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NBS TECHNICAL NOTE 1207

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

NBS Reactor:

Summary of Activities

July 1983 Through

June 1984

100

.115753

No . 1207

1985

c. 2
The National Bureau of Standards

1 was established by an act of Congress on March 3, 1901. The

Bureau's overall goal is to strengthen and advance the nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a

basis for the nation's physical measurement system, (2) scientific and technological services for industry and

government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety.

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 Center for Materials

Science.

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

produces, and distributes Standard Reference Materials; and provides

calibration services. 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 Engineering2

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 centers:

Programming Science and

Technology

Computer Systems

Engineering

The Center for Materials Science

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-country 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 Center consists of the following Divisions:

Inorganic Materials Fracture and Deformation 3 Polymers

Metallurgy Reactor Radiation

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Gaithersburg, MD 20899.

2 Some divisions within the center are located at Boulder, CO 80303. ^Located at Boulder, CO, with some elements at Gaithersburg, MD.
N nA n - NATIONAL BUREAU BS Reactor: LIBRARY Summary of Activities

^°'rc ' July 1983 Through /<*>

June 1984 M

^f5

no. ifoi

Frederick J. Shorten, Editor

Reactor Radiation Division

National Measurement Laboratory

National Bureau of Standards

Gaithersburg, MD 20899

/

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued February 1985
National Bureau of Standards Technical Note 1207

Natl. Bur. Stand. (U.S.), Tech. Note 1207, 161 pages (Feb. 1985)

CODEN: NBTNAE

U.S. Government Printing Office

Washington: 1985

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 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 operated at 1 MW during the past year and provided 25 experimental

facilities ranging from intense neutron beams to extensive irradiation facilities,

making it one of the most versatile high performance research reactors in the

country. Thus, it is able to serve a large number of scientists and engineers in a broad range of activities both within and outside the NBS.

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 these programs carried out by scientists in the Reactor Radiation Division

and their collaborators. The second section summarizes NBS work originating entirely

outside the Division which requires no collaboration with Division scientists. The

section entitled, "Service Programs," covers those programs originating outside NBS

but for which the Division provides 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 T. Lindstrom, P. Andrew, and S. Tassey for efforts in typing manuscripts.

n.A-U^fcR. S. Carter

Chief, Reactor Radiation Division

National Bureau of Standards

in
ABSTRACT

This report summarizes all those programs which depend on the NBS reactor. It

covers the period from July 1983 through June 198H. 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, radiation effects studies, neutron radiography, and nondestructive

evaluation.

Key words: Activation analysis; crystal structure; diffraction; isotopes; molecular

dynamics; neutron; neutron radiography; nondestructive evaluation;

nuclear reactor; radiation.

DISCLAIMER

Certain trade names and company products are identified in order to adequately

specify the experiment 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 The Influence of Individual Reflections in Least Squares Refinement ... 1 The Structures of the Transition Aluminas and Their Precursors 3 Structure Studies of RHO Zeolites with Unusually Small Unit Cells .... 4 Studies of Zeolites RHO and ZK-5 Prepared Under Various Conditions .... 4 Structural and Magnetic Characterization of a New Layered

Antiferromagnetic Compound, LiFeMoO.Cl 5

The Crystal Structures of the Chevrel Phases Li„ „Mo,S and Li^ nMo^Se„. . 6

3.3 68 3.2 6 8

Powder Neutron Diffraction Study of Zirconium Titanates 7 Neutron Diffraction Study of Zirconium Palladium Deuteride, Zr PdD ... 9 A Neutron Diffraction and A/C Conductivity Study of Pb c Ta

p fi c

9 The Structures of Lithium Inserted Metal Oxides: Li c Ti0 o (Anatase),

. 5 2 LiTi

2 4 (Spinel), and Li Ti 0^ 11 Structure of Bovine Pancreatic Trypsin Inhibitor 12

The Pressure Dependence of the Barrier to Methyl Group Reorientation

in Sold Nitromethane 15

Crystallographic and Microstructural Characterization of Uranium Alloys . 18

Crystallographic Study of Polynitro-Bishomocubane 22

Simulation of the Initiation of Detonation in an Energetic Molecular

Crystal 25

Advanced Neutron Methods 31 Determination of Pore Accessibility in Silica Chromatographic Particles

by Small Angle Neutron Scattering 34

Analysis of Beam Broadening Sans Data from Alumina Powder 36

Theory of Incoherent Multiple Small Angle Neutron Scattering: Phase

Shift Dependence of the Single Particle Scattering 37

Small Angle Neutron Diffraction Measurements of Diblock Copolymer PSD-PMMA

in the Bulk and in Solution Near the Point 39

Network Structure of Partially Deuterated Epoxys from Neutron Scattering . 42

Neutron Cloud Points and Concentration Fluctuations of Polymer Blends . . 43

v
TABLE OF CONTENTS

Neutron Small Angle Scattering and Pole Figure Analysis of Crept

Copper Specimens 50

Neutron Diffraction Studies of Amorphous Alloys 53

Neutron Scattering Studies of the Magnetism in Cu-Mn Single Crystals ... 56

Neutron Scattering Study of the Amorphous Invar Alloy Fe _,B

h 59

Studies of the Oscillatory Magnetic State in the Superconductor HoMo,Se

ft

. 63

Spin Correlations and Dynamics in Dilute Magnetic Semiconductors 66

Spin Stiffness Anomaly in the Reentrant Spin Glass (Fe_.Ni . ) r7r.P. ,B C A1^ . 68

d\) oU [j lb 3

Magnetic Correlations in the Reentrant Spin Glass (Fe^Ji 0n ) ar P 1 ,B,A1_ . . 70

dv oO 75 l o b 3 Applied Field Response of the Spin Glass State in Amorphous NdFe .... 73

Sans Evidence for the Absence of Long-Range Magnetic Order in

Amorphous Fe Zr 74

y i y Inelastic Neutron Diffraction Studies of Zeolites 76

1 Phonon SofteningB in the Mixed Layered J System K„ Rb C„ 76

1-x x 8

Theory of Alkali Cyanides 77

Structure of Alkali Cyanide-Alkali Halide Crystals 78

Nondestructive Characterization of Subsurface Residual Stress in

Depleted Uranium 78

Study of Materials Subject to Impact 82

Spherical-Model Estimate of the Upper Bound for the Absorption of

Capture-Gammas in the Neutron Cold Source 83

Cold Neutron Source - DO 85

Search for Charge Density Waves and other Experiments on Potassium .... 86

Recent Advances in Neutron Optics 90

Nonlinearity in Weak Magnetic Fields Induced by Neutron-Antineutron

Oscillations in Neutron Interferometry and Spin Resonance 91

Crystal Data 93

Identification by Lattice Matching 95

Neutron Activation Autoradiography Study of Paintings 104

B. NON-RRD PROGRAMS 107

Activation Analysis Group: Overview 107

Biological Materials Analysis 108

Multielement Analysis of an Aquatic Accumulator 110

Comparative Irradiations at UVAR and NBSR 113

Nitrogen Concentration Distributions by Neutron Depth Profiling 114

vi
TABLE OF CONTENTS

High Accuracy Determination of U-235 by Gamma-Ray Spectrometry in

Nondestructive Assay Standards 118

Summary of Activities Carried Out by the Neutron Field Standards Group . . 120

Neutron Personnel Dosimeter Calibration and Testing 123

C. REACTOR OPERATIONS AND SERVICES 125

D. SERVICES PROGRAMS 127

Neutron Activation Analysis at the Food and Drug Administration 127

Preparation of F-18 Labeled Radiotracers Using NBS Reactor-Produced F-1 8 . 128

Neutron Capture Prompt-Y Activation Analysis 128

Atmospheric and Environmental Studies by Instrumental Neutron

Activation Analysis 130

A Compton Profile Experiment in Graphite 137

E. PERSONNEL ROSTER 1 Hi

F. PUBLICATIONS 1 48

vii

A. Reactor Radiation Division and Collaborative Programs

THE INFLUENCE OF INDIVIDUAL REFLECTIONS IN LEAST SQUARES REFINEMENT

E. Prince

and

W. L. Nicholson

(Pacific Northwest Laboratory, Richland, WA)

The solution of a crystal structure is divided into two separate stages that

may be called determination and refinement. Although least squares methods are used

in both stages, it is only in the refinement stage that the statistical properties of

least squares are significant. Drawing an analogy with a mathematically simple

problem, determination corresponds to finding that a set of observations may be

described by a linear function of some experimental variable, whereas refinement

corresponds to precise determination of the values of the two parameters of that

linear function. Determination that the function is linear requires observations for

many values of the variable, but refinement is best achieved by careful measurements

at the extremes of the accessible values of this variable.

To extend this principle to the multiparameter, non-linear models found in

crystal structure analysis require some mathematical development. Designate by A the

matrix with elements A.. = [3M. (x)/Sx .]/o . , where M.(x) is the model function for the

ith observation and o. is its standard deviation. Let y be the vector of

i T -1 observations. The least squares estimate of x is x = (A A) Ay, and the

uncertainties of the elements of x are described by a variance-covariance matrix V = T -

1

(A A) . If V is the variance-covariance matrix after n observations, and z is a

n row vector corresponding to the n + 1 st row of A, the updated variance-covariance

T T matrix after one more observation can be shown to be V , = V - V z zV /(1+zV z ).

T

n+1 n n n n Tnus, the diagonal elements of the matrix V z zV /(1+zV z ) are the amounts by which

n n n the n + 1 st measurement will reduce the variance of the corresponding elements of x. In the Single Crystal Intensity Project of the International Union of

Crystallography, Hamilton and Abrahams refined the structure of D( + ) tartaric acid

using ten different data sets collected by different laboratories, and found that the

spread in values of refined parameters generally greatly exceeded what would be

expected from the computed standard deviations. In their study, however, the

standard deviations, o., of the observations were not known, and were somewhat

arbitrarily set to 0.1 |F |. The belief was that this would produce weights that were approximately correct except for a scale factor that could be estimated from the

overall goodness of fit, and that the reflections that departed from this would be
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

6.4 6.6 6.8 7.0

F

obs<

711 >

7.2 7.4 7.6

Figure 1. The value of B for atom 0(3) in D(+) tartaric acid, plotted against the

value of IF I of the 711 reflection for five different experiments. the

determination of this parameter is dominated by this single reflection.

few in number and would not badly distort the refinement. A study of the influence

of individual reflections on the various parameters has shown, however, that many

parameters are determined by small sets of weak reflections whose standard deviations

are underestimated in the weighting formula used. An extreme case is shown in Figure

1. here the value of B of atom 0(3) is plotted against the value of |F | for the

711 reflection, corrected for extinction. The two are strongly correlated: this

single reflection has a dominant influence on the determination of this parameter in

these five experiments.

1. W. C. Hamilton and S. C. Abrahams, Acta Cryst. A26, 18 (1970).
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE STRUCTURES OF THE TRANSITION ALUMINAS AND THEIR PRECURSORS

S. Kim and R. L. Snyder

(Alfred University, Alfred, NY)

and

E. Prince

The transition aluminas are a series of hydroxyl and microstructure stabilized

materials which result from heating gibbsite, bayerite or boehmite. They are not

true polymorphs of Al but rather contain varying amounts of residual hydroxyl

ions. The hydroxyl concentration, equivalent to a loss on ignition, ranges from more than 10% for "amorphous alumina" to less than \% for the best crystallized high

temperature phases like Theta and Kappa. The final high temperature product is the

irreversible transformation to alpha alumina.

The low temperature products are often called activated aluminas in that they

have high surface activity and very large specific surface areas. These materials

are of high technological importance being widely used as catylitic substrates.

On heating the trihydroxides of aluminum, proton migration occurs, allowing the

formation of water, which vaporizes. The resulting structure , and the role of the

remaining hydrogens in stabilizing it, is unknown. It is reasonable to speculate

that the layers A1(0H), octahedra lose their interconnecting hydrogen bonds first,

which induces the observed fine cracking in the material. In the first stage of

heating the structurally ordered regions are on the order of 100 A across, rendering

the material x-ray amorphous. Diffusion and ion rearrangment follows, increasing the

size of the structurally ordered regions. The reordering takes place within the

framework of the original hydroxide crystal, and thus the starting material helps

determine the structure at any subsequent temperature.

Structural information is desired on these materials because of their

technological importance. However the minimal effect of hydrogen scattering on x-ray

diffraction patterns has resulted in no information on the role of hydrogen in

stabilizing these structures.

This investigation will look at each of the three aluminum hydroxides and the

various transition products both in their hydrogen and deuterium forms using neutron

diffraction. The pattern fitting Rietveld method will be used to structurally

characterize these phases. Preliminary patterns of bayerite and eta alumina indicate

that significant new information can be obtained from neutron powder diffraction.

Analysis is continuing.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STRUCTURE STUDIES OF RHO ZEOLITES WITH UNUSUALLY SMALL UNIT CELLS

R. X. Fischer and W. H. Bauer

(University of Illinois at Chicago, Chicago, IL)

and

P. B. Parise, L. Abrams, T. Gier, D. Corbin, R. D. Shannon and G. D. Stucky

(E. I. DuPont de Nemours and Co., Wilmington, DE)

and

E. Prince

Dehydrated ND4-rho and Li-rho have been prepared with unit cell dimensions of

14.425(1) A and 14.492(1) at 11 K (neutron refinement results). These are among the

smallest cell constants determined for zeolite rho, substantially less than that

previously determined for dehydrated H-rho at the same temperature (14.65 A).

Structural refinements are being carried out in order to determine the frameworkcation interactions responsible for the small unit cell.

STUDIES OF ZEOLITES RHO AND ZK-5 PREPARED UNDER VARIOUS CONDITIONS

R. X. Fischer and W. H. Baur

(University of Illinois at Chicago, Chicago, IL)

and

L. Abrams, D. Corbin, T. Gier, R. D. Shannon and G. D. Stucky

(E. I. DuPont de Nemours and Co., Wilmington, DE)

and

E. Prince

Powder diffraction measurements were made on dehydrated samples of H-rho and

ZK-5 prepared with calcination at 500°C and 650°C in such a way as to maximize the

removal of framework aluminum atoms. Two phases were found in the data refinement

for the sample of H-rho (500°C) with cell constants of 14.49 A and 14.637(1) A, 143m.

H-rho (650°C) at 1 1 K shows an unusually large unit cell of 14.850(1) A, Im3m.

H-ZK5 (500°C) has a structurally well-characterized phase, a = 18.631(2) A,

Im3m. H-ZK5 (650°C) is predominantly amorphous with the crystallographic phase

having a = 18.440(7) A, Im3m.

The detailed structural reasons for the differences produced in the framework

structure with calcination temperature are being studied.

M^H^BHBB^^^H
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STRUCTURAL AND MAGNETIC CHARACTERIZATION OF A NEW LAYERED

ANTIFERROMAGNETIC COMPOUND, LiFeMoO^Cl

C. C. Torardi

(E. I. du Pont de Nemours and Co., Wilmington, DE)

and

E. Prince

Recently, the structure and magnetism of the new two-dimensional

ant if erromagnet Fe(III )MoO^Cl was described. In summary, FeMoOXl has a layered

structure consisting of sheets of corner-sharing FeO.Cl square pyramids, site

symmetry C^v, bridged by MoO. tetrahedra in tetragonal space group P4/nmm.

Intralayer exchange leads to a broad 2D maximum in the magnetic susceptibility

centered at 105 K while Mossbauer spectra confirm extended 3D antiferromagnetic

ordering with a Neel temperature of 69.2 K. The reaction of Fe(III)MoO^Cl with Lil in acetonitrile (under inert atmosphere)

yields LiFedDMoCvCl. This reversible reaction proceeds by a redox intercalation

mechanism. MQssbauer spectra confirm the essential purity of this new phase and

complete stoichiometric reduction of Fe(III )MoO^Cl. x-ray powder diffraction data

show that the new lithium intercalate is related to the starting tetragonal phase but

possesses monoclinic symmetry. The Mossbauer parameters are consistent with fivecoordinate, high-spin Fe(II) centers. LiFeMoO^Cl has virtually the same 3D ordering

temperature (68.5 K) as its precursor consistent with preliminary x-ray results that

indicate a decrease in the interlayer spacing. The new lithium intercalate is also a

2D antiferromagnet but with somewhat weaker intralayer exchange than its precursor

2

(i.e., the maximum in the magnetic susceptibility is centered at 73 K)

.

In order to further characterize the structure of this novel layered

antiferromagnetic intercalate (i.e., locate the lithium ions), room temperature

neutron powder diffraction data have been collected and a structural refinement is

currently in progress. If successful, a low temperature data set should give

additional magnetic information.

1. C. C. Torardi, J. C. Calabrese, K. Lazar, and W. M. Reiff, J. Solid State Chem.

51, 376 (1984).

2. C. C. Torardi, K. Lazar, and W. M. Reiff, presented at the 1983 ACS National

Meeting in Washington, D.C.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE CRYSTAL STRUCTURES OF THE CHEVREL PHASES Li J\oc SQ and Li„ Mo.Se

5. ioo 3-2 o o

R. J. Cava and J. W. Tarascon

(Bell Laboratories, Murray Hill, NJ)

and

A. Santoro

The large class of ternary molybdenum chalcogenides of formula M Mo,X

y 6 8

(M = metallic element, <_ y <_ 4, X = S, Se, Te) has been of great interest due to

unusual superconducting properties and extensive chemical variety of accommodation

for the "ternary element" M. The basic structural building blocks are Mo,XQ clusters

o o consisting of eight X atoms forming the corners of a cube around the octahedron of

six Mo atoms located near the cube face centers. The ternary elements are located

between the Mo,x o clusters in positions which are on the line of the cluster cube DO

diagonals (large M atoms), or displaced in sets of concentric rings centered about

the cube diagonal (small ions). The small M ions may either be ordered or disordered

in the rings.

We have employed neutron diffraction powder profile analysis to determine the

crystal J structures of the Chevrel phases y Li_ Mo £ S and Li„. Mo^Se . The Mo,-X 3.368 3-268 68

cluster geometries are quite similar to those found in other compounds of this type,

and the lithium atoms are randomly distributed over the inner and outer ring sites as found in other small ternary element phases. The lithium atoms show a strong

preference in both compounds to occupy the outer ring sites. The Cu Mo^Sft compounds

also show a tendency to occupy the outer ring for large values of X, but to a much

smaller degree. The geometry of the inner ring in Li_ _Mo r Se Q is similar to those

5 . <L D o found in other small ternary element phases but the inner ring in Li_ Mo

fi Sft has a unique puckered configuration.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

POWDER NEUTRON DIFFRACTION STUDY OF ZIRCONIUM TITANATES

P. Bordet

(C.N.R.S., Grenoble, France)

and

A. McHale

(Imperial College of Science and Technology, London, England)

and

A. Santoro

and

R. S. Roth

(Inorganic Materials Division)

Zirconium titanate exists in a number of modifications. The pure compound,

ZrTiO^, gives a disordered aPbO -like phase when quenched in water from temperatures

above -1150°C, while a modulated structure is obtained by slow cooling from

temperatures below 1150°C. With the addition of impurities, such as ~\% of Y _, the

compound Zr-Ti^Oo,. is formed. This phase is orthorhorubic with the a-axis about

three times that of the pure compound quenched in water. We have analyzed so far two

phases of zirconium titanate with the neutron powder technique and the Rietveld

method. Some of the results are briefly described in what follows.

ZrTiO. Quenched in Water

Lattice parameters measurements indicate that this form may be isomorphous with

ixiolite (space group Pbcn, general formula M0

?

, and Z = 4). In this model Zr and Ti

must be completely disordered in the 4c2 positions, i.e.,

M = (1/2) Zr + (1/2) Ti

A refinement with the initial parameters of ixiolite gave R. T = 14.07, R D

= 7.54, R = N r W 9.61, and R = 5.01. Although these results indicate that the structure is basically

hi disordered, the rather high value of R may reflect a slight ordering of the metal

atoms. Refinements were therefore attempted using models in which partial or total

ordering of the Zr and Ti atoms is possible.

In the first of such refinements the structure was assumed to be isomorphous

with woolframite (space group P2/c, general formula ABOj., and Z = 2). For this case

A = xZr + (0.5-x) Ti

B = (0.5-x) Zr + x Ti < x < 0.5
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

with A and B in positions 2e2. Results show that the best agreement is obtained with

x = 0.5, i.e., with a completely disordered structure, and no improvement with

respect to the first refinement was obtained.

Refinements were also carried out using a model isomorphous with tantalite

(space group Pbcn, general formula AB^O^ , and Z = 4). It is easy to show that, in

2

this case

A = xZr + (1-x) Ti

B = (0.75 - -|) Zr + (0.25 + |-) Ti <_ x <_ 1 .0

and with A in positions 4c2 and B in positions 8d1 . Here again, the best agreement

was obtained for the disordered structure (x = 0.5).

One last possibility is a model isostructural with wodginite (space group C2/c,

general formula ACBo , and Z = 4). We may write for this case

2 o 2ZrTiO„ * (Zr Ti, ) (Zr Ti, ) (Zr Ti, ) o and

4 x 1-x y 1-y z 1-z 8

A = xZr + (1-x) Ti

C = yZr + (1-y) Ti

B = [1-(x+y)/2]Zr + [(x+y)/2]Ti

where ^ x <_ 1 .0, <_ y £ 1 .0, and <_ (x+y) <_ 2.0.

These refinements are not yet complete, but the indication is that the structure does

not have any wodginite-type of ordering.

Zr-Ti^O.,, With Slow Cooling

5 I c"t Lattice parameters and peak intensities indicate that this compound is

isostructural with tantalite. Remembering the general formula AB 0, we have

A = xZr + (1-x) Ti

B = (0.625 - x/2) Zr + (0.375 + -|) Ti <_ x <_ 1.0

The best agreement between calculated and observed intensities was obtained for x = 1.0, with R„ - 10.05, R n

= 7.40, R„ = 9.35, and R^ = 4.49. The structure is

N P W E completely ordered. The crystallochemical features of this structure are still being

analyzed.

H^H
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON DIFFRACTION STUDY OF ZIRCONIUM PALLADIUM DEUTERIDE, Zr PdD

A. Santoro

and

A. J. Maeland

(Allied Corporation, Morristown, NJ)

Zr Pd which has the tetragonal MoSi structure, reacts readily with hydrogen at

room temperature to form hydrides (Maeland, J. Less-Common Met. (1983), 89_, 1 73— 1 82)

.

There are several potential interstitial sites for hydrogen in the MoSi structure.

We have used neutron diffraction to establish which sites are occupied. Three

compositions were studied Zr.PdD, Zr PdD, „. , and Zr„PdD, _ . The structures were

2 <l i . (\ c \ . yts refined by the method of total profile analysis of the neutron diffraction powder

patterns. The D atoms are located at the center of distorted tetrahedra of Zr atoms

in all these samples. The results for Zr PdD are representative. Space group

14/mmm, Z = 2, a = 3.3208(2)A, c = 1 1 .606(1 ) A. The atomic coordinates are: Pd at

000 (2(a) positions), Zr at OOz (4(e) positions) with z = 0.3565(2) and D at 1/2

1/4 (4(d) positions). Temperature factors were 0.4 for Pd and Zr and 1.0 for D.

Final R factors: R„ = 9.53, R = 7.11, R = 9.06, and R^ = 5.80.

N p w E

A NEUTRON DIFFRACTION AND A/C CONDUCTIVITY STUDY OF Pb, Tan0, c 1.5 2 D.5

F. Beech and C. R. A. Catlow

(Department of Chemistry, University College London, London, U.K.)

and

A. Santoro

and

B. C. H. Steele

(Department of Metallurgy & Materials Science, Imperial College, London, U.K.)

There has been considerable interest in recent years in defective pyrochlore

structured compounds. This class of compounds of general formula ABO, has an anion deficient fluorite structure with an ordered cation arrangement. Much of the

interest in these materials is due to their high oxygen ion conductivities. The

present study concerns a particularly intriguing defect oyrochlore, Pb, Ta 0, 1.5 2 0.5

This compound has been the subject of previous investigations which have left

unresolved the questions relating to the composition width, and the defect structure

of the material. These problems were examined in the present study carried out by

powder neutron diffraction and by electrical conductivity measurements.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The neutron intensity data were analysed using the Rietveld profile refinement

techniques. All peak shapes (including those at low angle) are accurately Gaussian,

making use of the Rietveld technique appropriate. The refinement assumed a defective

pyrochlore structure (space group Fd3m) with Pb vacancies on the 1 6d sites and oxygen

vacancies on the 8(a) sites. Occupation numbers of Pb and oxygen 8(a) sites were refined as were the temperature factors. Unlike an earlier x-ray study, separate

temperature factors were used for the two types of oxygen sites.

The following results of the refinements deserve note:

(i) The refined occupation numbers are very close to those expected for 50

percent vacancies on the oxygen 8(a) sites and 28 percent vacancy on the Pb sites.

(ii) The temperature factors for Pb and more specially the oxygen 8(a) sites

are high suggesting a considerable static displacement around these sites.

(iii) In contrast, the temperature factors for the Ta and oxygen (48f) sites

are normal suggesting that these sites are not strongly perturbed by the introduction

of vacancies.

We should also note that refinements were attempted with different Pb and

oxygen 8(a) occupation numbers and with these atoms displaced from these sites. In

every case, a higher R-f actor was obtained thus underpinning the stoichiometry of the

phase and also illustrating that while static displacements of the lead and oxygen

ions are observed no coherent long range displacements exist.

A key factor in causing the small composition width of this highly defective

phase may be the stabilization of anion vacancies by the bone pairs on the

2+

neighboring Pb ions.

10

IBB
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE STRUCTURES OF LITHIUM INSERTED METAL OXIDES: Li .JT i0 o ( ANATASE ) , LiTi„0„

(SPINEL), AND Li Ti 0.

P. J. Cava, D. W. Murphy, and S. Zahurak

(Bell Laboratories, Murray Hill, NJ)

and

A. Santoro

and

R. S. Roth

(Inorganic Materials Division)

Transition metal oxides with tunnel or framework structures have been

investigated extensively as hosts for lithium insertion at room temperature.

Compounds based on TiO provide a variety of such structures having related chemistry

and different host geometries. Both the Brookite and Rutile forms of TiO react with

only small amounts of Li. In contrast, the Anatase and TiO (B) forms have been found

to react extensively, to about .7 Li/Ti, on reaction with n-BuLi, or on

electrochemical insertion of Li. The host structure of Anatase is originally

tetragonal and becomes orthorhombic on Li insertion. The product, Li ._Ti0 o , is

obtained on reaction of n-BuLi with Anatase under mild conditions, and on heating to

450-500°C transforms from the orthorhombic phase to a cubic phase with a crystallographic unit cell and electrical properties identical to those of the

LiTipOj. phase synthesized at high temperatures. Reaction of this cubic phase LiTi 0^

with n-BuLi results in the accommodation of additional lithium, to a stoichiometry of

Li Ti

p0^, with only a small change in the cubic unit cell dimension.

In this report we elucidate the results of our structural studies of the

compounds Li ,_Ti0 o (anatase), of the LiTi o0„ cubic phase prepared by heating Li _TiO_

above 450°C, and of the Li Ti 0, product obtained by lithiation of the cubic LiTi 0.

phase at ambient temperature. The structures of all three phases were determined by

neutron diffraction powder profile analysis, as single-crystal of these materials are

not available.

We have found that the inserted Li ions occupy partially the octahedral

interstices in the highly distorted CCP oxygen array of Anatase TiO . Within those

interstices, their coordination is closer to 5 than to 6 fold, and their addition to

the structure decreases somewhat the distortion of the host. The limiting

stoichiometry of .7 Li/Ti is, therefore, not due to the number of available

interstitial sites (there is 1/Ti) but rather must be related to the strong mutual

interactions of the ions occupying those 'Sites. Further, we have found that the

11
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

distortion from tetragonal to orthorhombic is due to the formation of zig-zag chains

of Ti-Ti bonds, and that the non-metallic resistivity of the Li-anatase can be

attributed to localized electrons. On heating above 450°C, the compound becomes

electrically conductive, the structure changes to a spinel type LiTi 0. with the

coordination of Li changing from 5 to 4 fold. In this phase of the bonding is very

regular and the anion array is distorted only slightly from ideal CCP. The LiTi

?0u

phase formed at elevated temperatures has been assumed in the past to have the spinel

structure without direct confirmation until this time.

On further lithiation of the LiTi 0^ phase at ambient temperature, the lithium

is displaced and vacates completely the tetrahedrally coordinated interstices and

fills the octahedrally coordinated interstices of the TiO host to a stoichiometry of

Li o Ti o 0„ . This radical change in Li site occupancy explains the large drop in EMF

observed in the electrochemical insertion of Li into LiTi a

. The structure of

Li Ti 0. may be thought of as an ordered rocksalt type, with the CCP oxygen array

insignificantly distorted from ideal and the cation-oxygen bonding quite regular.

STRUCTURE OF BOVINE PANCREATIC TRYPSIN INHIBITOR

A. Wlodawer

(National Bureau of Standards, Gaithersburg, MD)

and

(National Institute of Arthritis, Diabetes, Digestive and Kidney Diseases,

Bethesda, MD)

and

L. Sj61in

(Chalmers Institute of Technology, Gothenburg, Sweden)

and

J. Walter and R. Huber

(Max-Planck-Institute of Biochemistry, Martinsried, West Germany)

The structure of deuterated crystals of form II of BPTI (space group P2 2 2 , a=74.1A, b=23. iJA, c=28.9A) has been refined using x-ray diffraction data extending to

1.0A, as well as 1.8A neutron diffraction data, x-ray intensities were collected in

Munich using standard dif f ractometry (Walter and Huber, 1983). The number of

observed x-ray intensities used in the refinement was 17,615. Neutron diffraction

data were collected from a large crystal (volume ~ 8mm ) which was deuterated by slow

exchange of its mother liquor for 3 months. The flat-cone diffractometer at NBS was used for the neutron data collection and each reflection was measured at least three

times, with a complete data set requiring about four months of instrument time. The

12
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

reflection intensities were integrated using a dynamic mask procedure (Sjolin and

Wlodawer, 1981). Symmetry R factors ranged from 0.048 for lower levels to 0.126 for

the level k=10, while the scaling R factor for the flat-cone and equatorial data was

0.076. The total number of unique observed reflections was H0HH (78% of the

theoretical maximum), with over half of the reflections observed in the shell at

1 .82A resolution.

Joined restrained refinement using both types of data utilized the procedures

of Wlodawer and Hendrickson (1982). Computer graphics were used between refinement

cycles to make larger corrections to the model. The R factors for the final model

were 0.200 (x-ray) and 0.197 (neutron). The bond lengths differed from the ideal

values by 0.02A, the departure from planarity was 0.01 9A, and the chiral volumes

3 differed by 0.232A . We were able to place almost all hydrogens, including the

methyl rotors, which were uniformly found in staggered conformations. We found that

1 1 out of 54 amide hydrogens were protected from exchange during the course of the

experiment. Nine of the protected hydrogens were involved in forming B~sheet

hydrogen bonds, one made a hydrogen bond to a side chain, while protection of Gly37

was caused by its interaction with the ring of Tyr35 (Figure 1). This type of

Figure 1 . Diagram of hydrogen bonds involving the main-chain atoms and the level of

protection of amide hydrogens. Only bonds shorter than 3.15 A and with expected

angles are shown. Filled circles correspond to protected amide hydrogens.

13
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

protection has not been previously reported in the literature. The agreement between

the extent of hydrogen exchange observed in this study and the 2-D NMR results of

Wagner and WUthrich (1982) is excellent, offering the first independent confirmation

of the latter technique.

The presence of neutron diffraction data allowed us to reconsider the

orientation of the side chain of Glu31 , to place the deuteriums in hydroxyls of side

chains such as theonines, tyrosines and serines, and contributed to the correct

placement of the two residues at the carboxyl terminus of the protein, which were not

visible in the initial x-ray maps.

The comparison of the new model with that for crystal form I shows r.m.s.

deviation between equivalent main chain atoms at . 4A . Deviations exceeding 0.5A

were observed near both termini, at the alpha carbons of Lys15, Lys26, Leu29, and in

stretches of residues 16-19, 39 _

41 , and 47~50. These deviations are most probably

due to crystal packing forces and their analysis should lead to better understanding

of the reasons for reported discrepancies between the crystallographically refined

structures of proteins and between the structures which were energy minimized.

The analysis of solvent structure yielded 63 ordered water molecules and one phosphate group. Half of the solvents have full occupancy, while the least occupied

solvent sites which could be assigned above the noise level contained about 0.4 water

molecules. It is clear that the analysis of solvent is in need of further

improvement

I.J. Walter and R. Huber, J. Mol . Biol., 167 , 911 (1983).

2. L. SjOlin and A. Wlodawer, Acta. Cryst., A37, 594 (1981).

3. A. Wlodawer and W. Hendrickson, Acta. Cryst., A_3_8, 239 (1982)

4. G. Wagner and K. WUthrich, J. Mol. Biol., 160, 3^3 (1982).

14

^M
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE PRESSURE DEPENDENCE OF THE BARRIER TO METHYL GROUP REORIENTATION

IN SOLID NITROMETHANE

S. F. Trevino

(Energetic Materials Division, AMCCOM, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

and

A. Magerl and D. Cavagnat

(Institute Laue-Langevin, Grenoble, France)

Nitromethane in the solid state has proven to be a prototypical system for the

study of the properties of the barrier to rotation of a molecular group. In one

sense it is the simplest system available for such studies since it consists of a single one-dimensional rotor with the same crystallographic phase for both the

protonated and deuterated species from the melt to 4.2°K, thus making the

interpretation of spectroscopic results relatively straightforward. On the other

hand, it has proven quite interesting and less than simple in that a simple potential

has not been found which explains entirely the measured level scheme, and the

measured activation energy for thermally activated notation of the methyl group.

1 In previous work the crystal structure and several dynamical properties of

both the protonated and deuterated species have been measured. In particular, the

crystal structure investigation has determined there is one formula unit in the

asymmetric unit leading to but one potential of three-fold symmetry hindering

reorientation. Since the barrier to re-orientation due to intramolecular

2 interactions is extremely small , the barrier observed in the solid will be dominated

by intermolecular interactions. The dynamical properties which had been determined

for the protonated isotopic species included the activation energy for thermally

activated reorientation, and for both isotopic species the quantum mechanical tunnel

splitting of the ground state and the position of the first excited state. The

present work was motivated as an attempt, by the application of pressure, to change

the position of the first excited states with respect to the top of the barrier

thereby changing their width in order to confirm the assignment.

The measurements of the pressure dependence of the first excited state of

CH NO were performed with the triple axis spectrometer located at BT4 of the NBS

research reactor. The instrument was configured to produce 1 meV resolution at an energy transfer of 7 meV. The pressure transmitting medium was He gas. The sample

3 container was cylindrical of dimension 2.4 mm interior diameter and 7.9 mm outside

diameter and was connected to the intensifier by a small capillary. A manganin gauge

15
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

4 5 6 7 8 9 10

E (meV)

Figure 1. Inelastic neutron scattering spectrum of CH NO at 4.2K and various

pressures

was used to measure the pressure which was applied before the sample was cooled to

4.2°K. A survey run ( 4 . 4^AE^1 il meV) with the sample pressurized to 4.8 Kbar showed

that no prominent features in the spectrum existed above 10 meV. Subsequent data was obtained only in the energy region from 4.4 to 10 meV. The results of the various

measurements are presented in Figure 1 . Our interpretation of the features exhibited

there is as follows. The peak at lower energy which moves from - 6.6 meV at ambient

pressure to 5.8 meV at 4.8 Kbar is due to the unresolved first excited states. The

higher energy feature at 7.8 meV which does not shift with pressure is assigned to a density of phonon states. We are led to this assignment due to: (a) a correct

assignment by a Raman study of the torsion mode to 6.6 meV at ambient pressure (as

opposed to our previous assignment to 6.6 and 8.4 meV); (b) the fact that this peak

is the most pressure dependent; and (c) a feature at ~ 7.8 meV in the spectrum of

1 CD NO which is clearly due to phonon density of states . We are left, however, with

a negative Gruneisen constant implying a lowering of the barrier with pressure.

An additional measurement which yields information concerning the barrier is

the tunnel splitting of the ground state. These measurements were performed at the

16
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

4.2Kbar

10 25 40 55

Energy (/*eV)

Figure 2. Inelastic neutron scattering spectrum of CH NO at 4.2K and various

pressures.

research reactor at the ILL. Figure 2 presents the results of these measurements as

a function of pressure. Note that the tunnel splitting increases with increasing

pressure, an effect opposite to that observed in all previous studies of the pressure

5 dependence of tunnel splitting in other systems . A search for a potential of the form

V V,

V (4) = 2

3

(1 - cos 3 <fr) + 2(1 - cos 6 <j>) which would explain this data resulted in the following values for V and V

fi

. At lb on. V = 26 meV, V

fi = 10.25 meV which produced a ground state splitting of 33 peV and

a first excited state at 7.2 meV in very good agreement with observations. At

4.8Khar, V = 26 meV and V

fi = 14.5 meV resulting in a ground state splitting of 45

peV and a first excited state at 5.8 meV. This potential correctly reproduces the

behavior of the energy levels with pressure. It also, however, predicts a second

bound level at -16.5 meV. A search for such a level was conducted using the time-offlight instrument at ILL at a temperature of 4.2K . In addition to the peaks at 2

meV due to the first excited state, there was found one at -18 meV which is assigned

to the bound search excited state predicted by the model.

17
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

We have now to explain an activation energy to thermally activated rotation of

-10 meV, substantially less than the barrier height of -24 meV predicted by the

single particle potential which so successfully explains the measured level scheme

and its pressure dependence. This phenomena, using an activation energy lower than a bound state is not unknown. It is a common occurrence in hydrogen in metals. The

mechanism of "phonon assisted tunneling" is invoked, in which a cooperative motion of

the metal atom when a phonon is thermally activated results in relaxing the cage

surrounding the hydrogen such as to enhance diffusion. A similar mechanism must be

at work in this system and to our knowledge it is the first instance of rotating

molecular groups exhibiting such behavior.

1. S. F. Trevino, J. Chem. Phys. 21_, 1973 (1979); S. F. Trevino, C. Hubbard, and E.

Prince, ibid. 23, 2996 (1980); S. F. Trevino and W. H. Rymes, ibid. 73, 3001

(1980); B. Alfeld, I.S. Anderson, A. Heidemann, A. Magerl, and S. F. Trevino,

ibid. 26, 2758 (1982)

2. E. Tannenbaum, R. J. Myers, and W. D. Gwinn, J. Chem. Phys. 25, 42 (1956)

3. We thank W. B. Daniels for providing the high pressure sample cells.

4. D. Cavagnat, J. Lascombe, J. C. Lassegues, A. J. Horsewill, A. Heidemann, and J.

B. Suck, J. Phys. 45 (1984)

5. J. Eckert and R. Youngblood , Solid State Comm. 4_4, 1393 (1982); M. Prager, W.

Press, A. Heidemann and C. Veltier, J. Chem. Phys. 77, 2577 (1982); J. Eckert, C.

R. Fincher, J. A. Goldstone and W. Press, J. Chem. Phys. 75_, 3012 (1981); S.

Clough, M. Paley, A. Heidemann and C. Veltier, J. Phys. C 12, L781 (1979);

CRYSTALLOGRAPHIC AMD MICROSTRUCTURAL CHARACTERIZATION OF URANIUM ALLOYS

C. S. Choi and H. J. Prask

(Energetic Materials Division, AMCCOM, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

Alloys of uranium can be produced which possess a variety of mechanical

properties ranging from very soft, low strength materials to extremely hard, high

strength materials. The crystallographic and microstructural properties of depleted

uranium alloys (0.75 wt. % Ti) with two different heat-treatments, "depleted uranium

as cast" (DUAC) and "depleted uranium with heat treatment" (DUHT), were studied by

neutron powder diffraction methods. The pole figures of both DUAC and DUHT samples

18
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS '

Table 1 . Structural Parameters of DUHT and DUAC Compared with Those

of Pure Uranium

(a) Cell dimensions (space group Cmcm)

Sample DUHT DUAC

a(A) 2.8610(1 ) 2.8574(1)

b(A) 5.8234(2) 5.8537(2)

c(A) 4.9736(2) 4.9640(2)

Oo

V(A^) 82.86(1) 83.03(1)

Pure-U (q-U ) (Cooper , 1962)

2.85373(5)

5.87010(6)

4.95573(6)

83.017(1

)

(b) Positional Parameters

Sample

x

y

z

DUHT DUAC

0. 0.

0.1028(1 ) 0.1025(1 )

0.25 0.25

Pure-U (a-U) (Lander, et al 1970)

0,

0.1027(3)

0.25

(c) Bond lengths and angles of the corrugated layer

Sample

zig-zag bonding

a-axis bonding

zig-zag angle

DUHT

2.760(1 )

2.8610(1 )

128.6(1)

DUAC

2.757(1)

2.8574(1

)

128.4(1

)

Pure-U*

2.756

2.8537(1 )

128.1

*based on Cooper's cell and Lander et al.'s positional parameters

19
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(d) Inter-layer atomic distances

Sample DUHT DUAC Pure-U

primary distance 3-2M4K2) 3-2569(2) 3-2635

secondary distance 3-342(1) 3-344(1) 3-342

2 2

(e) The coefficients of the width function H = U-tan 6 + V»tan9 + W, where

H is in 0.01 ° unit.

Sample DUHT DUAC

u 7619(295) 4372(163)

V -4274(271

)

-3582(116)

w 1980(80) 1736(43)

20
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

12000

Strain Broadening of DUHT

60 80 100

60 80 100 120

Scattering Angle (Degrees)

140

140

Figure 1. The strain broadening of DUHT as a function of scattering angle.

The observed broadening [H (DUHT) - H (DUAC)] are indicated by

the circles., and the predicted broadening curve after the leastsquares fit by the solid line.

showed no evidence of systematic texture. The neutron diffraction patterns of the

polycrystalline samples were measured with the high-resolution powder dif fractometer

using 10', 20', 10' collimat ions. To eliminate local texture or coarse grain

effects, the samples were spun constantly at 1 r.p.m. during the measurements. The

crystal structures, lattice parameters, and the coefficients of the width function

were refined by Rietveld's profile refinement method. The residuals, Rwp, Re, and R

D

were 9.256, 1.2%, and 3.9% for DUHT and 8.H%, 6.9$, and 3-0$ for DUAC. The results

are summarized in Table 1 . The crystallographic structures of DUAC and DUHT are essentially the same as that of pure uranium. However, the unit cell dimensions are quite different. The

deformation of the DUHT cell (from the pure uranium) is much larger in magnitude but

very similar in deformation mode to DUAC, which is attributed to the super-saturated

Ti impurities in the lattice. A comparison of the unit cell volumes suggests that

the Ti impurity in DUHT is mostly of the substitutional type.

Residual Stress Analysis by Width Function

2 The width function, H(0) = Utan + VtanO + W, obtained from the DUHT sample

was much broader than, but that of DUAC was in reasonable agreement with, those of

standard samples (e.g., A1

? 0^ or Cu powder). Therefore, it is assumed that the width

function of the DUHT is a convolution product of three Gaussian functions:

21
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

instrumental resolution, strain distribution, and particle size distribution. Using

the width function of the DUAC for the instrumental resolution, the r.m.s. strain

1/2 <e> and the particle size dimension L for the DUHT were determined by a non-linear

least squares refinement of the broadening function, AH: AH

2

= (TT/2)-<e>

1/2

(4 tanO)

2

+ [A/(L cos 0)]

2

where AH

2

= H

2 (DUHT) - H

2 (DUAC).

Tne results were <e>

1/2

= 0.00188(1) and L = 1.2 (9) x 10 A. The observed and

calculated width functions are shown in Figure 1

CRYSTALLOGRAPHIC STUDY OF PQLYNITRO-BISHOMOCUBANE

C. S. Choi

(Energetic Materials Division, AMCCOM, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

There is considerable current interest in the synthesis and chemistry of

strained energetic compounds. Polynitropolycyclic compounds are potential members of

this important class. However, very few nitro-containing polycyclic "cage" compounds

have been synthesized. This report consists of two independent studies for the newly

synthesized compounds: the crystal structure determination of trinitrobishomocubane, and the crystal structure determination of tetranitro-bishomocubane.

1 . The crystal structure of trinitro-bishomocubane

H. L. Ammon, C. S. Choi, 0. Sandus, A. P. Marchand, and S. C. Suri

The space group determination was made on the basis of precession photographs,

from which a monoclinic P2 structure with a = 9.349(4), b = 7.400(3),

o

I c = 1 6 . 007 ( 1 ) A , 6 = 97.78(4)°, and four molecules per cell were obtained. The

3 crystal density, based on the x-ray unit cell, is 1.61 g/cm . The crystal structure

was determined from 1339 reflection intensities measured by single crystal x-ray

diffraction. The molecular structure is shown in Figure 1 . The carbon cage of the

molecule consists of four puckered 5-membered rings and two 4-membered rings. The

average bond lengths and bond angles are summarized in Tables 1 and 2. The structure

will be discussed later, comparing with that of tetranitro-bishomocubane.

2. The crystal structure of tetranitro-bishomocubane

C. George, R. Gilardi, J. Flippen-Anderson, C. S. Choi, A. P. Marchand, and

D. S. Reddy

22

HH
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The preliminary study of the crystal symmetry by precession photographs

indicated that the space group is monoclinic, Pc or P2/c, with a = 7-761(1),

b = 11.500(2), c = 14.277(2), 3 = 108.63(2), and four molecules per unit cell. The

3 density calculated from the unit cell data is 1 .72 g/cm . The non-centrosymmetric

space group Pc was proven to be correct by the final crystal structure determination.

There are two crystallographically distinct molecules in the crystal, which we designate as molecules A and B. The ORTEP drawings of the molecules are given in

Figure 2. The average bond lengths and angles are summarized in Tables 1 and 2.

®S®

Figure 1. ORTEP drawings of trinitrc-bishomocubane molecule

Table 1 . The average bond lengths and the maximum spread from the mean. Compounds

C-C bonds

Bridging C-atom

Cubane skeleton

C-N bonds

C7-N

C9-N

C10-N

N-0 bonds

C

10

H

9

(N0

2

) 3

1.52 + 0.01

1 .55 _+ 0.03

1.48

1.51/1.52

1 .21 + 0.02

C

10

H

8

(NO

2

) 4 (A)

1 .52 +_ 0.02

1 .55 + 0.02

1 .51/1 .52

1.51/1.53

1 .20 + 0.01

(B)

1 .52 _+ 0.02

1 .55 + 0.03

1 .52/1 .51

1 .52/1 .52

1 .19 + 0.01

23
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 2. The average bond angles and the maximum spread from the mean.

Compounds

C-C-C (°)

4-membered ring

5-membered ring

Bridging C-atom

O-N-0 (°)

C

10

H

9

(N0

2

) 3

89.1 _+ 0.26

103.7 ^ 5.7

96.9 + 1.3

124.8 + 1 .3

C

10

H

8

(NO

2

) 4 (A)

89.2 +_ 2.8

103- 4 +_ 3-7

97.9 ±_ 0.2

125.3 + 0.8

(B)

89.2 +_ 3-2

103.4 .+ 3-5

98.3 + 0.2

125.2 + 1 .6

Figure 2. ORTEP drawings of tetranitro-bishomocubane molecules.

The carbon skeleton (bishomocubane ) of the three molecules in the tables

consists of four puckered 5-membered rings and two 4-membered rings. The 4-membered

rings are all bent about their diagonals by approximately 20° which causes the

average e-c-c angles to be 89.1° or 89.2°, instead of 90°. The bond angles of the

bridging carbon are distinctly smaller than others within each 5-membered ring.

Similarly, the bond lengths of the bridging carbons are consistently shorter than

others within the same ring by about 0.03 A for all three molecules. The C-N bond

length of the C(7) carbon with one NO group attachment is 1.48 A, but those of other

*- carbons with two NO groups each are considerably longer, approximately 1.52 A on the

average. This suggests that the number of electron withdrawing groups on the same

carbon atom is related to the elongation of the C-N bond. There are no unusual

intermolecular contacts and no evidence of hydrogen bonding.

24

^m
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SIMULATION OF THE INITIATION OF DETONATION IN AN ENERGETIC MOLECULAR CRYSTAL

D. H. Tsai

(National 3ureau of Standards, Gaithersburg, MD)

and

S. F. Trevino

(Energetic Materials Division, AMCCOM, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

Detonation in a chemically reactive system has been extensively studied from

the viewpoint of continuum mechanics under the assumption of local equilibrium in all

1 2 thermodynamic parameters except chemical composition. In a steady detonation

wave, this means that the various energy relaxation processes are assumed to occur at

3 a rate at least equal to the local sound velocity. Pastine et al . , however, have

pointed out that the average frequency of the intramolecular vibrations in a dense

system may be expected to be much higher than that of the intermolecular vibrations,

and consequently the relaxation processes for energy transfer between V-R , V-T, and

R-T (V = vibrational, R = rotational, T = translational ) degrees of freedom should be

rather slow. Assuming a constant relaxation time x , Pastine et al . constructed a

R simple model of shock initiation of detonation which predicted an initiation time

controlled by t , and hence by the duration of the shock pulse, in good agreement

R with experiment for one material. But for a different material they obtained poor

agreement.

The problems of energy relaxation are of very general interest in physics and

chemistry. With the development of lasers, computers and chemical studies in the

picosecond regime, studies of these problems have become more interesting because it

is now possible to investigate the energy transfer processes on the time scale of

real chemical reactions. The initiation of detonation is of special interest because

- 1 3 it is a limiting case of an extremely fast reaction, its time scale (10 to

-1

10 s) matching well the time scale of molecular dynamical (MD) computations. For

these reasons, and as a contribution toward answering some of the questions raised by

Pastine et al . , we have carried out an MD study of the initiation and propagation of

detonation in a model of an energetic molecular crystal. Our results show for the

first time the initiation and propagation of the reaction on a molecular scale. They

also show the energy transfer processes to be much slower than sound propagation, in

qualitative agreement with Pastine et al . These results contain many details of the

molecular motion and of the mechanisms of thermal and shock initiation. Moreover,

25
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

o

oo

Heated Planes

—i 1 1 r100 200

Lattice Plane Number, N Q 300

Figure 1. Profiles of the initiation of detonation at time step J=1800, Q=32, as functions of distance from the mirror plane. Distance expressed in

lattice plane number N of the undisturbed filament, spaced at 0.5^55 R

1 between neighboring planes. (1a) Average of normal stress components o (heavy curve) and individual X (o), Y (A), Z (a) components. (1b) Total

number of atoms per plane p (heavy curve), the number of dissociated (a)

and associated (o) atoms per plane. (1c) Average kinetic energy per

degree of freedom E (heavy curve) of the molecules and dissociated atoms,

and kinetic energies associated with velocities X (o), Y (A), Z (a)

directions. (1d) Same as (1c) but of dissociated atoms only. (1e) Same

as (1c) but of associated molecules only, in R (o), V (A) and T (a)

degrees of freedom. Data have been smoothed by averaging over +2

neighboring planes (+k for stress components in (1a)) and over 30 times

steps.

26
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

4 with those discussed by, for example, Nesbitt and Hynes who studied the theory of

vibrational relaxation of I in liquid CCl^. Our results thus demonstrate the

usefulness of the MD method for studying not only the dynamics of detonation, but

also the more general problems of energy transport and energy sharing.

Our model was a hypothetical diatomic bcc crystal capable of undergoing

dissociation: A = A + A + energy, similar to that described in Ref. 5-6. The atoms

were considered to be independent particles interacting with one another through a compound Morse potential V - V :

V = e{exp[-2a (R-R )]-2exp[-a (R-R )]}, for R>R

di3 ; V

2

= b

2 e{exp[-2a2

(R-0.15R

1 )]

2exp[-a_(R-0.15R, )]} + Qe, for R < R.. . 2 dis

Here R = R. . is the separation distance between atoms i and j , e is the unit of

energy, R =1.0 is the unit of length, a = 1n 2/0.255, a = In 2/0.05, b = 0.4,

and Q, the exothermicity parameter, is 32. With these values, V = V at R 0.2983- When R. . < R ,. , atom i forms a molecule with atom j and interacts with i ij dis

through V . Once formed, bond ij is saturated, such that other neighbors k of atom i interact with i through V, . When Ro. > R J . , molecule ij is dissociated, i and j now

1 ij — dis

interact also through V . The atomic mass m was taken to be unity and the unit of

i 1 time x to be R (m/c) r. In Ref. 5-6, we showed that the kinetic and energy sharing

properties of this simple model were reasonably realistic. At the high temperatures

involved here, quantum mechanical effects should be small.

7 In earlier work, we have investigated the energy propagation and energy

relaxation in a filament of a three-dimensional monatomic crystal and monatomic dense

liquid, subjected to shock compression and to pulsed heating. We combine the schemes

developed in Ref. 5~7 for this study. To save computation, we built up the filament

by joining together cubic blocks of crystallites each containing 128 molecules (256

atoms, 4x4x4 unit cells) and having periodic boundaries on opposite faces. The

coordinate axes were aligned with the crystalline axes, the longitudinal direction Z being the direction of propagation of detonation. The boundary at Z = was a stationary mirror plane. Before starting, the system was equilibrated in its

molecular form at a low temperature. The initial kinetic energy of the filament was

set at E = 0.26e, just below the threshold of spontaneous dissociation (cf. Ref. 5).

K Then the first six crystalline planes were rapidly heated to a higher temperature.

The heating was effected by scaling the velocities of the atoms in these planes by a factor 1.03526 per time step for 80 time steps. After heating, the system was

allowed to evolve without further adjustment. The heating initiated dissociation

27
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

reactions which caused further reactions to occur along the filament by thermal

conduction. The longitudinal expansion of the filament due to the initial heating

and due to the dissociation drove a strong shock wave into the filament. Between the

mirror plane and the shock front, the periodic boundary condition in the Z direction

did not apply. But beyond the shock front, the filament was not yet disturbed, so that it could be joined smoothly to a single block of crystallite still at

equilibrium, through the periodic boundary condition in the Z direction. This single

block thus served to terminate the computation at a given time step. As time

increased, we moved this block along, always keeping it ahead of the shock front.

The computation continued to a maximum of 2210 time steps with the shock front

reaching 335 lattice planes from the mirror plane. At this point the filament

contained over 11000 atoms. The total energy of the system was monitored and found

to be well conserved. From the dynamics of all the particles as a function of time,

we then obtained a description of the initiation of detonation on a molecular scale.

Figures 1a to 1e show a typical set of results (single case-history) with Q = 32 at time step J = 1800 (t = 18, At = 0.01, longitudinal sound velocity = 9.

lattice planes per unit t). Figure 1a gives the average of the normal stress

components o. Figure 1b gives the number of atoms per plane p. Figure 1c shows the

average kinetic energy of the atoms E per degree of freedom. In these figures the

shock front was at N = 280, and through the shock front o, p, and E increased

abruptly. Between N = 275 and N = 1^0, these quantities increased more slowly,

3. 3. reaching a peak around N = 160. In this region of shock compression there was also

a partial dissociation initiated at random sites (arrows in Figure 1b) after certain

induction time had elapsed. r But the main reaction occurred between N = 1 40 and N

a a 125, where the dissociation proceeded rapidly to completion. This was accompanied by

a sharp drop in o and p^ and a sharpr rise in E, . Between N =125 and N = 50, the

k a a components of the normal stresses and the kinetic energy (Figures 1a and 1c) have

equilibrated. The higher values of E, and the lower values of p for N < 50 resulted

k a from the initial heating of the first six planes.

Returning to the region of shock compression, we conclude from the persistent

difference between o and o , o and between E, and E, , E, that there was mass

z x y kz kx ky

motion in the Z direction in this region. This was clearly due to the thermal

expansion and the volume change AV (Reference 6) of the reacted region between the

mirror plane and N = 125. From the positions of the shock front at different times

a

it was possible to determine that the velocity of the shock front, as well as the

28

Mfl ifltfc
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

average peak stress, etc., had become very nearly steady after x = 14. The Mach

number of the nearly steady shock front was just under 1.5.

The reaction front (at N = 140) propagated more slowly than the shock front,

3. so that the disturbance from the reaction was greater nearer the reaction front.

This was responsible for the gradual decrease of the stress profile toward the shock

front. We shall return to this point concerning the lower velocity of the reaction

front. But we note that the random reaction sites also contributed to raising the

local kinetic energy and the local stresses, and thus to the gradual decrease

of o, p, ane E profiles toward the shock front. Except for the gradual decrease of

K these quantities, our results are qualitatively similar to the continuum results

described in Figure 11.9-2 of Ref. 2 for a steady detonation wave in a perfect gas.

Figure 1d shows the average kinetic energy of the dissociated free atoms per

degree of freedom. The various sites of reaction between N = 215 and N = 145

a a correspond to the arrows in Figure 1b. The disturbance was quite large and

undoubtedly generated stress pulses also in the transverse direction. These reaction

sites tended to grow in size with passage of time (e.g., at N = 150, Figure 1b).

3. They also moved with a mass average velocity as the filament expanded in the Z direction. These features may be responsible for the development of the cellular

structure observed in detonation wave experiments (Chapter 7, Reference 1), but

further studies will be needed to establish the connection.

Figure 1e is a plot of the average kinetic energy per degree of freedom of the

associated atoms. The data show clearly that the energy transfer between the shock

compression and the internal degrees of freedom was highly inefficient, in

qualitative agreement with the ideas advanced by Pastine et al . There was no thermal

equilibrium in the shock compressed region. Near the mirror plane, there were a few

recombined molecules.

From profiles such as those in Figure 1b at different times, we could also

determine the velocity of propagation of the reaction front. In the present case,

this velocity was definitely lower than the velocity of the shock front, so that the wave profile as a whole was not steady. With the stationary mirror plane as a boundary condition, our problem corresponded to the special case of zero piston

Q

velocity in the "piston problem" discussed by Fickett and Davis. We could simulate

the case of an "overdriven" detonation wave by giving the filament a uniform mass average felocity toward the mirror plane and determine the condition that would give

rise to a steady detonation wave. This investigation is now in progress.

29
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The energy released at the reaction front drives the shock wave which converts

the energy of reaction to the energy of compression. When both the reaction front

and the shock front have steady velocities (not necessarily equal velocities), as appeared to be the case here, we could determine the energy of reaction by

"measuring" the rate of energy propagation under the shock wave. For the present

case, the average energy released by the molecular dissociation was 12.22e per atom.

Our limited data for Q = 16 and Q = 24 appear to show a steadily weakening shock

wave, perhaps leading to extinction of the reaction.

In conclusion, our results show that the initiation of detonation may be

studied on a molecular scale by the MD method. This method is capable of providing

many details, such as those involving energy transfer and energy relaxation. But our work is clearly just the beginning and many important and difficult problems remain

to be studied. Among these are the problems of obtaining adequate data for ensemble

averaging, the development of a steady overdriven detonation wave, the limit of

detonation, a more realistic model of a molecular crystal, the role of defects and

others.

1. W. Fickett and W. C. Davis, "Detonation" (University of California, Berkeley,

1979) and the references therein.

2. J. 0. Hirschfelder , C. F. Curtiss and R. B. Bird, "Molecular Theory of Gases and

Liquids," (Wiley, New York, 1954) Chapt. 11.

3. D. J. Pastine, D. J. Edwards, H. D. Jones, C. T. Richmond, and K. Kim, in "High

Pressure Science and Technology", Vol. 2, edited by K. D. Timmerhaus and M. S.

Barber (Plenum, New York, 1979).

4. D. J. Nesbitt and J. T. Hynes, J. Chem. Phys. 7_7, 2130 (1982).

5. D. H. Tsai and S. F. Trevino, J. Chem. Phys. 79, 1684 (1983).

6. S. F. Trevino and D. H. Tsai, to be published in J. Chem. Phys.

7. D. H. Tsai and R. A. MacDonald, Phys. Rev. B J_4. 4714 (1976); High Temp. High

Pressures 8, 403 (1976); D. H. Tsai and S. F. Trevino, Phys. Rev. A 24, 2743

(1981).

8. W. Fickett and W. C. Davis, ibid, pp. 14-24.

30
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

ADVANCED NEUTRON METHODS

N. Berk, D. Fravel, C. Glinka, J. LaRock, and J. M. Rowe

1 . Small Angle Neutron Scattering (SANS)

The 'SANS spectrometer was fully utilized during the past year with demand for

instrument time exceeding available capacity by roughly 25 percent. During this

period of heavy utilization, no major modifications were made to the facility,

however, a number of minor improvements were carried out in order to improve its

efficient use. For example, a new six-position, computer controlled, specimen

changer was built primarily for solution scattering experiments. The holder can be

used in air or under vacuum and is equipped with cooling coils and individual

resistance heaters for maintaining samples at temperatures between 0-80°C. Also now

available for room temperature measurements in magnetic fields up to 13 Kgauss is a four-position automatic sample changer (designed and built by G. R. Odette et al.,

University of California at Santa Barbara), which translates samples between the pole

pieces of a vertical field electromagnet. For low temperature measurements in a magnetic field, the sample support of a controlled temperature cryostat has been

modified to fit between the pole faces of a large horizontal field electromagnet thus

enabling data to be taken at temperatures down to 4K in fields up to 15 Kgauss.

To reduce the time required to put SANS data on an absolute cross section

scale, the strong scattering from a sealed 1 mm thick sample of microporous silica

particles (pore diameter ~9 nm) has been calibrated against the incoherent scattering

of pure vanadium. The forward scattering from this silica sample can be precisely

determined in as little as one-half hour in many cases and is now routinely used as a secondary absolute intensity standard.

A detailed Users' Manual has been written to serve as both an introduction to

the facility for new users as well as a reference manual for experienced users. In

addition, nearly all of the SANS data reduction software is now documented and stored on the VAX computer and can be accessed by a user at a video terminal as needed.

Data analysis software continues to be developed or adapted for use within the

existing data reduction environment. For example, programs have been developed (by

N. Berk) for the analysis of beam broadening by micron sized inhomogeniet ies or particles. Programs for desmearing SANS data from systems of randomly oriented

identical particles (provided by V. Ramakrishnan, ORNL) and for extracting particle

size distributions (provided by R. Page, Southwest Research Institute) are also now

available.

31
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In order to improve the instrument's signal-to-noise ratio, tests have been

made of a new detector fill gas mixture of 3 He/CF H using the facility's backup 25 x

1 25 cm

2 area detector. This gas mixture has been reported to be far less sensitive

to gamma rays than the 3 He/Xe mixture presently used. Our test measurements confirm

these reports and indicate that an 8055 reduction in the gamma ray contribution to the

background is possible with the new fill gas. Consequently, the instrument's

primary, 65 x 65 cm 2

, detector will be refilled during the Summer 1984 reactor

shutdown. The doubling of the reactor power which will take place during this

shutdown, together with the new detector fill gas, should improve the signal-to-noise

ratio for weak scattering samples by factors of between two to five.

In the past year, approximately fifty scientists representing six NBS

divisions, ten universities and nine industrial and government laboratories have

carried out experiments in polymers, ceramics, metallurgy, magnetism and biology

using the SANS facility. Much of the recent work in polymers has concentrated on examining the density fluctuations which develop in polymer blends and block

copolymer melts near their miscibility gaps or microphase separation boundaries,

respectively. For example, C. Han of the Polymer Division along with collaborators

from the University of Massachusetts have studied the critical density fluctuations

in blends of deuterated polystyrene and polyvinyl methyl ether (PVME) as a function

of temperature and PVME volume fraction. While they find that the correlation range

of these fluctuations varies with temperature as predicted by mean field theory, they

have also observed, in contradiction to traditional theory, that the blend

interaction parameter x is strongly dependent on the relative volume fraction of the

polymers. A strong dependence on volume fraction for x nas also been found by F.

Bates (AT&T Bell Laboratories) in measurements on block copolymers of 1 , 4-deuteropolybutadiene and 1 ,2-polybutadiene near their microphase separation conditions.

These recent experiments by Han and Bates have provided some of the most detailed

data to date on the actual functional dependence of x« In their initial studies of epoxy thermosets, W. Wu and B. Bauer of the Polymer

Division have been able, using deuterium labeling techniques, to observe the

formation of paracrystalline-like networks in the solidified state. Furthermore, by

carefully varying the sample temperature in-situ, they have been able to follow the

network formation in real time.

In ceramics, the beam broadening produced by ceramic powders and compacts is

being studied experimentally by K. Hardman-Rhyne of the Inorganic Materials Division

and theoretically by N. F. Berk. Recent work has focused on determining the particle

32
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

size in alumina powders and the pore size in compacts prepared from such powders.

The analysis of such data entails complex, numerical, multiple scattering

calculations which include both the refractive and diffractive terms in the single

particle scattering. In related studies of pore accessibility in microporous

materials, contrast variation experiments using both polar and nonpolar solvents have

been carried out on coals by J. Gethner of Exxon Research Co. and on silica particles

used in liquid chromatography by L. Sander of the Organic Analytical Research

Division and C. Glinka.

A number of recent experiments in metallurgy have been concerned with the

microstructure of steels. M. Fatemi of the Naval Research Laboratory, for example,

has been measuring the size distribution and volume fraction of precipitates in

certain high strength, low alloy steels of interest to the Navy. G. R. Odette of the

University of California at Santa Barbara has been interested in the effects of

irradiation on reactor pressure vessel steels. In his SANS experiments he has

observed dramatic, radiation enhanced, precipitation of copper impurities which leads

to hardening and eventual embrittlement of the steel. R. Fields of the Fracture and

Deformation Division and B. Mozer have studied creep cavitation in stainless steel

and most recently in pure copper.

SANS studies of spin glass magnetic ordering in a number of amorphous rare earth-transition metal alloys have been carried out by J. Rhyne along with M. Spano

of the Naval Surface Weapons Center and S. Pickart of the University of Rhode Island.

They have shown that spin glass ordering, rather than long range ferro- or

f errimagnetic order, persists in these alloys at low temperatures even for very low rare earth element concentrations (e.g. in Fe A0 Tb n „) due to the random single-ion

anistropy field introduced by the rare earth atoms.

Some of the work mentioned above is described in greater detail in other

articles in this report.

33
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

DETERMINATION OF PORE ACCESSIBILITY IN SILICA CHROMATOGRAPHIC PARTICLES

BY SMALL ANGLE NEUTRON SCATTERING

Lane Sander

(Organic Analytical Research Division)

and

C. J. Glinka

We have been using small angle neutron scattering (SANS) to characterize the

size, surface area and volume fraction of micropores in silica particles used in size

1 exclusion liquid chromatography. Recently these measurements have been extended to

silica samples which have been saturated in solutions of H

? 0/D ? in order to

determine the extent to which the pores are accessible to solvents. This question is

relevant to the performance of this material for chemical separation in liquid

chromatography

Figure 1 shows the small angle scattering observed from a commercial silica

powder consisting of 6.5 micron particles whose pores are nominally 30 nm in

diameter. The dashed curve is the scattering from a dry silica sample while the

solid curve is the scattering measured after saturating the silica with a solution of

59 % DO, 41 # HO. This HO/DO mixture is calculated to have the same scattering

length density as silica assuming a skeletal density of 2.21 gm/cc. The scattering

from the saturated sample is reduced a thousandfold from that of the dry sample at

the smallest Q value measured (the Q-independent scattering at larger Q is due to

incoherent scattering from the HO in the solution) suggesting that virtually all of

the pores are accessible to the solution. This inference was confirmed by making

measurements as a function of the H

?0/D ? ratio in the saturating solution. These

results are summarized in Figure 2 in which the square root of the scattering above

background at the smallest Q measured is plotted versus the percentage of HO in the

solution. This quantity should be simply proportional to the scattering contrast

between the silica and the solution if all of the pores are filled. The linear

dependence seen in Figure 2 demonstrates that this is the case and implies that a

39.5/6 HO solution would completely mask all of the pore scattering. Measurements of

this type are now being extended to smaller pore materials.

The ability to completely mask the strong scattering from the porous structure

of silica particles suggests that SANS would be a powerful technique for the study of

absorbed phases on these high surface area materials. For example, it should be

possible to determine the conformation of polymer chains chemisorbed to the pore

surfaces. Such "bonded phase" materials are used in chromatography and SANS data

34
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1n 6 J 1 1

1

1

1 1 1 1 1 1 U 1

1

'

1

' 1 ' 1

'

10 5 - — Dry Silica

Silica in 59% D20,4I%H20

«2 10 4 -

\

\ c \

3 \

<> 10

3 i

\

\ c N

o \

5 10 2 -- ^ ^ •^

01 z

^ ^ ^ ^

10 1 -

10° 1 1

1 1 i

1

i

1 I 1 <J 1

1 1

|

1 | I | 1 0.2 0.4 0.6 0.8 1.0

Scattering Vector Q ( n m

1

)

Figure 1 . Comparison of the small angle scattering from microporous silica particles

before and after saturating the particles in a 59$ DpO/^l^ HO solution.

The water mixture has nearly the same scattering length density as the

silica and thus masks the scattering from filled pores.

30 Porous Silica - Vydac

Contrast Variation

Percent H2O

Figure 2. Plotted is the square root of the net scattered intensity (at Q = 0.1 nm ) from microporous silica particles saturated in H Q 0/D mixtures

of various concentrations. The observed linear dependence indicates that

the solutions fill the pores uniformly.

may, therefore, contribute to an understanding of their chemical selectivity.

Experiments along these lines are planned for the near future.

35
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

ANALYSIS OF BEAM BROADENING SANS DATA FROM ALUMINA POWDER

N. F. Berk

and

K. Hardman-Rhyne

(Inorganic Materials Division)

We are continuing the work begun in the previous report period of developing a practical theory for incoherent small angle neutron multiple scattering that takes

account of the general phase shift dependence of the single (spherical) particle

neutron scattering cross-section. This approach gives us a tool for analyzing small

angle neutron scattring data from ceramic and other materials and determining

particle or void size from data that is dominated by multiple scattering. An

important new example of the method is illustrated by Figure 1 . Alumina powder of

well-characterized, approximately monodisperse particle size was measured at several

neutron wavelengths, volume fractions, and sample thicknesses, and the beam

broadening data were fit with the theory, refining only on the particle size. The

result, particle radius R = .265 microns, is in good agreement with other estimates.

100 200 300 400 500

Sample Thickness/Mean-Free-Path

Figure 1. Collated alumina data (circles;) and theoretical curve (line). The

absissca is the radius of curvature, r , of the beam broadened neutron

c scattering intensity in units of QR, where R was determined by best fit.

Increasing r means increasing broadening. The ordinate is the

"scattering power", i.e. sample thickness in units of the scattering mean- free-path length. The collated data lie on a universal curve for small

angle multiple diffraction.

36
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

These particular data are described by multiple scattering in which the single

particle cross-section is well approximated by the diffractive limit (phase shifts in

the range 0.1-0.3) but where the mean-free-path is nevertheless small compared with

sample size. This multiple diffraction is observable because of the relatively high

density of scattering particles (volume fraction about 0.3) and the large values of

sample thicknesses (2-10 mm). The figure shows all the data on a single graph in

which the ordinate is the radius of curvature of the scattering curves at Q = 0--

essentially a measure of the width of the beam broadening--in dimensionless units of

QR (unbroadened single particle scattering corresponds to an ordinate of value 1.6 in

this method of presentation), and where the abscissa is the computed ratio of sample

thickness to scattering mean-free-path. The solid line is the theoretical

determination of the scattering radius of curvature. Thus, when the scattering

particle radius has been determined, the observed beam width is completely

characterized by the properly normalized sample thickness, and all data (from

monodisperse spheres) lie on the same curve. This may be taken to be the signature

of small angle multiple diffraction.

THEORY OF INCOHERENT MULTIPLE SMALL ANGLE NEUTRON SCATTERING:

PHASE SHIFT DEPENDENCE OF THE SINGLE PARTICLE SCATTERING

N. F. Berk

Work is continuing on the development of a practical theory of incoherent small

angle neutron multiple scattering that incorporates the complete phase shift

dependence of the single (spherical) particle neutron scattering cross-section. A

recent application of the approach to beam broadening SANS data from alumina powder

is given elsewhere in this Summary of Activities (N. F. Berk and K. Hardman-Rhyne)

.

The phase shift dependence of the single particle scattering cross-section has also

been examined in new detail. Among the results:

(1) The Porod law is independent of the phase shift, p, but its observability

decreases with increasing phase shift (i.e., pushed to larger scattering angle); the

observable asymtotic behavior may also appear to be Porod-like but strongly dependent

on p.

37
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. Single particle scattering cross-section of a sphere, o(QR,p). The

diffraction limit (Born approximation) lies along the front edge, p = 0.

The first big peak occurs near p = 7.

(2) The Born approximation for single particle scattering, which defines the

diffraction limit for p * 0, remains a very good approximation for p £ 2.0. For p > 3.0, deviations from the diffraction limit become significant, and the oscillatory

structure at QR > 1.0 is strongly amplified. This is illustrated in Figure 1, which

shows the single particle cross-section o(QR,p) over a range of QR and p. The

classical refractive (ray optical) limit, corresponding to p

-> °°, may not be

observable in practice.

These findings have implications for the interpretation of SANS data from large

particles, the inversion of SANS data to find particle size distributions, the

information content of SANS data under conditions of low wavelength resolution, and

other aspects of SANS analysis, even in the absence of strong multiple scattering.

38
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SMALL ANGLE NEUTRON DIFFRACTION MEASUREMENTS OF DIBLOCK COPOLYMER PSD-PMMA

IN THE BULK AND IN SOLUTION NEAR THE POINT

+ H. Benoit , B. Bauer, and W. Wu

(Polymer Division)

and

B. Mozer

Bulk samples of the copolymer prepared from deuterated polystyrene (PSD) and

polymethylmethacrylate (PMMA) were obtained from anionic polymerization and formed in a brass vacuum mold. The molding process resulted in bulk samples free of any gas

bubbles as analyzed by small angle x-ray diffraction. The characteristics of the

copolymer were ^3$ PSD and 57$ PMMA with Mn (DPS) = 83,000, n = 741, Mn = 110,000,

n = 1100 leading to a ratio of Mw /Mn = Mw /Mn = 1.25. The solution sample was prepared in cyclohexanol , a known solvent for PSD, PMMA and their copolymer. The

theta temperatures for both polymers are fairly close to each other which will lead

to simplifications in the analysis of the neutron data. The solution was 20$ by

weight of the polymer in the cyclohexanol.

In order to determine the background and incoherent scattering from the

solution, a mixture of low molecular weight liquids was prepared with the same ratio

of atoms as in the 20$ solution of H3% PSD content. This "background" mixture

contained weight fraction of 0.700 cyclohexanol, 0.185 acetone, 0.086 benzene-d6, and

0.02$ benzene.

Small angle neutron scattering (SANS) data were taken on the bulk sample at

20, 110, and 160°C, on the 20$ solution at 76, 82, and 110°C, and on the "background"

liquid mixture at room temperature. Background measurements, empty sample cell

measurements, and transmission measurements were also made. The NBS-SANS

spectrometer was employed in a configuration using the focused collimation system,

the sample translation system, the area detector at 3-6 meters, the center of the

detector at zero angle, and the incoming neutron beam of 5A. Only one position of

the sample translation system was used in order to fix precisely the position in the

beam of the bulk, 20$ solution, open beam, etc. measurements. There was no attempt

to determine the absolute intensity of the scattering of our samples.

Transmission measurements of the mixed liquid and the 20$ solution yielded the same value within one standard deviation of counting statistics. Thus, we have high

confidence in the method for subtracting the contribution of any extraneous and

incoherent scattering from the bulk or 20$ solution scattering data.

39
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

200

150

£100

50

O

Solid at 160 °C o o

o

o

o o

o

o

<*> °°o0(

J 1

1 uQOonnnnnAA , 0.1 0.2 0.3

Qx 10 _1

0.4

Figure 1. Corrected (SANS) intensity from bulk PSD-PMMA diblock coplymer at 160°C as

a function of Q = 4irsinQ/A.

280i210

g 140

70

n

D Solution Scattering Data

aa

a oO° a

^ aa °OoaD

aa

aa on

A a, OogD

A V .°

D%D

AA UC^DDD AA . H.VvTD

^AAaa

AA . ac aj

T = 76 °C

O T = 82 °C

a T = 110 °C

AaaAmDDq^o

J L

AA^aaaaa^S^A/

0.1 0.2 0.3

Q x 10

0.4

1 0.5 0.6 0.7

Figure 2. Corrected (SANS) intensity from a 20% solution of PSD-PMMA diblock

copolymer in cyclohexanol at 76, 82, and 110°C versus Q = 4irsin0/A.

40
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The corrected scattering intensity is shown for the bulk sample at only one temperature in Figure 1. Our measurements of the bulk sample showed no significant

change with temperature in terms of the overall scattering pattern. The intensity of

the maximum observed was very strong so that no corrections were needed for

background or incoherent scattering. We found that the specimen scatters so intensely that it is useful for aligning the beam stop for other experiments. The

corrected intensity for the scattering from the 20% solution is shown in Figure 2.

The most striking feature of these measurements is the appearance of a well defined

peak. This feature remains as the temperature is lowered to near the temperature

for the coplymer. Also evident is the large increase in intensity as the

temperature is approached.

A theoretical calculation of the scattering intensity for mult icomponent

systems with special application to homopolymer mixtures and copolymers has been

performed by H. Benoit and M. Benmouna and others. The calculation can account for

the observed scattering intensity for the bulk sample. Using the experimental

scattering intensity, it is possible to fix the parameter in the theory representing

the interference cross term of the scattering between the two different monomers.

The theoretical calculation for the intensity of the scattering for a 20% copolymer

in solution shows also the surprising feature of a peak that increases in intensity

as the temperature is approached.

+ Permanent address: Centre de Recherches sur les Macromolecules , 6, rue

Boussingault, 67083 Strasbourg, Cedex, France.

41
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NETWORK STRUCTURE OF PARTIALLY DEUTERATSD EPOXYS FROM NEUTRON SCATTERING

W. L. Wu and B. J. Bauer

(Polymer Division)

The physical properties of epoxy networks have been extensively studied due to

their great commercial importance. These studies are of macroscopic quantities.

Very little is known of the nature of the network structure, however. To gain

insight into the network structure, neutron scattering studies have been initiated.

A partially deuterated epoxy, the diglycidyl ether of Bisphenol A (DGEBA), was synthesized. Perdeuterated phenol and acetone were condensed to give perdeuterated

Bisphenol A. It was then reacted with epichlorohydrin to give an epoxy with 14

deuterium atoms in a central position. The network was formed by reacting the DGEBA

with di or triamines based on polypropylene oxide flexible chains.

The scattering was performed on the small angle facility and on the BT-6

diffractometer . Studies were made by varying the amine type, by swelling the samples

with solvent in order to assess the homogeneity of the network, and by quenching the

curing reaction at various stages, to gain insights to the network formation process.

The most striking result from neutron scattering is the observation of multiple

peaks in these AMORPHOUS materials. Such peaks are believed to be a consequence of

intranetwork correlation among the deuterated blocks. The short range (liquid-like)

correlation can only give rise to part of the first scattering maximum. The higher

order peaks provide a strong indication that the pair correlation within a network is more expanded than a Gaussian coil.

A theory of the scattered intensity from labeled networks has been developed to

analyze the experimental data. Parameters relating to network size and heterogeneity

can thus be deduced from the scattering curves. The initial results indicate that

the networks are far from uniform.

42
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON CLOUD POINTS AND CONCENTRATION FLUCTUATIONS OF POLYMER BLENDS

C. C. Han

(Polymers Division)

and

H. Yang, M. Shibayaha and R. S. Stein

(University of Massachusetts, Amherst, MA)

The phase diagram of polymer blends is traditionally studied by the light

scattering cloud point measurement. Transmitted or scattered light is normally used

for this purpose, the intensity of which abruptly changes at the vicinity of the

1 phase transition temperature. We have previously studied PSD/PVME blends by this

conventional light scattering technique and it was found that the lower critical

solution temperature (LCST) is about 40°C higher than that for hydrogeneous

polystyrene PSH/PVME. However, there is one disadvantage in the light scattering

technique. Because of the long wavelength involved one may not be able to detect the

onset of transition from a stable to a metastable phase. This may be important if

the polydispersity of polymers affects the phase separation phenomena. Small angle

x-ray (SAXS) or neutron scattering (SANS) techniques are alternative since they are

associated with radiation having appreciably shorter wavelengths. SANS is

appropriate for PSD/PVME blends to detect the "neutron cloud point" which is the

onset of phase transition in this case. This is because the scattering contrast

between PSD and PVME is appreciably high. Furthermore, this technique allows one to

obtain information about molecular parameters, such as the Flory-Huggins interaction

parameter (x) and the correlation length (£) in the miscible regions of the blend

system.

In this paper, we explore the feasibility of the neutron cloud point

measurements and discuss the critical concentration fluctuation of PSD/PVME blends.

Experimental

The system investigated was a blend of deuterated polystyrene (PSD) and poly

(vinyl methyl ether) (PVME). The characteristics of these components are listed in

Table 1 . Samples of SANS experiments were prepared by dissolving the components in

toluene and casting them into films, followed by drying in vacuum for a week at 70 °C

and then for 24 hours at 110°C in order to remove the residual solvent. The dried

samples were compression molded at 80°C into discs of 19 mm in diameter and 1.7 mm in

thickness.

43
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The experiments were performed using the SANS facility at the National Bureau

of Standards, Gaithersburg , MD , which has a two-dimensional position sensitive

dectector. The incident beam was monochromatized by a velocity selector and had an average wavelength (A) of 6A. A focusing collimation system was used to obtain the

-1 4tt lower limit of the scattering vector (q) of 0.005A , where q = —— sin (9/2) and 9

A is the scattering angle. The sample was mounted in a brass cell covered with copper

shims of 0.025 mm thickness in order to enhance heat conductivity.

The scattered intensity was collected over the two-dimensional detector pixels

-1 -1 (0.005A <_ q <_ 0.12A ) and the dark current intensity due to electronic noise and

room background was subtracted. There is no need for further detector response

correction in this case. Samples were heated at a rate of 1° C/min and total

intensities were recorded as a function of temperature. Phase separation was

characterized by an upturn in total scattered intensity with temperature increase as shown in Figure 1 . The intersection of straight lines drawn through portions of the curve below and above the break was taken as the neutron cloud point.

The sample temperatures for both SANS and LS experiments were carefully

calibrated in terms of a copper-constantan thermocouple.

The absolute intensity calibration was done using a dry silica gel sample as a secondary standard, which was calibrated in terms of a vanadium standard (2).

Results and Discussion

The scattering function, I(q,T), of a miscible polymer blend has been

calculated by de Gennes (3) based on the "Random Phase Approximation". This can be

written as

- - 2 X (*,T) (1) I(q ' T) WY

A,

q) \

Y

B

g

B (YA, q) *B

where Y. is the reduced degree of polymerization with respect to the unit cell

volume, K is a constant, depends on the scattering geometry and the scattering

lengths of monomers, $ is the volume fraction, x is the Flory-Huggins interaction

parameter, g (Y ,q) is the Debye scattering function. The polymer chains in the

blend are assumed to remain Gaussian, and at small q, eq. (1) can be written as: iRTrr-^B^-xCi.Tn-^;,^-

(2)

b 2 b 2

where b = [* a (-£- + -r5-) ] (3)

A B d> A

$ B

44
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. Experimental I ,_(T) (in open circle) and calculated I t (T) (in solid

tot tot

square) at various temperature for wt% 50/50 PSD/PVME blend. Solid lines

are drawn through portions of experimental points to determine the neutron

-t. N cloud point, T

cp

1.5

1.0

0.5

• 152 °C

+ 131 °C

> 25 °C

W"*\

"****Mt ^SimmttiMiHMM

2 4 6 8 10

q • 104

Figure 2. Scattered intensity as a function of q for the above blend at various

temperatures.

45
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

o 30-

• 10

Figure 3. Inverse intensity vs q plots for the above blend at various temperatures,

o

«Uj>

Figure 4. Inverse square correlation length, £

" as a function of T for 50/50 (in

solid circle) and 80/20 (in open circle) blends. Spinodal temperature is

-2

obtained at £ > 0.

1*6
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table I. The characteristics of the blend component (PSD purchased from Polymer

Laboratories, Stowe, OH and PVME for Scientific Polymer Products, Webster,

NY).

Component M

w PSD 255, 000

PVME 99, 000

M

46,500

M /M

w w

1 .08

2.13

Table II. Correlation Length at Various Temperatures for Two Different Compositions

PSD/PVME 50/50 PSD/PVME 80/20

Temp ( °C) £ (A)

121 36.5 ± 0.5

131 43.6 ± 0.6

136 50.6 ± 1 .2

141 57.4 ± 1.2

147 68.2 ± 1.2

152 90.6 ± 2.2

157 135.6 ± 4.8

Temp ( °C) £ (A)

121 34.8 ± 1 .0

131 36.4 ± 0.6

136 40.3 ± 1.1

141 41 .5 ± 0.9

147 47.5 ± 0.8

152 52.8 ± 1 .1 157 55.4 ± 1 .1 162 70.9 ± 1 .5

Table III. Calculated I tot

Temp. F U)

132 5.42

142 5.95

147 6.28

149 6.70

152 6.80

155 7.50

From Eq. (7) and Experimental L for PSD/PVME 50/50

tot

I v t 10 3 (calc)

tot

5.5*

6.0

6.4

6.6

6.9

7.6

I tQt

10

J (expt)

5.5*

6.1

6.4

6.7

6.9

7.6

^reference point

Table IV. The Neutron, Light Cloud Points and the Spinodal Temperatures for wt!

50/50 and 80/20 Blends

50/50

80/20

T

L

°C

cp

157.0

171 .0

T °C

cp

156.0

168.5

T °C

sp

160.0

176.0

47
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

and b. is the statistical segment length of i , x denotes the interaction parameter

J. o at the spinodal point. Eq. (2) can be written in a Lorentzian or Ornstein-Zernike

form

Kq.T) 1 I( °' T) ' 1 + q

2

^(T)

2 (4)

with 5(T) = | {VbCx

s U) " x(*.T)3>

1/2

(5)

This £(T) may be interpreted as the concentration correlation length at

temperature T.

The scattering function of PSD/PVME with 50/50 weight percent is shown in

Figure 2 for several different temperatures. Before we go into data analysis for

correlation length, we would like to discuss the integrated intensity and cloud point

study.

The total scattered intensity as a function of temperature in the miscible

regions is experimentally determined by

/qmax

q . min

I td (T) «/„ Kq.T) 2 n q d q

which can be integrated to yield:

_ -I _, _* (Cos[tan (£q . )]' - 2n l^lm r

-^ > % (T) (cos[tan Uqmax where q . and q are the lowest and highest limits of the scattering vector in our mm max SANS geometry. From both eq. (2) and eq. (5) 1(0, T) and E, (T) terms can be cancelled

out and lead eq. (7) to the following:

(Cos[tan~

1 Uq )])

I. (T) - ml ^?—} = F(0 (7)

(cosCtan1 (Cqmax )])

The correlation length was obtained from the I(q,T) vs. q plot as shown in

Figure 3 according to eq. 4. The extracted £'s at various temperature are listed in

Table II. It should be noted that the correlation length increses with increasing

temperature. We an calculate T (T) from the experimental correlation length by

tot

using eq. 7 as shown in Table III. By matching I (T=132°C) as the reference point,

it is clear that the data analysis schemes we have used so far are definitely

consistent. The total intensity (counts) of scattered neutron before the onset of

the phase separation has an insignificant increase.

From eq. (5) we know that £ diverges at the spinodal point (T ). Recently,

Schelten et al. used this correlation length approach to obtain the spinodal points

5

(T ) and described the phenomena of critical fluctuations for PSD/PVME blends . We

have used the same technique to determine T which is shown in Figure 4. These

o

48
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

N

values together with the neutron cloud point T are listed in Table IV. It is noted

cp

that the neutron cloud points are consistent with the light cloud points. Although

the cloud points are lower than the corresponding spinodal points as we expected, T

N

S (160. 0°C) for vt% 50/50 PSD/PVME sample is closer to the T (156. 0°C), but the T

° P

M

S

(176. 0°C) for wt? 80/20 PSD/PVME sample is significantly higher than T (168. 5°C).

cp

This is because the critical composition for this LCST system is around 30% of PSD.

The 80/20 sample is farther away from the critical composition. Further, studies of

N

T from the correlation length approach, together with T will be reported as a

s cp

K function of composition. The phenomena of critical fluctuations at various

compositions as well as temperature and composition dependence of x f° r this

particular system will also be discussed in the forthcoming paper .

1. H. Yang, G. Hadzi ioannou, and R. S. Stein, J. Polym. Sci., Polym. Phys. Ed. 21_,

159 (1983).

2. C. Glinka, private communication, National Bureau of Standards.

3- P. G. de Gennes, "Scaling Concepts in Polymer Physics," Ch. IV. Cornell Univ.

Press. NY (1979).

4. L. S. Ornstein and F. Zernike, Proc. Roy. Acad. Sci., Amsterdam 17, 793 (1914).

5. C. Herkt-Maetzky and J. Schelten, Phys. Rev. Lett., 51(10), 896 (1983).

6. M. Shibayama, H. Yang, R. S. Stein, and C. C. Han (to be submitted).

49
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SMALL ANGLE SCATTERING AND POLE FIGURE ANALYSIS

OF CREPT COPPER SPECIMENS

Richard Fields

(Fracture and Defomation Division)

and

Bernard Mozer

(Reactor Radiation Division)

Small angle neutron scattering (SANS) measurements were taken on crept copper

samples. The strained samples were copper rods given varying amounts of tensile

creep at 600°C. Neutron scattering samples were prepared from these rods in several

ways. One sample for each creep amount was cut so that the strain direction would be

parallel to the incoming neutron beam. Another set of samples were cut so that the

neutron beam was perpendicular to the strain direction. All these samples were

polished so that they could also be used for metallurgical examinations. Rods not

subjected to creep had samples prepared from them in the above manner to provide

standards for comparison. All rods used were not cast material but mechanically

formed and subjected to a 850°C anneal. The SANS spectrometer configuration used for

this work consisted of a 27 mm hole for entrance collimation of the flight path and a

12 mm hole for exit collimation. Sample holders of cadmium were prepared with a 10 mm hole to define the beam and were used in the automatic sample changer. The

detector was placed 3-6 meters from the sample at zero angle. Various wavelengths

were used to cover the range of wave vector difference and to have good overlap from

one wavelength to another so as to map out the scattering curve. Measurements were

taken with the neutron beam parallel and perpendicular to the strain direction, on

the respective standards, on the empty sample holder, the room background, and on the

transmissions for the different wavelengths.

Data taken on the crept and standard samples for the 5A neutrons showed an unusual effect where the scattering for the beam parallel to the strain axis was an order of magnitude larger than the scattering when the beam was perpendicular to the

strain axis. This increased scattering disappeared when longer wavelength neutrons

were used and it was concluded that we had observed double Bragg scattering from

oriented samples caused by contamination of neutrons in the wavelength distribution

which are not beyond the Bragg cut-off. As a consequence of this result, we decided

to do pole figure diffraction analysis on the specimens to see orientational effects

caused by creep. The results of the SANS measurements on two differently crept,

minimum and maximum creep, samples are as follows. We observe isotropic scattering

50
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

7 • • 6 o»

5

(D> 4 %

c % -J 3 V •

D O «i_

2

1

i i i i i ° i -5.5 -5.1 -4.7 -4.3 -3.9 -3.5 -3.1

Ln (Q(A

-

1 ))

Figure 1 . Summed scattering data from 6 A, 7.5A, and 9A impinging on a crept specimen

versus Q = HusinO/A. For clarity we have used a log-log plot. The

squares are 6A data, the open circles 7.5A data, and the closed circles

are 9 A data.

Figure 2. A Pole Figure Plot of the data obtained for sample U-C, the least crept

sample, for reflections from the (111) planes.

51
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

from all specimens excluding the 5A data. The most intensive scattering comes from

the specimen which received the most creep. The intensity of the two standards is

not zero but much less than the least crept specimen. There are differences in the

scattering from the samples cut in different directions and the possibility exists

that the scattering centers are structurally aligned. The data for three

wavelengths, 6, 7.5, and 9A, when summed so as to give the intensity versus Q =

4iT3inO/A, can be normalized to one of them and the resulting curve in figure 1 shows

nice overlap between the sets. The most striking feature of the experiment is that

the functional form of the intensity is the same for all the specimens, crept or

-N otherwise. The intensity varies as Q representative of the Porod region or asymptotic region of the scattering curve. N is very close to 4 for any sample and

lies between 4 and 5 if the scattering from the standard is subtracted from the

scattering of the crept sample. It was not possible with the present configuraton of

the SANS spectrometer to see another part of the scattering curve, e.g., the Guinier

region for small Q. Furthermore, it is necessary for us to do a calibration

measurement on a standard sample to fix the absolute intensity of our data so as to

obtain the surface to volume ration using the Porod approximation.

Pole figure analysis of the least crept specimen was performed on BT-.6'' spectrometer using the 4-circle goniometer for rotation of the sample. Figure 2 shows the pole figure plot of the data for the (111) reflections. The intensity in

the center is characteristic of fiber alignment along the strain direction. The

other large intensity contours scattered in the ring about the center probably arise

from the strain induced during production of the rod but not eliminated during the

850 °C anneal.

Work is continuing on SANS and the pole figure diffraction measurements to

complete our characterization of creep effects.

52
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON DIFFRACTION STUDIES OF AMORPHOUS ALLOYS

+ Bernard Mozer and Satish Singhal

and

Robert Shull

(Metallurgy Division)

and

Arnulf Maeland

(Allied Corporation, Morristown, NJ)

Neutron small angle scattering (SANS) and neutron diffraction (ND) measurements

have been performed upon a number of amorphous alloy systems to characterize the

structure of these alloys in the various states they traverse as a function of heat

treatment which carries them from the amorphous state to the crystallographic state

characteristic of the alloy in thermal equilibrium.

Metallic-glass ribbons of Cu Ti. and Cu Zr„ were prepared by melt spinning

x 1-x x 1-x

the molten alloy onto a copper wheel in an argon atmosphere. Long metallic glass

ribbons 2.0 mm wide and 25 X 1 mm thick can be prepared in this manner and show an absence of crystall ini ty when examined both by x-ray and neutron diffraction

techniques. All heat treatment of the samples occurred with the sample contained in a sealed quartz tube which had been evacuated to high vacuum and then filled with an atmosphere of helium. Differential thermal analysis and transmission electron

microscopy were performed on the samples at various heat treatments to have parallel

characterization with the neutron measurements.

The most extensively studied sample was the CucrTi,. c alloy. Both SANS and ND

55 45

data were taken in the as-cast condition, after an anneal of 300°C for 3 hours, 300°C

for a total of 9 hours, 350°C for 1 hour, 403°C for 1 hour, 475°C for 2 1/4 hours,

and 850°C for 20 hours. These temperatures are roughly below the glass transition,

the glass transition, the crystallographic transition, and ultimately the thermal

equilibrium state. Figure 1 shows SANS data characteristic of many of the alloys

studied at various heat treatments. The data for the as-cast state and for the 300 °C

anneals is similar to the spectra at 350°C. One of the most striking features of the

350°C spectra and in the 850°C spectra is the non-isotropic pattern which persists

throughout the heat treatment. Studies of other alloys showed that this pattern

arises from oriented "precipitates" or particles of flat disk shape whose short

dimension is oriented along the temperature gradient that exists when the alloy was

+ Now at Intel Corporation, Santa Clara, CA

53
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

quenched upon the spinning wheel. This pattern is observed in Cu Ti and Cu Zr, XX. XX

alloys and we plan to investigate if it is common to all non-magnetic amorphous

alloys. Its composition is unknown at the present time, but will be investigated

with the scanning transmission electron microscope. One also notes the high

isotropic scattering associated with a precipitating phase just at the

cry stallographi c transition. With subsequent heat treatment, this isotropic

scattering disappears probably with the growth and fusion of the fine particles with

heat treatment whose dimension is too large to be observed in our spectrometer.

Figure 2 exhibits the ND patterns for the alloy in the amorphous state and in

Figure 3 we see the patterns for the crystalline states, the non-equilibrium

crystalline phases just after the transition, and its evolution to the equilibrium

pattern after the two anneals. The sharp dip in the amorphous state that seems to

give rise to the two main peaks (one peak has been called a precursor of chemical

short range order by Sakata, Cowlam, and Davies ), we contend is caused by the

negative scattering length of titanium and that titanium and copper in these

amorphous systems are bound together in a molecular state giving rise to molecular

J 55"45

(J) x

<

>-

101.6

50.8

101.6

50.8 -

(a)

475 °C- 2^ hrs.

(b)

J—I L J l__l_

403 °C - 1 hr.

850°C-20 hrs.

(d)

_i—

i

i i 50.8 101.6X AXIS

50.8 101.6

Figure 1. Topological intensity mapping of the small angle neutron scattering about

the main neutron beam for an initial Cu Ti, metallic glass after having

the subsequent indicated thermal treatments. The axes indicate the

detector position (via channel number) and the cross in the middle of each

pattern indicates the center of the main beam. For each pattern, the

intensities for the designated levels a^e given in the boxed insets.

Between any two given levels the intensity varies linearly.

54
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Cu 55 Ti 45 Metallic Glass

75

50 -

g 25

X

>-H

</) 75

ciUJ

h-^ 50

Ld>

1—<

UJ 75

(T 50

25

_ As Melt Spun

- ii;;^S rorSo;o '--

. «••--.

_ '^r -. n

. r r«riff fOTM^MM —m- m^n^T^-r-^^.

-,

# £i£i.

_ . .

' -'.''.:'; ****£ *.. •**v . *•*.

; -*v

%C-

»j 300 °C - 3 hrs.

.*&>

- J%0^

- £|

1 1 V• i i i i 350°C-1 hr.

2 4

47T sin Q -

: (A"')

Figure 2. Relative Scattering Intensity (normalized to maximum intensity) vs. Scattering Vector, Q, for Cu,_,_Ti Iir. metallic glass heat treated at the

55 ^5 indicated temperatures and times.

Cu<==Ti

Figure 3« Relative scattering intensity normalized to maximum intensity of each

pattern versus wave vector Q for the CuTi^ alloy just after

crystallization, after heat treatment which does not produce equilibrium

state, and high temperature treatment yielding equilibrium state.

55
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

amorphous systems and not atomic amorphous systems. The sharp dip is characteristic

of a fixed length in the molecule and destructive interference because of the

negative scattering length. We further contend that an alloy with positive

scattering length isotope of titanium would show only a structure factor in the

amorphous state similar to that of a simple atomic liquid or to that observed using

x rays. One notes further that short range order peaks appear that eventually grow

to Bragg peaks as the alloy is heated to the crystalline state. The crystalline

pattern just after the transition appears to be that of a tetragonal TiCu (tP4) phase

which disappears and is replaced by a pattern of mixed phases of TiCu and Ti Cu,

after subsequent heat treatment.

References

1. M. Sakata, N. Cowlams, and H. A. Davies, Proceedings of the 4th International

Conference on Rapidly Quenched Metals, Sendai, Japan, p. 327 (1981); and M.

Sakata, N. Cowlams, and H. A. Davies, J. Physique 41, C8, 190 (1980).

NEUTRON SCATTERING STUDIES OF THE MAGNETISM IN Cu-Mn SINGLE CRYSTALS

S. A. Werner

(University of Missouri, Columbia, MO)

and

(National Bureau of Standards, Gaithersburg, MD)

and

J. Gotaas

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

J.J. Rhyne

We have carried out an extensive series of diffraction, inelastic, and small

angle scattering experiments on Cu -Mn , for x = 0.10, 0.15, 0.20, and 0.25. This

alloy system has historically been regarded as the prototype of spin glass behavior

and has attracted considerable theoretical and experimental attention. Despite this

level of activity, a satisfactory understanding of the origin of the magnetic

properties of Cu-Mn, including the cusp in the magnetic susceptibility, has not yet

become available. The discovery several years ago of the existence of incommensurate

1 magnetic peaks has led us to these new experiments and a new view of the origin of

magnetism in Cu-Mn. The incommensurate magnetic peaks occur at the positions

56
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2200

1600

V)§ 1000

o

O

400

T = 20K

(Cu 75 Mn25

-200

0.5 1.0

1200-

800-

(0c3

O

O

400-

Cu 85 Mn15 300-

150-

^^ -150

1.0

T = 25K

Cu 90 Mn 10

0.5 1.0

Figure 1. Scan along the line connecting the points (100) and (110). These are difference plots, i.e., the room temperature scan is subtracted from the

low temperature scan leaving the magnetic component at 20-25 K.

57
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(1, 0.5±5, 0) and equivalent positions in reciprocal space. These peaks are not as sharp as Bragg peaks, having a width corresponding to about 10 fee unit cells,

independent of Mn concentration. The magnetic scattering cross section is 3 to 5

times larger in this region of reciprocal space than near the origin of reciprocal

space, and therefore must be regarded as the main source of magnetism in this system.

The incommensurability parameter 6 is dependent upon Mn concentration and is 0.295,

0.254, 0.219, and 0.188 for x = 0.10, 0.15, 0.20, and 0.25 respectively. We have

studied in considerable detail the temperature dependence of these peaks, under

various spectrometer and energy resolution conditions. Example results are shown in

Figure 1. These data are the results of scans along the line connecting the (1,0,0)

point with the (1,1,0) point in reciprocal space. These are difference plots; that

is, low temperature minus room temperature data, so that the short range atomic order

peak at (1, 0.5, 0) is subtracted out. An example of the temperature dependence of

the incommensurate magnetic peaks obtained in a diffraction experiment (E =14.8

meV) is shown in Figure 2 for Cu 0l_Mn . ,_ . There is no apparent anomaly at the so-

.OO .10

called freezing temperature; in this case T

f

= 70°K. The inflection point of these

2000

1500

1000-

500

Cu Mn,,

85 15

(1. 1/2 + 8. 0)

50 100

Temp [K]

150

Figure 2. Temperature dependence of the intensity at (1, 1/2 ± 5, 0) and (1, 1/2, 0)

for Cu . Mn . This data was taken with the energy analyzer removed, and

incident neutrons of energy E = 14.69 mev.

58
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

intensity vs. temperature curves, plotted versus Mn content is a straight line. We

have carried out very high resolution experiments in which (E =3-6 meV, AE = 0.12

meV) in an effort to isolate the elastic component of the scattering. We have found

two important results in these high resolution experiments: (1) the elastic

component falls off much more rapidly than that shown in Figure 2, approaching zero

near 90K; and (2) the inelastic scattering component, for small energy transfers

peaks near T . The combination of these results, along with a wide variety of

additional measurements, leads us to believe that the so-called "spin glass" behavior

in Cu-Mn is due to spin density waves (SDW) with a coherence length of about 10 fee

unit cells, and that the "freezing" point T is the Neel point representing the

transition from a static "ordered" phase to a dynamic disordered phase.

1. S. A. Werner and J. W. Cable, J. Appl. Phys. 52, 1757 (1981)

NEUTRON SCATTERING STUDY OF THE AMORPHOUS INVAR ALLOY Fe Q ^B

.oo .11

J. A. Fernandez-Baca and 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 Corporation, Morristown, NJ)

The amorphous alloy Fe or B . „ has been shown to exhibit Invar characteristics

.oo . 1

4

in which the thermal contraction is nearly compensated by a large positive

2 3 magnetostriction. Previous studies of this system ' show that spin waves are ob-

-1

servable around the (0, 0, 0) point for wave vectors up to q = 0.12 A . The spin wave energies follow a normal quadratic dispersion relation and the stiffness con5/2 stant, D, has a T dependence, in agreement with the two magnon interaction theory

5/2 for a Heisenberg ferromagnet. This T ' dependence is exhibited over a very wide

range of temperatures as found in other amorphous ferromagnets. The stiffness

constant obtained from the neutron scattering experiments is almost twice as large as calculated from magnetization measurements. This anomaly has also been reported for

4 the crystalline Invar systems Fe C(_Ni „,. and Fe„Pt and is believed to be an intrin-

• o5 .35 3 sic dynamic property of the magnetic and magneto-elastic interactions peculiar to the

2 3 Invar state. '

59
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Ishikawa et al . have reported that the intrinsic spinwave linewidths, of the

2

Fe Q.-B ^ system, vary with wave vector q as r = a q , showing only limited temperature dependence. This behavior has also been reported for the Fe rc.Ni _._ and Fe.Pt

I, .65 .35 5

Invar systems, as opposed to the behavior of the amorphous

5 6

(Fe n Mo ) Q B P and (Fe ,_Ni ) „_P .,B n ,Al ._ non-Invar alloys, whose

.93 .07 .o .1 .1 .65 .35 .75 .16 .06 .03

H 2 7 linewidths are consistent with the q T relation.

We have performed a neutron scattering experiment on a sample of amorphous

Fe Q(-B ,..., in order to study the spin wave dispersion relation and the intrinsic

.ob . \ h . . linewidths of this system. Boron enriched to 98.5 percent B was used to reduce

the neutron absorption. The measurements were taken near the forward (0,0,0) beam

0_ 1 0_ "1 position for wave vectors 0.05 A <_ Q <_ 0.12 A , at temperatures ranging from room temperature (0.5M T ) to 500 K (0.90) T ). Well-defined spin waves were observed

1.0

6 8

-3 (10

10 12 14 16

» -2.

Figure 1. Spin wave dispersion relation for the Fe ft ,B h spectral weight function used was a Double Lorenlzian.

amorphous system. The

60
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Double Lorenzian — a— Halperin and Hohenberg —o- Harmonic Oscillator

(T/Tr) 5/2 (K 5/2 10")

Figure 2

Figure 3.

Temperature renormalization of the stiffness constant D with temperature

5/2

as D = D [ o (T/T )" ]. The curves and values correspond to Double

c Lorentzian, Halperin and Hohenberg, and Harmonic oscillator spectral

weight functions as shown.

0.25

>

<DE

0.20

0.15-

0.10-

0.05

200 400 600 800

q

4 [T ln(KT/fiw)] 2 A V

The intrinsic spin wave linewidths plotted versus q [T ln( —)]

2 as

hto

predicted for the two rnagnon interaction theory for a Heisenberg

ferromagnet

.

61
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

over the whole temperature range under study. Spin wave energies and damping information were obtained from the measured profile by convolution of theoretical cross

sections with the instrumental resolution. The resolution function has been CalCUlated using the method of Cooper and Nathans. We have used three different cross

9 sections corresponding to Double Lorentzian, Damped Harmonic Oscillator and Halperin

10

and Hohenberg spectral weight functions. The data were least-squares fitted to the

convoluted cross sections to obtain values of the spin wave energies and linewidths.

The three spectral weight functions all yield a dispersion relation of the form hw = 2

Dq + A; where D is the stiffness constant; q the wave vector; and A is an effective

gap, due primarily to dipole-dipole interaction. Figure 1 shows the dispersion

relations, calculated for the Double Lorentzian spectral weight function, for T =

300, 350, 400, 450, and 475 K. The gap A ~ 0.04 meV shows a slight temperature

5/2 dependence. The stiffness constant, D, renormalizes as D = D [1 - c(T/T ) ] in

o c the whole range of temperatures under study (see Figure 2), where D -132 meV A and

c - 0.87. For this system D values of 138 and 118 meV A have been reported in

references 2 and 3- In order to study the temperature and wave vector dependence of

4 kT 2 the spin wave intrinsic linewidths (r) we have plotted r vs. q [T ln(r—)] (see hw

Figure 3)- It is evident from this figure that the linewidth data are consistent

4 kT 2 with the form r « q [T ln(—-)] predicted from the two magnon interaction theory of a

j

nco Heisenberg ferromagnet. The small departures (lower left part of Figure 7) correspond to temperatures lower than 400 K where the intrinsic line broadening is much

smaller than the instrumental resolution (FWHM ~ 0.25 meV for the region of the spin

wave excitations) and the linewidths cannot be well determined.

The results in Figure 3 are in contradiction with the findings of Ishikawa et

3 a 2 al. who reported a dependence of the form r « T q with a <_ 1 . Our result also

confirms that there are no anomalies in the spin wave lifetimes which would contribute to the Invar effect seen in Fe, B systems.

1-x x

J

1. K. Fukamichi, H. Hiroyoshi, M. Kikuchi, and T. Masumoto, J. Mag. Mag. Mats J_0,

294 (1979).

2. J. J. Rhyne, G. E. Fish, and J. W. Lynn, J. Appl. Phys. 53_, 2316 (1982), and NBS

Technical Note 1178, June 1983, page 96, F. J. Shorten, Ed.

3. Y. Ishikawa, K. Yamada, K. Tajima, and K. Fukamichi, J. Phys. Soc. (Japan) 50_,

1958 (1981 ).

4. S. Onodera, Y. Ishikawa, and K. Tajima, J. Phys. Soc. (Japan) 50, 1513 (1981).

62
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

5. J. D. Axe, G. Shirane, T. Mizoguchi, and Y. Yamauchi , Phys. Rev. B1

5

, 2763

(1977).

6. J. A. Tarvin, G. Shirane, R. J. Birgeneau, and H. S. Chen, Phys. Rev. B1

7

, 241

(1978).

7. A. B. Harris, Phys. Rev. 1 75 , 674 (1968) and V. G. Vaks, A. I. Larkin, and

S. A. Pikin, Soviet Physics JETP 2_6, 647 (1968).

8. M. J. Cooper and R. Nathans, Acta Crystallogr. 23, 357 (1967).

9. See: R. A. Cowley, W. J. L. Buyers, P. Martel, and R. W. H. Stevenson, J. Phys.

C6, 2997 (1973).

10. B. I. Halperin and P. C. Hohenberg, Phys. Rev. 188, 898 (1969).

STUDIES OF THE OSCILLATORY MAGNETIC STATE IN THE SUPERCONDUCTOR HoMo,Se

o o

J. A. Gotaas, J. W. Lynn and R. W. Erwin

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. N. Shelton and P. Klavins

(Ames Laboratory, Ames, IA)

and

(Iowa State University, Ames, IA)

Small-angle neutron scattering (SANS) investigations have been continued on the

superconductor (T coo = 5.6K) HoMo,Se to probe the nature of the oscillatory magnetic

state which develops at low temperatures (T - 0.53K). This sinusoidal state develops

-1 2 with a characteristic wave vector of ~.09A , corresponding to a wavelength of - 1

A. This characteristic wave vector (q ) then decreases as the temperature decreases,

C

1 2 with the peak in the scattering growing in intensity. ' The new investigations

involved careful study of the time-dependence of the changes in the oscillatory state

upon changing temperature and the result of applying a magnetic field (up to 0.1 1T)

in the ordered state.

On cooling the sample to 0.286K (the lowest temperature attainable with a

3 -1

pumped-He cryostat), q rapidly reached a value of 0.063A . Over a period of more

than 100 hours, however, the value of q continued to decrease slowly, consistent

C

- At with an exponential decay of the form q (t) = q (<») + a e , where the asymptotic

value q (°°) = 0.0565A , although the integrated intensity remained essentially

constant. Warming the sample resulted in an initial rapid increase in q , followed

63
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

by a continued slow increase with time, again approaching an asymptotic limit at each

temperature. In all cases, the integrated intensity remained constant during the

gradual change in q . These long time constants for changes in q may result from

the comparatively slow adjustment of domains in which the oscillatory wave vector

lies along different directions.

Magnetic fields up to 0.1 1T were also applied to the sample in the ordered

state. The original scattering in zero-field was isotropic about the incident beam,

so that data taken on the two-dimensional SANS detector could be averaged over a complete annulus. The applied field induced asymmetries in the scattering; to study

these features the data taken were averaged over smaller sections parallel and

perpendicular to the direction of the applied field. Figure 1 displays such averaged

data for an applied field of 0.1 1T at a temperature of 0.29K. It can be seen that

the field induces additional scattering at very small wave vector; only the tail of

the additional scattering can be observed, the remainder falling behind the detector

beamstop. This small-q component is induced preferentially perpendicular to the

applied field, with an accompanying loss of intensity in the peak at q . There is no apparent shift in q either parallel or perpendicular to the field.

80

70

60

cEo

i—s

OT +>cO

O

><

50

40

30

- 20-

10

•

•

T = 0.29K

( > H = 0.11T

9 i q II H

<Fm^kr^ L h

T*5°y\ i i ^H

0.02 0.04 0.06 0.08 0.10 0.12

q(A

" 1

) Figure 1. Average intensity versus wave vector in 0.1 1T applied magnetic field (T = 0.29K), with averages calculated separately for sectors parallel and

perpendicular to applied field.

64
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Upon reducing the field to zero again, the original magnetic state is not

recovered, as can be seen from Figure 2. The anisotropic scattering at small-q

remains, and there is a small shift in q perpendicular to the applied field, leading

to constant-intensity contours which are prolate along the field. This post-field

state persisted for times up to H5 minutes after removal of the field with little

change. Upon warming the sample above the magnetic transition temperature, the

scattering disappears; upon cooling, the state which occurs retains the asymmetry of

the field-induced state. The source of this apparent memory of the anisotropic state

in the sample is unclear at present, but may be linked to the formation of a vortex

structure in the superconducting state under application of the magnetic field.

A complete understanding of the phenomena associated with this magnetic

transition will require further theoretical work and a determination of the magnetic

anisotropy present in HoMo,Se . b o

0.02 0.04 0.06 0.08 0.10 0.12

q(A" 1

)

Figure 2. Average intensity (parallel and perpendicular to field) versus wave vector

in OT (0.29K) after reducing applied field from 0.1 1T.

1. J. W. Lynn, J. A. Gotaas, R. W. Erwin, R. N. Shelton and P, Klavins, NBS Tech

Note No. 1190, p. 72 (F. Shorten, Ed., 1984).

2. J. W. Lynn et al., Phys. Rev. Lettr. 52, 133 (1984).

65
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SPIN CORRELATIONS AND DYNAMICS IN DILUTE MAGNETIC SEMICONDUCTORS

T. M. Giebultowicz

(Purdue University, W. Lafayette, IN)

and

J . J . Rhyne

Diluted magnetic semiconductors are alloys of ordinary semiconductors, and

magnetic semiconductors. One of the most extensively studied group of those

materials are manganese derivatives of the II-VI compounds, such as Cd„ Mn Te, 1-x x Hg„ Mn Te, Zn„ Mn Te, and similar selenides (referred to as DMS). In these °1-x x 1-x X materials the metallic atoms of the host crystal lattice are randomly replaced by Mn

atoms. The spin-spin exchange interactions between the localized magnetic moments of

+ + Mn ions and band electrons lead to several novel phenomena, occurring uniquely in

DMS (e.g., giant Faraday rotation, or formation of bound magnetic polarons). In

addition to that, the magnetic properties of DMS are interesting in their own right.

Several magnetic phenomena of current interest are seen in these systems, e.g. spinglass transitions, and magnon excitations in the spin-glass phase. From the point of

view of the classification of magnetic magnetic materials DMS are diluted Heisenberg

ant if erromagnets . The exchange interactions between Mn ions are extremely shortrange, J„..„ being only about one tenth of the J„„. Thus, DMS are closely related to

NNN NN

the "frustrated" (only J *0) fee systems, which are currently studied by various

modelling techniques. Experiments on DMS are therefore of importance for theory

development . So far, neutron diffraction studies on DMS revealed that long-range magnetic

order does not develop in these systems up to relatively high concentrations of Mn

(up to x=0.7). Those observation were in good agreement with the theoretical

predictions by Ching and Huber . Likewise, results of preliminary inelastic studies

showed similarity to the spectrum lines calculated by these authors. Quite recently,

additional theoretical results of Ching and Huber became available, namely,

quantitative analysis of the ranges of spin correlations, and further results of

dynamic modelling. Stimulated by this, we carried out scattering experiments on

1 1 1| Cd^ . cMn n ,_Te. Profiles of magnetic diffuse scattering maxima were measured at

(Job U .to

4.2K, along various directions in q-space. Results obtained by scanning through the

(1,-,0) point in x and y direction are shown in Figure l.The peak widths (HWHM) for x and y directions correspond to the inverse ranges of spin-spin correlations within

(100) planes (km), and between these planes (ki), respectively. From data shown

66
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

3000-

| 2000

in

</> C

3

O 1000

Q = (1.f ,0) Q = U. Vi. 0)

0.4 0.5 0.6

i 0.9 1.0 1.1

Figure 1. Scans through the (1,0.5,0) point of the q-space in [100] and [010]

directions for Cd„ „,_Mn„ r ,_Te single crystal at T = 4.2 K. 0.35 O.o5

in Figure 1 it can be estimated that the ratio kii/ki = 0.6, what is in quite good

agreement with the value 0.68 obtained by Ching and Huber for a system with the same

concentration of magnetic component. We measured also the inelastic magnetic neutron

v o 1 scattering at Q=—( 1 ,— ,0) , and several points along [100] and [010] directions in qspace. The main features of the observed spectra, namely: the broad excitation

modes, and stronger shift of the mean energy of excitations along the [100] than the

[010], are also in good agreement with model predictions. Detailed analysis of the

observed data in terms of Ching and Huber theory is under way.

We carried out also preliminary powder diffraction measurements for

Zn , Mn E.ir Te > a new material of the DMS group which technology of growing has been

recently worked out by Purdue University group. Unlike cubic DMS studied by now,

Zn, Mn Se possesses the vurtzite structure. Diffusive peaks seen in the diffraction

1-x x patterns at low temperatures indicate that the magnetic order is short-range, and

resembles the antiferromagnetic structure of vurtzite modification of MnS.

In parallel with the experiments, Monte Carlo computer simulations of the

magnetic properties of DMS were carried out. The studied model was a dilute

Heisenberg antiferromagnet with nearest and next-nearest neighbor interactions, which

is a classical analog of cubic DMS. In the course of this work temperature

67
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

dependences of several magnetic quantities were calculated for a system with x=0.70.

The results indicate a continuous process of temperature transition, and reproduces

quite satisfactorily the basic relations between results obtained by various

experimental techniques on Cd

Q oQ^no 70

Te *

W. Y. Ching, D. L. Huber, J. Appl. Phys. 52, 1715 (1981); Phys. Rev. B25, 5751

(1982), and B26, 61 6-4 (1982).

SPIN STIFFNESS ANOMALY IN THE REENTRANT SPIN GLASS (Fe,w%Ni ,J.„J>B,A:U 20 80 75 It) O 3

R. W. Erwin and J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

J . J . Rhyne

and

H. S. Chen

(Bell Laboratories, Murray Hill, NJ)

Low field magnetization studies have shown that the amorphous alloy

(Fe.-Ni^,. )„ r P. ,B £ A1_ becomes a demagnetization-limited ferromagnet below 200K. o / o l o 1 o o i

Extrapolation to zero applied field shows that the spontaneous magnetization vanishes

below a freezing temperature of 10K. Inelastic neutron scattering measurements have

been performed to study the spin-wave dynamics as the spin-glass state is reentered

from the ferromagnetic state. The observed magnetic excitations become critically

damped below a temperature which is weakly wave-vector dependent. The peaks in the

inelastic scattering at fixed q decrease in energy as the temperature is lowered

towards T

f and are overdamped below T over the entire range of wave-vectors measured

- T -1

(0.04 A < Q < 0.18A ). In the data analysis both the double Lorentzian and

harmonic oscillator forms of the spectral weight function have been employed for the

spectral line shapes. As shown in Figure 1, both of the spectral weight functions

show a decrease in the bare spin wave frequencies (uo ) as the temperature is lowered,

consistent with ant i ferromagnetic correlations appearing in the system. The degree

of softening is less when the harmonic oscillator analysis is applied to the

excitations, since the harmonic oscillator prevents a description in terms of

diffusive modes. In either case finite energy excitations are present in the spin

68
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

glass state, although the underdamped modes predicted by hydrodynamic theory are not

observed, but may be present at smaller Q. A resolution-limited elastic component of

the magnetic scattering appears below -80K as oj begins to decrease. As estimated

from an upper limit to any possible intrinsic linewidth, this scattering is due to

spins which are frozen for times at least two orders of magnitude longer than the

spin wave lifetimes. In this sense, the central component represents static spatial

fluctuations from the fully spin-aligned ferromagnetic state and can be interpreted

as a spin-glass order parameter, although these measurements are not able to

3 discriminate between the dynamic order parameter of Sompolinsky , and the static

Harmonic Oscillator

.'

-O- 25

xi<

c

(0 1 ° 1 w

0)c

(0 5

(0 JSw

200

-1

Figure 1. Spin wave energies in (Fe Ni „,.) ?5

P ^B

Q6

A1

Q3

at fixed q = 0.08 A as

a function of temperature. Curves are shown for the energies obtained from

the raw data using both harmonic oscillator and double Lorentzian forms of

the spectral weight function. Both forms show a significant decrease in

energy at the lower temperatures where ferromagnetism and spin glass order

co-exist. The large uncertainty in the points at low T is a result of the

overdamping of the spin waves. Also shown is the elastic intensity which

is related to the spin glass order parameter.

69
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

4 order parameter of Edwards and Anderson . In any case some type of spin-glass order

coexists with f erromagne t i sm in the range 1 0K < T < 80K. These results are

consistent with the measurement of a finite correlation length for the magnetic

fluctuations in the spin-glass state using small angle neutron scattering .

1. S. M. Bhagat, P. Mazumdar (to be published).

2. A. P. Murani, Phys. Rev. B 28, ^32 (1983).

3. H. Sompolinsky, Phys. Rev. Lett. H]_, 935 (1981).

4. S. F. Edwards and P. W. Anderson, J. Phys. F 5_, 965 (1975).

5. R. W. Erwin, J. W. Lynn, and H. S. Chen "(to be published).

MAGNETIC CORRELATIONS IN TIE REENTRANT SPIN-GLASS (Fe 0rtNi 0o )^^P, -Br Al

20 80 75 lb 5 3

R. W. Erwin and J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

H. S.. Chen

(Bell Laboratories, Murray Hill, NJ)

Small angle neutron scattering measurements (SANS) in the wave-vector range

-1

(0.01 < q < 0.10A ) have been employed to determine the instantaneous two spin

correlation function in the amorphous alloy (Fe Ni fl ) P J,A1 . Previous

measurements have established that the energy transfers in this wave-vector range are sufficiently small that the SANS will directly measure the wave-vector dependent

susceptibility.

The magnetic scattering above 119 K shows a conventional Lorentzian qdependence. The temperature dependence of the width of this distribution establishes

that the correlation length of magnetic fluctuations increases to an instrumental

limit (400 A) at 119 K. This agrees with low-field magnetization measurements which

show that the d.c. susceptibility is demagnetization-limited in the ferromagnetic

1 phase.

Below T = 119 K the intensity of magnetic scattering first decreases with

decreasing temperature as in a conventional ferromagnet and then below T = 80 K strongly increases. Energy analyzed scattering measurements for samples with higher

70
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

concentrations of Fe have shown that this increased intensity is largely due to a

2

component which is elastic to within limits determined by instrumental resolution.

This component is identified with the spin-glass order parameter of Edwards and

Anderson ,

qEA

= «S1 >>,

where the inner brackets represent the thermal spin average and the outer brackets

the conf igurational average. A model for the low temperature scattering function is

then,

S(q) = A

2 2

k + q

+ B

I 2.Z-1.5

(K

D

}

, 2 2.Z

(<

D

q )

cD

0.8

0.4

•» 0.8

c

=>

X)

0.4

40 80

T(K)

Figure 1 . Temperature dependence of the inverse correlation length, <, the amplitude

of the wave-vector dependent susceptibility, A, and q

- m . In the

lower half of the figure the low-field bulk magnetization is qualitatively

shown. The solid curves are guides to the eye.

71
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The first term is the Lorentzian wave-vector dependent susceptibility times the

thermal population factor in the case of small inelasticity. The coefficient A would

be temperature independent in an ideal ferromagnet. The second term is a generalized

form describing the scattering from clusters with a distribution of sizes and shapes.

For Z = 2 it reduces to the Debye or random field form of a squared Lorentzian. The

2 2 coefficient B is proportional to q - m where m is the square of the spontaneous

magnetization per spin (qRA _> m for all T).

For T _> 50 K the bulk magnetization measurements indicate that the spontaneous

magnetization is non-zero, so that it is reasonable to postulate that < = in this

temperature range. In fact the fits to the data are in agreement with this

conjecture. Below 50 K where the spontaneous magnetization vanishes, the best fits

to the data indicate that < is non-zero with k > < . When the parameter Z is allowed

to vary the best chi-squared value is found for Z ~ 6 above 50 K and for Z = 1.75

below 50 K. This indicates that larger clusters are more probable above 50 K in the

ferromagnetic phase than below 50 K.

The results in Figure 1 are presented for Z fixed at 2 over the entire

temperature range since this does not significantly change the quality of the fits

while reducing the number of free parameters. The cluster size information is then

contained in < which is zero down to 80 K. In addition < is zero down to 50 K and

is fixed equal to < below this temperature. This reflects the coexistence of

ferromagnetic and spin glass order between 50 K and approximately 80 K. The

2

temperature dependence of q - m is seen to be in qualitative agreement with the

bulk measurements of m. The order of magnitude increase of the wave-vector dependent

suscept iblity and the rise in k as the temperature is lowered below 80 K are both

consistent with a breakup of the ferromagnetic correlations in the spin-glass phase.

1. P. Mazumdar and S. M. Bhagat (private communication).

2. J. W. Lynn, R. W. Erwin, H. S. Chen, and J. J. Rhyne, Sol. St. Comm. 46_, 317

(1983).

3. S. F. Edwards and P. W. Anderson, J. Phys. F 5_, 965 (1975).

72
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

APPLIED FIELD RESPONSE OF THE SPIN GLASS STArS IN AMORPHOUS NdFe

M. L. Spano and H. A. Alperin

(Naval Surface Weapons Center, Silver Spring, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

J . J . Rhyne

and

S. J. Pickart, S. Hasanain, and D. Andrauskas

(University of Rhode Island, Kingston, RI)

The magnetic correlations and the response of the spin system to an applied

field has been studied in sputtered amorphous NdFe using high-resolution small angle

-1 -1 neutron scattering (SANS) techniques over the range 0.01 5A < Q < 0.08A . The zero field scattering shows only a weak anomaly at the spin freezing temperature of approximately 3^0 K (determined from magnetization data) and exhibits strong

"subcr it ical" scattering below T

f which increases rapidly in magnitude as the temperature is reduced. The lineshape of the scattering is Lorentzian down to the spin

freezing temperature. Below T , the lineshape becomes increasingly non-Lorentzian

and has been analyzed using a Lorentzian plus Lorentzian-squared cross-section appropriate for a random anisotropy field system. The correlation length shows a broad

maximum of 1 70A near 270K (which is below T ) and then decreases to a constant value

of =80A for T<100K. The Lorentzian squared coefficient is negligible down to below

300K and then rises monotonically to the lowest temperatures. A similar increase is

seen at low T in the Lorentzian component. The spin susceptibility defined by the

coefficient of the Lorentzian term divided by the inverse correlation length squared

exhibits a relatively sharp peak at 300K, close to the maximum in the correlation

length.

SANS data taken in applied fields up to 1 8k0e at 21 OK and 80K produced constant

intensity contours which are elliptically distorted with the Q H direction being

the major axis. The overall intensity and the calculated spin correlation length

both drop abruptly with increased field, the latter down to 30A (from 175 A at H = 0)

in a field of 4k0e at 210 K with only a small decrease at higher fields. Over the same field range, the Lorentzian squared component of the scattering is increased for

Q |

| H and decreased for Q i H relative to their H = values. This overall behavior

is consistent with the field driving the dominant part of the spin system into an infinite cluster with the residual smaller spin clusters exhibiting a super-paramagnetic type response.

73
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SANS EVIDENCE FOR THE ABSENCE OF LONG-RANGE MAGNETIC ORDER IN AMORPHOUS Fe Zr

J . J . Rhyne

and

G. E. Fish

(Allied Corporation, Morristown, NJ)

Small angle neutron scattering studies of an amorphous Fe ZrQ alloy have shown

that there is no transition to long-range magnetic order in contrast to results

1 obtained from bulk magnetization which indicated a transition to a ferromagnetic

state at 220K followed by a re-entrant spin glass state near 60K. Total scattering,

elastic scattering and inelastic scans were taken on a triple-axis spectrometer using

a pyrolytic graphite monochromator and analyzer with 1 5'-1 2'-1 1 '-25' effective Soller

collimation. Resolution corrections for both horizontal and vertical divergences

(1.5°, 2.2°, 3.8°, and 6.0°) were made.

-1 -1 The scattered intensity at small Q (0.04 A < Q <0.2 A ) shown in Figure 1 shows a relatively sharp cusp at 205K followed at lower temperatures by a broad

minimum. Below approximately 1 20K there is a further strong increase in the lowest Q

intensity. The lineshape is Lorentzian in Q down to below 1 50K and yields a spin

correlation length which reaches a maximum of only 27A at the transition T = 205K and

exhibits an essentially constant plateau of 23 A down to helium temperature, with no evidence of a second transition in the 60-80K range (see Figure 2). The lineshape

departs from Lorentzian below about 1 20K (reflecting the behavior of the lowest Q

2 data) and can be represented by a Lorentzian (L) plus Lorentzian-squared (L ) cross section as follows:

d o A B

d n ^2 2 ,.2 2,2

Q + K (Q + K )

2 where « is the inverse of the spin correlation length £ and the ratio A/< defines

the spin dependent susceptibility. This form of the cross-section is appropriate for

a system in which random fields destroy the long range order and converts the delta

2 function Q = scattering into the above lineshape. The ratio of the L to L terms

increases at low T reaching 0.011 at 8K. Inelastic scattering data gave no evidence

of coherent spin wave excitations at any temperature, and no significant quasielastic scattering.

74
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

30

^~* 25

<—

'

•WJ> 20

.c

+rf CDc

_j 15

c

o

CO 10

aii_o

O b

n O

o

o o o

(Arb. Units) -• •-

40 80 120 160 200 240 280 320 360

(T (K)

Figure 1 . Temperature dependence of the total scattering at several values of Q from

an amorphous Fe Zr alloy. The cusp near 220 K marks the spin freezing

temperature. The sharp upturn in the lowest Q curves below 1 20K reflects

the change in lineshape from Lorentzian to Lorentzian plus Lorentzian

squared.

40 80 120 160 200 240 280 320 360

T(K)

Figure 2. Temperature dependence of the spin correlation length g and of the wave

vector dependent susceptibility x for* amorphous Fe Zr . 91 9

75
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Tnese results confirm that Fe Zr enters a spin glass state below its freezing

y i y temperature of 205K with a relatively short correlation range, and no long range

order. Since the concentration of Fe is far above the percolation threshold, this

suggests that a very broad distribution of exchange fields arising from the random Fe

site coordinates may be responsible for the spin glass state.

1. H. Hiroyoshi and K. Fukamichi, J. Appl. Phys. 53, 2226 (1982)

INELASTIC NEUTRON DIFFRACTION STUDIES OF ZEOLITES

I). Corbin, L. Abrams and G. Stucky

(E. I. DuPont de Nemours and Co., Wilmington, DE)

and

R. Cavanaugh

(Surface Science Division)

and

J. J. Rush

Temperature dependent inelastic neutron diffraction studies of H-rho and NaCsrho have been initiated to study proton siting, vibrational, and mobility

characteristics as the zeolite temperature approaches the in-situ temperatures

commonly used in chemical catalytic processes. A pronounced change in siting is

observed between room temperature and 275 °C, with a shift to frequencies less than 50

meV. The constant integrated intensities at different temperatures confirm proton

rearrangement rather than desorption.

Detailed studies of proton behavior over a broader temperature range and with

sorbates by quasielastic and inelastic techniques are planned.

PHONON SOFTENING IN THE MIXED LAYERED SYSTEM K, Rb cJ

D. A. Neuman and H. Zabel

(University of Illinois, Urbana, IL)

and

J. J. Rush and N. F. Berk

Using inelastic neutron scattering, the dispersion of the longitudinal [OOq]

phonon modes has been measured for the first time in the mixed layered compound

76
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

K„ Rb C n over the whole composition range < x < 1 . Such graphite intercalation

1-x xo —

compounds (GIC's) provide a fertile test ground for the exploration of phonons in

layered mixed crystals because the phonon dispersion of the c-axis longitudinal modes

is well known for the pure compounds and can be accurately described by a simple

diatomic linear chain model with just two force constants. Our study shows that the

mixed system, as well, is described by the same model generalized to incorporate the

averaged areal mass density of the disordered alkalai layers and compositionally

dependent first-neighbor and second-neighbor force constants. Moreover, the secondneighbor force constant and the measured elastic constant C _,_ both show striking

softening at x = 0.65. Our work has led us to suggest that this softening, and

possibly other anamolies at this composition that have been recently reported, is

caused by an asymmetric composition-dependent charge transfer between the mixed

alkalai layers and the graphite layers. It is also interesting to note that the

study did not reveal any neutron scattering that could be attributed to defect

vibrational modes in the bands or in the gap.

1. D. A. Neumann, H. Zabel, J. J. Rush, and N. Berk, Phys Rev. Lett. 53, 56 (1984).

THEORY OF ALKALI CYANIDES

J. M. Rowe

and

K. H. Michel

(University of Antwerp, Antwerp, Belgium)

In the past year, significant progress has been made in the theory of

translation-rotation coupling in alkali cyanides. In particular, a new mode-coupling

approach shows promise for the explanation of the damping of optic phonons in the

cyanides--a fact well established experimentally (and in molecular dynamics

simulations) but not heretofore unexplained by theory. In addition, new calculations

of self-energies and other local properties are pointing towards modification of

earlier theoretical results for transition temperatures and neutron cross-sections.

77
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STRUCTURE OF ALKALI CYANIDE-ALKALI HALIDE CRYSTALS

J. M. Rowe and J. J. Rush

and

F. Lutz

(University of Utah, Salt Lake City, UT)

We have extended our earlier measurements of the structure of (KCN) (KBr) by

neutron powder diffraction to (KCN) (KC1), . In contrast to the KBr mixtures, which

x 1-x

first go to a monoclinic structure at low temperatures, KC1 mixtures go directly to an orthorhombic structure similar to that of pure KCN. This is true even at a value

x = 0.80, which is the lowest value of x at which a transition occurs. The KBr

samples for x = 0.6, the lowest x for which a transition occurs, go monoclinic and

remain monoclinic down to the lowest temperatures). This contrast in behavior must

be related to the different size of the Br and CI ions, but the origin of the

effect is as yet unknown. This new structural information helps to explain the

earlier observation that!--—lis quite different for the two systems. When one

/2Tc\ V 2X / comparesi *— for transition to the orthorhambic phase, the two systems are much more

similar. Since the monoclinic phase observed in the Br mixtures is closely related

to the metastable monoclinic phase observed in KCN subjected to repeated stresses, a possible explanation for all observations is that the range of existence of the

orthorhambic phase is the same in both systems, and that the monoclinic phase is not

stable against strains (such as the lattice mismatch caused by the CI ions).

NONDESTRUCTIVE CHARACTERIZATION OF SUBSURFACE RESIDUAL STRESS IN DEPLETED URANIUM

H. J. Prask and C. S. Choi

(U.S. Army Armament R&D Center, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

Depleted uranium -0.75 wt$ Ti alloy ("DU") has become a principal material for

armor-piercing projectiles because of its high density, hardness, ductility, and high

ultimate tensile and yield strengths. These properties are achieved by a fabrication

process which involves a fast quench to ambient temperature from the T-phase

800°C), followed by aging at - 400 o C. This yields the desired mechanical

properties with the Ti "dissolved" in the single-phase a'-U host lattice. However,

optimization of performance has probably not been achieved because of an inability to

characterize certain properties in the course of the fabrication process. One of the

most important of these is residual stress.

78
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table I. x-ray/Neutron Comparison

Element (Atomic Number) t^ (1.54 A X-rays) z }/2 (1.80 A Neutrons)

Al (13) 0.0530 mm 71 .0 mm

Ti (22) 0.0076 15.9

Fe (26) 0.0027 6.1

W (74) 0.0021 6.5

U 238 (92) 0.0015 13-6

Table 2. U -0.75 wt# Ti Samples

Property/Treatment DU1 DU2

Extrusion (10X Reduction in Area) X X

Solutionizing (2 hrs.

,

850°C, vacuum) X X

Furnace Cooled X

Quench X

Rotary Straightened X

Aged X

a-U + TiU 2 Structure X

a'-U Structure X

x-ray diffraction for residual stress analysis (XRDRSA) has been developed so successfully that it is now a routine method for nondestructive determination of

surface stresses in metals. In fact, in the last few years portable devices for

field use have become commercially available. However when applied to DU, grain

size, surface oxidation, and other effects have produced very serious problems for

XRDRSA. Alternative nondestructive techniques - such as ultrasonics, eddy current,

etc. - have seen only limited success on other metals and have not proven useful for

DU. Until now, the technique which has been used with the greatest degree of success

is the (destructive) Sach's boring-out method. Applied to DU , it is slow,

expensive, requires special surface coating, special boring equipment, and the use of

strain gauges. In addition, certain assumptions are required to extract stress

values for the cylindrical specimens. For example, hoop and axial stresses are assumed to vary only with radial distance from the cylinder axis. The fact that the

DU bars are bowed when removed from the quench bath shows this to be incorrect.

Recently, we have demonstrated that energy-dispersive neutron diffraction

(EDND) is a viable technique for the measurement of subsurface residual stress in

2 highly textured metallurgical samples. As shown by the attenuation thicknesses for

half-intensity loss, t . listed in Table 1, DU is a very favorable material for

neutron diffraction examination. In contrast, a 1.54 A x-ray beam is attenuated by

one-half in 1.5 um of DU, which is less than the typical grain size of 5-10 ym.

We have applied EDND to the determination of subsurface residual stresses in

two samples of DU which differed in thermo-mechanical history as shown in Table 2.

79
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

It was expected that DU1 , the furnace-cooled specimen, would exhibit near-zero

residual stresses, while the stresses in DU2 would be large with steep gradients.

The measurement geometry is shown in Figure 1. The indicated differential

volumes are defined by apertures in cadmium masks mounted on the incoming- and

2 scattered-beam collimators. Strains were determined for the (111) reflection at a scattering angle of 72.4° with an instrumental resolution Ad/d - 0.007. The

unstressed d-spacings, d (111), for both cx-u and a'-u were determined by highresolution neutron powder diffraction and total-profile analysis using 1 cm. diameter

x 1 cm. long samples and sample spinning (to minimize texture effects).

Neglecting shear stresses, measured strain is related to residual stress by

2 2 2 2 2

E ± = 1/2S„(hkl)[o cos Asin v + (i sin d>sin y + ° cos X^ +

<J>X 2 vr 89 zz Vhkl)[o

rr

+ °69+ °zz L

where z corresponds to the cylinder axis, x is tne angle measured from the z axis,

and <j> is measured relative to the r-direction.

1.5 x 1.5 x 30

*2

2.5 x 2.5 x 5

All Dimensions in Millimeters.

Figure 1. Overall geometry of the DU samples and points at which

measurements were made. Also shown are the differential volume

examined for Qs in the r-0 plane (upper right) and parallel to

-> the cylinder axis (Q ). The Q-direction corresponds to the

bisector of the angle between incident and diffracted beams.

80
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 2. Residual stresses in the two depleted uranium samples [DU1

results are shown as triangles at x(y) = 0]. The procedure

employed is described in the text.

In this case the anisotropic diffraction constants S. are approximated as

1/2 S (hkl) = (1+y)/E and S (hkl) = -y/E

where E is Young's modulus and y is Poisson's ratio, with E = 165480 MPa and y = 0.21

in this case. The residual stresses obtained for DU1 and DU2 are shown in Figure 2.

Because strains measured for several points in DU1 were constant within the standard

deviations of the least-squares fit d-spacings, only the axial point is shown.

The measured stress distributions confirm the applicability of the EDND

technique to DU . Overall, the stress distribution obtained for DU2 is in good

agreement with what would be expected for a rapidly-quenched cylinder and with Sach's

1 boring-out results. However, clear asymmetries in stress distributions are present

as indicated by the fact that measured stresses along the two orthogonal diameters

X Y ("X" and "Y") do not coincide (i.e., o ^ o etc.) These asymmetries may arise

rr rr from the rotary straightening of DU2; however, the rods are, in general, found to be

bent when removed from the quench bath. This suggests that either quenching is non- uniform (possible because many rods are "bundled") or texture in the uranium

introduces anisotropy in the stress distribution.

These results represent the first nondestructive determination of subsurface

residual stresses in DU by any technique. For the future this provides the prospect

of examining stress distributions—for DU and other materials--for a single piece in

each stage of the fabrication process.

81
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. F. A. Simonen, K. R. Kjarmo, C. J. Morris, K. 0. Nelson, E. M. Patton, L. A. Strope, and C. A. Williams, "Residual Stresses in Depleted Uranium Bars,"

Battelle Pacific NW Lab Rept. AM&S No. 5, September 1982.

2. H. J. Prask and C. S. Choi, NBS Tech. Note 1190, 31 ~3^ (1984).; NBSIR 84-2815, 53-

56 (1984); J. Nucl. Matls., in press.

STUD* OF MATERIALS SUBJECT TO IMPACT

H. Alperin

(Naval Surface Weapons Center, White Oak, Silver Spring, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

High resolution neutron diffraction measurements have been used to characterize

specimens used for fracture dynamic studies. Two samples of a Zirconium alloy

(cubes, 11 mm on a side) were measured: one as-received and the other after impact

by a 16 mm aluminum plate at 0.9 km/sec. Seventeen distinct reflections were

observed for each sample in the range 32-107 degrees at the neutron wavelength of

1.54 A. Least square Gaussian fits to the profile of each peak yielded a full-widthat-half-maximum (FWHM) for each reflection. Although the peaks for the as-received

sample were only slightly broadened as compared to an Al powder sample standard,

the peaks of the impacted sample were considerably broadened. For example, the (114)

reflection at 26 = 100.7° had a FWHM = 0.515° for the as-received sample but a FWHM = 0.715° for the impacted sample. The principal causes of peak broadening are a decrease in the size of the coherent diffracting regions (particle size broadening)

and internal strains. These two parameters were determined by fitting the data to

calculated expressions for the FWHM as a function of scattering angle with the result

-3

that the strain was determined to be 1.6 X 10 while the "particle size" was in

the range 1000 to 3500 A depending on the exact form of the distribution of strains

1 and particle sizes (Gaussian or Caudry). Of the two effects internal strains are

the main cause of the broadening. The magnitude of the resultant internal stress due

to these strains is of the order of the yield stress in this material. Although the

cube remained intact after impact, subsequent sectioning revealed many internal

cracks.

1. H. p. Klug and L. E. Alexander, X-Ray Procedures foi Polycrystalline and

Amorphous Materials, Chapter 9 (1974).

82
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SPHERICAL-MODEL ESTIMATE OF THE UPPER BOUND FOR THE ABSORPTION OF CAPTURE-GAMMAS

IN THE NEUTRON COLD SOURCE

R. S. Carter and R. C. Casella

We have considered an idealized model of the cold source which allows analytic

solutions for the absorption of those gamma rays which are produced by neutron

capture in the cold source. The model consists of a sphere of deuterated ice of

radius _a and gamma absorption coefficient n , surrounded by a contiguous aluminum

shell of uniform thickness t and absorption coefficient p, where t << a. Gammas are assumed produced in the shell at a rate s(0,<j>) = p(8,<j>)t per unit area per unit time.

Neutron capture within the ice is neglected. The model allows one to calculate the

fraction of the total gamma production rate a J d[l s(6,<j>) which is absorbed in (a)

the ice and (b) the aluminum shell in a simple way and can serve as a basis for more elaborate analyses. Since the surface-to-volume ratio is minimal for a sphere, one

expects a smaller fraction of the gammas will escape than would be the case from a non-spherical configuration of equal volume. Thus the model should yield an estimate

of the upper bound to the actual rate of absorption of the capture-gammas for a fixed

volume of ice and a given rate of neutron capture in the surrounding shell. The

treatment presented here deals with only one facet of the overall analysis of the

cold source. Even then, further corrections for the realistic configuration are

required and have been estimated. Nonetheless, the relatively simple approach

discussed contains the essence of this one aspect of the analysis.

Once produced via neutron capture in the outer shell, gammas are absorbed in

three stages: (i) primary local absorption by the shell immediately after their

production therein, (ii) absorption of the inwardly directed gammas by the ice sphere

during their traversal thereof, and (iii) secondary absorption in the surrounding

shell of gammas which have negotiated the sphere but must traverse the aluminum shell

from within to escape to the outside. In the limit as the thickness t -* such that

such that both y and s(6,<|>) remain finite, only the ice absorbs the inwardly directed

source current j (6,<j)) = (1/2) s(e,<|>). Of t s having traversed some part of the sphere, wheresource current j ( e ,

<J> ) = (1/2) s(e,<{>). Of this, a fraction f escapes after

f

in

= (1/2na)(1 - e 2u

i a

). (1) esc 1

The fraction of the total rate of gammas produced which escapes is equal to 1/2 + 1/2

f , whence the fraction absorbed is given by

esc & J

83
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

f° = (1/2)0 - f

in

). (2) abs esc

The above results hold for gammas produced at each point (6,<j>) on the surface. They

are exact in the limit as t * with y remaining finite. Moreover, they are

independent of the angular distribution of the source strength s(9,<j>).

To incorporate finite-thickness corrections when \it << 1, we employ the

infinite-plate approximation at each position (9,<j>) on the shell. This approximation

is valid when both (t/a) and O/pa) are small compared with unity. Then

j (8,<j>) = (pt/2) 0/ut)[1/2 - E (lit)], (3)

S 5

where E (x) is the tabulated exponential function:

E

n

(x) =

J dy (1/y

n

) e~ Xy

. (4)

loc The fraction locally absorbed f equals 1 - 2j /pt.

au s s .ice

Next finite-t corrections are considered for the fraction f , of gammas abs

absorbed in the ice (process ii). The fraction f of inwardly moving impinging

gammas which escapes the ice is independent of t and is given by eq. (1). the

fraction of these inward movers which is absorbed in the ice equals 1 - f , whence,

esc

r

l t e

= (j /pt)0 - f

in

). (5) abs s esc

Finally, we have estimated the amount of secondary absorption of the gammas in

the shell (process iii). In terms of the spherical average

< j > = (1/4tt) J dfl' j (8 ? ,<t>'), (6)

we find the approximate result

Cs (< J s >7< pt » C( V)[1 - E2 (ut)] - (7)

Here f (p. a) is given by eq. (1) and < j >/< pt > = j /pt, as given by eq. (3).

In the limit, as t -> 0, j /(pt) » 1/2 and E^(ut) * 1, whence f ° <: > 0, f ,. »• 0, while

s 2 abs abs

i_ (->p q

f . •* f . , the latter given by eq. (2). That is, the earlier result for zero shell

abs abs

thickness is recovered. For finite t/a, finite curvature corrections to the

infinite-plate approximation in treating the shell also enter.

84
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COLD NEUTRON SOURCE - DO

R. S. Carter

During the past year, additional funds became available to expedite the

installation of the DO ice cold source. The radiation shielding around the cold source cryostat is a separate unit

mounted on a separate plug (see Figure 1). The shielding material is primarily

bismuth, and the unit is referred to as the bismuth tip. This unit is completed and

ready for installation. The safety analysis has been completed, reviewed, and

approved by the NBSR Safety Evaluation Committee. It will be installed when the cold source cryostat is installed.

The original cold source cryostat was made of aluminum and included a beryllium

filter placed in the reentrant hole in the ice. The cryostat was redesigned to

provide complete helium containment of the insulating vacuum and to omit the

beryllium filter. Magnesium alloy was selected as the material of fabrication in

order to decrease heat generation from capture gamma rays. The low neutron capture

cross section of magnesium reduced the heat generation by a factor of three. The new design has been completed and put out for bids.

Figure 1. Cold neutron source,

85
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SEARCH FOR CHARGE DENSITY WAVES AND OTHER EXPERIMENTS ON POTASSIUM

S . A . Werner

(University of Missouri, Columbia, MO)

and

(National Bureau of Standards, Gaithersburg, MD)

and

A. W. Overhauser and T. M. Giebultowicz

(Purdue Univ., W. Lafayette, IN)

and

J. M. Rowe

The most straightforward method of studying charge density waves is by

diffraction experiments. CDWs lead to incommensurate modulation of the normal

crystalline periodicity, giving rise to satellites of Bragg reflections seen in X-ray

and neutron diffraction patterns. So far, such satellites have been observed in

1 layered and one-dimensional compounds , and in many metals, e.g. a-Uranium. There is

much evidence, however, that CDWs exist also in alkali metals; reviews of these

2 results are given in articles of Overhauser and co-workers . The feasibility of

diffraction studies on potassium is also discussed in these papers. As follows from

-> elementary considerations, the position of a satellite peak in Q-space is given by GQ, where G is the ( 1 1 0)-reciprocal lattice vector (|G|=1.414 ), and Q is the wave- ! a vector associated with CDW. Optical data indicate that Q in potassium is nearly

2ir parallel to one of the [110] axes, and its length is "1.38 . These numbers

a -> determine approximately the satellite positions (as domains with different Qs may

form in the crystal, satellites with various intensities should occur at 48 symmetry

related positions surrounding each bcc Bragg reflection). Unfortunately, the

-5

estimated satellite intensity is only ~10 of the intensity of the underlying bcc

Bragg reflections. This fact, combined with the small distance from the (110) Bragg

peak, clearly points out the scale of difficulty of an experiment. However,

diffraction data is crucial for the theory of CDWs in alkali metals: first, as a qualitative confirmation; secondly, for accurate determination of the Q vector,

important for quantitative analysis.

In view of this, we carried out neutron diffraction experiments on potassium.

The sample was a cylindrical single crystal (1'' in diameter, and 3'' in height),

with the [011] axis vertical. A triple axis spectrometer was used, with a pyrolytic

graphite (PG) monochromator and analyzer, and a PG filter. Several precautions were

taken in order to avoid spurious peaks. One class of such effects is multiple

86
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Q = ( £ ,0.97, 0.97)

2000 — •

• 1800 •

1600

c 1400

E

in 1200 ••*

• •

•

• • •

• • ••

V)

*-> C

3

<j1800

1600

1400

1200

1000

Q = U , 1.03, 1.03)

• •••

• • • •* •

J I L -0.04 -0.02 0.02 0.04

Figure 1. Peaks seen in the vicinity of the (011) Bragg reflection in potassium.

Small peaks in the center (£=0) are remanents of the Bragg peak. The

vertical bar is the width (FWHM) of the Gaussian instrumental resolution

function.

scattering. As multiple reflections vary strongly with wavelength, two different As were used. Another source of artifacts, thermal diffuse scattering (TDS), was taken

into consideration with special concern. TDS was reduced by maintaining a low sample

temperature (4..2K), and performing an energy analysis of the scattered beam. Such

precautions might still be insufficient. Therefore, calculations of TDS were carried

3

out. A computer program was employed , calculating the inelastic spectrum for a given scan direction, taking into account all essential crystal and instrumental

data. Computed results were "calibrated" by comparing calculated and measured phonon

peaks.

We carried out scans in various direction in Q-space in the neighborhood of the

(011) and (200) reflections. Several peaks were seen in diffraction patterns;

however, most of them could not be reproducibly observed. The only fully

reproducible effect were four peaks occurring in the scanning directions

q=U, 097, 0.97), and (£.1-03,1.03) for £= + 0.015 (Fig. 1). The widths of these peaks

87
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1500-

•

•Q = U. 0.04, 0.04)

• •

• ••

• ,.•••

*•••

°°

x 1/50

"'••S,

I i

I

Figure

I

1000

If) \

COco 500

o

1.90 1.95 2.00 2.05 2.10

As in Figure 1, for the (200) reflection.

are in agreement, with the corresponding instrumental resolution. Because of the

limited resolution in the longitudinal direction, we were not able to resolve the

peaks accurately enough from the (011) peak. Therefore, we still cannot exclude that

the effect observed is associated with a certain kind of "ridge" descending from the

main reflection. If assuming, however, that the peaks observed are CDW satellites,

one can estimate on that basis where other satellites should be seen. In the

vicinity of the (011) reflection these predicted peaks have either zero intensity, or interfere with the extended shoulders of the Bragg peak produced by a small fraction

of mosaic blocks deviated far from the mean orientation. More favorable conditions

are offered by the (200) reflection. Peak-like effects were reproducibly observed,

indeed, for scanning direction q=(2+£, 0.04, 0.04) at £=+0.045 (Fig. 2); this is

close to one of the predicted points. As before, the spectrometer resolution was

insufficient for obtaining convincing results for the perpendicular scan direction.

Scans performed at other expected regions of satellite occurrence gave negative

results. However, the estimated positions may be somewhat ambiguous, when based only

on two components of Q that can be evaluated from the peaks near the (011)

reflection. In fact, satellites may be located beyond the experimental plane and

missed because of too tight a vertical collimation.

So far, we have not collected enough evidence for drawing final conclusions.

More experiments are necessary; the data already existing provide indications for

further experimentation.

88
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

We also performed measurements of phonon dispersion relations in potassium.

This experiment is related to studies of the local field corrections to the

dielectric function. Investigation of the effects of the singularity in local field

H corrections at q=2k on the phonon spectrum by Wang and Overhauser shows that the

singularity will influence the phonon dispersion relations along certain trajectories

in q-space. As experimental data for potassium are available only for high-symmetry

directions, such studies require new research. We measured the inelastic phonon

spectra for trajectory --(0.36, 0.36, 2+£) , and several other lines in q-space

a. parallel to this direction. Experiments for other trajectories are also planned.

1. J. A. Wilson, F. J. DiSalvo, and S. Mahajan, Adv. Phys. 2_4_j_ 117 (1975)

2. A. W. Overhauser, Advances in Physics 27_, 3^3-363 (1978); G. F. Giuliani and A. W.

Overhauser, Phys. Rev. B 23, 3737-3743 (1981), and references therein

3. Unpublished; the program was originally created by R. Pynn and S. A. Werner

(1971); running versions are kept at NBS, and BNL.

4. Y. R. Wang, M. Ashraf, and A. W. Overhauser (1983), unpublished.

89
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

RECENT ADVANCES IN NEUTRON OPTICS

S. A. Werner

(University of Missouri, Columbia, MO)

and

(National Bureau of Standards, Gaithersburg, MD)

and

A. G. Klein

(School of Physics, University of Melbourne, Australia)

A range of phenomena similar or analogous to those of classical optics is

exhibited by slow neutrons. During the past decade considerable interest has been

generated in this field from the point of view of fundamental physics. This has been

due largely to the successful application of the perfect silicon crystal

interferometer to neutron experiments, and to the increased availability of more

intense sources of long wavelength neutrons. Neutron optical ideas and techniques

play an important role in all aspects of neutron scattering technology, in particular

in the extraction, filtering and monochromation of beams. This work represents the

most recent, comprehensive review of this important field of neutron science. It

will be published in the book Neutron Scattering , (Chapter 4), edited by D. L. Price

and K. Skold, Academic Press (1984). It is 78 pages in length, with 166 references

and 39 figures. It contains the following main sections:

1

.

The optical analogy and the refractive index.

2. Refraction and reflection.

3- Diffraction by macroscopic objects.

4. Interference and interferometry.

5. Applications of neutron interferometry in fundamental physics.

- Gravity and inertia

- Verification of quantum mechanical principles

- Tests of non-standard quantum mechanics

6. Neutron optics in perfect crystals.

7. Conclusion and future prospects.

90
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NONLINEARITY. IN WEAK MAGNSTEC FIELDS INDUCED BY NSU7R0N-ANTINEUTR0N OSCILLATIONS

IN NEUTRON INTERFEROMETRJf AND SPIN RESONANCE

R. C. Casella

The breaking of exact baryon-number conservatioa in unified theories of the

fundamental gauge interactions, has led to extensive searches for proton decay and

neutron-ant ineutron (nn) oscillations, thus far without confirmed experimental

evidence for either process. In some theories, nn oscillations can occur even in the

absence of proton decay. For unbound neutrons, the present experimental limit on the

-22

relevant paramenter 5 < 7 x 10 eV, is obtained by looking for annihilation in a downstream target of an n generated with probability P-(t) from an initial reactor1 n produced neutron after a flight time t. A more stringent, but less direct, limit

on 6 exists from stability in oxygen nuclei. I have examined the possibility of

detecting unbound nn oscillations, not by observing the n directly, but rather by

employing some very sensitive technique, such as neutron interferometry or spin

2

resonance, to detect a nonlinear variation with magnetic field B, which is

associated with a minute shift of the neutron energy induced by the exchange of heavy

X quanta endemic to unification theories.

Assuming CPT as well as CP invariance and neglecting decay, the

phenomenological Hamiltonian in the particle rest frame can be written in the form

-> -> -> + - H=m-u*B + 5A, where y = A, gu o is the n (or n) magnetic moment expressed in

terms of the nuclear magneton p., neutron g-factor, and Pauli spin matrices o. (A

and A are the analogues of isospin matrices in the |n >, |n > basis, where,

e.g., A |n,o > = |n,o >.) As is well known, the eigenvalues of H are M ± (B) = 2

X

? ^ /2

z m ± (3 + 6") , each doubly degenerate in ordinary spin (t,+). S/B = |guM

| ~ 6.0 x -12

10 eV/gauss. If, say , |^(t = 0) > = \n + >, then one obtains the known result,

which for (6/6) << 1 is

P-(t) = I < ntU(t) > I 2

= (6/B)

2

sin

2

6t. (1)

(For the moderately reduced fields and typical flight times employed in the current

2 2 nonstorage configuration, Bt << 1 and P-(t) « 5 t .) I have examined the other

connected amplitude which, for the same initial condition, reads

<n+|\b(t) > = e"

imt " i6t

e _i (6

2

/2B)t[1 - sin(23t)/(2&t)]

q

-(6 2

/2B

2

)sin

2

Bt

(2)

91
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2

when (6/3) is treated as a small expansion parameter. For free-flight times t and

magnetic fields B such that St ^ it, this amplitude contains the energy factor

exp[-iM (3)t], leading to a nonrelativistic laboratory energy

E

+

= p

2

/2m + 3 CI!'+ 5 2

/(2B

2

)]. (3)

The relative phase <J> (B) of coalescing wave fronts of an initial |nt> in an

interferometer with a field B present over a distance % in one leg (and much reduced

fields elsewhere) satisfies

d4> + /dB = gu

N Um/p) [1 - fi 2 /(2B

2 )]. (4)

Thus, there is an additional small B-dependent term in dcj> /dB, as a consequence of 5. Replacing the quantity (Slm/p) by the classical time-of-f light t through the region of

the introduced field B, one sees that observation of the effects of X-exchange

requires measuring <j> with sufficient precision that the experimental uncertainties

remain less than ~ A<J) , where

Ac}) +

= (3t)(6

2 /262

). (5)

For a given value of t, we can maximize A<J> by minimizing B subject to the constraint

3 > 3 = ir/t, which is implied in the discussion following Eq. (2).

I have also considered spin resonance as a means of determining 5. One

measures u = E - E where, including the effects of X-exchange,

co = 23 [1 + 5 2 /(23

2

)]. (6)

2 2 That is, one requires measuring to to a relative precision Aw/co < 6 /(23 ), while

satisfying the condition 3t > it. A measure of the precision attainable in the

resonance technique can be found in the more recent of a long series of experiments

seeking direct evidence of time-reversal noninvar iance outside the neutral kaon

3

** system by searching for an electric dipole moment (eD) of the neutron. (Aco/u) «

Meo(D)E_/2B in such experiments, where o(D) is the standard deviation of D.

Quite generally, for reasons of statistics, it appears that neither

implementation of the energy-shift method can compete with the beam approach for

1 5 detecting the antineutron directly, which is currently being pursued.

92
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. M. Baldo-Ceolin , Workshop on Reactor Based Fundamental Physics (Grenoble,

November, 1983); see also R. C. Casella, NBS Tech. Note No. 1142, p. 60 (F.

Shorten, Ed., 1981).

2. For a recent review of neutron interferometry , see A. G. Klein and S. A. Werner,

Rep. Prog. Phys. 46, 259 (1983).

3. J. H. Christenson, et al., Physical Review Lett. J_3, 138 (1964); R. C. Casella,

Phys. Rev. Lett. 21_, 1128 (1968); 22, 554 (1969).

4. N. F. Ramsey, in The Neutron and its Applications, 1982 (London, 1983), p. 5.

5. R. C. Casella, to be published.

CRYSTAL DATA

A. D. Mighell and J. K. Stalick

Two new volumes in the Crystal Data series were published in May 1984. The

fifth volume contains 11,225 entries on crystalline compounds for which data were published in the years 1975-1978. The sixth volume contains 12,339 entries for which

data were published in the years 1979-1981. These books contain information on organic and organometallic compounds. Data are also included on metal complexes

containing organic ligands. The volumes in the Third Edition series are used by the

industrial and academic communities for identification, for phase characterization,

and for many other applications in the materials sciences.

With the aid of computer programs, the data were evaluated by the Editors for

self consistency and errors or possible errors are noted. For classification and

identification, the unit cell parameters for each compound were transformed to a

2 conventional cell. NBS*AIDS83 is the principal evaluation program which was used.

This program not only evaluates the data but also builds a structured data base from

which the books were prepared. The volumes were produced with typesetting routines

which were written by the Data Systems Development Group of the Office of Standard

Reference Data.

Each entry in the books consists of a tabulated line plus additional chemical

and crystallographic data. The tabulated line contains the principal

crystallographic data: cell edge ratio(s), cell parameters, quality indicator, space

group or diffraction aspect, formula units per cell, observed, calculated, and

recalculated density and an indication of the extent to which the atomic positional

93
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

coordinates have been determined. Next come the chemical name, synonym, formula, and

literature reference. Additional information may include data on twinning, color,

melting point, temperature of data collection, transition point, and an indication if

powder data are in the original literature or if the study involves neutron data.

Each volume contains several chemical indexes and a lattice-formula index. The

chemical indexes include a formula and a permuted formula, as well as a permuted

compound name index. The lattice-formula index includes the reduced cell and the

formula for each entry. The index is ordered on the ascending magnitude of the

reduced cell parameters. This index is new and it permits the user to locate rapidly

compounds in the book or to identify substances on the basis of limited

crystallochemical data.

1. "Crystal Data Determinative Tables." 3rd ed. U.S. Department of Commerce,

National Bureau of Standards and the JCPDS— International Centre for Diffraction

Data, Swarthmore, PA, USA (1984); Vols. 5-6.

2. A. D. Mighell, C. R. Hubbard, and J. K. Stalick, "NBS*AIDS80: A FORTRAN Program

for Crystallographic Data Evaluation," NBS Technical Note 1141 (1981).

94
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

IDENTIFICATION BY LATTICE MATCHING

Vicky L. Himes and Alan D. Mighell

We have written a lattice-matching program to be used in conjunction with the

NBS Crystal Data File (1982) for the characterization and identification of

crystalline materials. The NBS Crystal Data Center maintains a data base that

contains evaluated crystallochemical data on approximately 60,000 commonly occurring

materials. The data fall into the following categories: organics, organometallics,

metals, intermetallics, inorganics, and minerals. There are two fundamental ways

that large crystallographic data bases can be used. As a source of critically

evaluated data, the data base can be used as a basis for scientific research, or as an aid to scientific research (i.e. to identify unknown compounds, to locate certain

molecules, to obtain bibliographic data, etc.). The type of data that can be

obtained through search and retrieval programs include chemical name and formula,

cell parameters and cell volume, crystal system, space group symbol and number,

density, bibliographic data, plus additional data. Since the data base is formatted,

many of these data items may be searched readily using systems software available at

a particular institution. However, general systems software will not be adequate for

certain types of information search and retrieval operations. One such example is

the identification of unknown compounds by matching unit cell parameters and, if

available, some chemical data. Although simple in principle, lattice-formula

matching is a complex operation that requires specialized scientific background in

order to design a practical computer search algorithm. The following section

summarizes the lattice-matching technique developed at NBS. It is planned to

incorporate the formula-matching operation in a subsequent version of this program.

Three relatively recent developments have given the lattice-formula method for

compound identification great potential as a routine analytical tool. First,

automated methods to determine a unit cell (and crystal structure) are in widespread

use. For the same reason, the data base of known crystalline compounds is large and

is rapidly growing. Second, new mathematical theories have practical applications in

lattice-matching procedures. These procedures permit fast and effective

identification in spite of certain experimental errors made in unit cell determinations. Third, advancements in computer technology have greatly increased the

efficiency of search strategies through direct access of computer file records and

increased mass storage capability.

95
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1 . Background and Theory

The identification of materials by powder diffraction is a well-established

analytical technique. With the powder method, identification is based on matching

the many diffraction positions and intensities with those of known materials. In

contrast, the method described herein identifies materials based on their crystalline

lattices as defined by the unit cell parameters. In theory, matching unit cell

parameters is equivalent to matching the positions of the diffraction lines (dspacings) in a powder pattern. Practically, however, there are many advantages to

the lattice-matching approach, mainly due to the very compact nature of the unit

cell as compared to a powder pattern. For example, it is far easier to treat the

experimental errors when matching unit cell parameters than it is to evaluate the

errors in all the observed (and unobserved) diffraction positions in a powder

pattern. In addition, the computer search times and mass storage requirements are significantly decreased since there are fewer search parameters for the latticematching method. Finally, with a given unit cell, mathematical procedures allow one

to calculate derivative unit cells which could result from certain errors made by the

experimentalists. Since the lattice-matching method is efficient, one is able to

routinely search the data base of known materials for the experimentally determined

unit cell as well as for its calculated derivative cells.

There are many unit cells that can be chosen to define a crystalline lattice.

When identifying a material using the powder method, unique sets of data are matched

since any unit cell defining the lattice gives the same calculated d-spacings. With

the lattice-matching method, this uniqueness is guaranteed by always comparing

reduced cells. The reduced cell is a unique, primitive cell based on the three

shortest lattice translations and satisfying a specified set of mathematical

conditions (International Tables for X-ray Crystallography, 1969). For

identification, each unknown cell and, if desired, its associated derivative cells

(Santoro & Mighell, 1973) are transformed to a reduced cell. These reduced cells are then checked against a reduced cell data base of known materials.

The NBS Crystal Data Center has prepared a data base designed for compound

identification and characterization. In the NBS Crystal Data File, all known cells

have been transformed to a reduced cell and the File has been sorted first on

increasing magnitudes of the unit cell parameters. With this classification scheme,

metrically similar lattices are located near each other in the File, making it

possible to design efficient lattice-search algorithms.

96
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A summary of the lattice-matching procedure is presented in Figure 1 . From the

unknown crystal, one determines a unit cell in reciprocal space. Next, a unit cell

in direct space is determined and reduced. The reduced cell is then checked against

a file of known materials. If desired, one calculates derivative lattices which are also reduced and checked against the file of knowns. This check can be carried out

either by hand using a printed listing of knowns, or by computer programs. Practical

examples of this identification procedure are illustrated in Figures 2 and 3-

In Figure 2, only one single crystal of the sample was available. Thus, a chemical analysis was not possible and a powder pattern could not be taken. The

initial cell was determined on an automated dif fractometer . This C-centered cell was transformed to a primitive cell and reduced. The reduced cell was then checked

against the NBS Crystal Data File. The sample was found to be sodium sesquicarbonate

by a direct match of the reduced cell parameters. A full structure determination by

neutron diffraction confirmed the identification (Choi and Mighell, 1982).

The example given in Figure 3 shows how an identification can be made by using

a derivative lattice procedure. In diffraction work, one may determine a supercell

or subcell rather than the correct cell of the lattice. For example, when using

powder methods, a supercell in direct space may be determined if one does not find

the smallest cell consistent with the set of d-spacings. In single-crystal work, a subcell in direct space is determined if reciprocal lattice nodes are missed on a diffraction photograph or a dif fractometer . In either case, it is possible to

systematically calculate derivative cells and identify the material. Here, the

unknown cell was correct and the known cell was a supercell. The initial cell and

space group were determined on a single-crystal diffractometer and a full set of

diffraction data was collected. The empirical formula was known. When checked

against the file of known compounds, there were no matches. Next, the seven

supercells of twice the volume were calculated; only three were unique because the

initial cell is metrically rhombohedral . One of the three calculated supercells

matched a cell in the NBS Crystal Data File. The known cell, which was a supercell

of the correct cell, had been determined from limited powder data only.

Nevertheless, it was possible to verify the correct composition and to find

appropriate literature references.

97
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Unknown Crystal

I

Unit CellI

| Reduced Cell r— Derivative

Supercelis and

Subcells

1 ' Match

Unknown Lattices

against the NBS

Crystal Data File

Reduced

Derivative

Cells

Verify

Identification

based on Known Chemistry

Figure 1. Identification by lattice matching,

PROBLEM: Crystal of Unknown Composition

Full Set of Diffraction Data

I nitial Cell 20.44 X

3.49

10.33

90.00°

106.48

90.00

Reduced Cell 3.49 X

10.33

10.37

106.24°

99.69

90.00

NBS CRYSTAL DATA FILE

3.49

3.49

3.49

10.13

10.31 10.43

12.08

10.35

12.17

90.0

106.1 90.0

90.0

99.7

90.0

90.0

90.0

90.0

CONCLUSION: Compound = Na3 H (C 03)2 • 2H2

Figure 2. Identification: direct cell match.

98
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Initial Cell 6.619 6.619 6.619

62.25 62.25 62.25

I Check File

I J

Generate 7 Supercells of Twice the Volume \. Only 3 are Unique

' r 6.62 6.62 11.72

92.2 105.2 117.8

6.62 6.84 9.52

90.0 92.7 90.0 6.84 6.84 11.33

72.4 72.4 60.0

' '

i Check File

1 Match

1

" Check File No Matches

6.62 6.80 9.43

90.0 90.0 90.0 Check File No Matches

NH4 SnF3

Figure 3. Identification: match of a derivative cell.

2. Algorithm

The theoretical basis for identification by lattice-formula matching was

discussed previously. Here, emphasis is placed on the computer strategy used to

match the unknown lattice(s) against the NBS Crystal Data File. Steps 1 to H outlined below summarize this procedure.

a. Preparation of a search file of known compounds.

NBS

Crystal Data File

1-Line File Sort

Search File

of Known

Compounds

Before using the NBS lattice-matching program, a compact search file of known

compounds must be prepared. This is done to save computer mass storage, to increase

the efficiency of a search, and to simplify the program's input and output

operations. Selected data from the NBS Crystal Data File are used to create a search

file in which each line of 132 characters corresponds to the data for one crystalline

compound. For a given computer, the 1-line search file is prepared only once.

99
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

b. Data items in the search file of known lattices.

Increasing

Cell Parameters

Reduced Cells

abca/3yVSG# Ref. Formula

a

2

b

2 c

2 a2 p2

y2

V SG # Ref. Formula

a„ bn c„ an Bn yn V SG # Ref. Formula n n n n ' n ' n

In the 1-line search file, each unknown lattice, regardless of its original

centering, is represented by its primitive, reduced cell. The entries are ordered by

increasing magnitudes of the reduced cell parameters. The space group, literature

reference, chemical formula and other, information are included in order to facilitate

identification.

c. Search strategy.

Unknowns

Direct Access

File of

Knowns

I Sorted

on Cell

Parameters

Unk3-—

10,000

Entry

Unkn

The 1-line search file used for identification is a direct access computer

file. Unlike sequential access files in which one may read only from the beginning

to the end in a forward manner, direct access enables one to go directly to a specified point in the file. One can access the file in any order, "forwards" or

100
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

"backwards". The direct access of file records is efficient as it can significantly

decrease the number of file reads. In this direct access code, a knowledge of the

data in the file of knowns Is used to set up a system of pointers which allows the

program to start searching in about the right region of the data file. A sequential

search is used only for the regions of the file in which a match is possible. In the

diagram, the search regions are designated by boxes.

Grouped-Entry Direct Access

Unknowns File of Knowns

Sorted on Cell Parameter*

Unk6

Unk15 Group 1 ... Unk2 | Group 2 —

Unk14|

Unk 44 Group 3--^

UnklOl

Unkn

Entry

Entry

Entry

--itsa

Entry

10,000

Sorted on Cell Parameters

3 15,000

m

A "grouped-entry" direct access search strategy is actually used in the

computer program. To carry out a grouped-entry direct access search, the unknowns

are first sorted on increasing values of the reduced cell parameters. Next, unknown

cells with similar values of a (A) are searched as a group against the appropriate

region of the data file. In the diagram, the regions that overlap are searched only

once. This approach is very efficient when one searches a number of unknowns against

the 1-line search file.

Grouped-Entry Direct Access Search

Prepare

Search File

of Knowns

Prepare File

of Unknowns

• Reduced Cells

• Reduced

Derivative

Cells

Carry Out

Grouped-Entry

Direct Access

Search

101
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The above diagram summarizes the lattice-matching procedure developed at NBS.

First, the 1-line search file of knowns is prepared from the NBS Crystal Data

File. For a given computer, this direct access file of knowns is prepared only once. Second, the file of unknowns is prepared. Each input cell may be a primitive or centered cell of the lattice. Derivative supercells and subcells may be calculated

from the input cell. All cells in the file of unknowns are reduced and sorted on

increasing values of the reduced cell parameters. Third, the grouped-entry direct access search is carried out. Each unknown cell as well as derivative supercells and

subcells may be matched against the file of knowns in a single run.

3. Lattice-Matching Based on a,b,c,V and Future Modifications of the Computer

Program

The identification of unknown materials by lattice-matching is possible because

all input cells are transformed to the standard, reduced cell. Reduction is a mathematical procedure that leads to a unique cell in all cases, provided there is no experimental error in the unit cell parameters. However, occasionally, the computer

program may yield a geometrically reduced cell that requires further reduction with

respect to the cell angles because of the interactions of the experimental errors

with the special conditions for reduction. Thus, in practice, two experimentally

determined cells defining the same lattice will always give the same a,b,c (within

experimental error) for the reduced cell, but in certain cases, the reduced cell

angles may differ. For this reason, the program matches only the cell edges and cell

volume of each unknown reduced cell against the known cells in the NBS Crystal Data

File. It is possible that every cell match obtained in this way does not define the same lattice. In the next version of the program, a mathematical procedure (Santoro,

Mighell, and Rodgers, 1980) will be used to distinguish between lattices that have

only a,b,c,V in common and lattices that are identical. For those cases in which

more than one match of a,b,c,V occurs, knowledge of the empirical formula or some

other chemical information is almost always sufficient to eliminate unwanted matches.

This chemical screening will be automated in a later version of the computer program,

completing the identification procedure by lattice-formula matching.

4. Concluding Remarks

The NBS lattice-matching procedure is reliable as one is commonly working with

well-characterized materials. The cells have usually been refined by least-squares

techniques and the chemistry is precisely known. The method of lattice-matching is

102
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

selective. In general, there are relatively few matches per unknown when using

tolerances of ±0.1 A on the cell edges and ±10 percent for the cell volume. For most

crystals, the lattice is unique. This means that the cell or the cell plus some chemical data is sufficient for identification.

The lattice-formula method of identification is a general procedure that may be

applied to any cell regardless of the techniques used for its determination,

including single crystal, powder, and film technique. For example, the method can be

applied to a compound analyzed by powder diffraction. One can index the powder

pattern and search the NBS Crystal Data File. If no matches are found, one can then

check the JCPDS Powder Diffraction File using a more complicated search technique

based on matching d-spacings and diffraction intensities.

Lattice-matching methods are subject to precise mathematical procedures and a high degree of computerization. They are fast, selective, and various types of

inter- and intra-lattice relationships can be established. Experience with practical

problems has shown that identification by matching reduced cells is very

straightforward and reliable when the correct cell of the lattice has been

determined. However, a material can often be identified even if an error has been

made in which a derivative cell of the unknown has been found. The ability to check

routinely for matches of 110 extra derivative cells for each unknown is only possible

because of the efficiency of the computer program and the selectivity of the method.

Finally, the entire identification procedure can be highly automated including the

determination of the unit cell. Both the unit cell determination and the

identification process can be carried out in one instrument.

1. Choi, C. S. and Mighell, A. D., Acta Cryst. B38, 2874-2876 (1982).

2. International Tables for X-ray Crystallography (1969). Vol. I, 3rd ed., pp. 530-

535. Reduced-cells section by A. D. Mighell, A. Santoro, and J. D. H. Donnay.

Birmingham: Kynoch Press.

3. NBS Crystal Data File (1982). A magnetic tape of crystal data distributed by the

JCPDS-International Centre for Diffraction Data, 1601 Park Lane, Swarthmore, PA.

4. Santoro, A. and Mighell, A. D., Acta Cryst. A29 , 169-175 (1973).

5. Santoro, A., Mighell, A. D., and Rodgers, J. R., Acta Cryst. A36, 796-800 (1980).

103
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON ACTIVATION AUTORADIOGRAPHY STUDY OF PAINTINGS

Yu-Tarng Cheng, M. J. Blackman, and J. S. 01 in

(Smithsonian Institution, Washington, D.C.)

and

(National Bureau of Standards, Gaithersburg, MD)

and

Martin Ganoczy

The neutron activation autoradiography project has progressed along three

fronts during the past year. The design of the facility to be located at the thermal

column portion of the reactor has been finalized and an engineering detailing study

is soon to begin to produce construction drawings so a more accurate estimate of the

cost can be obtained. Three paintings by American artists and one by an old master were studied using the existing thermal column facility.

The first painting may be attributed to the artist Ralph A. Blakelock. The

result of the autoradiography study exemplifies the uniqueness of this technique.

The painting on canvas was removed from its stretcher prior to the study, in this

case, as the painting had been relined in the course of conservation treatment and

was removed from the stretcher for that purpose. More generally the painting is

activated on the stretcher. The x-ray radiograph of the painting revealed only the

canvas weave and perhaps the heavy ground layer. Nine neutron- induced

autoradiographs of the painting were taken. The most prominent elements responsible

for the imaging of autoradiographs 1 , 6, and 9 are shown in Table 1 . The relative

strength of each element is normalized to the most prominent one in the same

autor adi ogr aph so one can readily follow the changes in relative strength of

different elements from one autoradiograph to another. These autoradiographs

demonstrate the unique capability of this technique; it allows one to see the spatial

distributions of different elements separately and even to quantify them. For

instance, in autoradiograph 6, pigments containing sodium and arsenic have left an entirely different picture from what is on the painting surface, a still life object

painted sideways. This type of information is important to art conservation and art

history study and cannot be obtained by any other conventional means. Autoradiograph

9 is also interesting. Though Zn was the most prominent element that was still

active at the time, the fact that one did not see any images of the surface painting,

the lanscape, before autoradiograph 9 indicates that it was mercury that was

responsible for the image. Zn has an isotope with a shorter* half-life that was very

active in the few earlier autoradiographs. Had it been Zn that was imaging the

104
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

landscape scene in autoradiograph 9, one would have been able to detect it on earlier

autoradiographs as well.

The other two American paintings, the "Duet" and the "Nude", are attributed to

Thomas W. Dewing. T. W. Dewing received classical training in Europe and in later

years changed his style to impressionism. The "Duet" differs markedly from a photograph of the painting found in a 1924 reference. The difference typifies the

changes in style. Wishing to be known as an impressionist, the artist appears to

have repainted his earlier paintings to conform to his new style. Though no earlier

photograph is available for the "Nude," there are studio paintings of similar period

indicating his earlier style. The autoradiographs of both paintings do show that

they have been reworked. These two paintings are part of a continuing effort to

systematically study Dewing' s works.

The fourth painting studied was a painting by a 17th century Dutch master. The

study was in colaboration with the New York Metropolitan Museum of Art where a number

of old master paintings have been studied using the Medical reactor at Brookhaven

National Laboratory. The autoradiography study can provide information concerning

the artist's style, technique, construction of painting images and type of pigments

used. This information then becomes an integral part of an interdisiplinary study of

the art history of the said artist.

The third area that we have devoted our effort to is in the understanding of

film response to beta and gamma radiations. This will enable us to interpret the

autoradiographs more accurately and also will help in identifying the most effective

film system among the different film and scintillation screen combinations. The last

information is important in that one is always concerned with the possible radiation

effect on the painting studied with this technique, and a more efficient system to

record the autoradiographs will in direct proportion reduce the amount of radiation

the painting receives. Table 2 shows the number of disintegrations from gold foil

needed to register a density of 1 D on the different film-screen systems. Currently,

the Kodak DEF film is used without a scintillation screen for the autoradiography

process. Table 2 indicates that the Kodak XAR film coupled with DuPont Quanta III screen gives the fastest response, almost a factor of 8 improvement over the current

DEF system alone. Prolonging the film development . t ime from the standard five

minutes to ten minutes further improves the speed by another -'factor of 3-5. Thus if

all these speed improvements can be realized, one can reduce the radiation the

painting receives for the autoradiography study to a level less than what it would

receive in a typical x-ray examination. The preliminary result indicated there would

105
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

be a trade off in degredation of image resolution with the increase of film speed

Further effort is being spent to lessen the negative effect.

Table 1

Autoradiograph

No.

Time After

Activation

5 min.

Film Exposure

Time

Prime Eler

Element

Mn

Cu

Na

V

nents

Re

Ex

Lat

posing Film

ive Strengh

1 5 min. 100

3114

4

6 17 hrs. 17 nrs. Na

Zn

As

Mn

100

65

17

10

9 1 1 days 24 days

Table 2

Zn

Hg

Cr

100

5

3

Kodak Fi l m Type

OH

0G

DEF

DEF

XAR

XAR

Scintillation Screen Type

Kodak Standard

Kodak Standard

DuPont Quanta III

DuPont Quanta III

No. of Disintegrations Needed

to Register a Film Density of ID

2.44 X 10

4.15 X 10

6

3.32 X 10

2.36 X 10

9.24 X 10"

6.61 X 10

106
B. Non-RRD Programs

ACTIVATION ANALYSIS GROUP: OVERVIEW

R. Fleming

The development and application of nuclear analytical techniques for greater

accuracy, higher sensitivity and better selectivity are the goals of the Activation

Analysis Group. A high level of competence has been developed in reactor-based

activation analysis, which includes instrumental and radiochemical neutron activation

analysis (INAA and RNAA), and in LINAC-based activation analysis using photons (PAA).

In addition, the group has a unique capability in neutron beam analysis with both

prompt gamma activation analysis (PGAA) and neutron depth profiling (NDP). The NDP

technique utilizes prompt charged particle emission to determine elemental

distributions within the first few micrometers of a surface while the PGAA technique

utilizes prompt gamma-ray emission to measure the total amount of an element present

regardless of its location in the sample. This variety of techniques provides an

arsenal of tools to address analytical problems in science and technology.

During the past year, research efforts in INAA have been directed toward

extending its multielement capability by investigating short-lived activation

products (T 1/p ~1 sec) and epi-thermal activation analysis using shielded

irradiations. The work with RNAA has continued to expand the number of elements

which can be quantified at or near the theoretical limiting sensitivity of the

method. Especially challenging have been gas-phase radiochemical separations which

Q

have allowed routine measurement of 1-129 at the 10 atom per gram level. Work on

the certification of U-235 standards has demonstrated that the precision of gamma-ray

spectrometry can be achieved well below the 0.1% level. Since this counting

uncertainty is the ultimate limitation on the accuracy of all activation

measurements, the challenge now exists to understand and, where possible, reduce

systematic biases to below this level.

During the past year there has been a continuing effort in the trace element

analysis of biological materials. In addition to the ongoing work on biological

Standard Reference Materials and the Pilot Environmental Speciman Bank program,

several new research areas have been established. Activation analysis is being used

to study the interrelationships among trace elements, bioanalyt ical separations and

biological macromolecules. Of particular interest is a new effort employing chromium

isotope dilution to measure the increase in total blood volume during pregnancy.

With the success of the Bureau's effort to establish a National Facility for

Cold Neutron Research at the N3S reactor (NBSR), both of the Group's neutron beam

107
NON-RRD PROGRAMS

techniques, PGAA and NDP, will improve in sensitivity and throughput by at least a factor of one hundred. This will give the Bureau an unprecedented ability for

materials analysis in metals, glasses, and semiconductors, as well as more complex

matrices.

The coming year will see an upgrade of the NBSR from its present 10 MW power

level to the full design power of 20 MW. This will provide a factor of two

improvement in many of our activation analysis sensitivities and in all of our PGAA

and NDP analysis. While this upgrade is taking place, we will install a new data

acquisition system based on a VAX computer to replace the outgrown 1 6-bit system now

in use. In addition to the control and processing of gamma-ray spectra now carried

out, the enhanced computational capability will be used for substantially improving

the modeling of the activation analysis process to improve its accuracy.

BIOLOGICAL MATERIALS ANALYSIS

R. Zeisler and D. Becker

(Inorganic Analytical Research Division)

During the past year there has been a continuing effort in the Activation

Analysis Group on trace element analysis of biological materials. This effort has

taken place in a number of subject areas, with the overall aim of improving the

accuracy and precision of such analyses. Brief descriptions of selected projects are given below.

a. Biological SRMS—The Non-Fat Milk Powder (SRM 15*19), reported in detail

last year, has now been issued and is certified for 15 elements. In addition, SRM

2670 (Toxic Metals in Freeze-Dried Urine) was issued at normal (5 elements certified)

and elevated (10 elements certified) levels. Upcoming biological SRMs to be analyzed

include re-issues of wheat flour and rice flour, and an apple leaves material,

intended to replace the out-of-stock Orchard Leaves SRM.

Special note: NBS Spec. Publ. 260-88 became available this year (1982

Compilation of Elemental Concentration Data for NBS Biological, Geological, and

Environmental SRMs). Contact the NBS Office of Standard Reference Materials

(Gaithersburg, MD 20899) for a copy.

b. Pilot Environmental Specimen Bank--The specimen bank project is continuing

under reduced funding, which limits the number of biological samples (human liver and

marine mussel) which are being collected, processed, analyzed, and stored. We firmly

believe in the viability and importance of the specimen bank concept, and are

108
NON-RRD PROGRAMS

exploring ways to revitalize the program. Copies of the extensive 1983 report of

this project, including protocols for sampling and storage of human liver tissue, and

accumulated analytical data on 32 elements in human liver, are still available.

Refer to NBS Spec. Publ. 656, The Pilot National Environmental Specimen Bank:

Analysis of Human Liver Specimens.

c. Total Blood Volume by INAA--An exploratory effort has been initiated on the

determination of total blood volume by chromium isotope dilution, in cooperation with

the National Institute of Child Health and Development. This project will explore

use of the separated chromium-50 isotope as label for red blood cells to determine

the change in total blood volume of pregnant women. This use requires the accurate

detemination of chromium-50 in the low ng/g range in whole blood. If successful,

blood volume measurements may provide a mechanism for identifying a high risk infant

mortality population.

d. Trace Elements in Brain Tissue--In a continuing cooperative effort with the

Sourthern Illinois University School of Medicine, analyses of selected brain tissues

are being used to assist in the diagnosis (postmortem) of Hallervorden-Spatz

Syndrome. This is a rare brain disorder which affects childhood development and

involves central nervous system degeneration. Analyses to date, including both human

and monkey brain tissues, suggest that high concentrations of iron are deposited in

the globus pallidus portion of the brain of affected persons. NMR studies of the

iron in these tissues are currently in progress elsewhere, with additional trace

element analyses to be made to further elucidate the mechanism of production and

ultimate impact of these deposits.

e. Bioanalyt ical Separations--Interrelat ionships among trace elements,

biological macromolecules , in-vivo and in-vitro mechanisms, and bioanalyt ical

separations are being investigated with the use of high sensitivity instrumental and

radiochemical neutron activation analysis. Among the systems being studied is the

behavior of selenium and other trace elements in the glutathione peroxidase system

under the influence of medication. Other investigations include the accurate

-1 2 determination of selenium in 10 MOL of transfer-ribonucleic acid.

109
NON-RRD PROGRAMS

MULTIELEMENT ANALYSIS OF AN AQUATIC ACCUMULATOR

Susan F. Stone and Rolf Zeisler

(National Bureau of Standards, Gaithersburg, MD)

and

Ronald W. Sanders

(Pacific Northwest Laboratories, Richland, WA)

A joint research program, involving the National Bureau of Standards and the

Environmental Protection Agency, has been concerned with the study of biological

specimens as monitors of the environment. Several analytical techniques have been

used to determine over 40 elements in selected specimens. In determining elemental

concentrations in biological specimens, steps were taken to assure the accuracy of

the reported measurements not only in the chemical analyses, but also during sampling

and sample preparation. This was especially important for elements occurring at

trace levels, such as pollutant elements.

The organism selected as the monitor for the marine environment was Myt ilus

edal i s , the marine mussel. Six thousand mussels were collected at a site in

Narragansett Bay, R.I., under controlled sampling conditions. The animals were

separated into batches and stored. Before analysis, the mussels were shucked and

then homogenized. An instrumental approach was applied to the analyses, employing

three techniques in sequence; backscatter with fundamental parameter x-ray

fluorescence (BFP-XRF), neutron-capture prompt gamma activation analysis (PGAA), and

instrumental neutron activation analysis (INAA). A radiochemical neutron activation

analysis procedure, specific for tin, was also applied after the instrumental

analyses were completed. The results of these techniques were combined to obtain

concentrations for a total of 44 elements. The same 300 mg portion was analyzed in

sequence by all three instrumental techniques using this scheme.

In order to analyze small subsamples that represent the bulk sample, a thorough

homogenizat ion procedure was necessary. This was accomplished with a cryogenic

1 homogenization technique . Possible contamination, arising from the sampling,

storage, and homogenization, was evaluated by analyzing high purity water treated in

the same manner as the biological samples. The results of this evaluation are shown

in Table 1 . Control samples, blanks, and samples of the reagents used for the final

cleaning of the Teflon mills and implements used in subsampling are included for

comparison. The data indicate that trace levels of contamination resulting from the

sampling and subsampling processes do occur for some elements. Although these values are above the measured reagent and bag blank levels, they are still much lower than

1 10
NON-RRD PROGRAMS

Table 1 . Evaluation of Contamination in the Sampling and Homogenization Procedure

Analysis by INAA (Concentrations in ng/mL, Uncertainties are Is for n = 3)

Commercial

Ultrapure Water Ultrapure Water Pure Ethyl Ultrapure Water Bag

Homogenate & Bag & Bag Alcohol & Bag & Bag Blank

Cr 18 ± 4 11.0 ± 0.2 10.8 ± 0.6 11.0 ± 0.8 11.1 ± 0.4

Fe 32 ±10 2.3±0.3 7.2 ± 1.0 <_3 3-8 ±1.5

Co 0.044 ± 0.010 0.023 ± 0.005 0.015 ± 0.003 0.043 ± 0.010 0.017 ± 0.006

Zn 25 ±3 1 3 ± 4 11.0 ± 0.2 7.6±0.2 7-0 ±1.3

As 0.035 ± 0.010 0.023 ± 0.005 <_ 0.06 0.060 ± 0.010 <_ 0.010

Se 0.030 ± 0.020 <_ 0.020 <_ 0.014 0.020 ± 0.010 0.015 ± 0.007

Br 0.89 ± 0.07 0.33 ± 0.02 0.56 ± 0.01 0.34 ± 0.04 0.24 ± 0.02

Mo 0.2 ± 0.1 0.043 ± 0.005 _< 0.030 _< 0.07 <_ 0.03

Ag 0.029 ± 0.003 0.45 ± 0.20 0.064 ± 0.010 0.074 ± 0.030 _< 0.009

Cd 0.34 ± 0.04 0.086 ± 0.010 <_ 0.060 <_ . 1 6 £0.30

Ce 0.075 ± 0.015 0.021 ± 0.003 <. 0.010 0.030 ± 0.008 0.022 ± 0.006

Hg 0.59 ± 0.07 0.115 ± 0.011 0.112 ± 0.005 0.16 ± 0.08 0.099 ± 0.007

aApparent concentration for a 50 mL sample.

111
NON-RRD PROGRAMS

Table 2. Elemental Concentrations (Dry Weight Basis) for Mytilus edulis

(Concentrations in pg/g unless otherwise specified)

Concentration ± 1s Analytical Techniques Employed

Uncertainty (a = XRF, b = PGAA, c = INAA, d = RNAA)

H (%) 5.9 ± 0.9 b

3 31 ± 2 b

C (%) 62 ± 12 b N (%) 7.6 ± 1 .8 b

Na {$) 5.65 ± 0.06 b,c

Mg (56) 0.69 ± 0.06 a

Al (%) 0.074 ± 0.003 a,c

Si (%) 0.300 ± 0.010 a

P (%) 0.900 ± 0.013 a

S (%) 2.2 ± 0.2 a,b

CI (%) 10.0 ± 0.2 a,b,c

K {%) 1 .4 ± 0.3 a,b,c

Ca (%) 0.54 ± 0.04 a,c

Sc 0.130 ± 0.006 c V ^2 c Cr 2.2 ± 0.5 c Mn 28 ± 3 a,c

Fe 475 ± 30 a,c

Ca 0.494 ± 0.013 c Ni 3-3 ± 0.3 a Cu 6.7 ± 0.6 a,c

Zn 122 ± 3 a,c

5.9 + 0.9

31 + 2

62 + 12

7.6 ± 1 .8

5.65 + 0.06

0.69 ± 0.06

0.074 ± 0.003

0.300 + 0.010

0.900 + 0.013

2.2 + 0.2

10.0 + 0.2

1 .4 + 0.3

0.54 + 0.04

0.130 + 0.006

^2

2.2 + 0.5

28 + 3 475 + 30

0.494 + 0.013

3-3 + 0.3

6.7 + 0.6

122 + 3

11 + 1 2.65 + 0.04

430 + 10

8 + 1 75 + 3

1 .4 + 0.3

0.691 + 0.010

2.2 ± 0.3

0.019 + 0.004

0.061 ± 0.003

6.9 + 1.5

0.056 ± 0.010

0.89 ± 0.08

0.096 + 0.01 1 0.013 + 0.002

0.060 + 0.003

0.360 + 0.010

0.23 ± 0.09

4.3 + 0.7

0.118 + 0.009

0.185 + 0.020

As 1 1 ± 1 a,c

Se 2.65 ± 0.04 a,c

Br 430 ± 10 a,c

Rb 8 ± 1 a,c

Sr 75 ± 3 a,c

Mo 1 . 4 ± .

3

c Ag 0.691 ± 0.010 c Cd 2.2 ± 0.3 bjC

Sn - d

Sb 0.019 ± 0.004 c Cs 0.061 ± 0.003 c Ba 6.9 ± 1.5 c La 0.056 ± 0.010 c Ce 0.89 ± 0.08 c Sm 0.096 ± 0.01

1

c Eu 0.018 ± 0.002 c Hf 0.060 ± 0.003 c Au 0.360 ± 0.010 c Hg 0.23 ± 0.09 c Pb 4.3 ± 0.7 a Th 0.118 ± 0.009 c U 0.185 ± 0.020 c

d Radiochemical neutron activation analysis technique in progress,

112
NON-RRD PROGRAMS

the measured concentration in the mussel tissue and do not make significant

contributions to the concentrations.

Utilizing the combination of techniques (XRF, PGAA, INAA, and RNAA), the mussel

tissue was analyzed for a total of 44 elements. The compiled results for one mussel

batch can be seen in Table 2. Some slight differences among results were found in

the sequential analysis procedure. The causes for those differences will be

evaluated, employing the quality control methods in place during the analyses.

1. Zeisler, R., Langland, J. K. , Harrison, S. H., Anal. Chem. , 55, 2431-2434 (1983:

COMPARATIVE IRRADIATIONS AT UVAR AND NBSR

T. G. Williamson

(University of Virginia, Charlottsville, VA)

and

R. M. Lindstrom

Samples of pure silicon and of potassium iodide were irradiated at the

University of Virginia Reactor (UVAR) and the NBSR in order to determine comparative

values of thermal and fission flux in the two reactors. At UVAR, the samples were irradiated in the hydraulic rabbit, separated from the fuel region by a graphite

element approximately 76 mm thick. The rabbit facility is of aluminum construction,

flooded with water, and surrounded with graphite on three sides and with water on the

side away from the core. At NBS, KI samples were irradiated in pneumatic tubes RT3

and RT4.

Irradiated silicon was assayed at UVa for Si— 31 and then for Al-29 activities

1 as outlined by Bickford and Fleming, correcting for the different geometries used in

the two measurements. The ratio of the saturated counting rates of these nuclides

provides an experimental figure of merit proportional to the thermal/fast flux ratio

which is independent of the detector calibration and of the nuclear parameters, some

of which are poorly known. The saturated activity ratio A(31)/A(29) at UVAR is 0.18;

for comparison, Bickford and Fleming reported 9.51 for RT4 and 0.74 and 0.83 for the

G2 and G4 in-core positions, respectively.

Samples of KI irradiated at both reactors were assayed for K-42 and 1-126

activity after a week's decay. Using thermal and fission-spectrum cross sections

2 from the IAEA tabulation, correcting counting efficiency for gamma energy, and

113
NON-RRD PROGRAMS

3 normalizing to the published thermal flux in RT4, the thermal and fission-spectrum

fluxes are as follows:

Facility Sample Thermal flux Fission flux

UVAR Si — 1 E 12

UVAR KI 1 .2 E 13 2 E 12

RT3 KI 4.9 E 13 3 E 12

RT4 Si (1

)

— 2 E 10

RT4 KI — 9 E 10

1. N. A. Bickford and R. F. Fleming, in "Neutron Transmutation Doping in

Semiconductors," J. M. Meese, ed., Plenum, New York, 165 (1979).

2. A. Calamand, in "Handbook on Nuclear Activation Cross Sections" (Tech. Rept. Ser.

156), IAEA, Vienna, 273 (1974).

3. D. A. Becker and P. D. LaFleur, J. Radioanal. Chem-. , 19, 149 (1974).

NITROGEN CONCENTRATION DISTRIBUTIONS BY NEUTRON DEPTH PROFILING

J. T. Maki, R. G. Downing, and R. F. Fleming

(Inorganic Analytical Research Division)

Neutron depth profiling (NDP) at the NBS facility has been successfully

carried out for He~3, Li-6, B-10, and Na-22, each of which has a reaction cross

section of - 1000 barns or more. The profiling of nitrogen concentrations using the

14 14

N(n,p) C reaction is much more difficult since the cross section for 2200 m/s

neutrons is only 1.8 barns. However, with special attention to background reduction,

nitrogen profiling has been accomplished using the BT~3 thermal neutron beam at the

10 MW NBSR. The increase of reactor power to 20 MW will improve NDP sensitivity by a factor of two, while the NBS Cold Source/Guide Hall facility would provide at least a 100 tidies improvement.

The nitrogen profiling measurements were made using two samples, a silicon

nitride (Si Jj layer on a silicon wafer, and an ion-implanted tungsten carbidecobalt 4 alloy. The Si N, layer was 50 nm thick corresponding to 3 X 1 17,N-14

2

'

'

! atoms per cm and was found to have an overcoating of - 500 nm of Si0„. The WC alloy

17 2

had been ion-implanted at 90 keV to a dose of 5 X 10 N-14 atoms per cm . Thus,

1 7 both samples were close to the estimated nitrogen sensitivity of 1.8 X 10

. 2 1 atoms/cm .

114
NON-RRD PROGRAMS

200 400

Depth (nm)

600

Figure 1. Depth profile of a helium surface layer on aluminum: concentration

profile ( ), convoluted profile ( ), measured data (•).

6

200 400 600 800 1000

Depth (nm)

Figure 2. NDP energy resolution for nitrogen in silicon dioxide

115
NON-RRD PROGRAMS

100 200 300 400

Depth (nm)

500 600

Figure 3- Nitrogen depth profile of a 50 nm layer of Si N. on a silicon wafer:

—

/

»

concentration profile ( ), convoluted profile (- measured data (•)

i i i

i

co

'•£COc

CDu

coO

: h V

:/• \

I

i, it c

0)o

+"> Z

/ ' A*

100 200 300

Depth (nm)

Figure 4. Nitrogen depth profile of a 90 keV implant into a WC-Co alloy to a dose of

5 X 10 ions/cm : concentration profile ( ), convoluted profile ( ),

measured data (•).

116
NON-RRD PROGRAMS

14 14

The protons from the N(n,p) C reaction have an initial energy of 583.85 keV

and retain an energy upon leaving the sample surface corresponding to the depth at

which the reaction takes place. The measured charged particle spectrum is this

distribution of degraded proton energies broadened by the measurement response

function. This response function is the energy broadening caused by system noise,

energy straggling, small-angle scattering, and geometrical pathlength broadening.

System noise was measured by determining the peak width for a precision pulse signal,

and was found to be independent of pulse amplitude. That this response function

adequately represented the system noise for protons was demonstrated (see Figure 1)

using a surface sample of He~3 for which the other three contributions to the

response function were negligible and for which there is excellent sensitivity. The

depth-dependent contributions to the response function - straggling, small-angle

scattering and pathlength broadening - were calculated analogous to the work of

2 Biersack . The total response function at a given depth was represented as a gaussian with a width determined from the widths of the four contributions added in

quadrature. For nitrogen at the depths investigated only energy straggling was

significant compared to the system noise. The relative importance of the

contributions to the response function are shown in Figure 2.

The convolution procedure was synthetic. An N-14 concentration distribution

was assumed and the resulting pulse height spectrum was computed using the response

3 function and the proton stopping power tabulation of Zeigler . The goodness-of-f it was determined by minimizing the chi-squared statistic. The results for the 50 rim layer of Si J, on silicon are shown in Figure 3- The assumed 50 nm layer at a depth

of 320 nm of equivalent, inactive silicon nitride is shown to give a good fit to the

measured data. This overcoat thickness is equivalent to 485 nm of SiO . Subsequent

Rutherford backscattering measurement confirmed a 470 nm SiO cap over the silicon

nitride layer. The nitrogen implantation into tungsten carbide was represented as a gaussian, truncated at the surface. Again the convoluted results, shown in Figure 4,

show good agreement with the measured data. The mean implantation depth is 56 nm with a standard deviation of 58 nm for the gaussian profile.

In summary, nitrogen profiling using NDP has been demonstrated and the

concentration distributions have been obtained by deconvolution. These measurements

are at the sensitivity limit of the thermal neutron NDP facility at NBS taking a day

or two of running time and could be improved by at least 100 times using an NDP

instrument on an NBS Cold Source beam.

117
NON-RRD PROGRAMS

R. G. Downing, R. F. Fleming, J. K. Langland, and D. H. Vincent, "Neutron Depth

Profiling at the National Bureau of Standards," Nuc . Inst . and Meth . 21

8

, 47

(1983).

J. P. Biersack, D. Fink, R. Henkelmann and K. Mtiller, "The Use of Neutron Induced

Reactions for Light Element Profiling and Lattice Localization," Nuc. Inst, and

Meth. 149, 93 (1978).

H. H. Andersen and J. F. Ziegler, The St o pping a nd Ranges of Ions in Matter:

Hydrogen , Volume 3, Pergamon Press, New York (1977).

We thank James Ehrstein of NBS for the silicon nitride sample and Daniel Oblas of

GTE, Waltham, Mass. for the implanted tungsten carbide alloy.

HIGH ACCURACY DETERMINATION OF U-235 3Y GAMMA-RAY SPECTROMETRY IN

NONDESTRUCTIVE ASSAY STANDARDS

R. R. Greenberg and B. S. Carpenter

(Center for Analytical Chemistry)

The joint project has been completed between the Central Bureau for Nuclear

Measurements (CBNM), Geel, Belgium, and the National Bureau of Standards (NBS), and a set of five uranium isotope abundance reference materials for nondestructive assay

(NDA) have been produced. These reference materials have been identified as NBS SRM

969 and the Commission of the European Communities certified reference material EC

NRM 171 and are intended for worldwide safeguards use as primary reference materials

for the determination of the U-235 abundance in homogeneous uranium bulk material by

gamma spectrometry. The reference material is in the form of uranium oxide (U_Oq)

235 and is placed in aluminum cans with nominal isotope abundances ( U/U) of 0.003,

0.007, 0.019, 0.029, and 0.045. The material at each isotope abundance is

characterized chemically by CBNM, NBS, and the DOE New Brunswick Laboratory for

235 U/U homogeneity and isotope abundance, uranium content, and material

1,2 impurities.

High precision/high accuracy gamma-ray measurements were made on 24

representative sample cans of the 140 total cans at each isotope abundance. The

measurements, using a high purity germanium detector, determined the counting rate

uniformity of the U-235 185.7 keV gamma-ray as well as the U-235 isotope abundance

for each sample. Since the samples were packaged such that the U-0^ was infinitely

thick for the 185.7 keV gamma-ray, the measured counting rate was almost independent

of the material density. In addition, the activity observed by the detector was

118
NON-RRD PROGRAMS

collimated to simulate calibration conditions used to measure bulk material in the

field.

This work, as seen in Table I, has demonstrated that it is possible to achieve

a precision of 0.05$ and a standard deviation of the mean of . 01 56 in gamma

spectrometry measurements. To obtain this level of precision, the analyst must give

careful attention to the factors associated with the measurement process. If all errors are controlled and a set of well characterized standards are available, it

appears that an accuracy of a few hundredths of one percent (2o) for U-235 isotope

abundance can be achieved by gamma spectrometry.

Table I. Preliminary Results for U-235 Abundances (Atom Percent) in NDA Samples as Determined by Gamma Spectrometry and Thermal Ionization Mass Spectrometry.

Th is Work - GS

ample Mean

. c o-abs

,c o-rel o-rel

031 0.3207 0.0003 0.11 0.021

071 0.7212 0.0005 0.07 0.015

194 1.9666 0.0010 0.05 0.01 1 295 2.9828 0.0019 0.06 0.013

446 4.5143 0.0026 0.06 0.012

NBS - MS

Mean

0.3207

0.7218

1 .9667

2.987

n/a

o-rel

0.08

0.02

0.02

0.02

n/a

CBNM - MS

C

Mean o-rel

0.3207

0.7208

1 .9668

2.9850

4.5183

0.05

0.05

0.02

0.02

0.04

a Preliminary values reported in reference 1

.

b Absolute sample standard deviation (in atom percent of U-235)

c Relative sample standard deviation (in percent).

d Relative standard deviation of the mean (in percent).

P. DeBievre, H. Meyer, J. Van Audenhove, B. S. Carpenter, and J. W. Gramlich,

"Progress Report on the Establishment of Uranium Isotope Abundance Reference

Materials for NDA," Proceedings of The Fourth Annual Symposium--ESARDA on Specialist Meeting on Harmonization and Standardization in Nuclear Safeguards,

Petten, The Netherlands, (1982).

R. R. Greenberg and B. S. Carpenter, "High Accuracy/High Precision Determination

of U-235 in Nondestructive Assay Standards by Gamma-Ray Spectrometry,"

Proceedings of the Fifth International Conference on Nuclear Methods in

Environmental and Energy Research, Mayaguez, Puerto Rico, (1984).

119
NON-RRD PROGRAMS

SUMMARY OF ACTIVITIES CARRIED OUT BY THE NEUTRON FIELD STANDARDS GROUP

D. Gilliam, J. Grundl, and E. McGarry

(Center for Radiation Research)

The Neutron Field Standards Group, attached to the Center for Radiation

Research (CRR), is engaged in the development and application of standard and

reference neutron fields as permanent facilities for neutron detector calibrations,

neutron dosimetry standardization, and reaction rate cross-section measurement.

A component of this group's activities makes use of the reactor thermal column

and the tangential beam tubes where facilities, designed and built by the Neutron

Field Standards Group, are in operation. Facilities, development, and measurement

programs which involve these facilities are as follows:

1

.

Production of Neutron Fluence Standards

The cavity fission source continued to be employed for the production of

neutron fluence standards for both national and international programs of reactor

pressure vessel dosimetry. For the first time this year, fluence standards -for the

Np and U-238 fission reactions were prepared. Eight species of fluence standards

have been produced to date for materials neutron dosimetry applications: In(n,n'),

Ni58(n,p), Fe54(n,p), Ti(n,p), Rh(n,n'), AJL(n,o), U238(n,f) and Np(n,f). Fission

1 4 neutron fluences certified for these standards are in the range 0.7 to 60 x 10

2 neutrons/cm .

2. Preparations for a New Neutron-Driven Gamma-Ray Standard

In cooperation with two European laboratories and the University of Virginia,

preparations are underway for the construction of a high-intensity gamma-ray standard

at the reactor thermal column. The basic design concept is to place thermal-neutron

black absorbers, formed as nested cylinders, into the thermal column cavity. The

resulting capture gamma ray source in the black absorber is directly proportional to

the incident thermal neutron intensity. The gamma ray dose at the center of the

cylinder from this source can be ascertained from capture gamma data, dose conversion

tables, and simple geometry calculations. Goal accuracies of ± 10% have been set for

an estimated free-field central x-ray dose of ~ 6KGy/h (14 megarads/day)

.

The system under construction will use initially an extruded cadmium cylinder

for the gamma- sour ce black absorber (rich in high energy gammas compared to

conventional Co gamma ray standards) and a segmented cylinder of Li-6 glass for a no-gamma-source black absorber.

120
NON-RRD PROGRAMS

Known Cd-gamma doses then are delivered to a detector on the basis of responses

obtained with and without the Li-6 glass cylinder. The cadmium cylinder is in hand

and Li-6 glass cylinders are being fabricated by the NBS Glass Research Group. A new

shield plug for the thermal column door penetration also has been fabricated.

Immediate applications of the new gamma source include (1) investigation of

photofission interference in U-238 fission dosimeters; and (2) calibration of a proposed Li-6 chip dosimeter for high intensity gamma dosimetry in fission reactor

environments.

3. Calibration of Helium Accumulation Fluence Monitors (HAFM)

A neutron fluence transfer irradiation was carried out in the Intermediate

Energy Standard Neutron Field (ISNF) in order to establish a neutron fluence scale

for the HAFM calibration irradiations reported in last year's summary.

In this final irradiation, the absolute value of the fission rate from a wellassayed deposit of U-235 was observed during the activation of two pairs of gold and

indium monitor foils. One pair of monitor foils was mounted against the platinum

backing of the U-235 deposit at the center plane of an active fission chamber, while

the other pair of monitor foils was mounted against the thin aluminum anode of the

fission chamber. The fluence for the calibration run was derived by relating the U235 fission rate to the corresponding fission rates observed for carefully

intercompared U-235 deposits at the Cf-252 facility. Fluence rates at a welldetermined distance at the Cf-252 facility are known on an absolute basis by

comparison of the Cf-252 source to the standard neutron source NBS-I via the

manganese bath method. Table I gives the results of the fluence determination and a list of error factors.

The last item in the error list is worth some explanation because it

illustrates some of the considerable but necessary efforts required to establish a reliable standard neutron field. In the fluence calibration run which compared foil

activation rates with the U-235 fission rate, the B-10 shell of the ISNF was

penetrated by the stem of the fission chamber. (This penetration was not present in

the HAFM calibration runs.) The penetration was closed to thermal neutrons by a cadmium flange and tube that extended out of the cavity into a region of negligible

neutron flux density. Any residual thermal neutron penetration has no effect because

of the background substraction method. However, epithermal neutrons (coming from

multiple scattering of the U-235 fission neutrons in the graphite) can cause a perturbation by leaking into the ISNF test region through the penetration for the

fission chamber. The magnitude of this epithermal leakage perturbation has been

121
NON-RRD PROGRAMS

assessed by two methods: (1) by adding a B-10 sleeve around the Cd tube and (2) by

comparing the ratio of U-235 and U-238 fission rates in the completely closed ISNF

with the ratio for the penetrated shell. The results of these assessments have been

somewhat inconsistent. The addition of a B-10 sleeve around the Cd tube did not

change the U-235 fission rate in the ISNF interior (± 0.355), yet the U-235 fission

rate (relative to that of U-238 was found to be (2 ± 1 % ) higher in the case of the

penetrated shell. A correction factor of 0.99 ± 1 . 5% has been applied to account for

the epithermal penetration effect. This uncertainty is the largest single entry in

the list of error factors.

TABLE 1

FLUENCE AND IRRADIATION TIMES FOR HAFM CALIBRATION IRRADIATION

2 Total Central Fluence: 1.257 E14 neutrons/cm

Total Irradiation Time: 164,882 ± 10 seconds

Uncertainty Factors in Total Central Fluence:

Fluence Transfer Errors

Cf neutron source strength

Geometry factors at Cf-252 facility

Scattering correction uncertainties at Cf-252 facility

Cf/ISNF cross section ratios for U-235, Pu-239

Pu-239 (n,f) reaction probability at Cf

Subtotal

Epithermal leakage in fluence calibration run

+ .9%

.6% M1 .6%

.7%

± 2 .156 ± 1 .5%

Total uncertainty ± 2 . 6%

4. Comprehensive Estimate of Errors in ISNF Fluence Scale

An effort is underway to establish a more complete estimate of Cf/ISNF cross

section ratio errors for fission reactions used to establish the ISNF neutron fluence

scale. This error component, presently quoted as ± . 3% (see Table 1), takes into

account only neutron spectrum uncertainties. The initial investigation of cross

section errors suggests that ( 1 ) an additional 1 . 5% or so should be included in this

fluence transfer ratio; and (2) a consensus fluence transfer involving threshold as

122
NON-RRD PROGRAMS

well as non-threshold fission reactions may be preferable to the present strategy of

using a single fluence transfer reaction (i.e., Pe-239 (n,f)).

NEUTRON PERSONNEL DOSIMETER CALIBRATION AND TESTING

Robert B. Schwartz

(Center for Radiation Research)

The reactor filtered beams, with energies of 2, 24, and 144 keV, together with

the beam from the thermal columm, were used for calibrating and testing personnel

dosimeters.

In particular, a new configuration for a personnel dosimeter was calibrated in

the thermal column beam for Lawrence Livermore Laboratory; dosimeters were irradiated

in the keV beams as part of the work for a Master's thesis from the University of

Michigan; and an improved type of track etch dosimeter was irradiated for the Centro

di Studi Nucleari. This latter irradiation is potentially most significant, since

tract etch dosimeters represent one of the most promising developments in personnel

dosimetry. Their drawback lies in the fact that their response falls off drastically

in the neutron energy region below about 50 keV. This new dosimeter is supposed to

respond to neutrons of 10 keV energy or lower, and thus represents a significant

improvement. Our 24 keV beam is the best source of monoenergetic neutrons in this

energy region anywhere in the world, and hence is essential for proving out the new

technique. (As of this writing, the results of these irradiations are not yet

known.

)

A new line of research for our group consists of measurements with a "tissueequivalent proportional counter." This is a counter whose gas filling has

approximately the same chemical constituents as tissue (i.e., oxygen, nitrogen,

hydrogen, and carbon, in the form of CO , N , and Ch\). By filling the counter to an appropriate pressure (typically 5 or & cm Hg) the counter will simulate a tissue

sphere about one micron in diameter, and the interactions in the counter gas will

simulate those in an actual small tissue volume. The spectra, when appropriately

analyzed, can be used to determine dose and dose equivalent as a function of the

energy deposited in tissue.

The first results with the 144 keV beam are shown in Figure 1. The abscissa is

the quantity "lineal energy," which is the energy imparted to the "tissue," divided

by the mean chord length of the (one micron diameter) tissue sphere. This quantity

is called "y," with units of keV/micron. The ordinate is "y" multiplied by the

123
NON-RRD PROGRAMS

quantity "D(y)," where D(y) is the integral absorbed dose distribution for events up

to lineal energy y. When plotted on semi-log paper (as is done here) equal areas represent equal doses. The peak, at about 60 keV/micron, represents the distribution

0.8

0.6|-

Q 0.4

0.2

1 1 1 1 1

1 1 1 I f ] I I I

|

I III do 1

' M

144 keV neutrons /

^o

1 micron cavity

v_7 o

D

X 20

/

o

o °

a

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

- o

O O OOonrt^on O.IO 09 -L

o

I

I I I 1

1

I III 1 1 1 i lo 0.4 0.6 1 2 3 5 7 10

y (keV/micron)

20 30 50 70 100

Figure 1. Microdosimetric spectrum, y D(y) vs. y, for 144 keV neutrons.

of dose due to recoil protons from the 144 keV neutrons. The small peak at about 0.6

keV/micron (data points multiplied by a factor of 20 to make the peak more visible)

represents the gamma dose. This peak is real: each channel represents >100,000

counts, but there is simply very little gamma dose in this beam. The shape is in

general agreement with recent calculations.

Further measurements with the other reactor beams are to be done shortly; these

measuements will be compared with calculations done by other members of CRR.

124
C. Reactor Operations and Services

The reactor was operated on a normal round-the-clock schedule for the entire

year. Other than scheduled shutdowns for maintenance, refueling, testing, and for

staff vacation, there were no interruptions in the operating schedule. The program

of modernization of reactor components and instrumentation is continuing. Licensing

activities to upgrade reactor power to 20 MW and renew the operating license were

completed. Extensive hearings were held before the Advisory Committee on Reactor

Safeguards as the final stage in the licensing process. In May 1984, the Nuclear

Regulatory Commission issued to NBS a new operating license allowing operation at

20 MW, double the existing power, and valid until the year 2004. This is a major

accomplishment and a milestone in the history of the facility. It is expected that

the reactor will be shut down this fall for upgrade and conversion to 20 MW . Tne

work is expected to be completed by the end of the year and testing for 20 MW

operations is to begin early in 1985.

Utilization of the reactor continued to be extensive and wide ranging. More

than 125,000 instrument hours involving 25 simultaneously operable experimental

facilities have been provided to more than 50 organizations from within and outside

NBS.

1

.

Reactor Operations

Reactor operations continued at a high level with on-line time and fuel

efficiency almost identical to that of the previous year which are among the best in

the history of the facility. A summary of the overall operating statistics for the

period July 1, 1983 to June 30, 1984 is presented in the following table.

NBSR Operating Summary July 83- June 84

No. of days at 1 MW 266

On-line time at 10 MW 73?

Average U-235 burnup 62%

No. of Irradiations 1900

Hours of Irradiations 5600

Hours per Irradiation 3

2. Irradiation Service

Heavy utilization of the reactor for major irradiation and activation analysis

programs continued. Tens of thousands of specimens, involving foods, drugs,

environmental monitoring, geological, and mineral examinations, forensic

125
REACTOR OPERATIONS AND SERVICES

investigation, and development of standard reference materials were irradiated at the

NBS reactor. Substantial quantities of fluorine-18 were produced on a regular basis

in support of a new medical research program at the National Institutes of Health.

3- Engineering Services

In addition to normal engineering and design services provided to reactor

operations, experimenters and users, the engineering staff was involved in a comprehensive program of reactor modernization.

Sixteen new reactor shim arm poison blades, arbors and bearings were completed,

received, and accepted by the NBSR engineering. The shim arm blades were made

previously by Argonne National Laboratory, but are no longer available from ANL since

they are no longer made for the CP-5 reactor. This is the first time the blades were

made commercially and new manufacturing techniques had to be developed which required

a great deal of engineering and quality control procedures. The production of these

blades solved one of the most difficult projects at the reactor since they must be

replaced periodically. The last blades available were put in service in 1979.

Thisaccomplishment will provide NBSR with a lifetime supply of these critical

components. The yokes for the shim arms have been designed and will be fabricated as

the schedule allows. A shim arm test assembly is in the process of fabrication which

in addition to testing shim arm mechanisms will be available as spare parts.

Qualification fuel plates have been accepted from the DOE contractor and were

fabricated into fuel element assemblies. Twenty-three fuel element assemblies have

been accepted by the NBSR engineering staff.

The spare regulating rod has been modified and the absorber section is being

fabricated for 20 MW operation. An engineering change notice (ECN) provided an improvement in the performance of the automatic regulating rod. By applying an electric braking technique, slippage of the regulating rod was reduced to a minimum,

if not eliminated. The dynamic brake allows more flexible mechanical tolerances

resulting in consistant up and down reg rod travel times.

Preparation for the modernization of the reactor instrumentation is continuing.

For example, the electronics for the Ph monitoring of the Secondary Cooling system

has been replaced by reliable modern equipment. Four new millivolt to current

converters with RFI immunity have been installed to replace present temperature MV/I

transmitters. One of the reactor level transmitters was replaced by a modern strain

gauge type transmitter, also incorporating the RFI immunity feature.

126
D. Services Programs

NEUTRON ACTIVATION ANALYSIS AT THE FOOD AND DRUG ADMINISTRATION

inf. C. Cunningham and W. B. Stroube

(U. S. Food and Drug Administration, Washington, DC)

The Food and Drug Administration maintains a neutron activation analysis (NAA)

unit in the reactor building of the National Bureau of Standards (NBS). The NAA

program at FDA includes analytical support for regulatory activities and special

projects as well as applications research. During the past year several projects

were conducted in FDA's NAA laboratory with emphases on quality assurance and

radiochemistry programs. The laboratory also participated in an analysis program

sponsored by the Nutrient Composition Laboratory of the USDA and the Chemistry and

Biology Research Institute of Agriculture Canada who have developed some new

biological reference materials.

Radiochemical work in progress includes both pre- and post-irradiation

techniques which are being developed and applied to food analyses. Chelex-100

chelating resin is being used for pre-irradiation separations. This work compliments

other work done in the Environmental and Elemental Contaminants Branch using an inductively coupled plasma spectrometer (ICP). For elements determinable by both

techniques, NAA will be used as a conf irmat ional technique in the Branch's QA

exercises. For other elements NAA's results are complementary and now provide more

complete characterizations. Post-irradiation separations are performed using

inorganic chromatographic resins. Limits of detection are low enough using this

technique for the toxic elements As, Cr, and Se to be detected in most of the foods

analyzed. Detection limits for Cr and Se were lowered by a factor of five to

seventy, depending on the food matrix. For As detection limits were lowered even more significantly, in some cases by more than three orders of magnitude.

Improvements were noted also for Ag, Mo, and Sb. Work is continuing to improve

recoveries for these elements.

The FDA NAA laboratory was invited to participate in the investigation of the

proposed biological reference materials (BRM's) being developed by Agriculture Canada

and the USDA. Our laboratory provided the instrumental neutron activation analysis

(INAA) results that will be used to generate the reference concentrations. We

analyzed eight subsamples from each of the proposed BRM's for twenty elements.

Results are currently being combined with those from the other techniques so that

they will be available when the BRM's are distributed.

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SERVICE PROGRAMS

PREPARATION OF F-18 LABELED RADIOTRACERS USING NBS REACTOR-PRODUCED F-18

W. C. Eckelman, M. Charming, and J. Bennett

(National Institutes of Health, Clinical Center, Bethesda, MD)

6 14

F-18 is produced by irradiating 0.4g enriched Li CO for 2 hours at 1 . 1 x 10

2 n/cm /sec. The quartz ampule is then returned to NIH for processing in a semiautomatic processing facility. The quartz ampule is cracked and Li

2

C0 is mixed

with cation exchange resin in water. The aqueous solution is transferred to a round

bottom flask containing base and carrier fluoride. The water is evaporated and

acetonitile is added. The acetonitile is evaporated and the process is repeated

twice again. The substrate is then added to the fluoride. To date, two substrates

have been used: (1) methyl 4 , 6-0-benzylidene 2,3-eyclic sulf ate-B-D-Mannopyranoside--a precursor to 2-f luoro-2-deoxy glucose, and (2) the 6-triflate

derivative of naltrexone. Both are produced in 60% radiochemical yield. Animal

experiments will begin in the next year to study the biochemistry.

NEUTRON CAPTURE PROMPT- I ACTIVATION ANALYSIS

D. L. Anderson, G. E. Gordon, W. B. Walters, W. H. Zoller, and M. E. Kitto

(University of Maryland, College Park, MD

)

In the past year, over 800 samples of various types have been analyzed at the

neutron capture prompt-gamma activation analysis (PGAA) facility at the National

Bureau of Standards (NBS) reactor. Much of the research involved dealt with

continuing studies of gas-phase species in the atmosphere, matrix effects encountered

in PGAA, and the analysis of lumped burnable poisons. Several new studies, primarily

of geochemical interest, were also initiated.

Although initially aimed toward the characterization of atmospheric boron, we have expanded one of our studies to encompass other elements, such as S, CI (via

PGAA) and Br, I and Se (using INAA). Using stacks of filters (described in last

year's report), we have measured the particle and gas-phase contributions for these

and several other elements in samples taken in Hawaii, Alaska, Wallops Island,

College Park and Gaithersburg. The concentration of B trapped on particles, is of

the order of 1 ng/m in all the tropospherie samples taken, regardless of location.

High altitude samples from Mauna Loa Observatory yield concentrations of less than

-0.2 ng/m for both the particle and gas phases. Tropospherie gas-phase boron varied

3 greatly (<0.1 to >100 ng/m ) from location to location and is believed to be largely

due to oceanic and fossil-fuel sources. Data on the other elements are only

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SERVICE PROGRAMS

preliminary. One interesting feature is that we observe gas-phase Se at levels 5 to

10 times lower than that reported by other groups. We believe our present gassampling method, designed to collect acidic gases, does not collect the Se in its

atmospheric chemical form (e.g., elemental or organic). We are considering other

approaches.

We noted last year that a potentially severe matrix effect is observed in PGAA

for hydrogenous samples; the sensitivity (counts/sec *mg) for all elements measured so far increases with increasing H content. An in-depth study involving prepared

standards is now underway to detail the variations for each important element and

their causes in a beam-oriented system such as ours.

In a new geochemical project, in collaboration with Dr. Nathalie Valette-Silver

of the Carnegie Institution of Washington, we are analyzing very interesting samples

from deep ocean hydrothermal vent areas. The mounds of sulfide deposits formed

(often referred to as "smokers" or "chimneys") contain relatively large amounts of

the elements Cu, Zn, Fe, Au and Ag, among others. The deposits and related fluids

are interesting not only because of the potential for understanding the formation of ore deposits, but also because of the implications for tectonic geochemistry in

general. Other geologically-oriented projects include the measurement of Cd in shale

oil and oil shale (with Battelle Pacific Northwest Laboratories) and the

characterization of a new raw oil shale standard (with Dr. Michael D. Glascock of the

University of Missouri).

Personnel from the Center for Analytical Chemistry have also made use of the

PGAA setup in the past year in a number of projects described elsewhere in this

document.

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ATMOSPHERIC AND ENVIRONMENTAL STUDIES B* INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS

G. E. Gordon and W. H. Zoller

(University of Maryland, College Park, MD)

We continue to make extensive use of instrumental neutron activation analysis

(INAA) to determine concentrations of about 35 elements in samples of atmospheric

particulate matter collected from ambient air (now mostly at remote sites such as Hawaii and rural sites in the continental U.S.) and in particles released from major

sources such as volcanoes. By measuring concentrations of such a large number of

elements, we are able to identify contributions from the sources to the atmospheric

burden at ambient sampling sites. Examples of some of these studies are discussed

briefly in the following sections.

1

.

Compositions of Atmospheric Particles at Mauna Loa Observatory, Hawaii

Until recently, there existed no long continuous record of concentrations of

elements on particles at a site remote from local activities despite demonstration of

the enormous value of the long-term C0 ? record (since 1957) at Mauna Loa Observatory

(MLO) in Hawaii for observing CO seasonal variations and long term increase.

Fortunately, since mid-1979, the National Oceanic and Atmospheric Agency (NOAA) has

supported weekly collections of filters at MLO and analysis of them by our group

using INAA. Results of analysis of the MLO samples through 1982 were discussed in

last year's progress report. Since January 1983, we have continued to collect

samples on a weekly basis, but analysis of the samples was interrupted because of

eruptions from Kilauea and Mauna Loa volcanoes off and on since that time. As

discussed below, we have instead analyzed samples of the volcanic material.

Recently, we have again begun to analyze MLO samples taken since January 1 983

Several papers based on this work have been submitted for publication and two

1 2

have been published '

.

2. Composition of Emissions from Volcanoes

In order to interpret the compositions of particles collected at MLO and other

remote sites, we must know the compositions of particles released by various natural

and anthropogenic sources. One potentially very important natural source is volcanic

emissions, which have been heavily investigated by this group for several years.

Last year's progress report described studies of four Central American volcanoes.

This year we have focused attention on the Hawaiian volcanoes, Kilauea and Mauna Loa.

Kilauea erupted in January 1983 and has continued to erupt at various times

since then. Emissions from the initial eruptive phase were inadvertently collected

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at our MLO sampling station (see Section 1) and analyzed by INAA at the NBS reactor,

revealing unusually large concentrations of Se, As, In, Au, and S, as expected for

volcanic emissions. In a paper published in Science, Zoller et al . noted that

strikingly large concentrations of Ir were also observed. As Ir enrichments have not

previously been observed in volcanic emissions, the results suggested that Kilauea is

part of an unusual volcanic system which may be fed by magmas from the earth's

mantle. The Ir enrichment appears to be linked with the high F content of the

volcanic gases, suggesting its release as IrF^.

4 Previous workers had observed huge Ir enrichments at the Cretaceous-Tertiary

(K-T) boundary layer in sediments, which they suggest arose from the impact of a very

large meteorite. The results obtained from Kilauea suggest that volcanic emissions

of this type might provide an alternate explanation.

We have subsequently taken samples much closer to the volcano to obtain much

greater masses of volcanic material and analyzed these samples at the NBS and Los

Alamos reactors. The results confirm and extend the results obtained from the MLO

samples. A paper concerning these results is nearly ready for submission.

Mauna Loa volcano began erupting on 24 March 1984. Members of our group began

collecting samples on 27 March and continued sampling, both with airplanes and on the

ground until 15 April. The samples are being analyzed by INAA at the NBS and Los

Alamos Reactors.

3. South Pole Aerosol

As a part of the study of particles in global circulation, particles have been

collected from the very pristine atmosphere of the South Pole since 1971 (e.g. Ref.

5). During the past year, G. Tuncel has analyzed most of the samples collected there

since 1977. Results for some of the elements observed are summarized in Table 1.

Most of the analyses of the South Pole samples are being done by INAA, which

involves only the taking of Y-ray spectra with Ge(Li) detectors after the

irradiations. However chemical separations are being used on some South Pole samples

in order to observe Ir, which is present in extremely small concentrations, typically

-4 3 10 pg/m of air. On the basis of concentrations of several metals at the South

5 Pole, Cunningham and Zoller estimated the total influx of meteoritic material to the

earth's atmosphere. However, Ir is a much more sensitive indicator of meteoritic

material than most other metals. Preliminary results from the Ir analyses suggest

that the influx of meteoritic material is much smaller than indicated by most experts

in the field.

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4. Arctic Haze

During the winter and spring of each year, the Arctic atmosphere contains high

concentrations of aerosol, which is largely pollution-derived. This Arctic haze is

observed over the entire Arctic basin and tends to appear in distinct layers or "haze

bands" which are typically several hundred to several thousand feet thick. Much of

the material is thought to have its source in Asia.

To gain a better understanding of the Arctic haze, P. Sheridan joined an aircraft experiment organized by NOAA specifically for study of the problem. He

collected particles from several flights taken in March and April, 1983. In order to

relate his results to the rest of the work being done on particles by this group, he

has analyzed the bulk filter samples by INAA for about 35 elements. Some very

lightly loaded samples were also collected on transmission electron microscope (TEM)

grids for study of the individual particle characteristics by a variety of

microscopic techniques, especially the analytical electron microscope (AEM) and the

laser microprobe mass analyzer (LAMMA). The latter studies are being conducted in

the Gas and Particulate Science Division of the Center for Analytical Chemistry of

the NBS, where Mr. Sheridan is employed while also being a graduate student at the

University of Maryland.

5. Composition of Particles from Polluted Cities

The Asia dust transported to MLO in Hawaii in large amounts each spring (see

Section 1 and Ref. 1) often has a composition quite unlike that of soils from other

parts of the world (e.g. high concentration of As). We suspect that the dust, which

originates from dust storms in China, picks up contaminants as it passes over the

populated and industrial areas along the coast of China and in Korea and Japan. As a starting point in testing this hypothesis, we obtained fifteen air filter samples

collected in Beijing, China by T. Novakov's group in Berkeley and previously analyzed

by x-ray fluorescence (XRF) by them. D. Hermann and Ilhan Olmez subjected them to

INAA to obtain data for additional elements. The INAA results are now being compared

with the XRF data in preparation for interpretation of the combined data set.

6. Size Distribution of Resuspended Particles Bearing Various Elements

Much of the suspended particulate matter in the atmosphere is wind-entrained

soil. Because of the importance of this component, we need to know its composition

rather well to interpret airborne particle compositions. C. M. Thompson designed and

built a chamber for the re-suspension of dried, sieved, soil samples and collection

of separate size fractions of the particles. Soils from several areas have been

resuspended, and the various size groups analyzed by INAA at the NBS reactor. The

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soils under investigation were collected from MLO , two places in China, and in

Laurel, MD.

7. Composition of Particles Released by Wood Combustion

Wood combustion is an important source of atmospheric particles, both

anthropogenic and natural (from forest fires, slash burning, etc.). Thus, it is

important to characterize these particles in order to identify their contribution to

ambient air. Frank Guenther made a sampling trip to Fairbanks, AK , from 7 to 1

5

February 1984, as that city has a major air pollution problem in winter due to

residential wood and coal burning and motor vehicles. Air samples were taken at a downtown and a residential location, the latter having a history of severe pollution

from wood-burning stoves, with complaints of visibility and respiratory problems.

Samples were also taken from various wood stoves burning aspen, birch, and spruce

wood, and of motor vehicle and coal-fired plant emissions in that area. The major

interest in this study is in identifying organic compounds associated with these sources. That part of the study is being done in the Organic Analytical Research

Division of the Center for Analytical Chemistry at NBS, where Mr. Guenther is an employee while also pursuing his graduate work at the University of Maryland. In

order to relate his observations to the other studies we are doing, he is also

analyzing many of the samples by INAA at the NBS reactor.

8. Shenandoah Valley Samples

One of the major environmental problems of our time is acid deposition. To

control acid deposition in an optimal way, we must identify the sources of acid

precursors, find out how they are transported and deposited, and how they are

chemically converted to acids. In work supported by EPA, we are trying to identify

elements borne by atmospheric particles that can serve as characteristic signatures

of certain types of sources or areas of the country. To do this, S. Tuncel and I. Olmez are subjecting samples collected by EPA to analysis by INAA. They collected

samples for 15 months at rural sites in Kentucky, Indiana, and Ohio , and for three

7 weeks in the Shenandoah Valley . They collected particles for two size Tractions,

greater and less than 2.5-pm diameter and analyzed them by x-ray fluorescence (XRF).

The XRF method is a rapid, highly automated technique for analyzing large numbers of

samples, but it mainly observes major elements. INAA is more expensive and timeconsuming than XRF, but it yields data for many trace elements that are potentially

useful tracers, e.g., Se , As, Sb, and In. The combined XRF and INAA results yield

data for about 40 elements. We are mainly analyzing fine particles, as they provide

much more information about sources than large particles, which are dominated by

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Table 1 . Summer and Winter Average Concentration for Some Elements at the

South Pole

Element

Na

Summer

Winter

Mg

Summer

Winter

CI

Summer

Winter

Al

Summer

Winter

Cone,

unit

3 ng/m

ng/m"

ng/m"

ng/m"

1978

12±9

30±28

3.5±1.9

7±9

40±34

2.8±2.

Concentration

1979 1980 1981 1982

6±4 1 .9±1 .2 5 ±2 1 3+1

28±41 3- 1 ±2.5 31 ±50 32±24

1 .4±0.7 0.8±0.6 1 . 1 ±0 .

5

1 .9±2.2

4±6 2.5+1 .4 3 ±5 3.8±2.5

4±6 3 ±5 1 0±1 3 7+1

3

45±70 14+17 41 ±48 36±25

0.46±0.3 0.8±0.6 1.3+0.6 0.8±0.5

0.37±0.5 0.2±0.1 0.3±0.2 0.2±0.1

Sc

Summer

Winter

Mn

Summer

Winter

Fe

Summer

Winter

mg/m"

ng/m"

ng/m"

0.37±0.3 0.07±0.05 0.07±0.05 0.26±0.13 0. 1 1 ±0.08

.8±4 0.03±0.01 0.03±0. 06 0.14±0.2 0.02±0.06

12±8 5.5±3 7±5 65+79 10±4

9±6 1 .1x0.9 5.2x0.5 5±5 3-9±2.4

76±0.7^> 0.38±0.25 0.36±0.3 5.2±0.6 0.92±0.6

1.U0.33 0.07±0.06 0.32±0.2 0.28±0.3 0.23x0.19

Summer

Winter

ng/m"

71 ±45

34±9

64±47

39+1

1

61 ±37

28±19

99±60

28±19

64±19

As

Summer

Winter

pg/m"

2.5±1 .8

1 .9±1 .4

3 ±2

1 .4±0.6

3±3

1.3±1 .4

19±23

2.2±1 .4

4.6±2.5

2.0±1 .1

Se

Summer

Winter

pg/m"

7±4

5±2

8±4

4±0.9

8±6

3 ±2

18±16

4.5±2

8±3

4.3±3

Br

Summer

Winter

ng/m"

0.12±0.08 0. 1 6±0. 1 6 0.07±0.05 1-1+1.3 0.17±0.08

0.05±0.02 0.08±0.03 0.04±0.03 0.06±0.06 0.07±0.06

Sb

Summer

Winter

pg/m"

3±3 1.4±1.1 2.8±1.9 3-8±3 4.0±2.9

0.69±0.32 2.0±2.1 1.1+1.0 0.9±0.9 1.4±1.8

Summer

Winter

ng/m"

0.37±0.5 0. 1 7±0. 1 5 0. 1 9±0. 1 3 0. 1 9±0. 1 3 0. 1 5±0.

1

0. 1 1 ±0.09 0. 1 1 ±0.08 0.06±0.03 0.1 5±0. 17 0.08±0.08

134
SERVICE PROGRAMS

Table 2. Average Concentrations and Standard Deviations of Elements and

Species Observed in Fine Fractions of Shenandoah Samples

Species Anal.

Method

No. spls

detected

Na INAA 33

Al INAA 32

Si XRF 32

S XRF 32

CI INAA 33

K INAA 32

Ca INAA 32

Sc INAA 30

V INAA 32

Cr INAA 30

Mn INAA 31 Fe INAA 31 Co INAA 32

Cu INAA 24

Zn INAA 32

As INAA 30

Se INAA 32

Br XRF 33

Cd INAA 24

Sb INAA 32

I INAA 21 Cs INAA 21 La INAA 27

Ce INAA 32

Sm INAA 25

W INAA 19

Pb XRF 32

Th INAA 17

NO^

H

+ 3

IC

IC

Chem.

28

15

26

C (total) Chem. 25

C (org.) Chem. 21

C (elem.)

+ Chem. 25

N (total)

IC 26

Chem. 26

Mass 6 32

Concentration (ng/m ) Arithmetic, x±o

51 ±27

42±28

1 33±1 60

4400±3300

13±14

66±32

37±26

0.012±0.015

1 .25±1 .01

0.6±0.6

2.5±1 .8

53±58

0.06±0.07

6.4±4.4

9±7

0.40±0.31

1 .3±0.94

7.5±2.3

2.4±7.4

0.30±0.14

0.48±0.30

0.028±0.021

0.09±0.09

0.23±0.21

0.008±0.005

0.06±0.04

51 ±18

0.024±0.031

13,600±10,100

600±1100

96±128

1750±970

540±460

1300±760

3400±2000

1270±730

42,000±29,000

Geometric, x ( j ) g g

46 :i .6)

28 :2.4)

87 :2.4)

3300 I [2.2)

8.6 :2.4)

59 :i .7)

31 I :i.9)

0.0080 [2.5)

0.97 [2.0)

0.40 [2.6)

2.0 [2.0)

43 [1.9)

0.047 [2.0)

5.2 [2.0)

7.4 [1.9)

0.27 [2.6)

1 .05 [2.0)

7.0 [1 .5)

0.93 [2.6)

0.26 [.1.8)

0.43 [1 .6)

0.022 [2.0)

0.056 I .3.6)

0.18 I ,2.1)

0.0063 I .2.1)

0.045 I ,2.0)

47 ( 1 .5)

0.014 ( 2.6)

10,500 ( 2.1 ) 340 ( 2.5)

40 ( 4.4)

1420 ( 2.1 ) 375 ( 2.4)

990 ( 2.4)

2900 ( 1.8)

1 100 ( 1.7)

33,000 ( 2.1)

XRF = x-ray fluorescence; INAA

IC = ion chromatography; Chem.

instrumental neutron activation analysis;

other chemical methods; 8 = beta gauge.

135
SERVICE PROGRAMS

local soil. Back-trajectories for air masses sampled during each period were

calculated by J. Parrington using a model and meterological data from NOAA to

identify the areas over which the air was transported in order to see if the

compositions of particles from different areas have characteristic signatures. The

INAA measurements have been done on all 33 Shenandoah samples, with the results shown

in Table 2. This work has been submitted for publication in Environmental Science

Technology.

Over 200 fine-fraction samples have been selected from the 1 400 collected in

the Ohio River Valley Study (KY, IM, OH sites). Most of these have been analyzed by

INAA for short-lived activities and are now being irradiated to observe long-lived

species.

9. Philadelphia Samples

During the summer of 1982, EPA sponsored detailed studies of the sources of

atmospheric particles in the atmosphere of Philadelphia. Particles were collected at

three ambient sampling sites in that area for one month using dichotomous samplers,

which collect particles with diameters above and below 2.5 iam separately. EPA

personnel analyzed all of the samples by XRF and sent the fine fractions here for

their analysis by INAA. I. Olmez and A. Sheffield analyzed these samples and have

submitted the results to EPA. We are not reporting the results here, as EPA may use

the combined data sets in a "blind", round-robin test of receptor models used for

various research groups. Samples were also collected from seven important sources of

particles in the Philadelphia area: a coal-fired power plant, two oil-fired plants,

a refinery, an incinerator, an Al plant, and an Sb roaster. They were first

o subjected to XRF , and then sent here for INAA. Three sets of fine and coarse

samples from each source were analyzed by Olmez and Sheffield, and the results are

being prepared for publication.

10. Deep Creek Lake Samples

During the summer of 1983, EPA, DoE, and EPRI and their contractors collected

ambient samples at a site near Deep Creek Lake, MD and in stacks and plumes of

several coal-fired plants upwind of the site. These samples have been subjected to

XRF in other laboratories and will be analyzed by INAA by our group. We have

received the ambient samples and A. Sheffield has began the analysis of them.

1. J. R. Parrington, W. H. Zoller, and N. K. Aras, Asia Dust: Seasonal Transport to

the Hawaiian Islands, Science 220, 195 (1983).

136
SERVICE PROGRAMS

A COMPTON PROFILE EXPERIMENT IN GRAPHITE

L. M. Pecora and A. C. Ehrlich

(Naval Research Laboratory, Washington, DC)

We report here on the use of the Compton effect to study the momentum density

of graphite. When a gamma ray scatters off an electron the wavelength of the gamma

ray changes. This measureable change is a function of the angle of scatter and the

value of the electron's momentum along the direction of the scattering vector (see

Figure 1 ) . By measuring the number of gamma rays scattered by the electrons of a solid at a particular fixed angle as a function of wavelength (energy) one gets a measure of the relative probability of finding an electron in the solid being studied

as a function of the component of the electron's momentum along the scattering

vector. This relative probability is related to the probability of an electron

having a certain vector value for its momentum. This latter probability is called

the momentum density. The data gathered on the momentum density in a Compton

scattering experiment of this nature is called the Compton profile.

r

Figure 1 . Diagram of the Compton scattering of a gamma ray from an electron with a particular initial value of momentum p . The gamma ray has initial

momentum k and final momentum k . The scattering vector is the

difference k -k and the projection of p along the scattering vector is

the component of p which is resolved in the detection of the scattered Yray.

137
SERVICE PROGRAMS

Scattered Beam

Figure 2. Diagram of the experimental apparatus showing the source container, source beam tube, target (graphite in this case), the scattered beam tube and the

detector.

Compton profiles taken for various orientations of a single crystal sample are particularly useful for inferring the structure of the 3 dimensional momentum density

of the electrons in the particular material being studied. The momentum density

itself relates directly to various physical quantities which are of great interest:

the Fermi surface, the band structure (energy states), and the structure of the

electron wave functions.

We have constructed an experimental apparatus for measuring Compton profiles of

various materials using gamma radiation from an Au-foil source which has been

irradiated in the National Bureau of Standards Reactor so that Au(198) is present in

the source (sec Figure 2). The source is transported to the High Radiation

Laboratory at the Naval Research Laboratory and placed in the lead source container

138
SERVICE PROGRAMS

so as to emit a collomated beam of gamma rays consisting primarily of 412 kev

photons. The sample whose electrons scatter the gamma rays is held in a specially

made sample holder which allows rotation of the sample about two axes. The apparatus

is shielded in such a way that the only gamma rays detected are those scattered at a 170° angle. The detection is accomplished by a germanium detector. The resolution

of the detector counts into energy channels is done by a multi-channel analyzer. The

analyzer is interfaced with a computer to facilitate the transfer of the data and the

data analysis.

• •

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I

I I %

50 100

Energy (keV)

150 200

Figure 3« Plot of the number of gamma rays detected as a function of energy

(channel) in a preliminary Compton profile experiment.

Figure 3 shows the first data taken with this apparatus. The target material

was highly ordered pyrolytic graphite. The orientation was such that the graphite c- axis was parallel to the source beam. The main peak in the plot results from the

compton scattering of 412 kev radiation from the electrons of the graphite. The

central part of the peak is due to the scattering from the conduction band electrons

and the nearby broader parts of the main peak are due to the scattering of the gamma

rays from the core electrons of the graphite. The smaller peaks at lower energies

result from the Compton scattering of lower energy gamma rays emitted from the Au source.

139
SERVICE PROGRAMS

At this point we are working to eliminate more background radiation from the

experimental set-up. We are also working on software for the analysis of the Compton

files, in particular the extraction of information on the momentum density from the

data. Future experiments will include measurements of the Compton profiles of highly

ordered pyrolytic graphite in various orientations.

140
E. Personnel Roster

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141
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142
PERSONNEL ROSTER

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1 43
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117
F. Publications

COLLABORATIVE PROGRAMS

BERK, N. F., ROSENTHAL, J., and YARMUS, L . , "Spin Relaxation of Triplet

Excitons in Molecular Crystals," Phys. Rev. B28, 4963-4969 (1983).

BERK, N. F. and GLINKA, C. J., "Data Reduction and Imaging System for Small

Angle Neutron Scattering," Nuclear Instruments and Methods (in press).

CASE, E. and GLINKA, C. J., "Characterization of Microcracks in YCrO Using

Small Angle Neutron Scattering and Elasticity Measurements," J. "Matls.

Sci. J_9 (1984).

CASELLA, R. C, "Generalized Theory of Neutron Scattering from Hydrogen in

Metals," Phys. Rev. B28, 2927 (1983).

CASELLA, R. C, "Nonlinear ity in Weak Magnetic Fields Induced by NeutronAntineutron Oscillations in Neutron Interferometry and Spin Resonance,"

Phys. Rev. Letters (in press).

CAVA, R. J., SANTORO, A., MURPHY, D. W., ZAHURAK, S., and ROTH, R. S. , "The

Structures of Lithium Inserted Metal Oxides: Li FeV Op," J. Solid State

Chem. 48_, 309~317 (1983).

CAVA, R. J., SANTORO, A., MURPHY, D. W., ZAHURAK, S., and ROTH, R. S., "The

Structures of the Lithium Inserted Metal Oxides Li ReO and

Li

gW0 " J. Solid State Chem. 50, 121-128 (1983).

CAVANAGH, R. R., RUSH, J. J., KELLEY, R. D., and UDOVIC, T. J., "Adsorption

and Decomposition of Hydrocarbons on Platinum Black: Vibrational Modes

from NIS," J. Chem. Phys. 80_ (7), 3478-3484 (1984).

CAVANAGH, R. R., RUSH, J. J., and KELLEY, R. D., "Comment on 'Quantum Motion

of Chemisorbed Hydrogen on Ni Surfaces'," Phys. Rev. Lett. 52_, 2100

(1984).

CHOI, C. S. and PRASK, H. J., " C ry stal lographi c and Microstructural

Characterization of Uranium Alloys by Neutron Powder Diffraction," J. of

Appl . Cryst. (in press).

DEY0RE0, J. J., MEISSMER, M., POHL , R. 0., ROWE , J. M., RUSH, J. J., and

SUSMAN, S., "Low Energy Excitations in (KBr) (KCN) in the

Orientational Glass State," Phys. Rev. Lett. 5J_,

1050-10*53 098*}).

EVANS, H. T. and PRINCE, E., "Location of Internal Hydrogen Atoms in the

Paradodecatungstate Polyanion by Neutron Diffraction," J. Am. Chem. Soc.

105 , 4338-4839 (1983).

HAROMAH-RHYNE, K., BERK, N. F., and FULLER, E. R., Jr., "Microstructural

Characterization of Ceramic Materials by Small Angle Neutron Scattering

Techniques", Journal of Research of the National Bureau of Standards 39_

January-February (1984).

148
PUBLICATIONS

HARDMAN-RHYNE, K. , RHYNE, J. J., PRINCE, E., CROWDER, C, and JAMES, W. J.,

"Magnetic and Crystallographic Structure of Y,Mn D ," Phys, Rev. B29 , 416-422 (1984). 3 3

HARDMAN-RHYNE, K. and RHYNE, J. J., "Short and Long-Range Magnetic Ordering

of Y r (Fe„ Mn )_„ and Related Compounds Using Neutron Scattering

o 1 — x x 2 3 Techniques," invited paper - Sixteenth Rare Earth Research Conference,

Tallahassee, FL (1983).

HIMES, V. L. and MIGHELL, A. D., "The Determination of Metric Lattice

Symmetry by Matrix Analysis", Acta Cryst. Sect. A (in press).

HODEAU, J. L., MAREZIO, M., SANTORO , A., and ROTH, R. S., "Neutron

Diffraction Structure Determination of the High-Temperature Form of

Lithium Tri tantalate , H-LiTa R

," J. Solid State Chem. 51_, 275-292

(1984). 5 b

KELLEY, R. D., CAVANAGH, R. R., and RUSH, J. J., "Co-adsorption and Reaction

of H and CO in Raney Nickel: Neutron Vibrational Spectroscopy," J.

Catalysis 83, 464-468 (1983).

KOKOSZKA, G. F., BARANOWSKI , J., GOLDSTEIN, C, ORSINI , J., MIGHELL, A. D.,

HIMES. V. L., and SIEDLE, A. R., "Two-Dimensional Dynamical Jahn-Teller

Effects in a Mixed-Valence Benzo t r

azo 1 a t o Copper Cluster,

Cu_(BTA) £ (RNC)", J. Am. Chem. Soc. 105, 5627-5633 (1983).

LUDEMAN, S. M. , SHAO , K., ZON , G. , HIMES. V. L., MIGHELL, A. D., TAKAGI , S.,

and MIZUTA, K., "0-Imino Esters of N,N-Bis(2-chloroethyl)

phosphorodiamidic Acid. Synthesis, X-ray Structure Determination, and

Anticancer Evaluation," J. of Med. Chem. 26, 1788-1790 (1983).

LYNN, J. W., "Magnetic Excitations in Transition Metals," invited paper at

Workshop on High Energy Excitations, LANL (1984).

LYNN, J. W., GOTAAS, J. A., ERWIN, R. W., FERRELL, R. A., BHATTACHARJEE

J. K., SHELTON, R. N., and KLAVINS, P., "Temperature-Dependent

Sinusoidal Magnetic Order in the Superconductor HoMo^Sen" , Phys. Rev.

Lett. 52, 133-136 (1984).

LYNN, J. W., "Neutron Scattering Studies of Magnetic Phase Transitions in

Superconductors," J. Less-Common Met. 9£, 75-83 (1983).

MAGERL, A., ZABEL, H., RUSH, J. J., and DIANOUX, A. J., "Dynamical

Properties of Alkali Intercalants in Graphite," Synthetic Met. 7_, 227"

232 (1983).

MAGERL, A., ROWE, J. M., RUSH, J. J., WIPF, H., and RICHTER, D., "Influence

of Impurities on Local Hydrogen Vibrations in a Niobium Host Lattice,"

Proc. of the Intl. Symp. on the Electronic Structure and Properties of

Hydrogen in Metals, Elec. Struc. & Prop, of Hyd. in Met., 171-176

(1983).

MIGHELL, A. D., HIMES, V. L. , and RODGERS, J. R., "Space-Group Frequencies

for Organic Compounds," Acta Cryst. Sect. A39_, 737-740 (1983).

149
PUBLICATIONS

MIGHELL, A. D. and STALICK, J. K. (series editors), "Crystal Data

Determinative Tables," Vol. 5 , 3rd ed., U.S. Department of Commerce,

National Bureau of Standards and the JCPDS--Internat ional Centre for

Diffraction Data, Swarthmore, PA (1984).

MIGHELL, A. D. and STALICK, J. K. (series editors), "Crystal Data

Determinative Tables," Vol . 6 , 3rd ed., U.S. Department of Commerce,

National Bureau of Standards and ten JCPDS--International Centre for

Diffraction Data, Swarthmore, PA (1984).

NEUMANN, D., ZABEL, H., RUSH, J. J., and BERK, N. F., "Phonon Softening in a Mixed Layered System K, Rb C " Phys. Rev. Lett. 53, 56-59 (1984).

1 - X X o —

PARISE, J. B. and PRINCE, E., "The Structure of Cesium-Exchanged Zeolite-RHO

at 293K and 493K Determined From High Resolution Neutron Powder Data,"

Mats. Res. Bull. Jl_8, 841-852 (1983).

PARISE, J. B., SHANNON, R. D., PRINCE, E., and COX, D. E. , "The Crystal

Structure of the Synthetic Zeolites (Cs, K)-ZK5 and (Cs, D)-ZK5

Determined From Neutron Powder Diffraction Data," Z. Kristallogr. 1 65 , 175-190 (1983).

PARISE, J. B., BRIXNER, L. H., and PRINCE, E. , "Refinement of the Structure

of La-W06Cl_ from Neutron Powder Diffraction Data," Acta Cryst. C39 , 1326-T328 (T983).

PRINCE, E., "The Effect of Finite Detector Slit Height on Peak Positions and

Shapes in Powder Diffraction," J. Appl. Cryst. _1_6, 508-511 (1983).

PRINCE, E., TAKAGI, S., MATHEW, M. and BROWN, W. E., "The Structure of

Dicalcium Potassium Heptahydrogen Tekrakis Phosphate," Acta. Cryst. C

( in press)

.

PRINCE, E. and NICHOLSON, W., "The Influence of Individual Reflections on

the Precision of Parameter Estimates in Least Squares Refinement,"

Crystallogr. Stat, (in press).

PRINCE, E. , "Precision and Accuracy in Structure Refinement by the Rietveld

Method," Crystallogr. Stat, (in press).

RHYNE, J. J. and GLINKA, C. J., "Critical Behavior and Magnetic Ordering in

Amorphous TbFe ," J. Appl. Phys. 55_, 1691 (1984).

RHYNE, J. J., SILBER, H., and MCCARTHY, G. J. (editors), "Proceedings of the

Sixteenth Conference on Rare Earth Research, The Rare Earths in Modern

Science and Technology," J. Less-Common Met. _4 (1983).

RHYNE, J. J., "Magnetism in Amorphous Metallic Glasses," (invited lectures)

Magnetic Phase Transitions , edited by M. Ausloos and R. J. Elliott,

Springer-Verlag, Berlin, 241-268 (1983).

ROWE, J. M., RUSH, J. J., and SUSMAN, S., "Neutron Powder Diffraction Study

of Phase Transitions and Structures of (KCN) (KBr) Mixed Crystals,"

Phys. Rev. B28, 3506-3511 (1983).

X X

150
PUBLICATIONS

ROWE, J. M., RUSH, J. J., and LUTY, F., "Tne Crystal Structure of Rubidium

Cyanide at 4 K Determined by Neutron Powder Diffraction," Pnys. Rev.

Brief Coram. 29, 2168-2170 (1984).

ROWE, J. M. and SUSMAN, S., "Diffuse Neutron Scattering in Sodium and

Potassium Cyanide", Phys. Rev. B29_, 4727-4732 (1984).

ROWE, J. M., RUSH, J. J., and MICHEL, K. H., "Comment on Dielectric

Susceptibility Measurements in (KCN) (KBr) Mixed Crystals," Phys.

Rev. Lett, (in press).

RUSH, J. J., ROWE, J. M., and RICHTER, D., "Direct Determination of the

Anharmonic Vibrational Potential for H in Pd," Z. Phys. B - Condensed

Matter, 55, 283-286 (1984).

SANT0R0, A., "The Role of Modern Neutron Powder Diffraction Techniques in

the Study of Solid State Ionics," Proceedings of the 4th International

Conference on Solid State Ionics: Grenoble, France, Solid State Ionics

9 & 10, 31-40 (1983).

SCHIOLER, L. J., WUENSCH, B. J., and PRINCE, E., "Relation Between

Structural Change and Fast-Ion Conduction in the NASICON Solid-Solution

System," Sol. St. Ionics (in press).

STALICK, J. K., HUBBARD, C. R., MIGHELL, A. D., RODGERS, J. R., and HORN, A. S., "2-Amino-6,7-dihydroxytetralin Hydrobromide C H NO HBr," Acta

Cryst. Sect. C40, 317*320 (1984). ' J

SUSMAN, C. J., DELBECQ, T. 0., BRUN , T. 0., and PRINCE, E., "Fast Ion

Transport in the NASICON Analog Na Sc (P0 J.: Structure and

Conductivity," Sol. St. Ionics (in press).

WERNER, S. A., GRIER, B. H. , and SHIRANE, G., "Magnetic Excitations in Pure

Chromium II," (submitted for publication).

WERNER, S. A. and KLEIN, A. G., "Recent Advances in Neutron Optics," Cnapter

4 of Neutron Scattering , ed. D. L. Price and M. Skold, Academic Press

(submitted for publication).

WERNER, S. A., KAISER, H., and GEORGE, E. A., "Neutron Interf erometr ic

Search for Quaternions in Quantum Mechanics," Phys. Rev. A (Rapid

Communications), 29, 2276-2279 (1984).

WERNER, S. A., GABLE, J. W., FELCHER, G. P., and WAKABAYASHI , N., "Neutron

Polarization-Analysis Study of the Spin Structure of Cu-Mn Spin

Glasses," Phys. Rev. B29 , 1268-1278 (1984).

WERNER, S. A., KAISER, H. , and GEORGE, E. A., "Direct Measurement of the

Longitudinal Coherence Length of a Thermal Neutron Beam," Phys. Rev.

Lett. 50, 560-563 (1983).

WERNER, S. A. and KLEIN, A. G. , "Neutron Optics," Rep. on Prog, in Phys. 46,

259-335 (1983).

151
PUBLICATIONS

WLODAWER, A. and SJOLIN, L. , "Application of Joint Neutron and X-ray

Refinement to the Investigation of the Structure of Ribonuclease A at

2.0 A Resolution," in "Neutrons in Biology", B. P. Schoenborn, ed.,

Plenum Press, 349-364 (1984).

WLODAWER, A., BORKAKOTI, N., MOSS, D. S. , and STANFORD, M. J., "Comparison

of Two Independently Refined Models of Ribonuclease A," Acta Cryst. (in

press)

.

WLODAWER, A., WALTER, J., HUBER, R., and SJOLIN, L., "Structure of Bovine

Pancreatic Trypsin Inhibitor: Results of Joint Neutron and X-ray

Refinement of Crystal Form II," J. Mol . Biol, (in press).

ZABEL, H., RUSH, J. J., and MAGERL, A., "Elastic Neutron Scattering Results

on C .RB(D ) in the Dilute Concentration Regime," Synthetic Met. ]_,

251-255 (198?).

ZOCCHI, M., GATTI, M., SANT0R0, A., and ROTH, R. S., "Neutron and X-ray

Diffraction Study on Polymorphism in Lithium Orthotantalate, Li TaO.,"

J. Solid State Chem. 48, 420-430 (1983).

INDEPENDENT PROGRAMS

BECKER, D. A., "Quality Assurance Techniques for Activation Analysis," in

Proceedings, Fifth International Conference on Nuclear Methods in

Environmental and Energy Research, U.S. Dept. of Energy, Report XXX,

Washington, DC 20585 (in press).

DOWNING, R. G., FLEMING, R. F., LANGLAND, J. K., and VINCENT, D. H.,

"Neutron Depth Profiling at the National Bureau of Standards," Nuclear

Instruments and Methods, 213, 47~51 (1983).

EHRSTEIN, J. R., DOWNING, R. G . ., STALLARD , B. R., SIMONS, D. S., and

FLEMING, R. F., "Comparison Depth Profiling of B-10 in Silicon by

Spreading Resistance Profiling Secondary Ion Mass Spectrometry, and

Neutron Depth Profiling," in Third Symposium on Semiconductor

Processing, ASTM Proceedings, Gupta, D., ed. (1984).

FLEMING, R. F., "Neutron Activation Foils," Chapter 10, in Calibration

Handbook: Ionizing Radiation Measuring Instruments, G. Lalos, ed.,

Department of Defense (1983).

GREENBERG, R. R., "Radiochemical Procedures Used for Improved Low-Level

Determinations of Critical Elements in Biological Materials,"

At.omkernenergie-Kerntechnik (in press).

GREENBERG, R. R. and CARPENTER, B. S., "High Accuracy /H i gh Precision

Determination of U-235 in Nondestructive Assay Standards by Gamma-Ray

Spectrometry," Proc. Fifth Intl. Conf. on Nuclear Methods in

Environmental and Energy Research (in press).

152
PUBLICATIONS

GREENBERG, R. R., FLEMING, R. F. , and ZEISLER, R. t "High Sensitivity Neutron

Activation Analysis of Biological/Environmental Standard Reference

Materials," Environ. International (in press).

KINGSTON, H. M. and GREENBERG, R. R., "An Elemental Ratioing Technique for

Assessing Concentration Data from a Complex Water System," Environ.

International (in press).

KINGSTON, H. M. , GREENBERG, R. R., BEARY, E. S., HARDAS, B. R., MOODY, J.

R., RAINS, T. C, and LIGGETT, W. S., "The Characterization of the

Chesapeake Bay: A Systematic Analysis of Toxic Trace Elements," NBSIR

83-2698, November (1983).

KOTRA, J. P., FINNEGAN, D. L. , ZOLLER, W. H., HART, M. A., and MOYERS, J.

L., "El Chichon: Composition of Plume Gases and Particles," Science

222 , 1018-1021 (1983).

LUTZ, G. J., ROOK, H. L., and LINDSTROM, R. M., "Determination of 1-129 at

Natural Levels by Thermal Activation Analysis," Journal of Trace and

Microprobe Techniques (in press).

PARRINGTON, J. R., ZOLLER, W. H. , and ARAS, N. K., "Asian Dust: Seasonal

Transport to the Hawaiian Islands," Science 220_, 195-197 (1983).

STONE, S. F. and ZEISLER, R. L., "Evaluation of Biological Samples for

Specimen Banking and Biomonitoring by Nuclear Methods," Proc. of Fifth

Intl. Conf. on Nuclear Methods in Environmental and Energy Research,

April 2-6 (in press).

ZOLLER, W. H., PARRINGTON, J. R., and KOTRA, J. M. P., "Iridium Enrichment

in Airborne Particles from Kilauea Volcano: January 1983," Science 222,

1118-1121 (1983).

153

NBS-114A (rev. 2-eo

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS/TN-1207

2. Performing Organ. Report No 3. Publication Date February 1985

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities July 1983 to June 1984

5. AUTHOR(S)

F. J. Shorten, Ed,

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

July 1983 to June 1984

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

10. SUPPLEMENTARY NOTES

I ]] Document describes a computer program; SF-185, FIPS 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 depend on the NBS reactor. It covers

the period from July 1983 through June 1984. 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, radiation effects studies, 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; neutron radiography; nondestructive evaluation; nuclear reactor; radiation

13. AVAILABILITY

[][] Unlimited

fjn For Official Distribution. Do Not Release to NTIS

I Xj 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

161

15. Price

USCOMM-DC <--"i43-P80
^m
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. As a special service to subscribers each issue contains complete citations to

all recent Bureau publications in both NBS and non-NBS media. 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.

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engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and

technical work.

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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 90-396).

NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published quarterly for NBS by

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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 1 1717 (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, iri paper copy or microfiche form.
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