- 11 of Inorganic Constituents of Milk Powder," IAEA Report - IAEA/RL/68 (1980).

5. A. R. Byrne, C. Camara-Rica, R. Cornells, J. J. M. de Goeij , G. V. Iyengar, G. Kirkbright, G. Knapp , R. Parr, and M. Stoeppler, "Results of a Co-ordinated

Research Programme to Improve the Certification of IAEA Milk Powder A-ll and

Animal Muscle H-4 for Eleven "Difficult" Elements," Proc . 2nd Int'l. Workshop

on Biological Reference Materials, Neuherberg, FRG , April 24-25, 1986 - in

press

.

142
NON-RRD PROGRAMS

6. R. Cornells, J. Hoste, and J. Versieck, Talanta 29 (1982) 1029-34.

7. D. A. Becker, J. Radioanal . Nucl. Chem 112 (1987) -in press.

8. R. Stella, N. Genova, M. Di Casa, M. Gallorini, and E. Orvini , J. Radioanal.

Chem 34 (1976) 59-63.

9. P. Lievens, R. Cornells, and J. Hoste, Anal. Chim. Acta, 80 (1975) 97-108.

10. L. T. McClendon, Proc . Trace Substances in Environ. Health-VIII, Columbia, MO

(1974) 255-257.

DETERMINATION OF TRACE ELEMENTS IN INTERNATIONAL DIETS

Venkatesh Iyengar

(Center for Analytical Chemistry)

An international project sponsored by the IAEA, and supported by the NBS , the

FDA and the USDA is currently in progress (1). This project is designed to assess

the daily dietary intake of minor and trace elements by selected target populations

in several countries. The countries involved are Australia, Brazil, Canada, China,

Iran, Italy, Spain, Sudan, Sweden, Thailand, Turkey and the U.S.A.

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 centers to determine a selected group of

inorganic elements

.

The U.S. efforts involves both as a collection center and as a reference

laboratory. The first part of the project was used to establish the analytical

approaches (2,3). An ion-exchange separation method to assay Cd, Co, Cr, Cu, Mn and

Mo in foods at low concentration levels has been established at the NBS Reactor

Facility. Guidelines have been developed for the preparation of mixed diet reference

standards for quality control. The collection of US benchmark samples of mixed diets

based on the FDA Total Diet Study scheme is in progress. Until now four such

collections have been completed. One portion of mixed diet from each of the four

collections has been stored in the National Environmental Specimen Bank.

Three of the four U.S. diets have already been analyzed for minor and trace

elements, proximate constituents, phytate and fiber. The results obtained for total

mixed diets for several elements show remarkable agreement with the daily intake

data calculated from the individual food analysis results of FDA-TDS study (4) , thus

confirming the validity of this approach for monitoring the dietary intake of minor

143
NON-RRD PROGRAMS

and trace elements. Recently, a set of 20 samples belonging to Italy, Spain and

Turkey has been analyzed. Sample preparation work for another batch of 24 samples is

currently in progress. As an example, concentrations of Cd and Mo in the diets from

different countries are shown in Table 1. The NBS Bovine Liver (SRM 1577a) was used

for quality control during the analysis, and these results are also shown in the

Table.

Besides determination of inorganic constitents of foods, Investigations are in

progress to study long-term stability of organic nutrients in mixed diets by

periodic monitoring of the diet material preserved under liquid nitrogen

temperature. Work is also in progress to prepare a mixed diet SRM.

Table 1. Concentrations of Cd and Mo in international diets.

(Results are ug/kg of dry diets, Mean + 1 S.D.)

Country n Cd Mo

Italy 5 39.3 ± 14.3 159.2 ± 51.0

Spain 7 24.9 ± 15.8 199.1 ± 124.2

Turkey 6 18.7 ± 10.9 562.7 ± 279.7

U.S.A. 3 28.9 ± 3.9 272.0 ± 25.5

Reference Material ( //g/g, Mean + 2 S.D.)

SRM 1577a 4 0.41 + 0.04 3.70 + 0.56

(Certified value 0.44+0.06 3.50+0.50)

1. Co-ordinated Research Programme on Human Daily Dietary Intakes of Nutritionally

Important Elements as measured by Nuclear and Other Techniques, International

Atomic Energy Agency, Vienna, Austria. Report of the First Research Coordination Meeting, Gaithersburg, Beltsville and Washington, D.C., March 19-22,

1985.

2. G.V. Iyengar, J.T. Tanner, W.R. Wolf and R. Zeisler Preparation of a mixed human

diet material for the determination of nutrient elements, selected toxic

elements and organic nutrients, A preliminary report, Sci. Total Environ.

61(1987)235-252.

3. G. V. Iyengar, Dietary intake studies of nutrients and selected toxic elements

in human studies: Analytical Approaches. Clin. Nutr . 6(1987)105-117.

4. J. Pennington, B.E. Young, D.B. Wilson, R.D. Johnson and J.E. Vanderveen Mineral

content of foods and total diets. The selected minerals in foods survey, 1982-

84. J. Am. Diet. Assoc. 86(1986)876-889.

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STATUS OF SPECIMEN BANKING ACTIVITIES AT THE NATIONAL BUREAU OF STANDARDS

S. A. Wise, B. J. Koster, R. R. Greenberg, S. F. Stone and R. Zeisler

(Center for Analytical Chemistry)

I . Introduction

Since 1975 the National Bureau of Standards (NBS) and the U.S. Environmental

Protection Agency (EPA) have been involved in the development of methods and

procedures for environmental specimen banking. In 1975 the Federal Republic of

Germany (FRG) and the U.S. EPA agreed to cooperate in the study of environmental

specimen banking activities and proposed the establishment of "pilot phase" specimen

banks in both countries. The purpose of the EPA/NBS Environmental Specimen Bank

Program was to determine the feasibility of long-term storage of environmental and

biological specimens for the determination of inorganic and organic constituents.

In 1980 a "pilot" environmental specimen bank was established at NBS to evaluate the

feasibility of a large-scale National Environmental Specimen Bank. The pilot

Environmental Specimen Bank program was to provide working experience in all aspects

of specimen banking, e.g., in specimen collection, processing, storage, and

analysis

.

The approach of the EPA/NBS pilot Environmental Specimen Bank was to gain

experience in the collection, storage, and analysis of four types of environmental

accumulators: (1) human tissue, (2) marine tissue, (3) food, and (4) air. The

goals of the pilot phase were:

1. To develop procedures for the sampling, processing, storage, and analysis

of four types of environmental accumulators;

2. To evaluate and improve analytical methods for the determination of trace

element and organic pollutants in biological matrices;

3. To evaluate the feasibility of long-term storage of environmental samples

under various conditions;

4. To establish baseline data on selected environmental samples, and;

5. To evaluate the potential application of specimen banking for trend

monitoring and for providing samples for retrospective analyses as concerns about new pollutants arise and as new analytical techniques are developed.

Since 1980 the EPA-NBS Pilot Environmental Specimen Bank has been involved in

the collection, storage, and analysis of the first sample type, human liver tissue.

However, the remaining three sample types (i.e, marine, food, and air accumulators)

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were not incorporated fully into the EPA pilot banking program as originally

designed because of funding limitations. During the past year the specimen banking

concept at NBS has been modified to reflect current funding levels from EPA and the

interest of other agencies in specimen banking activities. The pilot phase is near completion and has been described briefly above and in other publications [1-3] . Several agencies will be sharing the NBS/EPA Specimen Bank facility and will be

adapting the procedures developed in the pilot phase. New research has been

initiated to study the banking of other specimen types. The current components of

these efforts are described in the following sections

.

II. Biomonitoring Specimen Bank Research Project

As the "pilot phase" (1980-1986) nears completion, the program will move

towards a "project phase" of the Biomonitoring Specimen Bank Research Project. This

title reflects the change from solely environmental aspects to the inclusion of

specimens of nutritional and medical importance. At present there are five existing

specimen banking activities within the NBS specimen banking program, and several

other projects are proposed for incorporation into the program in the coming years

(see Table I)

.

EPA Specimen Bank Program

The EPA-NBS Specimen Bank Program will continue to serve as the focal point for

specimen banking- related activities during the project phase. The pilot phase of

the EPA specimen banking activities resulted in a number of outputs including the

following:

1. Development of protocols for the sampling, processing, and storage of

environmental/biological specimens (e.g., human liver and marine bivalves);

development of cryogenic homogenizat ion procedures for biological

specimens

2. Improved analytical methods for the determination of inorganic and organic

constituents in environmental/biological samples;

3. Analytical baseline data for inorganic constituents on 96 liver specimens

from three collection periods (1980, 1982, and 1984); analytical data for

organic constituents (PCBs and pesticides) on 60 liver specimens from two

collection periods (1982 and 1984);

4. An archive of over 500 human liver specimens and a large collection of

mussels which are available for future investigations.

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The expertise developed during the EPA pilot project has been implemented in

other specimen bank projects at NBS as well as by researchers in other programs.

For example, sampling and homogenization procedures for human liver and mussels

developed in the pilot project were used as the starting point for the development

of the protocols used in the National Status and Trends Program sponsored by the

National Oceanic and Atmospheric Administration (NOAA) (see discussion below) . The

existing analytical data base on inorganic and organic constituents in human livers

collected from 1980 to the present and the over 400 unanalyzed specimens in the bank

represent a substantial resource and a unique opportunity for EPA to investigate

pollution trends. During the next year the activities of the EPA-NBS project will be

directed towards the evaluation of the analytical data base for possible trends and

the evaluation of the compositional stability of the human liver specimens stored

under different conditions.

NOAA National Status and Trends Program

In 1985 a specimen banking project was initiated at NBS with the National

Oceanic and Atmospheric Administration (NOAA) as part of their National Status and

Trends (NS&T) Program to monitor the U.S. marine environment [4]. The NS&T program

consists of two monitoring programs: (1) the Benthic Surveillance Project, in which

sediment and fish tissue (muscle and liver) are collected annually from

approximately 50 coastal sites and (2) the Mussel Watch Project, in which bivalves

(mussels and oysters) and sediment are collected annually from approximately 150

coastal sites. As part of the NOAA NS&T program, NBS provides the following

specimen banking activities:

1. Develop sampling, homogenization, and storage protocols for sediment,

bivalve, fish muscle, and fish liver samples;

2. Archive specimens of sediment and tissue from 12 sites of the Benthic

Surveillance Project and mussels/oysters and sediment from 30 sites in the

Mussel Watch Project each year; a complete set of samples from all sites

will be archived after five years.

3. Analyze selected samples of sediment, bivalves, and fish livers for the

determination of selected trace elements (15 elements) and organic

compounds (organochlorine pesticides, PCBs , and PAH);

4. Analyze sediment and tissue intercalibration materials as quality assurance exercises

.

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In addition to the specimen banking activities for the NOAA NS&T program, NBS

is involved in the NOAA NS&T program as the laboratory responsible for organic

analysis quality assurance activities. These activities include the preparation and

distribution of control and/or intercalibration materials and calibration solutions

to the various laboratories involved in making analytical measurements for the NS&T

program and organizing annual quality assurance workshops to discuss the quality of

the analytical data generated within the program. NOAA is also supporting NBS in

the preparation of a marine sediment to be issued as a Standard Reference Material

for the determination of organic pollutants. Both of these activities complement

and support the efforts related to specimen banking of marine specimens.

IAEA/FDA/USDA/NBS Nutrients in Human Diet Program

NBS, the Food and Drug Administration (FDA), and the Department of Agriculture

(USDA) are collaborating in a coordinated research program sponsored by the

International Atomic Energy Agency (IAEA) to obtain comparative data on the dietary

intakes of 23 nutritionally important minor and trace elements in a number of

developing and developed countries [5] . In the U. S. effort, which combines the

expertise of the three participating government agencies, four aspects are

addressed: (1) benchmark total diet samples from the FDA Total Diet Study (TDS) are prepared and analyzed to provide data for the IAEA project; (2) representative

portions of these benchmark samples are stored in the NBS specimen bank facility;

(3) analytical research is carried out to develop analytical techniques for the

determination of a number of constituents in total diet samples and to develop a total diet reference material; (4) the immediate and long-term stability of such

total diet samples with respect to organic and inorganic nutrients during handling

and storage are investigated.

Several tasks related to the total diet study are included in the expansion of

specimen banking activities to this field:

1. Bank aliquots of mixed total diet samples based on the FDA market basket

collections

2. Methods development, analyses, and quality assurance;

3. Intercomparison of analytical methods for trace elements in existing

dietary reference materials;

4. Preparation of U.S. mixed diet research material from the 200 different

food groups in the FDA Total Diet Study (10 kg); and

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5. Determination of long-term stability of trace constituents in

the total diet composite.

Future collections of this total diet sample will include the variations in

season as well as the four major areas of FDA's TDS . Within several years, a complete inventory of the FDA market basket survey will exist in the proposed

Biomonitoring Specimen Bank.

National Cancer Institute (NCI) Chemoprevention Program

As part of a quality assurance program of the National Cancer Institute

Chemoprevention Program, NBS is serving as the reference laboratory for the NCI

contract laboratories involved in the determination of nutrients in human serum. The

following analytes are currently included in the study: zinc, selenium, betacarotene, retinol, alpha- tocopherol , and ascorbic acid. As part of this program NBS

prepares and distributes intercalibration samples to the various laboratories.

Since the long-term stability of these nutrients in serum (frozen and lyophilized)

is unknown, selected intercalibration serum samples and calibration solutions have

been archived under various storage conditions. These samples are periodically

removed from the bank and analyzed to determine the stability of these nutrients in

the specimens. These stability investigations will provide additional information on the behavior of various matrices with respect to long-term specimen banking.

NOAA Alaska Marine Mammals Tissue Archive

NOAA will be banking selected tissues from marine mammals for the future

determination of contaminants associated with offshore oil and gas development. A

pilot program has been initiated to develop and implement sample collection

protocols for liver, muscle, and adipose tissue from marine mammals. Fur bearing

seals will be the first specimen type included in this study. Additional species of

Alaska marine mammals will be incorporated into the archive in future years.

III. Analytical Work at the NBSR

Analysis of Human Livers

A representative portion of the samples included in the bank has been analyzed

to provide data for real time monitoring, determination of long term stability, and

evaluation of today's analytical capabilities. Initially, a combination of four

techniques provided a comprehensive data set for 36 human livers. However, several

key trace elements were not detectable in all samples or insufficient data was obtained from a particular analytical technique. Frequently, analyses had to be

repeated to detect low levels or to confirm results. This expensive approach needed

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improvement to reduce the amount of sample required and to limit the number of

techniques and analytical steps required. In addition, the naturally occurring

levels of several pollutant trace elements were approximately one order of magnitude

lower than previously reported, thus requiring more sensitive analytical procedures.

Since NAA had been used for the determination of most of the above elements, on individual 1 g (fresh weight) samples, further expansion of NAA and lowering of its

detection limits could effectively achieve this goal. Therefore, we modified the

instrumental NAA procedures and added radiochemical separation procedures that would

provide the additional sensitivity and precision required. The modifications

included full usage of the higher fluence rates after the upgrade of the NBSR, as well as application of Compton suppression high resolution gamma spectrometry and

multi-element separations in inorganic ion exchange columns (HMD, Carlo Erba) . The

details of these procedures are described elsewhere [6],

A major part of this work was to determine up to 30 elements for baseline

studies in human livers collected during 1982 and 1984. The ranges of elemental

concentrations found in the sixty selected specimens are summarized in Table II. As

discussed above, improved INAA and RNAA procedures were implemented to lower

detection limits and to include additional elements. The significant improvements

in detection limits achieved for the low level trace elements Cr, As, Ag, Sn, and Sb

are summarized in Table III. These detection limits represent the element

concentrations at which, with 95% probability, a sample with the given concentration

would generate a detectable signal. The lower detection limits permitted the

determination of the aforementioned elements in all 1984 specimens. The nuclear

procedures were complemented in an ideal manner by voltammetry. Results for nickel,

copper, cadmium and lead from this technique [7] have been included in Table I. Analysis of Fish Livers

Samples from twelve sites were selected for analysis from the thirty sites

collected and banked in the 1985/86 NS&T Benthic Surveillance program. The samples

consisted of up to 200 fish liver sections that were cryogenically homogenized and

then freeze-dried for analysis. Sequential INAA procedures were used as described

previously [8] to determine more than thirty elements in the tissues. The data

gives some indication of the variations due to sampling sites and species. For

Table IV, we have selected vanadium, chromium, and silver to illustrate these

variations and to indicate possible threats to the health of the marine environment.

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Table I Inventory of Specimens in the Biomonitoring Specimen Bank

SAMPLE TYPE DATE INITIALLY NUMBER OF RATE OF

BANKED SPECIMENS INPUT

ALIQUOT

DESCRIPTION

HUMAN

EPA: Livers 2/1980 520 35 per year Left lobe sectioned Into A

and B replicate samples of

approximately 150 grams each,

stored double -bagged in

teflon.

NCI: Serum 6/1986 991 750-1000 2mL clear or amber ampoule

per year and 5 mL clear glass rubber

stoppered bottles containing

serum with vitamins and/or

nutrients

.

MARINE

EPA:Mussels 3/1983 93 one time Narragansett mussels

collection approximately 70 per bag

stored double-bagged in

teflon.

NOAA:NS&T 7/1985

MW- Sediment

Bivalves

BS- Sediment

Fish Tissue

Fish Liver

63

62

20

18

17

MW-30 sites Sediment approximately 150

per year gram replicate samples stored

BS-10 sites double-bagged in teflon or per year teflon jars. Bivalves stored

double -bagged in teflon

containing 50 mussels with

A and B replicates or 30

oysters with A and B replicates. Fish liver and

fish tissue stored doublebagged in teflon,

approximately 150 gram

replicate samples.

FOOD

IAEA/USDA/FDA 8/1985 1-4 per Each diet is divided into 8 year aliquots of approximately 750

grams and stored double

bagged in teflon, 4 bags

remain in the bank and the

remaining 4 are used by other

agencies, currently a total of

17 bags are banked.

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Table II . Ranges of Trace Element Concentrations (mg/kg fresh weight) in

Sixty Selected Human Liver Specimens.

Element

1982 Collection

Low High

1984 Collection

Low High

Na

Mg

Al

CI

K

Sc

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

As

Se

Rb

Mo

Ag

Cd

Sn

Sb

Cs

La

Ce

Sm

Au

Hg

Pb

Th

720

81.5

0.525

1019

1645

0.000096

< 0.016

<<0.01

0.608

73.22

0.026

0.0027

3.62

29.3 < 0.001

0.327

1.74

0.241

< 0.003

0.28

< 0.0008

0.0012

< 0.008 < 0.01 < 0.0009

0.138

2265

171

2 22

2418

3942

00093

< 1.05

18

1 964

441.3

059

037

17.2

103

0268

631

8 07

1 41

0347

6 05

0122

019

417

52

0154

0.926

750 2140

104 246

0.29 7.31

984 1980

1330 3090

0.00028 0.00051

0.011 0.026

0.01 0.12

0.742 2.152

38.6 915 < 0.017 0.074

0.0029 0.036

2.60 23.8

36.97 99.87

0.0022 0.0203

0.348 0.838

2.701 8.930

0.332 1.41

0.00086 0.0341

0.440 3.268

0.050 2.420

0.0013 0.0772

0.0079 0.0146

0.0017 0.0191

< 0.022 0.086 < 0.0003 0.0033 < 0.00008 0.06164

0.0423 0.329

0.23 1.03 < 0.002 0.0047

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Table III. NAA Limits of Detection (^g/kg) for Seven Critical Elements in Human

Livers

.

MODIFICATION A

Element I NAA I NAA RNAA

Normal Suppressed

MODIFICATION B

INAA INAA RNAA

Normal Suppressed

Cr 10 4

As 30 5 Se 6 a

Mo 25 20

Ag 4

a

Sn 300 200

122

Sb( Sb)

124

Sb( Sb) 3 0.8

0.5

10

40 15 1.0

10 5 1.0

35 a 0.5

45 30 40

b

40

a 0.7

3000 2000 30

2 0.7 30

Due to coincident gamma lines, Ag and Se are not included.

b 99 The 739 keV line of Mo was used to avoid an additional decay period required for

99 99m

the Mo - Tc equilibrium to be established.

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Table IV. Selected Trace Elements in Benthlc Surveillance Fish Liver Samples

Determined by INAA. Concentrations in mg/kg fresh weight; uncertainties

are la counting statistics of samples and standards.

Location Species V Cr Ag

Dana Point

Elliott Bay

Nisqually Reach

Mississippi Delta

Corpus Christi

Charlotte Harbor

Boston Harbor

Buzzards Bay

Bodega Bay

Southampton Shoal

Santa Monica Bay

St. John's River

White Croaker

English Sole

English Sole

Atlantic Croaker

Atlantic Croaker

Spot

Winter Flounder

Winter Flounder

Starry Flounder

Starry Flounder

Hornyhead Turbo

t

Atlantic Croaker

< 3.030 290 + 004

644 ± 0.020 2 81 + 03

1397 ± 0.0083 4 21 + 03

0334 ± 0.0082 203 + 005

072 ± 0.012 146 + 005 < 0.10 125 + 006

457 ± 0.013 140 + 006

392 ± 0.012 012 + 005

258 ± 0.011 042 + 004

290 ± 0.013 021 + 005

584 ± 0.033 050 + 006

0348 ± 0.0085 045 + 005

0.3930 ± 0.0035

0.0509 ± 0.0022

0.0480 ± 0.0017

<0 0.0040

0.0711 ± 0.0017

0.0791 ± 0.0024

0.6187 ± 0.0053

0.1233 ± 0.0023

0.1638 ± 0.0020

0.0716 ± 0.0026

2.510 ± 0.020

0.0336 ± 0.0021

1. Zeisler, R., Harrison, S.H., and Wise, S.A. (1983), The Pilot National

Environmental Specimen Bank - Analysis of Human Liver Specimens, NBS Special

Publication 656, U.S. Government Printing Office: Washington, D.C., 135 pp.

2. Zeisler, R. and Wise, S.A. (1985), Quality Assurance and Protocols in Sample

Preparation of Biological Samples, In: Biological Reference Materials:

Availability, Uses, and Need for Validation of Nutrient Measurements, W.R. Wolf,

Ed., John Wiley & Sons, Inc.: New York, NY, pp 257-279.

3. Wise, S.A. and Zeisler, R. (1984), The Pilot Environmental Specimen Bank

Program, Environ. Sci. Technol. 18, 302A-307A.

4. Lauenstein, G.G. and Calder, J .A. (1987), Specimen Banking: A Key Element of

the National Oceanic and Atmospheric Administration's National Status and Trends

Program, Proc . 10th U.S. -German Seminar of State and Planning on Environmental

Specimen Banking, Oct. 6-8, 1986, Gloucester Point, VA.

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5. Co-ordinated Research Programme on Human Daily Dietary Intakes of Nutritionally

Important Trace Elements as measured by Nuclear and Other Techniques,

International Atomic Energy, Vienna, Austria. Report of the First Research

Coordination Meeting Gaithersburg, Beltsville and Washington, DC, March 19-22,

1985.

6. Zeisler, R., Greenberg, R.R., and Stone, S.F., (1987), Radiochemical and

Instrumental Neutron Activation Analysis Procedures for the Determination of Low

Level Trace Elements in Human Livers, J. Radioanal . Nucl . Chem., accepted for

publication.

7. Stoeppler, M. , and Ostapczuk, P., (1986), Report of Analysis, KFA Jlich.

8. Greenberg, R.R. , Fleming, R.F., and Zeisler, R. , (1984) High Sensitivity Neutron

Activation Analysis of Environmental and Biological Standard Reference

Materials. Environ. Intern. 10, 129.

ASTM TASK GROUP ON

NUCLEAR METHODS OF CHEMICAL ANALYSIS

D. A. Becker

(Center for Analytical Chemistry)

The newly-formed ASTM Task Group (TG) on Nuclear Methods of Chemical Analysis

has continued to expand. Formed in 1985, the group now has over 50 members. This

TG is part of ASTM Committee E 10.05 (Committee E 10 on Nuclear Technology and

Applications, Subcommittee .05 on Nuclear Radiation Metrology) and will address

needs for standards and information on the use of nuclear methods for the

determination of chemical composition. Initially, the primary interest of most TG

members is neutron activation analysis (NAA) , and members include scientists from

universities, government, and industries (both large corporations as well as small

analytical laboratories)

.

The TG has six subgroups, generally corresponding to analytical interests.

These subgroups are listed below along with their current activities:

Forensic NAA : Developing draft method for the analysis of trace elements in

bullet lead. When draft is complete, will run round robin using NBS SRM 2416,

Lead.

Neutron Generators : Rewriting ASTM Standard Method E 385-80, Oxygen Content

Using a 14-MeV Neutron Activation and Direct Counting Technique.

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Biology/Medicine /Health : Gathering information to write standard methods for

zinc and selenium in biological materials. Instrumental in organizing sessions on zinc analysis at Los Angeles ANS meeting (November, 1987) and on selenium at

the San Diego ANS meeting (June, 1988).

Geochemistry/Archeometry : Published listing of gamma-ray lines used by one laboratory for geochemical type samples, in the TG minutes from the New Orleans

meeting (January, 1987). Proposed that USGS-Reston compile data on Geochemistry/Archeometry reference materials.

Reactor Facilities : About to initiate research reactor irradiation facilities

intercomparison study, using foil techniques to measure thermal and fast

neutron f luence . Compiling listing of reactor facilities and laboratories

providing irradiation and/or NAA services

.

Quality Assurance : Initiates discussions on QA at TG meetings; in particular,

held several sessions on multielement standards and reference materials for

NAA. Will provide QA guidance for all ASTM NAA standard methods.

Interest and response to this new TG has been excellent, and the TG has

furnished improved contacts and communication between scientists working in the

field. It is hoped that with further development the TG will provide a substantial

force in the further development of NAA and nuclear methods of chemical analysis.

For further information on this group and their activities, contact Donald Becker

(Chairman) at the address shown above, or by telephone [(301) 975-6283; FTS : 879-

62831

.

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NDP AND FTIR STUDIES OF BOROPHOSPHOSILICATE CVD THIN FILM GLASSES

J.N. Cox, R. Hsu, and P.J. McGregor

(Intel Corp, Santa Clara, CA)

and

R.G. Downing

(Center for Analytical Chemistry)

Borophosphosilicate glass (BPSG) thin films are used as dielectric spacers

between metal layers in silicon semiconductor VLSIC technologies. Following

deposition and patterning, a controlled "reflow" of the glass, at a temperature low

enough to avoid the degradation of other device characteristics, is required to

smooth contours produced during the patterning step. The boron and phosphorus are added to reduce the reflow temperature. Prior to the patterning and reflow steps, a "densification" of the glass is often performed near the reflow temperature, as well

.

Typically about one micrometer in thickness, these glasses are produced by

chemical vapor deposition (CVD). There are several variants of the CVD technique.

Reactant gases in some systems are maintained at atmospheric pressure (APCVD) , while

other reactors are designed for low pressure (LPCVD) depositions. The wafers may

stationary (SW configuration) , or they may be placed on a moving belt (MW) . In the

latter case, the wafer may be conveyed through a continuous deposition zone (MW/CZ) , or through multiple zones (MW/MZ) . The reactant gases typically consist of

phosphine, silane or tetraethyl orthosilicate , and oxygen. Boron sources include

diborane , trimethyl borate, and boron trichloride.

1. Experimental Goals

This paper summarizes the characterization of various CVD BPSG by Fourier

transform infrared spectrophotometry (FTIRS) and Neutron Depth Profiling (NDP). The

thin films studied are restricted to levels ranging from 0.0 to 5.0 Wt % for boron

and from 0.0 to 7 . Wt % for phosphorus. FTIRS, which provides chemical bonding

information by analyzing the interaction of infrared radiation with the vibrational

motions of the constituents of the glass, shows that films in this compositional

regime are different chemically and structurally from simple mixtures of the

oxides. Furthermore, the different CVD processes produce films that differ

chemically from one another. Inhomogeneous distributions of chemical bonds, changes

in the relative amounts of these bonds, and internal strains or spectral

interferences due to the presence of contaminants, such as water, or of boron and/or

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phosphorus affect the peak full-width-at-half -maximum (FWHM) and other bandshape

parameters

.

Neutron Depth Profiling can nondestructively determine the distribution of

2 boron as a function of depth in a thin film. Thus, it can be used to compare the

boron profiles produced by reactors that employ SW, MW/CZ, and MW/MZ wafer

processing configurations. Also, the physical redistribution of boron during

densification and reflow cycles can be observed. Of particular interest is the

characterization of the diffusion of the boron from BPSG films into the contiguous

layers that initially contain less boron.

2. Results

One result of the study of the spectral bandshape properties of BPSG has been

the development of the FTIRS as a monitor for the quantitative determination of

boron in "as deposited" films. The required conversion factors, however, are found

to differ by as much as 13 % when APCVD MW/CZ films are compared with LPCVD SW

films. For certain LPCVD SW and APCVD MW/MZ glasses, no good calibration of the

FTIRS for the full range of boron contents has been achieved. For the former film,

the problem is attributed to interferences due to variable amounts of water, also

detected by FTIRS; for the latter, NDP reveals that the boron content in a nominally

2.0 Wt % film varies with depth by as much as 1.0 Wt %. This variation affects the

FTIR bandshape parameters in a complicated fashion. Figure 1 gives the NDP spectrum

for this APCVD MW/MZ film.

Also displayed in figure 1 are the profiles following heat treatments (room

temperature, 920 C, 1010 C) in a nitrogen ambient. The reflow properties and boron

redistribution are observed to limited by the dopant levels in the boron-deficient

zones. When an APCVD MW/CZ film of comparable B/P levels, but with a relatively

uniform NDP spectrum, is taken through the same temperature treatment, the FWHM of

the FTIR peak assigned to the SiO asymmetric stretching vibration is observed to

become progressively narrower: 135 to 119 to 121 cm

A -l (+/- 4 cmA -l). This is the

typical outcome of a densif ication cycle, since water and bonding inhomogeneities

are removed from the film. In contrast, for the same FTIR peak, the FWHM of the

APCVD MW/MZ glass with the profile shown in figure 1 changes from 130 to 114 to 125

cm" - 1 , respectively. Because the boron in a CVD film is presented as an oxide and

is to some extent chemically bound to the SiO host glass network, the NDP and FTIR

results suggest that the large chemical potential driving the redistribution of the

boron at 1010 C ultimately introduces additional strain into the film, causing the

observed increase in the FWHM.

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h

O

ffl

Be+zu

6e+20

4e+20

i ° ^ V "I a . '» m°

" «°

• " pi

2e+20

> «

B

H »„ >J \.

-0.2 0.0 0.2 0.4 0.6 Depth (jim)

0.8 1.0 1.2

Figure 1. NDP profile of Borophosphosilicate glass film on a silicon substrate:

( ) as deposited film; () after 920 C, 30 min. anneal in nitrogen;

( m ) after 1010 C, 30 min. anneal in nitrogen.

1. A. S. Tenny and J . Wong, J. Chem. Phys . , 56, No. 11, 5516 (1972).

2. R. G. Downing, R. F. Fleming, J. K. Langland, and D. H. Vincent, Nucl . Instr.

and Meth., 218, 47 (1983).

159
NON-RRD PROGRAMS

FISSION SPECTRUM AVERAGED CROSS SECTION OF THE

93Nb(n,n'

)

93Nb REACTION

D . McGarry

The following paragraphs discuss the use of the U-235 Fission- Spectrum Facility

in the thermal column of the NBS Reactor to measure the fission-spectrum-averaged

cross section of the Nb(n,n') TSTb reaction.

The NBS U-235 Fission Spectrum is known as the Cavity Fission Source (CFS)

because its geometry is a cadmium- cylinder with U-235 metal disks on the ends which

is irradiated in a 30-cm diameter cavity within the graphite thermal column of the

NBS Research Reactor. The lower-two portions of figure 1 depict the NBS-CFS. This

fission source was used to perform an irradiation, sponsored by the Department of

Energy, to measure the integral, spectrum- averaged cross section of the subject

niobium reaction.

Because the neutron fluence is produced by fissioning U-235 with thermalneutrons, the fluence is dependent upon the reactor's power history. The nickel

CO CO

Ni(n,p) Co reaction is used to monitor the absolute fluence in the U-235 spectrum

irradiations. The nickel (n,p) response is calibrated by a flux transfer from a known-fluence irradiation in a Cf-252 spectrum. Because high-purity niobium, with

less than 2 ppm of tantalum, was only available in wire form, the wire was spiraled

together with a nickel-wire monitor as shown in the upper- third view of figure 1.

Q ^m

Because the cross sections is only 150 millibarns and the half life of the ' Nb

isotopic state is 16.4 years, the subject irradiation required 30 days.

The nickel wire and nickel disks, 0.025-cm thick and 1.27-cm in diameter, are also used to monitor the axial and radial gradients within the cadmium pill box used

in the CFS . Because the disks are carefully repositioned, for each irradiation,

relative to the ends of the cadmium pill box (see figure 2) , the gradients are repeatable . The axial gradient is shown in figure 3 and is a result of repeated

irradiations of carefully-positioned nickel disks. Consequently, knowledge of the

relative positions of various 1.27-cm diam. foils permits determination of axialgradient corrections.

The effects of the radial gradient are shown in figure 4. The line is a leastsquares fit to the data points which were obtained by activating 1.27-cm diam.

nickel foils and then determining the specific activity of successively smallerdiameter disks punched, or machined, from their centers. If there had been no axial

gradient, the best fit would have been a straight line horizontal to the abcissa.

The resultant fit is a straight line because the mass ratio is proportional to

ratios of the activities, as well as the squares of the diameters.

160
NON-RRD PROGRAMS

Niobium wire coil 0.050cm diam.

High-purity Niobium Irradiation at the NBS 235U Fission Neutron Spectrum irradiation

facility located in a cavity at the thermal column of the research reactor at the National Bureau of

Standards in Gaithersburg, Maryland

235 U Sources

Nickel-disc, fluence-gradient monitor stack Cadmium enclosure

235 U Sources

Nickel wire coil 0.076cm diam.

Aluminum

coil-positioning annulus; 1.26cm

O.D., 0.99cm I.D.

Niobium wire coiled with nickel-wire, neutron-fluence monitor

Figure 1

.

High-purity niobium irradiation at the NBS U-235 Fission Neutron Spectrum

irradiation facility located in a cavity at the thermal column of the

research reactor at the National Bureau of Standards in Gaithersburg,

Maryland.

161
NON-RRD PROGRAMS

Figure 2. Picture of the spring- tight metal fingers that hold aluminum- encapsulated

U-235 metal disc on the top and bottom of a cadmium pill box containing

foils and disks to be irradiated in the NBS-CFS. One-half of the

graphite piece which forms the 30-cm diam. cavity in the NBSR thermal

column is visible.

1700 Measurement of the Flux Gradient Between the Fission Disks in the NBS

U-235 Cavity Fission Source. Experimental

Points Obtained with 0.076-mm Nickel 1660 K Foils. Least-Squares Fitted Curve

Given by A = 2091 —9.015X + 0.0377X2 A = Relative Activity of 58 Co

X = Distance in Mils

oo

o

o<

o

o

0)a

1620

2 1580

<D DC

1540 -

Bottom

80 100 120 140 160

Distance in Mils (0.001 inches) from the Bottom (see Item A)

of the Aluminum Foil Holder Insert.

Figure 3. Axial gradient in the NBS-CFS

162
NON-RRD PROGRAMS

tz .E H< <D o o iS

o --

LU CD

Q. = w 5

o o

o 5 < S.

1.13 I I I I

Effect of Radial Gradient in NBS 235 U

Cavity Fission Source on Specific Activity of Nickel Disks of Different Diameters.

Note: Mass Ratio ( M, /M 2 ) oo d ] I6\

1.10

R= -0.142 (M1 /M2) + 1-142-

1.05

1.00 l I

i i 0.2 0.4 0.6 0.8 MASS RATIO (After Cutting /Before Cutting)

1.0

Figure 4. Radial gradient in the NBS-CFS

To account for the different effects of the radial gradient on the nickel wire

and niobium wire, (because each wire section is located at a different radius),

numerical integrations of 16 segments of each of these wires were performed. The

effect of having a spiraled nickel wire rather than a 1.27-cm diam. disk as a monitor resulted in a 3 % correction.

163
NON-RRD PROGRAMS

A

10B(n,a,7) COINCIDENCE TECHNIQUE FOR ABSOLUTE NEUTRON COUNTING

D. M. Gilliam and G. P. Lamaze

(Center for Radiation Research)

A preliminary experiment has been carried out to explore the possibility of

using a

"" B(n,a,7) coincidence technique for absolute thermal neutron counting. The

motivation for this effort is the need for a highly accurate measurement of linear

neutron density for a beam-type neutron lifetime experiment which is being

undertaken collaboratively with the University of Sussex (Brighton, England) and the

Central Bureau for Nuclear Measurements (Geel, Belgium). The present scheme for

absolute counting of the thermal neutrons in a beam involves two steps: (1)

determination of the gamma efficiency (including the branching ratio factor) of a germanium gamma-ray detector by means of the alpha-gamma coincidence method (figure

1) , and (2) then replacing the thin B-10 target with a thick, "black" B-10 target so that the entire beam is stopped and counted by the calibrated gamma detector. The

first step of this scheme was carried out in a preliminary experiment at BT-7. The

gamma- ray efficiency obtained by the coincidence method was checked independently by

«

Vacuum Chamber *- ^

Nickel Coated Beam Tube

'Surface Barrier Dector *jf

Lithum Loaded

Polyethelene ft

Lead Brick

Figure 1. Experimental layout for the B(n,a,7) coincident measurements.

Detectors are in horizontal plane. Due to space limitation, the future

arrangement of two germanium detectors will probably be in the vertical

plane

.

164
NON-RRD PROGRAMS

10

C 4

oO

10

iW-vV^.v' 'V*^,,!.^.^,,

440 460 480 500

Energy (keV)

520

: 540

Figure 2. Gamma- ray spectra from B-10 targets on silicon. Dashed line indicates a bare silicon backing.

100 200 300

Channel Number

400 500

Figure 3. Charged-particle spectrum from B-10 on stainless steel backing.

165
NON-RRD PROGRAMS

10

10

*± 1 3

O

o

0'

10

1

1

o

1

0°

VI ' " p 'I

'vi *Jw^J

440 460 480 500 520 540

Energy (keV)

Figure 4. Coincident gamma-ray spectra from B-10 targets on silicon. Dashed line

represents the accidental coincident spectrum.

Table 1. Results of Present Measurements

Technique

Coincident Measurement 1 Coincident Measurement 2 Coincident Measurement 3

Coincident Method (Average)

Gamma Ray Source Method

Alpha Source Method

Efficiency

3.266 x 10

3.249 x 10

3.261 x 10

-4

-4

3.260 x

10" 4

3.279 x 10

-4

3.307 x 10

-4

Uncertainty (la)

+ 0.6 % + 0.8 % + 0.6 %

+ 0.4 % (stat. only)

+ 1.0 %

+ 0.8 %

166
NON-RRD PROGRAMS

means of calibration with both alpha particle and gamma ray standards. All three of

th

1)

these results for the gamma-ray efficiency agreed within a spread of 1.5 % (table

Figure 2 shows gamma-ray singles spectrum for the thin B-10 deposit compared

with the spectrum obtained when substituting a blank silicon wafer backing with

essentially zero B-10 content. The spectrum from the blank backing shows that there are no interfering lines in the region of the broad 478 keV peak, which is well

separated from the annihilation line at 511 keV. Figure 3 shows the alpha and Li-7

particle spectra, and figure 4 shows the true - coinc idence and chance - coincidence

gamma- ray spectra.

Although the accuracy of this preliminary measurement is far from the + 0.1 % goal of the neutron lifetime experiment, the results indicated no problems in

principle which would discourage further investment of effort in tests with improved

shielding and more careful treatment of electronic dead- time effects.

1. G. P. Lamaze, D. M. Gilliam, and A. P. Williams, "Prompt Gamma as a Fluence Rate

Monitor in Neutron Beam Experiments," Journal of Radioanaly tical Chemis try . to

be published.

FILTERED BEAMS

R. Schwartz

In response to questions concerning the purity of the NBS 2 keV filtered beam,

the neutron spectrum was carefully measured, using a He- 3 spectrometer with a new low-noise preamplifier and pile-up rejection circuitry. The pulse height spectrum

is shown in figure 1, where the pulse height analyzer channel numbers have been

3 replaced by the corresponding neutron energies, using the Q-valve for the He (n,p)

reaction (764 keV) . The ordinate is, as labelled, counts/channel, not corrected for

the approximately 1/v variation of the He- 3 cross section.

Small peaks between 7 keV and 40 keV , previously measured with a proton recoil

spectrometer, can not be resolved in this spectrum. Several previously unobserved

lines between 70 keV and 550 keV are now seen, however. The total fluence under

these newly observed lines is still only about 2 % of the 2 keV line. The rise at

—740 keV is due to pile-up from the main 2 keV peak, and there are no visible peaks

at higher energy.

167
NON-RRD PROGRAMS

CHARACTERISTICS Ot NBS FILTERED BEAMS

2 keV 24 keV n

(keV)

Fluence

(%)

En Fluence

(keV) (%)

24 97.1

74 0.2

135 1.6

280 1.0

364 0.2

144 keV

En

(keV)

Fluence

(%)

2

7 15

29

40

70

129

185

214

255

302

341

385

470

541

95.6

0.6

0.6

1.3

0.6

0.11

0.10

0.05

0.06

0.07

0.01

0.05

0.03

144

54

99.7

0.33

Beam

Diameter (cm)

Neutron

Current (n/s)

1.7

1.4 x 10

Dose Equivalent Rates (mSv-cm /hr)

MADE (ICRP 21) 51

H*(10) 31

2.5

1.6 x 10

112

98

2.5

3.1 x 10*

964

1,260

March 26, 1987

168
NON-RRD PROGRAMS

10?

E

10b

=r

iio5 .co

|104

o

o

10° E10

2 -

—

4- ~r \ ^r = 5

• • z

- •

•

• _ _ • • ^

E •

• z -

•: • -

-

••

•

• 1

• _ v.

• ^

= v \p.

- v v>

= V^^v-

• —

f - • _ - • . / -

I i H,^^v^/

200 400 600

Neutron Energy (keV)

800

Figure 1 . He-3 spectrometer data for 2 REV filtered beam.

The spectral composition of the 2 keV beam, derived from the older proton

recoil measurements and these He-3 data, is given in table 1. This is still, by

far, the cleanest 2 keV beam at any reactor facility in the world.

The 144 keV beam has been improved by increasing the amount of Ti in the

filter. This decreases the 55 keV impurity line from 1.5 % to 0.3 %, with only a slight loss of 144 keV neutrons.

The make-up of all three filtered beams is given in table 1. The 24 keV beam

is listed for the sake of completeness: there are no new measurements of this beam.

The filtered beams , together with a thermal column beam, continued to be used

for testing radiation protection instrumentation. This included quality control

measurements on neutron area monitors for the Naval Surface Weapons Center,

dosimeter irradiations as part of the Department of Energy Laboratory Accreditation

Program (DOELAP) , and testing of a new type of neutron detector developed at the

Chalk River Laboratories. This latter testing, done in collaboration with several

other laboratories in the United States and England, forms the basis for a paper to

be given at the Sixth Symposium on Neutron Dosimetry to be held in Neuherberg,

Germany, in October 1987.

169
C. Reactor Operations and Services

REACTOR OPERATIONS AND SERVICES

T. Raby and J. Torrence

Reactor operations continued at the higher power level of 20 MW for most of the

year. The reactor was shutdown in May 1987 in preparation for the installation of

the Cold Neutron Source. The shutdown period will also be used for major

maintenance including replacement of the shim arms and overhaul of the fuel

transfer system. This will considerably reduce future shutdowns.

For the first time in nine years, spent fuel was shipped for reprocessing. It

took all this time to get an appropriate spent fuel cask licensed by the NRC . Seven

shipments were made to date which were very timely since the storage pool has

reached its capacity.

During this period two new senior operators were licensed and a third was hired. This will bring the operating staff to an acceptable level. A summary of

the operating statistics for the year is prescribed in the following table. Fuel

utilization continues to be excellent.

No. of days at 20 MW 222

On-line time at 20 MW 61%

Average U-235 burnup 66%

No. of Irradiations 1570

Hours of Irradiations 1765

Hours per Irradiation 1.1

2. Irradiation Services

Extensive irradiation services were provided to many users from within and

outside NBS . In all, more than 1500 irradiations involving thousands of samples were performed in many areas of research and application.

170
ENGINEERING SERVICES

J . Nicklas

In addition to normal engineering and design services provided to reactor

operations , experimenters and users , the engineering staff is involved in a continuing effort to upgrade the reactor instrumentation in addition to normal

surveillance calibrations.

Thirty fuel assemblies, the last numbered S-575 have been inspected and

accepted from the DOE contractor by the NBSR staff. An additional 30 fuel

assemblies have been fabricated and are awaiting acceptance. Fuel compacts now being made contain 350 gms per element, a change from 300 gm elements. The first

200 plates of the 350 gm elements were radiographed and determined that the process

is under control.

The method developed to plug heat exchanger tubes with rubber plugs has been

used on several leaking tubes with success. The previous method of pounding metal

plugs into the tubes required entry into the bonnet with subsequent high radiation

exposure to personnel and was limited to personnel that could enter a 12 inch

manhole

A tool for pulling the fuel transfer arm bearings has been designed and

fabricated but has not been tested to date. The original carbon steel bearings are causing an occasional sticking of the transfer arms which causes some loss of feel

when transferring fuel.

The second tritium monitor has been installed, tested and completed. Two more modern design differential transmitters have been installed in the process

demineralized water system.

The shim arm yokes were fabricated and assembled with the shim arms, bearings,

and splines into a complete assembly for installation into the reactor. The last

replacement of shim arm assemblies required reuse of the old yokes in a tedious

underwater assembly method.

The telescopic cylinder for transferring fuel into and out of the reactor was completely rebuilt with new bearings, seals and end caps. It was not necessary to

rebuild the erecting cylinder nor replace the connecting stainless steel lines

because they were in excellent condition.

The installation of the 133 kVA uninterruptible power supply for the

experimental computer and associated instrumentation was completed and placed in

service

171
ENGINEERING SERVICES

Continued preparing and partially installing new transmitters and venturi at

the experimental level for the Cryogenics Bismuth Tip. Also the bismuth tip remote

readout meters, lights, push-buttons, and alarms were installed on the console in

the Reactor Control Room.

Completed modernizaton of the Reactor Conductivity and the Tritium measurement

instrumentation equipment:

Installed a new multipoint recorder on the Tritium Monitor system.

Replaced six conductivity amplifiers with new units. Replaced 11 temperature

compensated conductivity cells with associated wiring.

172
D. Service Programs

NEUTRON ACTIVATION ANALYSIS AT THE FOOD AND DRUG ADMINISTRATION

W . C . Cunningham

(U. S. Food and Drug Administration, Washington, DC)

The Food and Drug Administration (FDA) maintains a neutron activation analysis

(NAA) facility in the reactor building of 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 suport for special investigations and

applications research. NAA complements other analytical techniques used at FDA and serves as a reference technique and confirmatory quality assurance tool.

During the past year, this facility provided support in all of the areas noted

above. Both radiochemical and instrumental NAA procedures were utilized to provide

broad multielement information. This methods development and applications research was part of the ongoing FDA effort to improve overall analytical capabilities. The

most extensive work was in the application of NAA to the analysis of food

supplements. Efforts in this area have increased during the last few years because

of increased popularity of these products. Although these food materials are diverse and comlex, approximately 35 different product types have been analyzed by

NAA. Element concentrations are examined for label compliance and constituents of

possible toxicologic concern. In addition, data for future reference are being

compiled on interferences in the analysis, procedure modifications necessary to over come the interferences, and detection limits.

In a paper presented at the 1986 American Nuclear Society Winter Meeting in

Washington, DC, this laboratory focused attention on the determination of aluminum

in foods by NAA. The paper examined major interferences and discussed ways to

overcome or minimize them. It showed that when polyethylene bags were used to

contain the food, the detection limit was approximately 0.5 £tg/g, using an empty

polyethylene bag as the blank. When Whatman filter paper was used as the blank,

however, the detection limit was lowered to 0.15 /ig/g because of improvement in

measuring the precision of the blank. A pre- irradiation separation procedure that

was developed in the FDA NAA facility for the determination of aluminum was also

employed and findings presented. The procedure utilized Chelex-100 chelating resin

and provided a means of achieving detection limits of approximately 0.1 jig/g for

most foods.

1. W. C. Cunningham andW. B. Stroube, Jr., ANS Transactions, 53, 174-5, (1986)

173
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174
PERSONNEL ROSTER

NON-RRD NBS STAFF LOOTED AT REACTOR

Division 354

D. Brown

C. Campbell

I. Jensen

F. Moore

D. Nelson

J. Shubiak

J. Wang

Division 536

E. Boswell

C. Eisenhauer

D. Gilliam

J. Grundl

G. Lamaze

E. McGarry

R. Schwartz

GUEST WORKERS

Division 400

J. Cahn

Division 420

F. Brinckman

J. Blendell

T. Coyle

E. Fuller

K. Har dman - Rhyne

G. Olson

R. Roth

W. Haller

Division 430

R. Fields

Division 440

R. Briber

B. Bauer

C. Chiang

J. Clark

T. Davis

C. Han

R. Waterstrat

W. Wu

Division 551

D. Becker

S. Carpenter

G

.

Downing

K. Fitzpatrick

R. Fleming

C. Grazman

R. Greenberg

J

.

Langland

R. Lindstrom

G

.

Lutz

J. Maki

B. Norman

S. Stone

R. Zeisler

AND COLLABORATORS

Division 450

R. Reno

R. Shaefer

R. Shull

Division 520

G. Greene

Division 541

R . Cavanagh

R. Kelly

T. Madey

Division 543

G. Gillard

R. Harrison

A. Wlodawer

Division 552

B. Koster

L. Sander

S. Wise

175
PERSONNEL ROSTER

Division 553

C. Poston

H. Rook

C. Stone

J. Small

Division 725

J. Ehrstein

Division 774

H. Hanley

J. Straty

Ames Laboratory

W. Kamitakahara

Armed Forces Institute of Pathology

D. Nagarajan

Army Armament Research and

Development Command

C. Choi

H. Prask

S . Trevino

Federal Bureau of Investigation

R. Bilko

J

.

Haverkost

J. Kilty

P. Kostella

M. Moscop

C. Peters

J. Riley

P

.

Tangren

P. Thompson

Food and Drug Administration

W

.

Cunningham

A. Kyah

W. Stroube, Jr.

J

.

Tanner

National Institutes of Health

J. Bennett

M . Channing

W. Eckelman

M. Geller

R. Finn

R. Frank

A. Katki

M. Neuder

R. Nossel

National Oceanic and

Atmospheric Administration

G. Lauenstein

Naval Research Laboratory

K. Grabowski

D. Gubser

N. Koon

S

.

Lawrence

M. Osofsky

L. Toth

S. Wolf

Naval Surface Weapons Center

J . Cullen

G. Riel

M . Spano

Smithsonian Institution

R. Bishop

M. Blackman

T. Chase

Y. Cheng

J. Mishara

E. Myers

J. Olin

Department of Agriculture

G. Igengar

Argonne National Laboratory

T . Brun

176
PERSONNEL ROSTER

Battelle Pacific Northwest

Laboratories

L. Brackenbush

F. Brauer

G

.

Endres

M. Failey

R. Sanders

Brookhaven National Laboratory

D. Cox

C. Maryzak

Chalmers University of Technology

L. Sjolin

R. Alenljung

C.N.R.S. Grenoble, France

B. Barbara

C. Chaillout

D. Gignoux

M. Marezio

S. Miraglia

D. Schmitt

D. Tran Qui

CSIRO - Australia

R. Hill

Energy Research Foundation

(The Netherlands)

J. Woittiez

Hahn-Meitner Institute

(Berlin)

D . Behne

Institut Laue-Langevin

Grenoble, France

A. Magerl

R

.

Pynn

D. Richter

J Soubeyroux

KFA Jiilich. Germany

R. Hempleman

M. Stoepler

ETH, Zurich, Switzerland

I . Anderson

Los Alamos National Laboratory

J

.

Eckert

R. Robinson

J. Wilkerson

M. Yethridge

Max-Planck Institute

R. Kirchheim

J. Walter

Oak Ridge National Laboratory

J . Hayter

F. Kam

Sandia National Laboratory

J. Schirber

D. Varsick

Alfred University

R. Snyder

R. Zhow

Auburn University

B . Taterchuck

Cambridge University (U.K.)

J. Horton

G. Squire

Carnegie-Mellon University

E. Boltich

W. Wallace

College of William and Mary

E. Schoe

R. Wright

Iowa State University

P. Klavins

H. Ku

R. Shelton

H. Yang

177
PERSONNEL ROSTER

Kyoto University (Japan)

H. Hasegawa

T. Hashimoto

Q

.

Trancong

S Sakurai

McMaster University

W. Clarke

R. Barr

Miami University (Ohio)

J . Cantrell

Michigan State University

E. Case

Y. Fan

S. Solin

M.I.T.

J. Didiskein

M. Green

B. Wuensch

Nagoya University

Y. Muroga

Northwestern University

J. Ketterson

C. Sellers

J . Weertman

Ohio University

R. Cappelltetti

Oregon State Graduate School

P. Davis

Princeton University

J. Kolberstein

Purdue University

A. Overhauser

Stanford University

W . Tang

San Jose State University

A. Ling

Stanford Unversity

W . Tang

University of Annecy (France)

J. Bouillot

University of Antwerp (Belgium)

K. Michel

University of California (Irvine)

V . Guinn

University of California

(Santa Barbara)

M. Eddy

J

.

Fint

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 Delaware

S. Satija

University of Exeter (U.K.)

R. Slade

178
PERSONNEL ROSTER

University of Illinois

J

.

Borchers

R. Du

J

.

Cunningham

C. Flynn

S. Landobliger

D

.

Neumann

M. Salamon

H. Zabel

U. of Illinois (Chicago)

M. Said

J

.

Kowel

University of Leiden (The Netherlands)

J. Mydosh

Universitv of Maryland

D. Anderson

A. Bates

J. Copley

J. Dodd

J. Fernande z - Bac

a

A. Fiesel

G. Gordon

F. Guenther

M. Han

D. Herman

J. Hoff

M. Kitto

S. Krueger

C. LeCompte

Q. Li

w. Li

J. Lynn

L. Mackie

L. McCarthy

J. Nicol

J. Ondov

A. Sheffield

P. Sheridan

T. Sullivan

G. Tuncel

S. Tuncel

J. Valette- Silver

W. Waters

Y. Yu

University of Massachusetts

H. Yang

University of Michigan

D. Vincent

University of Milan (Italy)

M. Zocchi

University of Missouri

W. Ching

W. James

T. Little

S

.

Werner

University of Muenster

F. Kemper

University of Nebraska

D. Sellmyer

University of Nancy (France)

P . Mangin

University of New Hampshire

R. Blakemore

University of Notre Dame

J . Furdyna

T. Giebultowicz

University of Odense

E. Anderson

University of Pennsylvania

P. Davis

University of Peruglia

G. Alberti

179
PERSONNEL ROSTER

University of Rhode Island

D . Andrauskas

S . Hasanain

S. Pickart

University of Vermont

T. Flanagan

University of Virginia

T. Williamson

University of Washington

K. Mottet

W. Zoller

University of Wisconsin

D . Huber

Utah State University

T. Isenhour

Yale Univeristy

D. Ehgelman

J . Flanagan

Swiss Institute for Nuclear Research

I . Anderson

University of Leiden

(The Netherlands)

J . Mydosh

Aerospace Corporation

R . Bowman

J . Knudsen

Alcoa Technical Center

C. Jensen

R. Rioja

Allied Corporation

G. Fish

A. Maeland

J. LaSalle

Atomic Energy of Canada. LTD

W . Lennard

Bell Laboratories

R . Cava

H. Chen

D. Johnson

J. Mitchell

D . Murphy

J. Remeika

W. Rhodes

J. Riley

L. Scheemeyer

S . Sunshine

J . Waszazak

S . Yognasubiamian

Bell-Northern Research Ltd.

F. Shepherd

W. Vandevorst

Bell Communictions Research

Laboratories

P. Miceli

Directed Technologies. Inc.

N. Chesser

Eastman Kodak

T. Hossain

M

.

Landry

J. O'Reilly

C

.

Swanson

E. I. DuPont de Nemours Co.

D. Corbin

G. Jones

F. Tebbe

C. Torardi

Exxon

R. Busch

J. Dozier

J

.

Huang

M. Kim

D. Lohse

R. Overfield

S. Sinha

180
PERSONNEL ROSTER

General Electric Co.

L. Provo

W. R. Grace

M. Wax

R. Wormsbecker

GTE Laboratories

M. Downey

G. Hamill

D. Oblas

IBM (Yorktown Heights)

R. Gambino

IBM (San Jose)

G. Hadziioannou

T. Russel

Intel Corporation

N. Cox

Lockheed EMSCO

D. Lindstrom

Mobil Central Research Laboratory

D. Olsen

Motorola. Inc.

S. Wilson

Shell Oil

V. Soni

D. Hart

Westinghouse-Hanford Corp.

W. McElroy

Mobil Solar Research

J . Gregory

181
F. Publications

COLLABORATIVE PROGRAMS

Alberi, J.; Jeenicke, E.; Ost, R. ; Wilson, R. ; Schroder, I. G.; Avenier, A.;

Bagieu, G.; Benkoula, H.; Cavaigmac, J. F. ; Adrisi, A.; Koang, D. H.; and

Vignom, B.; "Studies of Parity Violation Using Polarized Slow Neutron Beams,"

International Conference on Parity Violation in the Nucleon-Nucleon

Interactions, Vancouver, BC . May 1987.

Anderson, I. S.; Rush, J. J.; Udovic , T. J.; and Rowe , J. M. ; "Hydrogen Pairing

and Anisotropic Potential for Hydrogen Isotopoes in Yttrium." Phys . Rev.

Lett 57, 2822 (1986).

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, in press.

Beech, F. ; Miraglia, S.; Santoro, A.; and Roth, R. S.; "Neutron Study of the

Crystal Structure and Vacancy Distribution in the Superconductor Ba.Y Cu_

o

" Phys. Rev. B 35, 8778-8781 (1987).

Berk, N. F. ; "Scattering Properties of a Model Bicontinuous Structure with a Well Defined Length Scale." Physical Review Letters 58, No. 25, 2718

(1987).

Boggs, P. T. ; Collins, D. M. ; Finger, L. W. ; Konnert, J. H. ; Prince, E.; and

Spiegelman, C. H. ; "International Tables for Crystallography, Vol. C, Part 8 Refinement," in press.

Borchers, J.; Sinha, S.; Salamon, M. B.; Du, R. ; Flynn, C. P.; Rhyne , J. J.; and

Erwin, R. W.; "Magnetic and Structural Characterization of Dy-Y Multilayers,"

J. Appl. Phys. 61, 4049 (1987).

Borchers, J.; Salamon, M. B.; Du, R. ; Flynn, C. P.; Erwin, R. W. ; and Rhyne, J. J.; "Characterization of Structural and Magnetic Order of Er/Y

Superlattices . " Superrlattices and Microstructures (to be published in

1988.

Bouillot, J.; Rowe, J. M.; and Rush, J. J.; "Structure of the Mixed Crystal

(KCN)

n (KBr)_ _ Determined by Neutron Powder Diffraction, Phys. Rev.

B. , July 1987

Cahn, J. W. ; Gratias , D.; and Mozer, B.; "Patterson Fourier Analysis of the

Icosahedral (Al , Si) - Mn Alloy," Phys. Rev. Letters, in press.

Carr, M. J.; Chambers, W. F. ; Melgaard, D.; Himes, V. L. ; Stalick, J. K. ; and

Mighell, A. D.; NBS/Sandia/ICDD Electron Difraction Database.

Technical Report (Sandia) , 1987 in press.

Casella, R. C; "Coherent Scattering of Low Energy Neutrinos from

Macroscopic Objects," in Intersections Between Particle and Nuclear Physics -- 1986 . ed. D. F. Geesman, AIP Conf. Proc . No. 150, p. 1040, American Institute

of Physics, New York, (1986).

Casella, R. C. ; "On the Theory of Coherent Neutrino Scattering from Crystals,"

Nuovo Cimento 94A, 42 (1986).

182
PUBLICATIONS

Cava, R. J.; Santoro, A.; Johnson, D. W. ; and Rhodes, W. W. ; "Crystal

Structure of the High Temperature Superconductor La.. . Sr. Cu

above and below T ." Phys . Rev. B. 35, 6716-6720 (1987).

c Cava, R. J.; Santoro, A.; Murphy, D. W. ; Zahurak, S. M. ; Fleming, R. M. ; Marsh, P.;

and Roth, R. S.; "The Structure of the Lithium Inserted Metal Oxide 6-

LiV " J. Sol State Chem. , in press.

Cavagnat, D.; Magerl , A.; Trevino , S.; Pesquer, M. ; and Vettier, C; in

Dynamics of Molecular Crystals, Ed, J. Lascombe, Elsevier Science

Publishers, Amsterdam, p649 (1987).

Choi, C. S.; Prask, H. J.; "Neutron Diffraction Study of Age-Hardened U

0.75wt% Ti Alloy," J. Nucl. Mater., in press.

Didisheim, J. J.; Prince, E.; and Wuensch, B. J.; "Neutron Rietveld Analysis of

Structural Changes in Nasicon Solid Solutions Na. Zr_Si P_ 0- _ at Elevated

Temperatures: x = 1.6 and 2 . at 320° C," Solid State Ionics 1$ & 19 . 944-958

(1986).

Dougherty, D. A.; Choi, C. S.; Kaupp , G.; Buda, A. B.; Rudzinski, J. M. ; and

Osawa, E.; "Effects of Substituents on the Length of Central C(sp )- C(sp ) bond in Anthracene Photodymers and Related Molecules," J. Chem. Soc. Perkin

Trans. II, 1063-1070 (1986).

Erwin, R. W. ; Rhyne , J. J.; Salamon, M. B.; Borchers , J.; Sinha, S.; Du, R. ; Cunningham, J. E.; and Flynn, C. P.; "The Magnetic Structure of Dy-Y

Superlattices," Phys. Rev. B 35, 6808 (1987).

Fan, Y. B.; Solin, S. A.; eumann, D. A.; Zabel , H.; and Rush, J. J.; "Phonons in

Graphite Intercalated with Potassium and Ammonia," in Graphite Intercalation

Compounds . edited by M. S. Dresselhaus , G. Dresselhaus , and S. A. Solin,

Materials Research Society, Pittsburgh, 165 (1986).

Fan, Y. B.; Solin, S. A.; Neumann, D. A.; Zabel, H.; and Rush, J. J.; "Elastic

Neutron Scattering Study of the Structure of Graphite Intercalated with

Potassium and Ammonia," Phys. Rev. B, (in press).

Fernandez -Baca, J. A.; Lynn, J. W. ; Rhyne, J. J.; Fish, G. E.; "Spin Dynamics of

Amorphous Fe /n _ .Ni Zr n _

, r

" J. Appl. Phys. 61, 3406 (1987). (90-x) x 10 rr J —

Fernandez -Baca, J. A.; Lynn, J. W. ; Rhyne, J. J.; and Fish, G. E.; "Study of the

Long Wavelength Spin-Wave Energies and Linewidths of the Amorphous Invar Alloy

Fe.._,. B ," Phys. Rev. (to be published). 100-x x

J r

Fischer, R. ; Neumann, D. A.; Zabel, H.; Morkoc , H.; Choi, C; and Otsuka, N.;

"Dislocation Reduction in Epitaxial GaAs on Si (100)," Appl. Phys. Lett. 48,

1223 (1986).

Fischer, R. X.; Baur , W. H.; Shannon, R. D.; Staley, R. H. ; Viga, A. J.; Abrams , L. ; and Prince, E.; "Neutron Powder Diffraction Study and Physical Characterization

of Zeolite D-rho," J. Phys. Chem., 90, 4414-4423 (1986).

Fischer, R. X.; Baur, W. H. ; Shannon, R. D.; Staley, R. H.; Vega, A. J.; Abrams, L. ; and Prince, E. ; "Neutron Powder Diffraction Study and Physical Characterization

183
PUBLICATIONS

of Zeolite D-ZK-5 Deep-bed Calcined at 500 C and 650 C

, " Zeolites, 6, 378-387

(1986).

Giebultowicz , T. M. ; Rhyne , J. J.; and Furdyna, J. K. ; "Mn-Mn Exchange Constants in

Zinc -Manganese Chalcogenides , " J. Appl . Phys . 61 (8), 3537 (1987).

Giebultowicz, T. M. ; Rhyne, J. J.; Furdyna, J. K. ; and Debska, U. ; "Neutron

Diffraction Study of the Wurtzite-Structure Dilute Magnetic Semiconductor

Zn„ . c Mn_ cc Se," J. Appl. Phys. 61 (8), 3540 (1987).

.45 . 55

Giebultowicz, T. M. ; and Holden, T. M. ; "Neutron Scattering Studies of the Magnetic

Structure and Dynamics of Diluted Magnetic Semiconductors," in Diluted

Magnetic Semiconductors, series on Semimetals and Semiconductors, by Academic

Press (in press)

.

1 Glinka, C. J.; Rowe , J. M. ; and LaRock, J. G.; "The Small Angle Neutron Scattering

Spectrometer at the NBS , " J. Appl. Cryst. 19, 427-439 (1986).

Gotaas , J. A.; Rhyne, J. J.; Wenger, L. E.; and Mydosh, J. A.; "Magnetic Fieldinduced Transition in Y Gd , " J . Appl. Phys. 61, 3415 (1987).

Gotaas, J. A.; Lynn, J. W. ; Shelton, R. N. ; Klavins , P.; and Braun, H. F. ; "Suppression of Superconductivity by Antiferromagnetism in Tm_Fe_Si '' Phys.

Rev. B in press

.

Hanley, H. J. M. ; Straty, G. C; Glinka, C. J.; and Hayter, J. B.; "Low-Q

Neutron Diffraction from Supercooled D-Glycerol," Molecular Physics, in

press

.

Hempelmann, R. ; and Rush, J. J.; "Neutron Vibrational Spectroscopy of

Disordered Metal -Hydrogen Systems." Proceedings of NATO Workshop,

Rhodes, Greece; Physics B, (in press).

Himes, V. L. and Mighell, A. D.; "A Matrix Approach to Symmetry," Acta Cryst. A43 . 375-384 (1987).

Himes, V. L. and Mighell, A. D.; "NBS*SEARCH: A Program to Search NBS CRYSTAL

DATA," Crystallo graphic Databases (to be published) 1987.

Jin, L. ; James, W. J.; Lemaire , R. ; and Rhyne, J. J.; "Magnetic Structure of

DyFe " Jour. Less-Common Metals , 118, 269 (1986).

Kircheim, R. ; Huang, X. Y. ; Carstanjen, H. D.; Rush, J. J.; and Udovic , T. J.;

"Inelastic Neutron Scattering and Resistivity of Hydrogen in Cold- Worked

Palladium." J. Less Common Metals, (in press).

Li, Q.; Lynn, J. W. ; and Gotaas, J. A.; "Absolute Measurement of the Ordered Moment

in Holmium-rich (Er n Ho )Rh,B " Phys. Rev. B35, 5008 (1987). 1-x x 4 4

Loidl, A.; Knorr, K. ; Rowe, J. M. ; Mclntyre, G. J.; "Glass and Phase

Transitions in (KBr) l-x(KCN) , Phys. Rev. B., in press.

Lynn, J. W. and Rhyne, J. J.; "Spin Dynamics of Amorphous Magnets," Chapter

14 in Spin Waves and Magnetic Excitations , edited by S. K. Sinha and

A. S. Borovik-Romanov, North Holland Physics Publishers, in press.

184
PUBLICATIONS

Maeland, A. J.; Lukacevic , E.; Rush, J. J.; and Santoro, A.; "Neutron Powder

Diffraction and Inelastic Scattering Study of the Structures of Zr Pd,

Zr PdDn _,_ and Zr PdD. Q

" J. Less Comm. Metals 129, 77 (1987).

Mangin, P.; Bomazouza, D. ; Tete, C; Rhyne , J. J.; and Erwin, R. W. ; "Re-entrant

Spin-Glass Properties of a-

(

Fex

Cr

1 . x

) 75

p

1 5 C10

' " J - APP1 - Phys . 61, 3619 (1987).

Miceli, P. F. ; Youngquist, S. E.; Neumann, D. A.; Zabel , H.; Rush, J. J.; and Rowe

,

J. M. ; "Quasicrystalline and Crystalline Phonon Density of States: Neutron

Scattering Measurement on Al.Mn," in Phonon Scattering in Condensed Matter V . Springer Series in Solid-State Sciences vol. 68, edited by A. C. Anderson and

J. P. Wolfe, (Springer-Verlag, Berlin, 1986) p. 344.

Miceli, P. F. ; Youngquist, S. E.; Neumann, D. A.; Zabel, H.; Rush, J. J.; and Rowe,

J. M. ; "Neutron Scattering Study of the Vibrational Density of States in

Icosahedral and Crystalline Al

80

Mn " Phys . Rev. B 34 8977 (1986).

Mighell, A. D. ; Stalick, J. K. ; and Himes, V. L. ; "NBS CRYSTAL DATA: A Comprehensive

Database with Chemical, Physical and Crystallographic Data on Solid- State

Materials," Crystallographic Databases , edited by G. Bergerhoff, Int. Union of

Crystallography, in press.

Neumann, D. A.; Zabel, H. ; Rush, J. J.; Fan, Y. B.; and Solin, S. A.; "Quasielastic

Neutron Scattering Study of Rotations and Diffusion in KC (NH ) " (in

press)

.

Nicol, J. M. ; Udovic, T. J.; Kelley, R. D.; and Rush, J. J.; "Isotope Dilution

Neutron Spectroscopy: A Vibrational Probe of Hydrogen/Deuterium Interactions on Palladium Black, Langmuir, in press..

Nossal, R. ; Glinka, C. J.; and Chen, S.-H.; "SANS Studies of Concentrated Protein

Solutions. I. Bovine Serum Albumin, " Biopolymers, 25, 1157-1175 (1986).

Prask, H. J.; and Choi, C. S.; "Residual Stress Measurements in ArmamentSystem Components by Means of Neutron Diffraction." ASM 1987 Conference on Residual Stress, Cincinnati, OH, in press.

Prince, E. ; "Diffraction Patterns from Tilings with Five-fold Symmetry," Acta.

Cryst. A43, 393-400 (1987).

Prince, E. ; "Applications of Fixed Wavelength Neutron Powder Diffraction,"

Transactions ACA, 2_3, in press.

Prince, E. ; "Phase Extension by Combined Entropy Maximization and Solvent

Flattening," Acta Cryst. A, in press.

Rhyne, J. J.; Erwin, R. W.

;

Salamon, M. B.; Sinha, S.; Cunningham, J. E.; Borchers

,

J.; and Flynn, C. P.; "Long-Range Incommensurate Magnetic Order in Dy-Y

Multilayers," Invited Paper, Seventeenth Rare Earth Research Conference,

Hamilton, Canada, Jour. Less-Common Metis. 126 . 53 (1986).

Rhyne, J. J.; Erwin, R. W. ; Salamon, M. B.; Sinha, S.; Cunningham, J. E.; Borchers,

J.; Du, R. ; and Flynn, C. P.; "Occurrence of Long-Range Helical Spin Ordering

185
PUBLICATIONS

in Dy-Y Multilayers," Invited Paper, Thirty-first Annual Conference on Magnetism and Magnetic Materials, J. Appl . Phys . 61, 4043 (1987).

Rhyne , J. J.; "Highlights from the Exotic Phenomena of Lanthanide Magnetism,"

Chapter 76, Handbook on the Physics and Chemistry of Rare Earths . Vol. 11,

edited by K. A. Gschneidner and LeRoy Eyring, North Holland Publishing (to be

published in 1988)

.

Rhyne, J. J.; Neumann, D. A.; Gotaas , J. A.; Beech, F. ; Toth, L. ; Lawrence, S.;

Wolf, S.; Osofsky, M. ; and Gubser, D. U.; "Phonon Density of States of

Superconducting YBa Cu„0 and the Non- Superconducting Analog YBa9 Cu„0- , " Phys.

Rev. B 36, 2294 (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 ., in press

.

Rhyne, J. J.; "Neutron Scattering in Intermetallics , " Invited Paper, International

Symposium on Magnetism of Intermetallic Compounds, Kyoto, Japan, Jour. Mag. and

Mag. Matls . , in press.

Richter, D.; Hempelmann, R. ; Rush, J. J.; Rowe , J. M. ; Eckert, J.; Goldstone,

and Tonks , D.; "Localized Vibrations of Hydrogen in Metals." Physica B,

(in press)

.

Rowe, J. M. ; "The NBS Cold Neutron Research Facility," NBS Special Publication 711,

(1986).

Rowe, J. M. ; Rush, J. J.; Schirber, J. E.; and Mintz , J. M. ; "Isotope Effects in the

PdH system - Lattice dynamics of PdT_ ," Physical Review Letters, 57 . (1986).

Rowe, J. M. ; Rush, J. J.; and Michel, K. H. ; "Comment on Dielectric

Susceptibility Measurements in (KCN) (KBr)

1 Mixed Crystals." Phys. Rev.

Lett, (in press)

.

Santoro, A.; Miraglia, S.; Beech, F. ; Sunshine, S. A.; Murphy, D. W. ; Scheemeyer, L. F. ; and Waszczak, J. V.; "The Structure and Properties Ba„Y

Cuo

" Mat. Res. Bull. 22, 1007-1113, (1987).

Schroder, I.; Gilliam, D.; Carlson, A. D.; Bright, S. W. ; and Hutchinson, J. M. R. ; International U-235 Fission Foil Mass Intercomparision,

Transactions American Nuclear Society 53, 473 (1986).

Smith, H. K. ; Rhyne, J. J.; Hardman - Rhyne , K. A.; and Wallace, W. E. ; "Thermodynamics of Hydrides and Deuterides of R,Fe_„ and R,Mn „," Jour. LessCommon Metis . 130, 421 (1987).

Spano, M. L. ; Rhyne, J. J.; Pickart, S. J.; Hasanain, S. K. ; Gambino, R. J.; and

McGuire, T. R. ; "Magnetic Correlations in an Amorphous Gd-Al Spin Glass," J. Appl. Phys. 61, 3639 (1987).

Spano, M. L. and Rhyne, J. J.; "Neutron Scattering Study of the Spin Freezing in

Amorphous Tb /c Fe cc and Tb oc Fe^ " J. Appl. Phys. 61, 4100 (1987).

45 55 25/5

186
PUBLICATIONS

Stalick, J. K. and Mighell, A. D.; " Crystal Data Version 1.0 Database

Specifications," NBS Technical Note 1229, (1986).

Stalick, J. K. and Mighell, A. D. ; "NBS CRYSTAL DATA. A Magnetic Tape of Chemical

and Crystallographic Data Compiled and Evaluated by the NBS Crystal Data

Center," NBS Tech . Note 1229, U.S. Dept. of Commerce, NBS, (1987).

Stalick, J. K. and Mighell, A. D.; Crystal Data Version 1.0 Database Specifications,

American Crystallographic Association Annual Meeting June 22-27, 1986, McMaster

University, Hamilton, Ontario (in press).

Torardi , C. C; Reiff, W. M. ; Lazar, K. ; and Prince, E.; "Synthesis Structures and

Low Temperature Magnetism of the New Lithium and Sodium Insertion Compounds:

LiFe(II)ClMo0 and NaFe(II)CLMo0 " J. Phys . Chem. Solids, 47, 741-750 (1986).

Trevino , S. F. and Tsai , D. H.; "The Simulation of Condensed Matter Chemistry and

Detonation," Proc . Army Sci. Conf., West Point (1986), in press.

Trevino, S. F. ; "The Rotational Potential of Solid Nitrome thane , " Quantum Aspects

of Molecular Motions in Solids , ed. by A. Heidemann, A. Magerl, M. Prager D. Richter, and T. Springer, p. 9 Springer-Verlag, (1987).

Udovic, T. J. and Kelley, R. D.; "Neutron Scattering Studies of Hydrogen in

Catalysts," Hydrogen in Catalysis: Theoretical and Pratical Aspects, (Z. Paal

and P. G. Menon, eds . ) Marcel Dekker, Inc , New York (1987) pp 167-182.

Udovic, T. J.; Cavanagh, R. R. ; Rush, J. J.; Wax, M. J.; Stucky, G. D.; Jones,

G. A.; and Corbin, D. R. ; "Neutron Scattering Study of NH, Dynamics During

the Deammoniation of NH, -rho Zeolite," J. Phys. Chem. in press.

Wax, M. J.; Cavanagh, R. R. ; Rush, J. J.; Stucky, G. D.; Abrams , L. ; and

Corbin, D.; "A Neutron Scattering Study of Zeolite Rho." Phys. Chem.

90, 532 (1986).

Werner, S. A.; Giebultowicz , T. M. ; and Overhauser, A. W. ; "Charge Density Wave

Satellites in Potassium?" Physica Scripta (materials of the 1987 European

Physical Society Meeting, Piza, Italy), in press.

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 , in press.

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.; "Uniaxial Deformation of

Rubber Network Chains by Small Angle Neutron Scattering," (submitted to

Macromolecules)

.

Yu, S. C; Lynn, J. W. ; and Lau, B. W. ; "X-ray Diffraction Studies of Amorphous

(Fe 1 Ni )^^Si inB1 _ alloys. 1-x x 77 10 13

Zabel, H. ; Hardcastle, S. E.; Neumann, D. A.; Suzuki, M.; and Magerl, A.; "Dynamics

of Two-dimensional Melting on a Periodic Substrate," Phys. Rev. Lett. 5_7, 2041

(1986).

187
PUBLICATIONS

INDEPENDENT PROGRAMS

Bowman, R. C, Jr., Robertson, R. E., Knudsen, J. F. , and Downing, R. G., "Studies

of Boron Implantation through Photochemically Deposited Si02 Films on Hg(lx)Cd(x)Te" , Soc. Photo Optical Instru. Eng. Proc . 686, 18-25 (1986).

Bowman, R. C, Jr., Marks, J., Downing, R. G., and Knudsen, J. F., "Effects of Boron

Implantation on Silicon Dioxide Passivated HgCdTe" , Mat. Res. Soc. Symp . 90,

279-286 (1087).

Fleming, R. F. and Lindstrom, R. M. , "Precise Detemination of Aluminum by

Instrumental Neutron Activation (to be published)

.

Gilliam, D. M. , Hocken, D., Humphreys, J. C. and Lamaze , G. P., "Neutron Sensitivity

of LiF Chip Gamma Dosimeters at Megagray Doses", Proc. of the ASTM-EURATOM

Symposium on Reactor Dosimetry (in press)

.

Greenberg, R. R. , and Zeisler, R. , "A Radiochemical Procedure for the Determination

of Chromium in Biological Materials", J. Radioanal . Nucl . Chem. , (in press).

Grundl , J., "Derivation of Neutron Exposures Parameters from Threshold Detector

Measurements", Proc. of the ASTM-EURATOM Symposium on Reactor Dosimetry (in

press)

.

Lamaze, G., Gilliam, D. M. , Williamson, T. G., "Calibration of a Neutron Driven Gamma

Ray Source", Proc. of the ASTM-EURATOM Symposium on Reactor Dosimetry (in

press) .

Lamaze, G. P., Gilliam, D. M. , and Williams, A. P., "Prompt Gamma as a Fluence Rate

Monitor in Neutron Beam Experiments", J. of Radioanal. Chem. (in press).

Lindstrom, R. M. , Zeisler, R. , and Rossbach, M. , "Activation Analysis Opportunities

Using Cold Neutron Beams", J. Radioanal. Nucl. Chem. 112, No. 2 (1987).

Lindstrom, R. M. , "Nuclear Analytical Methods in Standards Certification", to be

published in proceedings of IAEA Advisory Group Meeting on Comparison of

Nuclear Analytical Methods with Competitive Methods (1987).

McGarry, E. , Ruddy, F. , Gold, R. , Kellogg, L. S., Preston, C. C, Roberts, J. H. , "Updated PCA Physics-Dosimetry Results and Analyses", Proc. of the ASTM-EURATOM

Symposium on Reactor Dosimetry (in press).

Riley, J. E., Jr., and Lindstrom, R. M. , "Determination of Boron in Borosilicate

Glasses by Neutron Capture Prompt Gamma-Ray Activtion Analysis", J. Radioanal.

Nucl. Chem. 109, 109-115 (1987).

Schwartz, R. B., "Neutron Personnel Dosimetry Calibrations at NBS", NBS Special

Publiction, NBS 250-12, (1986).

Williams, J. G. , Cogburn, C. 0., Hodgson, L. M. , Apple, S. C, McGary, E. D.,

Lamaze, G. P., Gilliam, D. M. , Schima, F. J., Rogers, J. W. , Gehrke , R. , Baker,

J. D., Wheeler, Q „F. J., ."Measurements of Fission Spectrum Averaged Cross

Sections for the Nb(n,n')

m

Nb Reaction", Proc. of the ASTM-EURATOM Symposium

on Reactor Dosimetry (in press).

188
PUBLICATIONS

Williamson, T. G., Ayers T. A., Hammers ten, W. L. , Lamaze , G. P., Schima, F. J.,

"Measurement of the NB(n,n') Fission Spectrum Cross Sectin" , Proc . of the ASTMEURATOM Symposium on Reactor Dosimetry (in press).

Williamson, T. G., Lamaze, G. P., Gilliam, D. M. , Eisenhauer, C. E., "Iron and

Cadmium Capture Gamma Ray Photofission Measurements", Proc. of the Am. Nucl.

Soc. Topical Conf. on Radiation Shield ing and Dosimetry (in press).

Zeisler, R. , Stone, S. F. , "Analysis of Marine Bivalves and Sediments", Trans. Am.

Nucl. Soc. 53:201 (1986).

Zeisler, R. , Stone, S. F. , and Sanders, R. W. , "Sequential Analysis of 45 Trace

Elements in Marine Bivalves", Anal. Chem. (in press).

Zeisler, R. , Greenberg, R. R. , and Stone, S. F. , "Radiochemical and Instruemtnal

Neutron Activation Analysis Procedures for the Determination of Low Level Trace

Elements in Human Livers", J. Radioanal . Nucl. Chem. (in press).

189

NBS-114A (REV. 2-8C) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS/TN-1240

2. Performing Organ. Report No, 3. Publication Date

November 1987

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities July 1986 Through June 1987

5. AUTHOR(S)

Frederick J. Shorten, Editor

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

July 1986 through

June 1987

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

Same as item #6 above.

10. SUPPLEMENTARY NOTES

[] Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This report summarizes all those programs which use the NBS reactor. It covers

the period for July 1986 through June 1987. 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; crystal structure; diffraction; isotopes; molecular dynamics;

neutron; cold neutrons; neutron radiography; nondestructive evaluation: nuclear

reactor; radiation.

13. AVAILABILITY

[^ Unlimited

| | For Official Distribution. Do Not Release to NTIS

/T~2 Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

]] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

197

15. Price

lent Printing Office: 1987 0-201-490 (60174) USCOMM-DC 8043-P80

NBSTechnical Publications

Periodical

Journal of Research—The Journal of Research of the National Bureau of Standards reports NBS research and development in those disciplines of the physical and engineering sciences in which the Bureau is active. These include physics, chemistry, engineering, mathematics, and computer sciences. Papers cover a broad

range of subjects, with major emphasis on measurement methodology and the basic technology underlying

standardization. Also included from time to time are survey articles on topics closely related to the Bureau's

technical and scientific programs. Issued six times a year.

Nonperiodicals

Monographs—Major contributions to the technical literature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with interested industries, professional organizations, and regulatory bodies.

Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists,

engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and

technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties

of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide pro- gram coordinated by NBS under the authority of the National Standard Data Act (Public Law 90-3%).

NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published quarterly for NBS by

the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints,

and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials,

components, systems, and whole structures. The series presents research results, test methods, and perfor- mance criteria related to the structural and environmental functions and the durability and safety

characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject

area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized re- quirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private

sector standardizing organizations.

Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological marketplace.

Order the above NBS publications from: Superintendent of Documents, Government Printing Office,

Washington, DC 20402. Order the following NBS publications—FIPS and NBSIR 's—from the National Technical Information Service, Springfield, VA 22161.

Federal Information Processing Standards Publications (FIPS PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register serves as the official source of information in the Federal Government regarding standards issued by NBS pursuant to the Federal Property

and Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS

for outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161, in paper copy or microfiche form.
U.S. Department of Commerce

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Gaithersburg, MD 20899

Official Business

Penalty for Private Use $300